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ACRC Technical Report 129PDF


Title:Modeling of the Evaporation and Condensation of Zeotropic Refrigerant Mixtures in Horizontal Annular Flow
Author(s):Hurlburt, E.T.
Contributor(s):Newell, T.A.
Subject(s):two-phase modeling
annular flow regimes
stratified flow regimes
Abstract:Zeotropic refrigerant mixtures are of interest to the air-conditioning and refrigeration industry. In experiments on evaporators and condensers using zeotropic mixtures, heat transfer has been observed to be less than the ideal limit. The cause of this heat transfer reduction is explored in this work. In the experimental work, an optical technique for determining properties in liquid film flows is developed. The technique makes use of the total internal reflection at a liquid-vapor interface to determine the liquid film thickness and wave velocity in thin films. In the theoretical work, a circumferential film thickness model is developed based on work by Laurinat. Laurinat's momentum analysis is simplified to a balance between the normal Reynolds' stress in the circumferential direction and the circumferential component of the weight of the film. A model for the normal Reynolds' stress in the circumferential direction is proposed. A circumferential symmetry correlation is used to close the model. Using the circumferential film thickness model, a model for the evaporation and condensation of zeotropic refrigerant mixtures in horizontal annular flow is developed. Mass and energy are tracked locally to predict circumferential and axial composition and temperature gradients in the liquid film. Local heat transfer coefficients are determined using a resistance network in the liquid film. Model predictions include local wall temperature, pressure drop, local heat transfer coefficients, and local composition during evaporation and condensation. The model demonstrates the mechanisms which cause circumferential and axial composition and temperature gradients in the liquid film when zeotropic mixtures undergo evaporation and condensation. Heat transfer in mixtures is shown to be less than the ideal limit due to mass transfer resistance in the vapor. The mass transfer resistance causes bulk temperatures to differ from equilibrium bulk temperatures thus decreasing the temperature difference which drives heat transfer.
Issue Date:1997-08
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-129
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 45
Date Available in IDEALS:2009-04-29
Identifier in Online Catalog:4224060

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