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ACRC Technical Report 98PDF


Title:Modeling of Two-Phase Flows in Horizontal Tubes
Author(s):Vij, A.K.; Dunn, W.E.
Subject(s):microchannel condenser tubes
Abstract:This work focusses on the modeling of two-phase flows in horizontal, constant-crosssection tubes by a two-fluid approach. The objectives are to develope a framework for two-fluid modeling, to highlight issues related to two-phase phenomena and to implement the model on a computer. The two-fluid equations are derived from the basic conservation laws for mass, momentum and energy by assuming a steady state and averaging the conservation laws over the cross-section plane of the tube. It is shown that the integration of the two-fluid equations along the axial direction of the tube requires models for the distribution of the liquid and vapor in the cross-section plane of the tube, as well as models for the transport of heat, mass and momentum at the boundaries of each phase. Several phenomena are identified that affect the liquid-vapor distribution by causing wetting of the tube wall. Mechanistic models are proposed for these phenomena and several dimensionless groups are derived by nondimensionalizing the governing equations for each model. Models are proposed for the calculation of shear stresses at the wall using a single-phase friction factor approach. The interfacial shear stress is considered to be significantly greater than the shear stress at the wall due to the dissipative effect of wave generation and decay. The effect of condensation on interfacial friction is also condsidered. Heat fluxes from each phase into the wall and into the interface are modeled by a singlephase heat transfer coefficient approach. Two approaches are suggested for determining the mass transfer flux at the interface. One of these assumes a temperature jump at the interface and employs the kinetic theory of gases. The other approach utilizes the difference between the liquid and vapor heat fluxes at the interface to determine the mass transfer rate. A computer program was developed to solve the two-fluid model numerically. The use of this program is illustrated by solving a condensing-flow problem.
Issue Date:1996-05
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-98
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 48
Date Available in IDEALS:2009-04-22
Identifier in Online Catalog:4011950

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