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Mass imbalance in Volume of Fluid

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Old   August 17, 2023, 05:34
Default Mass imbalance in Volume of Fluid
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Sumit Sharma
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I am trying to simulate evaporation in a plate heat exchanger using the Volume of Fluid model and the LEE model for phase change. As the LEE model is empirical, we must specify the evaporation and condensation frequencies. When the frequencies are low (default 0.1), the solution and mass imbalance converge. However, on increasing the frequencies to higher orders, I encounter reversed flow, and the mass imbalance takes a severe hit and keeps oscillating. I have tried improving the mesh quality near the outlet and extending the outlet sufficiently, but nothing seems to work. Following are the boundary conditions and setup

General:
Steady-state, pressure-based solver, gravity

Multiphase:
VOF, implicit, 2 phase, Surface tension modelling, Evap/Cond (Tsat)

Boundary Conditions:
Operating Pressure (Psat)
Inlet: Mass Flux (G_liq and G_vap at Tsat)
Outlet: Pressure outlet (Psat), vapor Backflow volume fraction = 0
Wall_Thermal: heat flux
Wall_Momentum: No slip, contact angle for wall adhesion 1 (highly wetting fluid)

I start by solving the single-phase flow and then use the flow profile for the multiphase simulation. I keep the URFs low initially and increase them gradually.

Any suggestions will be highly appreciated. Thanks in advance.
-SS
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evaporation condensation, mass balance, multiphase flow, reversed flow., volume of fluid.

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