There are many applications of ejectors, including refrigeration, power generation, and chemical sectors. On the one hand, ejector technology needs limited maintenance, has low operating costs, and has no restrictions on working fluids; on the other hand, complex single-phase and multiphase fluid dynamics make ejector design and performance prediction a real challenge.

This article explores major advances in ejector technology and proposes a critical discussion that looks to future research; the proposed discussion is based on the multi-scale relationship between ‘local-scale’ phenomena and ‘component-scale’ performance. After examining the past, this article reviews current research activities related to four cutting-edge research areas, namely refrigeration systems, energy conversion systems, chemical processes and numerical methods. For the different research areas discussed, opportunities for future research activities are evaluated. Finally, this article defines a key challenge that needs to be addressed in future long-term activities: the multi-scale ejector challenge.