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Periodic boundary conditions

Posted May 22, 2012, 12:55 a.m. EDT Version 3.5a 4 Replies

Sin Kim
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Hi, all

Does any one knows what are the suitable boundary conditions for heat transfer scenario applied at the inlet and exit of a domain when the boundary conditions for turbulent kinetic energy (k) its dissipation (e) and axial velocity (w) are set as periodic conditions. Note that the temperature of the fluid always increases in the stream wise direction if a constant heat flux acts at the wall of the pipe. Since periodic conditions are used to reduce the computational burden only a small segment of the domain is modeled in this case which means we cannot set a Dirichlet boundary condition for the temperature at the inlet and exit.

Thanks for any sort of help
4 Replies Last Post May 22, 2012, 5:26 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 22, 2012, 2:45 a.m. EDT
Hi

but one should dissociate periodic heat and flow conditions. For me if you set up periodic heat equations you are transaforming your 2D problem into a 1D problem, in stationary you will en up with straight T contours, no ?

One can use symmetric heat conditions but this does neihter allow a heat flow perpendicular to the plane, so not valid for the fluid flowing

--
Good luck
Ivar
Hi but one should dissociate periodic heat and flow conditions. For me if you set up periodic heat equations you are transaforming your 2D problem into a 1D problem, in stationary you will en up with straight T contours, no ? One can use symmetric heat conditions but this does neihter allow a heat flow perpendicular to the plane, so not valid for the fluid flowing -- Good luck Ivar
Sin Kim
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Posted: 1 decade ago May 22, 2012, 4:45 a.m. EDT
Actually yes this exactly means that the problem is now 1D. I have seen the manual describing the use of periodic boundary conditions in 3.5(a) but they have used a Dirichilet boundary condition on temperature at the inlet while a convective flux at the exit the b.c for k,e and v are set to periodic however. If I use the same conditions for heat transfer in my problem which is simply a turbulent pipe flow with constant heat flux acting at the wall I am not getting accurate results for the Nusselt number however I am getting good result for the friction factor. I am confused regarding what boundary conditions I can use to model the heat transfer in the liquid??? Moreover I cannot find how to implement the periodic boundary conditions in comsol 4.2 as there is no page available for source vertices and destination vertices also how to add a variable in the solver groups if the variable is defined as an ODE in comsol 4.2?

Thanks for your suggestions
Actually yes this exactly means that the problem is now 1D. I have seen the manual describing the use of periodic boundary conditions in 3.5(a) but they have used a Dirichilet boundary condition on temperature at the inlet while a convective flux at the exit the b.c for k,e and v are set to periodic however. If I use the same conditions for heat transfer in my problem which is simply a turbulent pipe flow with constant heat flux acting at the wall I am not getting accurate results for the Nusselt number however I am getting good result for the friction factor. I am confused regarding what boundary conditions I can use to model the heat transfer in the liquid??? Moreover I cannot find how to implement the periodic boundary conditions in comsol 4.2 as there is no page available for source vertices and destination vertices also how to add a variable in the solver groups if the variable is defined as an ODE in comsol 4.2? Thanks for your suggestions
Sin Kim
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Posted: 1 decade ago May 22, 2012, 4:48 a.m. EDT
I am sorry but what do u mean by disassociate the periodic heat and flow conditions how can one achieve this?
I am sorry but what do u mean by disassociate the periodic heat and flow conditions how can one achieve this?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 22, 2012, 5:26 a.m. EDT
Hi

I cannot remeber how it was back in 3.5, but in v4 you have 2 periodic boundary conditions for conjugated heat transfer (NITF) one per physics, you do not need to set a heat periodic boundary condition, even if you use flow periodic boundary conditions. But perhaps 3.5 did not distinguish ?

--
Good luck
Ivar
Hi I cannot remeber how it was back in 3.5, but in v4 you have 2 periodic boundary conditions for conjugated heat transfer (NITF) one per physics, you do not need to set a heat periodic boundary condition, even if you use flow periodic boundary conditions. But perhaps 3.5 did not distinguish ? -- Good luck Ivar

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