FR3154793A1 - Thermal heater for heat transfer fluid with electric rods. - Google Patents

Abstract

The present invention relates to a thermal heater (1) for a heat transfer fluid, comprising a closed enclosure (11) comprising a cylindrical tube (10) having an upstream end (12) and a downstream end (13), at least one bundle (2) of a plurality of electric rods (20) for heating this fluid, these rods (20) being arranged axially inside said tube (10), an inlet conduit (4) and an outlet conduit (8) for the heat transfer fluid into and out of the enclosure (11). This heater is remarkable in that it comprises an annular chamber (3) for introducing the heat transfer fluid into the enclosure, arranged around the tube (10) from its upstream end (12) and over part of the length thereof, in that the inlet conduit (4) opens into this introduction chamber (3) and in that the upstream end (12) of the tube (10) of the enclosure comprises several orifices (5) for introducing the heat transfer fluid, distributed around the periphery of the tube (10). Figure for abstract: Fig. 3

Description

Thermal heater for heat transfer fluid with electric rods. FIELD OF THE INVENTION

The invention is in the field of thermal energy storage.

The present invention relates more particularly to a thermal heater of a heat transfer fluid using a bundle of electric rods.

STATE OF THE ART

A number of installations produce electricity intermittently, such as photovoltaic panels, heliostat fields or wind turbines.

It is therefore desirable to be able to store the electrical energy produced at a given time by these installations, in order to use it later at a time when there is no more sun or wind, for example, but when the demand for electricity is high.

For this purpose, thermal heaters are already known in the state of the art, which make it possible to heat a heat transfer fluid, generally a molten salt, using the surplus electricity produced by the aforementioned installations, to constitute an energy storage in thermal form. This thermal energy is subsequently used to produce electricity, for example using a standard steam turbine cycle and an electricity generator.

There FIG. 1 attached illustrates an example of a first embodiment of a thermal heater, known from the state of the art.

As can be seen in this figure, such a heater comprises a cylindrical enclosure A, inside which is arranged a bundle of axial electric rods B. These electric rods extend from one end of enclosure A to the other. A radial inlet tube C and a radial outlet tube D are provided at each end of enclosure A to respectively introduce into it or extract from it the fluid (molten salt) to be heated.

Each rod B is a tube which internally contains an electrical resistance E and this resistance is supplied with electricity from a power supply box F. Each rod B thus allows heating by Joule effect, the salt circulating in the heater.

However, if the heater must produce salt heated to a specific temperature at its outlet D, the temperature reached locally by the molten salt, in enclosure A, must also not exceed a certain threshold. Indeed, beyond this temperature threshold, the chemical properties of the salt risk degrading, as well as its performance.

However, when electric rods are used to produce thermal energy by the Joule effect in a closed enclosure, if this energy is not uniformly evacuated, that is to say uniformly transferred to the fluid (molten salt) which circulates in this enclosure, then the temperature of this fluid can locally reach very high values, which leads to its irreversible degradation.

As a purely illustrative example, for a nitrate salt used in a heater and composed of 60% NaNO and 40% KNCl, it must be brought from a low temperature (around 300°C) to a high temperature (around 580°C), but without exceeding the threshold of 600°C beyond which this salt degrades irreversibly.

In a heater having the geometry shown in the FIG. 1 , we observe a local inhomogeneity of the temperature of the molten salts. Indeed, the salts entering through tube C directly impact the rods B and the electrical resistances E contained therein. These salts tend to flow more quickly towards the inside of the heater (arrows F1) and to stagnate in the heater zone referenced A1, located upstream of the inlet tube C. We observe the same stagnation phenomenon in the heater zone referenced A2, located downstream of the outlet tube D.

In these two stagnation zones, we observe a problem of overheating of the molten salts, due to the fact that the salts remain in contact with the electric rods B for longer.

Furthermore, heat transfer from the rods B to the salts is better at locations where the salts flow more quickly around the rods than at locations where the salts flow more slowly around them, because the heat transfer coefficient is related to the flow speed. In both stagnation zones A1 and A2, there is therefore also a risk of overheating of the electric rods, which can lead to their deterioration.

In order to overcome this problem, a thermal heater illustrated in the figure is also known in the state of the art. FIG. 2 attached.

