WO2025233520A1

WO2025233520A1 - Aerosol-generating device with an external heater assembly

Info

Publication number: WO2025233520A1
Application number: PCT/EP2025/062768
Authority: WO
Inventors: Johannes Petrus Maria Pijnenburg
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2024-05-10
Filing date: 2025-05-09
Publication date: 2025-11-13
Anticipated expiration: 2026-11-10

Abstract

There is provided an aerosol-generating device comprising a tubular heat-conducting element (20). The tubular heat-conducting element comprises an inner surface (26) and an outer surface (28). The inner surface of the tubular heat-conducting element at least partially defines a chamber (14) for receiving an aerosol-generating article. The inner surface of the tubular heat-conducting element comprises a plurality of recessed regions (30) and a plurality of non-recessed regions (32). The aerosol-generating device also comprises a resistive heater (50) extending around at least a portion of the outer surface of the tubular heat-conducting element. The resistive heater comprises a resistive heating element. The resistive heating element comprises a plurality of first regions each having a first electrical resistance. The resistive heating element also comprises a plurality of second regions each having a second electrical resistance. Each first electrical resistance is greater than each second electrical resistance. Each first region of the resistive heating element overlies one of the non-recessed regions of the inner surface of the tubular heat-conducting element. Each second region of the resistive heating element overlies one of the recessed regions of the inner surface of the tubular heat-conducting element.

Description

AEROSOL-GENERATING DEVICE WITH AN EXTERNAL HEATER ASSEMBLY

The present disclosure relates to an aerosol-generating device comprising a tubular heat- conducting element and a resistive heater. The present disclosure also relates to an aerosolgenerating system comprising the aerosol-generating device.

It is known to evolve an aerosol from an aerosol-forming substrate of an aerosol-generating article by the application of heat to the substrate, without burning or combustion of the substrate. The aerosol-generating article may be cylindrical, like a cigarette, and the aerosol-forming substrate may comprise tobacco material. It is known to use an aerosol-generating device to apply heat to such an aerosol-generating article. In some examples, the aerosol-generating article is received within a chamber of the aerosol-generating device. It is known to use a heat source that is external to the aerosol-generating article, or use a heat source located within the interior of the aerosol-forming substrate.

It is also known to provide the chamber receiving the aerosol-generating article with airflow channels which provide fluid communication between a first end of the chamber and a second end of the chamber. The airflow channels may facilitate the flow of air through the aerosolgenerating device to an upstream end of the aerosol-generating article. However, in devices comprising a heat source that is external to the aerosol-generating article, the presence of one or more airflow channels may adversely affect the transfer of heat from the external heat source to the aerosol-generating article.

It is therefore desired to provide an aerosol-generating device with an external heater that facilitates more efficient heating of an aerosol-generating article.

According to the present disclosure there is provided an aerosol-generating device. The aerosol-generating device may comprise a tubular heat-conducting element. The tubular heat- conducting element may comprise an inner surface. The tubular heat-conducting element may comprise an outer surface. The inner surface of the tubular heat-conducting element may at least partially define a chamber for receiving an aerosol-generating article. The inner surface of the tubular heat-conducting element may comprise a plurality of recessed regions. The inner surface of the tubular heat-conducting element may comprise a plurality of non-recessed regions. The aerosol-generating device may comprise a resistive heater. The resistive heater may extend around at least a portion of the outer surface of the tubular heat-conducting element. The resistive heater may comprise a resistive heating element. The resistive heating element may comprise a plurality of first regions each having a first electrical resistance. The resistive heating element may comprise a plurality of second regions each having a second electrical resistance. Each first electrical resistance may be greater than each second electrical resistance. Each first region of the resistive heating element may overlie one of the non-recessed regions of the inner surface of the tubular heat-conducting element. Each second region of the resistive heating element may overlie one of the recessed regions of the inner surface of the tubular heat-conducting element.

According to the present disclosure there is also provided an aerosol-generating device. The aerosol-generating device comprises a tubular heat-conducting element. The tubular heat- conducting element comprises an inner surface. The tubular heat-conducting element comprises an outer surface. The inner surface of the tubular heat-conducting element at least partially defines a chamber for receiving an aerosol-generating article. The inner surface of the tubular heat-conducting element comprises a plurality of recessed regions. The inner surface of the tubular heat-conducting element comprises a plurality of non-recessed regions. The aerosolgenerating device comprises a resistive heater extending around at least a portion of the outer surface of the tubular heat-conducting element. The resistive heater comprises a resistive heating element. The resistive heating element comprises a plurality of first regions each having a first electrical resistance. The resistive heating element comprises a plurality of second regions each having a second electrical resistance. Each first electrical resistance is greater than each second electrical resistance. Each first region of the resistive heating element overlies one of the nonrecessed regions of the inner surface of the tubular heat-conducting element. Each second region of the resistive heating element overlies one of the recessed regions of the inner surface of the tubular heat-conducting element.

As used herein, the term “aerosol-generating device” is used to describe a device that interacts with an aerosol-forming substrate to generate an aerosol. Preferably, the aerosolgenerating device is a smoking device that interacts with an aerosol-forming substrate to generate an aerosol that is directly inhalable into a user’s lungs through the user’s mouth.

The term “heat-conducting element” is used herein to describe an element comprising one or more heat-conducting materials having a bulk thermal conductivity of between about 10 Watts per metre Kelvin and about 500 Watts per metre Kelvin, preferably between about 15 Watts per metre Kelvin and about 400 Watts per metre Kelvin, at 23 degrees Celsius and a relative humidity of 50 percent as measured using the modified transient plane source (MTPS) method.

Advantageously, providing an aerosol-generating device in accordance with the present disclosure allows for improved efficiency of heat transfer from the resistive heater to an aerosolgenerating article inserted into the chamber of the aerosol-generating device. In particular, by positioning regions of the resistive heating element with a lesser resistance over the recessed regions of the tubular heat-conducting element, a lower proportion of the overall heat dissipated by the resistive heating element may be dissipated into the recessed regions. In addition, by positioning regions of the resistive heating element with a greater resistance over the nonrecessed regions of the tubular heat-conducting element, a greater proportion of the overall heat dissipated by the resistive heating element may be dissipated into the non-recessed regions. As a result an overall greater proportion of the heat dissipated by the resistive heating element is directed to portions of the tubular heat-conducting element which may be in direct contact with an aerosol-generating article.

The tubular heat-conducting element may have a length extending between a first end of the tubular heat-conducting element and a second end of the tubular heat-conducting element. The tubular heat-conducting element may define a longitudinal direction parallel with the length of the tubular heat-conducting element. The tubular heat-conducting element may further define a circumferential direction extending around the longitudinal direction. The tubular heat- conducting element may further define a radial direction perpendicular to the longitudinal direction and normal to the circumferential direction.

The resistive heater may extend along only part of the length of the tubular heat-conducting element. In other words, the resistive heater may extend around only a portion of the outer surface of the tubular heat-conducting element. This may be particularly advantageous in examples in which the aerosol-generating device is used to heat an aerosol-forming substrate having a length that is shorter than the length of the tubular heat-conducting element.

The resistive heater may extend along the full length of the tubular heat-conducting element. This may be particularly advantageous in examples in which the aerosol-generating device is used to heat an aerosol-forming substrate having a length that is equal to or greater than the length of the tubular heat-conducting element. Alternatively, the resistive heating element may extend along only part of the length of the tubular heat-conducting element.

Preferably, the resistive heater is in direct contact with the outer surface of the tubular heat- conducting element. Advantageously, direct contact between the resistive heater and the outer surface of the tubular heat-conducting element may increase or maximise heat transfer from the resistive heater to the tubular heat-conducting element. Advantageously, this may increase or maximise heat transfer to an aerosol-generating article contained within the chamber at least partially defined by the inner surface of the tubular heat-conducting element.

The plurality of first regions of the resistive heating element, each having a first electrical resistance, may each have a first path length. The plurality of second regions of the resistive heating element, each having a second electrical resistance, may each have a second path length. The first path length of each first region and the second path length of each second region may be selected in order to vary the electrical resistance of each first region of the resistive heating element and each second region of the resistive heating element. For example, each first path length may be greater than each second path length.

The term “path length” is used herein to describe the shortest electrically conductive path between a first point of the resistive heating element and a second point of the resistive heating element.

The plurality of first regions of the resistive heating element, each having a first electrical resistance, may each have a first cross-sectional area. The plurality of second regions of the resistive heating element, each having a second electrical resistance, may each have a second cross-sectional area. The first cross-sectional area of each first region may be different to the second cross-sectional area of the second region. In other words, the first cross-sectional area of each first region and the second cross-sectional area of each second region may be selected so that the electrical resistance of each first region of the resistive heating element is different to the electrical resistance of each second region of the resistive heating element. Preferably, each first cross-sectional area is less than each second cross-sectional area.

