| Thermally-driven absorption heat pump cycles have several advantages over conventional vapor compression cycles. Current absorption systems are dominated by dual-pressure cycles using a solution pump. Single-pressure cycles remove the need for a pump, which makes them portable, inexpensive, reliable, and silent. An entirely different approach to a single-pressure absorption cycle was taken by Einstein and Szilard in the 1930s. Their cycle decouples the temperature lift from the generator temperature, which allows the selection of a refrigerant that matches the application temperature requirements.; The configuration of the Einstein cycle was examined, and changes were made to increase the coefficient of performance. The bubble pump performance was increased through selection of optimum operating parameters. An external heat exchanger was added between the generator and the condenser/absorber to improve heat recovery, and the partial internal heat exchanger in the generator was expanded to a full internal heat exchanger in order to minimize entropy generation. The Einstein Cycle has been modeled using two separate property models: (1) a corresponding states/ideal solution property model, and (2) a Patel-Teja/Panagiotopoulos and Reid property model. The first model was used to predict which parameters would increase the COP and the second model was used to more accurately predict the behavior the cycle. For this study, three temperature conditions were evaluated that are suitable for gas water heating. The highest COP for the first temperature configuration, which can produce 125 F water from ambient conditions (flue gases could be used to help to maintain the evaporator at 72 F), is 1.51. The best COP for the second set of temperatures, which require a hotter evaporator, is 1.88. Finally, the COP for the third set of temperatures, where the Einstein cycle would be used as a preheater, is 1.76. An Einstein cycle gas heat pump water heater would cut the operating costs of a conventional gas water heater by 33%. This could result in large economic and environmental savings. |
