Browsing by Author "Menegay, Peter"

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    A Computational Model for Two-Phase Ejector Flow
    Menegay, Peter (Virginia Tech, 1997-01-29)
    A CFD model to simulate two-phase flow in refrigerant ejectors is described. This work is part of an effort to develop the ejector expansion refrigeration cycle, a device which increases performance of a standard vapor compression cycle by replacing the throttling valve with a work-producing ejector. Experimental results have confirmed the performance benefit of the ejector cycle, but significant improvement can be obtained by optimally designing the ejector. The poorly understood two-phase, non-equilibrium flow occuring in the ejector complicates this task. The CFD code is based on a parabolic two-fluid model. The applicable two-phase flow conservation equations are presented. Also described are the interfacial interaction terms, important in modelling non-equilibrium effects. Other features of the code, such as a mixing length turbulence model and wall function approximation, are discussed. Discretization of the equations by the control volume method and organization of the computer program is described. Code results are shown and compared to experimental data. It is shown that experimental pressure rise through the mixing section matches well against code results. Variable parameters in the code, such as droplet diameter and turbulence constants, are shown to have a large influence on the results. Results are shown in which an unexpected problem, separation in the mixing section, occurs. Also described is the distribution of liquid across the mixing section, which matches qualitative experimental observations. From these results, conclusions regarding ejector design and two-phase CFD modelling are drawn.
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    Experimental investigation of an ejector as a refrigerant expansion engine
    Menegay, Peter (Virginia Tech, 1991)
    The use of an ejector to improve the performance of a vapor compression refrigeration system was investigated. The ejector harnesses kinetic energy developed during the throttling process and returns it to the compressor in the form of a pressure boost. An ejector was designed taking into account the expected nonequilibrium behavior in the motive nozzle, and assuming equilibrium conditions in the other components. A standard vapor compression system using R-12 was modified to test the ejector. Included in the resulting ejector cycle was a hot gas bypass arrangement which was found to effectively control the condenser and evaporator flowrate. Hot gas bypass was used instead of a throttling valve, which would have undermined the benefit of the ejector. Experiments were conducted by running the ejector cycle at varying amounts of hot gas bypass flow. Performance results for the ejector and the overall cycle were obtained which showed that while the ejector recovered some of the kinetic energy of the expansion process, its design needed optimization. Recommendations were made for a more in-depth study of the ejector cycle.
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    Method of reducing flow metastability in an ejector nozzle
    (United States Patent and Trademark Office, 1994-09-06)
    A method of reducing flow metastability in a liquid refrigerant in an ejector nozzle by generating dispersed bubbles in the flow entering the nozzle by first forming relatively large bubbles and then breaking them down into small finely dispersed bubbles, so as to reduce the density of the flowing mixture and provide nucleation sites allowing control of flow rate and causing the mixture to expand in substantial thermodynamic equilibrium with maximum nozzle velocity.