The term “cross-sectional area” when referring to the resistive heating element is used herein to refer to a cross-sectional area of the resistive heating element perpendicular to the direction of current flow through the resistive heating element during use.

The first cross-sectional area of each first region of the resistive heating element may be constant along the path length of the first region. The first cross-sectional area of each first region of the resistive heating element may vary along the path length of the first region.

The second cross-sectional area of each second region of the resistive heating element may be constant along the path length of the second region. The second cross-sectional area of each second region of the resistive heating element may vary along the path length of the second region.

The resistive heating element may have a thickness extending in the radial direction. Preferably, the thickness of the resistive heating element in each of the first regions is the same as the thickness of the resistive heating element in each of the second regions. Advantageously, providing the resistive heating element with a uniform thickness may simplify manufacture of the resistive heating element. For example, the resistive heating element may be cut from a sheet of material having a uniform thickness.

The resistive heating element may have a width extending parallel to at least one of the longitudinal direction and the circumferential direction. The resistive heating element may have a first width in each of the first regions and a second width in each of the second regions. Preferably, each first width is different to each second width. Preferably, each first width is less than each second width. Advantageously, varying the width of the resistive heating element facilitates the first and second regions of the resistive heating element having different cross- sectional areas while retaining a uniform thickness of the resistive heating element.

The plurality of first regions of the resistive heating element, each having a first electrical resistance, may each have a first cross-sectional shape. The first cross-sectional shape of each first region may be circular, oval, elliptical, square, or rectangular. Preferably, the first cross- sectional shape of each first region may be square or rectangular. Advantageously, a square or rectangular cross-sectional shape may increase or maximise a contact area between each first region and the tubular heat-conducting element. The plurality of second regions of the resistive heating element, each having a second electrical resistance, may each have a second cross-sectional shape. The second cross- sectional shape of each second region may be circular, oval, elliptical, square, or rectangular. Preferably, the second cross-sectional shape of each second region may be square or rectangular. Advantageously, a square or rectangular cross-sectional shape may increase or maximise a contact area between each second region and the tubular heat-conducting element. Preferably, the second cross-sectional shape is the same as the first cross-sectional shape. Advantageously, forming the first and second regions with the same cross-sectional shape may simplify the manufacture of the resistive heating element.

The term “cross-sectional shape” when referring to the resistive heating element is used herein to refer to a cross-sectional shape of the resistive heating element perpendicular to the direction of current flow through the resistive heating element during use.

The plurality of first regions of the resistive heating element, each having a first electrical resistance, may each be formed of a first material with a first electrical resistivity. The plurality of second regions of the resistive heating element, each having a second electrical resistance, may each be formed of a second material with a second electrical resistivity. The first material may be the same as the second material. The first material may be different to the second material so that the first electrical resistivity is different to the second electrical resistivity. In other words, the first material with a first electrical resistivity of each first region and the second material with a second electrical resistivity of each second region may be selected in order to vary the electrical resistance of each first region of the resistive heating element and each second region of the resistive heating element. For example, each first material with a first electrical resistivity may have a higher electrical resistivity than each second material with a second electrical resistivity.

Advantageously, varying one or more of the path length, the cross-sectional area, and the material forming each second region when compared to each first region permits a great degree of control over the electrical resistance of each first region and each second region of the resistive heating element. This allows a great degree of control over the spatial distribution of heat dissipated by the resistive heating element.

The plurality of first regions of the resistive heating element with a first electrical resistance may have the same first electrical resistance. The plurality of first regions of the resistive heating element with a first electrical resistance may have the same first path length. The plurality of first regions of the resistive heating element with a first electrical resistance may have the same first cross-sectional area. The plurality of first regions of the resistive heating element with a first electrical resistance may be formed of the same first material with the same first electrical resistivity.

Preferably, the plurality of first regions of the resistive heating element with a first electrical resistance have the same first electrical resistance. Preferably, the plurality of first regions of the resistive heating element with a first electrical resistance are formed of the same first material with the same first electrical resistivity.

The plurality of second regions of the resistive heating element with a second electrical resistance may have the same second electrical resistance. The plurality of second regions of the resistive heating element with a second electrical resistance may have the same second path length. The plurality of second regions of the resistive heating element with a second electrical resistance may have the same second cross-sectional area. The plurality of second regions of the resistive heating element with a second electrical resistance may be formed of the same second material with the same second electrical resistivity.

The entire resistive heating element may be made of one material. In embodiments in which the entire resistive heating element is made of one material, the first material with the first electrical resistivity which forms the first regions of the resistive heating element is the same as the second material with the second electrical resistivity which forms the second regions of the resistive heating element.

The first resistance of the first region of the resistive heating element may be less than 300 milliohms. Preferably, the first resistance of the first region of the resistive heating element is less than 290 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 280 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 270 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 260 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 250 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 240 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 230 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 220 milliohms. More preferably, the first resistance of the first region of the resistive heating element is less than 210 milliohms.

The first resistance of the first region of the resistive heating element may be greater than 100 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 110 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 120 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 130 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 140 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 150 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 160 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 170 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 180 milliohms. More preferably, the first resistance of the first region of the resistive heating element is greater than 190 milliohms.

For example, the first resistance of the first region of the resistive heating element may be between 100 milliohm and 300 milliohms. Preferably, the first resistance of the first region of the resistive heating element may be between 110 milliohms and 290 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 120 milliohms and 280 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 130 milliohms and 270 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 140 milliohms and 260 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 150 milliohms and 250 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 160 milliohms and 240 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 170 milliohms and 230 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 180 milliohms and 220 milliohms. More preferably, the first resistance of the first region of the resistive heating element may be between 190 milliohms and 210 milliohms.

The first resistance of the first region of the resistive heating element may be about 200 milliohms.

The second resistance of the second region of the resistive heating element may be less than 50 milliohms. Preferably, the second resistance of the second region of the resistive heating element is less than 45 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 40 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 35 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 30 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 25 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 20 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 15 milliohms. More preferably, the second resistance of the second region of the resistive heating element is less than 12 milliohms.

The second resistance of the second region of the resistive heating element may be greater than 1 milliohm. More preferably, the second resistance of the second region of the resistive heating element is greater than 2 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 3 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 4 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 5 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 6 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 7 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 8 milliohms. More preferably, the second resistance of the second region of the resistive heating element is greater than 9 milliohms.

For example, the second resistance of the second region of the resistive heating element may be between 1 milliohm and 50 milliohms. Preferably, the second resistance of the second region of the resistive heating element may be between 2 milliohms and 45 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 3 milliohms and 40 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 4 milliohms and 35 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 5 milliohms and 30 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 6 milliohms and 25 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 7 milliohms and 20 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 8 milliohms and 15 milliohms. More preferably, the second resistance of the second region of the resistive heating element may be between 9 milliohms and 12 milliohms.

The second resistance of the second region of the resistive heating element may be about 10 milliohms.

The ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be greater than 2. Preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 4. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 6. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 8. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 10. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 12. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 14. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 16. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is greater than 18.

The ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be less than 75. Preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 60. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 55. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 50. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 45. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 40. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 35. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 30. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element is less than 25.

For example, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 2 and 75. Preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 4 and 60. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 6 and 55. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 8 and 50. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 10 and 45. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 12 and 40. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 14 and 35. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 16 and 30. More preferably, the ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be between 18 and 25.

The ratio of the first electrical resistance of the first region of the resistive heating element to the second electrical resistance of the second region of the resistive heating element may be approximately 20.

The resistive heater may have a first end. The resistive heater may have a second end.

The resistive heating element may have a first end. The resistive heating element may have a second end. The first end of the resistive heating element may coincide with the first end of the resistive heater. The second end of the resistive heating element may coincide with the second end of the resistive heater. Both the first end and the second end of the resistive heating element may coincide with the first end of the resistive heater. Both the first end and the second end of the resistive heating element may coincide with the second end of the resistive heater. The first end of the resistive heating element may be between the first and second end of the resistive heater. The second end of the resistive heating element may be between the first and second end of the resistive heater.

The first end of the resistive heating element may define a first electrical connection portion. The second end of the resistive heating element may define a second electrical connection portion. In embodiments in which the aerosol-generating device comprises a power supply and control circuitry, preferably the first and second electrical connection portions are electrically connected to at least one of the power supply and the control circuitry.

