A numerical study on the air-side heat transfer of perforated finned-tube heat exchangers with large fin pitches

For a finned-tube heat exchangers (FHEXs) with large fin pitches, the enhancement of air-side heat transfer performance by using perforated fins has been numerically investigated in this paper. The effects of the perforation size and number on the air-side j factor and heat transfer rates of the FHEX are analyzed in detail at different large fin pitches. Numerical simulation results indicate that an optimal perforation design can be obtained to realize maximum increase in the j factor for the perforated FHEX compared with those of the plate FHEX without perforations. It is also found that the enhancement of the j factor increases with the rising air-side Reynolds number from 750 to 2350. For the perforated FHEX with fin pitch of 10.0 mm, the j factor increases by 0.3% at Re = 750 and 8.1% at Re = 2350, respectively, with the optimal perforation design. In addition, the results present that the j factor increase of the perforated FHEX compared with that of the plain FHEX is more obvious at smaller fin pitches. When the fin pitch varies from 20.0 mm to 7.5 mm, the increase in the j factor varies from 2.7% to 9.2% at Re = 2350. However, the total heat transfer surfaces of the perforated FHEX are reduced by perforations, its heat transfer rates may be decreased. The results show that the air-side heat transfer rate is reduced by 6.3% at Re = 750 when the fin pitch is 7.5 mm. For this case, two methods are further proposed to compensate total surfaces for the perforated FHEX in order to obtain higher air-side j factor while ensuring identical heat transfer rate.