Experimental and numerical study of frost formation with natural convection in a triangular arrangement of slender vertical tubes

Abstract

Frost formation is an undesirable phenomenon in heat exchangers, where a thin layer of frost forms, negatively influencing the performance and operation of the equipment. The frost layer increases the thermal resistance between the air flow and the cold surfaces in evaporators, which reduces the heat transfer rate and decreases the thermal efficiency. In the present study, the phenomenon of frost growth on a triangular array of slender vertical tubes was investigated experimentally in a wind tunnel. Fast CCD cameras were used for frost thickness measurement. A numerical investigation was conducted to simulate the frost thickness growth on the cold tube surface. Volumetric mean approach for frost formation modelling was applied and a modified formulation for calculation of the local Nusselt number in the vertical slender tube case was proposed. The numerical predictions showed a reasonably good agreement in relation to the mean values of the frost thickness measured in experimental tests up to the range of 5,000 to 6,000 s of simulation. Afterwards, in model predictions, the frost growth is bigger than the experimental results in the range of 14% to 33% higher in relation to mean values.