The first electrical connection portion of the resistive heating element may be a first region of the resistive heating element. The first electrical connection portion of the resistive heating element may be a second region of the resistive heating element. The second electrical connection portion of the resistive heating element may be a first region of the resistive heating element. The second electrical connection portion of the resistive heating element may be a second region of the resistive heating element. Preferably, both the first and the second electrical connection portions of the resistive heating element are second regions of the resistive heating element.

Adjacent regions of the resistive heating element may be directly connected to each other, such that they are in direct electrical contact. For example, first regions of the resistive heating element may be directly connected to second regions of the resistive heating element, such that they are in direct electrical contact. First regions of the resistive heating element may also be directly connected to other first regions of the resistive heating element, such that they are in direct electrical contact. Second regions of the resistive heating element may also be directly connected to other second regions of the resistive heating element, such that they are in direct electrical contact.

Alternatively, adjacent regions of the resistive heating element may be connected to each other by electrically-conducting connecting elements, which form an electrically conducting channel between the adjoining regions. For example, first regions of the resistive heating element may be connected to second regions of the resistive heating element by an electrically-conducting connecting element. First regions of the resistive heating element may also be connected to other first regions of the resistive heating element by an electrically-conducting connecting element. Second regions of the resistive heating element may also be connected to other second regions of the resistive heating element by an electrically-conducting connecting element. Advantageously, electrically-conducting connecting elements allow for greater flexibility between adjacent regions of the heat-conducting element, permitting the heat-conducting element to adopt a variety of spatial configurations.

The resistive heating element may comprise a plurality of electrically-conducting connecting elements.

The resistive heating element may contain an equal number of first regions and second regions. The resistive heating element may contain more first regions than second regions. The resistive heating element may contain more second regions than first regions. Preferably, the resistive heating element comprises at least two first regions and at least two second regions.

The resistive heating element may contain an alternating series of first regions and second regions. All of the adjacent regions may be directly connected to each other. All of the adjacent regions may be connected to each other by an electrically-conductive connecting element between each region. Some of the connections between the adjacent regions may be direct connections. Some of the adjacent regions may be connected by electrically-conductive connecting elements.

The resistive heating element may form a series electrical circuit between the first electrical connection portion and the second electrical connection portion. In other words, all of the components of the resistive heating element between the first electrical connection portion and the second electrical connection portion may be in series with each other.

The resistive heater may comprise a substrate. The substrate may be formed from a non- electrically conductive material. The resistive heating element may be arranged on the substrate. Preferably, the substrate is formed from a flexible material. Advantageously, a flexible substrate may facilitate wrapping the resistive heater around the tubular heat-conducting element. The resistive heating element may comprise a heating wire, filament or an electrically- conductive flexible sheet. The resistive heating element may be formed from an electrically- conductive flexible sheet.

Suitable materials for forming the resistive heating element may include on or more of: semiconductors such as doped ceramics, electrically “conductive” ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum and metals from the platinum group. Examples of suitable metal alloys include stainless steel, nickel-, cobalt-, chromium-, aluminium- titanium- zirconium-, hafnium-, niobium-, molybdenum- , tantalum-, tungsten-, tin-, gallium-, manganese- and iron-containing alloys, and super-alloys based on nickel, iron, cobalt, stainless steel, Timetai® and iron-manganese-aluminium based alloys. The electrically resistive track may comprise a heating wire or filament, for example a Ni- Cr (Nickel-Chromium), platinum, tungsten or alloy wire or filament.

Preferably, the aerosol-generating device comprises a power supply and control circuitry connected to the resistive heating element of the resistive heater. Preferably, the power supply and the control circuitry are configured to provide a direct electric current to the resistive heating element to resistively heat the tubular heat-conducting element.

The plurality of first regions of the resistive heating element, each having a first electrical resistance, may each be configured to reach a first temperature when power is supplied to the resistive heating element by the power supply and the control circuitry. The plurality of second regions of the resistive heating element, each having a second electrical resistance, may each be configured to reach a second temperature when power is supplied to the resistive heating element by the power supply and the control circuitry. Preferably, each first temperature is greater than each second temperature. Advantageously, this facilitates efficient heat transfer from the resistive heater to an aerosol-generating article inserted into the chamber of the aerosolgenerating device.

When the power supply provides a direct electric current to the resistive heater, the total voltage drop over the plurality of first regions of the resistive heating element is a first voltage drop. The total voltage drop over the plurality of second regions of the resistive heating element is a second voltage drop.

The first voltage drop may be at least 60% of the total voltage drop across the entire resistive heating element. Preferably, the first voltage drop is at least 65% of the total voltage drop across the entire resistive heating element. More preferably, the first voltage drop is at least 70% of the total voltage drop across the entire resistive heating element. More preferably, the first voltage drop is at least 75% of the total voltage drop across the entire resistive heating element. More preferably, the first voltage drop is at least 80% of the total voltage drop across the entire resistive heating element. More preferably, the first voltage drop is at least 85% of the total voltage drop across the entire resistive heating element. More preferably, the first voltage drop is at least 90% of the total voltage drop across the entire resistive heating element.

The second voltage drop may be less than 40% of the total voltage drop across the entire resistive heating element. Preferably, the second voltage drop is less than 35% of the total voltage drop across the entire resistive heating element. More preferably, the second voltage drop is less than 30% of the total voltage drop across the entire resistive heating element. More preferably, the second voltage drop is less than 25% of the total voltage drop across the entire resistive heating element. More preferably, the second voltage drop is less than 20% of the total voltage drop across the entire resistive heating element. More preferably, the second voltage drop is less than 15% of the total voltage drop across the entire resistive heating element. More preferably, the second voltage drop is less than 15% of the total voltage drop across the entire resistive heating element.

The resistive heater may comprise both a resistive heating element and a substrate. The resistive heating element may comprise a heating wire, filament or an electrically-conductive flexible sheet. The resistive heating element may be formed from an electrically-conductive flexible sheet. The substrate may be formed from a non-electrically conductive material. The resistive heating element may be arranged on the substrate.

Preferably, each first region of the resistive heating element exclusively overlies one or more non-recessed regions of the tubular heat-conducting element. In other words, preferably each first region of the resistive heating element does not overlie any of the recessed regions of the tubular heat-conducting element. Preferably, each second region of the resistive heating element exclusively overlies one or more recessed regions of the tubular heat-conducting element. In other words, preferably each second region of the resistive heating element does not overlie any of the non-recessed regions of the tubular heat-conducting element. Advantageously, this facilitates efficient heat transfer from the resistive heater to non-recessed regions of the tubular heat-conducting element which may directly contact an aerosol-generating article inserted into the chamber.

Preferably, each non-recessed region of the tubular heat-conducting element exclusively underlies one or more first regions of the resistive heating element. In other words, preferably each non-recessed region of the tubular heat-conducting element does not underlie any of the second regions of the resistive heating element. Preferably, each recessed region of the tubular heat conducting element underlies one or more second regions of the resistive heating element. In other words, preferably each recessed region of the tubular heat-conducting element does not underlie any of the first regions of the resistive heating element. Advantageously, this allows for improved heat transfer from the resistive heater to regions of the tubular heat-conducting element which may directly contact an aerosol-generating article inserted into the chamber defined by the inner surface of the tubular heat-conducting element.

Each non-recessed region of the tubular heat-conducting element may underlie only one first region of the resistive heating element. Each non-recessed region of the tubular heat- conducting element may underlie a plurality of first regions of the resistive heating element.

Each recessed region of the tubular heat-conducting element may underlie only one second region of the resistive heating element. Each recessed region of the tubular heat- conducting element may underlie a plurality of second regions of the resistive heating element.

The resistive heater may comprise only one resistive heating element. Advantageously, providing a resistive heater consisting of one resistive heating element may simplify the manufacture of the resistive heater.

The resistive heater may comprise a plurality of resistive heating elements. Each resistive heating element may have any of the features or properties as described above. In embodiments in which the resistive heater comprises a plurality of resistive heating elements, each resistive heating element may extend around the circumference of the tubular heat-conducting element, and adjacent resistive heating elements may be spaced apart from each other along the longitudinal direction of the tubular heat-conducting element. Alternatively, each resistive heating element may extend along the length of the tubular heat-conducting element, and adjacent resistive heating elements may be spaced apart from each other along the circumferential direction of the tubular heat-conducting element.

In embodiments in which the resistive heater comprises a plurality of resistive heating elements, wherein each resistive heating element has any of the features or properties described above, each resistive heating element may be individually connected to at least one of the power supply and the control circuity, such that each resistive heating element may be controlled independently. Alternatively, the resistive heating elements may be connected such that the resistive heater comprises a parallel circuit comprising a plurality of resistive heating elements connected in parallel. Alternatively, the resistive heating elements may be connected such that the resistive heater comprises of a series circuit comprising a plurality of resistive heating elements connected in series.

