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Investigation of new mechanical heat pump systems for heat upgrading applications

In this study, two novel high‐temperature heat pump systems based on vapor compression cycles are introduced and examined. Three fluids (water, cyclohexane, and biphenyl) are selected and analyzed thermodynamically as prospective working fluids for the high‐temperature heat pumps. These working fluids are used in cascaded cycles to upgrade the heat to a temperature of 600°C. The equations of state used in performance analysis are Peng‐Robinson, non‐random two‐liquid model, and International Association for the Properties of Water and Steam 95. A parametric analysis is carried out to study the effects of isentropic efficiency, sink temperature, source temperature, and ambient temperature on the system performance. Both energetic and exergetic coefficients of performance (COPs) of the overall and individual cycles are determined. The COP values obtained are found to range from 2.3 to 3.8, depending upon the cycle and temperature levels. The high COP values in some instances make these systems promising alternatives to fossil fuel and electrical heating. As a possible sustainable scenario, these pumps can utilize low‐grade heat from geothermal, nuclear, or thermal power plants and derive work from clean energy sources (solar, wind, nuclear) to deliver high‐grade heat. The high delivery temperatures make these heat pumps suitable for processes with corresponding needs, like high‐temperature endothermic reactions, metallurgical processes, distillation, and thermochemical water splitting.