Background
【0002】 The use of heat exchangers to dissipate heat in power electronics applications is well known. Heat exchangers or heat sinks are typically metal heat dissipating components designed to dissipate heat from power electronic components, particularly power transistor modules, by heat conduction, convection, and radiation. The performance and reliability of the power electronics without the heat exchanger will be reduced.
【0003】 Heat exchangers are often constructed to have a maximum number of fins per unit volume that radiate in a direction perpendicular to the surface being heated. In certain demanding applications, heat exchangers use forced convection to dissipate heat to a cooling fluid passing through the heat exchanger to increase the heat rejection of the exchanger. More efficient means for discharging heat use foams, more particularly metal foams having more effective heat transfer surface areas. Metal foams have recently been used in power electronics applications to dissipate heat; however, they are not used in thermoelectric systems.
【0004】 Accordingly, there is a need for a foam heat exchanger to be used with thermoelectric elements to construct a system for multiple heating and cooling systems to reduce energy consumption in these systems and increase heat pumping capacity.
Disclosure of Invention
【0005】 It is an object of the present invention to provide a thermoelectric heating and cooling system using a foam heat exchanger.
【0006】 It is a further object of the present invention to provide a thermoelectric heating and cooling system using a metal foam heat exchanger.
【0007】 It is another object of the present invention to provide thermoelectric heating and cooling systems that use foam heat exchangers to dissipate heat.
【0008】 It is a further object of the present invention to provide a thermoelectric heating and cooling system having thermoelectric elements that uses a foam heat exchanger to reduce the energy consumption of the thermoelectric elements.
【0009】 It is another object of the present invention to provide a thermoelectric heating and cooling system having thermoelectric elements that uses a foam heat exchanger to increase the heat pumping capacity of the thermoelectric elements.
【0010】 It is a further object of the present invention to provide a method of enhancing heat transfer of a thermoelectric element using a foam heat exchanger.
【0011】 A system for enhancing the efficiency of a thermoelectric heat pumping system comprising an array of thermoelectric elements having a temperature at a first surface of the array and a temperature at a second surface of the array opposite the first surface, and further providing at least one foam heat exchanger positioned adjacent one of the first and second surfaces. Fluid flow through the at least one foam heat exchanger reduces the difference between the temperature at the first surface of the array and the temperature at the second surface of the array, thereby enhancing the efficiency of the system.
【0012】 A method is provided for enhancing the efficiency of a thermoelectric system having a thermoelectric array with a series of thermoelectric arrays of thermocouples arranged electrically in series. The method provides: a first foam heat exchanger adjacent a first surface of the thermoelectric array and a second foam heat exchanger adjacent a second surface of the thermoelectric array opposite the first surface; generating a temperature at a first surface of the thermal array and a temperature at a second surface of the array, the temperature at the second surface of the array being different from the temperature at the first surface of the array; wherein the fluid flowing through the first foam heat exchanger and the second foam heat exchanger reduces the temperature differential between the first surface and the second surface, thereby enhancing the efficiency of the thermoelectric system.
Drawings
【0013】 FIG. 1 illustrates a thermoelectric system having a foam heat exchanger of the present invention;
【0014】 Figure 2 shows a table in which the heat transfer coefficients of different foams used in the thermoelectric system of the present invention are compared and the weight savings compared to conventional heat exchangers.
【0015】 Figure 3 illustrates a thermoelectric system used in a heating mode and using the foam heat exchanger of the present invention.
【0016】 FIG. 4 illustrates a graph showing the increased coefficient of performance of a thermoelectric system as the heat transfer coefficient of the heat exchanger increases.
【0017】 FIG. 5 illustrates the foam heat exchanger of the present invention shown in FIG. 3; and
【0018】 Fig. 6 illustrates a foam heat exchanger according to a second embodiment of the heat exchanger of the present invention.
Detailed Description
【0019】 Referring to fig. 1, a thermoelectric system 10 with a thermoelectric element 15 is shown. The thermoelectric element 15 is composed of a PN pair or PN-couple 20 arranged electrically in series. Electrical connectors 25 provide connections between adjacent PN-couplings 20 and to a power source (not shown). Substrates 30 and 35 are ceramic substrates that provide insulation for system 10. Substrates 30 and 35 mechanically support system 10 together and electrically isolate PN coupling 20. The substrate 30 has a surface 40 that is in contact with a foam heat exchanger 45. Similarly, the substrate 35 has a surface 50 that is in contact with the foam heat exchanger 55. Fans 60 and 65 are used to move the fluid through heat exchangers 45 and 55, respectively. Although fans 60 and 65 are shown passing air through heat exchangers 45 and 55, respectively, other types of mechanisms for moving other types of fluids may be used. Surfaces 40 and 50 may be integral to heat exchangers 45 and 55, respectively, and form a base to which surfaces 30 and 35 of the thermoelectric array are attached.
【0020】 In fig. 1, foam heat exchangers 45 and 55 are placed in close proximity to substrates 30 and 35 to maximize heat transfer from surfaces 70 and 75 of thermoelectric elements 15. Foam heat exchangers 45 and 55 provide enhanced heat transfer areas from surfaces 70 and 75, respectively.
