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Heat exchanger

Posted Mar 12, 2014, 10:29 a.m. EDT Fluid & Heat, Heat Transfer & Phase Change Version 4.3b 2 Replies

Elham Hosseinzadeh
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Hi

I have a question regarding modeling an air-air heat exchanger I hope you can help me with. I have a serpentine flow pipes and a box for the air forced convection. I started with a very simple physics, non-isothermal flow. It converges but looking at the velocity profile, it looks like the pipes are invisible for the air flow. what I expect is a significant increase for the air velocity as the area decreases between the pipes.
also I can not choose the pipes boundary to add convective heat flux. I attached my model here. I appreciate if you could give me some tips.

Best Regards,
Elham

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2 Replies Last Post Mar 13, 2014, 6:36 a.m. EDT
Zoran Vidakovic, COMSOL COMSOL Employee

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Posted: 1 decade ago Mar 12, 2014, 11:29 a.m. EDT
Dear Elham Hosseinzadeh,

To separate the fluid domains of the two streams (pipe and surrounding) you need to define interior walls (infinitely thin) at the pipe boundaries. Per default internal boundaries are defined as "continuity" (with "Form Union"). Currently, the "Wall" is only applied to (external) boundaries that are not overridden by inlets and outlets. Correct your pipe wall selection such that cross section boundaries between pipe segments are not included. Extrude the fan inlet/outlet geometry (e.g. 5mm) and use a boundary layer mesh to resolve the strong velocity gradients in the near wall regions (e.g. via Physics-controlled mesh).

A similar example can be found here: www.comsol.com/model/shell-and-tube-heat-exchanger-12685

If you need further help from us feel free to contact our support: www.comsol.com/support

Good luck and best regards,
Zoran


PS: Have a look also here:
www.comsol.com/video/shell-tube-heat-exchanger-model-tutorial
www.comsol.com/video/creating-2d-models-cross-sections-3d-geometries


Dear Elham Hosseinzadeh, To separate the fluid domains of the two streams (pipe and surrounding) you need to define interior walls (infinitely thin) at the pipe boundaries. Per default internal boundaries are defined as "continuity" (with "Form Union"). Currently, the "Wall" is only applied to (external) boundaries that are not overridden by inlets and outlets. Correct your pipe wall selection such that cross section boundaries between pipe segments are not included. Extrude the fan inlet/outlet geometry (e.g. 5mm) and use a boundary layer mesh to resolve the strong velocity gradients in the near wall regions (e.g. via Physics-controlled mesh). A similar example can be found here: http://www.comsol.com/model/shell-and-tube-heat-exchanger-12685 If you need further help from us feel free to contact our support: http://www.comsol.com/support Good luck and best regards, Zoran PS: Have a look also here: http://www.comsol.com/video/shell-tube-heat-exchanger-model-tutorial http://www.comsol.com/video/creating-2d-models-cross-sections-3d-geometries

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Elham Hosseinzadeh
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Posted: 1 decade ago Mar 13, 2014, 6:36 a.m. EDT
Dear Zoran

Thank you for your reply. I made the changes you suggested. Unfortunately I have some issues with adding the interior wall boundary condition. It diverges immediately, seems like it needs more inputs now. I even tried it with a very fine mesh, but it didn't help. Please take a look at my model. I appreciate your help.

Bests,
Elham
Dear Zoran Thank you for your reply. I made the changes you suggested. Unfortunately I have some issues with adding the interior wall boundary condition. It diverges immediately, seems like it needs more inputs now. I even tried it with a very fine mesh, but it didn't help. Please take a look at my model. I appreciate your help. Bests, Elham

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