An Example of the Manipulation of Effective Vapor Pressure Curves by Thermodynamic Cycles

The performance of a two-stage Rankine cycle employing a working fluid mixture and solution circuits has been computed with reference to heat pump applications. Its performance is compared to the single-stage version of this cycle and one operating with pure refrigerants. It is found that the two-stage cycle operates along an “effective” vapor pressure curve of very flat slope, resulting in pressure ratios that are reduced to about one third compared to conventional cycles. For large temperature differences between heat sink and source the Coefficient of Performance (COP) can be increased by up to 50 percent.