CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > STAR-CCM+

porous inertial resistance

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   August 31, 2009, 06:57
Default porous inertial resistance
  #1
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Hallo,

I want to model an tube bundle heat exchanger. The tube bundles are replaced by a porous media.
My problem is, that the porous inertial resistance is a function of to the fluid velocity.

Is it possible to create a table, where the porous inertial resistance is shown for x,y,z -components with the according velocity?

Star-CCM+ should compute with the porous inertial resistance for the equal velocity from the table.

Lukas
Lukas is offline   Reply With Quote

Old   August 31, 2009, 09:03
Default
  #2
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
Your inertial resistance is in function of your velocity??? OK I have never heard of this but for everything a first time.
When i derive my inertial and viscous factor, i usually have experimental pressure drops vs volume flow rates. Convert these in a plot where you have velocity on the X axis and pressure loss at the Y axis, then use excel or matlab to derive this 2nd degree polyline. Convert according to porous media expression and voila you have your inertial and viscous resistance.

dp/dl=Av2+Bv
use A and B to find inertial and viscous


If now these factors are again dependant of velocity, this would mean a third degree polyline, just derive 3rd degree factors and make sure to use the correct ones to form your inertial and viscous terms.
bramv101 is offline   Reply With Quote

Old   August 31, 2009, 10:44
Default
  #3
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
I calculated the pressure drop with equations from the VDI heat atlas.
The porous inertial resistance can be calculated like this:

Pi = dp/dl * 1/vē

Is it allowed to remove the porous viscous resistance because of high Re-numbers (Re about 10^5)?

dp is a function of velocity, so Pi is a function of velocity, too?!
Lukas is offline   Reply With Quote

Old   August 31, 2009, 15:45
Default
  #4
Senior Member
 
Aroon
Join Date: Apr 2009
Location: Racine WI
Posts: 148
Rep Power: 8
vishyaroon is on a distinguished road
You can model your inertial (as well as viscous) porous media co-efficient as a function of anything you want (Temp, velocity). Define new Field Function using Tools > Field Function > User Defined Field Function. Name it appropriately and then in Porous Inertial Resistance select Field Function under Method and you can set it to the defined field function.

Hope this helps
vishyaroon is offline   Reply With Quote

Old   September 1, 2009, 04:30
Default
  #5
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Thanks for your answer,

but how I have to declare the field function, that it is according to my table?

Lukas
Lukas is offline   Reply With Quote

Old   September 1, 2009, 09:07
Default
  #6
Senior Member
 
Aroon
Join Date: Apr 2009
Location: Racine WI
Posts: 148
Rep Power: 8
vishyaroon is on a distinguished road
Hello Lukas,

I guess you have a table or a function of Pi = f(V). You can enter this function in the new field function. If you have a table you can always fit a curve and define the new field function based on the defined curve.

Regards
Aroon
vishyaroon is offline   Reply With Quote

Old   September 1, 2009, 09:17
Default
  #7
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Ok,
it sounds plausible, but Iīm not a expert in using Star-CCM+
Can you give me a step by step manual to do that.
I just managed to create a table where the porous inertial resistance is shown for x,y,z -components with the according velocity.
But I canīt combine this table with my field function.

Lukas
Lukas is offline   Reply With Quote

Old   September 2, 2009, 09:21
Default
  #8
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
Visharoon,

I dont think he needs resistance in function of velocity,

Lukas
Pi = dp/dl * 1/vē --> this is your formula, so I have no idea where you get that Pi is in function of v???
Pi is a constant value, the second derative from your 2nd order poly that is dp=f(v)

Last edited by bramv101; September 2, 2009 at 10:30.
bramv101 is offline   Reply With Quote

Old   September 2, 2009, 12:15
Default
  #9
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
The problem is ,that my velocity isnīt constant, so my Pi changes, too.

Lukas
Lukas is offline   Reply With Quote

Old   September 8, 2009, 08:17
Default
  #10
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
Thats the whole idea of a porous media coefficient, your Pi and Pv stay constant while your dp and v change.

for dp/dl=Pi*v^2+Pv*v

--> dl, Pi and Pv remain constant

Just plot your pressure drop (Y axis) and your velocity (X axis) in excel, you will see that this is a perfect 2nd degree polyline.


