A NUMERICAL STUDY TO PREDICT THE EFFECTS OF STRUCTURED ROUGHNESS ELEMENTS ON PRESSURE DROP AND HEAT TRANSFER ENHANCEMENT IN MINICHANNELS AND MICROCHANNELS

摘要

Better understanding of laminar flow at microscale level is gaining importance with recent interest in microfluidics devices. The surface roughness has been acknowledged to affect the laminar flow, and this feature is the focus of the current work to evaluate its potential in heat transfer enhancement. A numerical model is developed to analyze the thermal and hydrodynamic characteristics of minichannels and microchannels in presence of roughness elements. Structured roughness elements following a sinusoidal pattern are generated on two opposed rectangular channel walls with a variable gap. A detailed study is performed to check the effects of roughness height, roughness pitch, and channel separation on pressure drop and heat transfer coefficient in the presence of structured roughness elements. As expected, the structured roughness elements on channel walls result in an increase in pressure drop and heat transfer enhancement as compared to smooth channels due to the combined effects of area enhancement and flow modification. This is due to the fact that the roughness element as a small obstruction in the flow passage of narrow channels which introduces flow modifications in the flow and increases the energy transport. The improvement in global heat transfer enhancement is observed in rough channels due to velocity fluctuations. At the same time, it also causes pressure drop to increase as compared to smooth channels. The fully developed friction factor and Nusselt number results obtained from CFD simulations for smooth and rough channels are compared with the experimental data carried out in the same laboratory. The current numerical scheme is validated with the experimental data and can be used for design and estimation of transport processes in the presence of different roughness features.