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Multiphase modelling of stirred tanks

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Old   June 8, 2007, 07:37
Default Multiphase modelling of stirred tanks
  #1
Harish Appa
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Hi,

I am modelling a 3-D steady model of a stirred tank, using the Euler-Euler multiphase model and MRF model for the impeller rotation. The turbulence was accounted using the k-e model. A velocity inlet was used to simulate the spargers and pressure outlet at the top surface. I have noticed that there was accumulation of air in the tank, which should not occur.

I would be grateful for any help or any advice.

Kind Regards

Harish
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Old   June 8, 2007, 08:26
Default Re: Multiphase modelling of stirred tanks
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KP
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have you accounted for the following correctly: inter phase closures? boundary conditions at the top of the reactor?

KP http://myweb.dal.ca/kpodila
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Old   June 10, 2007, 06:54
Default Re: Multiphase modelling of stirred tanks
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Harish Appa
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Dear Krishna Podila,

I am currently using the Euler-Euler model and velocity inlet for the spargers and pressure outlet for the outlet (at the top of the reactor). I presume the model should account for the inter-phase closures.

Thanks for your advice. Kind Regards Harish

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Old   June 10, 2007, 08:49
Default Re: Multiphase modelling of stirred tanks
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KP
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no the model only accounts for Drag that to the coeff is schiller Naumann which is not good for your case. Also Pressure outlet is not corect either use degassing or velocity inlet as prescribed in Ranade's book. KP
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Old   June 10, 2007, 09:03
Default Re: Multiphase modelling of stirred tanks
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Harish Appa
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Dear Krishna Podila,

How does one account for interphase close? Is there need for a UDF or is it provided by the software.

I have also tried a velocity inlet for the outlet. I have achieved convergence but the gas hold up was always increasing. But is that a good idea, won't that suck the air on top eventhough there is no air at the boundary. For instance at tthe start when the air has no reached the top surface yet.

Also, is it fine to run a steady state model.

Kind Regards kevin
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Old   June 10, 2007, 09:10
Default Re: Multiphase modelling of stirred tanks
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KP
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Yes there are macros which provide access points to customize them. You should be using unsteady state as the flow is inherently unsteady. You can try the Patch route with pressure outlet. Try to read best practice guidelines for bubble columns provided by Fluent which can be obtained from user service center. KP
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Old   June 10, 2007, 09:32
Default Re: Multiphase modelling of stirred tanks
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Harish Appa
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Dear Krishna Podila,

I have read and tried the help instructions as per the Fluent guidelines for bubble columns. But achieved no success.

Can u please help me about the interphase closure. How should i go about it.

Thanks Harish
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Old   June 10, 2007, 09:35
Default Re: Multiphase modelling of stirred tanks
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KP
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DEFINE_EXCHANGE_PROPERTY macro can be sued for customizing drag coeff.

KP
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Old   June 10, 2007, 09:40
Default Re: Multiphase modelling of stirred tanks
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Harish Appa
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Dear Krishna Podila,

Yeah i have done that to change the drag coefficient, and consequently to change the gas hold up in the tank. Eventhough i had convergence the gas hold up never stabilised it just increased with no sign of stabilisation.
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Old   June 10, 2007, 10:11
Default Re: Multiphase modelling of stirred tanks
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Harish Appa
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Dear Krishna Podila,

I would be really grateful you could help me on achieving the interphase closure.

Thanks Harish Appa
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