Mass Transfer & VOF
I'm trying to solve a condensation problem. To do this, I use the VOF model and have written a complex condensation model. There are several problems:
- 1) The Absolute Pressure drops BELOW zero.
This should not be possible ofcourse. My operating pressure is 4 bar abs.
- 2) The mass transfer works not like it should:
I've tested this with a very simple condensation model (UDF):
from species = water.
to species = steam.
DEFINE_MASS_TRANSFER(Condensation,cell,mix,from_in dex, from_species_index, to_index, to_species_index)
Thread *gas = THREAD_SUB_THREAD(mix, from_index);
Thread *liq = THREAD_SUB_THREAD(mix, to_index);
real T_sat = 406;
m_lg = 5000;
This means that if the cell temperature exceeds the saturisation temperature, evaporation should occur. Otherwhise evaporation occurs.
But if I solve the problem (unsteady) this is not the case. In my simulation, at one place the mass transfer is 5000 kg/(m3-s) from water to steam. This is true indeed if I look to the temperatures, but if I look to the phase, the opposite occurs (condensation instead of evaporation).
I use the explicit VOF sceme, no turbulence models, energy equation. Unsteady with dt=1e-6 sec.
p-v coupling: coupled
VOF : modified HIRC
Please, can anyone help me??
Thanks in advance!
R Liew, Technical University of Eindhoven
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