Transparent Bridgman Furnace-Heating Coil Questions

Thread Starter

Crystalgrower

Joined Feb 6, 2018
3
I am trying to create a transparent Bridgman furnace (tube furnace) with two zones. The furnace will consist of two quartz tubes concentric with each other and the inner tube will have coils of heating wire wrapped around it. The two zones of heating (two seperate coils each spanning half the length of the inner tube) will be powered by a PID controller rated at 115V and 17.4A.

Inner tube: Inner Diameter 55mm (~2.2in), Outer Diameter 59mm (~2.3in), Length 36in
Outer tube: Inner Diameter 70mm (~2.8in), Outer Diameter 74mm (~2.9in), Length 36in

I would like both the top and bottom zones to be capable of creating up to 1000C temperatures inside the inner tube. Due to the small size of the ampoule use for the crystal growth it can be safely assumed that the interior of the tube is just air.

Questions:
What gauge wire and what type of wire should I use to create the resistance heater coils without harming my PID controller?
What length of wire can I use to form the wire coils using the chosen wire gauge?

If someone could show me with calculations that if I were to purchase ___ guage of ___ type of heater wire I could easily create 1000C without getting even close to hurting my instruments I would be ecstatic.The specifics of these calculations are confusing me and the PID controller is much too expensive to trust my level of knowledge. A good reference image for something similar to what I am creating is http://www.tvu.com/TFOps850C5Mar11.jpg though I am not using any form of gold coatings. Thank you for any replies you give me!
 

philba

Joined Aug 17, 2017
960
I've never done anything close to this so take what I say with a grain of salt. Nichrome has a melting point of about 1400C so you might be able to use that. There is a lot of guessing from that picture but assuming 60 turns of wire on a 59 mm form it looks like there is one continuous 11 meter length of wire. The problem I see is with that long, single length wire, you will have to go to a pretty low gauge to be able to use 115V and that will take a lot of amps. More than your controller is capable. More than a 115VAC wall outlet is capable of. The online calculators I looked only go down to 10 ga and 14KW would be needed to get to 1000C but that was at like 200V. Your PID controller can do about 2KW.

Not sure what to suggest. Maybe there is more information out there than just a picture...
 

Thread Starter

Crystalgrower

Joined Feb 6, 2018
3
Thank you for the response. Which online calculator were you using to come up with the 14KW number? If you walk me through the steps of what you are doing to come up with your numbers I can start crunching the numbers myself. I obviously see P=IV but the rest is foreign to me.

Some additional details:
1) There will be two zones which each comprise one half the length of the quartz tube, so 1.5ft each. I can select the number of turns/length of wire to whatever is needed to create the desired temperature.
2) If 1000C is not possible I can compromise and do 800C instead.
3) The length of the tube can be reduced if necessary to reach the temperature.
 

philba

Joined Aug 17, 2017
960
Here's one calculator - https://www.easycalculation.com/engineering/electrical/nichrome-wire-calculator.php

With 2 zones, you can cut the wire length in half. A 5.5M length of 18 ga nichrome will get to 800C with 112V and 14.8 A. You will need two of those, on different circuits.

I would investigate using 230VAC, it's what most kitchen ovens use.

Also, I wonder if that many turns (in the picture) are needed. Guess it depends on heat loss - insulation is your friend.
 
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