Watanawanavet, Somsak (2006-05). Optimization of a high-efficiency jet ejector by computational fluid dynamic software. Master's Thesis. Thesis uri icon

abstract

  • 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.

publication date

  • May 2006