This heater differs from the previous one in that the electric heating resistors E do not extend to both ends of each electric rod B. Consequently, in the heater zone referenced A3, which includes zone A1 and that located opposite the inlet tube C and in the heater zone referenced A4, which includes zone A2 and that located opposite the outlet tube D, the salts are not heated.

While this solution solves the aforementioned problems of overheating salts and canes, it has the disadvantage of unnecessarily increasing the total length of the heater to obtain the same heating temperature at its outlet. Each zone A3 and A4 is approximately 1m long.

Finally, in both of the above-mentioned heaters, there is a problem of vibration of the B rods, linked to the fact that the molten salts introduced via the inlet tube C directly impact the rods. There is therefore an additional risk of damage to the B rods.

The invention aims to solve the aforementioned problems and in particular to propose a thermal heater with a bundle of electric rods, which allows:

- to reduce or eliminate the phenomenon of the appearance of hot spots and therefore of inhomogeneity in the heating of the heat transfer fluid (in particular molten salts) to be heated,

- to respect the temperature thresholds not to be exceeded to avoid the degradation of this fluid,

- to obtain a more homogeneous and more reproducible temperature of the fluid leaving the heater,

- and to eliminate the problem of vibration of the rods, linked to the lateral introduction of a fluid at high speed.

The invention also aims to provide a heater which also allows:

- to limit the length of the rod not having electrical resistance,

- to minimize the overall length of the heater for the same thermal power and therefore its footprint,

- and to be able to possibly connect several heaters.

To this end, the invention relates to a thermal heater for a heat transfer fluid, in particular a molten salt, comprising:

- a closed enclosure comprising a cylindrical tube having an upstream end and a downstream end relative to the direction of flow of the heat transfer fluid inside the enclosure,

- at least one bundle of a plurality of electric rods for heating this fluid, these rods being arranged axially inside said tube of the enclosure,

- an inlet conduit for the heat transfer fluid into the enclosure and an outlet conduit for this heat transfer fluid outside the enclosure.

According to the invention, this heater comprises an annular chamber for introducing the heat transfer fluid into the enclosure, this annular introduction chamber being arranged around the tube of the enclosure and coaxially with it and extending from the upstream end of the tube over part of the length thereof, the inlet conduit is connected to this annular introduction chamber and opens into the interior thereof and the upstream end of the tube of the enclosure comprises several orifices for introducing the heat transfer fluid, these introduction orifices being distributed around the periphery of the tube and placing the annular introduction chamber and the interior of the enclosure in fluid communication.

Thanks to these features of the invention, the heat transfer fluid enters via the inlet duct, then circulates in the annular fluid introduction chamber before entering the enclosure, but at the end of the latter and while being distributed around the periphery of the latter via the fluid introduction orifices, instead of entering the enclosure at a single lateral point. This results in better optimization of the heating of the fluid and there is no fluid stagnation zone.

Furthermore, unlike the state of the art where there was a single jet of incoming fluid which struck certain heating rods and subjected them to strong vibrations, having fluid inlets distributed around the periphery of the tube makes it possible to reduce or eliminate this vibration of the rods.

According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:

- the heater comprises an annular chamber for discharging the heat transfer fluid from the enclosure, this annular discharge chamber being arranged around the tube of the enclosure and coaxially with it and extending from the downstream end of the tube over part of the length of the latter, the outlet duct is connected to this annular discharge chamber and opens into the interior thereof, and the downstream end of the tube of the enclosure comprises several orifices for discharging the heat transfer fluid, these evacuation orifices being distributed around the periphery of the tube and placing the interior of the enclosure and the annular discharge chamber in fluid communication;

- each electrical rod of the bundle or of at least one of the bundles comprises an electrical resistance arranged inside a tube longer than said electrical resistance, so as to form at the upstream end of said tube a zone free from electrical resistance, called the upstream non-heating zone and the orifices for introducing the heat transfer fluid are formed in the part of the tube of the enclosure located around the upstream non-heating zones of the electrical rods of the bundle of electrical rods;

