A Computational Fluid Dynamics Study of Fluid Flow and
Heat Transfer in a Micro channel

Abstract

A theoretical study of single phase microchannel heat exchanger has been carried out. The computational fluid dynamics (CFD) model equations are solved to predict the hydrodynamic and thermal behaviour of the exchanger. The geometry of the problem and meshing of it have been made in ANSYS Workbench. The models have been solved by ANSYS Fluent 12.0 solver. The utility of nonmaterial as a heat enhancer has been justified by studying a circular microchannel thermal behaviour. Water and its nanofluids with alumina (Al2O3) are used as the coolant fluid in the microchannel heat sink. The present CFD calculated heat transfer coefficient values have compared with the analytical values and very close agreement is observed. The result shows that nanofluids help to increase the heat transfer coefficient by 15% and 12% respectively in laminar and turbulent zone. Thus use of nanofluids has been found beneficial both in laminar and turbulent zone. The relation between heat transfer coefficient and thermal conductivity of the fluid i.e. h k is proved in the present study.The entrance length for the fully developed velocities depends on Reynolds number. The temperature rise between outlet and inlet depends on the Reynolds number, Re and Peclet number, Pe. Temperature distribution is found to be independent of radial position even for Pe 1.0. The hydrodynamic and thermal behaviour of the system have been studied in terms of velocity, pressure and temperature contours. The velocity contours at the exit show that wall effect penetrates more towards the center and the thicknes of the zone with maximum velocity shrinks with increase in Re. The pressure drop across the channel increases with increase in Re.The experimental work done by Lee and Mudawar (2007) has been predicted by the present CFD results. The hydrodynamics and thermal behaviour of a rectangular microchannel are studied here. The variation wall temperature, pressure drop in the channel and the friction factors calculated using ANSYS Fluent can well predict the experimental data. The effect of Re on the behaviour the channel are also studied. Its behaviour also have been analysed with the help of temperature, pressure and velocity contours.