Molecular dynamics simulation and experimental study of heat transfer and phase change of water with slit effect

Abstract

The condensation water-bridge phenomenon of the heat exchanger surface fins is a common undesirable phenomenon in refrigeration systems and heat pump systems, which would significantly affect the heat exchanger's thermal efficiency due to insulation and obstruction of airflow. Based on the lack of experimental studies on louvered-fin heat exchangers and surface energy for fin-surface condensation, this paper experimentally investigates the effect of wettability (surface energy) on the condensation mechanism and heat exchanger performance. Firstly, hydrophilic and hydrophobic coatings are formed by reagent deposition, which regulates the surface energy of the fins. Experiments are designed to investigate the effect of surface energy on heat exchanger performance at different temperatures, humidity, and wind speed. Finally, the key issues such as condensation morphology are discussed in detail by molecular dynamics simulation, thus filling the gap and providing a reference for heat exchanger surface construction. The experimental results show that the wet condition has a faster condensation rate, with an average rate reduction of 33.2%. Both hydrophilic and hydrophobic fins could improve the performance of the heat exchanger compared to bare fins due to their inherent uniqueness. The hydrophilic fins have a smaller pressure drop, maintain a more stable heat transfer rate, and improve the heat transfer performance by 13.4% in a typical environment (60%) or with lower water content. While the hydrophobic fins show advantages in a wet environment (80%), improving the heat transfer performance by 17.8% due to the severe deterioration of the bare heat exchanger performance. Further, molecular-scale condensation patterns were analyzed, and condensation rates and adsorption forces were quantified. The experimental and simulation results guide the construction and selection of surface energy to optimize the heat transfer surface.