Variable cross-sectional flow area for an enhanced thermo-hydraulic performance in microchannels

Abstract

Fins, protrusions, dimples, cavities are the common surface modifiers used in microchannels to augment its thermo-hydraulic performance passively. Among these surface modifiers, fins and protrusions have received the most attention because of its outstanding and promising heat transfer enhancement in both conventional channels and microchannels. However, a search in the literature revealed that V-shaped protrusions are only investigated in macro-sized channel with air as the working fluid. Therefore, the thermo-hydraulic performance of V-shaped protrusions in microchannels remains uncertain. Furthermore, significant effort has been placed into the geometrical parameters of the fins and protrusions with the view point of producing an optimal design with an efficient and effective thermo-hydraulic performance. Particularly, the cross-sectional flow area, that is affected by the protrusion height, has been identified as a key influence of the thermo-hydraulic performance. However, the thermo-hydraulic effect of variable cross-sectional flow area in enhanced microchannels has also yet to be explored. Therefore, the present study aims to investigate on the effect of V-shaped protrusions as well as the variable cross-sectional flow area in microchannels. A steady-state experimental and a three-dimensional numerical study are conducted in microchannels with single-walled V-shaped protrusions under three separate configurations: (a) uniform cross-sectional flow area, (b) contracted cross-sectional flow area and (c) expanded cross-sectional flow area. The average hydraulic diameters of the microchannels are kept constant at 600 µm for all three configurations. The purpose is to compare Darcy’s friction factor and Nusselt number between different configurations as well as to understand the thermo-hydraulic effects of variable cross-sectional flow area in microchannels. The study concluded that the V-shaped protrusions are effective heat transfer enhancers and the enhanced microchannel with expanded cross-sectional flow area has the highest thermo-hydraulic performance among all other experimented microchannels. The findings of the present studies carry the research a step closer to producing an optimal design for the future microchannel heat sink.