Advanced exergy analysis on an ejector using zeotropic mixture in a refrigeration system

Abstract

Ejector performance plays a vital role in overall cycle efficiency of an ejector refrigeration cycle. This work focuses on reducing irreversibility within the ejector by conducting both advanced and conventional exergy analysis of the ejector using R600a/R290, evaluating exergy destruction and the possibility for performance enhancement in each component of the ejector. Effects of primary flow pressure, secondary flow pressure, mass fraction, mixing chamber diameter, nozzle throat diameter and the ejector efficiency on exergy destruction in each component were discussed, and improvement potential of each component was provided. Results show that the exergy destruction of mixing chamber is the main contributor. The improvement potential from large to small recommended by avoidable endogenous exergy destruction analysis are nozzle (48.3 %), suction chamber (45.1 %), diffuser (34.8 %), and mixing chamber (21.7 %). In addition, the total exergy destruction in the ejector increases from 924 W to 1109 W as the low-boiling-point mass fraction varies from 0.1 to 0.9, but the improvement priority will not change. Moreover, the diameters of nozzle throat and mixing chamber affect ejector performance greatly, and the ejector exergy destruction is more sensitive to the changes in nozzle throat diameter. With every 0.1 mm increment in both diameters, the maximum increment of total exergy destruction reaches 1.4 % and 9.2 % with mixing chamber diameter and nozzle throat diameter, respectively. Ejector efficiency has great impact on ejector performance, as ejector efficiency changes from 0.80 to 0.90, the exergy efficiency of the ejector increases from 4 % to 19 %.