Heat transfer in low reynolds number flows through miniaturised channels

Abstract

The use of miniaturized channels as heat sinks/ heat exchangers is of great importance due to advantages of compact size and high heat sinking capabilities. The small hydraulic diameters of these miniaturized channels imply a higher pressure drop and consequently higher pumping power. Therefore, where possible, the pumping power required may be reduced by running applications at low flow velocities. This paper therefore investigates the heat transfer in low Reynolds number flow through miniaturized channels. Forced convection experiments were performed on 2 instrumented metal plates with 0.5 mm and 0.25 mm deep channels respectively. The channels were 2 mm wide and 270 mm long. A propylene glycol-based heat transfer fluid for solar collectors, Tyfocor® LS, was used as the working fluid. Reynolds numbers were in the range 10 – 100 and fluid inlet temperatures ranged from 5 – 60 °C. The measured Nusselt numbers were observed to depend more on the Peclet number and less on the geometry. Peclet number dependent Nusselt numbers was attributed to miniaturization scaling effects. A correlation for estimating the Nusselt number in terms of the Peclet number and hydraulic diameter was proposed. The results are significant in predicting the heat sinking performance in applications having low Reynolds number flows through miniaturized channels such as compact solar thermal collectors.