Conduction and entrance effects on laminar liquid flow and heat transfer in rectangular microchannels

Abstract

The paper presents both three and two-dimensional numerical analysis of convective heat transfer in microchannels. The three-dimensional geometry of the microchannel heat sink followed the details of the experimental facility used during a previous research step. The heat sink consisted of a very high aspect ratio rectangular microchannel. Two channel spacings, namely 1 mm and 0.3 mm (0.1 mm), were used for three-dimensional (two-dimensional) numerical model, respectively. Water was employed as the cooling liquid. The Reynolds number ranged from 200 to 3000. In the paper, thermal entrance effects and conduction/convection coupling effects are considered both for the test case of uniform channel inlet conditions and the complete geometry of the experiment. Finally, the comparison between measured and computed heat flux and temperature fields is presented. Contrary to the experimental work, the numerical analysis did not reveal any significant scale effect on heat transfer in microchannel heat sink down to the smallest size considered (0.1 mm).

Single-phase heat transfer in microchannels: The importance of scaling effects

“…Gamrat et al [42] studied conduction and entrance effects in rectangular microchannels both experimentally and numerically, with a 3D conjugate heat transfer model, Reynolds numbers in the range 200-3000, d h between 0.2 and 2 mm, and using water as the test fluid. They observed a significant reduction in the measured Nu when the hydraulic diameter was below 1 mm.…”

“…Another investigation into flow and heat transfer through an individual circular microchannel The experimental apparatus of Gao et al [20] was considered in the papers of Gamrat et al [42] and Bavière et al [59]. Gamrat et al [42] performed detailed numerical analysis of the experimental system, modelling its 3D geometry and accounting for entrance effects and 3D conjugate heat transfer in the fluid and the solid walls.…”

“…Gamrat et al [42] performed detailed numerical analysis of the experimental system, modelling its 3D geometry and accounting for entrance effects and 3D conjugate heat transfer in the fluid and the solid walls. Nevertheless, they couldn't predict the reduction in Nu for d h < 1 mm.…”

Numerical Analysis About the Influence of Inappropriate Shape of the Cross-Section of Microchannels in Laminar Flow

“…A lot of experimental studies [1,2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], besides theoretical [22][23][24] and numerical studies [5,[25][26][27][28], have been carried out, in the past decades, seeking to investigate the hydrodynamics and heat transfer characteristics in microscale. The results obtained in several of these studies show diversions among themselves and, also, with the conventional theory.…”

“…Some numerical studies [45,46] showed that the Nusselt number is more sensitive to the shape of the cross-section of the microchannels in comparison to other parameters, such as surface roughness, for example. Furthermore, there are numerical and theoretical studies that consider simplifications which differ a lot from what actually should occur experimentally as, for example, the negligence of viscous dissipation in numerical model [28,47], the true boundary condition at the limits [44] and the consideration of the fluid with constant thermophysical properties, in general.…”