[EXTERNAL] In this paper, (2008) Stefan Elbel of Creative Thermal Solutions & Predrag Hrnjak University of Illinois at Urbana-Champaign explain; 

Abstract; Ever since the renaissance of transcritical R744 systems in the late 1980s, ejectors have been considered to improve energy efficiencies. However, the invention of the ejector dates back far longer. This review paper gives an overview of historical and recent developments regarding air-conditioning and refrigeration systems that use ejectors. More than 150 ejector papers available in the open literature have been studied and important findings and trends were summarized. Included are the early beginnings starting with the invention of the ejector and major fields of use are outlined. Research on refrigeration cycles that utilize low-grade energy to produce a refrigeration effect is summarized. Another major field, expansion work recovery by two-phase ejector, is described next. This application appears very promising when used in transcritical R744 cycles. Less commonly encountered setups, such as systems in which ejectors are used to raise the compressor discharge pressure instead of the suction pressure are also introduced.

Download the full Paper here >> Ejector Refrigeration ; An Overview of Historical and Present Developments with an Emphasis on Air Conditioning Applications