Radiation through vacuum with s2s model
 

Hi everybody,

I am simulating a particular counterflow heat exchanger constitued of two coaxial tube; in the outer tube flows the hot fluid, in the inner tube flows the cold fluid.
This two tubes are separated by a gap in which high vacuum is created; heat is transfered in this gap through radiation (i'm using the s2s model).
My problem is:
Is it possible to create void cells in fluent? (I mean cells with no materials associated, in which no equation is solved and the heat is transferred only via radiation from surface to surface).

Thank you in advance,

Andrea

You cannot have a "no material" region. It is either a region populated with material or it is not a region.

For void cellls. It is better not to do this in Fluent. Your geometry and mesh should have already taken care of the void cells when you first generated it.

But if you really want to suffer the pain... In Fluent, you can cut up your mesh into regions and then delete the unwanted regions (your void cells). You then apply symmetry boundary conditions to the remaining exposed faces.

Another way to do it is to separate the problem into different zones and do a similar trick. You can disable the computation of entire zones so that no equation is solved for that zone. But you have to be careful not to remove the walls of the heat exchanger.

Keep in mind that Fluent is meant to solve Fluid Flows. Hence it is not a good solver to use if you just want purely s2s radiation (that is more of an algebra problem).

First of all thank you for your reply,

I use fluent because I also have to solve the convective heat transfer :)
Can you please explain me how to disable the computation for one zone?

Andrea

from the dropdown menu
mesh => zone => deactivate

Thank you again,

can I ask you another question? I'm solving the problem in exagonal symmetry; when the solution reaches the steady state I expect that the power exchanged by cold and hot fluid to be in balance (namely the product (mass flow rate)*(Cp,out*Tout - Cp,in*Tin) is the same for the two fluids) but this doesn't happen. Do you believe this can be related to problems with the symmetry boundary condition?

Regards,

Andrea

There shouldn't be any problems related to the symmetry, so no. Double check your calculations / make sure your solution is well converged. If the energy balance isn't coming out right then it's probably not converged.

Hello,
I also need to model radiation through vacuum enclosure with s2s model. But, my case has only one zone and when I deactivate it, the walls of it are also removed!
Is it possible to have the walls of the zone and deactivate the zone simultaneously?
Thanks in advance.

hi sagila,
FLUENT requires a fluid domain next to surface for S2S radiation.Dont know why..