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Moisture Transfer

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Old   December 6, 2020, 21:45
Default Moisture Transfer
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Abbas Raza
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I am writing a udf for a defining moisture from Air to Lcl solution. In between two fluid, a membrane(solid) is inserted, Now, I want to define mass fraction just above the membrane first layer of cells. Can any one help me in this matter?
#include "udf.h"
#define Xm 0.0032
{
DEFINE_PROFILE(mass_x_inlet, thread, face)
Thread *t;
face_t f:
cell_t c:
{
begin_f_loop(f,thread)
F_CENTROID(x,f,thread)
}
This is not a complete udf.

This loop will be used for all cell faces in the boundary zone. I just want to specify first layer above the membrane. with what command I can do it?
Seniors please help me.
Thanks in advance.
Regards,
Abbas Raza
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Old   December 7, 2020, 00:10
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Why in the first layer of cells?

Why don't you use the faces of the membrane, with a normal boundary condition?
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Old   December 7, 2020, 00:50
Default Moisture Transfer across membrane
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Quote:
Originally Posted by pakk View Post
Why in the first layer of cells?

Why don't you use the faces of the membrane, with a normal boundary condition?
Actually, I need to make moisture content across the membrane. How I can give command in udf that moisture content in above the cell of membrane.

If i induce moisture at inlet, How I would be able to know that moisture content is just above the cells of membrane? In short, How cell to cell moisture can be modelled with what command?

Thanks in advance.

Regards,
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Old   December 7, 2020, 01:44
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I'm not talking about setting the moisture on the inlet. I'm talking about setting the moisture on the faces of the membrane.
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Old   December 7, 2020, 01:50
Default Moisture Transfer across membrane
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Quote:
Originally Posted by pakk View Post
I'm not talking about setting the moisture on the inlet. I'm talking about setting the moisture on the faces of the membrane.
I was asked by group leader to do so. I am beginner in this field. I need your suggestion how to do this? If I use cell approach what will be consequence? And using face of membrane will be easier?

Thanks in advance!

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Old   December 7, 2020, 04:47
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Quote:
Originally Posted by Abbas20000220 View Post
I was asked by group leader to do so. I am beginner in this field. I need your suggestion how to do this? If I use cell approach what will be consequence? And using face of membrane will be easier?

Thanks in advance!

Regards,
If you use face approach, you just go to the boundary equation in Fluent, and set the "moisture content" to the value that you want, if you want a fixed value. (I don't know how you plan to model moisture content, but it can be a UDM, it can be with species, it does not matter: just set the value that you want.)
if you don't want a fixed value, but want to use an equation, then you need a UDF.

If you use cell approach, you have to use UDF, you might run into stability problems, you might get a big mesh-dependency, you have to write something that only finds cells directly touching the membrane, and in general you make your life complicated for no reason.
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Old   December 8, 2020, 02:27
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Quote:
Originally Posted by pakk View Post
If you use face approach, you just go to the boundary equation in Fluent, and set the "moisture content" to the value that you want, if you want a fixed value. (I don't know how you plan to model moisture content, but it can be a UDM, it can be with species, it does not matter: just set the value that you want.)
if you don't want a fixed value, but want to use an equation, then you need a UDF.

If you use cell approach, you have to use UDF, you might run into stability problems, you might get a big mesh-dependency, you have to write something that only finds cells directly touching the membrane, and in general you make your life complicated for no reason.
Thankyou very much for your response.

I have another query.

I have two fluids. one is Air & other is Licl solution. & I want to insert a PVDF membrane between two. I modelled platein XYplane ( Length, width =100mm) & thickness 2mm in zaxis using extrude option. I select another plane having offset from zaxis 2mm.& draw another plate of having same dimensions. One is modelled as air while other is Licl. Both of them are stacking to each other. In mesh option, I deleted contact region (that automatically made) & named all regions manually like (inlet, outlet, airinterface, liclinterface etc) & meshed by using default method.

In Fluent setup, I used mesh interface, & joining airinterface & liclinterface and named the coupled wall as a mmebrane & its shadow is also formed.

After having a simulation, I am getting a message: Zone surface cannot create from sliding interface zone. creating empty surface zone.

looking forward your kind response for settling the issue.
I used in ansys16 & 20. both have same issue.

Thanks in advance.

Regards
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Old   December 9, 2020, 02:20
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read log file on the second picture, I can see, you have an error on line 38 of your UDF
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Old   December 9, 2020, 02:34
Default Moisture Transfer
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Quote:
Originally Posted by AlexanderZ View Post
read log file on the second picture, I can see, you have an error on line 38 of your UDF
Thank you for your response.

This was an attempt for interpreting UDF. However, my prime concern is regarding empty surface zone by using mesh interface. For my case, I am trying to consider this interface of both fluids is acting as a membrane. Fluent post processing isn't helping me in this matter.

I want to know that my approach is wrong or i need to do something else?

Thanks in Advance.

Regards,
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