Thermofluidics and energetics of a manifold microchannel heat sink for electronics with recovered hot water as working fluid

A detailed thermo-hydrodynamic analysis of a hot water cooled manifold microchannel heat sink for electronic chip cooling is presented. The hot water cooling enables efficient recovery of heat dissipated by the even hotter chip by using hot water recovered from a secondary application. Contrary to usual expectation of laminar flow in electronic cooling, high flow rate and high fluid temperatures result in turbulent flow conditions in the inlet and outlet manifolds of the heat sink with predominantly laminar flow conditions in microchannels. To simulate these complex flow conditions, a three dimensional (3D) conjugate heat transfer model with turbulent flow is developed. Microchannel heat transfer structure is modeled as porous medium with permeability parameters extracted from a 3D model for a single microchannel. The energetic performance of the heat sink is analyzed in terms of 2nd law efficiency and sources of exergy destruction are identified by detailed local entropy generation analysis at low and high Reynolds number conditions of 2400 and 11200 respectively. This analysis shows that entropy generation due to heat transfer dominates the net entropy generation in the heat sink for both conditions. Although entropy generation due to viscous dissipation increases significantly with increased Reynolds number, it still contributes less than a third to the total entropy generated at high Reynolds numbers. Use of hot water reduces the heat transfer component of entropy generation significantly, thus leading to higher 2nd law efficiency.