An Experimental-Theoretical study on heat transfer aspects of indirect Sublimation, for application in CO2-based refrigeration systems

Recent advances in CO2-based refrigeration systems have made it necessary to derive heat transfer correlations for the design of the corresponding industrial equipment. The current study focuses on the derivation of such correlation for indirect sublimation, whereby a material is sublimated on a hot surface by transferring energy to it via a conduction mechanism. We took an experimental-theoretical approach to investigate the subject in the case of constant wall temperature. An apparatus with real-time temperature and weight display was built to sublimate the dry ice blocks of different sizes, with circular and rectangular geometries. When the temperature of the hotplate was changed from -30 to 200 degrees C, the heat transfer coefficient "hsub" decreased from 126 to 70 W/ m2K. Such coefficients are about one-fourth of the corresponding values in flow (direct) sublimation. Weight and area of the block had positive/negative effects on heat transfer, respectively. In the theoretical part, two "lineargradient" and "semi-analytical" models were developed. The more accurate semi-analytical model could estimate "hsub" with 6.4 and 21.3 % average error in circular and rectangular geometries. Linear-gradient was analytic, with respective errors of 17.3 and 25.9%.