Effects of fin corrugation and tube geometry on the airside performance of fin-and-tube heat exchangers - Part I; dry surface

Abstract

For a cooling or heating coil of a building air conditioning system, large diameter tubes (over 12.7 mm) with wave fins are frequently used. Furthermore, there have been attempts to apply oval tubes to the heating or cooling coils. In this study, nine samples - three herringbone wave fin/round tube, three smooth wave fin/round tube and three smooth wave fin/oval tube samples - were tested under dry condition. All of the samples had the same original tube diameter (12.7 mm). For the smooth wave fin samples, fins were identical, and for the round tube samples, fin corrugation angles were almost the same. Tests were conducted varying the frontal air velocity from 1.0 to 4.0 m/s. Results showed that the round tube samples yielded higher conductance per volume (η_o h_o A_o / V_o ) than the oval tube sample. Similarly, the smooth wave fin samples yielded a higher conductance per volume than the herringbone wave fin samples. At one row configuration, however, a significant difference among samples existed between the heat transfer conductance per volume and the heat transfer coefficient, and the reason was explained by the difference in fin efficiency between the round and the oval geometry. The pressure drops of the round tube samples were larger than those of the oval tube samples. Similarly, the smooth wave fin samples yielded larger pressure drops than the herringbone wave fin samples. A performance evaluation revealed that the smooth wave fin samples yielded larger heat transfer conductances per volume than the herringbone wave fin samples at the same pumping power per volume.