DEVICE AND PROCESS FOR THE PRODUCTION AND TRANSFER OF HEATING AND COOLING POWER

Abstract

A device and process for the production and transfer of heating and cooling power are described, in which a resonant electric circuit having at least one capacitor with a dielectric of electrocaloric material connected to an inductor is used. The resonant circuit comprises a variable electrical power supply section with a working frequency corresponding to the resonance frequency of the circuit.

Claims

1. A device comprising an electrical resonant circuit having a first inductor connected to a first capacitor, an electrical power supply section to power said electrical resonant circuit, wherein said first capacitor has a dielectric of electrocaloric material for the production and transfer of heating and cooling power, and wherein the electrical power supply section of said electrical resonant circuit comprises a constant voltage source and a pulse source with a predetermined duty cycle for modulating said constant voltage.

2. The device according to claim 1, wherein said electrical resonant circuit is free of resistors and diodes.

3. The device according to claim 1, wherein the dielectric of electrocaloric material of said first capacitor comprises one or more layers of a thin film, a thick film or crystals of either a terpolymer or a ferroelectric ceramic material able to heat up when it is subjected to an electric field.

4. The device according to claim 1, wherein the dielectric of electrocaloric material of said first capacitor comprises one or more layers of a thin film, a thick film or crystals of a ferroelectric ceramic material able to cool down when it is subjected to an electric field.

5. The device according to claim 1, wherein said first inductor comprises nanocrystalline magnetic cores.

6. The device according to claim 1, wherein said first inductor comprises windings of conductors made of carbon nanotubes.

7. A process comprising the steps of a) providing an electrical resonant circuit having a first inductor connected to a first capacitor, and b) electrically powering said first capacitor and said first inductor with a voltage having a working frequency equal to the resonance frequency of the electrical resonant circuit, wherein said first capacitor has a dielectric of electrocaloric material for producing and transferring heating and cooling power, and wherein step b) provides a constant voltage and modulates said constant voltage with a pulse source having a predetermined duty cycle.

8. The process according to claim 7, wherein the production and transfer of heating power comprise heating a solid body, a fluid or a combination thereof by means of said first capacitor, and wherein the dielectric of electrocaloric material of said first capacitor comprises one or more layers of a thin film, a thick film or crystals of either a terpolymer or a ferroelectric ceramic material.

9. The process according to claim 7, wherein the production and transfer of cooling power comprise cooling a solid body, a fluid or a combination thereof by means of said first capacitor, and wherein the dielectric of electrocaloric material of said first capacitor comprises one or more layers of a thin film, a thick film or crystals of a ferroelectric ceramic material.

10. The process according to claim 7, wherein said resonance frequency f.sub.r is greater than or equal to 2 kHz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further characteristics and advantages of the present invention will be more evident from the following description, made for illustration purposes and without limitation, with reference to the attached schematic drawings, wherein:

[0037] FIG. 1 is an electric diagram of a possible embodiment of a resonant circuit according to the present invention with a single inductor and a single capacitor;

[0038] FIG. 2 is a diagram similar to that one in FIG. 1 but with a different connection of the single capacitor;

[0039] FIG. 3 is a diagram of another embodiment of the resonant circuit comprising two inductors and two capacitors connected to each others in various ways;

[0040] FIG. 4 is a diagram similar to that one in FIG. 3 but with a different connection of the components;

[0041] FIG. 5 is a diagram similar to that one in FIG. 1 but with a pair of inductors connected in parallel to one another;

[0042] FIG. 6 is diagram of an embodiment of a resonant circuit according to the present invention, wherein two inductors are magnetically coupled to one another;

[0043] FIG. 7 is a diagram similar to that one in FIG. 6 but with a different connection of one of the capacitors of the resonant circuit;

[0044] FIG. 8 is a diagram similar to that one in FIG. 6 with the addition of inductors connected in parallel to the two coupled inductors;

[0045] FIG. 9 is a diagram of a resonant circuit according to another embodiment of the present invention, in which there are multiple couplings between inductors;

