Transient analysis of thermal junctions within a thermoelectric cooling assembly

The performance of a thermoelectric (TE) heat exchanger assembly is greatly affected by the quality of the thermal junctions connecting the modules and the mounting surfaces of the heat/cold sinks. The quality of this junction, in turn is affected by many different variables. These include heat sink surface quality, quantity of thermal grease, contaminates in the thermal grease, assembly screw torque, tapped hole quality, surface finish of the modules and the variance in module heights. Until now, junction quality could only be verified by disassembly of the heat exchanger or inferred from a full cooling performance test of the assembly. This paper details a new, transient test method which accurately and dependably characterizes the module-to-heat-sink thermal junctions. A small current is applied to the TE modules in a thermoelectric assembly. This induces a small temperature difference across the module and between the ceramics of the module and its neighboring heat/cold sink. Power is then removed and the module's ceramics return to the temperature of its neighboring heat sink. The rate of temperature decay is directly proportional to the junction quality. Thus, the residual Seebeck decay waveform directly correlates to thermal junction quality, providing the means for rapidly and accurately characterizing assembly quality.