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A numerical investigation is conducted to study the heat transfer characteristics of laminar flow in three-dimensional rectangular microchannels with aspect ratios of 0.1–1 and Reynolds numbers of 5–400. In this paper, the effects of aspect ratio and Reynolds number on the local and mean Nusselt numbers are presented in detail. Good agreement on Nusselt numbers is observed between the present results and the data reported in the literature. The results show that the Reynolds number has a great impact on the local Nusselt number in the thermally developing region, especially at lower Reynolds number, while the Reynolds number is independent of the developed Nusselt number. The local Nusselt number is found to increase with decreasing aspect ratio at the same Reynolds number. Additionally, the effects of these parameters on the dimensionless thermal entrance length are also investigated. The dimensionless thermal entrance length for rectangular microchannels monotonously increases by increasing aspect ratio and decreasing Reynolds number, whereas the effect of Reynolds number on the dimensionless thermal entrance length can be basically ignored when Reynolds number is more than 50. Generalized correlations are developed for the local Nusselt number and the dimensionless thermal entrance length.

In this paper, the fluid flow and heat transfer characterizations in trapezoid shaped microchannel with H1 (axially constant heat flux and circumferentially constant temperature) and H2 (constant axial and circumferential wall heat flux) boundary conditions are studied. A three-dimensional numerical model is developed for trapezoidal geometries with side-angles of 30° and 60° with different aspect ratios ranging from 0.1 to 10 to evaluate the Nusselt number and Poiseuille number for fully-developed and developing flow conditions. Experiments are performed on a trapezoidal microchannel and experimental results are compared with the three-dimensional conjugate heat transfer numerical model. It is found that the experimental results are close to the H1 boundary condition. The Nusselt number and Poiseuille number are found to be increasing with the side-angle and aspect ratio of trapezoidal channel. Generalized correlations for Poiseuille number, Nusselt number and entrance length are developed for trapezoidal channel with side angles in the range of 30°–60° and aspect ratios of 0.1–10. These correlations can be used for designing of trapezoidal microchannel in future heat transfer applications. • Studied fluid flow and heat transfer behavior in trapezoid shaped microchannel. • Experiments are performed on a trapezoidal microchannel with side angle of 55.7°. • Compared Nusselt number from conjugate heat transfer model, H1 and H2 boundary conditions. • Empirical generalized correlations are developed for H1 and H2 boundary conditions. [ABSTRACT FROM AUTHOR]

In this paper, the characterization of laminar convective heat transfer in rhombic shaped microchannel with H1 (axially constant heat flux and circumferentially constant temperature) and H2 (constant axial and circumferential wall heat flux) boundary conditions is presented. A three-dimensional numerical model is developed for hydrodynamically and thermally developing flow in different rhombic geometries with side-angles varying from 10° to 90°. The numerical model is first validated with the other model developed in the literature for rectangular geometry and subsequently the results are compared with rhombic channel with different side-angles. This model is then extended to determine the temperature and heat flux distributions in rhombic microchannel, which is used to find the local and hydrodynamically and thermally fully developed Nusselt numbers. It is found that the fully developed Nusselt number varies only with the side-angles of rhombic channel and generalized correlations are developed as a function of side-angles for H1 and H2 boundary conditions. Correlations for developing length, local and fully-developed Nusselt numbers for rhombic channels are currently not available. These results will be useful in design and optimization of rhombic microchannel for electronic cooling applications. [ABSTRACT FROM AUTHOR]