Additionally, the volumetric composition and saturation temperature of zeotropic blends change when used in refrigeration systems, wheras the azeotropic blends do not. In other words, the components of a zeotropic blend (say R401A which contains R-22, R-152a and R-124) have different vapor pressures and boiling points; so when the fluid evaporates or condenses, the liquid and vapor components will have different compositions.
for example: Refrigerant R-410A is becoming more common in residential, and commercial units. More applications will begin using it as the year 2010, R-22 phase-out deadline approaches. R-410A is a 50-50% blend of 2 refrigerants, it is a non-azeotrope by definition. However,it behaves as a "near-azeotrope" in that the vapor phase change of the two refrigerant components occur so close together, (in temperature and pressure)the refrigeration system performance does not degrade when a bit of lost refrigerant has been replaced. The ratio stays 50-50. Other blends, such as R-407C have a real system problem when a portion of the refrigerant is lost, as the blend component ratios do not stay equal to the origional since the vapor pressure of each refrigerant component is different. In operation this is refered to as "glide".
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