The present study tested the fin-and-tube heat exchangers with slit fin and plain fin geometry. A totals of twenty-four different specifications of heat exchangers were tested both in open type wind tunnel and close type wind tunnel, The effects of the number of rows, fin pitches and fin pattern of the airside heat and mass transfer performance were experimentally investigated. The results were compared and presented as Colburn j factor and fanning friction factor f against Reynolds number Re00 based on the fin collar diameter D(subscript c) in the range from 300 to 8,000 in open type wind tunnel and from 500 to 4,500 in close type wind tunnel, respectively.
In open type wind tunnel, the test results indicated that the heat transfer performance increased as the fin pitch decreased for one row configuration. However, when row number was more than four, the effect of fin pitch on the heat transfer performance was reversed. In addition to the effect of fin pitch, the heat transfer performance decreased as the number of tube row in creased. But the friction characteristic was relatively independent of the number of tube row. Based on the present results and those from the former investigation by Nakayama, a general correlation is proposed to describe the airside performance of slit fin configuration. The mean deviation of the proposed heat transfer and the friction correlation are 5.23% and 3.59%, respectively.
In close type wind tunnel, the test results indicated that the heat transfer performance was relatively independent of inlet relative humidity. However, when Re(subscript Dc)>2,000 with smaller fin pitch, the heat transfer performance slightly increased with inlet relative humidity. The test results showed that the heat transfer performance in close type wind tunnel had a similar trend compared with open type wind tunnel. Friction factor f increased with decreasing fin pitch, and also as the function of the slit fin geometry. The humidity of the inlet conditions in one row configuration showed as the function of the inlet relative humidity under high frontal velocity condition.