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Viscous resistance coefficients in porous medium

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Old   July 29, 2013, 12:20
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Hi
you're welcome. Yes, my main focus is porous media in PEM fuel cell, and catalytic reactions.
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Old   July 29, 2013, 12:33
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Hi
you're welcome. Yes, my main focus is porous media in PEM fuel cell, and catalytic reactions.
Hi,

Please have a look on my problem and if you have any comment, please let me know.I am trying to model a 2D porous zone filled with sand placed above a perforated pipe and water will pass through it. I faced a weird problem. When I active multiphase flow, input button for rotation axis direction,inertial resistance and viscous resistance simply disappears!! only porosity parameter remains active. I tried with 3D also, same case happened. But I need to model multiphase flow.

Then I have found something. I have to define porosity from mixture phase. And for which zone I defined porosity, I can assign viscous and inertia resistance for that phase which I assigned in porous zone. For example, I named one zone as water. I defined water zone as porous zone from mixture phase, then I can assign other permeable parameter for water zone by selecting phase-2 ( I assigned water as phase 2). Is this the way to define porous parameter in two phase flow?


Could you please suggest the solution methods and ranges for porous media modeling in two phase flow. I am just lost. I am using PISO right now.


Thank you very much in advance
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Old   July 29, 2013, 17:10
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Hi,

Please have a look on my problem and if you have any comment, please let me know.I am trying to model a 2D porous zone filled with sand placed above a perforated pipe and water will pass through it. I faced a weird problem. When I active multiphase flow, input button for rotation axis direction,inertial resistance and viscous resistance simply disappears!! only porosity parameter remains active. I tried with 3D also, same case happened. But I need to model multiphase flow.

Then I have found something. I have to define porosity from mixture phase. And for which zone I defined porosity, I can assign viscous and inertia resistance for that phase which I assigned in porous zone. For example, I named one zone as water. I defined water zone as porous zone from mixture phase, then I can assign other permeable parameter for water zone by selecting phase-2 ( I assigned water as phase 2). Is this the way to define porous parameter in two phase flow?


Could you please suggest the solution methods and ranges for porous media modeling in two phase flow. I am just lost. I am using PISO right now.


Thank you very much in advance

First, let me ask you something. Why do you insist on using multiphase model for your problem, if you consider the filled sand zone as porous media? As you know, porous media considers as fluid not solid! So, I don't see any necessity using multiphase model, as long as there's no further complexity in your model. But, it's hard to make any more comment. Please give me an image of the model, if you would.
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Old   July 29, 2013, 22:20
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First, let me ask you something. Why do you insist on using multiphase model for your problem, if you consider the filled sand zone as porous media? As you know, porous media considers as fluid not solid! So, I don't see any necessity using multiphase model, as long as there's no further complexity in your model. But, it's hard to make any more comment. Please give me an image of the model, if you would.
Hi,

Please find the image attached herewith.

This is my model. Upper red portion is porous zone which I consider filled with sand. For doing this, I used porosity of sand and inertial and viscous resistance of sand. I want to model in such way that porous zone is filled with water also and it will flow towards the lower pipe ( Pink pipe) and water will enter the red zone continuously from the inlet ( topmost line) so that water height remain constant. Since pink pipe is initially filled with air and water will go through it, so I used VOF model(considering the immiscible fluid). In between red and pink box, i used - - - - line as perforated pipe. I didn't use any BC here, except "-" as wall. ( Actually I am not sure whether I have to use porous jump BC here or since I allowed opening, it will works as perforated pipe automatically). I don't know the inlet velocity, so I used pressure inlet.


Please correct me if I am doing something wrong. Thanks in advance.
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Old   July 31, 2013, 04:34
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Sorry for late
Is perforated area part of porous zone or it is a separate zone? Why did you consider the perforated area? Maybe you need to eliminate this zone. Anyway, if the perforated area is part of model, I don't think that a porous jump B.C should be used for this, because it's not a very thin porous media but a perforated area and these two are quite different. One more thing and the foremost, instead of using a pressure in inlet, use mass flow rate. Keep in mind that adjust "Direction specification method " option to " Normal to boundary" . It's important. Is the upper line of porous zone the inlet boundary? If so, maybe you should extend the model and add an inlet boundary as well. This is what I understand from the image.
I hope it helps.
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Old   July 31, 2013, 04:35
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Originally Posted by Tanjina View Post
Hi,

Please find the image attached herewith.

