Please can you help me how can I introduce or define porosity in my udf, I am working on catalytic packed bed reactor.

Misama

hi I had tried this profile [ UDF ] for a similar problem

DEFINE_PROFILE(bed_por, thread, np) { cell_t c; real x[ND_ND]; real y;

begin_c_loop (c,thread)

{

C_CENTROID(x,c,thread);

y =x[1];

F_PROFILE(c,thread,np) = ***********;

} end_c_loop (c,thread) }

But, it was not showing any effect on the velocity profile. i.e. velocity profiles remain same even the porocity along bed was varying,

You can try this with your problem.

Also, any comments about this UDF will be appreciated.

pk

Thank you Pk for your help; but my problem is not on velocity profile is just how can I spacify porosity of packed bed in the fluent. I read the fluent manual but they do not mention ( to be more correct I DO NOT SEE ) how to specify the porosity.

I am sure I can get help on it

Regards R. Misama

hi

Read case file.

Define - boundary Conditions- fluid - porous zone- resitences and porosity

just enter value of porosity.

by

Or you can use a DEFINE_PROFILE udf in FLUENT - though I have had problems saving and loading with a udf defined for the porosity.

The manual says you need a DEFINE_PROPERTY but this clearly doesn't work in my version 6.1.18. The DEFINE_PROFILE works, but you need to turn it off/on to avoid errors during saving and loading.

Note when dealing with velocity which formulation you are using.

Greg

hi

i tried to run my case with different values of porosity, but it didn't show change in the results. even the velocity magnitudes remain same.

I am doubtful whether fluent considers porosity, or only the resistances are considered.

Also, the manual gives some info about " physical velocity" consideration. But how to give the input/get results in terms of physical velocity.

Probably, physical velocity values can give better results with different porosity values.

What's your experience.....

Thanks --pk

For different porosities you won't see any differences in velocity if using the superficial velocity formulation - since it doesn't represent the physical velocity in the medium - just the mass flux/density - which will remain the same.

In fact if you only change porosity you shouldn't expect to see much change - it will only effect diffusion processes and the transient terms. Other terms remain the same.

I would expect changing permeability will have a much greater change on the flow and pressure drop.

If you use the physical velocity formulation you should expect to see the velocity double if you halve the porosity. But this is just a way of reporting the velocity - the solution should be equivalent to the superficial velocity in other ways

Greg

hi Thanks for your reply,

Still i had one doubt.

How can we report values in terms of physical velocaity. whether fluent gives any option or else we have to determine it ourselves using equations.

Regards,

You can choose the velocity formulation in the solver panel I think.

Try reading the Manual - I think chapter 6 talks about the porous media model.

Greg

[soumendu.dasgupta]

Hi all.

I am new to fluent. Please tell me where to how and where to patch the udf for variation in solid volume fraction in Fluent 15.0.

P.S: My udf's are already compiled and loaded.
Please reply at soumendu.dasgupta@gmail.com

Thanks

[Naveed Ullah]

hi
i think if we change the porosity of bed then it will also change the permeability and inertial resistance of bed. so one should also write code for permeability and inertial resistance also because these are interdependent. then you will see change in profile