NY-14-C080 -- The Impact of Fin Surface Wettability on the Performance of Dehumidifying Heat Exchangers PDF

In this study, the impact of fin surface wettability on the performance of dehumidying heat exchangers are investigated using two groups of heat exchangers with identical geometry (plain fin, round tube) but two different fin spacing 2.2 mm (0.079 in) and 5.2 mm (0.205 in). Each group contains four identical heat exchangers with surface wettability controlled by conversion coatings. The surfaces range from completely wetting to contact angles over 100°. A study of condensate drainage and retention behavior in a closed-loop wind-tunnel is undertaken and steady state retention data are provided for a range of test conditions. Data for thermal-hydraulic performance are also reported. It is shown that hydrophilic fins significantly improve condensate drainage, whether the heat exchanger has a large or small fin spacing. The data also suggest that the impact of surface wettability is largely dependent on the compactness of the heat exchanger. For heat exchangers with large fin spacing, pressure drop across the heat exchanger is less sensitive to the change of fin wettability. Hydrophilic treatment causes heat-transfer degradation due to the filmwise mode of condensation and the degradation is larger for specimens with wide fin spacing. Hydrophilic treatment works the best for heat exchangers withhigh fin density and fin interruptions.