[0046] FIG. 10 is a diagram of a resonant circuit according to another embodiment of the present invention, in which a number of stages are powered in parallel with the power supply voltage;

[0047] FIG. 11 is a diagram of a resonant circuit similar to that one in FIG. 10, in which a number of stages of coupled inductors is provided;

[0048] FIG. 12 is a diagram of a resonant circuit similar to that one in FIG. 11, in which each stage comprises coupled inductors and inductors connected in parallel to the coupled components;

[0049] FIG. 13 is an equivalent diagram of a capacitor prototype experimentally implemented and tested; and

[0050] FIG. 14 is a diagram of an apparatus comprising a device for the production and transfer of heating and cooling power according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

[0051] In the simplest embodiment shown in FIG. 1, the resonant circuit of a device according to the present invention comprises a first inductor L1 and at least one first capacitor C1 with a dielectric of electrocaloric material, connected in parallel to one another.

[0052] In regards to the inductors described here and below, the windings have to be preferably made of conductors having low resistivity, such as for example conductors made of carbon nanotubes. Alternatively, windings of conductors made of more common conductive alloys, for example copper-based alloys or the like, can also be used.

[0053] The inductors can also be wound on magnetic cores to increase their inductance while leaving unchanged the overall size. Particularly suitable materials for making cores have high permeability, for example nanocrystalline materials of FeCuNbSiB, which allow to make inductors having high inductance values even with a limited number of windings. Alternatively, in the absence of specific limitations to size and/or if no particularly high values of inductance are required, the magnetic cores can also be common ferrite cores.

[0054] The components L1 and C1 are powered by a power supply section 50 including a constant voltage source V1 modulated by a pulse source V2, with a predetermined duty cycle, which is applied by means of a semiconductor device M1, preferably a gallium nitride FET in order to limit as much as possible commutation losses, otherwise by means of equivalent devices though having less significant performances, such as for example a MOSFET type transistor IRFH5020 manufactured by International Rectifier (USA). The duty cycle applied to the circuit is preferably reduced in order to have high gain.

[0055] Here and below the symbol adopted for the pulse source V2, in which a square or rectangular wave pulse is stylized, is merely indicative; therefore, the pulses provided by the source V2 can take any shape, for example triangular, sinusoidal or the like.

[0056] In the embodiment shown herein, by modulating the constant voltage generated by the source V1 it is possible to set the proper resonance frequency f.sub.r in the connection between C1 and L1, defined by the formula:

[00001]$f_r=\frac{1}{2.Math..Math.\sqrt{\mathrm{LC}}}$

[0057] where L is the inductance of L1 and C is the capacitance of C1.

[0058] In order to obtain high outputs, the circuit has to be powered at a frequency preferably higher than 2 kHz. It was observed, in fact, that the electrocaloric effect occurs in any case with significant performances even using frequencies much higher than 1 Hz: taking into account that the work is produced in this way by the only reactive power, the obtained effect is still considerable if compared to the extremely low power consumption of the circuit.

[0059] In the electric diagrams described below, the same reference abbreviations of FIG. 1 indicate the same components, if not otherwise specified. Similarly, all the additional capacitors which will be described in the following diagrams have to be considered always provided with a dielectric of electrocaloric material.

[0060] For example, in the diagram of FIG. 2 there are all the same components of FIG. 1, even though the capacitor C1 is no longer arranged in parallel with the inductor L1 but is instead grounded by one of its terminals.

[0061] The diagram of FIG. 3, in addition to the capacitor C1 and to the inductor L1 connected in parallel to one another, also includes an additional inductor L1 and a further capacitor C1 connected in series to one another, the terminals of the series connection of C1 and L1 are in turn connected in parallel to components L and C.

[0062] In FIG. 4 a similar circuit is shown but where the series connection of the capacitor C1 and the inductor L1 has differently a terminal connected to ground (or negative pole) rather than connected to the positive pole of the constant voltage source V1.

