Propene/isobutane mixtures in heat pumps: An experimental investigation

Zeotropic mixtures in heat pumps, based on thermodynamic analysis, should lead to higher coefficients of performance (COP) due to the temperature glide which decreases exergy losses in the heat exchangers. However, fluid mixtures influence every component of a plant and the total system performance. In addition to the various theoretical studies in this field, a laboratory scale vapour compression heat pump test rig was designed and set up. In the present experimental investigations, the operating performance for the pure fluids isobutane and propene, and their mixtures are systematically investigated. COPs and exergetic efficiencies as a function of evaporation temperature, compressor speed and composition of the mixture are presented and compared with a theoretical approach. Contrary to theoretical expectations, the experimental results show only a slight increase of the COP for the mixture, compared to the better pure fluid, because heat exchanger pressure drops reduce the temperature glide.