EP0086730B1 - Microwave boiler for the production of a heated fluid for domestic or industriel use or for room heating, and process used by this boiler - Google Patents

Abstract

1. A microwave boiler producing hot fluids for domestic or industrial use or for room heating, comprising a metallic conducting and/or absorbing chamber (7) containing a fluid to be heated (6), a source of microwave energy (2) of the klystron or magnetron type, a device (3) of the waveguide, coaxial cable or similar type, transmitting said energy from the source (2) to the chamber (7) and a diffuser (5) which is fluid-tight and permeable to the waves, characterised in that, the fluid to be heated being a particular fluid among a plurality of fluids - particularly industrial oils -, between said device (3) of the waveguide type and said chamber (7) is interposed an applicator device (4) which co-operates with said chamber (7) in such a manner that it enables said microwave energy to be applied to said particular fluid (6) at a frequency corresponding to the natural frequency of relaxation oscillation of the particular fluid in question at a given temperature, said applicator device (4) being closed by said diffuser (5) which is fluid-tight and permeable to the waves, said applicator device (4) radiating said microwave energy towards said particular fluid (6) to be heated.

Description

The present invention relates to the field of heating fluids for domestic, industrial or space heating use, and relates to a microwave boiler intended for this purpose.

Currently, the heating of hot fluids for domestic, industrial, or space heating, is essentially carried out by means of boilers with liquid, gaseous or solid fuel, of dimensions appropriate to the needs.

These existing boilers generally have acceptable thermal yields and are of relatively simple construction and therefore inexpensive. However, due to the scarcity of fuel supply sources and the rapid rise in the price of these fuels, the operating cost of these known boilers increases rapidly, and other energy sources become competitive for heating. fluids. Thus, the production of hot water by application of electrical energy has become common, in particular by transformation of this energy by means of heating resistors or by means of heat pumps.

However, this method of heating a fluid by means of electrical energy does not allow optimum exploitation of the latter, and therefore a satisfactory overall energy balance.

The present invention aims to overcome these drawbacks.

It has, in effect, a microwave boiler for the production of a hot fluid for domestic, industrial, or space heating.

Boilers of this type are known from US-A-4,165,455, US-A-4,029,927, US-A-4,114,011, as well as from GB-A-2,048,629.

Thus, US-A-4 165 455 describes a steam or hot water generator which comprises a resonant cavity of small volume and a vapor collector, the resonant cavity being in the form of a grid arranged horizontally in order to favor the correct operation of the steam generating device. The production of steam is carried out by an air-water interface and by a regulation of the water level by means of a sensor and a valve, the resonant cavity ensuring the transfer of heat at the level of the water surface. to produce steam, so that the effective heating of the water, by application of microwave energy, occurs only inside said resonant cavity.

In addition, the resonant cavity is necessary to heat or vaporize the water by applying microwave energy, and this cavity must be electrically isolated and have very small dimensions, namely of the order of the wavelength of the microwaves produced by the magnetron, so that large volumes cannot be processed. In addition, products other than water or steam cannot be treated because the shape and dimensions of the waveguide and the diffuser are immutable. Adjustment of the tuning of the resonant cavity is not possible, so that optimal efficiency of the radiation of energy cannot be obtained.

Furthermore, US-A-4 029 927 discloses a microwave water heater having a balloon in which is provided a water distribution device comprising a flat separating element provided with openings. In this water heater, the microwave source is only adjustable in two positions, namely all or nothing, and there is no application device allowing agreement with the fluid to be heated.

Finally, US-A-4114 011 describes a device for heating water indirectly, in which an absorption chamber is traversed by a pipe with a specific configuration; in which the fluid or water to be heated flows, and which promotes the absorption of microwaves. The device according to US-A-4 114 011 does not however allow direct heating of any fluid and has the same drawbacks as the devices according to US-A-4 165 455 and US-A-4 029 927.

Also known from GB-A-2 048 629 is a microwave water heating process in a central heating installation. This method uses a boiler provided with a fluid inlet to be heated and a hot fluid outlet as well as a microwave energy source. The method described in GB-A-2 048 629 does not, however, allow the heating of any fluid with optimal efficiency.

The object of the present invention is a boiler as defined in the preamble of claim 1, which, thanks to the characteristics mentioned in the characterizing part of said claim 1, allows optimum efficiency.

