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A fan. My kingdom for a fan!

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A fan. My kingdom for a fan!

Unread postAuthor: D_Hall » Sat Nov 05, 2011 12:26 pm

Odd situation....

I need a fan to move air around. A 6" muffin fan (ie, largish computer cooling fan) would be ideal. Brushless. Small. Inexpensive. Designed for the kind of air movement I need.

There's just one catch: My fan needs to operate in a 350 degree F environment.

Ya'll seem to be up on weird fans more than I am.

Thoughts?
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Unread postAuthor: MRR » Sat Nov 05, 2011 12:32 pm

350°F would obviously be to hot for a computer fan. You could salvage a fan from a baking oven on a scrapyard.
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Unread postAuthor: Fnord » Sat Nov 05, 2011 12:54 pm

Will this need to be a direct-drive fan? I'm guessing yes, but a belt drive or long shaft would simplify things.
Duty cycle? Required lifespan? Any other concerns (like soot/grease?).

I don't have anything laying around, but...
A quick scouring of the internet turns up a few fans of similar specification (mostly chimney fans), but I don't think you'd be interested in these, since they're sold by fan companies and probably expensive.

Would it be possible to find a small heat-resistant or fire-rated motor and stick a set of blades on it? Small aluminum fan blades are pretty easy to come by.

edit, microwaves are built to run pretty hot due to manufacturing costs... I wonder if the fan motors from one could take the heat? You can probably get one for free so it's worth a try.
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Last edited by Fnord on Sat Nov 05, 2011 1:04 pm, edited 1 time in total.
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Unread postAuthor: D_Hall » Sat Nov 05, 2011 1:02 pm

Perhaps the biggest issue is that things need to be light weight and cheap. The fan will be used to stir air in an oven, but the oven will be destroyed before all is said and done.

There's more to it, but I'm not sure how much I can say (it's for work, obviously).

The heat-resistant or fire-rated motor and throwing blades on it would work just fine but I've not seen such a motor for a reasonable cost (say, under $75). That doesn't mean it isn't out there, mind you. It just means I haven't found it.
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Unread postAuthor: Fnord » Sat Nov 05, 2011 1:14 pm

Is "explosion proof" going to be a requirement also? (meaning no possibility of igniting anything).
For an alternative, and I'm not making any assumptions about the time and effort you're willing to spend here, but something ion-based could be used for moderate airflow at high temperatures, since the HV driver circuit can be completely isolated.
Cheap and lightweight also.
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Unread postAuthor: D_Hall » Sat Nov 05, 2011 1:15 pm

Fnord wrote:Is "explosion proof" going to be a requirement also? (meaning no possibility of igniting anything).

Yes and no.

Functionally, yes.

But I don't require certifications.

For an alternative, and I'm not making any assumptions about the time and effort you're willing to spend here, but something ion-based could be used for moderate airflow at high temperatures, since the HV driver circuit can be completely isolated.
Cheap and lightweight also.

I've no idea what you're talking about here. Educate me?
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Unread postAuthor: Mr.Tallahassee » Sat Nov 05, 2011 1:25 pm

He's talking about a "bladeless fan" that uses high voltage circuits to create airflow. I wish I could explain how it works but I really can't. They actually just started making fans like that commercially. Google is your friend!
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Unread postAuthor: Labtecpower » Sat Nov 05, 2011 1:49 pm

Basically works like this.

[youtube]http://www.youtube.com/watch?v=kZsrrJDlrDM[/youtube]

I believe there is some stupid stuff in this video, but it should give an idea.

Click the link and read the description for more information :wink:
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Unread postAuthor: jimmy101 » Sat Nov 05, 2011 2:26 pm

You might get lucky and a standard PC case or CPU fan might just survive 350F. Probably worth a try since they are so cheap. Stick one in the oven at home (when your wife is away) and see what happens. :D

A convection oven fan is a good idea but I suspect they are pretty pricey and the chances of finding one at a junk yard are probably pretty slim.

Possible to locate the motor outside the chamber and run the shaft through a bushing?
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Unread postAuthor: jrrdw » Sat Nov 05, 2011 3:51 pm

Would the heat rising turn a set of blades good enough to move the needed amount of air flow? A set of blades on a pivet pin on a all steel roller bearing lubed with Permatex Anti-Seize...
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Unread postAuthor: saefroch » Sun Nov 06, 2011 4:19 pm

I did some research a while ago and I found that those "bladeless" fans as you call them are infamous for creating ozone and if they do that, I imagine they also produce all sorts of oxides of nitrogen. So if you're okay with that... that's probably your answer.
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Unread postAuthor: D_Hall » Sun Nov 06, 2011 5:16 pm

jrrdw wrote:Would the heat rising turn a set of blades good enough to move the needed amount of air flow? A set of blades on a pivet pin on a all steel roller bearing lubed with Permatex Anti-Seize...

Heat rising implies a temperature gradient. That's the very purpose of the fan; preventing temperature gradients. So even if it would work, the very fact that it would work means I've already failed. (Did that make sense?)

jimmy101 wrote:Possible to locate the motor outside the chamber and run the shaft through a bushing?

I've done that in the past. I works.... barely. It's that "barely" part that bothers me and why I'm trying to do something better.
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Unread postAuthor: jrrdw » Sun Nov 06, 2011 6:46 pm

D_Hall wrote:
jrrdw wrote:Would the heat rising turn a set of blades good enough to move the needed amount of air flow? A set of blades on a pivet pin on a all steel roller bearing lubed with Permatex Anti-Seize...

Heat rising implies a temperature gradient. That's the very purpose of the fan; preventing temperature gradients. So even if it would work, the very fact that it would work means I've already failed. (Did that make sense?)


Yea it did make sense. If you use a motor driven fan (direct drive) how are you going to run in the power supply with out cooking the leads? If you work fast enough before they melt and short...
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Unread postAuthor: POLAND_SPUD » Sun Nov 06, 2011 7:30 pm

hmmm get a small air motor
THough I guess you need one that has a port for vented air
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Unread postAuthor: D_Hall » Sun Nov 06, 2011 10:27 pm

jrrdw wrote:Yea it did make sense. If you use a motor driven fan (direct drive) how are you going to run in the power supply with out cooking the leads? If you work fast enough before they melt and short...

High temperature wiring is readily available. That part is easy.

POLAND_SPUD wrote:hmmm get a small air motor
THough I guess you need one that has a port for vented air

Yeah, an air motor is possible but they're a tad bit expensive for a single use item.
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