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April 2, 2005, 05:48 
superficial velocity

#1 
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hi,
I couldn't find what the exact difference between superficial velocity and physical velocity is. Fluent user guide 6.1 always defines it using porous medium, however my model do not consist of any porous medium. Moreover physical velocity condition gives a much better solution when compared to superficial. can anyone make a short description of their difference? Thanks for any help Taskin 

April 2, 2005, 15:18 
Re: superficial velocity

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The superficial velocity in a monophasic flow is equal to its mean velocity, while in multiphase flows it's defined as the ratio of the velocity and the volume fraction of the considered phase in a multiphase system.
Best regards, ap 

April 3, 2005, 00:31 
Re: superficial velocity

#3 
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ap is right. However, some people prefer to call it as the "Actual velocity" of a phase.
For Instance: Actual velocity of gas phase = (Superficial velocity of gas phase) / (volume fraction of gas phase) When you feed velocities and a guess for the volume fraction for a phase in fluent, you use the above equation to determine the 'Actual velocity' and enter this in the "Velocity inlet" panel. For the dispersed phase volume fraction you will have to enter the volume fraction guess that you used to calculate 'Actual velocity'. 

April 3, 2005, 18:00 
Re: superficial velocity

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hi, you mean in superficial velocity, it doesn't make a varying velocity distrubution along the cross section. It just takes a mean value, but physical velocity models the real situtation, I mean varying velocity distribution. did I understand correctly? Thanks for your help
Regards, Taskin 

April 4, 2005, 03:16 
Re: superficial velocity

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Well, no. If you wish to specify a distribution profile for velocity across a boundary, you can either you ASCII profile definitions or UDF's to do it. Simply inserting values into the "Velocity inlet" panel just means a uniform constant distribution across the boundary, not a profile.


April 5, 2005, 07:48 
Re: superficial velocity

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hi, I mean, varying velocity distribution due to viscous effects. I give a constant velocity but, due to viscous effects, it should have a bell shaped profile after the flow is fullydeveloped. so is that what superficial velocity takes as a mean? Thanks for you help, Regards, Taskin


April 5, 2005, 14:50 
Re: superficial velocity

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Superficial velocity is simply a number (defined as):
Volumetric flow rate  Cross section area 

April 5, 2005, 16:41 
Re: superficial velocity

#8 
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hmm I got it I think.. Thanks for your help Regards Taskin


August 15, 2010, 16:10 
superficial velocity

#9 
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Superficial velocity is nothing but the velocity of a fluid in a pipe,conduit,column etc in the absence of packing or obstruction. like in packed columns the actual velocity of the fluid through it is actually the volumetric flow rate divided by the cross sectional area. so the velocity achieved by the same fluid in the same column in absence of the packing is called superficial velocity.


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