Air-side heat transfer and pressure drop of the fin-and-tube heat exchangers having oval tubes under wet condition

摘要

It is well known that the replacement of a round tubes to an oval tube in a fin-and-tube heat exchanger reduces an air-side pressure drop as well as a low performance region behind the tube, and improves the thermal performance of the heat exchanger. However, experimental evidences are lacking, especially for generic heat exchangers. In this study, three generic samples with oval tubes were obtained and tested under wet condition. The samples had different oval tube dimensions and tube pitches. One interesting result was that the highest j factor was obtained at a two row configuration. Possible explanation was provided considering the effect of fin efficiency. The wet surface j factors were slightly lower and the wet f factors were significantly higher than those of the dry surface, probably due to the condensate on the fin surface. A thermal performance comparison (based on the conductance per unit volume (η_olh_oA_o/V_o) to the pressure drop per unit length (ΔP/L)) revealed that, the oval tube samples yielded higher performances than the round tube samples with some exceptions at a large number of tube row. Furthermore, it was found that the oval tube geometry is more effective under wet condition than under dry condition. Correlations were developed, which predicted all they factor and 98% of the/factor within ±20%.