Working fluid selection for a solar driven ejector cooling system operating under variable conditions

摘要

The three most important factors influencing the performance of an ejector are the working fluid, ejector geometry and operating conditions. In the present work, six low environmental impact working fluids were evaluated for their use in an ejector cooling system running on low temperature thermal energy, like solar thermal. The analysis was based on a numerical model applying the 1D constant pressure mixing theory. The model was validated with available literature data. Ejector cooling performance (entrainment ratio and COP) was assessed for generator, evaporator and condenser temperatures in the range of 80-120°C, 5-15°C and 25-40°C, respectively. It was concluded that isobutane (R600a) is a good choice for a refrigerant, due to its high COP and moderate operating pressures throughout the entire cycle. The results also indicate that the area ratio required for operating the ejector in critical mode, under variable generator and condenser conditions, varied in a significant range, regardless of the selected refrigerant. This clearly indicates the importance of a variable geometry ejector design to strengthen the position of ejector cooling systems among other refrigeration technologies.