Conjugate heat transfer analysis of sidewall-heated rectangular microchannels with different bottom wall materials

Abstract

In this study, the conjugate heat transfer in a microchannel under four sidewalls (left, right, top, and bottom wall facing upstream) heating conditions is investigated experimentally and numerically. The microchannel has a width of 500 μm and a depth of 100 μm. Micro-Particle Image Velocimetry (Micro-PIV) and Temperature Sensitive Paint (TSP) are respectively applied to measure the velocity and temperature fields at a Reynolds number (Re) of 20. The experimental results demonstrate that the temperature gradient exists in both the left, right, and bottom wall, indicating the existence of conjugate heat transfer. Thus, 3D conjugate heat transfer simulations are subsequently conducted. Good agreements are attained between numerical and experimental data only with the non-ideal boundary condition. Otherwise, there is a significant discrepancy between them. Further parametric studies on bottom wall to fluid thermal conductivity ratio (kb/kf) and Re show that the fully developed overall Nusselt number (Nu‾) in the conjugate heat transfer case is approximately 4.55, much higher than the analytical solution 0.87 without accounting for conjugate heat transfer. As kb/kf is varied from 0.21 to 6.48, there exists a critical kb/kf=1.79, before and beyond which the total heat flux respectively increases and decreases with kb/kf. However, Nu‾ is a monotonically increasing function of kb/kf, with a peak value of 5.75 occurring at kb/kf = 6.48.