Abstract: Condensation heat transfer of R32 in a horizontal circular microchannel with the inner diameter of 1 mm is numerically simulated with VOF model. The inlet saturation temperature of R32 is 40℃ and the wall temperature is 30℃. The vapor and liquid phases are assumed to be turbulent and laminar, respectively, and the effects of gravity and surface tension are considered. The simulation results show that the vapor quality decreases nearly linearly along the tube and reaches 0.62 at the outlet of the channel, and the liquid film thickness at the top of the tube increases first and then maintains almost constant while the liquid film thickness at the bottom of the channel increases consistently along the channel. As the thermal conductive resistance of the liquid film is dominant in condensation heat transfer, the heat transfer on the top surface tube is stronger than that on the bottom surface. The liquid film on the top surface flows to the bottom of the tube due to the effect of gravity. The results show that the gravity effect cannot be neglected when the hydraulic diameter of channel is 1 mm. Axial velocity distribution of the liquid film is linear with the vapor quality. Vapor-liquid interface velocity on the top surface in the tube increases first and then decreases a little along the channel while interfacial velocity on the bottom increases consistently. Simulated heat transfer coefficients increase with vapor quality, and the simulation results are lower than the experimental results in the overlapped vapor quality region while the deviations are still within the experimental error.

Key words: condensation, microchannels, numerical simulation, VOF, gravity

摘要： 采用VOF模型对R32在内径为1 mm水平圆管内的凝结换热进行了数值模拟.圆管进口饱和蒸气和壁面温度分别为40℃和30℃.假设气相为湍流、液相为层流,考虑重力和表面张力的影响,模拟分析了干度、液膜厚度和轴向速度沿管长的变化.结果表明,沿管轴向顶部液膜先增厚后基本保持不变,管底部液膜持续增厚.表明当量直径在1 mm时重力作用仍不可忽略.传热系数的模拟值随干度的增大而增大;与实验结果相比,模拟值小于实验值,但二者差别在实验误差范围内.

关键词: 凝结, 微通道, 数值模拟, VOF, 重力