• la figure 1 est une vue en coupe d'une chaudière conforme à l'invention ;
• les figures 2 et 3 représentent en des vues en coupe, respectivement le montage de la chaudière dans un circuit de chauffage et le détail du dispositif de commande et de régulation ;
• la figure 4 montre la variation de la constante diélectrique de l'eau avec la fréquence à une température de 25 °C ;
• la figure 5 représente la courbe de la puissance optimale dissipée dans l'eau en fonction de la fréquence et
• les figures 6 à 12 montrent d'autres variantes dé réalisation de l'invention.

The invention will be better understood thanks to the description below, which relates to preferred embodiments, given by way of nonlimiting examples, and explained with reference to the appended schematic drawings, in which:

• Figure 1 is a sectional view of a boiler according to the invention;
• Figures 2 and 3 show in sectional views, respectively the mounting of the boiler in a heating circuit and the detail of the control and regulation device;
• FIG. 4 shows the variation of the dielectric constant of water with the frequency at a temperature of 25 ° C;
• FIG. 5 represents the curve of the optimal power dissipated in water as a function of the frequency and
• Figures 6 to 12 show other alternative embodiments of the invention.

According to the invention, and as shown more particularly. by way of example, FIG. 1 of the accompanying drawings, the microwave boiler producing a hot fluid for domestic, industrial or space heating use, comprising an enclosure 7 containing the fluid to be heated 6, a source of energy in microwave 2, of the klystron or magnetron type, a device 3 of the waveguide type, coaxial cable, or the like, transmitting said energy from the source 2 to the enclosure 7, is remarkable in that between said device 3 of the waveguide type and said enclosure 7 is interposed an applicator device 4 making it possible to apply said microwave energy to the fluid 6 at a frequency corresponding to the relaxation frequency of the fluid considered at a given temperature, said applicator device 4 being closed by a diffuser 5 fluid-tight and permeable to waves, said applicator device 4 radiating said microwave energy towards the fluid 6 to be heated and cooperating with the enclosure 7.

The enclosure 7 is a conductive and / or absorbent metallic enclosure of cylindrical shape which delimits the heat treatment zones of the fluid.

The enclosure 7 can also have a parallelepiped, spherical or other shape.

The applicator 4 can advantageously be completed by at least one radiating antenna 8, the elements of which have an effective electrical length equal to a whole number representing a quarter of the wavelength of the frequency of the radiated energy. This applicator 4 and / or the antenna 8 radiate the microwave energy in the enclosure 7 of the fluid to be heated 6 in such a way that optimum efficiency of said energy is obtained.

The types of applicators can be any, so that any volume of fluid can be treated. Likewise, the dimensions of the enclosure are provided so as to correspond to the frequency used.

The microwave boiler according to the invention is provided with a conductive and / or absorbent enclosure 7 provided with a protective envelope 12, with thermal insulation 7 ′, and at least one inspection hatch 9 provided a closure device 10 made of a conductive and / or absorbent material allowing the stopping of microwaves and having a sealing device 11 for the fluid and allowing stopping of microwave radiation.

The boiler is further provided with openings 13 to 16 allowing the circulation of the fluid 6 towards the pipes of the energy distribution network and of the radiators as well as the filling or emptying of the enclosure by means of pipes 17 and 18, these openings 13 to 16 each accommodating a device for stopping microwaves 19 to 22 allowing the reflection and / or absorption of said microwaves and thus preventing them from leaking through said pipes and the various auxiliaries 23 to 25 connected to the boiler.

The shape of the stop devices 19 to 22 depends on the diameter of the openings 13 to 16 and the wavelength of the microwaves used, and these devices are each provided with one or more openings allowing the flow of the fluid 6 while preventing the passage of microwaves.

It is also possible, according to another characteristic of the invention, to produce the pipes in the form of conductive and / or absorbent elements, so that the microwave stop devices become unnecessary.

The boiler is, moreover, provided with at least one safety device against overheating of the enclosure 7, not shown, in the form of a lack of fluid detector, of a device for measuring micro energy. -wave, or the like, of at least one thermocouple 26, of a control and operating table 27 of the boiler having control and signaling members 28, of a pressure gauge 29, of a control device 30 and regulating the device 1 for applying microwave energy cooperating with one or more thermal controllers 31.

The walls of the enclosure 7 are advantageously made of all conductive materials allowing the stopping of electromagnetic radiation and / or the absorption of this radiation, for example by black body effect, these materials possibly being metals and light alloys such as aluminum alloys, or stainless steel.

