Constructal design of two-phase stacked microchannel heat exchangers for cooling at high heat flux

Abstract

Constructal design of high heat flux two-stacked horizontal microchannel heat sinks are presented for cooling of electronic devices. Using ANSYS Computational Fluid Dynamics (CFD) code for subcooled nucleate boiling, fixed volume constraints were invoked for the heat sinks and microchannels to achieve optimal flow velocities and pressure drops at global minimum thermal resistances of the microchannel heat sinks; this is in line with constructal design principle. Validation of the CFD code was done by comparing its results with those of experimental data in the open literature. The closeness of the two results showed the CFD code to be accurate in predicting subcooled flow boiling for cooling of microelectronic devices. Heat fluxes of 1100 and 1200 W/cm2 (1.1 × 107 W/m2 and 1.2 × 107 W/m2) were used in the simulations and optimizations. The thermal resistance, pumping power and Bejan number were based on microchannels that an optimal heat sink of 1 cm width could accommodate. The thermal resistances and base temperatures for optimal microchannel heat sinks at these high heat fluxes (the focus of the study) are low; the pumping power requirements are also low, which show that they are useable in the cooling of electronic devices and other similar applications. Also, this is an indication that optimal two-stacked microchannel heat sinks operating in subcooled flow boiling could be considered as a viable alternative in the cooling of electronics. Optimal two-stacked microchannel heat sink operating at 1200 W/cm2 and in counterflow and parallel flow arrangements, was used for the critical heat flux study and the results show that both have good CHF performance, although counterflow arrangement was better.