Heat transfer performance of a compact heat exchanger based on metal foam and Thermal Interface Material (TIM)

This article reports on the heat transfer performance of a compact heat exchanger based on metal foam and thermal interface material (TIM), which was built in-house. The heat exchanger was 20 x 18 cm, almost the size of a car radiator. The assembly method mimics the plate-type heat exchanger. This study investigates the effects of different commercially available TIMs, different pores per inch (PPI) foams, and compressive loads. The experiments were conducted with copper foams of 20 and 40 PPI with 1 mm thick plate fins and three commercially available TIMs (pad types): TIM 1 (4 W/mK), TIM 2 (5 W/mK), and TIM 3 (12.8 W/mK). Various configurations of the compact finned copper foam heat exchanger were tested at different Reynolds numbers in the range from 0 to 45,000. Nusselt number and pressure drop ratio of the heat exchanger with 3% (5 mm) and 6% (10 mm) compression were measured with a self-built test rig. In general, the Nusselt numbers ratio were dependent on the Reynolds number; they increased as the Reynolds number increased. The results show that the 20PPI_TIM 3 finned copper foam heat exchanger has the highest increase in Nusselt number ratio at a compression of 3%, which increases by 29% at a Reynolds number of 25,000 (compared to 20PPI_NoTIM). The heat exchanger configuration with the highest thermal conductivity (TIM 3, 12.8 W/mK) achieved the best heat transfer performance among the heat exchanger configurations tested. On the other hand, the pressure drop ratio in the finned copper foam heat exchanger of 40PPI_TIM 1 at 6% compression was 33% higher than that of 40PPI_NoTIM at a Reynolds number of 20,000 (the highest pressure drop ratio), which is due to the limitation of airflow through the heat exchanger caused by the smaller pores of the foams. This study shows that the combination of metal foam and fins with TIM in a heat exchanger can increase the surface area between the mating parts and thus increase heat transfer. It also provides an insight into an alternative way of bonding metal foams with other metals (or a base plate) to develop high performance heat exchangers.