Preferably, the tubular heat-conducting element extends in a longitudinal direction.

The tubular heat-conducting element may have a first end and a second end. The second end may be opposite the first end. The tubular heat-conducting element may extend longitudinally between its first end and its second end.

Preferably, the tubular heat-conducting element is arranged for insertion of an aerosolgenerating article into the chamber along the longitudinal direction.

Preferably, the tubular heat-conducting element comprises a cylindrical wall defining the inner surface and the outer surface of the tubular heat-conducting element, wherein the cylindrical wall defines a radial direction extending perpendicular to the longitudinal direction and has a thickness in the radial direction, and wherein the thickness of the cylindrical wall at the recessed regions is less than the thickness of the cylindrical wall at the non-recessed regions.

The minimum thickness of the cylindrical wall at each recessed region may be less than 90% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 85% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 80% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 75% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 70% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 65% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 60% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 55% of the maximum thickness of the cylindrical wall at each non-recessed region. The minimum thickness of the cylindrical wall at each recessed region may be less than 50% of the maximum thickness of the cylindrical wall at each non-recessed region.

Preferably, the tubular heat-conducting has a circular cross-sectional shape at the outer surface.

Preferably, the non-recessed regions of the inner surface of the tubular heat-conducting element are arranged to directly contact the surface of an aerosol-generating article received within the chamber. Advantageously, this facilitates efficient heat transfer between the nonrecessed regions of the inner surface of the tubular heat-conducting element and an aerosolgenerating article received within the chamber.

Preferably, each recessed region of the inner surface of the tubular heat-conducting element extends in the longitudinal direction along which the tubular heat-conducting element extends. Each recessed region of the tubular heat-conducting element may extend from the first end of the tubular heat-conducting element to the second end of the tubular heat-conducting element.

Each recessed region of the tubular heat-conducting element may have a length which extends in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction. The width of the recessed region may vary along the length of the recessed region. The width of the recessed region may be constant along the length of the recessed region. Preferably, each non-recessed region of the inner surface of the tubular heat-conducting element extends in the longitudinal direction along which the tubular heat-conducting element extends. Each non-recessed region of the tubular heat-conducting element may extend from the first end of the tubular heat-conducting element to the second end of the tubular heat-conducting element.

Each non-recessed region of the tubular heat-conducting element may have a length which extends in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction. The width of the non-recessed region may vary along the length of the non-recessed region. The width of the non-recessed region may be constant along the length of the non-recessed region.

Preferably, the recessed regions and non-recessed regions are arranged to form an alternating series of recessed regions and non-recessed regions on the inner surface of the tubular heat-conducting element. The widths of the recessed regions and non-recessed regions of the tubular heat-conducting element may be different. For example, the widths of the nonrecessed regions may be greater than the widths of the recessed regions. The widths of the nonrecessed regions may be less than the widths of the recessed regions. The widths of the nonrecessed regions may be the same as the widths of the recessed regions.

Preferably, each recessed region and each non-recessed region may extend linearly and in parallel with the longitudinal direction. However, each recessed region and each non-recessed region may extend in any manner along the length of the inner surface of the tubular heat- conducting element. For example, the recessed regions and non-recessed regions may form a series of alternating spirals along the inner surface of the tubular heat-conducting element.

The tubular heat-conducting element may comprise any number of recessed regions and any number of non-recessed regions. Preferably, the tubular heat-conducting element comprises at least two recessed regions and at least two non-recessed regions. For example, the tubular heat-conducting element may comprise four recessed regions and four non-recessed regions.

The recessed regions of the tubular heat-conducting element may be in any form. Preferably, the recessed regions are in the form of a channel defined by the inner surface of the tubular heat-conducting element.

The non-recessed regions of the tubular heat-conducting element may be in any form. Preferably, the non-recessed regions are in the form of a rib defined by the inner surface of the tubular heat-conducting element.

The aerosol-generating device may comprise an inductor coil. The inductor coil may extend around at least a portion of the tubular heat-conducting element. The inductor coil may extend around at least a portion of the resistive heater. The power supply and control circuitry may be connected to the inductor coil and configured to provide an alternating current to the inductor coil such that, in use, the inductor coil generates an alternating magnetic field. Advantageously, in embodiments comprising an inductor coil, the inductor coil may be used to inductively heat a susceptor element contained within an aerosol-forming substrate in an aerosol-forming article received within the chamber. At the same time, the resistive heater may provide external heating of an aerosol-forming substrate of an aerosol-generating article received within the chamber. Advantageously, simultaneous internal and external heating of the aerosolforming substrate may facilitate more uniform heating of the aerosol-forming substrate.

Advantageously using a separate inductor coil and resistive heater to provide inductive heating and resistive heating respectively means that the characteristics, shapes and materials of the inductor coil and the resistive heater may be individually adapted and optimised to more efficiently heat an aerosol-forming substrate. For example, the inductor coil may be optimised for inductive heating and the resistive heater may be optimised for resistive heating.

Preferably, at least one of the control circuitry and the tubular heat-conducting element is configured to prevent inductive coupling between the tubular heat-conducting element and the inductor coil during use.

As used herein, the term “inductively couple” refers to the heating of a material when penetrated by an alternating magnetic field. The heating may be caused by the generation of eddy currents in the material. The heating may be caused by magnetic hysteresis losses.

The control circuitry may be configured to provide the alternating electric current in the form of an alternating current having a frequency selected to reduce or prevent inductive coupling between the tubular heat-conducting element and the inductor coil during use. Preferably, the alternating current is provided at a frequency that reduces or prevents inductive coupling between the inductor coil and the tubular heat-conducting element and increases or maximises inductive coupling between the inductor coil and a susceptor element. The frequency at which inductive coupling occurs will vary depending on the materials, physical properties and configuration of the inductor coil, the tubular heat-conducting element and the susceptor element, such as the inductance of the inductor coil and the magnetic permeability of the material or materials from which each of the heat-conducting element and the susceptor element are formed.

The inductor coil may extend between a first end and a second end. An electrical resistance between the first end and the second end of the inductor coil may be less than 250 milliohms, preferably less than 150 milliohms, preferably still approximately 100 milliohms. A relatively low electrical resistance may ensure that minimal power is dissipated in the inductor coil as heat.

The tubular heat-conducting element may be formed from a material that reduces or prevents inductive coupling between the inductor coil and the heat-conducting element. The tubular heat-conducting element may be formed from a non-electrically conductive material. The non-electrically conductive material may comprise at least one of a glass, a ceramic, a silicone, a polymeric material, and a composite material comprising two or more non- electrically conductive materials. A suitable ceramic may comprise at least one of alumina and aluminium nitrate. Advantageously alumina and aluminium nitrate have been found to possess suitable thermal properties to ensure that heat is efficiently transferred from the resistive heater to an aerosol-forming substrate.

The term “electrically conductive” is used herein to refer to materials having an electrical conductivity of at least 0.8 x 106 Siemens per metre. The terms “non-electrically conductive” and “electrically insulating” are used herein to refer to materials having an electrical conductivity of less than 0.8 x 10⁴ Siemens per metre.

The tubular heat-conducting element may be formed from a non-inductively heatable material. The non-inductively heatable material may comprise any of the non-electrically conductive materials described above. The non-inductively heatable material may comprise an electrically conductive material that exhibits poor or no inductive coupling with the inductor coil. The non-inductively heatable material may comprise a metal. The metal may comprise at least one of aluminium and a paramagnetic steel. The paramagnetic steel may comprise an austenitic steel. The heat-conducting element may be formed from a 316 stainless steel.

Preferably, the chamber at least partially defined by the inner surface of the tubular heat- conducting element comprises a first end defining an opening for receiving an aerosol-generating article and a second end opposite the first end. Preferably, the second end of the chamber is a closed end.

The aerosol-generating device may comprise at least one protrusion extending into the chamber from the closed second end of the chamber. Advantageously, the at least one protrusion may abut an upstream end of an aerosol-generating article received within the chamber to space the upstream end of the aerosol-generating article apart from the closed end of the chamber. Advantageously, spacing the upstream end of the aerosol-generating article from the closed end of the chamber may facilitate airflow into the aerosol-generating article during use.

Preferably, the at least one protrusion comprises at least two protrusions. Advantageously, providing at least two protrusions may facilitate secure and correct positioning of an aerosolgenerating article in the chamber. Preferably, the chamber has a longitudinal axis defining a first direction along which at least a portion of an aerosol-generating article may be inserted into the chamber, wherein the at least two protrusions are equidistantly spaced from each other in a circumferential direction around the longitudinal axis. The at least two protrusions may preferably comprise three protrusions or four protrusions.

