FR2666141A1 - Zeolite heat pump which can be regenerated by high-frequency electric heating - Google Patents

Abstract

The invention relates to a heat pump using pumping of the thermodynamic fluid by adsorption on zeolites; the particular feature of the system according to the invention being the mode of regeneration by high-frequency heating. It comprises: a condenser (1) filled with zeolites (7) and an evaporator (2) which are separated by a thermal insulant (3). Inside the condenser (1), a hollow electrode (4) is found, making it possible to collect the vapour, which electrode is supplied with high voltage at high frequency via the transformer (5) by the generator (8). It can be used in all known applications of heat pumps.

Description

TECHNICAL DESCRIPTION
The present invention relates to the heat pump, or more generally, all refrigeration machines using a thermodynamic cycle based on the pumping of steam by means of zeolites. Very frequently the thermodynamic fluid is of water.

A particularity of these thermodynamic cycles, which are now very well known, is the discontinuous nature of their operation, which is imposed by the need to periodically regenerate the zeolite pump. Thus, a cycle includes an operating period during which cold can be obtained from the evaporator, followed by a regeneration period where the evaporator behaves as a condenser and therefore gives off heat.

The disadvantage of known systems of this kind comes precisely from this necessary regeneration which is often very long, which reduces the useful part of the cycle and heavily affects the performance of the machine, both in terms of efficiency and specific power.

The first achievements used purely thermal regeneration systems; the heating of the condenser (which contains the zeolites) being obtained by electrical resistances or by means of a burner, fuel, oil or gas.

Very high regeneration times (for example 3 hours) were then required at high temperatures (for example 3000C). This is due to the fact that the heat propagates very poorly in the zeolite which is a thermally insulating medium and which is moreover very strongly endothermic due to the energy of desorption of the water.

These drawbacks have led the designers of refrigeration machines to use bulk heating, which therefore overcomes the limitations of thermal conductivity. This is obtained in known systems by a microwave beam from a magnetron which is sent into a cavity with conductive walls, filled with a powder of zeolites, which constitutes the "condenser" of the thermal machine.

This process has made it possible to obtain very substantial progress since the regeneration can be carried out in as short a time as 8 minutes, at a temperature as low as 110 C. it however still presents some disadvantages such as
- poor energy efficiency,
- uneven heating of the volume of zeolites,
- difficulties in avoiding the breakdown of the electromagnetic wave in the
low pressure water vapor,
- a relatively high cost.

The device according to the invention avoids these drawbacks since it has a very high energy yield, it provides perfectly homogeneous heating throughout the volume of zeolites, it avoids all the problems of breakdown in steam at low pressure and that it has a very low construction cost.

The invention relates to heat pumps using an adsorption-desorption cycle of water or thermodynamic fluid suitable for zeolites comprising
- means (1), (4), making it possible to subject the entire volume of the zeolites to
an electric field,
- means (5), (8), suitable for supplying electrical energy
the so-called means (1), (4),
According to another characteristic, the means making it possible to subject the zeolites to a high frequency electric field essentially consist of a capacitor, of which the zeolite (7) is the dielectric, comprising
- an external metal frame (1) constituting the sealed tank which contains the zeolites (7), which can advantageously be electrically connected to earth,
- a central electrode (4), placed at a substantially constant distance from (1); the space between the two being filled with zeolites, on which a high frequency electrical voltage is applied.

 According to another characteristic, the central electrode (4) is hollow, has on its entire surface micro-holes suitable for letting diffuse the thermodynamic gas entering or leaving the volume of zeolites (7), and is connected to a metal tube ( 10) which collects said gas to lead it to the evaporator (2).

 According to another characteristic, the tube (10) for discharging the thermodynamic gas is extended by a conductive tube (5) wound in the form of a solenoid, which solenoid constitutes the secondary of a transformer which supplies high voltage at high voltage. frequency of the electrode (4).

 According to another characteristic, the means (8) enabling the condenser (1), (4), (7) to be supplied with electrical energy during the zeolite regeneration phase, consist of a transistorized chopper using any circuit known in static converters, which attacks a transformer of which this secondary consists of the solenoid (5).

 According to another characteristic, the means (8) enabling the condenser (1), (4), (7) to be supplied with electrical energy during the zeolite regeneration phase, are constituted by a transistorized chopper using any known circuit. in static energy converters, driving the LC series resonant circuit, directly between the masses of the exchangers (1) and (2).

 According to another characteristic, the transistorized chopper is set on the resonance by means of a self-resonant type control circuit.

