Alan B
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| posted on 14/11/11 at 03:46 PM |
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Thermal question...back to basics help needed
Guys,
It's so long since I did any thermal calcs I've almost forgotten most of it...
Basically I have a brass block I need to heat to about 155 degrees C that weighs around 180 grams and then have a controller hold it at around that
temperature. I need to know what wattage of cartridge heater will do the job without needing to be switched on and off too frequently. I guess there
is a theoretical wattage that will maintain the temperature based on room temp ambient temp and I'll need to select a bit higher in rating.
Cheers,
Alan
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Neville Jones
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| posted on 14/11/11 at 03:50 PM |
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Surface area and ambient temp have a big influence.
You'll need less heat in the tropics and in a heated room, than in the open in Antarctica. 
Cheers,
Nev.
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Alan B
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| posted on 14/11/11 at 03:58 PM |
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Nev,
The application is indoors in a factory setting in N. Carolina with a surface area of about 8 sq in.
Cheers,
Alan
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rodgling
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| posted on 14/11/11 at 05:22 PM |
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It probably depends on the exact brass alloy. The fact that WP doesn't list this sort of data makes me suspect there's a fair bit of
variability in its properties.
Easiest way is probably to heat it to 160 and see how long it takes to cool to 150 in an ambient environment (temperature and humidity) that roughly
matches the target environment. Then put in heat at about that rate.
Note that it won't lose much heat through the air, most will be through whatever it's in physical contact with.
[Edited on 14/11/11 by rodgling]
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Madinventions
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| posted on 14/11/11 at 05:24 PM |
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Did something very similar for work recently... Used a 1/2" diameter 1" long 150W 36V cartridge heater from Watlow and a CAL3300
controller from Farnell, but that was a 150g brass block that had to get to 550°C in a vacuum. I reckon you'd get away with 50-60W, but make
sure your hole fit is very good (10-20µm) if you're using cartidge heaters.
Ed.
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pewe
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| posted on 14/11/11 at 05:47 PM |
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For those amongst us who aren't qualified metallurgists WTF would you want to do that?
Cheers. Pewe 
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Alan B
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| posted on 14/11/11 at 06:14 PM |
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Thanks guys, good input.
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