[kzf]

hello

maybe i not quite enough read a manual but..

Can someone tell me how can I calculate C0 and C1 in porous media model in fluent? In fluent manual is very little information about C0 and C1 using with porus media domain.

On this moment i Use C2 and 1/alpha, from Deltha P for velocity but,

If i correctly udnerstand manual, power law model of porus media can be use instead superficial velocity model, yes?

which optsion is better?

[litzj]

for these value, u need experimental curve for that material

[kzf]

experimental curve for material? what kind of experiment i have to do?

[bpulat]

Using Porous domain is dependent on your needs.
To use the Power Law Model you need the pressure drop to be isotropic.

On this moment i Use C2 and 1/alpha, from Deltha P for velocity

From your sentence i assume you have the pressure drop data so you obtained the Deltha P.
To use the Power Law Model open an Excel file and make a grap of Pressure Loss (Pa) and Velocity (m/s).
Basically y(Pressure Loss) = x (velocity).
Get the y = x equation as power.

From there
Deltha P = C0. V^C1. Delthan,
Deltha P = Pressure Difference,
C0 and C1 are coefficients,
V = Velocity,
Delthan = Thickness of the porous domain.
For example your equation is y = 172,77 x ^ 1,784.

Resistance Coefficients from the equation are:
C0. Delthan = 172,77
C1 = 1,784
A quick note which is also written in the Fluent Manual. The units for C0 are SI.

Hope it helps,

Baris

[kzf]

many thanks baris,

Im also need to simulate the heat flow on this case, but it is fucking hard.

i have very geometry complicated tube packet, where in tube i have pressure drop, and deltha temperature from 1200 C to 60 C, to be honest i want to simulate pressure drop and heat transfer in porus media model, fluid inside tube have density and viscouse depend on temperature, so calculate pressure drop from C2 and alpha isnt simply case. To have correctly pressure drop from alhpa and C2 i have to make two - three round of aproximation because looks likes this model isnt perfectly fit for this problem

I see that when im change porosity the temperature field inside tube also changing, (but why when im decrease porosity, pressure drop go down also hmmm, more porous material= greater pressure drop? not in this model) i wonder if porous media model is good idea to "simplify" heat transfer and pressure drop in this case.

[kzf]

ok now i understand,Baris you are a Big Boss! so you mean linear [edit]- exponential correlation from pressure drop vs velocity funcion, is need to calculate C0 and C1.

That is what i need to calculate C0 and C1 -- thanks!.

it looks like Deltha of energy from min pressure to max pressure.

[bpulat]

Delthan is the thickness of your model in order to calculate power law as i wrote above.
To calculate porous domain you are in need of experimental pressure drop data or an emprical formula specific for the case.
Using porous domain is basically a simplification to reduce the complexity of the geometry in most cases.
If you can properly mesh and solve your model you should go that way.
I suggest you to read the manual and tutorial again since you have some confusion of the concept.

[kzf]

To calculate porous domain you are in need of experimental pressure drop data or an emprical formula specific for the case.
Using porous domain is basically a simplification to reduce the complexity of the geometry in most cases.

yes i know,

Maybe i should start once again from begining.

////// AIM: Simplify tube from geometrcial complicated geometry to cylinder
////// with wall "0", or wall as metal domain.

////// Conditions:
////// * Range temperature gas inside tube from 1774 to 293 K
////// * Heat transfer from gas to steel wall and fromm steel to the
////// outside,
////// * I want to have the same as experiment DELTHA P, and outlet gas temperature,
////// * Gas model: viscosity and density depend from temperature, (linear ////// points from 1774 to 293 K)
////// * I have experimental data, DELTHA P for inlet velocities

I want to simulate Deltha P, outlet gas temperature, and heat transfer from gas to wall and from wall to the outside of tube,

i use a porous media domain to simplify this tube,

But i found tutorial with

////// Conditions:
////// * Air 20 C
////// * Constant density and viscosity,
////// * low range velocity
////// * Without heat transfer,

So i have some questions:

1. My idea is:

to simulate Deltha P, as porous media model, heat transfer to simulate as convection with ALPHA on "0" wall, and writing UDF for temperature profile on wall,

But:

Results with simplify model with C2 and 1/alpha from experiment is not suitable to exeperiment data. I have to calculate a few iteration with
different much more higher values than experimental valuesa porous domain coeff. to have close Delta P and outlet temperature valeu results with experiment.

