Conference Year
2016
Keywords
CO2, cycle, sublimation heat transfer
Abstract
Carbon dioxide (CO2) is a well-known and established refrigerant with many advantageous properties and therefore used in many applications. However, the lowest achievable temperature is limited by the triple conditions at approximately 217 K and a corresponding pressure of 5.2 bar. Below these triple conditions CO2 only exists is gaseous or solid state. Commonly, the occurrence of solid particles in vapor compression cycles is carefully avoided and hence CO2 in solid state no option as well. With respect to increasing legal restrictions and upcoming bans for synthetic refrigerants CO2 might be also a reasonable alternative in low temperature refrigeration – despite the upcoming challenges with the solid phase. In this paper we give an overview on previous research activities with CO2 sublimation cooling in literature. Further, the theoretical efficiency of a CO2 cycle with a sublimation temperature of 198 K is compared to a conventional R404A/R23 cascade. Finally, a closer look to the heat transfer characteristics of solid-gaseous flow in the sublimation heat exchanger is given and challenges discussed. Â