A comparative study of frosting behavior on finned tube heat exchanger under different fan control modes

Although a large number of studies have been carried out on investigating the frosting behaviors and its impacts on finned tube heat exchangers (FTHXs), comparative studies for frosting behaviors on FTHXs among using different fan control modes were still lacking. Hence, a related experimental study comparing two different outdoor air fan control modes has been carried out, and the study results are presented in this paper. The study results demonstrated that compared to the constant outdoor air fan speed control mode, the constant air flow rate control mode can make the frost at the exit from leeward fins more compact and uniform, and lead to an accelerated frost growth on the surfaces of fins and tubes but an impeded frost growth on the edge of windward fins. At the end of a 60-min frosting duration, the protruded thickness of frost on the edge of windward fins, and frost thickness at the entrance to the windward fins under the constant air flow rate control mode were 7.9% and 11.1% smaller than those under the constant outdoor air fan speed control mode. In contrast, frost mass on the FTHX and the averaged frost density on the surfaces of fins and tubes under constant air flow rate control mode were 6.7% and 16.7% larger than those under constant outdoor air fan speed control mode. Furthermore, the averaged air side pressure drop, air velocity and total heat transfer rate of the FTHX under the constant air flow rate control mode were 134.5%, 82.4% and 13.4% larger than those under the constant outdoor air fan speed control mode during the 60-min frosting duration.