As shown in Figure 2, the boiler according to the invention can be used for direct direct heating of a fluid by microwaves, this fluid circulating in a thermal energy distribution network. Such a network consists of the boiler described above and designated by the reference 32, by inlet 33 and outlet 34 pipes of the treated fluid, connected to a use circuit comprising radiating elements 35 such as radiators , and by members 36 for controlling the circulation of the fluid.

. The device 30 for controlling and regulating the device 1 for applying microwave energy (FIG. 3) acts directly on the emission of electromagnetic radiation, to which the fluid 6 is subjected inside the enclosure 7, thus allowing the said fluid to be brought to the desired temperature, and which is constituted by an electrical receiver 37 connected to the hyper-frequency energy source 2 by means of a static converter 38, or similar device, acting on the supply circuit 39 of the source 2, and by a microprocessor processing unit 40, or other electronic device, ensuring the regulation and operational safety of the entire boiler as well as the auxiliaries 23 to 25, and to which the thermal controller 31, the thermostat 26, the temperature sensors 41 and the operating safety devices 42-43 are connected, the device 30 being further provided with a cooling circuit 2 ′ of the micro source -waves 2, of so that calories can be recovered to improve the efficiency of the boiler.

The fluid to be heated 6, present in the enclosure and subjected to microwave radiation, undergoes heating under very rapid conditions and controlled by the processing unit 40.

Thus, the fluids or mixtures used in the enclosure have, for the most part, loss factors large enough to allow their heating by high HF currents. As a result, the lower this loss factor, the slower the heating. On the contrary, the higher this factor, the more rapid the HF currents will be. In reality, this processing unit controls the treatment of the fluid which heats up by dielectric losses and / or by relaxation losses.

The main characteristics of this regulation are expressed by the power factor of the product to be heated since it is on its value that the possibility of heating a given product depends.

The active power consumed in the boiler, inside enclosure 7 is, in all approximation, equal to the real value of the complex power:

avec

• E l'intensité du champ électrique
• V est le volume du fluide à traiter
• k : est un coefficient
• ε' tg8 : est le facteur de pertes
• f : est la fréquence de la source micro-onde

This expression is better known in the form:

with

• E the intensity of the electric field
• V is the volume of the fluid to be treated
• k: is a coefficient
• ε 'tg8: is the loss factor
• f: is the frequency of the microwave source

This expression shows that the power dissipated in the fluid 6 is proportional to the square of the electric field. The loss factor ε 'tgδ is a function of frequency due to the fact that various electric charges are affected by electric fields at very specific wavelengths.

mettant en évidence le déphasage entre le champ E et l'induction D, lié à des freinages de l'orientation des dipôles sous l'action du champ.e is the absolute value of the permittivity of the dielectric. Knowing that the permittivity of a material is a complex value, it can be put in the form:

highlighting the phase shift between the field E and the induction D, linked to braking of the orientation of the dipoles under the action of the field.

The variations of e 'and e "as a function of the frequency characterize a material and its behavior as a function of the frequency. If the dipole relaxation is of the DEBEYE type, e" takes a maximum value at a frequency f _D called the DEBEYE frequency ; this frequency corresponds to the maximum heat dissipation in the dielectric. This frequency F _D is a characteristic of the material. Also the method used in the microwave boiler according to the invention allows to implement this physical principle shown in Figure 4 for the case of water. FIG. 4 represents, by way of example, the variation of the dielectric constant of water with the frequency at the temperature of 25 ° C. The values of e 'and e "change as a function of temperature, the same is true of the DEBEYE frequency.

The experimental results indicate that by using a microwave source operating at the frequency of 2450 MHz, a frequency commonly used in microwave ovens, we can heat a liter of water to 65 ° C in six minutes with a device with a maximum power of 1,200 W. By comparison with an electrical resistance of the same power, it takes about ten minutes, hence the high efficiency of this heating process. Instead of using the slow conduction process, microwaves simultaneously produce heat in all matter. They constitute direct and intense heating with instantaneous volume dissipation and avoid the heating of the treatment enclosure and the corresponding losses, which results in a considerable reduction in the duration of heat treatment, and therefore very energy savings. important. Figure 5 shows the optimal power dissipated in water as a function of frequency and volume for a microwave boiler with 1200 W of nominal power installed. The efficiency obtained at the DEBEYE frequency is very important since it indicates that to heat a volume of 1 liter of water to 60 ° C, the heating time will be much lower than that of the frequency of 2450 GHz.

