Thermal analysis of a microchannel heat sink cooled by two-phase flow boiling of Al2O3 HFE-7100 nanofluid

According to advances in high heat flux devices, sufficient thermal management methods shall be developed to dissipate high heat fluxes, especially for small-scale devices. In this research, highly subcooled flow boiling of HFE-7100 containing different concentrations of alumina nanoparticles are simulated in a microchannel heat sink using Computational Fluid Dynamics (CFD). The alumina nanofluids are considered homogenous and their equivalent properties are obtained using correlations. The operating conditions of the current study include Reynolds numbers in the range of 530 to 2000 and boiling numbers in the range of 2.3 x 10(-3) to 7.1 x 10(-3). The Volume of Fluid (VOF) model is employed in two-phase flow simulations. Two sets of experimental data are used to confirm the numerical model of two-phase boiling flows in microchannel heat sinks. The results indicate that disturbance in the thermal boundary layer caused by gas-phase bubble movements near microchannel walls enhances heat transfer in the flow boiling in comparison with the single-phase flow. Therefore, the local heat transfer coefficient increases after the onset of nucleate boiling. Additionally, it is observed that the wall temperature distribution is significantly affected by boiling nucleation and bubble movements. It is concluded that the heat transfer enhancement obtained from adding alumina nanoparticles to the base fluid is not impressive in comparison with the heat transfer enhancement obtained by two-phase flow boiling instead of single-phase flow in thermal management systems.