Forced Convection Heat Transfer of Liquid-Gas Foam around a Circular Cylinder

水-气泡沫是一种新型的冷却剂材料，有望在未来的各种工业领域中得到应用。为了研究流动泡沫的热特性，采用加热圆柱体进行了强制对流换热实验。研究中使用了具有宽膨胀比范围和不同泡沫速度值的泡沫。通过1999年和2000年的研究，得出以下结论：○当受热面温度小于373K时，泡沫流的平均传热系数介于水和空气流之间。这一结果表明，通过使用液-气泡沫，可以获得介于水冷和空冷之间的中间冷却速率。传热系数随泡沫流速的增加和泡沫膨胀比的减小而增加。结果表明，在低速高流速条件下， ...更多信息 泡沫的膨胀率。传热系数随加热面与泡沫之间的温差的增大而增大。这一结果与通常的单相流体的传热特性有很大的不同。数值分析表明，在较高的温度范围内，水蒸气在泡沫中扩散的潜热传递是提高传热系数的重要因素之一。○当温度升高到373K以上时，随着热流密度的逐渐增大，受热面温度逐渐升高，达到373K，即，水的沸点。进一步增大热流密度，使温度在373K附近保持一段时间，然后开始迅速升高。在过热区域，热通量随表面温度的增加率相对较低。泡沫流的这种沸腾传热特性也与单相液体的沸腾传热特性有很大不同。在373K附近的温度范围内，泡沫流的热通量大于水。在其他温度范围内，泡沫流动的热通量低于水。少

Water-air foam is a new material for a coolant and expected to be applied in various industrial fields in the future. To clarify thermal properties of the flowing foam, forced convection heat transfer experiments were conducted by using a heated circular cylinder. Foam with wide rage of expansion ratio and various values of foam velocity was used in this study. We can draw the following conclusions from the study conducted in the academic years of 1999 and 2000.○When the temperature of the heating surface is less than 373K.The value of mean heat transfer coefficient for foam flow ranges between those for water and the air flows. This result suggest that intermediate cooling rate between water cooling and air cooling is obtained by using a liquid-gas foam. The heat transfer coefficient increases with increasing foam velocity and with decreasing the expansion ratio of the foam. It was indicated that the-value of the coefficient extremely decreases in a condition of low velocity and high … More expansion ratio of the foam. The heat transfer coefficient increases with the temperature difference between the heating surface and the foam. This result is much different from the heat transfer characteristics of usual one-phase fluids. Numerical analysis shows that the latent heat transfer by water vapor diffusion in the foam is the one of the important factors that increases the heat transfer coefficient at higher temperature range.○When the temperature increases over 373K.When the heat flux is increased gradually, the temperature of the heating surface increases and reaches 373K, i.e., the boiling point of water. Farther increase in the heat flux result in the temperature remains 373K for a while, and then begin to increase rapidly. The rate of increase in the heat flux with the surface temperature is relatively low in a super heated region. This boiling heat transfer characteristic of the foam flow is also much different from those for one phase liquids. In the temperature range around 373K, the heat flux for the foam flow is greater then that for water. In other temperature ranges, the heat flux for foam flow is lower than that of water. Less