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Research Papers

Frictional and Internal Leakage Losses in Rotary-Vane Two-Phase Refrigerating Expanders

[+] Author and Article Information
Ahmad M. Mahmoud, W. E. Lear

Department of Mechanical and Aerospace Engineering, University of Florida, P.O. Box 116300, Gainesville, FL 32611-6300

S. A. Sherif

Department of Mechanical and Aerospace Engineering, University of Florida, P.O. Box 116300, Gainesville, FL 32611-6300sasherif@ufl.edu

J. Energy Resour. Technol 132(2), 021007 (Jun 11, 2010) (10 pages) doi:10.1115/1.4001571 History: Received February 25, 2009; Revised April 08, 2010; Published June 11, 2010; Online June 11, 2010

Increasing the coefficient of performance of a vapor compression refrigeration system may be realized by utilizing work recovering expansion devices that additionally lower the enthalpy of the refrigerant at the inlet of the evaporator. Depending on the operational and geometrical parameters of the expander, laminar and viscous two-phase leakage flows within the expander may be present. Single-phase leakage models available in the literature must then be modified or rederived accordingly. A dynamic frictional model for the expander must also be developed for ideal operation (i.e., no internal leakage) and modified to account for internal leakage accordingly. This paper presents a comprehensive component-level model of inherent friction and internal leakage losses in a two-phase circular rotary-vane expander used in a vapor compression refrigeration system. The model establishes the performance of the expander as a function of geometric and fluid parameters. Accurate modeling and prediction of frictional and internal leakage losses is vital to being able to accurately estimate the efficiency, rotational speed, and the torque and power produced by the expander. Directions for future work are also discussed.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of nomenclature used and leakage paths of a circular rotary-vane expander with general orientation and (a) conventional or (b) modified intake ports

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Figure 2

Schematic of a typical leakage path used in this study

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Figure 3

Shear and pressure driven Couette flow

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Figure 4

Free-body diagram of a vane protruding outward from a rotor slot at a local angle θ

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Figure 5

Schematic of generalized Couette flow in the axial gap between rotor and end-plate

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Figure 6

Variation of reaction forces on a vane with no vane-tip curvature as a function of angular displacement

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Figure 7

Variation of reaction forces on a vane with a circular vane-tip profile as a function of angular displacement

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Figure 8

Variation of leakage from/to the expander cavity as a function of angular displacement due to nonaxisymmetric flow between the rotor and stationary end-plates for different intake angle spreads

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Figure 9

Variation of nonaxisymmetric leakage from/to the expander cavity for the ideal and throttling cases

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Figure 10

Variation of leakage from/to the expander cavity through the gap between the sides of the vanes and end-plates for different intake angle spreads

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Figure 11

Variation of leakage to the expander cavity from the rotor slot (modified intake) through the gap between the face of the vanes and rotor slot

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Figure 12

Variation of the ideal and actual mass flow-rates through the expander as a function of rotational speed

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Figure 13

Variation of the ideal and actual mass flow-rates through the expander as a function of the number of vanes

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