Abstract:
This invention is a compact, high-performance thermoelectric device for cooling air. Several variations on compact heat sinks are disclosed as well as several optimized configurations for maximized cooling effect, a mechanism to preventing overheating, and robust configuration to withstand rugged applications such as cooling automobile seats, air ducts, and power and temperature control circuitry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present Utility patent application claims priority benefit of the U.S. provisional application for patent No. 60/649,718 filed on Feb. 3, 2005 under 35 U.S.C. 119(e). The contents of this related provisional application are incorporated herein by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     This invention discloses a compact and high-performance thermoelectric heat exchange device (TED) which can be used in an air-conditioning system to deliver cold air and cool any object, such as an automobile seat.  
       BACKGROUND  
       [0003]     Thermoelectric cooling modules are also known as Peltier modules and are heat pumps that operate on the physical principles established over a century ago by Jean Charles Athanase Peltier in France.  
         [0004]     In a thermoelectric (TE) module, semiconductor materials with dissimilar characteristics are connected electrically in series and thermally in parallel, so that two junctions are created. The semiconductor materials are N and P-type, and are so named because either they have more electrons than necessary to complete a perfect molecular lattice structure or not enough electrons to complete a lattice structure. The extra electrons in the N-type material and the holes left in the P-type material are called “carriers” and they move the heat energy from the cold to the hot junction.  
         [0005]     A typical TE module is comprised of two ceramic substrates that serve as a foundation and electrical insulation for P-type and N-type semiconductor couples that are connected electrically in series and thermally in parallel between the ceramics. The ceramics also serve as insulation between the modules&#39; internal electrical elements and an electrically conductive material, usually copper pads attached to the ceramics, and maintains electrical connections inside the module.  
         [0006]     With the application of Direct Current (DC) to the TE module, heat is absorbed on the cold side of the ceramic, passes through the semiconductor material, and is dissipated at the hot side of the ceramic.  
         [0007]     A heat sink should be attached to the hot side of the ceramic for efficiently dissipating the heat from the TE module to the surrounding environment. Without a heat sink, the TE module would overheat and fail within seconds. Another heat sink may be attached to the cold side of the ceramic to cool the air or any other substance that passes through the heat sink.  
         [0008]     Such a configuration of the thermoelectric assembly is generally known as thermoelectric device (TED). This type of TED, along with other components, such as a blower, air duct, power supply, temperature sensing and control loop, can be used as a heat exchange device in an air conditioning system to deliver conditioned cold air for cooling applications. Some examples may be found in U.S. Pat. No. 5,623,828, which discloses a thermoelectric air cooling device for supplying cooled air to the driver or passengers of a vehicle; U.S. Pat. No. 6,758,193, which discloses a super-chilled air induction system used to reduce the air temperature in an air-fuel mixture during operation of an internal combustion engine; U.S. Reissue Pat. No. RE38,128, which discloses an integrated temperature climate control system for an automotive seat that comprises one heat sink that is used on both sides of the TED, with a switch to reverse the polarity of the current; and U.S. Pat. No. 5,547,019, which discloses a thermoelectric intercooler for heating or cooling the gas exiting a compressing stage of a turbocharger in an automobile. Some of these patents focus on integrating a thermoelectric device with the existing engine parts to improve engine performance. In U.S. Pat. No. 6,758,193, the thermoelectric device only indirectly cools the air with liquid coolant. In U.S. Pat. No. 5,547,019, the thermoelectric device may be used for both cooling and heating. In U.S. Reissue Pat. No. RE38,128, because the heat sink is the same on both sides, and the polarity is simply reversed, the heat sink is not as effective at dissipating heat, and the performance of the cooling function is not as strong or efficient as it could be. U.S. Pat. No. 5,623,828 details a thermoelectric device which directly cools air passing through the heat sink that is attached to the cold side of the thermoelectric module, but is not very efficient, and is not suitable for placement in an automobile seat.  
         [0009]     However, no mechanism is disclosed in the prior art to prevent potential overheating of the TE module during prolonged operation or extreme conditions. Further, none of these devices discloses a TE module of sufficient robustness, durability, and compactness as desired.  
