Flow Boiling Heat Transfer of HFE7000 in Manifold Microchannels through Integrating Three-dimensional Flow and Silicon Nanowires

In this study we presented and characterized a compact silicon based manifold microchannel heat sink with embedded SiNWs in order to enhance heat transfer and reduce flow instability during two phase flow boiling. The manifold consists of parallel longitudinal microchannels etched in a silicon substrate and transverse microchannels etched on a transparent glass substrate. The microchannels in the silicon substrate were then etched with silicon nanowires. In this work, flow boiling heat transfer of HFE 7000 in such SiNWs embedded manifold microchannels were investigated. Two series of experiments with relatively small mass fluxes were carried out under different heat fluxes at a constant subcooled inlet temperature. The heat transfer and pressure drop characteristics were compared under different experimental conditions as well as the flow instability during the phase change process. A heat flux of about 141.5 W/cm² was reached with a relatively small mass flux of 116 kg/m²s. A remarkable performance of flow instability control was observed for HFE 7000 over both the single phase and the two-phase periods. Before the onset of nucleation, the temperature variations over a period of 100s are were about 0.2 °C. After the onset of nucleation, the maximum temperature fluctuations were still within 0.5 °C. This implies that our manifold microchannel design benefits from a strong impingement effect which delivers the coolant evenly to every corner of the hotspot and forms a more uniform temperature distribution.