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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Different Approaches to FVM Method Fluid Flow and Heat Transfer Simulation Inside Thermosyphon

Get access (open in a dialog) DOI: 10.1615/IHTC15.cpm.009302
pages 1721-1735

摘要

Different approaches to numerical simulation of vertical two phase closed thermosyphon are presented. Various Finite Volume Method models are cosidered – from simplified one phase to two phase with interface tracking/reconstruction algorithms. They are implemented using popular, commercial CFD code – ANSYS FLUENT. One phase simplified model considers only vapor flow without liquid phase (or with assumption of very thin liquid layer that can be ignored in problem formulation). Phase change processes are approximated by vapor mass sources (positive for evaporation, and negative for condensation). Magnitude of mass sources can be obtained by use of different source term correlations. Difference in two phase models lies in numerical method of solving Navier-Stokes equations – treating both phases as inter-penetrating (Eulerian-Eulerian) or distinct with sharp interface (VOF method). One phase simplified model is the most computationally inexpensive, but least physical and have to be supported by empirical correlations. Numerical problems are also present - e. g. with solving closed domain absolute pressure change caused by net mass source terms inequality (pressure change by increase of vapor mass inside thermosyphon). Two-phase methods are more physical, although expensive. VOF and Eulerian-Eulerian deal with two-phase flow, but rate of evaporation/condensation needs to be specified to match experimental data, most often by setting vaporization/condensation frequency coefficient (Lee model). Every model is analyzed and compared to others in terms of physical validity, implementation difficulties, solution time and convergence.