Forced convective heat transfer in vertical air-water bubble flow

The dependence of heat transfer on the cross-sectional distribution of void fractions in a diabatic two-phase bubble flow has been explored experimentally. A vertical tube of 16.9 mm ID was employed in the investigation. Two different types of the mixer were installed to realize the flows with different distributions of void fractions even at the same flow rates of both phases. It was found that these two types of flows present different heat transfer coefficients due to the difference in the void fraction distributions. Increasing the void fraction near the tube wall causes an increase in heat transfer coefficient. The effect of bubble agitation on the thermal diffusivity in the radial direction is discussed based on the distributions of both void fractions and liquid temperatures. (author)