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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]

Study offluid flow characteristics at microscale is gaining importance with shrinking device sizes. Better understanding offluid flow and heat transfer in microchannels will have important implications in electronic chip cooling, heat exchangers, MEMS, and microfluidic devices. Due to short lengths employed in microchannels, entrance header effects can be significant and need to be investigated. In this work, three dimensional model of microchannels, with aspect ratios (x = a/b) ranging from 0.1 to 10, are numerically simulated using CFD software tool FLUENT. Heat transfer effects in the entrance region of microchannel are presented by plotting average Nusselt number as a function of nondimensional axial length x*. The numerical simulations with both circumferential and axial uniform heat flux (ff2) boundary conditions are validated for thsting data set for four wall heat flux case. Large numerical data sets are generated in this work for rectangular cross-sectional microchannels with heating on three walls, two opposing walls, one wall, and two adjacent walls under H2 boundary condition. This information can provide better understanding and insight into the transport processes in the microchannels. Although the results are seen as relevant in microscale applications, they are applicable to any sized channels. Based on the numerical results obtained for the whole range, generalized correlations for Nusselt numbers as a function of channel aspect ratio are presented for all the cases. The predicted correlations for Nusselt numbers can he very useful resource for the design and optimization of microchannel heat sinks and other microfluidic devices. [ABSTRACT FROM AUTHOR]