Experimental Study on Spray Cooling Heat Transfer of LN2 for a Large Area

Abstract

Spray cooling has been considered one of the most promising thermal control methods of high-heat flux devices. Most of the spray cooling research focuses on electronic components as the main application object to achieve higher heat dissipation heat flow in ambient temperature regions for small areas. Water is the most common cooling medium. This paper investigates the application of spray cooling thermal control over large areas. In this study, the heat-transfer characteristics of liquid nitrogen (LN2) for large areas was investigated by conducting experiments. The test surface is 500 mm × 500 mm, which was cooled by a nine-nozzle array. The spray nozzles used in the experiment were conical nozzles with an orifice diameter of 1.6 mm, a spray angle of 120°, and a spray height of 42 mm. Liquid nitrogen was forcefully ejected from nozzles by the high pressure of a liquid storage tank to cool the test surface. According to the cooled surfaces, spray directions, and spray pressures, three groups of experiments were conducted. The results showed that the smooth flat surface has the best heat-transfer performance in three kinds of surface structures, which are macro surface, porous surface, and smooth flat surface. The heat-transfer coefficient varied by ±20% with different spray directions, and the surface heat-transfer coefficient increased linearly with increasing spray pressure. Most of the spray cooling research focuses on heat dissipation in the ambient temperature region for equipment over small areas. The results can benefit thermal control application in various fields. The research in this paper can provide a reference for the application of large-area spray cooling, and the application areas mainly include metal manufacturing processing cooling, aircraft skin infrared radiation characteristics modulation, and laser weapon equipment cooling.