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Help with Flow Simulation in Simple Enclosure

Question asked by John Highet on May 24, 2016
Latest reply on May 24, 2016 by John Highet

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Hello,

I'm trying to run what I thought would be a simple natural convection flow simulation of an enclosure with a 150W node inside. All I want to find is max temperature of the internal air and how it flows through the enclosure. I am new to Flow, so I've only done a couple of the tutorials to learn the basics, but I must have missed something because my results do not seem right. I'm only getting a temperature rise of a couple degrees inside the enclosure. Also, inlets are supposed to be the lower, rear louvers and outlets are supposed to be the front lid overhang vents. When I do a dynamic trajectory, the air is coming in through the lid vents. ?!?!?! I've attached my Pack&Go, any help, tips and tricks would be greatly appreciated.

Thanks,

John

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Cut Plot FNE(1).jpg39.0 KB
FNE for CFD.zip1.9 MB

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Amit Katz May 24, 2016 11:44 AM

Look at your mesh resolution in the inlet, it's awful:

You've got half a cell covering the entire length of the open area.

I recommend you start with a 2D analysis. It will allow you to greatly increase the mesh resolution that you need for these relatively small inlets. It's not a very realistic model, but it should give you some idea of how you need to structure the enclosure to get the best flow around your hot components.

I would also recommend modeling your mounting fixture. Right now your hot box is just floating in the middle of this enclosure, not very realistic.

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John Highet @ Amit Katz on May 24, 2016 6:42 PM

Thanks for the reply Amit. I'm not sure how to do a 2D analysis, but I did find how to refine my local meshes for my inlet and outlet lids and am running another sim now. I was also wondering about my wall conditions. I'm just using wall temperature because I'm not sure how to input the correct heat transfer coefficient (the tutorials always have a number to put in there, but don't tell you where it comes from) - do I need to calc that?

I was trying for super-simple, but as you suggested I did add the mounting bracket for my node ("hot box").

I'll upload again after running with the refined mesh.

Thanks again,

John

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Amit Katz May 24, 2016 11:44 AM
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Look at your mesh resolution in the inlet, it's awful:
You've got half a cell covering the entire length of the open area.

I recommend you start with a 2D analysis. It will allow you to greatly increase the mesh resolution that you need for these relatively small inlets. It's not a very realistic model, but it should give you some idea of how you need to structure the enclosure to get the best flow around your hot components.
I would also recommend modeling your mounting fixture. Right now your hot box is just floating in the middle of this enclosure, not very realistic.
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- John Highet @ Amit Katz on May 24, 2016 6:42 PM
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  Thanks for the reply Amit. I'm not sure how to do a 2D analysis, but I did find how to refine my local meshes for my inlet and outlet lids and am running another sim now. I was also wondering about my wall conditions. I'm just using wall temperature because I'm not sure how to input the correct heat transfer coefficient (the tutorials always have a number to put in there, but don't tell you where it comes from) - do I need to calc that?
  
  I was trying for super-simple, but as you suggested I did add the mounting bracket for my node ("hot box").
  
  I'll upload again after running with the refined mesh.
  
  Thanks again,
  John
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Help with Flow Simulation in Simple Enclosure

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