Abstract

The conjugate effect, also known as the coupling effect, involves the thermal profiles of the solid and the fluid domain due to heat interactions between the solid and fluid domains. A detailed three-dimensional numerical study is conducted to understand the effect of solid substrate heat conduction on the fluid convection in diamond (diverging-converging) microchannels. Experiments have also been conducted to validate the mathematical model employed in the present study. The first part of the study covers the impact of solid-fluid thermal conductivity and solid-fluid thickness ratio on thermal conditions at the solid-fluid interface with the help of peripheral heat flux and solid-substrate isotherms. The isotherms show multi-directional thermal gradients for low solid-fluid thermal conductivity ratios, whereas only axial thermal gradient is seen for a higher solid-fluid thermal conductivity ratio. The second part covers the influence of solid-fluid thermal conductivity ratio and solid-fluid thickness ratio on Nusselt number characteristics of a diamond microchannel with different divergence-convergence angles and width ratios. The analysis also reveals that at a particular intermediate solid-fluid thermal conductivity ratio, the Nusselt number becomes maximum. The last part covers the quantification of conjugate effects in diamond microchannels by employing a non-dimensional wall conduction number. The analysis reveals that the wall conduction effect is inconsequential in diamond microchannels when the non-dimensional wall conduction number is <0.01.

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