180 the convergent divergent nozzle 220 has an inlet 224 and an outlet 226 and a throat 228 between the inlet and the outlet a flow cross sectional interior surface area of the throat is less than that of the smaller of the inlet and outlet e g 10 95 more narrowly 20 80 or 40 60 an exemplary flow cross sectional interior surface area of the outlet is greater or less depending on the outlet refrigerant velocity requirement higher velocity demands the outlet area be greater less for lower velocity than that of the inlet e g 20 175 more narrowly 50 150 the outlet cross sectional area may be nominally the same as that of the ejector primary inlet and any intervening conduit line the inlet cross sectional area may be the same as the conduit line from the heat rejection heat exchanger further variations on the means involve omitting the control valve 182 fig9 for the nozzle 220 in such situations the dimensions of the nozzle 180 or 220 are pre selected to maintain the ejector inlet pressure below the critical pressure over the anticipated range of operating conditions yet further variations of the means modify the nozzle 220 to have a controllable flow cross section for a convergent divergent nozzle 240 fig1 this may involve a controllable throat cross section e g via a needle valve having a needle 242 and an actuator not shown the needle may be controlled to control the nozzle outlet pressure or system parameters such as flow.