A modeling study of spatial and temporal frost growth on the edge of windward fins for a tube-finned heat exchanger

Abstract

Frosting on the surface of tube-finned heat exchangers is a serious and common problem in the fields of air source heat pump and vaporization of liquid nitrogen. To reveal the frosting characteristics, a frosting model on the edge of windward fins was developed. Based on the previously reported experimental visualization results, the model was simplified by regarding the flat surface of the edge of windward fins to a half-cylindric surface. The predicted frost thickness and frost mass according to the proposed frosting model agreed well with the previously reported experimental data. The numerical results showed that frost layer on the edge of a windward fin grew the fastest along the opposite airflow direction and gradually slower with the increasing θ, angular position relating to the center axis of fin, showing a streamlined profile. The frost thickness, density, and surface temperature all decreased by 31.9%, 19.0%, and 2.2 °C, respectively, while θ increased from 0° to 90° at the end of a 3,600 s frosting period. Additionally, the average water vapor mass flux, total, sensible, and latent heat flux decreased by 17.6%, 17.9%, 18.1%, and 17.6%, respectively. The frosting surface area, frosting rate, total, sensible, and latent heat transfer rates increased by 141.0 times, 119.6 times, 119.0 times, 118.6 times, and 119.8 times, respectively. This study is meaningful for the accurate control of defrosting and thus energy saving.