Fluids for high temperature heat pumps

The theoretical performances of some 250 potential work fluids in vapour compression heat pumps condensing at 150°C and evaporating at 100°C have been predicted, using expression for coefficient of performance (COP) and minimum superheat that involve only easily accessible physical properties. Expected correlations were found between COP and critical temperature, between specific compressor displacement and normal boiling point, T_bp, and between condensing pressure and T_bp. Correlations were also found between minimum superheat and both molecular weight and critical pressure. From these correlations, the desirable basic properties of a high temperature heat pump fluid are deduced. The principle of corresponding states is invoked to explain the connection between minimum superheat and critical pressure, and hence the reason why perfluorinated compounds tend to make poor work fluids.