1) the fiberglass is capable to witstand the 200 C but never the 700. You should look for rockwool (basalt wool) fabric capable to stand for near the 1000 C.
2) The any resistive wire, and canthal is not any exclusion, needs to have a current between the minimum and maximum current density. The maximum density is specified in datasheet, You cannot to overstep it to avoid the fast degradation of wire. But minimum stays very near to maximums, about 3/4 or so. Just take the power You calced using Stefan-Bolcmann formula, and guess the heat transfer 99% is made via radiation. Means, You evaluate the appropriate wire walls surface. Need to adda the 50% constructors specifically here makes the giant mistakes what results in very short exploitation longevity.
3) The chosen diameter gives a certain resistance, thus may calc the needed length for the given voltage.
4) Particularly, very much good handbook for the aim is http://mtixtl.com/machineflyer/handbook.pdf
5) For ordinary vacuum system de-gassing the most simplest "DEWA cable" of Dewa heated floors may be used, but it hardly stands over 100 C.
6) For vacuum systems specifically, more effective as heating-cooling is process of inner etching, just apply the coronating thin wire somewhere inside connected with MOT transformer with standard magnetron voltage multiplier (3 kV) in series with 50W 20 kOhm resistor to limit the current. The de-gassing time span is lesser and vacuum cleanness is better after that.

 

1) the fiberglass is capable to witstand the 200 C but never the 700. You should look for rockwool (basalt wool) fabric capable to stand for near the 1000 C.
2) The any resistive wire, and canthal is not any exclusion, needs to have a current between the minimum and maximum current density. The maximum density is specified in datasheet, You cannot to overstep it to avoid the fast degradation of wire. But minimum stays very near to maximums, about 3/4 or so. Just take the power You calced using Stefan-Bolcmann formula, and guess the heat transfer 99% is made via radiation. Means, You evaluate the appropriate wire walls surface. Need to adda the 50% constructors specifically here makes the giant mistakes what results in very short exploitation longevity.
3) The chosen diameter gives a certain resistance, thus may calc the needed length for the given voltage.
4) Particularly, very much good handbook for the aim is http://mtixtl.com/machineflyer/handbook.pdf
5) For ordinary vacuum system de-gassing the most simplest "DEWA cable" of Dewa heated floors may be used, but it hardly stands over 100 C.
6) For vacuum systems specifically, more effective as heating-cooling is process of inner etching, just apply the coronating thin wire somewhere inside connected with MOT transformer with standard magnetron voltage multiplier (3 kV) in series with 50W 20 kOhm resistor to limit the current. The de-gassing time span is lesser and vacuum cleanness is better after that.

Thank you bud. Kanthal is rated well over my temp and the fiberglass heat tape I have is rated at over 1400f continuous operation. Nither my heat Element or shield will be over 50% of their max tolerances.

 

Oh geeze! I thought You gonna play with vvacuum, but the goal is to distill the sulfuric toward the conc useful for illegal drug making? (joke). So, the standard "Czecsk glass" flasks are ready to stand about 350-400 C and no more. Only imagine the 5 liters of smoking sulfuric lake slow filling Your room floor and sliding down the staircase!
Thus, one of rather cheap materials capable to stand the sulfuric is phosphorous cement smeared over the stainless kettle. However the stainless also not loves any temperature over 500-600 C and loss of form begins. May strengthen it by porous schamot bricks. Phosphorus cement may be produced from kaolin clay or with some additional ingredients from SiO2. It can more easy be done from MgO, but then it cannot stand those 1200-1400 C what clay gives. To clay must be added ortophosphoric acid by small portions until clay is formable. Yet cannot comment how to form it if one touching with fingers produce several burns healing a half dozen of years, but that is solvable, somehow. When the form is pressed and acid is dried bit, put it in old kitchen cooker and warm up to 180 C for about 20 minutes or bit longer. Result - electric resistance about 10 GOhm per cm, mechanic strength about like the average steel, thermal expansion similar like cast iron, absolute acid-proof, most of alkali-proof, methanol-proof, ant-acid-proof etc etc benefits. But for Young modulus rather similar to glass.
Once I had to make a larger HCl cistern at 150 C and it worked impressively well.

