Analysis of the Condensate Carryover Phenomenon on Fin and Tube Evaporators

Abstract

Possible carryover of the condensate from the surface of the evaporator has always been a problem that in practice has been solved by limiting the air velocity. However, the need for more compact solutions and especially for the reduction of the frontal area in many applications requires the increase of the air velocity and therefore new solutions to overcome this problem must be developed. In this contribution, the authors develop an analytical model to estimate the evolution of the condensing drops over the fin surface of a heat exchanger as a function of the fin surface properties and air velocity. This model allows the estimation of the drop size when it starts to move and its trajectory and evolution along the fin. The possibility of drops forming water bridges in between the fins is also analyzed with estimation of the minimum fin separation to avoid its formation depending on the air velocity and the wettability of the fin surface. Finally, the results of an experimental campaign performed with two fin and tube coils of exactly same dimensions and geometry but with different fin materials: one with the standard aluminum fin and the other one with a specially outer hydrophilic layer, are presented, showing that this kind of coating avoids the condensate carryover with no appreciable penalty on the heat transfer performance.