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

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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