HEAT-TRANSFER ANALYSIS OF AIR-TO-CARBON DIOXIDE 2-PHASE HEAT ABSORPTION AND SUPERCRITICAL HEAT REJECTION

Regulations restricting the present and future use of fluorocarbon-bas ed refrigerants have prompted a worldwide investigation of new refrige rants and refrigeration cycles. In particular, carbon dioxide is a flu id with a history of being used as a refrigerant that has recently bee n considered for certain applications that may take advantage of its u nique thermophysical properties. The high volumetric heat capacity of carbon dioxide is a particular feature that could make a carbon-dioxid e-based refrigerating/air-conditioning device appropriate for a weight or space-limited application. This study presents a comparison of hea t-exchanger models of the hear absorption (evaporation) and heat rejec tion process for both carbon dioxide and R-22 air-conditioning cycles. The heat exchangers were modeled as single straight tubes with outsid e fins of constant thickness and spacing. Diameters for each tube were based on operating pressure and allowable power loss. The required le ngth, weight, smd volume for the heat exchangers were determined and c ompared.