Effects of contact angle on condensate topology, drainage and efficiency of a condenser with minichannels

Epoxy coatings with good adhesion characteristics have been developed that are suitable for large-scale manufacturing and application in compact heat exchangers. Two of them, with a static contact angle for water of 105° and 79° have been tested in a finned-tube condenser comparing flat plate minichannels on the gas-side. Contrary to the expectation, the thermal efficiency of the 105° condenser is slightly less than that of the 79° one. This is due to a reduction of condensate drop size at detachment, resulting in relatively small dry paths after drainage. In the present study, geometry and coating thickness of the two coated exchangers used have not been optimized, since emphasis has been on the effect of contact angle. The finned-tube geometry is shown to be less favourable, for a condenser, than the compact cross-flow plate geometry with minichannels on both the gas- and coolant side that was tested previously.