The techniques used in the assembly of a thermoelectric (T.E.) system can be as important as the selection of the proper device. It is imperative to keep in mind the purpose of the assembly – namely to move heat. Generally a T.E. device, in the cooling mode, moves heat from an object to ambient. All of the mechanical interfaces between the objects to be cooled and ambient are also thermal interfaces. Similarly all thermal interfaces tend to inhibit the flow of heat or add thermal resistance. Again, when considering assembly techniques every reasonable effort should be made to minimize thermal resistance.

Mechanical tolerances for heat exchanger surfaces should not exceed 0.001 in/in with a maximum of 0.003" Total Indicated Reading. If it is necessary to use more than one module between common plates, then the height variation between modules should not exceed 0.001" (request tolerance lapped modules when ordering). Most T.E. assemblies utilize one or more "thermal grease" interfaces. The grease thickness should be held to 0.001 ± 0.0005" (a printers ink roller works well for this). When these types of tolerances are to be held, a certain level of cleanliness must be maintained. Dirt, grit and grime should be minimized; this is very important when "grease" joints are utilized due to their affinity for these types of contaminants.

Once the T.E. modules have been assembled between the heat exchangers, some form of insulation/seal should be provided between the exchangers surrounding the modules. Since the area within the module, (i.e. the element matrix), is an open DC circuit and a temperature gradient is often present, gas flow (which may contain water that could condense) should be minimized. Typically, a T.E. module is about 0.2" thick, so any insulation that can be provided will minimize heat leak. The presence of the insulation/seal also offers some protection from physical damage.

The insulation/seal is often most easily provided by inserting sections of closed cell polyurethane foam about the cavity and sealing with either an RTV type substance or, for more physical integrity, an epoxy coat. Whatever form is used, it should provide the protection outlined above. It is often desirable to provide strain relief for the input leads, not only to protect the leads themselves, but to help maintain the integrity of the seal about the modules.

We have included an Assembly Tips drawing (Fig. 6). This drawing shows the details of the recommended construction of a typical assembly. The use of a "spacer block" yields maximum heat transfer, while separating the hottest and coldest parts of the system, by the maximum amount of insulation. The "spacer blocks" are used on the cold side of the system due to the lower heat flux density. In addition, the details of a feed thru and vapor sealing system that can be used for maximum protection from the environment are shown.

If you follow the recommendations shown in these drawings that you will see a significant improvement in performance. When testing an assembly of this type it is important to monitor temperature. Measuring temperature of the cooling fluids, inlet and outlet temperatures as well as flow rates is necessary. This is true if either gas or liquid fluids are used. Knowing input power to the T.E. device, both voltage and current, will also help in determining the cause of potential problems.

In addition we have enclosed step-by-step procedures for assembling CP and OptoTEC™ modules, Solderable or Lapped modules to heat-exchangers.