[0063] In both the embodiments of FIGS. 3 and 4, the capacitance value of the capacitor C1 can be equal to that of the capacitor C1 so that the electrocaloric effect is substantially evenly distributed on both of them, whereas the inductance values of the inductors L1 and L1 can also be different from each other, depending on the desired resonance frequency at which the circuit should operate.

[0064] In the diagram of FIG. 5 a circuit similar to that one of FIG. 1 is shown, in which there are two inductors L1 and L1 connected in parallel and preferably having the same inductance. This allows the distribution of any excessive current load in the oscillating circuit. As evident to a skilled in the art, there can also be more than two inductors connected in parallel and the two or more inductors can have windings made without any magnetic core, or else wound on the same magnetic core or on distinct magnetic cores.

[0065] Instead, in the embodiment of FIG. 6 two inductors L1 and L2 magnetically coupled to each other are provided. The first capacitor C1 is connected in parallel to the first inductor L1, as already shown for example in FIG. 1, whereas a second capacitor C2 is connected in parallel to the second inductor L2. Due to the magnetic coupling between the two inductors L1 and L2, also the two components C2 and L2 connected to each other are subjected to the same working frequency applied to the components C1 and L1 and may share the same values of capacitance and inductance therewith.

[0066] The inductors can be magnetically coupled through air or through a magnetic core. In this case, the magnetic core for coupling the inductors L1 and L2 shown in FIG. 6 is also preferably made of materials having high permeability, such as nanocrystalline materials of FeCuNbSiB. Similarly to the individual inductors described hitherto, the coupling magnetic cores can also take the form of common ferrite cores, such as those available on the market with the abbreviation ETD (Economical Transformer Design). This also applies to all the coupled inductors of the circuits described below.

[0067] In regards to the magnetic coupling between the inductors shown in FIG. 6, as well as for the coupling of those described below, the ratio of coupling, or of transformation, can be 1:1, that is to say with coupled inductors having the same inductance value, or else with different ratios, either with a step-up transformation ratio or with a step-down transformation ratio, whereby the inductors will have inductance values different from each other. The capacitance values of the capacitors connected to the coupled inductors will in turn be selected to comply with the resonant frequency set in the circuit. The circuit of FIG. 7 is similar to that of FIG. 6, the only difference between them being that one of the terminals of the capacitor C1 is connected to ground rather than to the positive pole of the generator V1.

[0068] The circuit of FIG. 8 is another variation of the circuit of FIG. 6, with further inductors L1 and L2 connected in parallel respectively to the coupled inductors L1 and L2 in the case where high currents are caused in the resonant circuit. All the inductors preferably have the same inductance value, although variations to this solution can also be provided in particular cases. The additional inductors connected in parallel to the coupled inductors may also be more than those shown.

[0069] FIG. 9 shows another diagram of a resonant circuit according to the invention, in which groups of cascade-coupled inductors are provided. In particular, in addition to the coupled inductors L1 and L2, which are connected to respective capacitors C1 and C2, a further inductor L2 is connected in parallel to the inductor L2 and is in turn coupled to a further inductor L3 connected to a respective capacitor C3. Also in this case, more groups of components can follow the principle of cascade-coupling the inductors to each other. The values of inductance and capacitance of the various components in each group are determined so as to keep the resonance of all the groups at the same frequency.

[0070] In the circuit of FIG. 10 a number of stages of inductors and capacitors connected to each other are used; all stages are in turn connected in parallel to the same source V1 of DC voltage modulated by the same pulse source V2. In practice, the same power supply is applied simultaneously to the stages C1a-L1a, L2a-C2a, C3a-L3a up to the n-th stage Cna-Lna. For example, the number n of inductor/capacitor stages can depend on the heating power required for the particular application and/or on the size of the body or fluid to be heated/cooled. In this embodiment, all the inductors preferably have an identical inductance value but, in particular cases, variations to this solution can also be provided; the capacitors will therefore have an identical capacitance value, or a value calculated to comply with the resonance frequency set in the circuit.

