Optical investigation of cryogenic frost formation under forced convection

Abstract

Experimental research was conducted to observe the frost growth under forced convection and cryogenic conditions (−180 °C). A laser was installed as a light source to investigate the frost microscopically, and the frost film and frost seed were observed on the test surface. The process of frost growth under cryogenic conditions was classified into four periods and it was compared with those under general-low temperature conditions. The frost coverage factor was defined based on the pixel intensity of the frost image, and the shape of the frost layer could be visualized using the frost coverage factor. The heat flux of the test surface was compared with the frost coverage factor, and it decreased by 40% when the frost coverage factor was 1. Therefore, the frost coverage factor can be used as a useful index to evaluate the heat transfer performance of the heat exchanger operating under cryogenic conditions.