 According to another characteristic, the transistorized chopper is used as a refrigerating machine or as a drying machine.

 According to another characteristic, the means (8) used to supply energy to the capacitor (1), (4), (7), during the zeolite regeneration phase, consist of at least one electronic tube mounted as an oscillator and operating in a frequency range between 1 MHz and 1 GHz. At high frequency, the capacitors are constituted by a transformer (11) whose secondary is tuned to the operating frequency and whose primary is attacked by a transistorized modulator (12).

 According to another characteristic, the modulators (9) or (12) are supplied directly by the sector and are of the "half-bridge" type.

The invention will in any case be better understood with the explanations which follow, given for information and, of course in no way limitative, referenced in the appended drawings in which
.Figure 1 represents the diagram of the principle of a heat pump with adsorption-desorption cycle on zeolites.

. FIG. 2 represents an electronic circuit making it possible to obtain an output voltage Vs of very large amplitude by virtue of the series resonance phenomenon.

 . FIG. 3 represents an embodiment of a zeolite heat pump, in which the regeneration of said zeolites is carried out by high frequency heating, the high frequency high voltage being obtained here by means of a resonant air transformer.

 . FIG. 4 represents another embodiment of a zeolite heat pump also with regeneration by high frequency heating, in which the high voltage is obtained by helical resonator producing a series resonant circuit.

These figures are given for information only, in order to better understand the principle of the device, they are therefore in no way limiting and do not therefore take anything away from the generality of the invention. The different elements have not always been represented according to their real proportions, when this did not interfere with the understanding of the figures.

Referring to Figure 1, we can understand the principle of the heat pump based on the operation of an adsorption-desorption cycle on a material with very large specific surface such as zeolites. There are many different possibilities with regard to the nature of the thermodynamic fluid. In general, polar molecules are well suited (C02, H20 etc ...). The choice of this fluid will depend on the temperatures to be obtained on the evaporator (2). In most applications, water will be chosen which has, in fact, a particularly favorable heat of vaporization, moreover it leads to the production of non-polluting machines. Water will be useful in the construction of dryers, air conditioners and heat pumps (provided, however, that there is a heat source above 0 C).

Conceptually, the heat pump thus produced comprises a sealed enclosure (1) filled with zeolites (7) which should be called according to the terminology in force in the compressor heat pump, "condenser" as well as an enclosure (2 ) which will be called, for the same reasons "evaporator".

In reality, the enclosure (2) will alternately be a condenser during regeneration and an evaporator during the operating period.

These two enclosures are connected by a pipe (10) in which the gases of the thermodynamic fluid circulate. A valve (6) makes it possible to periodically obstruct the pipe (10) and consequently to regulate the pumping speed of the vapors and therefore the production of cold at the evaporator (2). Enclosures (I) and (2) exchange thermal energy with the outside (which can be air or water) by means of exchangers not shown in FIG. 1. These can be completely nondescript.

When the pump is started, there is water in the evaporator and the zeolites are regenerated, that is to say in a state of pumping water molecules. The valve is opened (6) which causes a drop in the pressure of the water vapor in equilibrium with the liquid water in (2). There is therefore evaporation of the latter, and consequently, production of cold. The water vapor is then absorbed on the zeolites which gives off heat in the enclosure (1).

When the zeolites are saturated, the pumping stops and it is necessary to regenerate them. This is achieved by heating the enclosure (1) to at least 100 "C. The water vapor thus released will condense in the enclosure (2) where a certain amount of heat is released. This amount of heat released is exactly equal to the heat absorbed during the operating period.

The problem that must be overcome when designing such a heat pump is that of the method of heating zeolites. These are indeed very heat conductive which means that any heating of the wall of the enclosure (1) is more difficult to transmit to zeolites as they are the seat of a degassing reaction which is very strongly endothermic.

To avoid this drawback, there is provided in the invention, heating to the core of the zeolites using the well-known principle of high frequency heating.

To do this, each volume element of zeolites must be subjected to a high frequency electric field E such that E = EOsinxt
The zeolite, which is an insulating body, can be assimilated to a dielectric with relative permitivity r and having an angle of losses characterized by tg8. It is shown that the power P released by the dielectric losses per unit of volume is worth
P = (r.Eo / 2) tg 3.co.E02 (SI)
If the electric field is homogeneous throughout the volume of zeolites, the power released at each point is the same, and therefore the temperature is uniform, which means that thermal conductivity no longer has any role to play. Under these conditions, the heating can be very rapid; it is limited, in fact, only by the power of the electric generator supplying the regeneration system.