 

RE:""Kanthal is rated well over my temp""
The question is not about rating of canthal per se, even nichrome stands 1100 C shortly and 1000 C for a long, and canthal at least some 200-600 C better. But question is about CORRECT choice of wire side walls surface , and without of keeping inside the handbook I gave a link recommended boundaries Your job and material will go to the junk. Hardly suggest to read it before any motion.
PS - Do You are from Europe if noted my post just immediately? With US I have half day difference. Just now I have 19:41 o clock.
If so, the absolutely best shop for canthal wire is here some 20 km off from me www.keramserviss.lv - how far I remember they are able to send the purchases by post and are well trained to work in all three Baltic republics and Scandinavia.

 

If look deeper about picture given by Shortbus, it is rather wise construction of heavy elements but completely short by heater element. The inner wall must be organized like horizontal channels. When make the form, of course You`ll use the schamot clay, let use the plywood plate on which nail the small 8x8 mm window wood glass-keeper stakes, then press the clay and soon after rol it in third coordinate as You wish. When dried, set the windings into that channels and smear a bit in rare points (avoiding to shade the wire surface too much) let wire cannot to fall out.

Last but no least - the ends of wire must be winkled double or three-double to itself like litz-wire uses to do. Other-how wire will like to degrade first at connection points not in the hot zone. For 1100 I would recommend 3x, but 700 C may use a 2x winkle.

 

For 8feet of heat tape

You keep throwing that 8 feet number out but you said your flask is only 5 inches in diameter. Did you even bother to figure the circumference of 5"? It's only ~15 3/4 inches. And that's at the middle of the round, as it goes down it will get shorter on each wrap.

Then there is the glass flask, it's MAX temp is ~500C but working temp is ~350C. The you don't seem to know the boiling point of sulfuric acid. It's not what you think but only " The boiling point (at 1013 hPa) is 290°C for 100% sulphuric acid and 310 to 335°C for 98% sulphuric acid. "

I don't want to see you hurting your self or others around you. I, personally, think you need to do some more research before really getting farther into your project.

 

1) the fiberglass is capable to witstand the 200 C but never the 700. You should look for rockwool (basalt wool) fabric capable to stand for near the 1000 C.
2) The any resistive wire, and canthal is not any exclusion, needs to have a current between the minimum and maximum current density. The maximum density is specified in datasheet, You cannot to overstep it to avoid the fast degradation of wire. But minimum stays very near to maximums, about 3/4 or so. Just take the power You calced using Stefan-Bolcmann formula, and guess the heat transfer 99% is made via radiation. Means, You evaluate the appropriate wire walls surface. Need to adda the 50% constructors specifically here makes the giant mistakes what results in very short exploitation longevity.
3) The chosen diameter gives a certain resistance, thus may calc the needed length for the given voltage.
4) Particularly, very much good handbook for the aim is http://mtixtl.com/machineflyer/handbook.pdf
5) For ordinary vacuum system de-gassing the most simplest "DEWA cable" of Dewa heated floors may be used, but it hardly stands over 100 C.
6) For vacuum systems specifically, more effective as heating-cooling is process of inner etching, just apply the coronating thin wire somewhere inside connected with MOT transformer with standard magnetron voltage multiplier (3 kV) in series with 50W 20 kOhm resistor to limit the current. The de-gassing time span is lesser and vacuum cleanness is better after that.

Thank you bud. Kanthal is rated well over my temp and the fiberglass heat tape I have is rated at over 1400f continuous operation. Nither my heat Element or shield will be over 50% of their max tolera

You keep throwing that 8 feet number out but you said your flask is only 5 inches in diameter. Did you even bother to figure the circumference of 5"? It's only ~15 3/4 inches. And that's at the middle of the round, as it goes down it will get shorter on each wrap.

Then there is the glass flask, it's MAX temp is ~500C but working temp is ~350C. The you don't seem to know the boiling point of sulfuric acid. It's not what you think but only " The boiling point (at 1013 hPa) is 290°C for 100% sulphuric acid and 310 to 335°C for 98% sulphuric acid. "

I don't want to see you hurting your self or others around you. I, personally, think you need to do some more research before really getting farther into your project.

