An experimental study and 1-D analysis of an ejector with a movable primary nozzle that operates with R236fa

•The critical entrainment ratios of an ejector at different nozzle positions are experimentally studied.•The critical entrainment ratio first increases with the nozzle exit position and then remains constant.•A 1-D model is proposed to explain the experimental results.

The nozzle exit position is an important structural parameter of an ejector. Research shows that movable primary nozzle enhances performance of ejectors. The present work experimentally studied the critical entrainment ratios of an ejector at different nozzle positions, finding that the critical entrainment ratio first increases with the nozzle exit position and then remains constant. A 1-D model proposed to explain this phenomenon found that in a certain range, the critical entrainment ratio is determined by choking of the secondary flow in the converging cone. When the nozzle moves upstream, the mixed flow reaches sound speed at the constant area section, and the critical entrainment ratio remains unchanged.