| Summary: | Most of numerical studies on microchannel heat sinks (MCHS) performed up to now are for a two-dimensional domain using constant properties of the coolant and solid part. In this study, laminar fluid flow and heat transfer of variable properties water in a trapezoidal MCHS, consisted of five trapezoidal microchannels, are studied. The three dimensional solution domains include both the flow field and the complete MCHS silicon made solid parts with variable conductivity. Four entry/exit configurations and three pressure drops of 5, 10 and 15 kPa are assumed. The results indicate that the A-type heat sink, for which the entry and exit are placed horizontally at the center of the north and the south walls, has a better heat transfer performance, smaller thermal resistance and provides more uniform solid temperature distribution. For pressure drop of 15 kPa, temperature-dependent properties of water increases the heat transfer between 2.73% and 3.33%, decreases the thermal resistance between 3.46% and 5.55 % and decreases the ratio of difference between the maximum and minimum substrate temperatures to the heat flux, θ, between 3.42% and 11.15%. Also by assuming temperature-dependent conductivity of silicon, the heat transfer increases between 0.75% and 2.58%, the thermal resistance decreases between 1.15% and 4.97 % and θ decreases between 2.41% and 6.49%.
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