- each electrical rod of the bundle or of at least one of the bundles comprises an electrical resistance arranged inside a tube longer than said electrical resistance, so as to form at the downstream end of said tube a zone free from electrical resistance, called the downstream non-heating zone and the orifices for discharging the heat transfer fluid are formed in the part of the tube of the enclosure located around the downstream non-heating zones of the electrical rods of the bundle of electrical rods;

- the heater comprises, inside the tube of the enclosure, a so-called "upstream" bundle of electrical rods and a so-called "downstream" bundle of electrical rods, arranged end to end axially in the tube so that the downstream end of the upstream bundle is located close to the upstream end of the downstream bundle, the electrical rods of the upstream bundle comprise an upstream non-heating zone and the electrical rods of the downstream bundle comprise a downstream non-heating zone;

- the inlet duct opens radially or substantially radially into the annular introduction chamber and/or in that the outlet duct opens radially or substantially radially into the annular evacuation chamber;

- the fluid introduction orifices and/or the fluid discharge orifices are aligned in the form of at least one row of orifices which extends in a plane perpendicular to the longitudinal axis of the tube, preferably in the form of at least two parallel rows of orifices;

- the distribution density of the fluid introduction orifices is greater in the part of the enclosure tube located opposite that where the inlet conduit opens and/or the distribution density of the fluid discharge orifices is greater in the part of the enclosure tube located opposite that where the outlet conduit opens;

- the fluid introduction orifices and/or the fluid discharge orifices are circular, semi-circular, square or rectangular in shape;

- the fluid introduction orifices are arranged in the form of at least two rows of parallel orifices and in that each fluid introduction orifice of a row located further downstream has an area smaller than the area of each fluid introduction orifice of a row located further upstream and/or the fluid discharge orifices are arranged in the form of at least two rows of parallel orifices and in that each fluid discharge orifice of a row located further upstream has an area smaller than the area of each fluid introduction orifice of a row located further downstream;

- the heater comprises a plurality of deflectors arranged alternately inside the tube of the enclosure, these deflectors extending perpendicular to the axis of the tube to ensure a zigzag circulation of the heat transfer fluid inside the enclosure.

DESCRIPTION OF FIGURES

Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

FIG. 1 is a diagram showing in longitudinal section an example of an embodiment of a thermal heater known from the state of the art.

FIG. 2 is a diagram showing in longitudinal section another example of the embodiment of a thermal heater known from the state of the art.

FIG. 3 is a diagram showing in longitudinal section the thermal heater according to the invention.

FIG. 4 is a perspective view of a portion of the thermal heater according to the invention.

FIG. 5 is a partial sectional view of the upstream end of the thermal heater according to the invention.

FIG. 6 is a diagram representing a first possible variant of the heat transfer fluid introduction or evacuation orifices.

FIG. 7 is a diagram representing a second possible variant of the heat transfer fluid introduction or evacuation orifices.

FIG. 8 is a diagram representing a third possible variant of the heat transfer fluid introduction or evacuation orifices.

FIG. 9 is a diagram representing a fourth possible variant of the heat transfer fluid introduction or evacuation orifices.

FIG. 10 is a perspective and partial sectional view of the heater of the invention showing the positioning of the deflectors.

FIG. 11 is a perspective and partial sectional view of the heater of the invention showing the positioning of the deflectors, the section being made along a plane perpendicular to that of the FIG. 10 .

FIG. 12 is a perspective view of a heater comprising two bundles of electrical rods, arranged at each end of the heater.

DETAILED DESCRIPTION OF THE INVENTION.

The thermal heater 1 of a heat transfer fluid according to the invention will now be described in connection with figures 3 to 5.

The heat transfer fluid to be heated is in particular a molten salt, which allows energy to be stored in thermal form, at a sufficiently high temperature, so that it can be used later in the production of electrical energy. As a purely illustrative example, we can cite a salt composed of 60% NaNO and 40% KNCl. Other molten salts or other heat transfer fluids can also be used.

This heater 1 comprises a cylindrical tube 10, with a central longitudinal axis X-X’.

A bundle 2 of several electric rods 20 for heating the heat transfer fluid is arranged inside the tube 10, so that its rods 20 extend axially inside this tube, that is to say parallel to the axis X-X'.

Each rod 20 comprises a tube 21, inside which is arranged an axial electrical resistance 22, the latter being supplied with electricity from an electrical connection box 23.