It can therefore be said that when a fluid and / or a material is subjected to a high frequency electric field, it absorbs a certain amount of electromagnetic energy which is found in the form of heat. This absorbed energy is proportional to the loss factor of the fluid and / or of the material e 'tg δ product in which ε' denotes the dielectric coefficient and tgδ the tangent of the angle of loss of the body considered.

Thus according to the invention, the microwave boiler which uses the optimal wave performance electromagnetic and physical absorption properties of the fluids to be heated, allows to see its implementation in applications as diverse as heating premises of all kinds in the residential, tertiary, industrial and other sectors, because the temperature level of the fluid to be heated (air or water from 50 ° to 70 ° C) is close to the best coefficients of performance of this heating principle at the appropriate frequencies.

The invention consists in the use of thermal agitation generated by the excitation states of the molecules to be heated of said fluid contained in a conductive and / or absorbent enclosure.

The method according to the invention uses one of the fundamental mechanisms of interaction of microwaves with a fluid, at the molecular level, which is the rotation of the polar molecules induced in the field. Placed in an electric field, molecules like water are subjected to a torque which tends to align them with the field, so as to reduce the potential energy of the dipoles as much as possible. When the polarity or the direction of the field changes, the cyclic reorientation of the dipoles depends on the viscous energy dissipation to which the molecule is subjected.

A polar molecule therefore has a critical absorption frequency, called the relaxation frequency, which is a function of the characteristics of the molecule, of the viscosity of the fluid and of the temperature. At the critical frequency of rotation, the field transmits the maximum energy to the molecule and the energy of rotation is transformed into thermal energy.

This mode of interaction explains the behavior of permittivity as a function of frequency. In the microwave spectral segment (10 MHz to 300 GHz), several modes of molecular movement occur. For example, the water which can constitute the heating element has a relaxation frequency, the absorption peak of which is in the frequencies 2 to 80 GHz. In practice, the interactions between radiation and molecules are integrated into the electrical permittivity of the material, and the energy absorbed by said fluid becomes calculable by the equations of energy conservation and the equations of waves called Maxwell's equations.

Figures 6 to 18 give, by way of non-limiting examples, various possible applications of the microwave boiler according to the invention.

FIG. 6 represents an alternative embodiment of the device of the microwave boiler according to the invention, in which a device for applying microwave energy 1 is placed in a radiator element 44 and constitutes a heating system by Autonomous convection with simple and closed circuit of small size.

It is also possible to integrate this device 1 into an accumulation circuit 45 (FIG. 7), or into an air heater 46 (FIG. 8), in any form and at any location.

FIG. 9 represents another example of application of the invention, in which the microwave energy application device 1 is mounted on a conductive pipe 47 of a geothermal energy distribution network 48, in which circulates or parks a fluid, devices 49 for stopping the microwave radiation being provided inside the network 48, on either side of the source 2, and of the possible antenna 8.

It is also possible to mount in series or in parallel a number of boilers or microwave sources of the type described above.

Thus, as shown in FIG. 10, a mixed microwave boiler 50 can be provided simultaneously for space heating and the production of domestic hot water, the microwave energy necessary for heating the two enclosures 51 and 52 can be supplied by a single source or by several sources.

FIGS. 11 and 12 represent two other possible applications of the microwave boiler, on the one hand, by adaptation on a heating circuit with a conventional electric boiler 53 (FIG. 11), in which the fluid contained in the exchanger 54 of the boiler 53 is heated inside the microwave boiler 56, the radiators 57 being heated directly, and, on the other hand, by adaptation in a conventional heating circuit, the fluid of which is heated to the inside of the boiler 58.

Thanks to the invention, it is possible to carry out direct heating of fluids, such as water, air, oil, etc., for example for heating premises.

The boiler according to the invention allows, for example, a production of hot water with a higher yield than that produced by traditional solutions with less energy consumption. It therefore follows that the heating provided by these radiations is direct and intense, and the heating of the usual treatment enclosure in most traditional systems is avoided and thus the corresponding losses are saved.

The power used is therefore generally much lower than that required for a conventional heating system, especially since the precise location of the area of action of the radiation at the heart of the material can lead to reducing the volume to be heated due to that the processing time is extremely short, so that significant energy savings can be achieved.

