Zeotropic and azeotropic blends
Also known as: zeotrope, azeotrope, refrigerant blend, 400 series
Short definitionThe two kinds of refrigerant blend. A zeotropic blend (R4xx) boils over a temperature range at constant pressure; an azeotropic blend (R5xx) changes state at a single temperature, like a pure substance.
Most of today’s refrigerants are blends of two to four gases. Because the components have different boiling points, a zeotropic blend evaporates colder at the evaporator inlet and warmer at the outlet. R404A, R407C, R449A and R454C behave this way. In azeotropic blends the components act as one substance at a certain ratio; R507A and R513A belong to this group and their glide is close to zero.
The difference shows during commissioning and service. A zeotropic gas is drawn from the cylinder as liquid; taken as vapour, the components leave in different proportions and the blend is spoiled. The composition can also shift in a leak, and after a large leak the whole charge is replaced. Superheat is calculated from the dew point and subcooling from the bubble point. With an azeotropic gas one column is enough.