Frost formation and frost meltwater drainage characteristics on aluminum surfaces with grooved structures

Abstract

Frost frequently forms on refrigeration and cryogenic engineering systems. Frost on finned surfaces increases the air-side thermal resistance and reduces the airflow area, which consequently reduce the heat transfer rate. Structured fin surfaces may be an effective solution to delay frost formation and promote meltwater drainage. This study experimentally studied condensation, frost crystal growth, frost melting and meltwater drainage characteristics on aluminum surfaces with parallel and crossed grooves with comparisons to these effects on a flat aluminum surface. The results show that condensed droplets freeze later with less frost accumulation on the grooved surfaces than on the flat surface and that the frost prefers to grow at the top edges and corners of the structures instead of inside the grooves on the grooved surfaces. During melting, the frost melts and the meltwater breaks up into small meltwater streams and droplets at the top of the structures or between the structures on the grooved surfaces. The parallel grooved surface has better drainage than the flat surface with a smaller meltwater retention ratio, while the surface with crossed grooves has worse drainage. In addition, the meltwater retention ratio is related to the frost thickness. Lower surface temperatures and longer frosting time results in more frost accumulation and larger meltwater films, which are more easily shed from the surface by gravity so that the meltwater retention ratio is smaller.