Ezejector Blog - Steam ejectors, ejector efficiency explained, the many uses of ejectors, effect of steam pressure, how to control an ejector, isentropic and isenthalpic expansion compared and more, 

In the previous post the potential benefit of single critical ejectors was presented. Here we discuss this further. An ejector that is designed for single critical flow may be move sensitive to pressure and flow changes - please refer to the figure below. As can be seen, a change in back pressure will impact on the entrainment ratio and vice versa. In contrast, the entraiment ratio and discharge pressure are independent of each other for the double critical design.

Will you get a higher discharge pressure for an ejector designed for single critical or double critical flow? Single critical is where the motive gas flow is choked (sonic) in the nozzle but the entrained gas is not choked (subsonic). For double critical both are choked. To compare realistically, the motive and entrained flow rates, temperatures and pressures must be identical. The short answer: sometimes yes, there is some benefit - up to a point. As can be seen in the plots