         [0010]     Also, the performance of the heat sinks directly affects the performance of the thermoelectric device. In a TED, a temperature sensor is generally inserted into the heat sink on the hot side to measure the temperature of the heat sink, so that overheating of the thermoelectric module can be prevented. However, due to the temperature difference between the heat sink and the hot ceramic side of the module, the temperature measured does not accurately reflect the temperature of the module and overheating could, nevertheless, result because of this inaccuracy. Thus, there is a long felt need in the industry for a temperature sensor that accurately measures the temperature of the hot ceramic side of the module rather than within the heat sink. Accordingly, it is an aim of this invention to disclose an innovative and highly efficient design of heat sink.  
       SUMMARY OF THE INVENTION  
       [0011]     This invention is directed towards overcoming the above shortcomings by providing a compact thermoelectric device with an optimized configuration for maximized cooling effect, mechanism for preventing overheating, and robustness to withstand rugged applications such as cooling automobile seats, air ducts, and power and temperature control circuitry.  
         [0012]     This thermoelectric device consists of a Peltier thermoelectric module, hot side heat sink, cold side heat sink, a temperature sensor such as Negative Temperature Coefficient (NTC) thermistor directly embedded inside the thermoelectric module, assembly material such as thermal glue or metal bracket, and a foam-type insulation material to fill in the space along the side of the heat sink and minimize heat loss. A separate heat sink is mounted to each side of the thermoelectric module using either thermal glue or a metal bracket with thermal grease at the interface, which can enhance the heat transfer and provide additional rigidity. The said device, if placed in a snuggly shaped plastic enclosure with one air intake port and two air exit ports, can be positioned at the discharge of a blower and used as a heat exchange device to cool one portion of the divided air stream while the other portion of the air passes over the exposed hot side heat sink and is heated.  
         [0013]     The more effective the heat dissipation system for the hot side of the TE module, the cooler the cold side will be and the more efficiently the TE unit will operate. When power is applied to the module, the hot side of the module will begin ejecting its heat to the heat sink causing its temperature to rise. The ability of the heat sink to dissipate this heat as well as the heat being pumped from the cold side will determine the actual operating temperature of the hot side and thus, the cold side. The lower the thermal resistance of the heat sink on the hot side, the lower the temperature on the cold side will be.  
         [0014]     In one of the disclosed embodiments, a copper heat sink is used for the hot side for its better thermal conductivity relative to aluminum. Rather than a conventional extruded or bonded heat sink with fins, this copper heat sink is fabricated in the shape of a compressed accordion, allowing for more surface area and greater heat dissipation. The heat sink fins are formed in straight channels because such a configuration has less resistance to airflow and thus, greater heat dissipation.  
         [0015]     Accordingly, the main purpose of the heat sink on the cold side for this device is to let the air passing through undergo as much heat exchange as possible with the cold side of the ceramic. The longer the path of the air traveling through over the cold side, the greater the heat exchange that occurs, hence the lower the temperature of the air passing over the heat sink. Two variations on the heat sink shape are disclosed that achieve this purpose: one is a compressed accordion shape copper heat sink as described above but with “wave” type ridge lines, the other one is an aluminum heat sink with fins in an “S” shape. Both are fabricated to maximize the length of air passage over the cold side of the heat sink. These two variations are disclosed because, in tests, they have provided the best performance.  
         [0016]     As mentioned above, two methods of assembly can be used to package the TED: a metal bracket or thermal glue. When the metal bracket is used, thermal grease is applied at the interface between heat sink and ceramic of the TE module. The thermal glue results in an even lighter package because of reduction of metal parts. Combined with a rather small footprint of the device (approximately 45×45×24 mm in the current configuration), the result is a relatively compact and robust device that can be used in demanding conditions such as the vibration within automobiles.  
         [0017]     In order to accurately control the temperature of the hot side of the TE module and prevent possible overheating, an NTC thermistor is embedded within the TE module for direct contact with the hot side. The data from the thermistor measurement is fed to a control loop that is used to supply the power to the TE module. Thus, if the temperature measured from the hot side exceeds a certain threshold, the power supply to the TE module can be cut off to eliminate possible detrimental damage to the TE module.  
         [0018]     One advantage of this configuration is its fast response time and high cooling efficiency. Within 10 seconds of applying power to the TE device, a several degree reduction of the temperature measured at the exit point of the cold side air is achieved.  
         [0019]     Another advantage of the invention is that air passing over the cold side can be directed outwards to cool other objects, such as automobile seats.  
         [0020]     Other variations and advantages of this invention will become apparent from the following descriptions of several possible embodiments of the invention, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  illustrates a perspective view of an embodiment of the invention in which a straight copper heat sink is used on the hot side, a wave type copper heat sink is used on the cold side, and the device is assembled using a metal bracket.  