The rods 20 allow the heat transfer fluid circulating in the tube 10 to be heated by the Joule effect.

Preferably, each tube 21 is longer than the electrical resistance 22, so as to form at the upstream end of said tube 21, a zone free from electrical resistance, called the “upstream non-heating zone” 211.

Also preferably, each tube 21 is longer than the electrical resistance 22, so as to form at the downstream end of said tube 21, a zone free from electrical resistance, called “downstream non-heating zone” 212.

The tube 10, closed at its two ends as will be described later, constitutes a closed cylindrical enclosure 11, inside which the heat transfer fluid flows from upstream to downstream, that is to say from left to right in Figures 3 and 4.

In the remainder of the description and the claims, the terms “upstream” and “downstream” are to be taken into consideration in relation to the direction of flow of the heat transfer fluid inside the enclosure 11.

The tube 10 comprises an upstream end 12 and a downstream end 13.

An annular chamber 3 for introducing the heat transfer fluid into the enclosure 11 is arranged around the tube 10 of the enclosure and coaxially therewith. The axis X-X' also constitutes the central axis of the chamber 3. This introduction chamber 3 extends from the upstream end 12 of the tube 10 and over a part of the length thereof, as is better seen on the left part of the FIG. 3 .

According to a possible embodiment of the introduction chamber 3, shown in figures 3 and 4, an upstream cylindrical sleeve 30 is arranged around the upstream end 12 of the tube 10 of the enclosure, at a distance from the latter and coaxially with this tube.

The upstream sleeve 30 is closed on the one hand at its downstream end by a downstream annular disc 31 and on the other hand, at its upstream end, by an upstream cover 32, which also closes the tube 10, more precisely the upstream end 12 thereof.

Thus, the upstream sleeve 30, the downstream annular disc 31, the upstream cover 32 and the upstream end 12 of a part of the length of the tube 10 together delimit said annular chamber 3 for introducing the heat transfer fluid into the enclosure 11.

An inlet conduit 4 is connected to the annular chamber 3 for introducing the heat transfer fluid and opens into it.

Preferably, this inlet duct 4 opens radially into the annular chamber 3, as shown in the figures. In other words, the axis of the duct 4 is preferably perpendicular to the axis X-X' of the tube 10. It can also open substantially radially into the chamber 3, that is to say that its axis is not strictly perpendicular to the axis X-X'. Also preferably, this inlet duct 4 consists of a tube.

Several orifices 5 for introducing the heat transfer fluid are formed through the upstream end 12 of the tube 10 of the enclosure (i.e. through the wall which constitutes this tube). These orifices 5 make it possible to put the annular introduction chamber 3 in fluid communication with the interior of the enclosure 11.

Thus, the heat transfer fluid enters the heater through the inlet duct 4 (arrow i), from where it flows over 360° of the annular introduction chamber 3 (arrows ii), before passing through the introduction orifices 5 (arrows iii) radially and finally flowing axially in the space provided between the different electric rods 20 (arrows iv).

The introduction orifices 5 are formed on the periphery of the upstream end 12 of the tube 10, preferably over the entire periphery (i.e. over 360°).

Preferably also and as it appears better on the FIG. 5 , these introduction orifices 5 are aligned so as to form at least one row 50 of orifices. Preferably, this row 50 of orifices extends in a plane P perpendicular to the longitudinal axis X-X' of the tube 10.

As shown in Figures 5 to 9, the introduction orifices 5 can take very varied shapes. Preferably, these orifices are circular, as shown in the FIG. 6 , squares as shown in the FIG. 9 or rectangular, as shown in Figures 5 and 8, because these shapes are simpler to manufacture. They can, however, take any other shape, for example hexagonal or triangular, as shown in the FIG. 7 , without departing from the scope of the invention.

Furthermore, the introduction orifices 5 can be located at a distance from the cover 32, as shown in Figures 6, 7 and 9, or on the contrary, open onto the cover 32, as shown in Figures 5 and 8. In the latter case, the orifices 5 can also be semi-circular.

Advantageously, on the same row 50, the distribution density of these introduction orifices 5 can also vary.

