The development of an ammonia ethane azeotropic refrigerant for low temperature applications

The use of ammonia as a refrigerant offers significant benefits over many conventional refrigerants, although it also possesses some less favourable characteristics, such as those associated with relatively high normal boiling point, high discharge temperature and oil miscibility. Therefore it would be desirable to develop an ammonia mixture that overcomes these disadvantages of pure ammonia. An ongoing development project has identified one such mixture comprising ammonia (R-717) and ethane (R-170), which under certain compositions forms an azeotrope. The objective of this part of the project was to determine the appropriate proportions of R-717 and R-170 that would produce the most favourable properties. Since the R-717 and R-170 mixture produces rather unusual behaviour, a major part of this study was to better understand the phase characteristics.

Because of the relatively high normal boiling point, high discharge temperatures and poor miscibility with oils, systems operating at low evaporating temperatures are more likely to suffer from related problems. This blend overcomes these drawbacks by significantly altering the refrigerant properties so that it can be more readily applied in low temperature applications such as blast freezing.