In this paper a microchannel heat sink with expanded microchannels and nanofluids is
numerically investigated. The object of this paper is to study and improve the cooling performance
of microchannel heat sink. Both the geometrical parameters and working fluids were studied and a
comparison was made between them. Expanded microchannels (sudden expanded and diverging)
were used instead of straight microchannels, also micro pin fins with square and triangular shapes
were used for heat transfer enhancement. Sudden expanded microchannels were studied with
different expansion ratios and expansion lengths. Three types of nanofluids (Cu-water, Al2O3-water
and Diamond-water) with volume concentration (1 – 5) % were studied as working fluids and their
effects on overall performance of heat sink were compared with pure water. The results obtained
shows that the overall performance of microchannel heat sink increased with increasing the
expansion ratio or decreasing the expansion length. For the same expansion ratio the sudden
expanded microchannels gives higher modification compared with diverging microchannels. Also
using of nanofluids lead to enhance the heat transfer and the improvement got by geometric
parameters such as using of expanded microchannels or fins is much larger than that obtained by
using nanofluids for the same heat sink.