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Justin April 30, 2007 13:14

Computer chassis airflow
 
I'm trying to learn CFX by doing an airflow analysis through a 2U rackmount chassis. I created a solid representing the air-mass and set the inlet and outlet boundary conditions. The solver completes, but I'm having problems getting the data I need.

What should I look at to find the pressure drop/system resistance to determine the fan's characteristics?

I'm using CFX 11 in workbench on a Windows XP 64-bit workstation.

Thanks, Justin

Glenn Horrocks April 30, 2007 18:08

Re: Computer chassis airflow
 
Hi,

Where are your inlet and outlet boundaries? Is it at the fan inlet or outlet? Or do you generate the flow using a momentum source?

Glenn Horrocks

Justin May 1, 2007 08:12

Re: Computer chassis airflow
 
There are inlets at the front and side of the chassis, which are modeled as a momentum source, and the outlet is an opening at atmospheric pressure.

Glenn Horrocks May 1, 2007 18:18

Re: Computer chassis airflow
 
Hi,

A suggestion would be to replace the fan with an inlet with a specified mass flow rate. Do a series of runs covering the range of flow rates you expect the system to operate at. Use CFX-Post to measure the pressure drop in the system at various flow rates. Then you have the system characteristic line. It can be matched against the fan operating curve (which I assume the fan manufacturer can provide or you can generate it through simulation) and where the lines intersect is the system operating point.

Glenn Horrocks

Justin May 2, 2007 09:14

Re: Computer chassis airflow
 
Mass flow rate - that's actually what I did, not momentum. My confusion (based on ignorance, of course) is how to find the pressure drop in CFX-Post. I feel like this should be the easiest step based on how hard it has been to get to this point.

At least I'm on the right track so far, I've just hit a wall in trying to find the pressure drop.

I do have some problems with CFX crashing when I try to generate certain plots - I've just chalked this up to the newness of version 11. Maybe something is wrong with my simulation though.

Glenn Horrocks May 2, 2007 18:17

Re: Computer chassis airflow
 
Hi,

To get the pressure drop, in CFX-Post use the function calculator and do an area average of pressure at the inlet patch. Do the same for the outlet patch and the difference is the pressure drop.

Glenn Horrocks


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