So, for example on the FIG. 6 , it can be seen that the density of the introduction orifices 5 is higher in the lower part of the figure and lower in the upper part thereof. Advantageously, it is possible to provide that the distribution density of the introduction orifices 5 is higher in the part of the tube 10 of the enclosure opposite the inlet duct 4, (i.e. on the left on the FIG. 5 ) and on the contrary is less important in the part of the tube 10 located opposite this inlet conduit 4, so as to be able to modulate the flow which enters radially into the tube 10. »

It is possible to have a single row 50 of orifices 5, as shown in figures 5, 6 and 8, or on the contrary to have several rows of orifices 5, referenced 50, 51 and 52, as shown for example in figures 7 and 9. More preferably, there are at most four parallel rows of orifices 5.

Finally, even with 5 holes of identical shape, it is possible to have some holes smaller than others.

Thus, for example, when the introduction orifices 5 are arranged in the form of at least two rows of parallel orifices, it is possible for each introduction orifice 5 of a row located further downstream (for example row 51 or 52 in FIGS. 7 and 9) than a row 50 located further upstream, to have an area smaller than the area of each introduction orifice 5 of said row 50 located further upstream. This arrangement is particularly advantageous if it is desired to modulate the inlet speed of the fluid as well as its circumferential distribution. In addition, the axial length of the upstream 211 and downstream 212 non-heating zones of the tube 10 can be significantly reduced, for example to approximately 10 cm.

Furthermore, although this is not shown in the figures, it is also possible to have, on the same row of introduction orifices 5, orifices 5 which are smaller than others.

As can be seen on the FIG. 3 , preferably, the introduction orifices 5 are formed at the upstream end 12 of the tube 10 so as to be located opposite the upstream non-heating zones 211 to avoid finding oneself in a situation where the end of the rod 20 which comprises the electrical resistance 22 would be insufficiently cooled.

As can be seen on the FIG. 5 , preferably, the angle θ1 between the two circumferential ends of an opening 5 can be between… 5° and 10° to obtain a homogeneous circumferential distribution of the introduction of the fluid into the cavity 11 of the FIG. 3 and not create overly dynamic fluid jets.

Furthermore, preferably, the angle θ2 between the centers of two neighboring openings 5 is between 5° and 10°. Such a value is notably chosen to be consistent with the angle θ1 retained for the dimensions of the openings. Such a value makes it possible to maximize the passage sections, to be able to modulate a homogeneous circumferential distribution of the fluid which enters the cavity 11 of the tube 10 and to give the possibility of reducing the non-heating zone 211.

The thickness E1 of the annular introduction chamber 3, that is to say the distance between the inner face of the cylindrical sleeve 30 and the outer face of the tube 10 is, advantageously, between 5% and 20% of the diameter of the enclosure 11. The objective is not to have high speeds in the introduction chamber 3 itself, which could cause additional pressure losses.

Advantageously, and as is better shown in Figures 4 and 10 and 11, the heater 1 also comprises several deflectors 6, arranged alternately so as to form a baffle passage for the heat transfer fluid to be heated.

Thus, this fluid is better mixed and passes well into contact with all the electric rods 20, extracting all the heat energy, which guarantees good homogeneity of its temperature at the outlet of the heater.

In the embodiment shown in the figures, each deflector 6 has the shape of a truncated circular plate (i.e. one of which is missing a circular segment) and which therefore comprises a rectilinear edge 60 along a chord of the circle.

The deflectors 6 are arranged alternately head to tail (i.e. at 180° from one to the next), so that the edge 60 of one is oriented towards the bottom of the heater and the edge 60 of the next is oriented towards the top of the heater (the bottom and the top being defined in relation to the normal position of use of the heater 1 which is horizontal).

Each deflector 6 is pierced with a plurality of holes 61, each of which allows the reception of an electric rod 20. Preferably, the rods 20 are mounted in the holes 61, with a small functional clearance (or mounting clearance). Thus, the majority of the flow of heat transfer fluid circulates around the rods 20 (i.e. axially) then when it comes into abutment against a deflector 6, goes around it around the edge 60 and continues to the next deflector, and so on, until the outlet (see arrow F1 in FIG. 11 which represents the zig-zag circulation of the heat transfer fluid). Only a minor part of the flow circulates through the functional clearance.

