CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Meaning of Porosity

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 18, 2003, 02:39
Default Meaning of Porosity
  #1
sumi
Guest
 
Posts: n/a
Dear all,

This query is regarding liquid redistribution in a packed column, where as an intrinsic property, the porosity of the packed bed varies along the radial distance (ending up to almost unity at the walls). Can we define the porosity to vary like this in FLUENT? With reference to some previous suggestions, I tried to divide the bed radially into discrete zones, with different porosities, and then ran the simulation for a countercurrent Gas-Liquid flow. But whatever be the value of the porosities in the different zones, the velocity patterns, the gas phase fractions etc. do not seem to change at all. What I had presumed is that due to flow restrictions in a porous zone, as compared to an unpacked zone, the velocity profiles should have changed. Where am I wrong?

Sumi.
  Reply With Quote

Old   April 21, 2003, 10:59
Default Re: Meaning of Porosity
  #2
Steven
Guest
 
Posts: n/a
Hi,

I also got confused about how Fluent treat porosities. I checked the manual and did not find any information of the way that Fluent uses porosity. Anybody has any idea on this? Thanks a lot.

Steven
  Reply With Quote

Old   April 21, 2003, 13:30
Default Re: Meaning of Porosity
  #3
Evan Rosenbaum
Guest
 
Posts: n/a
I assume you're referring to the porosity of a porous medium in FLUENT. The FLUENT porous media model only adds a sink term to the momentum equation, it doesn't constrict the flow physically. All calculations are performed using superficial velocities, not actual velocities. Other than the extra momentum sink, porous zones are identical to fluid zones.
  Reply With Quote

Old   April 21, 2003, 15:22
Default Re: Meaning of Porosity
  #4
eric
Guest
 
Posts: n/a
hi, sumi.

in past versions of FLUENT only superficial velocities could be computed in porous regions. functionality is now available in the latest FLUENT release, 6.1, to compute physical (interstitial) velocities in porous zones. this allows fluid acceleration due to constriction in the porous media to be considered. in FLUENT 6.1, porosity may also be specified as a spatially varying function.

eric.
  Reply With Quote

Old   April 21, 2003, 15:45
Default Re: Meaning of Porosity
  #5
Murali
Guest
 
Posts: n/a
That is news. Can porosity be specified through a UDF ? Has that facility come yet ?

Murali
  Reply With Quote

Old   April 21, 2003, 16:00
Default Re: Meaning of Porosity
  #6
eric
Guest
 
Posts: n/a
hi, murali.

yes. spatially varying porosity has to be defined via UDF. the profile definition is:

DEFINE_PROFILE(por, t, nv)

eric.

  Reply With Quote

Old   April 21, 2003, 16:35
Default Re: Meaning of Porosity
  #7
Murali
Guest
 
Posts: n/a
Sorry to be a tough ass. But does this mean that, we can "solve" for porosity using a UDS ? coz, there are models where we have solids depositing thus altering the porosity of the model in time and space. We would then have an eqn similar to:


de
-- = f(u,x,t)
dt



where u is the set of other dependent variables, x is the space vector and t time. Can this be solved by specifying the DEFINE_UDS_FLUX as zero and be solved along with other variables ?

Murali
  Reply With Quote

Old   April 22, 2003, 02:25
Default Re: Meaning of Porosity
  #8
sumi
Guest
 
Posts: n/a
Hi eric. The version of Fluent which I am using is Fluent 6.0. Do you mean that I cannot do such calculations with the interstitial velocities in the pore constrictions in this version? That means that I have to wait for the Fluent 6.1 version? When has that been released?

Sumi

  Reply With Quote

Old   April 22, 2003, 12:04
Default Re: Meaning of Porosity
  #9
eric
Guest
 
Posts: n/a
hi, sumi.

you are correct. you cannot do such calculations with the interstitial velocities in the pore constrictions in FLUENT 6.0. you need to use FLUENT 6.1. FLUENT 6.1 was released in February 2003, and is available for FTP download from our User Services Center

www.fluentusers.com

eric.
  Reply With Quote

Old   April 22, 2003, 12:24
Default Re: Meaning of Porosity
  #10
eric
Guest
 
Posts: n/a
possibly, murali. i'll admit i'm not an expert with UDSs and UDFs, but i think this sort of approach would be worth investigating.

i would encourage you to contact your local technical support representative to discuss your particular needs in more detail.

eric.
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem in setting porosity region for rhoPorousSimpleFoam run_cfd OpenFOAM Pre-Processing 1 May 31, 2011 10:02
Porosity field in Fluent wojciech FLUENT 1 September 20, 2010 12:19
UDF for porosity Giacomo FLUENT 3 July 23, 2007 10:23
porous media with variable porosity Kevin A. FLUENT 3 December 24, 2006 11:56
porosity of baffle raymond Siemens 4 April 4, 2002 05:03


All times are GMT -4. The time now is 11:58.