Performance Evaluation Of Peripheral-Finned Tube Evaporators Under Frosting Conditions

The peripheral finned-tube (PFT) is a novel air-side geometry for compact heat exchangers. Previous studies (Pussoli et al., 2012) evaluated the thermal-hydraulic performance of the PFT geometry under dry conditions (i.e., no frost or condensate formation on the air side). The present study focuses on quantifying the thermal-hydraulic performance of the PFT geometry under frosting conditions. A PFT prototype was tested in a closed-loop wind tunnel calorimeter to determine the influence of the tubewall temperature, air velocity and psychrometric properties (temperature and relative humidity) on the heat transfer rate, air-side pressure drop and mass of frost built up on the surface. A mathematical model was developed to predict the behavior of the evaporator in a variety of operating conditions. The model treats the air flow paths as a porous medium, whose porosity, equivalent particle diameter and thermal properties change with time due to the frost accumulation. The time-dependent characteristics of rates of heat transfer and moisture deposition and of the air-side pressure drop were well correlated by the mathematical model.