Heat transfer and pressure drop in micro-channels with different inlet conditions for water in the laminar and transitional regimes

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

Heat transfer by means of microchannels is an efficient method of cooling small but high-heat-dissipating objects. With very high heat transfer coefficients, the application of microchannels, especially in the field of electronics cooling, shows potential. With the aid of different inlet conditions, an experimental investigation to measure the heat transfer and pressure drop in a single copper microchannel, with a constant surface heat flux boundary condition, was undertaken in the laminar, transitional, and early turbulent regimes. Three test sections of hydraulic diameters 1.05 mm, 0.85 mm and 0.57 mm and of equal lengths of 200 mm were experimentally investigated using two inlet conditions: a sudden contraction inlet and a bellmouth inlet. Friction factors were determined for three heat input conditions per test section. Results show lower values of the friction factor than the conventional theory in the laminar and turbulent regimes for the sudden contraction inlet. The bellmouth inlet results show an early onset of transition compared to the sudden contraction, with a longer and smoother transition profile. Nusselt number results were higher in the laminar regime, while increasing until the onset of transition. Turbulent results show convergence to the Gnielinski equation for both inlet conditions.