One-dimensional model of an optimal ejector and parametric study of ejector efficiency

Significant numerical and experimental analyses have been devoted to understanding the variety of flow regimes present in steady flow ejectors. Certain regimes are more conducive to achieving high performance (i.e. high entrainment ratios). In particular, the entrainment ratio is seen to be highest when the entrained fluid reaches a choked condition in the mixing region. In addition, the expansion regime of the motive nozzle (under-, perfectly- or over-expanded) appears to influence performance. In this paper, we propose a method to model an ejector of optimal geometry, designed for a favorable flow regime. Then, rather than focusing upon the maximization of efficiency, we seek operational conditions that maximise ejector efficiency, specifically the reversible entrainment ratio efficiency. Ejector efficiency is found to be highest at low compression ratios and at low driving pressure ratios. However, at lower compression ratios, the optimal area of the mixing chamber becomes large relative to the motive nozzle throat area.