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where to define the prandtl number?

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Old   June 5, 2008, 22:56
Default where to define the prandtl number?
  #1
James Phone
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Hi, everybody. I want to calculate thermal conductivity by using Prandtl number. But I am not sure where to define Pr. Only kinctic theroy option is present for the calculation of thermal conductivity.

Give me a hand. Thanks.
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Old   June 6, 2008, 05:29
Default Re: where to define the prandtl number?
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Victor
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Helo,

You can't really define it in Fluent, it's a result of the configuration of your problem.

Said you're looking for Pr = 100.

c_p is specific heat of the fluid mi is the viscosity k the thermal conductivity.

as you have, by the definition:

Pr = c_p*mi/k

You'll have just to set the proper c_p, mi and k to have 100 as a result for Pr. Like c_p = 1, mi = 100 and k = 1. But that is just too unreal as properties...

I'd would take a real material - water, for example - and then adjust the properties slightly to approach the value of Pr you're looking for, like so you'll not have a fluid too away from reality.

My best regards, Victor
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Old   June 6, 2008, 08:56
Default Re: where to define the prandtl number?
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Rakesh Jha
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Engine oils can have Pr more than 100. Well said that the Pr is just a material properties nothing else.

You can use the formula, Pr = (Dynamic viscosity * Specific heat capacity)/(Thermal conductivity).

You can put the other three properties here and get thermal conductivity.

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Old   June 6, 2008, 09:04
Default Re: where to define the prandtl number?
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Rakesh Jha
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You can put this formula in an user deined function and insert it Define -> Material -> User -Defined databse. go to drop down menu in thermal conductivity (where you saw the option kinetic theory) and opt for user defined.

Hope this helps!
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Old   June 12, 2008, 01:23
Default Re: where to define the prandtl number?
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James Phone
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Hi, I am modeling interface between two immiscible compressible fluids. But Fluent.Inc say only one compressible fluid can be defined when using its VOF slover. Then which code or software will meet my simulation?
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