The aerosol-generating device may comprise a housing, wherein the tubular heat- conducting element and the resistive heater are positioned within the housing. In embodiments comprising a power supply and control circuitry, preferably the power supply and the control circuitry are positioned within the housing. In embodiments comprising an inductor coil, preferably the inductor coil is positioned within the housing, Preferably, the housing comprises an end wall defining the closed second end of the chamber. In embodiments comprising at least one protrusion, preferably the at least one protrusion extends into the chamber from the end wall. Preferably, the at least one protrusion is formed integrally with the end wall.

According to the present disclosure there is also provided an aerosol-generating system comprising an aerosol-generating device according to the present disclosure. The aerosolgenerating system also comprises an aerosol-generating article comprising an aerosolgenerating substrate.

The aerosol-forming substrate may be a solid aerosol-forming substrate. The aerosolforming substrate may comprise tobacco material. The aerosol-generating article may comprise one or more susceptors. The one or more susceptors may be in the form of at least one strip or at least one rod or at least one particle. Advantageously, in such embodiment the aerosolgenerating device does not need to include a susceptor as a component of the aerosol-generating device.

When the aerosol-generating article is received within the chamber of the aerosolgenerating device, an outer surface of the aerosol-generating article may contact the nonrecessed regions of the inner surface of the tubular heat-conducting element of the aerosolgenerating device. Advantageously, this ensures efficient heat transfer between the tubular heat- conducting element and the aerosol-generating article.

When the aerosol-generating article is received within the chamber of the aerosolgenerating device, each recessed region of the inner surface of the tubular heat-conducting element of the aerosol-generating device may form an airflow pathway. Preferably, each airflow pathway extends between the first end of the chamber and the second end of the chamber.

Preferably, the aerosol-forming substrate is a solid aerosol-forming substrate. However, the aerosol-forming substrate may comprise both solid and liquid components. Alternatively, the aerosol-forming substrate may be a liquid aerosol-forming substrate.

Preferably, the aerosol-forming substrate comprises nicotine. More preferably, the aerosol-forming substrate comprises tobacco. Alternatively or in addition, the aerosol-forming substrate may comprise a non-tobacco containing aerosol-forming material.

If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosolforming substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, strands, strips or sheets containing one or more of: herb leaf, tobacco leaf, tobacco ribs, expanded tobacco and homogenised tobacco.

Optionally, the solid aerosol-forming substrate may contain tobacco or non-tobacco volatile flavour compounds, which are released upon heating of the solid aerosol-forming substrate. The solid aerosol-forming substrate may also contain one or more capsules that, for example, include additional tobacco volatile flavour compounds or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate.

Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, strands, strips or sheets. The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid aerosol-forming substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non-uniform flavour delivery during use.

In a preferred embodiment, the aerosol-forming substrate comprises homogenised tobacco material. As used herein, the term “homogenised tobacco material” refers to a material formed by agglomerating particulate tobacco.

Preferably, the aerosol-forming substrate comprises a gathered sheet of homogenised tobacco material. As used herein, the term “sheet” refers to a laminar element having a width and length substantially greater than the thickness thereof. As used herein, the term “gathered” is used to describe a sheet that is convoluted, folded, or otherwise compressed or constricted substantially transversely to the longitudinal axis of the aerosol-generating article. Preferably, the aerosol-forming substrate comprises an aerosol former. As used herein, the term “aerosol former” is used to describe any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol and that is substantially resistant to thermal degradation at the operating temperature of the aerosol-generating article.

Suitable aerosol-formers are known in the art and include, but are not limited to: polyhydric alcohols, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as propylene glycol, triethylene glycol, 1 ,3-butanediol and, most preferred, glycerine.

The aerosol-forming substrate may comprise a single aerosol former. Alternatively, the aerosol-forming substrate may comprise a combination of two or more aerosol formers.

The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Ex. 1. An aerosol-generating device comprising a tubular heat-conducting element comprising an inner surface and an outer surface, wherein the inner surface at least partially defines a chamber for receiving an aerosol-generating article and wherein the inner surface comprises a plurality of recessed regions and a plurality of non-recessed regions; and a resistive heater extending around at least a portion of the outer surface of the tubular heat-conducting element, the resistive heater comprising a resistive heating element, wherein the resistive heating element comprises a plurality of first regions each having a first electrical resistance; and a plurality of second regions each having a second electrical resistance, wherein each first electrical resistance is greater than each second electrical resistance, wherein each first region overlies one of the non-recessed regions of the inner surface of the tubular heat-conducting element, and wherein each of the second regions overlies one of the recessed regions of the inner surface of the tubular heat-conducting element.

Ex. 2. An aerosol-generating device according to example 1 , wherein the resistive heater extends along the full length of the tubular heat-conducting element.

Ex. 3. An aerosol-generating device according to example 1 , wherein the resistive heater extends along only part of the length of the tubular heat-conducting element.

Ex. 4. An aerosol-generating device according to example 1 or 2, wherein the resistive heating element extends along the full length of the tubular heat-conducting element.

Ex. 5. An aerosol-generating device according to example 1 , 2 or 3, wherein the resistive heating element extends along only part of the length of the tubular heat-conducting element.

Ex. 6. An aerosol-generating device according to any preceding example, wherein the resistive heater directly contacts the outer surface of the tubular heat-conducting element.

Ex. 7. An aerosol-generating device according to any preceding example, wherein each first region has a first path length, wherein each second region has a second path length, and wherein each first path length is greater than each second path length.

Ex. 8. An aerosol-generating device according to any preceding example, wherein each first region has a first cross-sectional area, wherein each second region has a second cross-sectional area, and wherein each first cross-sectional area is less than each second cross-sectional area. Ex. 9. An aerosol-generating device according to any preceding example, wherein each first region is formed of a material with a first electrical resistivity, wherein each second region is formed of a material with a first electrical resistivity, and wherein each first electrical resistivity is greater than each second electrical resistivity.

Ex. 10. An aerosol-generating device according to any preceding example, wherein the plurality of first regions each having a first electrical resistance have the same first electrical resistance. Ex. 11. An aerosol-generating device according to any preceding example, wherein the plurality of second regions each having a second electrical resistance have the same second electrical resistance.

Ex. 12. An aerosol-generating device according to any preceding example, wherein the ratio of the first electrical resistance to the second electrical resistance is at least 3.

Ex. 13. An aerosol-generating device according to example 12, wherein the ratio of the first electrical resistance to the second electrical resistance is at least 10. Ex. 14. An aerosol-generating device according to any preceding example, wherein the first electrical resistance is greater than 150 milliohms.

Ex. 15. An aerosol-generating device according to any preceding example, wherein the second electrical resistance is less than 50 milliohms.

Ex. 16. An aerosol-generating device according to example 14 or 15, wherein the first electrical resistance is 200 milliohms.

Ex. 17. An aerosol-generating device according to example 14, 15 or 16, wherein the second electrical resistance is 10 milliohms.

Ex. 18. An aerosol-generating device according to any preceding example, wherein the resistive heater has a first end and a second end, wherein the resistive heating element has a first end and a second end, and wherein both the first end and the second end of the resistive heating element coincide with either the first end of the resistive heater or the second end of the resistive heater.

Ex. 19. An aerosol-generating device according to any preceding example, wherein the resistive heating element comprises at least one electrically-conductive connecting element connecting a pair of adjacent regions of the resistive heating element.

Ex. 20. An aerosol-generating device according to any preceding example, wherein the resistive heating element comprises at least two first regions and at least two second regions.

Ex. 21. An aerosol-generating device according to any preceding example, wherein the resistive heating element is formed from an electrically-conductive flexible sheet.

Ex. 22. An aerosol-generating device according to any of examples 1 to 20, wherein the resistive heating element comprises a heating wire or filament.

Ex. 23. An aerosol-generating device according to any preceding example, wherein the resistive heater comprises a substrate and wherein the resistive heating element is arranged on the substrate.

Ex. 24. An aerosol-generating device according to example 23, wherein the substrate is formed from a non-electrically conductive material.

Ex. 25. An aerosol-generating device according to any preceding example, wherein the resistive heater comprises only one resistive heating element.

Ex. 26. An aerosol-generating device according to any preceding example, further comprising a power supply and control circuitry connected to the resistive heating element, wherein the power supply and the control circuitry are configured to provide a direct electric current to the resistive heating element to resistively heat the tubular heat-conducting element.

