Flow boiling heat transfer and pressure drop characteristics of water in a copper foam fin microchannel heat sink

Flow boiling of water in a copper foam fin microchannel (FFMC) heat sink is investigated experimentally. The heat sink has nine channels, which are 487 μm in width and 1061 μm in height. Experiments are conducted under a wide range of operating conditions: inlet temperature of 80 ℃, outlet pressures of 100 ∼ 134 kPa, mass fluxes of 76 ∼ 408 kg/m2s, effective heat fluxes of 0 ∼ 296.5 W/cm2, and outlet qualities of −0.020 ∼ 0.874. Heat transfer and pressure drop characteristics of the FFMC are compared with those of a solid fin microchannel (SFMC) heat sink with the same geometry. The heat transfer coefficient of the FFMC is improved by up to 80 %, and the pressure drop is increased to 1.2 to 2 times. The critical heat flux of the FFMC is improved by 25% at the mass flux of 102 kg/m2s. Flow instability of the FFMC is mitigated significantly, including the reverse flow, the wall temperature fluctuation and the pressure drop fluctuation. Heat transfer mechanisms in the FFMC are analyzed with the help of the flow visualization. Nucleate boiling and thin film evaporation dominate in different Bo number ranges. The heat transfer coefficient of the FFMC first increases and then decreases with increasing the heat flux (also the quality) at low mass fluxes, and increases monotonically at high mass fluxes. The reduction of the wall temperature fluctuation and the pressure drop fluctuation are due to the transverse flow between the channels in the FFMC heat sink.