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Vortex Tube flow simulation in Fluent

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Old   November 9, 2018, 15:02
Default Vortex Tube flow simulation in Fluent
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Hey everyone!

New to this forum but it has been an invaluable resource so I'm really glad that it exists!

I am a university student trying to model the flow in a Ranque-Hilsch vortex tube and have been able to successfully obtain the vortex flow behaviour (see attached picture).

However, I am not able to see a proper temperature/heat exchange between outer and inner vortices take place, as a result I'm not able to get a temperature difference at the Hot and Cold end. A contour plot of the tube at its midpoint doesn't really show any heat transfer taking place...

Does this have to do with setting a Backflow temperature for Hot and Cold outlets? I am using the K-e model with Viscous heating, compressibility effects and pressure gradient effects enabled.

Looking forward to your input, I would be happy to provide any additional information. Thank you so much!
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Old   November 12, 2018, 14:30
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Quote:
Originally Posted by CFDguy11 View Post
I am using the K-e model with Viscous heating, compressibility effects and pressure gradient effects enabled.

Note that you probably do not need compressibility effects or pressure gradient effects because these options are for the turbulence model. The vortex tube can work even in a totally laminar flow, it really has nothing to do with turbulence.


Make sure you are using a compressible equation of state (i.e. ideal gas) and not constant density of temperature dependent density.


Are you using the pressure based solver? The kinetic energy term is generally disabled in the energy equation when you use the pressure based solver. This means you do not see the adiabatic compression/expansion effects due to conversion between bulk kinetic energy of the flow and flow temperature. To enable it, you need to type something like:
Code:
/define/models/energy
then follow the prompts to activate the terms
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Old   March 11, 2019, 18:18
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Quote:
Originally Posted by LuckyTran View Post
Note that you probably do not need compressibility effects or pressure gradient effects because these options are for the turbulence model. The vortex tube can work even in a totally laminar flow, it really has nothing to do with turbulence.


Make sure you are using a compressible equation of state (i.e. ideal gas) and not constant density of temperature dependent density.


Are you using the pressure based solver? The kinetic energy term is generally disabled in the energy equation when you use the pressure based solver. This means you do not see the adiabatic compression/expansion effects due to conversion between bulk kinetic energy of the flow and flow temperature. To enable it, you need to type something like:
Code:
/define/models/energy
then follow the prompts to activate the terms
Thank you for your reply LuckyTran,

I am using the Pressure Based solver with the Energy equation enabled. In fluent, under 'Model' on the left-hand side, clicked on 'Energy' and checked the box.

On second thought, I wonder whether I am running enough iterations. I set max iterations to 20000, and K and epsilon terms are squiggling and hovering between 1E-3 and 1E-4. The energy term is between 1E-5 and 1E-6. Continuity term at 1E-2, all squiggly. Would you recommend letting it solve for longer? say, 50000 iterations?

Thank you so much for your help!

Last edited by CFDguy11; March 11, 2019 at 21:31.
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Old   March 11, 2019, 22:26
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As you can see from the attached image, this is the temperature contour I am getting. I set the total temperature in the 'THERMAL' tab of the inlet to 300K (assuming this was the inlet temperature of the air). The pressure-outlets (hot end and cold end) are set to 0 gauge pressure, and the 'THERMAL' tab has a backflow temperature setting of 300K for each of the outlets. I am unable to see a proper temperature gradient on both hot and cold ends even after 20000 iterations.
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