According to a first embodiment of the invention, it is possible to have a heater 1 comprising an annular introduction chamber 3 at its upstream end and having at its downstream end, only one outlet tube, such as the outlet tube D of the state of the art.

However, advantageously and as shown in the FIG. 3 , the heater 1 may also have at its downstream end, an annular chamber 7 for discharging the heat transfer fluid from the enclosure 11. This makes it possible to benefit from the aforementioned advantages, in particular in terms of homogeneity of heating, elimination of vibration of the rods and reduction of the length of the heater.

In this case, and in a similar manner to what has been described for the upstream end of the heater, and which will therefore not be described again in detail, this annular evacuation chamber 7 is delimited by a downstream cylindrical sleeve 70, arranged around the downstream end 13 of the tube 10 of the enclosure, at a distance from the latter and coaxially with this tube, by an upstream annular disc 71 and by a downstream cover 72.

An outlet duct 8 is connected, preferably radially or substantially radially to the sleeve 70 and opens into the annular discharge chamber 7. The outlet duct 8 could also be connected axially to the sleeve 70, since the electrical connections of the resistors 22 are located at the upstream end.

Finally, several evacuation orifices 9 for the heat transfer fluid are formed through the downstream end 13 of the tube of the enclosure, so as to put the interior of the enclosure 11 and the annular evacuation chamber 7 into fluid communication.

What has been described for the introduction orifices 5 of the heat transfer fluid applies to these evacuation orifices 9, in particular with regard to the shape, the distribution density, the dimensions and positions of these orifices and their number of rows, and will therefore not be described again in detail.

Finally, as shown in the FIG. 12 , it is possible according to an alternative embodiment of the invention to have a heater 1' whose tube 10 contains two bundles of electric rods, arranged end to end axially in the tube 10. These bundles are called respectively upstream bundle 2 and downstream bundle 2' and they are arranged so that the downstream end of the upstream bundle 2 is located close to the upstream end of the downstream bundle 2'.

Only two rods 20, respectively 20', of each beam 2, 2' have been represented schematically and in dotted lines on the FIG. 12 The 20' rods of the 2' downstream beam are connected to a 23' electrical connection box.

Advantageously, the electric rods 20 of the upstream bundle 2 comprise an upstream non-heating zone 211, as described previously and the introduction orifices 5 are preferentially arranged in front of this zone 211 and the electric rods 20' of the downstream bundle 2' comprise a downstream non-heating zone 212' and the evacuation orifices 9 are preferentially arranged in front of this zone 212'.

Inside the 1' heater, the ends of the electrical rods of the two bundles can be very close to each other.

This embodiment makes it possible to have a heater 1' longer than the heater 1 described previously and producing a greater heating power. It is also possible to construct two heaters 1 as previously described but without an annular chamber at one of their two ends and to assemble them end to end by their respective tubes 10 to obtain the heater 1'.

Claims (11)

