Influence of the ratio of nozzle inlet to nozzle throat areas on the performance of a jet pump for vacuum applications using computational fluid dynamics

The nozzle design is one of the most important issues because it determines the pressure range and the other dimensions to guarantee an adequate performance of a jet_pump. An incorrect design of this part can cause shock waves and unnecessary overexpansion of the power fluid. The nozzle’s main purpose is to allow the high-pressure, low-velocity primary fluid to be accelerated in such a way as to substantially decrease the fluid pressure while increasing its velocity. This is achieved because the subsonic flow accelerates when entering the convergent part of the nozzle, obtaining a sonic or supersonic flow at the nozzle throat that accelerates even more when entering the divergent part of the nozzle. Therefore, to achieve the highest possible nozzle discharge velocity, the nozzle must be able to change the flow conditions from subsonic to supersonic. Considering the high importance of the nozzle design in the jet_pump performance, five cases are simulated in the present work, where the ratio of nozzle inlet to nozzle throat areas is modified (10,15,20,25 y 30), to study the behavior of three performance parameters, namely, drag coefficient (Cd), pressure ratio (PR) and Energy Efficiency (η), as well as the Mach number (Ma) and velocity fields.