PhD Dissertation submitted to the Faculty of the Virginia Tech in partial fulfillment of the requirements for the degree of
Alan A. Kornhauser, Chair
Douglas J. Nelson
Demetri P. Telionis
William C. Thomas
January 29, 1997
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.
List of attached files
File Name Size (Bytes) appa.pdf 84,014 Bytes appb1.pdf 74,370 Bytes appb2.pdf 90,029 Bytes back.pdf 63,915 Bytes ch1.pdf 105,666 Bytes ch2.pdf 98,247 Bytes ch3.pdf 123,529 Bytes ch4.pdf 149,316 Bytes ch5a.pdf 68,182 Bytes ch5b.pdf 57,618 Bytes ch5c.pdf 219,600 Bytes ch5d.pdf 69,823 Bytes ch5e.pdf 30,194 Bytes ch6.pdf 33,052 Bytes etd.pdf 88,153 Bytes
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