Challenges in micro-channel heat transfer experiments: Insight on conjugate heat transfer effects

A numerical study was performed to obtain insight into conduction/convection conjugate heat transfer processes during a typical experiments performed at the micro scale. The experimental work of Wang et al. [1] was used as a baseline to quantify such effects. It consisted of a 225 μm× 18.5 mm × 1.5 mm microchannel with a pillar, which had jet slits. Commercially available software package, Star CCM+, was used for the simulations. Fluid, solid and heater regions were modeled together with heat transfer interfaces at the contact surfaces. Reynolds number of 123, 200, and 280 were simulated. Each case includes jet introduction to the flow quantified with momentum coefficient of 3%, 5%, and 10%. The numerical model was verified by the Grid Convergence Index methods using three different grids and agreed with experimental results within a 10% discrepancy. The discrepancies between numerical and experimental results were found in terms of heat transfer distribution and heat transfer coefficients, which were mainly due to inevitable assumptions made while post processing the experimental data. Therefore, the main aim of this study is to decouple the heat transfer processes inside the three different regions and to provide guidance for future micro scale experimental studies in terms of experimentally non-measurable parameters, such as heat flux paths, local heat transfer coefficients, local boundary heat fluxes, and local temperature values on the heater surfaces.