It is therefore understandable that it is important to subject the entire volume of zeolites to a uniform electric field. This can be obtained by making a double capacitor, a plane like the one shown in FIG. 3. Inside the metal enclosure (1), which can advantageously have the shape of a parallelepiped, a metal electrode is placed ( 4) also of parallelepipedal shape, having suitable dimensions so that the distance e which separates (1) from (4) is everywhere constant. The electrode (4) is hollow and has side walls perforated with small holes, not visible in FIG. 3. These holes are small enough not to allow zeolites to penetrate inside the electrode (4), which collects or distributes thermodynamic gas to the entire volume (7) without excessive pressure losses. This gas comes or goes to the evaporator (2) via a pipe (10) made of copper or any other metal tube. low resistivity, which enters the enclosure (1) through an insulating terminal (9) and connects to the electrode (4).

The pipe (10) thus makes it possible to supply electrically (4) and it is therefore conceivable that one has actually produced a capacitor of which the dielectric (7) is introduced into the space located between (4) and (1).

A very important point must be pointed out: it is the risk of breakdown in the vapor of the thermodynamic fluid which is necessarily, at least for a time, under low pressure, hence the risk of achieving a discharge at low pressure which would short-circuit the generator that powers (4). To protect against this accident, it is necessary to avoid that a gas column can be established between (1) and (4). For this purpose, the entire volume between these two elements will be completely filled with zeolites, which is enough to prevent the appearance of a discharge. I1 then remains only to avoid a breakdown in the tube (10).

This is obtained by using this tube to make the high voltage generator and as can be seen in Figure 3 or in Figure 4, the pipe (10) is in all points conductive and allows to connect (1) to (2 ) without the gas passing inside being subjected to any electric field. The clicks are therefore impossible.

où C est la capacité fournie entre (1) et (4). Le circuit de commande du primaire fournit une puissance élevée car on est, en général, intéressé par une régénération rapide, avec un rapport cyclique T/T élevé (T étant la durée totale d'un cycle et X le temps de régénération). Si on désigne par Po la puissance frigorifique de la pompe à chaleur pendant son fonctionnement normal, la puissance de régénération Pr doit être telle que
Pr=T/T .Po
Elle peut atteindre en pratique plusieurs kW, ce qui suffit à montrer que les solutions de régénération par micro-ondes seraient beaucoup trop coûteuses si on voulait atteindre de telles puissances.The generator which supplies high voltage can be produced as shown diagrammatically in FIG. 3, where the pipe (10) constitutes a solenoid (12) so that (11) and (12) constitute a transformer tuned to the driving frequency f primary, by the generator (8). We have:

where C is the capacity supplied between (1) and (4). The primary control circuit provides high power because we are generally interested in rapid regeneration, with a high T / T duty cycle (T being the total duration of a cycle and X the regeneration time). If the cooling capacity of the heat pump is designated by Po during normal operation, the regeneration power Pr must be such that
Pr = T / T .Po
In practice, it can reach several kW, which is enough to show that the microwave regeneration solutions would be much too expensive if it were desired to reach such powers.

In FIG. 3, the generator (8) is a chopper of the "symmetrical half-bridge" type.

 I1 comprises two transistors, or transistor batteries T1 and T2 which can advantageously be of the power MOS type. The chopper can operate at a frequency of the order of 1 MHz, if care is taken over the transformer not shown in the figure, which provides control of the "gates" of said transistors. It will be noted that the rectifier is directly attacked by the sector, which considerably reduces the size and the cost of the electronics.

Another way of obtaining a high voltage is shown diagrammatically in FIG. 2. It consists in arranging in series, with the generator of square slots (8), the circuit
LC We demonstrate that in such a circuit, the output voltage Vs is Vs = 1.27 Qe E where Qe is the overvoltage coefficient of the circuit under load, that is to say, account for losses in the dielectric, and where E is the amplitude of the square slots.

We see that if E = 155 V as is the case with sector recovery and if
Qe = 100 which is realistic, we obtained
Vs = 19.7 kV.