[0071] The same principles of the circuit of FIG. 10 can also be found in the circuit of FIG. 11, in which a plurality of n stages comprising a second inductor L1b, L2b, L3b . . . Lnb are provided, respectively coupled to each first inductor L1a, L2a, L3a . . . Lna. Each inductor L1a, L2a, L3a . . . Lna is connected in parallel to a respective capacitor C1a, C2a, C3a . . . Cna, as well as each inductor L1b, L2b, L3b . . . Lnb is connected in parallel to a respective capacitor C1b, C2b, C3b . . . Cnb. Also in this embodiment, all the inductors may have an identical inductance value or, in particular cases, may also be different from each other, therefore taking into account that the capacitors will have a capacitance value suitable to comply with the resonance frequency set in the circuit.

[0072] The diagram of FIG. 12 is a combination of the various embodiments already illustrated herein, in which a plurality of stages are connected in parallel to the same sources V1 and V2. In practice, the first stage in the upper part of the diagram includes coupled inductors L1a and L1b which are connected in parallel to respective inductors L1a and L1b and respective capacitors C1a and C1b; in the second stage, the coupled inductors L2a and L2b are connected in parallel to respective inductors L2a and L2b and respective capacitors C2a and C2b; in the third stage, the coupled inductors L3a and L3b are connected in parallel to respective inductors L3a and L3b and respective capacitors C3a and C3b, and so on up to the n-th stage, in which the coupled inductors Lna and Lnb are connected in parallel to respective inductors Lna and Lnb and respective capacitors Cna and Cnb. In this embodiment, as well as in those described hitherto, the inductance and capacitance values of inductors and capacitors will be determined so as to comply with the resonant frequency set in the circuit.

[0073] An example of an apparatus 100 comprising a device for the production and transfer of heating and cooling power according to the present invention is shown in FIG. 14 power supply section 50 is similar to that shown in FIG. 1. The capacitor C1 includes a single heat exchanger 10 having electrodes 11 and 12, dielectric material 15 with electrocaloric properties, plate 20 to be heated/cooled, plate 30 to be cooled/heated, and channels 31 for heating/cooling fluid.

[0074] The electrocaloric material to be used as a dielectric for capacitors is selected based on the various heating or cooling applications to be implemented. In case of heating, a suitable material may be for example a terpolymer, whereas in case of cooling it is possible to use a ferroelectric ceramic material, for example.

[0075] These materials may be used in the form of thin films, thick films or crystals to make flat capacitors that can be applied to a heat exchanger, for example a heat-exchange apparatus of the waterblock type or the like, i.e. a solid block in which a heat-exchange fluid is made to flow. Flat capacitors may be applied to the surface of the solid body of the exchanger, possibly by interposing a film of electrically insulating material having, however, high heat transfer properties, for example that one with the trade name KAPTON available by DuPont.

[0076] However, in manufacturing a heating apparatus, limitations of electrocaloric materials known hitherto should be considered. For example, the aforementioned terpolymer (PVDF-TrFE-CFE) has a melting temperature of about 80 C. Therefore, in order to prevent the capacitor dielectric from being damaged, it should be used at lower temperatures, for example not exceeding temperatures of 50 C. If it is necessary to achieve a greater thermal drop T, it is however possible to put in series several heat exchangers having heating elements (capacitors) of the same type.

[0077] If an instantaneous water heater has to be implemented, assuming a target thermal drop T of 25 C., the desired temperature can be achieved by several heat exchangers in series and, based on the water flow rate to be heated, an automatic control can be carried out by acting on the power supply voltage and/or by enabling or excluding individual heating elements.

[0078] For heating houses or, in general, buildings, because very high temperatures have to be achieved it is possible to use, for example, a boiler with thermal stratification. Assuming that the maximum temperature achievable by the hot water is 50 C., to protect the heating elements, an apparatus of this type may increase the temperature up to more than 75 C.

[0079] In case of cooling, being carried out as already mentioned by implementing capacitors with dielectrics constituted by thin films, thick films or crystals of ferroelectric ceramic materials, the same solutions can be used.

