Experimental assessment on heat transfer characteristics of falling-film evaporation under mutual parameters’ coupling between circular and half-oval tubes

The falling-film evaporation is frequently used in air-conditioning system to improve the heat transfer performance, whereas the influencing parameters and their mutual effect on heat transfer characteristics of circular and half-oval tubes have received limited attention. To elucidate this issue, experimental investigations are conducted to analyze the synergistic impact of five parameters. They are wind/air velocity, liquid Reynolds number, spray height, heat flux, and spray water temperature. Results indicate that the convective heat transfer coefficient (CHTC) for liquid film over circular and half-oval tube increases with these parameters, and the CHTC for the half-oval tube exceeds that of the circular tube by at least 7.9 %. Higher liquid Reynolds number and spray water temperature amplify the relative change of CHTC induced by wind velocity, while the increase of heat flux and spray height reduce the relative change of CHTC with wind. The coupling of liquid Reynolds number and spray height, heat flux, spray water temperature enhances the heat transfer of liquid film. In specific, the relative change of CHTC induced by spray height obviously decrease with the increase of heat flux, whereas the relative change of CHTC caused by spray height and heat flux increase with the rising of spray water temperature. Empirical correlations of CTHC for circular and half-oval tube are fitted based on the experimental results, with the average deviation of 5.83% and 5.11%, respectively. The findings provide experimental data support for the further research of evaporative condenser.