An experimental study of a two-phase ejector with R134a as the working fluid is presented in this paper. The main objective is to determine the effects of the divergent section of the nozzle on the ejector performance under various working conditions. For the same conditions of operation, the ejector with a convergent nozzle presents a higher critical primary mass flow rate and a lower critical pressure in comparison to the version with a convergent-divergent nozzle. Globally the ejector with the convergent-divergent nozzle provides a higher entrainment ratio. The nozzle geometry has no impact on the optimal position of the nozzle. The same position giving the best entrainment ratio was found for the two tested nozzles. Unlike the convergent-divergent nozzle, the convergent nozzle has an entrainment ratio almost insensitive to a wide range of primary inlet subcooling. Primary and secondary mass flow rates increase with the subcooling level in a proportional way, resulting in a quasi-constant entrainment ratio.
Keywords experiments, two-phase, ejector, R134a, nozzle geometry