[0080] Hereinbelow are some examples to determine the actual possibility of exploiting an electrocaloric material, in particular a terpolymer, able to heat up although subjected to a high frequency electric field.

Example 1: Implementation of a Prototype of Heating Element

[0081] A prototype of flat capacitor having the dielectric made up of two layers close to each other and adhering to the plates has been implemented. The first dielectric was a terpolymer PVDF-TrFE-CTFE (electrocaloric material), whereas the second layer was constituted by air. Thus, the equivalent diagram is that of two capacitors connected in series, as depicted in FIG. 13.

[0082] The characteristics of the dielectric terpolymer were as follows:

[0083] Side=0.030.03 m

[0084] Surface S=0.0009 m.sup.2

[0085] Thickness of the PVDF-TrFE-CTFE film=10 m

[0086] Taking into account the dielectric constant in the vacuum (.sub.0=8.854*10.sup.12 F/m), the values of the capacitances C1 (terpolymer) and C2 (air) were calculated.

[0087] The value of C1 was calculated as follows:

Relative permittivity of the terpolymer .sub.r1=37

1=327.6*10.sup.12 F/m=.sub.r1.sub.0

C1=29.480*10.sup.12 F(1*Surface/Thickness)

[0088] The value of C2 was in turn calculated as follows:

Air thickness=4.23 m

Relative permittivity of air &2=1

2=8.854*10.sup.12 F/m=.sub.r2.sub.0

C2=1883.8*10.sup.12 F(2*Surface/Thickness)

[0089] The series connection of the two capacitors corresponds to a total capacitance calculated according to the formula:

[00002]$\mathrm{Ctotale}=\frac{1}{\frac{1}{C.Math..Math.1}+\frac{1}{C.Math..Math.2}}=1773{10}^{-12}.Math.F=1,773.Math..Math.\mathrm{nF}$

Example 2: Experimental Tests

[0090] The capacitor made according to the example has been connected in parallel to an inductor, as in the circuit of FIG. 1.

[0091] A sinusoidal voltage with a working frequency of 87,600 Hz (87.6 kHz) and effective value of the voltage of 200 V.sub.rms was selected to be set in the circuit.

[0092] Once the total capacitance of the capacitor is known, the inductance value that satisfies the relation with the working frequency of 87.6 kHz was calculated to be 1.86 mH.

[0093] The heat generated by the PVDF-TrFE-CTFE film was compared with the heat generated by an electrical resistance of 220 powered at 22.69 volts and a current absorption of 0.103136 A.

[0094] As the temperature of the two systems reached 50 C., it was possible to calculate the thermal power generated by the electrocaloric film by detecting the electric power consumed by the resistor, equal to 2.34 W.

[0095] The power shares absorbed by each part of the capacitor prototype of Example 1 were calculated by taking into account the overall reactance X.sub.C and single reactances X.sub.C1 and X.sub.C2 according to the known formula:

[00003]$\mathrm{Xc}=\frac{1}{2.Math..Math..Math.f.Math..Math.C}$

[0096] from which it follows:

[0097] Ctotal=1773 pF Xc=1025.3 Vrms=200 A=0.195 Watt=39;

[0098] C1=29480 pF Xc1=61.66 Vrms=12 A=0.195 Watt=2.34;

[0099] C2=1883.8 pF Xc2=964.6 Vrms=188 A=0.195 Watt=36.66.

[0100] Knowing the total voltage, the partial voltage applied to the electrocaloric film and the partial voltage applied to the air were calculated. Therefore it was possible to calculate the actual power absorbed by the electrocaloric film, since air absorbs power without returning heating power.

[0101] Various modifications may be made to the embodiments described herein without departing from the scope of the present invention. For example, instead of the components schematically shown with V2 and M1, a suitably programmed oscillator can be adopted as long as it is able to provide the required characteristics of frequency and duty cycle. Furthermore, other suitable materials having the electrocaloric effect can be used in addition to those explicitly mentioned in the description.