**10. Mixtures of propane and isobutane**

Propane and Isobutane will combine pretty happily as both are non-polar. Butane molecules will be broken and are replaced by the molecules of butane and Propane molecules. Propane-isobutene mixture has the benefit of modulating the capacity to permit their use with compressor designed for use with CFC-12. The binary mixture ratio can conceivably be designed using boiling point as a guideline such that the disparate requirements of the freezer and the fresh food compartment in domestic refrigerators can be balanced. The normal boiling point temperature for HC-290/ HC-600a mixture (each 50% by mass) ranges from 32 deg. C to 24 deg. C which is very close to normal boiling point of CFC-12 [17].

The mixture in comparison to CFC-12 possesses very high latent heat of vaporization and low value of density (1/3 of CFC-12), which makes the mixture attractive because of its low charge requirement and circulation rates. The charge levels are approximately 40% that of CFC-12. One of the important advantages of

#### *Refrigerant Mixtures DOI: http://dx.doi.org/10.5772/intechopen.99024*

R-600a/ R-290 blends is that it is compatible with mineral oils and commonly used materials for manufacturing of refrigeration systems and requires minimal changes in the refrigeration systems. The mixtures do not contain any halogen atom and hence the possibility of forming acids in the presence of moisture is eliminated [6].

This is also a factor for better stability of these mixtures. **Table 4** shows the thermodynamic properties of few hydrocarbons and CFC-12. It follows from **Table 4** that pure hydrocarbons cannot be exact alternative to CFC-12. Meyer conducted experimental investigation with the use of hydrocarbon refrigerants for domestic refrigerators. It was found that an unchanged CFC-12 single temperature refrigerator had lower energy consumption with a refrigerant mixture of 50% propane and 50% isobutene compared to CFC-12. Based on these encouraging results FORON decided to develop single temperature refrigerators using hydrocarbon mixtures as refrigerants. This was the beginning of use of hydrocarbon mixtures as refrigerants in domestic refrigerators. Domanski et al. carried out a study of hydrocarbon refrigerants for residential heat pump systems and concluded that these mixtures were promising substitute. He examined the various benefits and discussed the Rankine Cycle System and component design issues and limitations when using a wide range of single component refrigerants, hydrocarbons, with the help of the READER code for residential size heating and cooling systems (Domanki, 1994).

Liu et al. (1994) conducted an experimental test with propane-isobutane as a drop in substitute in a domestic refrigerator/freezer unit. They kept all hardware components of the refrigerator/freezer as that of CFC-12 except the capillary tube, which was, lengthen to control the flow rate. They concluded that highest savings of 6.5% were achieved with a blend of 70% HC-290 and 30% HC-600 with a charge of 70 g.Kruse performed a theoretical evaluation of hydrocarbons and its mixtures as refrigerants in refrigerators, unitary air conditioners and heat pumps. He concluded that in general, **hydrocarbons have an inherent possibility of lower energy consumptions.** He also mentioned that refrigerators with hydrocarbons mixtures as refrigerant shows further possibility of energy improvement if they are designed by using Lorenz-Meutzner cycle. The major drawback of these mixtures, like other hydrocarbons, is the high inflammability. But the charge is only 1/3 to ½ that of CFC 12. Owing to the fact, inflammability does not pose a problem. However, proper safety precautions should be taken at different stages of manufacturing, charging and operating (Cichong Liu, 2016).

When the Montreal Protocol has phased out CFCs in the developed countries and has a regulatory regime for the phase out of HCFCs, the problem still is a major problem in developing countries. Awareness is to be created among the common people to save the planet earth. Developing countries should phase out ozone depleting chemicals in a very careful manner.

Global market will continue to develop & introduce new refrigerant chemicals. Statutory requirement is necessary to control the UN –organized sector who are dealing in HVAC industry.
