Influence of Gravity on Passively Cooled Heat Sink Using Experimental Data and Finite Element Analysis

Abstract

This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to evaluate the accuracy of Siemens Flotherm XT 2021.2 simulation software. In order to determine the influence of heat sink orientation, experimental measurements were performed on the resistor and heat sink temperature using thermocouples. Siemens Simcenter Flotherm XT 2021.2 software (Siemens, Munich, Germany) was used to perform finite element simulation. The influence of the heat sink position was evaluated on two setups, one where the resistor is placed directly on the heat sink using screws, and the second one, where a thermal pad was placed between the resistor and the heat sink. Screws were to clamp the parts in both cases. In total, four experiments and simulations were performed with two assemblies with two different gravity orientations for each assembly. In all the cases, the heat sink was placed on a wooden structure to prevent heat transfer through conduction, due to poor thermal conductivity of wood, and to allow unrestricted air flow underneath and around the heat sink. The first simulation was then calibrated for the first scenario, and the rest of the simulations were made using the calibrated one. No other changes in boundary conditions were made. Temperature measurements show an improved cooling when the air speed between the heat sink fins is enhanced due to natural hot air movement generated by the gravity. Gravity has an influence on the cooling regardless of the presence or absence of a thermal interface material. Measured temperatures were reduced up to 8.2 °C due to the rotation of the heatsink. Finite element analysis shows similar temperature values to the measured ones in all the scenarios.