Separated condensation and cascaded evaporation – A novel method to improve ejector-compression heat pump cycle using zeotropic mixtures

The ejector is widely used to improve the vapor compression heat pump performance because of the recovery of expansion work via the ejector. To improve the ejector-compression heat pump efficiency further, a novel method was introduced to improve the ejector-compression heat pump cycle using low global warming potential zeotropic mixtures. The novel cycle applies the separated condensation and cascaded evaporation principle to reduce the irreversible loss of heat pump under the large temperature lifted conditions. The conventional heat pump and conventional ejector-compression heat pump were selected for comparison to investigate the energy-saving potential of the novel ejector-compression heat pump under the mid-high temperature condition for wastewater heat recovery. The performances of selected cycles were compared and discussed. The main results are listed as follows: The coefficient of performance of the novel ejector-compression heat pump initially increases and then decreases with the mass fraction of carbon dioxide ranging from 0.1 to 0.3, and the maximum values reach 6.73 and 6.67 with the mass fraction of carbon dioxide reaching 0.22 and 0.18 for carbon dioxide/2,3,3,3-Tetrafluoropropylene and carbon dioxide/trans-1,3,3,3-tetrafluoroprop-1-ene mixtures, respectively. Compared to the maximum coefficient of performance of conventional ejector-compression heat pump and conventional heat pump, the novel ejector-compression heat pump achieved maximum improvements of 30.7% and 69.0% with r carbon dioxide/2,3,3,3-Tetrafluoropropylene, and of 15.5% and 62.3% with carbon dioxide/trans-1,3,3,3-tetrafluoroprop-1-ene mixtures, respectively. Additionally, the operational parameters affect the performance of novel ejector-compression heat pump significantly. The coefficient of performance increases by ranging from 2.93 to 5.18 % and 3.08 to 5.08 % with the wastewater inlet temperature increases by one degree Celsius for carbon dioxide/2,3,3,3-Tetrafluoropropylene and carbon dioxide/trans-1,3,3,3-tetrafluoroprop-1-ene mixtures, respectively. The results provide a novel method to improve ejector-compression heat pumps for mid-high temperature condition using zeotropic mixtures.