If you have a Pi dependant on your velocity, that is third degree and this is highly unlikely. Cant imagine such a media....
Inertial = mass*acceleration
bramv101 is offline   Reply With Quote

Old   September 8, 2009, 10:09
Default
  #11
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
This is fact. Iīm aware of this. But the velocity of my fluid, before it permeates the porous media, is between 0 and 2,5 m/s. And for this velocity I have to define my coefficients. If i have a constant velocity before the fluid permeates the porous media, I will have constant coefficients.
Because of the various velocities I want to make the coefficients a function of the velocity.
Lukas is offline   Reply With Quote

Old   September 8, 2009, 10:35
Default
  #12
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
I understand, but when you say that your velocity goes from 0 to 2.5 [m/s]. Do you mean distributed over the face of the porous media? or is varying in time?
Either way, I still can not find a good enough reason to model your resistance values in function of velocity. In terms of physics this doesn't make sense...

Say you can model your dp=f(v) with a third degree poly, what is your goal?
bramv101 is offline   Reply With Quote

Old   September 10, 2009, 06:17
Default
  #13
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Yes, the velocity is distributed over the face of the porous media. Because of this I think, that I will make a failure, if I calculate one coefficient for this different velocities.
Lukas is offline   Reply With Quote

Old   September 10, 2009, 06:46
Default
  #14
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
Unless your velocities range from 0 to 5000 m/s (unlikely), go for 1 constant value.

If your resistance is constant and your velocity fluctuates then your pressure is a direct result of this.
Adapting your resistance to your velocity is like adapting the young modulus of a material to the local force applied -> very wrong

So in porous materials inertial and viscous resistance are material properties, these are inherent to the material itself and therefore a material constant.
If you have experimental pressure drops vs approach velocity for this type of material just use Darcy to derive Pi and Pv
bramv101 is offline   Reply With Quote

Old   September 11, 2009, 04:24
Default
  #15
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
I want to make the coefficients a function of the velocity outside of the porous media, because this velocity isnīt constant.
Lukas is offline   Reply With Quote

Old   September 11, 2009, 05:15
Default
  #16
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
Could you tell me what your case is a representation off:
* filter applications
* geological
* solid/gas/liquid
* ......
bramv101 is offline   Reply With Quote

Old   September 11, 2009, 09:54
Default
  #17
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Ok, I will go for one constant Pi and Pv.
Iīve got a tube bundle heat exchanger with liquid media. The tube bundle should be replaced by a porous media.

If I plot the dp/L (y- axis) and v (x-axis) I got a equation like this:
y= ax^2+ bx +c
a is Pi, b is Pv.

Do I have to respect the coefficient c?
Lukas is offline   Reply With Quote

Old   September 11, 2009, 11:23
Default
  #18
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
you can ignore this c value, usually this is neglible
bramv101 is offline   Reply With Quote

Old   September 11, 2009, 11:24
Default
  #19
New Member
 
Join Date: Aug 2009
Posts: 12
Rep Power: 8
Lukas is on a distinguished road
Ok, I have the solution.
Bramv101, thanks for your help.
Lukas is offline   Reply With Quote

Old   September 11, 2009, 11:24
Default
  #20
Member
 
Bram
Join Date: Apr 2009
Location: Belgium
Posts: 81
Rep Power: 8
bramv101 is on a distinguished road
And to simulate u tube heat exchanger I would go for the heat exchanger tutorial from StarCCM+
bramv101 is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Viscous resistance coefficients in porous medium fpingqian FLUENT 33 July 3, 2015 07:13
viscous resistance coefficients in Porous media choyong FLUENT 9 December 15, 2014 21:01
inertial resistance UDF Arnout Klinkenberg FLUENT 3 June 22, 2011 06:07
Porous Media Inertial and Resistance giogio FLUENT 3 June 21, 2011 18:09
tube bank inertial resistance coefficients Brian FLUENT 0 September 8, 2004 09:04


All times are GMT -4. The time now is 04:49.