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March 30, 2017, 15:23 |
Evaporative phase change modeling in FLUENT
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#1 |
New Member
Join Date: Jun 2016
Posts: 17
Rep Power: 10 |
Hi all,
I am working on a micro scale simulation of evaporation inside a porous structure, using ANSYS FLUENT. It is a transient two phase model (VOF) considering water and vapor inside a micro scale pore. I am using UDF codes to apply the source terms relative to the mass transfer according to Schrage's model formulation. The results that I get seem to be logical, but my problem is that the time steps that I have to use are very small ( in the order of ~1e-9 s), which make it impossible to reach convergence. Every time I increase the time step, I face the error that the "Global Courant number is greater than 250.00. The velocity field is diverging. check the solution and reduce the time step". I really appreciate it if you have any suggestions or solutions for this problem or you have any recommendations for me to increase the time steps to more realistic values. |
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March 31, 2017, 05:36 |
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#2 |
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May 12, 2017, 00:39 |
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#3 | |
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Hao su
Join Date: May 2017
Posts: 4
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Quote:
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May 12, 2017, 07:53 |
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#4 |
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David Chou
Join Date: Nov 2015
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Courant number = v*dt/dx
if C is huge enough to lead to divergence, decrease dt or increase dx hope this will help |
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May 13, 2017, 02:43 |
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#5 |
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Hao su
Join Date: May 2017
Posts: 4
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thanks for your reply. the problem is that i drcrease the time step size ,but the problem also appear. i think the problem may be caused by the surface tension
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July 4, 2017, 02:44 |
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#6 | |
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Quote:
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January 23, 2019, 02:22 |
UDF evaporation, standard state enthalpy specification?
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#7 | |
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vidyadhar
Join Date: Jul 2016
Posts: 138
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Quote:
Hello Kimia, I have also written an UDF to simulate evaporation. The UDF can be found in the link below: UDF with VOF method to predict evaporation mass/heat flux at vapor-liquid interface But, I am also facing similar problems: 1) The interface is moving but faster than predicted by analytical solution of Stefan problem. 2) For large time steps, I am also facing divergence problems. I request you to go through the above link and kindly let me know if there is any mistake in the UDF. Also, how to specify the Standard state enthalpy(J/kgmol) values in Fluent so that required Latent heat(J/kg) is accomplished. Can I specify any values of standard state enthalpy such that the difference (in values between the two phases) divided by molecular weight of liquid or vapor gives the desired latent heat? Thanks in advance! vidyadhar Last edited by vidyadhar; January 23, 2019 at 02:23. Reason: text added |
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May 26, 2020, 01:19 |
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#8 |
New Member
Zicheng Li
Join Date: Dec 2019
Posts: 8
Rep Power: 6 |
Can you upload your file and study it together?
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Tags |
courant number, evaporation, phase change, timestep, transient 2d |
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