Convective heat transfer of falling film around the horizontal half-oval tube with reverse airflow in an evaporative condenser

Abstract

Horizontal falling-film evaporation is frequently used in industrial air conditioning system to improve its thermal performance. Transient heat transfer characteristics on the surface of a circular tube have been investigated, while the non-circular tube such as half-oval tube has been rarely reported. This study aims to investigate the thermal performance of liquid film around a half-oval tube by adopting transient simulations with laminar and SST k-ω models, respectively. Simulations consider varying wind velocity, liquid Reynolds number, heat flux and length-width ratio of the tube. Simulated results are quantitively validated by comparing with reported experimental results, and the average differences are below 9.5 %. Results indicate that the local convective heat transfer coefficient (CHTC) increases with wind and the average CHTC is at least 5.98 % higher than the case without wind. Although the influences of liquid Reynolds number and heat flux show slight differences, they still can improve the convective heat transfer. The local CHTC exhibits an escalating trend with length-width ratio of 1–5. Meanwhile, the average CHTC for the four tested half-oval tubes is at least 6.8 % higher than the values of the circular tube. An empirical correlation for predicating the average CHTC is established by regression fitting with a mean deviation of 4.6 %. These findings help to design the falling-film evaporation system by adopting the half-oval tube in industrial air conditioning system.