Effect of spray characteristics on spray cooling with liquid nitrogen

Operation of power electronics at liquid nitrogen (LN2) temperature is a very attractive possibility. However, a high heat flux (over 100 W/sq cm) cooling technique like spray cooling will have to be used to realize all the advantages of low-temperature operation. This study provides empirical correlations for LN2 spray cooling. A general semiempirical correlation (based on macrolayer dryout model) for spray cooling critical heat flux (CHF) is obtained. This correlation is shown to be very accurate for predicting spray cooling CHF for different liquids and spray conditions. An empirical correlation for heat flux is also presented. This study also shows the importance of surface roughness for spray cooling with liquid nitrogen. The rougher surfaces were shown to have significantly higher heat transfer rates and similar CHFs occurring at lower temperatures. (Author)