Numerical Investigation of Heat Transfer Enhancement of Nanofluids with Rod-Like Particles in Micro Pin Fin Heat Sink Channel

Flows of nanofluids with rod-like nanoparticles in a microscale channel having cylindrical micro pin heat sinks were numerically simulated to analyze the effect of the aspect ratio of the rod-like particles on the heat transfer and flow in the microscale channel. Furthermore, the optimal aspect ratio was investigated by examining the trade-off relationship between the pressure drop and the thermal efficiency. The Hamilton-Crosser model and Brenner’s model were used to describe the thermal conductivity and viscosity of nanofluids, respectively. The numerical simulations revealed that heat flux around the cylinders was more active in the upstream region and increased with increasing the inlet particle volume fraction ϕin and the particle aspect ratio s and that the effect of the aspect ratio tended to decrease gradually. Furthermore, it was found that the thermal efficiency improved with increasing ϕin and s but saturated above ϕin = 0.04 and s = 30, whereas the pressure drop increased further and the increase was more pronounced at large aspect ratios. These results imply that nanofluids with relatively low particle concentration and small particle aspect ratio are suitable as working fluids for heat exchangers.