         [0022]      FIG. 2  illustrates a perspective view of another embodiment of the invention in which a straight copper heat sink is used on the hot side, an aluminum heat sink is used on the cold side, and the device is assembled using a metal bracket.  
         [0023]      FIG. 3  illustrates a perspective view of another embodiment of the invention in which a straight copper heat sink is used on the hot side, a wave type copper heat sink is used on the cold side, and the device is assembled using thermal glue.  
         [0024]      FIG. 4  illustrates a perspective view of another embodiment of the invention in which the straight copper heat sink is used on the hot side, aluminum heat sink is used on the cold side, and the device is assembled using thermal glue.  
         [0025]      FIG. 5A  illustrates a perspective view of the straight copper heat sink prior to being compressed into its final shape.  
         [0026]      FIG. 5B  illustrates a perspective view of the straight, copper heat sink in its relaxed condition, prior to assembly.  
         [0027]      FIG. 6A  illustrates a perspective view of the “wave” type copper heat sink in its final compressed shape.  
         [0028]      FIG. 6B  illustrates a perspective view of the “wave” type copper heat sink in its relaxed condition, prior to assembly.  
         [0029]      FIG. 7A  is a perspective view of the S-shaped aluminum heat sink.  
         [0030]      FIG. 7B  illustrates a top plan view of the S-shaped aluminum heat sink.  
         [0031]      FIG. 7C  is a side elevation view of the S-shaped aluminum heat sink.  
         [0032]      FIG. 8A  illustrates a perspective view of the TE module with NTC thermistor directly embedded beneath the hot side of the ceramic at the center of the thermoelectric module.  
         [0033]      FIG. 8B  illustrates a perspective view of the TE module with A NTC thermistor directly embedded beneath the hot side of the ceramic at one end of the thermoelectric module.  
     
    
     DETAILED DESCRIPTION  
       [0034]      FIG. 1  illustrates a perspective view of an embodiment of the invention in which a straight copper heat sink is used on the hot side, a wave type copper heat sink is used on the cold side, and the device is assembled using a metal bracket. A TE module  22  is sandwiched between “straight” copper heat sink  24  and “wave” copper heat sink  26 . An NTC thermistor  21  is attached to TE module  22  at the center of the hot side of the ceramic. A foam insulation material  23  and  25  is used to fill the space along each side of the heat sink, which would otherwise allow air to pass without coming in full contact with the heat sink passages. Metal brackets  27  are used to assemble the TED  20 . The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0035]      FIG. 2  illustrates a perspective view of another embodiment of the invention in which a straight copper heat sink is used on the hot side, an aluminum heat sink is used on the cold side, and the device is assembled using a metal bracket. The TED  30  has a straight copper heat sink  24  on its hot side and an S-shaped aluminum heat sink  28  on its cold side. TE module  22  is sandwiched between the “straight” copper heat sink  24  and S-shaped aluminum heat sink  28 . An NTC thermistor  21  is inserted into TE module at the center of the hot side of the ceramic. A foam insulation material  23  and  25  is used to fill the space along each side of the heat sink which would otherwise allow air to pass without coming in full contact with the heat sink passages. Metal brackets  27  are used to assemble the TED  30 . The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0036]      FIG. 3  illustrates a perspective view of another embodiment of the invention in which a straight copper heat sink is used on the hot side, a wave type copper heat sink is used on the cold side, and the device is assembled using thermal glue. A TE module  22  is sandwiched between a “straight” copper heat sink  24  on the hot side and a “wave” copper heat sink  26  on the cold side. An NTC thermistor  21  is inserted into the TE module  22  at the end of the hot side of the ceramic. The TED  40  is assembled using thermal glue  29 . The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0037]      FIG. 4  illustrates a perspective view of another embodiment of the invention in which the straight copper heat sink is used on the hot side, aluminum heat sink is used on the cold side, and the device is assembled using thermal glue. A TED  50  has a straight copper heat sink  24  on its hot side and an S-shaped aluminum heat sink  28  on its cold side. TE module  22  is sandwiched between “straight” copper heat sink  24  and S-shaped aluminum heat sink  28 . An NTC thermistor  21  is inserted into TE module at the end of the hot side of the ceramic. The TED is assembled using thermal glue  29 . The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0038]      FIG. 5A  illustrates a perspective view of the straight copper heat sink in its final compressed condition. At this stage, the heat sink  24  has triangle shaped air passages or channels. The ridge lines of these passages or channels are straight so this configuration has less air resistance and, thus, air flow is greater with this relative to a “wave” type copper heat sink  26 , as shown in  FIGS. 6A and 6B .  
