Condensate Retention and Shedding Effects on Air-Side Heat Exchanger Performance

The effects of condensation on the air-side performance of plate-fin-tube heat exchangers have been experimentally investigated by conducting experiments under dry conditions and then repeating these experiments under condensing conditions. Sensible air-side heat transfer coefficients and friction factors are reported and compared for these cases. Realtime and steady-state measurements of condensate retention are reported for both coated and uncoated heat exchangers with fin spacings of 4, 8, 10 and 12 fpi (fins per inch). An initial model has been developed to predict the quantity of condensate retained on plate-fin-tube heat exchangers with wide fin spacings as a function of the heat exchanger geometry, advancing and receding contact angles, and air-side Reynolds number. This model demonstrates condensate retention modeling techniques and possible improvements to these techniques are discussed. Experiments were conducted in an optically accessible test section and photographs of retained condensate are provided. These photographs identify the modes of condensation and condensate geometries observed during the experiments. Advancing and receding contact angle were measured using a contact angle goniometer for typical heat transfer surfaces. These measurements indicated a significant increase in surface wettability during the first 100 hours of wet-dry cycling.Air Conditioning and Refrigeration Project 6