Experimental study on the distribution of local heat transfer coefficient of falling film heat transfer outside horizontal tube

Abstract

An experimental system was built up to measure the outer circumferential distributions of the local heat transfer coefficient of horizontal tube falling film flow. The wall temperature along the angle were measured. Based on the experimental data, the local heat flux distribution on the tube surface were obtained by numerical calculation. The local heat transfer coefficient distribution outside the tube were obtained. The effects of spray density, tube spacing, average heat flux and fluid temperature on local heat transfer coefficient were investigated. The results show that the local heat transfer coefficient decreases sharply with the increase of angle, then decreases steadily, and finally increases slightly. According to the distribution of the local heat transfer coefficient and heat transfer mechanisms, the tube surface is divided into the impingement zone, the heat diffusion transfer zone and the tail detachment zone. The increase of spray density has little influence on the heat transfer in the impact zone, but make the heat transfer increases slightly in the heat diffusion transfer zone and the tail detachment zone. The influence of tube spacing is mainly concentrated in the impingement zone. The heat transfer is enhanced with the increase of tube spacing in the impingement zone. The average heat flux has no obvious effect on heat transfer. With the increase of fluid temperature, the heat transfer is greatly increased all over the cycle. Besides, based on the experimental data, new correlations of local heat transfer coefficient of falling film flow outside a horizontal tube are proposed.