Heat transfer of a gas and liquid two-phase flow in helical coils (effects of coil diameter and set angle)

The distributions of local void fraction and heat-transfer coefficient of an air-water two-phase flow in helical coils were measured, and the effects of coil diameter and set angle on the heat-transfer characteristics were investigated. When the coil axis is horizontally placed, it is found that, at a high gas-phase velocity which forms the annualr flow, there are still fairly large differences in the void fraction and the local heat-transfer coefficient between the upper and lower positions on the coil. It is shown that the average heat-transfer coefficients can be divided into three regions by Martinelli's parameter, 1/Xtt, for coils of any diameter. Among these regions, the effects of the set angle are significant at the second and third region. Finally, correlations between the average heat-transfer coefficient and 1/Xtt are proposed.