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Old   December 15, 2007, 11:02
Default Boundary conditions
  #1
Rashmi
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Hi

Iam doing simulations for stationary fluid inside a closed cylinder. its left wall is hot at 310K and right at 285K and the curved wall is adaibatic. I want to measure the thermal conductivity of the fluid inside. what boundary conditions i should apply for this. there is only temperature flow.

thank U Rashmi
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Old   December 15, 2007, 12:55
Default Re: Boundary conditions
  #2
Ramesh.K
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Hi,

specify left wall and right wall separately next, the curved surface is also specify as wall in fluent, you can specify the left wall at 310k and right wall at 285k.

Imagining this to be a horizontal cylinder where u can visualize the things

try it, it may work

bye

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Old   December 15, 2007, 12:59
Default Re: Boundary conditions
  #3
Ramesh.K
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HI In the materilas panal, you take density to vary with temperature you may take density variation to be of boussinesq's approximation

do this with the above said conditions bye
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Old   December 15, 2007, 13:36
Default Re: Boundary conditions
  #4
Vijay
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Hi Rashma,

In ur presprocessor(gambit) select left surface and give one name, and do the same for rest right hand and curved surface and go to fluent, select left wall give the value and do the same for right and curved walls.

With Regards, Vijay
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Old   December 16, 2007, 07:59
Default Re: Boundary conditions
  #5
Rashmi
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Hi Ramesh

yes i did exactly the same..Iam uisng UDF for density, viscosity of fluid and mixture viscosity, specific heat and thermal conductivity. when i spcify left wall at 310K and right at 285k and curved wall at 0k my results converge in just two iterations at 1e-6.and whn i try to plot the UDM values all gives me zero..pls chk my UDF for viscosity.my udf dosent read the value of T frm fluent. DEFINE_PROPERTY(vis_eff,c,t) { real vis_ref,vis_f,vis_eff,Tref,T,phi_p;

Tref = 293; T = C_T(c,t); vis_ref = 0.001788; phi_p = 0.01;

vis_f = vis_ref*((exp(-1.704-5.306(Tref/T)+7.003(pow(Tref/T),2))); vis_eff = ((1+(2.5*phi_p)*vis_f);

C_UDMI(c,t,8) = vis_eff;

return vis_eff; }

Ia following the paper my Ramesh K Agarwal for numerical simultion of natural convection heat transfer in nanofluids

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Old   December 17, 2007, 07:18
Default Re: Boundary conditions
  #6
sushii
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Yeah vijay have suggested right thing...! you hv to give different names to these three walls..! n wen you go to fluent you can set the temp for walls or you can set it to adiabatic ..!

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Old   December 18, 2007, 02:46
Default Re: Boundary conditions
  #7
Rashmi
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ok thanks vijay and sushil

how do i set adaibatic wall? by setting temp =0 right. but when i try to iterate it gives me floating point error: invalid number
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Old   December 18, 2007, 06:34
Default Re: Boundary conditions
  #8
Ramesh. K
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Hi, Temp cant be zero, U should make Heat flux to be zero I suppose, for that boundary condition of curved wall. Just check it.

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Old   December 18, 2007, 08:50
Default Re: Boundary conditions
  #9
Rashmi
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Thx Ramesh

I did that...I was getting floating point error because I entered temp as zero for curved surface. But my simulations get converged in just 4 iterations to 1e-6...i dont think so it is correct...any more suggestions..??

Rashmi

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Old   December 19, 2007, 00:12
Default Re: Boundary conditions
  #10
Vijay
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Hi Friend,

In wall B.C panel enter the value of heat flux as zero for adiabatic condition.........

With regards, Vijay
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