So maybe I use wrong model, or my assumptions isn`t good?

Please express your opinion.

2. Is this model is suitable to my case?
If no then what model Can I use to simplify problem what i show?
3. Can someone suggest me some other tactics to simplify model as i
describe?

[bpulat]

Results with simplify model with C2 and 1/alpha from experiment is not suitable to exeperiment data.

Can you give more information about the differences between the experimental values and the ones from fluent (C2 and 1/alpha approach)?
How did you do your comparison and what is the percentage of error ?
Is your porous domain homogeneous ?
For the Heat transfer which energy transport method did you choose in porous domain ?

[kzf]

ofcourse i can
(apologize for my dialectical english, if it is neccesary please fell free to pay me attenion when my sentences isnt clearly enough i try to correct it)

so

the differences in Delta P for calculete step by step as mention in 6.2.3.7.11 fluent manual guide 1/alpha and C2,
for condition as I presented is (!) 40-50%; compared to experiment,

temperature outlet (this isnt a suprise) is about 40%, so maybe i use wrong recepture to assume C2 and alpha, fluent theory guide shows some more way to calculate it. Maybe porous media model isnt good to simplify this type of geometry.

i have to waste my time to search correlation variability alpha and c2 to deltha P and temperature to aproximate correct values of porous media perimeter. Because model didnt work correctly for me.

ok maybe it isnt wrong but is not physicaly to searchicng empirical correlation.

[bpulat]

Can you share your porous domain inputs, experimental results and your mesh (also quality table skewness, orthogonality) via screenshot ?
Let's check things before saying porous modeling is not a good approach for your example.

[kzf]

thats great idea, sorry for delay but i have lot of working, please be patient, and I post here neccesary information

[kzf]

So to be honest unfortunately i Cant publish sensitive data of our experiment, my company forbade me to post it here.

[bpulat]

If you need theoretical help on porous domain, just write it here.
I will try to help as much as i can and good luck in your simulation.

Baris

[gfoam]

Hello, I know this is a old post but may be someone can help me. I'm trying to model a perforated plate in Fluent and I calculate the coefficients for the pressure loss of the perforated plate with some correlations I found in the blibliography and I get this equation:
DP=65000*Vmag^(-1)
That equation is for low Re numbers, in the order of 1 or less.

So, C0=62540 and C1=-1 (I have taken into account the thickness of the porous media)

But, when I put the coefficients in Fluent, the solver diverges all the time. If I put C1=1 the solver converges but that's not the solution I'm looking for. Can someone help me? Thanks. Regards

[gfoam]

Originally Posted by gfoam

Hello, I know this is a old post but may be someone can help me. I'm trying to model a perforated plate in Fluent and I calculate the coefficients for the pressure loss of the perforated plate with some correlations I found in the blibliography and I get this equation:
DP=65000*Vmag^(-1)
That equation is for low Re numbers, in the order of 1 or less.

So, C0=62540 and C1=-1 (I have taken into account the thickness of the porous media)

But, when I put the coefficients in Fluent, the solver diverges all the time. If I put C1=1 the solver converges but that's not the solution I'm looking for. Can someone help me? Thanks. Regards

I have solved my problem. I was plotting pressure loss coefficient vs velocity instead of Pressure Loss vs velocity so the parameters of the curve fit were negative.:P Now my problem is another with multiphase flow through porous media. When I rise the pressure loss for one phase the another phase is also restricted to pass through, and I dont understand why. Does someone have experience with that kind of problems? Regards