**9.3 Isobutane**

Isobutane exhibits a higher normal boiling point (11.85 deg. C) compared to CFC-12 (29.8 deg. C) and requires about 80% larger displacement volume in the compressor than CFC-12 to obtain an equivalent cooling capacity. Ray Riffe et al. investigated the use of isobutane as a refrigerant in refrigerator/ freezer with the use of dual cycle (D.R, 1995). His conclusions were


From the above discussion it is quite apparent that there are **limited numbers of pure fluids that can function as substitute for CFCs.** mixing of refrigerants allow adjustments or tuning of the most desirable properties to provide suitable alternatives. Of course, other properties are also altered and thus the craft of developing a mixture is to obtain a final fluid with all desirable properties in the operating range. Mixtures provide a flexibility of modulating the capacity by varying the composition of the constituents. Refrigerant mixtures are solutions, i.e. they have constituents, which are equally dispersed and cannot be mechanically separated. There are three categories of mixtures.
