A microchannel heat sink with convergent-divergent (CD) shape and bifurcation is presented, and flow and heat transfer characteristics are analyzed for Re ranging from 120 to 900. The three-dimensional governing equations for the conjugate heat transfer with temperature-dependent solid and fluid properties are solved using the finite volume method. Comparisons are carried out for four cases, namely, rectangular shape with and without bifurcation and CD shape with and without bifurcation. The pressure drop, flow structure, and average Nusselt number are analyzed in detail, and the thermal resistance and overall performance are compared. It is shown that the CD shape with bifurcation has more uniform and lower temperature at the bottom wall and better heat transfer performance compared to other geometries. The heat transfer augmentation in the CD shaped microchannel with bifurcation can be attributed not only to the accelerated and redirected flow toward the constant cross section segment but also to periodically interrupted and redeveloped thermal boundary-layers due to bifurcation. It is also shown that increasing Re leads to thinning of thermal boundary-layers resulting in an enhanced heat transfer in terms of an increased average Nusselt number from 38% to 74%. However, there is an increased pressure drop due to channel shape and obstacle in fluid flow. Further, due to a high pressure drop penalty at high Re, CD shaped microchannel with bifurcation loses its heat transfer effectiveness.

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