|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
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.
|Publisher:||Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
|Series/Report:||Air Conditioning and Refrigeration Center TR-98
|Sponsor:||Air Conditioning and Refrigeration Project 48
|Date Available in IDEALS:||2009-04-22
|Identifier in Online Catalog:||4011950