Ex. 27. An aerosol-generating device according to example 26, wherein the first end of the resistive heating element defines a first electrical connection portion, wherein the second end of the resistive heating element defines a second electrical connection portion, and wherein the first electrical connection portion and the second electrical connection portion of the resistive heating element are connected to at least one of the power supply and the control circuitry.

Ex. 28. An aerosol-generating device according to examples 26 or 27, wherein the power supply and the control circuitry are configured so that, when power is supplied to the resistive heating element, each first region of the resistive heating element heats to a first temperature, each second region of the resistive heating element heats to a second temperature, and wherein each first temperature is greater than each second temperature.

Ex. 29. An aerosol-generating device according to examples 26, 27 or 28, wherein when power is supplied to the resistive heating element, the total voltage drop across the plurality of first regions of the resistive heating element is at least 75% of the total voltage drop across the entire resistive heating element.

Ex. 30. An aerosol-generating device according to example 29, wherein when power is supplied to the resistive heating element, the total voltage drop across the plurality of first regions of the resistive heating element is at least 90% of the total voltage drop across the entire resistive heating element.

Ex. 31. An aerosol-generating device according to any preceding example, wherein each first region of the resistive heating element exclusively overlies a non-recessed region of the tubular heat-conducting element.

Ex. 32. An aerosol-generating device according to any preceding example, wherein each second region of the resistive heating element exclusively overlies a recessed region of the tubular heat- conducting element.

Ex. 33. An aerosol-generating device according to any preceding example, wherein each nonrecessed region of the tubular heat-conducting element exclusively underlies at least one first region of the resistive heating element.

Ex. 34. An aerosol-generating device according to any preceding example, wherein each recessed region of the tubular heat-conducting element exclusively underlies at least one second region of the resistive heating element.

Ex. 35. An aerosol-generating device according to any preceding example, wherein the tubular heat-conducting element extends in a longitudinal direction.

Ex. 36. An aerosol-generating device according to any preceding example, wherein the tubular heat-conducting element comprises a cylindrical wall defining the inner surface and the outer surface of the tubular heat-conducting element, wherein the cylindrical wall defines a radial direction extending perpendicular to the longitudinal direction and has a thickness in the radial direction, and wherein the thickness of the cylindrical wall at the recessed regions is less than the thickness of the cylindrical wall at the non-recessed regions. Ex. 37. An aerosol-generating device according to example 36, wherein the minimum thickness of the cylindrical wall at each recessed region is less than 75% of the maximum thickness of the cylindrical wall at each non-recessed region.

Ex. 38. An aerosol-generating device according to any preceding example, wherein the tubular heat-conducting element has a circular cross-sectional shape at the outer surface.

Ex. 39. An aerosol-generating device according to any preceding example, wherein the nonrecessed regions of the inner surface of the tubular heat-conducting element are arranged to directly contact an aerosol-generating article received within the chamber.

Ex. 40. An aerosol-generating device according to any preceding example, wherein each recessed region extends in the longitudinal direction.

Ex. 41. An aerosol-generating device according to any preceding example, wherein the tubular heat-conducting element has a first end and a second end opposite the first end, and wherein each recessed region extends from the first end to the second end.

Ex. 42. An aerosol-generating device according to any preceding example, wherein each recessed region has a length extending in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction, and wherein the width is constant along the length of the recessed region.

Ex. 43. An aerosol-generating device according to any preceding example, wherein each nonrecessed region extends in the longitudinal direction.

Ex. 44. An aerosol-generating device according to any preceding example, wherein the tubular heat-conducting element has a first end and a second end opposite the first end, and wherein each non-recessed region extends from the first end to the second end.

Ex. 45. An aerosol-generating device according to any preceding example, wherein each nonrecessed region has a length extending in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction, and wherein the width is constant along the length of the non-recessed region.

Ex. 46. An aerosol-generating device according to any preceding example, wherein the recessed regions and the non-recessed regions are arranged to form an alternating series of recessed regions and non-recessed regions on the inner surface of the tubular heat-conducting element.

Ex. 47. An aerosol-generating device according to any preceding example, wherein the widths of the recessed regions and the non-recessed regions are the same.

Ex. 48. An aerosol-generating device according to any preceding example, wherein each recessed region and each non-recessed region extends linearly and in parallel with the longitudinal direction.

Ex. 49. An aerosol-generating device according to any preceding example comprising four recessed regions and four non-recessed regions. Ex. 50. An aerosol-generating device according to example any preceding example, wherein each recessed region is a channel defined by the inner surface of the tubular heat-conducting element. Ex. 51. An aerosol-generating device according to example 50, wherein each channel extends in the longitudinal direction.

Ex. 52. An aerosol-generating device according to example 50 or 51 , wherein the tubular heat- conducting element has a first end and a second end opposite the first end, and wherein each channel extends from the first end to the second end.

Ex. 53. An aerosol-generating device according to example 50, 51 or 52, wherein each channel has a length extending in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction, and wherein the width is constant along the length of the channel.

Ex. 54. An aerosol-generating device according to example any preceding example, wherein each non-recessed region forms a rib defined by the inner surface of the tubular heat-conducting element.

Ex. 55. An aerosol-generating device according to example 54, wherein each rib extends in the longitudinal direction.

Ex. 56. An aerosol-generating device according to example 54 or 55, wherein the tubular heat- conducting element has a first end and a second end opposite the first end, and wherein each rib extends from the first end to the second end.

Ex. 57. An aerosol-generating device according to example 54, 55 or 56, wherein each rib has a length extending in the longitudinal direction and a width extending in a circumferential direction about the longitudinal direction, and wherein the width is constant along the length of the rib.

Ex. 58. An aerosol-generating device according to the combination of any of examples 50 to 53 with any of examples 54 to 57, wherein the channels and the ribs are arranged to form an alternating series of channels and ribs on the inner surface of the tubular heat-conducting element.

Ex. 59. An aerosol-generating device according to example 58, wherein the widths of the ribs and the channels are the same.

Ex. 60. An aerosol-generating device according to example 58 or 59 wherein each channel and each rib extends linearly and in parallel with the longitudinal direction.

Ex. 61. An aerosol-generating device according to example 58, 59 or 60 comprising four channels and four ribs.

Ex. 62. An aerosol-generating device according to any preceding example wherein the tubular heat-conducting element is formed from at least one of a non-inductively heatable material and a non-electrically conductive material. Ex. 63. An aerosol-generating device according to any preceding example, wherein the chamber comprises an open first end through which at least a portion of an aerosol-generating article may be inserted into the chamber and a closed second end opposite the open first end.

Ex. 64. An aerosol-generating device according to example 63, further comprising at least one protrusion extending into the chamber from the closed second end of the chamber.

Ex. 65. An aerosol-generating device according to example 64, wherein the at least one protrusion comprises at least two protrusions.

Ex. 66. An aerosol-generating device according to the combination of any of examples 26 to 30 with any other preceding example, further comprising a housing, wherein the tubular heat- conducting element, the resistive heater, the power supply and the control circuitry are positioned within the housing.

Ex. 67. An aerosol-generating device according to any preceding example comprising an inductor coil extending around at least a portion of the tubular heat-conducting element.

Ex. 68. An aerosol-generating device according to example 67, wherein the inductor coil extends around at least a portion of the resistive heater.

Ex. 69. An aerosol-generating device according to the combination of any of examples 26 to 30 with either of examples 67 or 68, wherein the power supply and the control circuitry are connected to the inductor coil and configured to provide an alternating current to the inductor coil such that, in use, the inductor coil generates an alternating magnetic field.

Ex. 70. An aerosol-generating device according to example 69, wherein at least one of the control circuity and the tubular heat-conducting element is configured to prevent inductive coupling between the tubular heat-conducting element and the inductor coil during use.

Ex. 71. An aerosol-generating device according to the combination of example 66 with any of examples 67 to 70, wherein the inductor coil is positioned within the housing.

Ex. 72. An aerosol-generating system comprising: an aerosol-generating device according to any preceding example; and an aerosol-generating article comprising an aerosol-forming substrate.

Ex. 73. An aerosol-generating system according to example 72, wherein the aerosol-generating article comprises a susceptor element.

Ex. 74. An aerosol-generating system according to examples 72 or 73, wherein each recessed region of the aerosol-generating device forms an airflow pathway when the aerosol-generating article is received within the chamber.

