Model verification of heat exchangers in a flow test rig

Paper in proceeding, 2015

In power electronics, more efficient removal of heat from the junction of power devices leads to a higher power rating per die, which in turn leads to fewer die and reduced system volume. Since temperature is a main driver in expected failure modes an increase in cooling capability can also enhance margins of the device reliability. Previously, CFD simulations of two novel heat exchanger designs that will be used in a power module with double sided cooling have been reported on. The heat exchangers are fabricated by direct 3D manufacturing of copper structures, which allows almost complete freedom in geometric design. Two novel geometries of heat exchanger cooling structures have previously been modeled in terms of thermal performance and expected pressure drop. A flow rig has been designed and calibrated to measure thermal performance and pressure drops of these heat sinks. For calibration purposes, measurements of the thermal response of wave structured and unstructured heat sinks are reported here. The results show that, as expected, the heat sink temperatures are lower for all flow rates in the wavestructured geometry. A thermal CFO model accurately predicts the behavior of the temperature difference between inlet and outlet versus flow rate, but predicts higher absolute temperature values. It was also found that the model underestimates the pressure drop over the tested heat sillies. The pressure drop across a novel pine cone geometry heat sink fabricated by additive manufacturing methods was also measured. Comparisons to a reduced model, which neglects everything before the inlet and after the outlet of the tested device, showed that the behavior of this pine structured heat sink was not predicted correctly. The pressure drop increased more rapidly with flow rates in the model than in the measurements. The main source of error in the measurements and simulations comes from a lack of thermal loading. Future work to improve the flow rig includes possibilities to increase the temperature loading at the bottom of the heat sink under test.