         [0039]      FIG. 5B  illustrates a perspective view of the straight copper heat sink in its relaxed condition prior to assembly. After being compressed horizontally along the axis parallel with the top and bottom surface, the heat sink&#39;s  24  triangle shaped air passages or channels are formed to allow for maximum heat transfer between the heat sink and the passing air.  
         [0040]      FIG. 6A  illustrates a perspective view of the “wave” type copper heat sink  26  in its final compressed shape with its triangle shaped air passages or channels formed. The ridge lines of these passages or channels are wave shaped so this copper heat sink has more air resistance and hence the air flow is less as compared to the straight line copper heat sink  25 , in  FIGS. 5A and 5B .  
         [0041]      FIG. 6B  illustrates a perspective view of the “wave” type copper heat sink  26  in its relaxed condition prior to assembly. After being compressed horizontally along the axis parallel to the top and bottom surface, its triangle shaped air passages or channels are formed.  
         [0042]      FIG. 7A  is a perspective view of the S-shaped aluminum heat sink.  FIG. 7B  illustrates a top plan view of the S-shaped aluminum heat sink.  FIG. 7C  is a side elevation view of the S-shaped aluminum heat sink. In each drawing, an S-shaped heat sink  26  is diagrammed from a different perspective. Unlike conventional aluminum heat sinks that feature multiple fins extending from the base plate with same the length, this heat sink features partially blocked air entrances and exits at the aluminum fins. These blockages serve to form the “S” shape of the configuration and allow for greater air resistance and air flow path compared to conventionally shaped fins. Thus, the air exiting the heat sink will allow more net cooling for colder temperatures.  
         [0043]      FIG. 8A  illustrates a perspective view of the TE module with NTC thermistor directly embedded beneath the hot side of the ceramic at the center of the thermoelectric module. A TE module  22  with NTC thermistor  21  directly embedded underneath the hot side of the ceramic is illustrated. The thermistor  21  is shown placed in at the center beneath the TE module  22 . The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0044]      FIG. 8B  illustrates a perspective view of the TE module with an NTC thermistor directly embedded beneath the hot side of the ceramic at one end of the thermoelectric module. A TE module  22  is shown with a thermistor  21  beneath and at the end of the TE module. The thermistor  21  needs to be in thermal contact with the ceramic plate on the hot side of the TE module but electrically insulated from the thermocouples within the TE module. This is done during the fabrication process of the TE module and cannot be accomplished after the TE module is fabricated. The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source.  
         [0045]     The four thermoelectric devices depicted in these four embodiments represent some possible variations in the present invention based on different combinations between two different types of heat sinks on the cold side, and two different methods of assembling. More variations can be formed by varying the position of the NTC thermistor.  
         [0046]     Any of the said thermoelectric devices,  20 ,  30 ,  40  or  50 , can be placed in a plastic enclosure (not shown) with one air intake port and two air outlet ports. This plastic enclosure should house the TED rather snuggly, so that any space between the TED and the internal wall of the enclosure is minimized as is any possible air leakage. The orientation of the TED in this plastic housing should be such that the intake port is aligned with the passages or channels on the heat sinks. One of the outlet ports on the enclosure should be situated close to the cold side of the heat sink, while the other outlet port close to the hot side of the heat sink. TE module  22  would act as an air-diverter to divide the singular air source into two air streams, a hot air stream and a cold air stream. The hot air stream may be treated as waste stream and exhausted, and the cold side air stream can be used to cool an object.  
         [0047]     The electric leads  31  and  33  of the thermoelectric module can be connected to the positive and negative leads of a DC power source. The operating range of the thermoelectric module is between 6 to 16 Volts. The power applied to the TE module can be controlled by a Power Width Modulation circuitry that is also connected to a temperature control circuitry to control the temperature of the object being cooled, or other similar circuitry. The two leads of NTC thermistor  21  can be connected to this power control circuitry to further regulate supply of the power to the TE module. When the signal from the thermistor  21  indicates that the temperature of the hot side of the TE module exceeds a preset value, the power supply to the TE module would be shut off to prevent any overheating of the TE module and TED.  
         [0048]     While certain exemplary embodiments of the invention have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad aspects of the invention, and that the embodiments of the invention are not to be limited to the specific constructions and arrangements shown and described, because various other modifications are possible.