Mechanisms of Enhanced Cooling by Sidewall Modification in a Microtube Cold Plate

Abstract The thermofluidic effectiveness of a microtube cold plate with sidewall modification has been disputed. This study settles the dispute by detailing how such sidewall modification—hemi-circular cavities arranged along a straight circular microtube embedded with a cold plate—enhances cooling. To this end, a series of numerical simulations for a single microtube cold plate in a practical range of Reynolds numbers (20 ≤ ReD ≤ 200) are carried out. For experimental validation, flow development and pressure drop in both reference and modified microtubes are characterized respectively by microparticle image velocimetry and pneumatic pressure measurements, while surface temperatures on both cold plates' substrates subjected to uniform heat flux are measured by infrared thermography. The results agree that the boundary layer development in each throat, a short straight coolant passage that connects successive cavities, indeed enhances the cooling in the cold plate with the wall modification. However, in contrast to its sole contribution argued previously, a non-negligible source of thermal enhancement is identified. The coolant flow approaching each throat noticeably bifurcates across the throat and cavity sidewall. Thereafter, a boundary layer develops along concave sidewalls and subsequently circulates within each cavity, generating high wall shear stresses upstream of each throat and significantly elevating local cooling. In conclusion, the local cooling both “upstream” and “in” throats plays a dominant role in enhancing the overall cooling in the cold plate with wall modification, up to 40% over the reference microtube cold plate in the Reynolds number range considered.