This is my model. Upper red portion is porous zone which I consider filled with sand. For doing this, I used porosity of sand and inertial and viscous resistance of sand. I want to model in such way that porous zone is filled with water also and it will flow towards the lower pipe ( Pink pipe) and water will enter the red zone continuously from the inlet ( topmost line) so that water height remain constant. Since pink pipe is initially filled with air and water will go through it, so I used VOF model(considering the immiscible fluid). In between red and pink box, i used - - - - line as perforated pipe. I didn't use any BC here, except "-" as wall. ( Actually I am not sure whether I have to use porous jump BC here or since I allowed opening, it will works as perforated pipe automatically). I don't know the inlet velocity, so I used pressure inlet.


Please correct me if I am doing something wrong. Thanks in advance.
Sorry for late
Is perforated area part of porous zone or it is a separate zone? Why did you consider the perforated area? Maybe you need to eliminate this zone. Anyway, if the perforated area is part of model, I don't think that a porous jump B.C should be used for this, because it's not a very thin porous media but a perforated area and these two are quite different. One more thing and the foremost, instead of using a pressure in inlet, use mass flow rate. Keep in mind that adjust "Direction specification method " option to " Normal to boundary" . It's important. Is the upper line of porous zone the inlet boundary? If so, maybe you should extend the model and add an inlet boundary as well. This is what I understand from the image.
I hope it helps.
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Old   July 31, 2013, 09:56
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Sorry for late
Is perforated area part of porous zone or it is a separate zone? Why did you consider the perforated area? Maybe you need to eliminate this zone. Anyway, if the perforated area is part of model, I don't think that a porous jump B.C should be used for this, because it's not a very thin porous media but a perforated area and these two are quite different. One more thing and the foremost, instead of using a pressure in inlet, use mass flow rate. Keep in mind that adjust "Direction specification method " option to " Normal to boundary" . It's important. Is the upper line of porous zone the inlet boundary? If so, maybe you should extend the model and add an inlet boundary as well. This is what I understand from the image.
I hope it helps.

Hello. thanks for your reply.

1)Actually it's not a perforated area, just a line by which I wanted to represent the upper surface of a perforated pipe. Because in my model, we assume only upper surface of the pipe is perforated. Now I ask the question again, should I use porous jump BC or this line will work as a perforated pipe automatically? After running the model, there was flow through this perforated line. Please see the attached image which shows the flow after 2.37 sec.

2)What is the advantages of mass flow inlet against the pressure inlet ?

3)Yup, upper line of the porous zone is inlet boundary. I didn't understand your last suggestion. Could you be a little bit more specific that what do you mean by extend the model and add an inlet boundary though there is a inlet already exists?

Thanks a lot again. Any suggestions will be really appreciated.
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Old   August 1, 2013, 16:08
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Originally Posted by Tanjina View Post
Hello. thanks for your reply.

1)Actually it's not a perforated area, just a line by which I wanted to represent the upper surface of a perforated pipe. Because in my model, we assume only upper surface of the pipe is perforated. Now I ask the question again, should I use porous jump BC or this line will work as a perforated pipe automatically? After running the model, there was flow through this perforated line. Please see the attached image which shows the flow after 2.37 sec.

2)What is the advantages of mass flow inlet against the pressure inlet ?

3)Yup, upper line of the porous zone is inlet boundary. I didn't understand your last suggestion. Could you be a little bit more specific that what do you mean by extend the model and add an inlet boundary though there is a inlet already exists?

