Computational Analysis of Thermal Performance and Entropy Generation of Nanofluid Flow in Microchannels

High heat loads of mechanical, chemical, and biomedical microsystems require heat exchangers which are very small, robust, and efficient. Nanofluids are dilute suspensions of nanoparticles in liquids, which may exhibit remarkable heat transfer characteristics, especially for heat removal in micro-devices. Minimization of entropy generation is potentially a design tool to determine best heat exchanger device geometry and operation. Focusing on microchannel heat sink applications, the thermal performance of pure fluid flow as well as different nanofluids (i.e., Al2O3+water and ZnO+EG) with different volume fractions are discussed. The local and volumetric entropy rates caused by frictional and thermal effects are illustrated for different coolants, geometries and operational parameters. The Feng-Kleinstreuer (F-K) thermal conductivity model, which consists of a base-fluid static part, k(bf), and a new "micro-mixing" part, k(mm), i.e., k(nf) = k(bf) + k(mm), was adopted in the thermal performance study of nanofluid flow in microchannels. In addition, two effective nanofluid viscosity models have been analyzed and are compared in the current study. In summary, the friction factor, pressure gradient, pumping power, local heat transfer coefficient, thermal resistance and entropy generation are evaluated for different nanofluids. The experimentally validated computational study provides new physical insight and criteria for design applications towards effective micro-system cooling.