Analysis of a solar Rankine cycle powered refrigerator with zeotropic mixtures

A solar organic Rankine cycle (ORC) powered vapor compression cycle (VCC) for refrigeration is under investigation in this paper. To improve the overall system performance, zeotropic mixtures are proposed to be used in the integrated ORC-VCC system for the first time. A thermodynamic model is developed, and a total of eight pure fluids and five zeotropic mixtures with various compositions are evaluated and compared to identify the best combinations of fluids for yielding high system efficiencies. Besides, the influences of generating temperature, refrigerating temperature, superheating and internal heat exchanger (IHE) in ORC on the system performance are analyzed. For the ORC-VCC operating between -5 and 80 degrees C, dry fluid R600a shows the highest system efficiency (0.2212) among the pure fluids. For zeotropic mixtures, there exists a composition range within which binary mixtures always show higher system efficiency than the component pure fluids. Mixture R161/R600a with an R161. mass fraction of 0.25 shows the highest system efficiency (0.3089) among all fluids, which is increased by 39.6% and 54.7% comparing with R600a and R161, respectively. Adding IHE in ORC benefits the system efficiency, and the benefit is much more evident for dry fluids. Superheating makes wet fluids become applicable in ORC-VCC, but it becomes ineffective in improving the system efficiency when there is no IHE in system.