Circumferential distribution of local heat transfer coefficient during steam stratified flow condensation in vacuum horizontal tube

An experimental system was built up to measure the wetted angle and circumferential distributions of local heat transfer coefficient during the steam stratified flow condensation in vacuum horizontal tube. The wetted angle is mainly affected by vapor quality. It decreases with vapor quality and steam mass flow rate, and increases with the steam saturation temperature. The Biberg's correlation and Rouhani's void fraction correlation are used together to predict the experimental value of wetted angle accurately. The tube wall is divided into filmwise condensation section and liquid accumulation section by the stratified interface. The local heat transfer coefficient in filmwise condensation section is significantly higher than that in liquid accumulation section. The local heat transfer coefficient increases with vapor quality and steam mass flow rate for all locations along the circumferential direction. The increase of temperature difference between steam and cooling water causes the decrease of local heat transfer coefficient in filmwise condensation section and has less effect on that in liquid accumulation section. With the change of steam saturation temperature, the heat transfer coefficients in two sections of the tube appear different variation tendencies. Based on the experimental values, new correlations for local heat transfer coefficient of steam condensation flow in stratified flow pattern are proposed.