| Summary: | Research was performed to optimize high-efficiency jet ejector geometry
(Holtzapple, 2001) by varying nozzle diameter ratios from 0.03 to 0.21, and motive
velocities from Mach 0.39 to 1.97. The high-efficiency jet ejector was simulated by
Fluent Computational Fluid Dynamics (CFD) software. A conventional finite-volume
scheme was utilized to solve two-dimensional transport equations with the standard k-??
turbulence model (Kim et. al., 1999). In this study of a constant-area jet ejector, all
parameters were expressed in dimensionless terms. The objective of this study was to
investigate the optimum length, throat diameter, nozzle position, and inlet curvature of
the convergence section. Also, the optimum compression ratio and efficiency were
determined.
By comparing simulation results to an experiment, CFD modeling has shown
high-quality results. The overall deviation was 8.19%, thus confirming the model
accuracy. Dimensionless analysis was performed to make the research results applicable
to any fluid, operating pressure, and geometric scale. A multi-stage jet ejector system
with a total 1.2 compression ratio was analyzed to present how the research results may
be used to solve an actual design problem.
The results from the optimization study indicate that the jet ejector efficiency
improves significantly compared to a conventional jet-ejector design. In cases with a
subsonic motive velocity, the efficiency of the jet ejector is greater than 90%. A high
compression ratio can be achieved with a large nozzle diameter ratio. Dimensionless
group analysis reveals that the research results are valid for any fluid, operating pressure,
and geometric scale for a given motive-stream Mach number and Reynolds ratio
between the motive and propelled streams. For a given Reynolds ratio and motivestream
Mach number, the dimensionless outlet pressure and throat pressure are
expressed as Cp and Cpm, respectively.
A multi-stage jet ejector system with a total 1.2 compression ratio was analyzed
based on the optimization results. The result indicates that the system requires a lot of
high-pressure motive steam, which is uneconomic. A high-efficiency jet ejector with
mixing vanes is proposed to reduce the motive-steam consumption and is recommended
for further study.
|
|---|
