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

Abstract

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.