Effects of geometrical parameters and Reynolds number on the heat transfer and flow characteristics of rectangular micro-channel using nano-fluid as working fluid

The combined effects of Reynolds number and geometrical parameters on heat transfer and flow of Al₂O₃–H₂O nanofluid under laminar flow condition in single rectangular microchannel was investigated numerically. In the process of the actual flow and heat transfer of nanofluids, the nanoparticles concentration distribution is nonuniform in the flow field. A proposed simulation method carefully considering the nanofluids thermophysical properties are nonuniform and dynamic in the channels was adopted to improve the simulation accuracy. The results show that the local heat transfer coefficients increase with the aspect ratio and design variable β (the ratio of the microchannel width to the wall thickness) at the fully developed flow region because the nanoparticles enriched near the solid-fluid interface and then heat transfer is enhanced as the aspect ratio and design variable β increase. The effect of aspect ratio on heat transfer coefficient is remarkable. But design variable β has a very mild effect on heat transfer compared with aspect ratio. The difference of heat transfer performance between a conventional channel and a microchannel is decreased with the increase of aspect ratio. The Poiseuille number of the microchannel is related to not only aspect ratio but also the design variable β and Reynolds number, and it is smaller than that of the conventional scale rectangular channels when the Reynolds number is less than about 1000.