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-   -   Steam Reformer example (http://www.cfd-online.com/Forums/openfoam/114593-steam-reformer-example.html)

elephantwalker March 13, 2013 17:29

Steam Reformer example
 
Hi,
I am new to openFoam, so please be kind. This is a repost from the "progamming openFoam forum", I think maybe the general forum is more appropriate now.

I am looking at reproducing Comsol's example for a steam reformer:

http://www.comsol.com/showroom/downl...m_reformer.pdf

You may have to create an account to download this.

In the first step, I am just going to put a hot gas into a catalyst bed using the latest version, as we can use rhosimpleFoam with the porous runtime switch. What I would like to do is also add the reactions, and the heat transfer.

Is there a go by, or example I can use that does or similar?

I am presuming I will have to create a new solver with all of the partial differential equations.

Thanks,

Lawrence

wyldckat March 18, 2013 18:35

Greetings Lawrence,

I've deleted the previous thread you mentioned, just to avoid duplication ;)

:confused: Having to register on a website just to figure out what you're trying to reproduce... uhm... it's not going to be easy for anyone to do so for you! ;)

OK, so looking at the Wikipedia page for Steam Reforming: http://en.wikipedia.org/wiki/Steam_reforming
A quick read and it seems that you want to perform a chemical reaction for dissociating H2 from CH4 or similar, by using steam...

reactingFoam comes to mind, although there aren't many tutorials on the subject... OpenFOAM still only carries "combustion/reactingFoam/ras/counterFlowFlame2D".
chemFoam and XiFoam also come to mind, although I'm not familiar with any of them.

Then there is also the topic of "Fuel Cells OpenFOAM"... for which this seems to be one of the top Google results: http://www.openfoamworkshop.org/2012...SlidesOFW7.pdf

And for now, this is all I can figure out. If you could detail a bit more what exactly you want to perform, it might be easier to outline where to look for information! In the mean time, have a good look at the summary description about each solver: http://www.openfoam.org/docs/user/standard-solvers.php

Best regards,
Bruno

elephantwalker March 18, 2013 22:18

Thanks, the link to the catalytic example is good. Although not the same, some of the physics is similar.

Here is a description of the problem:

A cylindrical reactor with a fixed catalyst bed. Propane and steam go into one end of the reactor at 700 Kelvins, and hydrogen and carbon dioxide come out the other end of the bed. Counter current flow of steam within internal tubes are used to heat the endothermic reactor at 900 Kelvins. The reactor is insulated. Dirichlet and Neuman mixed boundary conditons apply (fixed inlet outlet pressures, fixed inlet temperatures, fixed inlet compositions, gradiant equations for temperature or heat fluxwhere necessary).

The domain is setup so that only 1/4 of the reactor is actually modeled, as symetry is used.

Reaction:

propane + 6 *steam = 10 H2 + 3co2

this is endothermic.

Bed/Fluid Reactor domain:

reaction mixture /catalyst bed momentum balance is darcy's law:


Del . (rho(-kappa/nu Del( P_sr))) = 0 ...its steady-state.

P_sr is pressure in the catalyst bed (Pa), kappa is the permeability of the catalyst (m2), nu is the viscocity (Pa.s).

the energy balance for the reaction fluid is:

Del . (-k_sr Del T_sr) + (rhoCp)_f u . Del T_sr = Q,

where Q is the reaction heat Delta Hr * r, where r is an arrhenius term, and Delta Hr is the reaction heat.

The heat flux to the steam tubes is described by newton cooling:

q_s = h_s (T_sr - T), where T is the steam temperature, and h_s is the heat transfer coefficient.

Similarly, the heat flux to the outer insulation is:

q_oi = h_oi(T_sr - T_ambiant), where T_ambiant is the ambiant air temperature, and h_oi is the outside/insulation heat transfer coefficient.

The temperature gradient of the insulation is described by:

Del . (-k_i Del T_i) = 0, where T_i is the temperature of the insulation, and k_i is the thermal conductivity of the insulation.

A convective profile is used for the temperature gradient of the steam heating tubes:

F . (-k_steam Del T_steam) = 0

The mass transport of the reacting species are assumed to be by Maxwell-Stefan multi-component diffusion/convection :

Del . ( Maxwell -Stefan equations convection - diffusion + thermal ) = Ri

Where Ri are the reaction rates for each component as calculated by arrhenius term and stochiometry/mw.


In the steam tubes, a weakly compressible Naviers Stokes equation is used for steam momentum:

ρu ∇⋅u + ∇⋅[pI η (∇u +uT)+ ( 3)(∇⋅ u) I] = 0


and the mass balance on steam is of course:


∇⋅(ρu) = 0

Finally, the energy balance in the steam tubes are described:

⋅ (k_ht(T)) + ρCp uT = 0








I hope this more clearly explains the problem.

Thanks,

Lawrence






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