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

对电子设备浸没式冷却模块用下置浸没式冷凝器进行了强化传热实验研究。沿着40 mm宽的矩形测试表面的中心线沿着安装一个光滑表面和两个带翅片的表面（翅片间距为0.61和1.36 mm），该表面带有和不带有多孔排水条（厚度为2 mm，有效孔半径为0.6 mm）。将测试表面和用于模拟散热芯片的电加热器分别组装在测试容器的上部和下部。将试料液的初始液位设定在测试表面上方20 mm处。为了比较，还用蒸气空间冷凝器进行了实验。对于浸没式冷凝器，在低热通量区观察到冷凝表面下形成蒸汽空间，而在高热通量区表面被上升的气泡覆盖。对于后一种情况，浸没式冷凝器的传热性能比蒸汽空间冷凝器最多提高35%。对于浸没式冷凝器和蒸汽空间冷凝器，翅片表面提供了比光滑表面值更显著的传热增强。对于较小的翅片间距和具有较高的表面张力与液体密度比的甲醇，增强更显着。对于低热流密度工况下的蒸汽空间冷凝器和浸没式冷凝器，多孔排水带的使用提供了进一步的传热强化。R-113冷凝在冷凝温差为5 K时，浸没式冷凝器和蒸汽空间冷凝器的最大强化比分别为4.5和7.1。

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.