K. Narrein, Krishnasamy (2016) Numerical study of heat transfer and fluid flow characteristics in microchannel heat sink / K. Narrein Krishnasamy. PhD thesis, University of Malaya.
Abstract
Numerical investigation is performed to study the heat transfer and fluid flow characteristics in a Microchannel Heat Sink (MCHS) with the combination of various active and passive enhancement methods. Convective heat transfer analyses are performed on the MCHS and the governing equations are solved using the finite volume method. The performances of the MCHS are tested by varying the geometrical parameters, magnitude of external forces, boundary conditions, flow type and different fluids. For the study on effects of geometry, the thermal field results show that Helical MCHS (HMCHS) can contribute to better heat transfer enhancement as compared to a straight microchannel of similar length and hydraulic diameter due to the presence of secondary flow. Geometrical parameters such as helix radius, pitch and channel aspect ratio have significant effect on the performance of the MCHS due to the variation in flow characteristics. It is also noted that the modified two-phase mixture model method produce more accurate results as compared to single phase nanofluid model, hence, this new model can be used in future research for better results. In addition, pulsating inlet flow condition is able to increase the convective heat transfer substantially with marginal reduction in pressure drop compared to steady condition. Pronounced enhancement in Nusselt number is also achieved in the HMCHS with porous medium compared to the non-porous straight and helical microchannel. The study on the effects of external forces showed that presence of magnetic field lead to thermal enhancement with additional pressure drop. The external force prevents the flow from reaching a fully develop state, hence the larger fluid velocity at the bottom wall result in better convective heat transfer.
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