An investigation on the irreversibility in the CO2 two-phase ejector based on the one-dimensional distribution model

Abstract

The irreversibility inside a CO2 two-phase ejector was investigated based on the one-dimensional distributed parameter method and experiment measurement. The global ejector model was developed, in which the suction chamber was modeled by the conservation equations, and the mixing chamber and diffuser model was established by the double-flow model. The validity of presented model was verified by the experimental data. The entropy change rates and exergy destructions of each component of ejector were discussed under different nozzle exit positions (NXP) and throat areas of motive nozzle. Then the conical structure of mixing chamber was compared to the cylindrical structure to optimize the mixing performance. The results showed that the entropy generation rates of motive nozzle increased with the raise of NXP, and there was optimal NXP to decrease entropy change and irreversible loss of suction chamber. Moreover, the increment of specific entropy of primary flow in the mixing chamber and diffuser occupied 68.6% of the total entropy increase of the ejector. The largest exergy destruction in the ejector derived from the mixing chamber, followed by the motive nozzle, suction chamber and diffuser. The convergent conical mixing structure brought about the large increment of the entropy generation and pressure lift of the ejector. While the divergent conical mixing structure contributed to controlling pressure lift and reducing the entropy generation during the diffuser.