A Rather Obscure Cooling Problem...

Terminal_Boy

Terminal_Boy

Terminal_Boy

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Joined
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I'm looking for a fan solution to cool a rectangular RF test chamber of approximately 1/8 of a cubic meter. As it sits in a room which is held at 22˚C, finding cool air to force into the chamber isn't an issue.

Conveniently, the chamber has mounting locations on either side for a 92mm case fan.

The problem is that, for RF isolation requirements, these mount locations consist of a grid of 3.5mm holes piercing the 5-6mm thick sides of the chamber.

Even using static pressure fans, having the fan mounted against a surface which blocks 75-80% of the airflow means that there's very little cool air being pushed into and extracted out of the chamber.

I'm guessing that some sort of stand-off ducting is the answer, but my Google attempts to find something suitable has failed.

Any ideas?
 
are you wanting something like this only to convert down to 92mm?

would it be possible to modify the ventilation but still meet the requirements for RF isolation? (for example a larger number of smaller holes), or add additional ventilation mounts?

edit, found the right sized one

only other possibility i could think would be to rig up an air compressor to blast air through the system, although that's not exactly going to be cheap or effecient.
 
Just use long bolts with nuts or washers to provide standoffs, and wrap the assembly in duck tape to provide ducting.
 
adolf hamster said:
are you wanting something like this only to convert down to 92mm?

would it be possible to modify the ventilation but still meet the requirements for RF isolation? (for example a larger number of smaller holes), or add additional ventilation mounts?

edit, found the right sized one

only other possibility i could think would be to rig up an air compressor to blast air through the system, although that's not exactly going to be cheap or effecient.
Click to expand...

I had seen those, but I don't think they provide enough distance between the fan and the side of the chamber to allow stable airflow.

Alas, modifying the ventilation holes or adding more would reduce the amount of RF isolation, possibly causing local radio interference.
 
You could even go full Blue Peter and use sticky-backed plastic over the the cornflakes packet!

Seriously, though, using a compressor is a good idea, but you should cool the air after it exits the compressor and before it enters the box as the act of compressing the air will warm it up. A compressor can also be noisy.
 
Enough RPM and air will move.
Might just need to use some pressure tolerating tubing as standoff...


Quartz said:
Seriously, though, using a compressor is a good idea, but you should cool the air after it exits the compressor and before it enters the box as the act of compressing the air will warm it up. A compressor can also be noisy.
Click to expand...
That cooling is needed in compression stage to fit air into smaller volume.
Hence heavily ribbed outer surface of piston blocks in properly powerful air compressors.
Compressed air coming out again cools because of its expansion.
 
EsaT said:
Compressed air coming out again cools because of its expansion.
Click to expand...

True, but the air still ends up hotter than it was before compression unless it's cooled when compressed, which can seriously cool the expanded gas.
 
Quartz said:
True, but the air still ends up hotter than it was before compression unless it's cooled when compressed, which can seriously cool the expanded gas.
Click to expand...

depends on the flow rate but pretty much yes.

thing is, it's a really inneffecient way of getting cooler air, although wether the application is worth it is up to the op.
 
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