Investigation on the heat transfer characteristics of liquid film over the horizontal circular tube with reverse wind velocity

Unsaturated falling film evaporation has numerous applications due to its high heat transfer efficiency. Heat transfer characteristics of circular tube without wind has been extensively investigated, while the heat transfer with wind velocity is rarely studied. In this study, the heat transfer characteristics of liquid film outside the circular tube is investigated by using a transient simulation model. The influence of wind velocity, liquid Reynolds number, heat flux and tube diameter are elucidated. Comparisons of simulation data and experimental value is conducted with a mean deviation of 5.6 % and 4.3 % under the condition with and without wind velocity. The results show that the local heat transfer coefficient (HTC) increase with wind velocity, and the average HTC with wind is about 5.28 %–15.83 % larger than the condition without wind. The increase of liquid Reynolds number and heat flux can effectively enhance the HTC before the critical value of 576 and 40$\mathrm{kW}/\left(m^2·K\right)$. The HTC decrease with the increase of diameter, and the average HTC of 14 and 19 $\mathrm{mm}$ circular tube is approximately 15.72 %, 6.96 % greater than that of 25.4 $\mathrm{mm}$. Furthermore, a correlation for calculating the average HTC is developed according to the simulation data with a mean difference of 4.3 %. The research results provide a theoretical support for the development and design of evaporative condenser.