【0021】 The foam heat exchangers 45 and 55 are made of a highly conductive material such as aluminum, copper or graphite. Exchangers made of these materials are not only highly conductive, but, because they are made as foams, have a high porosity and surface area, further enhancing their heat transfer capability. Conventional heat exchangers for thermoelectric applications have fins to dissipate heat. The finned heat exchangers have a very limited surface area compared to foam heat exchangers. In addition, the conventional heat exchangers are relatively heavier than the foam heat exchangers 45 and 55 of the present invention. When using both small and large heating and cooling thermoelectric systems, it is important to reduce the weight and/or volume of the heat exchanger and increase the heat transfer capacity of the heat exchanger.
【0022】 Referring to table 1 in fig. 2, the heat transfer coefficient, maximum temperature, and weight savings of a conventional heat sink compared to three foam heat exchangers with different porosities are shown. The heat transfer coefficient of foam a exceeds the heat transfer coefficient of a conventional heat sink by more than 87 times compared to foam a having a porosity of 10PPI (pores per inch). By doubling the porosity of the foam heat exchanger to 20PPI, the heat transfer coefficient of foam B increases to 130 times that of the conventional heat sink. By doubling the porosity of the foam heat exchanger up to 40PPI, the heat transfer coefficient of foam C increased to 188 times that of the conventional heat sink. Not only is there a tremendous increase in heat transfer capacity, but the weight savings of the foam heat exchanger are also significant. The tremendous weight savings in using these exchangers reduces the overall weight of the thermoelectric cooling or heating system. In addition, by reducing the maximum temperature of the system, the overall temperature differential across the thermoelectric array is also greatly reduced. The coefficient of performance (COP) of a thermoelectric system is defined as the heating or cooling capacity divided by the power consumed. COP is inversely proportional to the highest temperature difference across the array.
【0023】 Referring to fig. 3, a first embodiment of the invention is shown with a thermoelectric system 90, the thermoelectric system 90 using foam heat exchangers 95 and 100 configured in a heating mode. A dc voltage from power supply 105 is applied across te element 120 and current 110 flows in the direction shown. Pairs 115(P and N pairs) of thermoelectric elements 120 absorb heat from surface 125 and release heat to surface 130 located opposite component 120. The surface 125 where the thermal energy is absorbed becomes cold and the opposite surface 130 where the thermal energy is released becomes hot. The phenomenon of "heat pumping" known as the peltier effect is often used in thermoelectric cooling or heating. In this embodiment, the fan 135 passes air through the heat exchanger 100 that absorbs heat, and then the heat exchanger 100 is cooled. A fan 140 passes air through the heat exchanger 95 to transfer heat away from the heated surface 130. The power source 105 used in this configuration may be a battery, fuel cell, or other similar component that provides electrical current. By reversing the polarity of the dc power supply 105, the thermoelectric system 90 can be switched from a heating mode to a cooling mode.
【0024】 The foam heat exchangers 95 and 100 provide a large heat transfer capability across surfaces 130 and 125, respectively, to increase the efficiency of the system 90 as compared to conventional heat sinks. Due to the foam heat exchangers 95 and 100 having high heat transfer coefficients, a lower temperature difference between the opposing surfaces of the thermoelectric element 120 is achieved. This lower temperature differential consumes less energy and thus improves the performance of the overall system 90. Thus, the overall system, whether it is configured as a heating system or a cooling system, has very high performance.
【0025】 Figure 4 shows the relationship between system performance and heat transfer coefficient for a typical thermoelectric system using a foam heat exchanger. The coefficient of performance is defined as the heating or cooling capacity divided by the power consumed by the system.
【0026】 Referring to fig. 5, a foam heat exchanger system 150 is shown in a second configuration. The foam heat exchanger system 150 has a thermoelectric array 155 with a series of thermocouples 160 arranged electrically in series. Thermoelectric element array 155 has surfaces 165 and 170. The system 150 is arranged to have a separate foam heat exchanger 175 that rejects heat from the surface 170. Depending on the application, a second foam heat exchanger may not be required. Or a conventional heat exchanger may be used in place of the foam heat exchanger and placed adjacent to surface 165 depending on the application. Different configurations of the laying foam heat exchangers can be used to maximize heat transfer, and different configurations of the laying foam heat exchangers are application-dependent. Similarly, a single system may include multiple thermoelectric arrays, each having one or more foam heat exchangers.
【0027】 A third embodiment foam heat exchanger system 180 is shown in fig. 6. The system 180 is arranged similarly to the system of fig. 5, except that the heat exchanger is a combination foam and fin heat exchanger 185. The system 80 has an array 190 of thermoelectric elements 195. Cell 195 has surfaces 200 and 205. In the embodiment of fig. 5, a second foam heat exchanger may not be required. Or a conventional heat exchanger may be used in place of the foam heat exchanger depending on the application. Furthermore, different configurations of the laying foam heat exchangers can be used to maximize heat transfer, and are application-based.
【0028】 While the present disclosure has been described in connection with one or more illustrative embodiments, those skilled in the art will appreciate that: various modifications may be used, and equivalent modules may be substituted for the elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.