Study of the Enhancement of Condensation Heat Transfer on Downward Facing Submerged Surfaces by Use of Capillary Action

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Experiments were performed to enhance heat transfer on downward facing submerged condensers to be used for immersion cooling modules of electronic equipments. A smooth surface and two finned surfaces (0.61 and 1.36 mm in fin pitch) with and without a porous drainage strip (2 mm in thickness and 0.6 mm in effective pore radius) was fitted along the center line of the 40 mm wide rectangular test surfaces. The test surface and an electric heater for simulating heat dissipating chips were assembled in a test vessel at the upper and lower parts, respectively. The initial level of the tast fluid was set at 20 mm above the test surface. For comparison, experiments were also performed with vapor space condensers. For the submerged condenser, formation of vapor space under the condensing surface was observed in the low heat flux regime, whereas the surface was covered with rising bubbles in the high heat flux regime. For the latter regime, heat transfer performance of the submerged condenser was enhanced by a maximum of 35 % over the vapor space condenser. For both the submerged and vapor space condensers, significant heat transfer enhancement over the smooth surface value was provided by the finned surfaces. The enhancement was more significant for smaller fin pitch and for methanol with higher value of surface tension to liquid density ratio. For the vapor space condenser and the submerged condenser operated in the low heat flux regime, further heat transfer enhancement was provided by use of the porous drainage strip. The maximum values of the enhancement ratio, obtained for R-113 condensation at the condensation temprature difference of 5 K, were 4.5 and 7.1 for the submerged and vapor space condensers, respectively.