Adding a fan to a explosion proof enclosure 2

[tienti]

Hi,

Any help is appreciated and thanks in advance.

We have a large brake resistor inside an enclosure and we're thinking of adding a fan inside for cooling because the inside can reach temperatures as high as 70-80 celcius.

The problem is that explosion proof enclosures usually don't have any openings so its like a catch 22. Any ideas to solve this?

Thanks!

Doing Work

 

[StoneCold]

You say that you have an explosion proof enclosure.
Do you have a true cast aluminum enclosure with a bunch of bolts holding it closed or is it a purged Nema4x enclosure that you have made explosion proof?
Do you have the whole VFD inside the enclosure?
How big is the enclosure?
Do you currently have any cooling media available? Tower Water, Chiller, Compressed air, Nitrogen?

Thanks
StoneCold

 

[MiketheEngineer]

IMHO - if it blows - it blows and takes the fan with it. Maybe a minor explosion will expel through the fan hole - but I doubt it.

I strongly believe you need real expert help in this situation.

 

[racookpe1978]

Be careful.... Adding a fan inside a closed system will force the fan's motor energy energy (all inefficiencies such as friction, rotation losses, electrical resistance, etc.) to remain inside as heat energy.

Now, what will happen is a (perhaps large) increase in thermal heat transfer between a the initial case of a non-moving atmosphere with forced convection/conduction all around the whole case's interior. That will help.

Outside heat removal (water-based heat exchanger outside the box using natural convection of the water?) possible?

 

[IRstuff]

Just need to cover the inside and outside with pin fins for the fan air to impinge on.

TTFN
faq731-376

 

[DRWeig]

Make no holes!

The only acceptable ventilation is by labyrinth-style listed explosionproof breathers or breather/drains.

Do what IRstuff said, and consider an external (explosionproof) fan blowing across the outside fins. Calculating the cooling effect is beyond my (electrical) focus, but based on my knowledge of heat sink design, it could be quite substantial.

Another question: Is there anything in this box other than the resistors? If so, consider separating the resistors into their own enclosure (with a disconnect switch if necessary) and choose products rated for the extra-high temperature. Add a warning sign about the hot surface that shouldn't be touched, and you should be good to go.

Good on ya,

Goober Dave

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[tienti]

Thanks All! Some more info on this, the resistor will be running for 20 minutes tops and will be in its own enclosure, so we're thinking of using a larger aluminum enclosure and use the breathers that DRweig suggested.

Doing Work

 

[CastMetal]

If you are redesigning the enclosure that extensively I would also reconsider IRstuff's suggestion. Fins or pins even with only natural convection will be very beneficial. A larger enclosure only marginally increases surface area and the labyrinth breather/drains are very narrow and likely will not create much air flow relative to your enclosure volume.
Just my two cents.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

 

[StoneCold]

If you are going to re-design why not go with a NEMA 4X design with a purge kit to get your rating. You can use the purge and limited venting to carry your heat away.

Regards
StoneCold