Effect of aligned and offset roughness patterns on the fluid flow and heat transfer within microchannels consist of sinusoidal structured roughness

This research aims at numerical study of the effect of aligned and offset roughness patterns on the fluid flow and heat transfer phenomenon within rectangular cross section microchannels containing structured sinusoidal roughness. To do this, the pressure losses, heat transfer coefficients as well as thermal performance indexes in aligned pattern are compared with corresponding offset pattern at different roughness pitches, heights and microchannel heights. In this work, the upper and lower microchannel walls involve sinusoidal roughness and other walls are assumed to be smooth. Air and water are also chosen as the working fluids. To validate the current numerical model, comparisons are also made with previous experimental, theoretical and numerical results and reasonable agreements are observed. Results show that for the air, the effect of change in the channel parameters on the heat transfer coefficient is of little significance compared to the water and the two roughness arrangements represent a same behavior. It is found that, at high roughness height or low channel height, the offset arrangement provides lower pressure loss for the considered fluids and also lower heat transfer rate for water than the aligned pattern. It is shown that for both fluids, as the roughness pitch increases, the offset pattern provides lower pressure loss than the aligned pattern. Numerical results indicate that for water, the increase in roughness pitch leads to negligible variation in the heat transfer rate in aligned configuration while different behavior is observed in offset pattern. Results exhibit that both air and water represent a same thermal performance index and the offset effect could increase the thermal performance of microchannel with the increase in roughness pitch ratio. It is also revealed that, in both roughness patterns, the decrease in constricted relative roughness leads to the increase in the thermal performance index and high thermal performance is achieved at low roughness height.