A multi-ejector system is difficult for a single-stage ejector to keep the system running at optimum conditions because of the critical back pressure. This motivates researchers to solve this problem by using multi-stage ejector refrigeration systems, developing a two-stage ejector, consisting of a traditional first stage without a diffuser and an annular second stage which is directly located at the outlet of the first stage mixing chamber. Figure 2.6 schematically describes such ejector structure and whole system as well as its P-h diagram. The vapor from the generator is divided into two parts to enhance the ejector performance, both acting as the primary flow for different secondary flows in the two-stage ejector.