Study on air-side performance of air-cooled heat exchangers under large air velocity and wet conditions

Abstract

Humidity condensation and carryover from air-cooled heat exchanger affects human comfort and equipment security in the working environment. Surface treatment with a hydrophilic coating is an effective water drainage and carryover resistance solution. In present study, the condensation carryover and air-side performances of a fin-and-tube heat exchanger (FTHX) and microchannel heat exchanger (MCHX) with different fin pitches and surface treatments were experimentally investigated under large air velocities and different inlet humidity conditions. Hydrophilic treatment of FTHX improved heat transfer and condensation drainage, and reduced air pressure loss. In contrast, with MCHX, hydrophilic treatment did not improve heat transfer and rather increased the air pressure loss. For FTHX, the results showed that, compared with the bare fin, the hydrophilic surface treated fin enhanced the Colburn j factor by 20–60 and 10–40% at inlet air dry/wet bulb temperature of 26.7/19.4 °C (normal humidity condition) and 26.7/23.9 °C (high humidity condition), respectively. The air friction factor f was reduced by namely by 10–40 and 20–40% under normal- and high-humidity conditions, respectively. Condensing water flowed or retained over the fin surface in film, which suppressed the formation of a water bridge among fins, improved water carry-over, and increased the critical air velocity by 50%. However, water film formation over the MCHX enlarged the water stagnant around the fin corner, which increased the air resistance by 5–10%, and increased the probability of the continuous water bridge formation and carryover.