Heat transfer characteristics of fin-tube heat exchangers coated with single-walled carbon nanotubes under various coating concentrations

The application of single-walled carbon nanotube (SWCNT) coatings to heat exchanger surfaces can improve energy efficiency owing to its excellent thermal properties. However, studies on the heat transfer characteristics of fin-tube heat exchangers (FTHXs) coated with SWCNTs (SCNTHXs) are limited. In this study, the heat transfer performances of SCNTHXs with various coating conditions were measured and compared with those of an uncoated FTHX (UCHX) under dry and wet conditions. Additionally, the effect of coating concentration on the condensation mechanism of SCNTHXs was examined. The effects of coating thickness on the Colburn j- and f- factors were negligible within ±5% deviation at a 0.20 wt% coating concentration. In addition, as the coating concentration increased at a 2.2 μm coating thickness, the Colburn j-factors under dry and wet conditions increased by up to 10.5 and 7.3%, respectively. However, as the coating concentration decreased, the f-factors under dry and wet conditions decreased by up to 9.1 and 7.6%, respectively. The Webb efficiency of SCNTHXs at a 0.20 wt% coating concentration increased by 12.2% and 8.8% under dry and wet conditions, respectively. Overall, the use of SCNTHXs in heat pumps can improve heat transfer performance, providing opportunities for energy conservation.