Other uses can be envisaged in particular in industrial, agricultural and food-processing heating applications for heating water, steam and other fluids or mixtures, as well as for heating swimming pools with high efficiency.

The microwave boilers according to the invention can also completely complement or replace conventional gas, fuel oil, electric boiler devices. to heat pumps. They are interesting for geothermal energy, solar thermal energy and in general in addition to devices to solar energy.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims (7)

1. A microwave boiler producing hot fluids for domestic or industrial use or for room heating, comprising a metallic conducting and/or absorbing chamber (7) containing a fluid to be heated (6), a source of microwave energy (2) of the klystron or magnetron type, a device (3) of the waveguide, coaxial cable or similar type, transmitting said energy from the source (2) to the chamber (7) and a diffuser (5) which is fluid-tight and permeable to the waves, characterised in that, the fluid to be heated being a particular fluid among a plurality of fluids - particularly industrial oils -, between said device (3) of the waveguide type and said chamber (7) is interposed an applicator device (4) which co-operates with said chamber (7) in such a manner that it enables said microwave energy to be applied to said particular fluid (6) at a frequency corresponding to the natural frequency of relaxation oscillation of the particular fluid in question at a given temperature, said applicator device (4) being closed by said diffuser (5) which is fluid-tight and permeable to the waves, said applicator device (4) radiating said microwave energy towards said particular fluid (6) to be heated.

2. A boiler, according to claim 1, characterised in that the applicator device (4) further comprises at least one radiating antenna (8), the elements of which have an effective electrical length equal to a whole number of X/4, being the wavelength of the frequency corresponding to said natural frequency of relaxation oscillation of said particular fluid in question at a given temperature.

3. A boiler, according to claims 1 and 2, characterised in that it is equipped with a conducting and/or absorbing chamber (7) provided with a protective casing (12) and with at least one inspection flap (9) provided with a closing device (10) of a conducting and/or absorbing material enabling the microwaves to be stopped and having a sealing device (11) for the fluid and enabling the microwave radiation to be stopped, and the walls of the chamber (7) are advantageously made of any conducting materials enabling the electromagnetic radiation to be stopped and/or this radiation to be absorbed, which materials may be metals and light alloys such as aluminium alloys, or stainless steel.

4. A boiler, according to either one of claims 1 and 3, characterised in that it is further equipped with openings (13 to 16) permitting the circulation of the fluid (6) towards the lines of the energy distribution network and of the radiators as well as the filling or emptying of the chamber by means of pipelines (17 and 18), these openings (13 to 16) each accommodating a device (19 to 22) for stopping microwaves, permitting the reflection and/or the absorption of said microwaves and thus preventing the escape of the latter through said lines and the various auxiliary equipment (23 to 25) connected to the boiler.

5. A boiler, according to either one of claims 1 and 2, characterised in that the device for the application of microwave energy (1) is mounted on a conducting conduit (47) of a distribution network for geothermal energy (48) in which a fluid circulates or is stationed, devices (49) for stopping the microwave radiation being provided inside the network (48), at each side of the source (2) and of the possible antenna (8).

.6. A boiler, according to any one of claims 1 and 3 to 5, characterised in that it is equipped with at least one safety device against the overheating of the chamber (7), in the form of a detector of lack of fluid, of a device for measuring the microwave energy or the like, of at least one thermocouple (26), of a panel (27) for the control and operation of the boiler comprising control and signalling members (28), of a pressure gauge (29), of a device (30) for the control and regulation of the device (1) for the application of microwave energy co-operating with one or more thermal controllers (31).

7. A boiler, according to claim 6, characterised in that the device (30) for the control and regulation of the device (1) for the application of microwave energy acts directly on the emission of the electromagnetic radiation to which the fluid (6) is subjected inside the chamber (7), thus enabling said fluid to be brought to the desired temperature, and which consists of an electric receiver (37) connected to the source of microwave energy (2) by means of a static converter (38) or similar device, acting on the supply circuit (39) of the source (2) and of a microprocessor processing unit (40), or other electronic device, ensuring the regulation and the security of operation of the assembly of the boiler and the auxiliary equipment (23 to 25), and to which there are connected the thermal controller (31), the thermostat (26), temperature sensors (41) and operational safety devices (42-43), the device (30) being further equipped with a circuit (2') for cooling the microwave source (2).

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