FIG. 4 represents an implementation of this type of the circuit with the use of a helical resonator (13), comprising an inductance in copper tube (14) placed in a copper shielding (15) whose role is to '' avoid intense emission of electromagnetic radiation
We recognize in this figure the same elements as those encountered in Figure 3
the hollow electrode (4) which is surrounded by zeolites (7),
-the metal cavity (1) which surrounds (4) and which has on either side of the fins (16) suitable for ensuring a heat exchange with an air flow which circulates according to the arrows in phantom,
a vacuum-tight insulator (9), which is crossed by the tube (10) which simultaneously ensures the electrical supply of (4) and the circulation of the thermodynamic fluid,
an inductor (14) consisting of a copper tube inside which the thermodynamic fluid circulates,
an electrically controlled valve (6) which makes it possible, during normal operation, that is to say during the production of cold, to control the temperature of the evaporator (2) by virtue of an electronic circuit not shown in FIG. 4 .This valve has the particularity of functioning as a non-return valve, that is to say that during the regeneration phase it lets the thermodynamic fluid pass freely in the condenser-evaporator direction, that is to say in the direction (4) ---> (2),
an evaporator (2) which has fins (17) on its lateral faces suitable for exchanging energy with an air flow represented in FIG. (4) by arrows in dashed lines,
an electric generator (8) constituted by a square slot modulator which can be of any of the known models (non-isolated chopper, pushpull, forward, fly-back, asymmetrical bridge, half-bridge, etc.). FIG. 4 shows an arrangement of the "symmetrical bridge" type using four transistors or groups of transistors T1, T2, T3, and T4 which can advantageously be of the "power MOS" type.

The figure does not represent the control of gates which is of the self-resonant type which means that the frequency of the switch automatically locks on the resonance frequency of the LC circuit, which is necessary because the values of L and
C can fluctuate with temperature or the rate of saturation of zeolites.

The chopper is supplied with direct voltage directly from the mains, at least in all cases where the cost of electronics is to be reduced.

The outputs of the generator (8) directly attack the mass of the exchangers (1) and (2). It should be noted that, in the case where a transformer is not used to supply the circuit (8), the masses of the exchangers (1) and (2) must be protected by insulating covers for safety reasons.

The invention can be used in all applications of refrigeration machines and in particular
-the thermodynamic dryers,
- domestic or industrial heat pumps,
-refrigeration units,
-air treatment units and generally all
cold applications.

Claims (10)

1. Heat pump using an adsorption-desorption cycle of water or of thermodynamic fluid suitable for zeolites, characterized in that it comprises:  means (1), (4), making it possible to subject the entire volume of the zeolites to a high frequency electric field, suitable for heating the water therein,  - means (5), (8), suitable for supplying electric power to said means (1), (4), 2. Device according to claim 1, characterized in that the means making it possible to subject the zeolites to a high frequency electric field consist essentially of a capacitor, the zeolite (7) of which is the dielectric, comprising:  - an external metal frame (1) constituting the sealed tank which contains the zeolites (7), which can advantageously be electrically connected to earth,  - a central electrode (4), placed at a substantially constant distance from (1); the space between the two being filled with zeolites, on which a high frequency electrical voltage is applied. 3. Device according to claim 2 characterized in that the central electrode (4) is hollow, has over its entire surface of the micro-holes suitable for letting diffuse the thermodynamic gas entering or leaving the volume of zeolites (7) and is connected to a metal tube (10) which collects said gas to lead it to the evaporator (2). 4. Device according to claim 3 characterized in that the evacuation tube (10) characterized by the thermodynamic gas is extended by a conductive tube (5) wound in the form of a solenoid, which solenoid constitutes the secondary of a transformer which supplies high voltage at high frequency to the electrode (4). 5. Device according to claims 1 or 2, characterized in that the means (8) for supplying electrical energy to the condenser (1), (4), (7), during the regeneration phase of the zeolites, are formed by a transistorized chopper using any circuit as in static converters, which attacks a transformer of which this secondary is constituted by the solenoid (5). 6. Device according to claims 1 or 2 characterized in that the means (8) for supplying electrical energy to the condenser (1), (4), (7), during the zeolite regeneration phase, consist of a transistorized chopper using any circuit known in static energy converters, driving the LC series resonant circuit, directly between the masses of the exchangers (1) and (2). 7. Device according to claims 5 or 6, characterized in that the transistorized chopper is set on the resonance by means of a self-resonant type control circuit. 8. Device according to claims 2, 3 or 4 characterized in that it is used as a refrigerating machine or as a dryer. 9. Device according to claims 2, 3 or 4, characterized in that the means (8) used to supply energy to the capacitor (1), (4), (7), during the regeneration phase of the zeolites, are formed at least one electronic tube mounted as an oscillator and operating in a frequency range between 1 MHz and 1 GHz. At high frequency the capacitors are constituted by a transformer (11) whose secondary is tuned to the operating frequency and whose primary is attacked by a transistorized modulator (12). 10. Device according to claim (5) characterized in that the modulators (9) or (12) are supplied directly by the sector and are of the "half-bridge" type.