Survey on non flammable low GWP refrigerant mixtures based on carbon dioxide for applications below 220 K.

This paper describes an analysis of finding possible R744 blends for refrigeration application in the temperature range from 170 to 220 K. The aim of this work was to find possible non flammable low GWP refrigerant blends based on carbon dioxide. To use R744 below its triple point (216.58 K), it can be mixed with a lower freezing fluid or a higher freezing fluid which has a small molar heat of fusion. Ways to calculate the decrease of the freezing temperature of R744, the evaporating temperatures and critical temperatures are shown. This paper describes possible fluid mixtures based on carbon dioxide which are non flammable or difficult to ignite. The flammability limits of the blends are shown, and the effects of the temperature on these limits are discussed.