# Boundary conditions in Fluent

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 January 7, 2003, 15:21 Boundary conditions in Fluent #1 Ankan Kumar Guest   Posts: n/a Sponsored Links Hi I am new to Fluent. Can anybody tell me how do I put a FULLY DEVELOPED inlet boundary condition for pipe flow in Fluent? The velocity inlet conditon gives me plug flow which is not what I want. Thanks Ankan

 January 7, 2003, 22:50 Re: Boundary conditions in Fluent #2 Keil Guest   Posts: n/a Hi, All we can do such a thing is that we have to customize the boundary condition via User Defined Function(called UDF) . Or, how about extend the inlet to be fully developed flow?. I mean , we make the inlet region(called entrance region, or inlet length , enctrance length) This length is given by Boussineq or Nikuradse in laminar flow . Latzko in turbulence. When we make this length ,Fully developed flow is got automatically. This way is the most easy way I guess. Regards,

 January 10, 2003, 21:08 Re: Boundary conditions in Fluent #3 Alamgir Guest   Posts: n/a For your help further just look UDF manul 1st-3rd chapters and you have a clear idea about your problem. cheers Alamgir

March 20, 2016, 12:13
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 Originally Posted by Alamgir ;104033 For your help further just look UDF manul 1st-3rd chapters and you have a clear idea about your problem. cheers Alamgir

Dear expert.. I have to use Superficial gas velocity 0.0016 m/s. But In fluent we have to put Velocity Magnitude at VELOCITY INLET boundary conditions.( INLET VELOCITY) How can I calculate INLET GAS VELOCITY form superficial gas velocity??? ( Reactor dimensions are 20*5*50 cm W*D*L and inlet dimensions are 2.4*1.2 L*D )

November 8, 2016, 06:40
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 Dear expert.. I have to use Superficial gas velocity 0.0016 m/s. But In fluent we have to put Velocity Magnitude at VELOCITY INLET boundary conditions.( INLET VELOCITY) How can I calculate INLET GAS VELOCITY form superficial gas velocity??? ( Reactor dimensions are 20*5*50 cm W*D*L and inlet dimensions are 2.4*1.2 L*D )
Hi Muhammad, I'm at the same point as you. Did you figure it out?

Cheers,
Antonio

November 9, 2016, 04:44
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 Originally Posted by maalan Hi Muhammad, I'm at the same point as you. Did you figure it out? Cheers, Antonio
Yes, I have solve this question.

Superficial velocity is a velocity that gives the same mass flow rate at any reactor cross-section (or volumetric flow rate, we do not care about density is varying or not - superficial velocity is engineering value based on the mean values). Superficial velocity is just Q/A, i.e. volumetric flow rate / cross-section.
As you have circular cross-section for reactor and inlet, the area A is PI*D^2/4. Q is fixed (to hold continuity principle).
If you have superficial velocity = 0.0016 for reactor (r-r) cross-section, you have to convert it 0.0016*(PI * Dr-r^2 / 4)/(PI * Dinlet^2 / 4) = 0.0016*Dr-r^2/Dinlet^2. Both D values should be put in the same units!
If you have superficial velocity = 0.0016 for inlet, no conversion is needed.

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