Thanks a lot again. Any suggestions will be really appreciated.
Hello again
Well, as I told you before, it seems that there's no need to use porous jump B.C. Respecting to mass flow rate, I think it doesn't make sense to use pressure B.C in inlet. If so, how do you inject the water into system? Do you patch it? From the image, it seems that you use a pressure outlet B.C for outlet as well. As far as I understand, a flow of water flows on the top surface of the system (porous zone). Right? Here, you should use mass flow B.C. By saying " extend your model" I meant that you add an inlet to the model and it helps the physics of the model a bit more sensible. But, it's up to you to decide. By the way, the solution is not converged yet. But I guess the problem is due to inappropriate choose of boundary condition.
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Old   August 1, 2013, 17:24
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Hello again
Well, as I told you before, it seems that there's no need to use porous jump B.C. Respecting to mass flow rate, I think it doesn't make sense to use pressure B.C in inlet. If so, how do you inject the water into system? Do you patch it? From the image, it seems that you use a pressure outlet B.C for outlet as well. As far as I understand, a flow of water flows on the top surface of the system (porous zone). Right? Here, you should use mass flow B.C. By saying " extend your model" I meant that you add an inlet to the model and it helps the physics of the model a bit more sensible. But, it's up to you to decide. By the way, the solution is not converged yet. But I guess the problem is due to inappropriate choose of boundary condition.
Hi,

Thanks for your reply.

1) Yup, there is flow of water on the top of surface. I wanted to keep the water height remain constant although the time. So I put 1 in pressure inlet as water -liquid volume fraction. Is it possible to select the mass flow inlet, if I don't know the mass flow rate ? And if I want to remain the water height constant what should I do for mass flow inlet ? Please enlighten me.

2) I patched 'water" in porous zone. And yes, I used pressure outlet.

3) Where should I use another inlet? what will the the BC there? Should I use inlet at the end of porous zone ?

4)So you are saying that perforated pipe defining is ok with my - - - - - - wall? It will work as perforated pipe?

5) for my existing model( I send the image in earlier message), mass flow rate in outlet is showing -250~-350 kg/s. Is it due to wrong BC ?


Please help me by giving any suggestions. I am stuck here for long time.
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Old   August 11, 2013, 14:04
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Hi,

Thanks for your reply.

1) Yup, there is flow of water on the top of surface. I wanted to keep the water height remain constant although the time. So I put 1 in pressure inlet as water -liquid volume fraction. Is it possible to select the mass flow inlet, if I don't know the mass flow rate ? And if I want to remain the water height constant what should I do for mass flow inlet ? Please enlighten me.

2) I patched 'water" in porous zone. And yes, I used pressure outlet.

3) Where should I use another inlet? what will the the BC there? Should I use inlet at the end of porous zone ?

4)So you are saying that perforated pipe defining is ok with my - - - - - - wall? It will work as perforated pipe?

5) for my existing model( I send the image in earlier message), mass flow rate in outlet is showing -250~-350 kg/s. Is it due to wrong BC ?


Please help me by giving any suggestions. I am stuck here for long time.
Hello again
I'm terribly sorry for the late. I'm too busy and I need to focus on my works. The perforated model is OK and I rant into a model in Fluent specifically defined for perforated model. The model calculates the pressure drop cross the plate. Have a deep look at conditions in porous media in Fluent theory guide. Do have the velocity of the flow? If yes, you can get the mass flow by multiply it by flow density and cross area of the flow.
If you are interest, send the model to me and I will have a look at it.
Good luck
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Old   September 14, 2013, 06:17
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hello guys ,

I have trouble finding the alpha and beta values for modelling plasma (blood ) flow through a porous media which acts as the filter. All i have is the porosoity report and material properties.
Is it possible to calculate the inertial and viscous co-efficients ?
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Old   July 15, 2014, 18:15
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i am working with oily water separation using ceramic membrane
i drew the geometry and mesh and i am stuck on modeling flow through porous media using oily water which has a lot of contaminants
please help me if you have any examples of how to do it and i can see an example that would help
i would appreciate any help
thanks so much
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Old   March 24, 2015, 11:29
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Hello,

I am working on CFD analysis of humidifier. In this two fluids (Air and water) are mixing and the heat and mass transfer will takes place. Water and air are in counter flow. Also at the middle portion of humidifier I have porous media.I am using Ansys-CFX for the simulation. Please help me for this, I don't know how to solve the multiphase problem with porous media in CFX.

Do anyone have idea about this? how to do the analysis of this in ANSYS-CFX?

Thanks in advance....
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Old   July 3, 2015, 07:13
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The viscous and inertial resistances to flow in a porous medium can be calculated from the Ergun equation, which gives the total pressure drop through a porous medium.
Check any book on fluid mechanics for the Ergun equation
Total pressure drop = Viscous loss + inertial loss

dp/dl = [150*mu*(1-e)^2/phi^2*D^2*e^3]*v + [1.75*rho*(1-e)/phi*D*e^3]*v^2

The first term is the viscous loss (proportional to velocity) and the second term is the inertial loss (proportional to velocity squared).

