Subcooled flow boiling in diamond/Cu microchannel heat sinks for near-junction chip cooling

Materials for thermal management that possess low coefficient of linear thermal expansion and high thermal conductivity can achieve “near-junction cooling” for chips. However, limited research exists on the application of the latest generation of diamond/Cu (DC) composites in microchannel phase-change heat dissipation. In this study, three structurally functional integrated open microchannel heat sinks (DC60, DC75, and MoCu50) were innovatively created using low-linear-expansion materials such as DC and molybdenum-copper as the substrates. Experiments involving flow boiling were performed with deionized water serving as the operational fluid. The heat transfer characteristics were investigated by combining visualization techniques. Results indicated that during boiling, under the influence of high thermal conductivity network, the diamond/Cu microchannel surface has more nucleation sites compared to MoCu50 microchannels. This results in nucleate boiling predominantly governing the phase-change heat transfer process, which substantially increases the efficiency of heat transfer. DC75 maintained its dominant advantage even at the highest heat flux of q'' = 4012.14 kW/m2. Compared with MoCu50, DC75 exhibited a threefold improvement in heat transfer coefficient, reaching a peak of 127.48 kW/m2K, without experiencing the dry-out phenomenon. DC75 showed the lowest bottom temperature, minimal deformation, and strong thermal stability. In the process of transitioning from slug to stratified flow, a synergy of slug-stratified flow was observed. This coexistence led to small-scale fluctuations in the pressure drop, with the maximum pressure drop not exceed 3.5 kPa.