The invention is further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a side cross-sectional view of an aerosol-generating device according to a first embodiment of the present invention; Figure 2 shows an axial cross sectional view of the aerosol-generating device of Figure 1 along line 1-1 ;

Figure 3 shows a top-down view of the resistive heater of the aerosol-generating device of Figure 1 when laid out flat;

Figure 4 shows a top-down view of an alternative resistive heater for the aerosolgenerating device of Figure 1 ;

Figure 5 shows a side cross-sectional view of an aerosol-generating device according to a second embodiment of the present invention;

Figure 6 shows a side cross-sectional view of an aerosol-generating system comprising the aerosol-generating device of Figure 1 ; and

Figure 7 shows a side cross-sectional view of an aerosol-generating system comprising the aerosol-generating device of Figure 5.

Figures 1 and 2 show an aerosol-generating device 10 in accordance with a first embodiment of the present invention. The aerosol-generating device 10 comprises a housing 12 and a chamber 14 for receiving a portion of an aerosol-generating article. The chamber 14 comprises a first end 16 through which an aerosol-generating article may be inserted into the chamber 16 and a closed second end 18 opposite the first end 16. The chamber 14 extends in a longitudinal direction between the first end 16 of the chamber 14 and the second end 18 of the chamber 14.

The aerosol-generating device 10 also comprises a tubular heat-conducting element 20. The tubular heat-conducting element 20 extends in the same longitudinal direction as the chamber 14, between a first end 22 of the tubular heat-conducting element 20 and a second end 24 of the tubular heat-conducting element 20. The first end 22 of the tubular heat-conducting element 20 coincides with the first end 16 of the chamber 14.

The tubular heat-conducting element 20 comprises a wall defining an inner surface 26 of the tubular heat-conducting element 20 and an outer surface 28 of the tubular heat-conducting element 20. The wall of the tubular heat-conducting element 20 extends between the first end 22 and the second end 24 of the tubular heat-conducting element 20. The inner surface 26 defines four recessed regions 30 and four non-recessed regions 32. Each recessed region 30 is in the form of a channel in the inner surface 26 and extends longitudinally from the first end 22 of the tubular heat-conducting element 20 to the second end 24 of the tubular heat-conducting element 20. Each non-recessed region 32 is in the form of a rib on the inner surface 26 and extends longitudinally from the first end 22 of the tubular heat-conducting element 20 to the second end 24 of the tubular heat-conducting element 20. The non-recessed regions 32 of the inner surface 26 are arranged to be in direct contact with an aerosol-generating article received within the chamber 14. Advantageously, direct contact between the non-recessed regions 32 of the inner surface 26 and the aerosol-generating article facilitates the transfer of heat from the tubular heat- conducting element 20 to the aerosol-generating article. Advantageously, the recessed regions 30 of the inner surface 26 define a series of airflow channels when an aerosol-generating article is received within the chamber 14. The airflow channels extend from the first end 22 of the tubular heat-conducting element 20 to the second end 24 of the tubular heat-conducting element 20.

The inner surface 26 and the outer surface 28 of the tubular heat-conducting element 20 define the wall of the tubular heat-conducting element 20. The wall thickness of the tubular heat- conducting element 20 at the recessed regions 30 is less than the wall thickness of the tubular heat-conducting element 20 at the non-recessed regions 32. The wall thickness of each recessed region 30 is the same. The wall thickness at each non-recessed region 32 is the same. The outer surface 28 of the tubular heat-conducting element 20 has a circular cross-sectional shape.

The channels on the inner surface 26, which are defined by recessed regions 30, and the ribs on the inner surface 26, which are defined by non-recessed regions 32, are equidistantly spaced and alternate about the circumference of the inner surface 26. Each channel has the same width. Each rib has the same width. The channels and ribs have approximately the same width as each other. The channels have the same depth.

A resistive heater 50 comprising a resistive heating element 52 extends around the outer surface 28 of the tubular heat-conducting element 20. The resistive heater 50 extends along the full length of the tubular heat-conducting element 20 and is in direct contact with the outer surface 28 of the tubular heat-conducting element 20. Advantageously, positioning the resistive heater 50 in direct contact with the outer surface 28 of the tubular heat-conducting element 20 facilitates the transfer of heat generated by the resistive heater 50 to the tubular heat-conducting element 20. The resistive heater 50 and the tubular heat-conducting element 20 are arranged concentrically about a central axis 34 of the aerosol-generating device. The central axis 34 extends in the longitudinal direction.

The housing 12 defines a plurality of protrusions 36 extending into the chamber 14 from the second end 18 of the chamber 14. The plurality of protrusions 36 function to maintain a gap between an end of an aerosol-generating article and the second end 18 of the chamber 14 when the aerosol-generating article is fully inserted within the chamber 14. In the embodiment shown in Figures 1 and 2, the housing 12 defines four protrusions 36 spaced equidistantly about the central axis 34 of the aerosol-generating device 10. The protrusions 36 are aligned with the nonrecessed regions 32 . The skilled person will appreciate that the housing 12 may define more or fewer protrusions 36 and the arrangement of the protrusions at the closed second end 18 of the chamber 14 may be varied.

The aerosol-generating device 10 also comprises control circuitry 40 and a power supply 42 connected to the resistive heating element 52 of the resistive heater 50. The control circuitry 40 and power supply 42 are configured to provide a direct current to the resistive heating element 52 of the resistive heater 50 to resistively heat the resistive heater 50 and therefore heat the tubular heat-conducting element 20.

Figure 3 depicts a top-down view of the resistive heater 50 of Figure 1 when the resistive heater 50 is laid out flat. The resistive heater 50 comprises the resistive heating element 52 which is formed from an electrically conductive flexible material. The resistive heating element 52 comprises a plurality of first regions 54 each having a first electrical resistance and a plurality of second regions 56 each having a second electrical resistance. Each first electrical resistance is greater than each second electrical resistance. In this particular embodiment, each of the first regions 54 of the resistive heating element 52 has a first electrical resistance of approximately 200 milliohms. Each of the second regions 54 of the resistive heating element 52 has a second electrical resistance of approximately 10 milliohms. Therefore, the ratio of the electrical resistance of each first region 54 of the resistive heating element 52 to the electrical resistance of each second region 56 of the resistive heating element 52 is approximately 20.

The resistive heating element 52 is formed from the same flexible and electrically conductive material of uniform thickness. Therefore, the first regions 54 and the second regions 56 have the same thickness and the same electrical resistivity. The electrical resistances of the first regions 54 and the second regions 56 are varied by varying the path length and the cross- sectional area of the resistive heating element. In particular, the first regions 54 of the resistive heating element 52 have a greater path length and a smaller cross-sectional area than the second regions 56 of the resistive heating element 52.

The resistive heater 50 extends longitudinally between a first end 58 of the resistive heater 50 and a second end 60 of the resistive heater 50. When the resistive heater 50 is wrapped around the outer surface 28 of the tubular heat-conducting element 20, the first end 58 of the resistive heater 50 is adjacent to the second end 60 of the resistive heater 20.

The resistive heating element 52 also extends between a first end 62 of the resistive heating element 52 and a second end 64 of the resistive heating element 52. As shown in Figure 3, in the resistive heater 50 according to the first embodiment of the present invention, both of the first end 62 of the resistive heating element 52 and the second end 64 of the resistive heating element 52 are located towards the first end 58 of the resistive heater 50.

As is further demonstrated in Figure 3, the resistive heating element 52 according to the first embodiment of the present invention comprises an electrically-conductive connecting element 66 connecting the two first regions 54 of the resistive heating element 52 located towards the second end 60 of the resistive heater 50.

The first end 62 of the resistive heating element 52 defines a first electrical connection portion of the resistive heating element 52 and the second end 64 of the resistive heating element 52 defines a second electrical connection portion of the resistive heating element 52. The first end second electrical connection portions of the resistive heating element 52 are connected to the control circuitry 40 and the power supply 42 such that the control circuitry 40 and the power supply 42 may deliver a direct current through the resistive heating element 52.

The resistive heater 50 is wrapped around the tubular heat-conducting element 20 so that each first region 54 of the heating overlies only a non-recessed region 32 of the tubular heat- conducting element 20, and so that each second region 56 of the heating element 52 overlies only a recessed region 30 of the tubular heat-conducting element 20. Therefore, the first regions 54 of the resistive heating element 52 are configured to heat the non-recessed regions 32 of the tubular heat-conducting element 20 to a first temperature and the second regions 56 of the resistive heating element 52 are configured to heat the recessed regions 30 of the tubular heat- conducting element 20 to a second temperature, wherein the second temperature is lower than the first temperature. Advantageously, the second temperature being lower than the first temperature causes the resistive heating element 52 to transfer more heat to the non-recessed regions 32 of the tubular heat-conducting element 20 which directly contact an aerosol-generating article inserted into the chamber 14. Advantageously, this improves the overall efficiency of heat transfer from the resistive heater 50 to an aerosol-generating article received within the chamber 14. The first end and second ends 58, 60 of the resistive heater 50and the first and second ends 62, 64 of the resistive heating element 52 all overlie the same recessed region 30 of the tubular heat-conducting element 20 and are configured to resistively heat the recessed region 30 of the tubular heat-conducting element 20 which they overlie to the same second temperature to which each second region 56 of the resistive heating element 52 heats each of the remaining recessed regions 30.

