Recommendation for a heater blower
Recommendation for a heater blower
(OP)
Hi,
My application involves heating an enclosed area of 6'X 2'X 3'(36 ft^3) to a temperature range of 150 F ~ 200 F for a period of 12 hours. This enclosure will be made out of Al sheets & insulated with foam.
(This setup is used to dry out an assembly for further testing)
Can anyone suggest a heater blower for my application? The BTU requirement comes out to be 5400 btu/hr. I came across some heater blowers through a google search, but I am not sure what kind of heater I need to use for such a small enclosure. Any ideas?
Thanks,
Mike
My application involves heating an enclosed area of 6'X 2'X 3'(36 ft^3) to a temperature range of 150 F ~ 200 F for a period of 12 hours. This enclosure will be made out of Al sheets & insulated with foam.
(This setup is used to dry out an assembly for further testing)
Can anyone suggest a heater blower for my application? The BTU requirement comes out to be 5400 btu/hr. I came across some heater blowers through a google search, but I am not sure what kind of heater I need to use for such a small enclosure. Any ideas?
Thanks,
Mike





RE: Recommendation for a heater blower
If it will be used often the solutions would be much different.
There are many types of "box heaters". They are just metal box with a bunch of nichrome coils weaved around inside that you blow air thru.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Recommendation for a heater blower
RE: Recommendation for a heater blower
RE: Recommendation for a heater blower
The application involves maintaining the hardware in that temp range for a period of 12 hours. So this will have to work without supervision.
RE: Recommendation for a heater blower
(2W/m^2-K)*(5m^2)*(200R-70R)=2464 BTU/hr, which would be the worst-case, i.e., an uninsulated box.
TTFN
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RE: Recommendation for a heater blower
Each one should have a small blower mounted to it to force air at a high velocity thru it.
They each should have included on them, from the factory, a manual-reset over temperature switch to trip them off when a blower fails.
They should be mounted vertically in corners.
They should have ducting to make them draw air from the floor and blow it out at or near the ceiling. This is how you homogenize the air/temperature.
You control it all with a single panel-mount PID controller. You need to control the actual power with relays, possibly solid state relays, depending on the accuracy desired.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Recommendation for a heater blower
The btu is calculated using a factor for average insulation which is 1.25 in this case. So for a 120 rise in temp (worst case), I get 6 X 2 X 3 X 120 X 1.25 = 5400 btu/hr
Infact I get an even higher btu/hr value from this online calculator below,
http://www.heatershop.com/btu_calculator.htm
RE: Recommendation for a heater blower
That might work but I want to keep it simple by just installing a single heater. There must be something out there that blows air between 150 F & 200 F right???
Thanks,
Mike
RE: Recommendation for a heater blower
It's all about mixing! You need to have the air mixed. If you don't then you will get major stratification.
It doesn't matter how hot the air is out of the heater because it is supposed to be blowing all over and rapidly mixing.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Recommendation for a heater blower
RE: Recommendation for a heater blower
However, that raises the question of how long, how fast, i.e., how fast does it need to reach temperature, and how long are you doing this?
TTFN
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RE: Recommendation for a heater blower
First, figure out the surface area:
For a 6x2x3 box it's:
6x2x2+6x3x2+2x3x2=72 square feet or 6.7 square meters.
Then look up the conductivity of the chosen insulation. Since the OP hasn't told us what type of "foam" he intends to use, let's just go for expanded polystyrene which has a thermal conductivity of 0.03 W/mK.
Then, let's not forget that we need to know the thickness of the insulation. Again, the OP hasn't told us, so let's guess an inch (0.0254 meters)
Then let's remember that the delta-T term is the difference of temperature across the insulation. We know that the desired inside temp is 200 F (93 C). We'll assume a 23 C ambient to give a nice round 70 K delta-T.
Now we can plug it all together:
q = k A dT / s
.03 x 6.7 x 70 /.0254 = 554 watts or 1890 BTU/hr.
RE: Recommendation for a heater blower
Oh, smoked. Just like an EE. Personally, I'd use a more complex device, called a THERMOSTAT. Temp drops, switch goes on, temp rises, switch goes off. They've only been around about a million years, and even us dumb mech types can figure them out.
Yeah, I know, "how are you going to tune the loop with a dumb thermostat". :)
RE: Recommendation for a heater blower
TTFN
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RE: Recommendation for a heater blower
Drying requires air turnover. Which certainly implies more heating capacity than just the enclosure loss. Probably means no insulation too. Now we are getting to the crux of the problem. Essentially the OP just wants to blow 200F air all over something.
There are many ways to dry paint, including just lights, like a paint drying booth.
Look in www.grainger.com for heaters.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Recommendation for a heater blower
Are there any limits on air velocity?
The power input required will be much much higher than merely meeting the thermal losses through the enclosure because if this rig is going to dry the equipment then it has to carry the liquid out in the vapour state, so there is the latent heat of vapourisation to deliver, plus whatever the entrained heat in the exhaust stream turns out to be.
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If we learn from our mistakes I'm getting a great education!
RE: Recommendation for a heater blower
The assembly will be soaked in water & no limits on air velocity.
itsmoked,
The paint drying booth is an interesting idea. It didn't occur to me to use something like a quartz lamp to provide infrared heat. I guess I would need to connect a blower of some sort to circulate air though?
I could also connect it to a thermostat to turn it off once the temp exceeds 200F & turn it back on once the temp drops below 150F like bluetrueblood pointed out.
MintJulep,
You are right. The BTU/hr requirement after I recalculated it came out to be ~ 2000 BTU/hr or 593 Watts. A Quartz lamp can provide 600 Watts. Take this one for example,
http://www.mcmaster.com/#3343k17/=2xwqq3
The only questions I am concerned with are,
1. Will this Quartz bulb provide enough energy to dry this assembly? (I mean would I need to install a blower to circulate air?)
or do I need to go for something like a blower heater,
http://www.grainger.com/Grainger/items/4Z717
2. How many vent holes would I need to punch in this enclosure?
Thanks for you replies,
Mike
RE: Recommendation for a heater blower
Put in a few heat lamps of the 250W variety. Spread them around to try to evenly "light" your fixture.
You would want a little ventilation. So little, that convection would probably be fine. That could be a large central ceiling opening and a few low openings around the periphery.
Run your lights and measure the temperature one your fixture with a temp gun to make sure you don't exceed the allowed temp on any spots. If some spot seems too cold add or move the lights. Since it is metal you will automatically get some heat spreading about so that light pointing shouldn't be too finicky.
If you get the air flow and lighting correct you can probably skip the temp control all together.
Keith Cress
kcress - http://www.flaminsystems.com