Combined effects of heat input and clamping pressure on the thermal performance of phase change thermal interface materials for electronics cooling applications

This work deals with experiments on the thermal performance of phase change materials (PCMs) used as thermal interface materials (TIMs) between a heat pipe cooling system and an electronic component. A test rig is conceived and realized so that experiments can be carried out under various heat input powers, clamping pressures, and cooling temperatures. Three commercial PCMs (Hi-flow 105, Hi-flow 200, and Hi-flow 625), having different thicknesses, thermal conductivities, and phase change temperatures, were tested. A heat transfer enhancement factor is introduced to compare the contact thermal resistance obtained without PCMs to that obtained with PCMs. The experimental results show that the thermal performances obtained by Hi-flow 105 and Hi-flow 625 are affected greatly by the heat input power and they are less sensitive to the clamping pressure. The maximum heat transfer enhancements obtained by these two PCMs, which increase with the heat input power, are 75 % and 55 % for Hi-flow 105 and Hi-flow 625, respectively for a heat input power of 115 W. However, with Hi-flow 200, the thermal performances are sensitive to heat input power, and the clamping pressure for heat input powers lower than 100 W. The heat transfer enhancements obtained by Hi-flow 200, which decrease with the heat input and the clamping pressure, are lower than those obtained with Hi-flow 105 and Hi-flow 625 PCMs whatever the heat input power and the clamping pressure, and they do not exceed 25 %. Thermomechanical simulations were carried out to analyze the combined effects of the heat input load, the temperature level, and the clamping pressure. The comparison between the results issued from the thermomechanical model and those obtained from the experiments which are relative to axial temperature distribution along the heating and cooling blocks shows a good agreement that is demonstrated by statistical indicators. An analytical model is developed to calculate the contact thermal resistance between two rough surfaces including or not PCMs. The comparison between the analytical results and those issued from the literature and the present study shows a good agreement.