When the first electrical connection portion at the first end 62 of the resistive heating element 52 and the second electrical connection portion at the second end 64 of the resistive heating element 52 are connected to the control circuitry 40 and the power supply 42, the combined voltage drop across all of the first regions 54 of the resistive heating element 52 during use is about 95% of the total voltage drop across the entire resistive heating element 52.

Figure 4 shows a top-down view of an alternative resistive heater 150 for the aerosolgenerating device 10 of Figure 1. The resistive heater 150 is similar to the resistive heater 50 described with reference to Figure 3 and like reference numerals designate like parts.

The resistive heater 150 differs from the resistive heater 50 by removal of the electrically- conductive connecting element 66. The resistive heater 150 also differs from the resistive heater 50 by locating the first end 62 of the resistive heating element 152 at the first end 58 of the resistive heater 150 and locating the second end 64 of the resistive heating element 152 at the second end 60 of the resistive heater 150. Finally, the resistive heating element 152 of resistive heater 150 differs from the resistive heating element 52 of resistive heater 50 by comprising fewer first regions 54 and fewer second regions 56. Figure 5 shows an aerosol-generating device 210 according to a second embodiment of the present invention. The aerosol-generating device 210 is similar to the aerosol-generating device 10 described with reference to Figure 1 and like reference numerals designate like parts. The aerosol-generating device 210 differs from aerosol-generating device 10 by the addition of an inductor coil 251. The inductor coil 251 is connected to the control circuitry 240 and the power supply 242. The control circuitry 240 and the power supply 242 are configured to provide a direct current to the resistive heater, which may be either resistive heater 50 or resistive heater 150, and an alternating current to the inductor coil 251 to generate an alternating magnetic field. As will be explained below, the aerosol-generating device 210 according to the third embodiment may be used in conjunction with an aerosol-generating article comprising a susceptor element. Advantageously, an aerosol-generating article comprising a susceptor element may be externally heated by the resistive heater 50 and internally heated by inductive heating of the susceptor, facilitating a consistent heating profile across the aerosol-generating substrate.

Figure 6 shows a cross-sectional view of an aerosol-generating system 300 comprising the aerosol-generating device 10 of Figure 1 and an aerosol-generating article 302.

The aerosol-generating article 302 comprises an aerosol-forming substrate 304 in the form of a tobacco plug, a first hollow acetate tube 306, a second hollow acetate tube 308, a mouthpiece 310, and an outer wrapper 312. During use, a portion of the aerosol-generating article 302 is inserted into the chamber 14 so that the aerosol-forming substrate 304 is positioned inside the tubular heat-conducting element 20 and the resistive heater 50. The control circuitry 40 provides a direct electric current from the power supply 42 to the resistive heater 50 to heat the tubular heat-conducting element 20, which externally heats the aerosol-forming substrate 304 to generate an aerosol.

Airflow through the aerosol-generating system 300 during use is illustrated by the dashed lines 316 in Figure 6. When a user draws on the mouthpiece 310 of the aerosol-generating article 302, a negative pressure is generated in the chamber 14. The negative pressure draws air into the aerosol-generating device 10 through the channels formed by the recessed regions 30 of the inner surface 26 of the tubular heat-conducting element 20. The air entering the closed second end 18 of the chamber 14 from the channels then enters the aerosol-generating article 302 through the aerosol-forming substrate 304. Airflow into the aerosol-generating article 302 is facilitated by the gap maintained between the upstream end of the aerosol-generating article 302 and the second end 18 of the chamber 14 by the plurality of protrusions 36. As the airflow passes through the aerosol-forming substrate 304, aerosol generated by heating of the aerosol-forming substrate 304 is entrained in the airflow. The aerosol then flows along the length of the aerosolgenerating article 302 and through the mouthpiece 310 to the user.

Figure 7 shows a cross-sectional view of an aerosol-generating system 400 comprising the aerosol-generating device 210 of Figure 5 and an aerosol-generating article 402. The aerosol-generating article 402 comprises an aerosol-forming substrate 404 in the form of a tobacco plug, a first hollow acetate tube 406, a second hollow acetate tube 408, a mouthpiece 410, and an outer wrapper 412. The aerosol-generating article 402 also comprises a susceptor element 414 arranged within the aerosol-forming substrate 404. During use, a portion of the aerosol-generating article 402 is inserted into the chamber 14 so that the aerosol-forming substrate 404 and the susceptor element 414 are positioned inside the tubular heat-conducting element 20, the inductor coil 251 and the resistive heater 50. The control circuitry 240 provides an alternating electric current from the power supply 242 to the inductor coil 251 to generate an alternating magnetic field that inductively heats the susceptor element 414, which internally heats the aerosol-forming substrate 404 to generate an aerosol. Additionally, the control circuitry 240 provides a direct electric current from the power supply 242 to the resistive heater 50 to resistively heat the tubular heat-conducting element 20, which externally heats the aerosol-forming substrate 404 to generate an aerosol. Airflow through the aerosol-generating system 400 during use is illustrated by the dashed lines 416 in Figure 7 and is the same as the airflow described with reference to Figure 6.

Claims

1. An aerosol-generating device comprising: a tubular heat-conducting element comprising an inner surface and an outer surface, wherein the inner surface at least partially defines a chamber for receiving an aerosol-generating article and wherein the inner surface comprises a plurality of recessed regions and a plurality of non-recessed regions; and a resistive heater extending around at least a portion of the outer surface of the tubular heat-conducting element, the resistive heater comprising a resistive heating element, wherein the resistive heating element comprises: a plurality of first regions each having a first electrical resistance; and a plurality of second regions each having a second electrical resistance, wherein each first electrical resistance is greater than each second electrical resistance, wherein each first region overlies one of the non-recessed regions of the inner surface of the tubular heat- conducting element, and wherein each of the second regions overlies one of the recessed regions of the inner surface of the tubular heat-conducting element.

2. An aerosol-generating device according to claim 1 , wherein the resistive heater directly contacts the outer surface of the tubular heat-conducting element.

3. An aerosol-generating device according to claim 1 or 2, wherein each first region has a first path length, wherein each second region has a second path length, and wherein each first path length is greater than each second path length.

4. An aerosol-generating device according to claim 1 , 2 or 3, wherein each first region has a first cross-sectional area, wherein each second region has a second cross-sectional area, and wherein each first cross-sectional area is less than each second cross-sectional area.

5. An aerosol-generating device according to any preceding claim, wherein the ratio of the first electrical resistance to the second electrical resistance is at least 3.

6. An aerosol-generating device according to any preceding claim, wherein the first electrical resistance is greater than 150 milliohms.

7. An aerosol-generating device according to any preceding claim, wherein the second electrical resistance is less than 50 milliohms.

8. An aerosol-generating device according to any preceding claim, further comprising a power supply and control circuitry connected to the resistive heating element, wherein the power supply and the control circuitry are configured to provide a direct electric current to the resistive heating element to resistively heat the tubular heat-conducting element.

9. An aerosol-generating device according to claim 8, wherein the total voltage drop across the plurality of first regions of the resistive heating element is at least 75% of the total voltage drop across the entire resistive heating element when power is supplied to the resistive heating element.

10. An aerosol-generating device according to any preceding claim, wherein the nonrecessed regions of the inner surface of the tubular heat-conducting element are arranged to directly contact an aerosol-generating article received within the chamber.

11. An aerosol-generating device according to any preceding claim, further comprising an inductor coil extending around at least a portion of the tubular heat-conducting element.

12. An aerosol-generating device according to claim 11 in combination with claim 8 or 9, wherein the power supply and the control circuitry are connected to the inductor coil and configured to provide an alternating current to the inductor coil such that, in use, the inductor coil generates an alternating magnetic field.

13. An aerosol-generating system comprising: an aerosol-generating device according to any preceding claim; and an aerosol-generating article comprising an aerosol-forming substrate.

14. An aerosol-generating system according to claim 13, wherein the aerosol-generating article comprises a susceptor element.

15. An aerosol-generating system according to claim 13 or 14, wherein each recessed region of the aerosol-generating device forms an airflow pathway when the aerosol-generating article is received within the chamber.