Influence of Temperature and Aging on the Thermal Contact Resistance in Thermoelectric Devices

Abstract

In the first phases of the development of thermoelectric systems, such as the thermoelectric generators, when the thermal design is carried out, the most important parameters affecting the performance are the thermal resistances of the components. This paper focusses on the thermal contact resistance (TCR), analyzing the influence of aging and temperature on different thermal interface materials (TIM), i.e., thermal paste, graphite and indium. In previous papers, TCR has been studied depending on parameters such as surface roughness, bonding pressure, thermal conductivity and surface hardness. However, in thermoelectric applications, a relevant aspect to consider when choosing a TIM is aging due to thermal stress. The exposure of this type of materials to high temperatures for long periods of time leads to deterioration, which causes an increase in the thermal contact resistance which impairs the conduction of the heat flow. Therefore, there is a need to study the behavior of thermal interface materials exposed to temperatures typical in thermoelectric generators, to make a correct selection of the TIM. It has been observed that exposure temperatures of around 180 °C induce a significant increase in the thermal impedance of the three TIM's under study, although this effect is much more relevant for the thermal paste. The contact comprising steel, thermal paste and ceramic presents a 300% increase in the thermal impedance after 70 days of aging, whereas that exceeds 185% for the contact of aluminum, thermal paste and ceramic. In the tests with exposure temperature of 60 °C, there is no observed decrease in the thermal impedance.

Computational study of geothermal thermoelectric generators with phase change heat exchangers

“…Different materials such as thermal grease, graphite sheets, or even phase change materials are nor-355 mally introduced in order to improve this contact. The value of the thermal resistance depends on the interface material and the pressure distribution, but it is estimated to be between 0.01 and 0.1 K/W per module [54,55].…”

“…Thus, for a TPCT inserted 3 m, whose evaporator measures 1.5 m, the input temperature is the value at a depth of 2.25 m. On the ambient side, the average temperature and wind velocity of the park, 20.8 °C and 5.43 m/s, have been taken as reference [62]. Regarding the contact between the different parts, per each module, a thermal 600 contact resistance of 0.05 K/W and a thermal bridge resistance of 41.6 K/W have been considered [54,55].…”

Experimental measurement of thermal conductivity of stereolithography photopolymer resins

“…It is based on the generation of an unidirectional heat flow and the temperature difference of the sample studied, which will be a function of the thermal conductivity. In the ITF (Thermal and Fluid Engineering-Ingeniería Térmica y de Fluidos) research group, thermal conductivity studies have already been carried out using this test bench of their own design and manufacture [18].…”

“…To register data, the sample is placed between the upper and the lower fluxmeter, a pressure is applied on the sample (the same for all tests), it is insulated, and the hot Fig. 2 Sample and temperature sensors [18] sink is heated (always supplying, for each test, the same power). The temperature measurements were recorded in the ALMEMO 5690-2M09TG3 connected to a computer.…”

“…Some improvements have been applied to the bench described in the article by Rodríguez et al [18]. Since the bench was designed to measure relatively high conductivities (steel, aluminium, etc.)…”