Thermal heater (1, 1') for a heat transfer fluid, in particular a molten salt, comprising:
- a closed enclosure (11) comprising a cylindrical tube (10) having an upstream end (12) and a downstream end (13) relative to the direction of flow of the heat transfer fluid inside the enclosure (11),
- at least one bundle (2, 2') of a plurality of electric rods (20, 20') for heating this fluid, these rods (20, 20') being arranged axially inside said tube (10) of the enclosure,
- an inlet conduit (4) for the heat transfer fluid into the enclosure (11), and
- an outlet conduit (8) for this heat transfer fluid outside the enclosure (11),
characterized in that it comprises an annular chamber (3) for introducing the heat transfer fluid into the enclosure, this annular introduction chamber (3) being arranged around the tube (10) of the enclosure and coaxially with it and extending from the upstream end (12) of the tube (10) over part of the length thereof,
in that the inlet duct (4) is connected to this annular introduction chamber (3) and opens into it,
and in that the upstream end (12) of the tube (10) of the enclosure comprises several introduction orifices (5) for the heat transfer fluid, these introduction orifices (5) being distributed around the periphery of the tube (10) and placing the annular introduction chamber (3) and the interior of the enclosure (11) in fluid communication. Thermal heater (1, 1') according to claim 1, characterized in that it comprises an annular chamber (7) for discharging the heat transfer fluid from the enclosure, this annular discharge chamber (7) being arranged around the tube (10) of the enclosure and coaxially with it and extending from the downstream end (13) of the tube (10) over part of the length thereof,
in that the outlet duct (8) is connected to this annular evacuation chamber (7) and opens into it,
and in that the downstream end (13) of the tube (10) of the enclosure comprises several discharge orifices (9) for the heat transfer fluid, these discharge orifices (9) being distributed around the periphery of the tube (10) and placing the interior of the enclosure (11) and the annular discharge chamber (7) in fluid communication. Thermal heater (1, 1') according to claim 1 or 2, characterized in that each electrical rod (20, 20') of the bundle (2, 2') or of at least one of the bundles (2, 2') comprises an electrical resistance (22) arranged inside a tube (21) longer than said electrical resistance (22), so as to form at the upstream end of said tube (21) a zone free of electrical resistance, called the upstream non-heating zone (211),
and in that the introduction orifices (5) for the heat transfer fluid are formed in the part of the tube (10) of the enclosure located around the upstream non-heating zones (211) of the electric rods (20, 20') of the bundle of electric rods (20, 20'). Thermal heater (1, 1') according to claim 2, characterized in that each electrical rod (20, 20') of the bundle (2, 2') or of at least one of the bundles (2, 2') comprises an electrical resistance (22) arranged inside a tube (21) longer than said electrical resistance (22), so as to form at the downstream end of said tube (21) a zone free of electrical resistance, called the downstream non-heating zone (212, 212'),
and in that the discharge orifices (9) for the heat transfer fluid are formed in the part of the tube (10) of the enclosure located around the downstream non-heating zones (212, 212') of the electric rods (20, 20') of the bundle of electric rods (20, 20'). Thermal heater (1') according to claims 3 and 4, characterized in that it comprises inside the tube (10) of the enclosure, a bundle (2) called "upstream" of electric rods (20) and a bundle (2') called "downstream" of electric rods (20'), arranged end to end axially in the tube (10) so that the downstream end of the upstream bundle (2) is located close to the upstream end of the downstream bundle (2'),
in that the electric rods (20) of the upstream bundle (2) comprise an upstream non-heating zone (211),
and in that the electric rods (20') of the downstream bundle (2') comprise a downstream non-heating zone (212'). Thermal heater (1, 1') according to one of the preceding claims, characterized in that the inlet duct (4) opens radially or substantially radially into the annular introduction chamber (3) and/or in that the outlet duct (8) opens radially or substantially radially into the annular evacuation chamber (7). Thermal heater (1, 1') according to one of the preceding claims, characterized in that the fluid inlet orifices (5) and/or the fluid outlet orifices (9) are aligned in the form of at least one row (50, 51, 52) of orifices which extends in a plane perpendicular to the longitudinal axis (X-X') of the tube (10), preferably in the form of at least two parallel rows of orifices. Thermal heater (1, 1') according to one of the preceding claims, characterized in that the distribution density of the fluid introduction orifices (5) is greater in the part of the tube (10) of the enclosure located opposite that where the inlet conduit (4) opens,
and/or in that the distribution density of the fluid discharge orifices (9) is greater in the part of the tube (10) of the enclosure located opposite that where the outlet conduit (8) opens. Thermal heater (1, 1') according to one of the preceding claims, characterized in that the fluid introduction orifices (5) and/or the fluid discharge orifices (9) are circular, semi-circular, square or rectangular in shape. Thermal heater (1, 1') according to one of the preceding claims, characterized in that the fluid introduction orifices (5) are arranged in the form of at least two rows of parallel orifices and in that each fluid introduction orifice (5) of a row (52) located further downstream has an area smaller than the area of each fluid introduction orifice (5) of a row (50, 51) located further upstream,
and/or in that the fluid discharge orifices (9) are arranged in the form of at least two rows of parallel orifices and in that each fluid discharge orifice (9) of a row located further upstream has a smaller area than the area of each fluid introduction orifice (9) of a row located further downstream. Thermal heater (1, 1') according to one of the preceding claims, characterized in that it comprises a plurality of deflectors (6) arranged alternately inside the tube (10) of the enclosure, these deflectors (6) extending perpendicular to the axis of the tube (10) to ensure a zigzag circulation of the heat transfer fluid inside the enclosure (11).