The Effects of Hydrophilicity on Water Drainage and Condensate Retention on Air-Conditioning Evaporators

An experimental study is conducted to investigate condensate drainage and retention and the attendant thermalhydraulic effect associated with changes in surface hydrophilicity on air-conditioning evaporators. Three heat exchangers that have controlled wettability covering a range of contact angles and a baseline untreated aluminum heat exchanger are tested. Results from dynamic dip-testing as well as wind-tunnel experiments under fully wet conditions are presented. The data show that for the heat exchangers used in this study the Colburn j factor is not strongly influenced by condensate retention, but the friction factor is significantly reduced by the enhancement of surface hydrophilicity. Heat exchangers with improved wettability hold slightly more water than the baseline in a dynamic dip-test, but retain remarkably less than the untreated coil in a wet wind-tunnel experiment. Steady-state mass retention in wind-tunnel tests decreases with increasing air flow rate, and the retention is more sensitive to the air-side Reynolds number for heat exchangers with higher contact angles.