Compare this to the Fluent's expression for momentum sink:

dp/dl = Rv*mu*v + (Ri/2)*rho*v^2

This gives the values for Rv and Ri,


Rv = [150*(1-e)^2/phi^2*D^2*e^3]


Ri = [2*1.75*(1-e)/phi*D*e^3]


Nomenclature:
Rv: Viscous resistance
Ri: Inertial resistance
mu: Viscosity
rho: Density
e: Porosity of the medium
phi: Sphericity of the particles making the medium (can assume 0.75)
D: Diameter of particles making the medium
v: Average velocity

Thanks for the wonderful info

I completed an experiment where porous material length increases along the height with time. To start with Zero Length porosity but as time passes, part of the material solidifies and becomes Porous.

Average porosity is 11%. Any idea how to I calculated parameters for Fluent ? There is no specific porosity hole size(diameter). It is Zigzag but I have experimental pressure drop results across the two faces.

Thanks in advance.

Shane
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Old   November 21, 2015, 08:30
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I appreciate your answer but how do I get different values of Ri & Rv in different directions using given formulae?
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Old   November 21, 2015, 16:51
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I appreciate your answer but how do I get different values of Ri & Rv in different directions using given formulae?
I think Ri and Rv in different directions you can get only in experiment, i think =)

But i have other problem. I have a cylindrical sample with a diameter of 50 mm and a thickness of 3 mm. Porosity 0.3. According to calculation Rv = 7*10^11 and Ri = 4*10^6. For dP = 5.9 kPa i have Q = 0.008 m3/min. BUT in Fluent a have 0.00037 kg/sec -> 0.018 m3/min. 0.018 is not 0.008 !!!!

Whats happend?
22-11-2015 1-38-06.jpg
22-11-2015 1-50-11.jpg

Can you help me? thx a lot!
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Old   December 20, 2015, 05:08
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Anybody helped me?
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Old   January 5, 2016, 11:44
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hi everybody! I've some problem setting the viscous resistance too. hope that someone want to help me i'm trying to simulalte the flow through a bundle of fiber, considering the bundle of fiber as an anisotropic porous medium. As the entire bundle is an anular cilynder, I was trying to use the conical/cilyndrical coordinate.
What i have actually is the value of the viscous resistance in axial direction (corresponding for me to 0°), in radial direction (corresponding to 90°) and also in a direction of 30° and 60° . I was wondering if there is something that I can do to iclude this data setting the viscous resistance in the porous zone using fluent.
Using the conical/cilyndrical coordinate system in fluent, I can set three different values of viscous resistance, respectively for : axial, radial, and circumferential direction. the problem is that I don't have the value for the circumferential, and i have more values in more than one angle in the plane given by radial and axial direction. hope I've been clear.
thanks a lot!!!!!
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Old   January 6, 2016, 16:21
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Hi There,

Today is my first day here in this web site. I am also rather new to porous medium, did some tutorials and read text, but cannot figure out how I can do my task. Maybe you can help me?
I have a porous cylinder. The cylinder is filled with gas. Outside the cylinder is gas also and the pressure for both gas inside and outside the cylinder is same at 2180 psi. As time passes, the outside pressure is reduced from 2180 to atmospheric pressure with time e.g. 10 hours. I want to know how the pressure inside the porous cylinder changes with time? I think I need inlet. How can I put inlet for this application?
As petroleum engineer, I know porosity, permeability, but do not know how to convert them to what fluent wants (porous cylinder permeability=0.016 milli darcy and porosity=2%)? Can someone tell me what I should do? I appreciate your replies. You can also email me with rahman.ashena.313@gmail.com.
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Old   January 7, 2016, 06:04
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Dear Whoever Can Help


As a petroleum engineer, I have a porous cylindrical rock saturated with gas under pressure 2185 psi. Outside the cylinder is gas with the same pressure at time zero. As time passes, the pressure outside the cylinder is reducing with time. I wanna see how the pressure inside changes. Where should I put the inlet and outlet surfaces? The outlet surface should look like a cylindrical layer around the cylinder? The How can I convert porosity 2% and permeability 0.016 Milli Darcy to fluent?
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