Study of thermal and hydraulic performances of circular and square ribbed rough microchannels using LBM

Abstract

The effects of roughness geometries and relative roughness height at the slip flow regime to investigate the thermal and hydraulic performances of microchannel have been considered in the present article using a thermal Lattice Boltzmann Method (TLBM). A two dimensional 9-bit (D2Q9) single relaxation time (SRT) model is used to simulate this problem. In micro-flows, the local density variation is still relatively small, but the total density changes, therefore, in order to account this density variation and its effect on the kinematic viscosity v, a new relaxation time proposed by Niu et al.[13] is used. The roughness geometry is modeled as a series of square and circular riblets with a relative roughness height from 0% to 10% of the channel height. The friction coefficients in terms of Poiseuille number (Pn) and the dimensionless heat transfer rate in terms of Nusselt number (Nu) have been discussed in order to analyze the roughness effects. The thermal-hydraulic performance (η) is calculated considering the simultaneous effects of thermal and fluid friction (pressure drop) at the slip flow regime at Knudsen number, Kn, ranging from 0.01 to 0.10 with other controlling parameters for both kind of geometries. The results have been compared with previous published works and it is found to be in very good agreement.