You should watch those vids I linked bud. And I appreciate your concern. So much mixed information out there

 

Rather than try to create a tape to wrap around what I am guessing would be a glass flask, I suggest creating a refractory cup sort of arrangement that aould include a recess grove that the coiled heater wire could reside. That would tend to have the heat distributed a bit more evenly because the transfer mechanisms will be radiation and convection, rather than localized conduction. The other benefit is that it will avoid the problem of the tape loosening as both the heater wire and the fiberglass tape will expand a bit as they heat. Creating a suitable groove in the refractory material as it hardens can be done either with a carving tool, or by pressing a suitable material in to create the groove, and then removing that material, which could be insulated wire of a suitable outside diameter, or plastic rope, or even plastic hose of a small diameter. any inaccurate areas can be opened up with the carving tool when the refractory is closed to the solid final set. Certainly some advanced planning would be required, but that would be based on having decided the total length of the heater element,
I agree that eight feet is quite a long bit to wrap around a one liter flask of any shape that I have seen. But I am not aware of how close the covering of the flask surface is planned on. With fairly close spacing eight feet may be a reasonable length.

 

1) the fiberglass is capable to witstand the 200 C but never the 700. You should look for rockwool (basalt wool) fabric capable to stand for near the 1000 C.
2) The any resistive wire, and canthal is not any exclusion, needs to have a current between the minimum and maximum current density. The maximum density is specified in datasheet, You cannot to overstep it to avoid the fast degradation of wire. But minimum stays very near to maximums, about 3/4 or so. Just take the power You calced using Stefan-Bolcmann formula, and guess the heat transfer 99% is made via radiation. Means, You evaluate the appropriate wire walls surface. Need to adda the 50% constructors specifically here makes the giant mistakes what results in very short exploitation longevity.
3) The chosen diameter gives a certain resistance, thus may calc the needed length for the given voltage.
4) Particularly, very much good handbook for the aim is http://mtixtl.com/machineflyer/handbook.pdf
5) For ordinary vacuum system de-gassing the most simplest "DEWA cable" of Dewa heated floors may be used, but it hardly stands over 100 C.
6) For vacuum systems specifically, more effective as heating-cooling is process of inner etching, just apply the coronating thin wire somewhere inside connected with MOT transformer with standard magnetron voltage multiplier (3 kV) in series with 50W 20 kOhm resistor to limit the current. The de-gassing time span is lesser and vacuum cleanness is better after that.

Thank you bud. Kanthal is rated well over my temp and the fiberglass heat tape I have is rated at over 1400f continuous operation. Nither my heat Element or shield will be over 50% of their max tolera

You keep throwing that 8 feet number out but you said your flask is only 5 inches in diameter. Did you even bother to figure the circumference of 5"? It's only ~15 3/4 inches. And that's at the middle of the round, as it goes down it will get shorter on each wrap.

Then there is the glass flask, it's MAX temp is ~500C but working temp is ~350C. The you don't seem to know the boiling point of sulfuric acid. It's not what you think but only " The boiling point (at 1013 hPa) is 290°C for 100% sulphuric acid and 310 to 335°C for 98% sulphuric acid. "

I don't want to see you hurting your self or others around you. I, personally, think you need to do some more research before really getting farther into your project.

You should watch those vids I linked bud. And I appreciate your concern. So much mixed information out there

Rather than try to create a tape to wrap around what I am guessing would be a glass flask, I suggest creating a refractory cup sort of arrangement that aould include a recess grove that the coiled heater wire could reside. That would tend to have the heat distributed a bit more evenly because the transfer mechanisms will be radiation and convection, rather than localized conduction. The other benefit is that it will avoid the problem of the tape loosening as both the heater wire and the fiberglass tape will expand a bit as they heat. Creating a suitable groove in the refractory material as it hardens can be done either with a carving tool, or by pressing a suitable material in to create the groove, and then removing that material, which could be insulated wire of a suitable outside diameter, or plastic rope, or even plastic hose of a small diameter. any inaccurate areas can be opened up with the carving tool when the refractory is closed to the solid final set. Certainly some advanced planning would be required, but that would be based on having decided the total length of the heater element,
I agree that eight feet is quite a long bit to wrap around a one liter flask of any shape that I have seen. But I am not aware of how close the covering of the flask surface is planned on. With fairly close spacing eight feet may be a reasonable length.

Np. Yeah in the video by nurd rage he BARLEY covers his 100ml flask coiling 4ft of wire. So I did the mafs that if a 2.5" rbf needs 4' of tape to cover it, my 1lrbf that is roughly 5" base would need roughly twice the length. 8feet.(case you don't have time for those vids)
@shortbus
And @MisterBill2 I like that design idea. It may be to much work for me intially here and I def don't have the materials or anything for that but end goal here would be to have a very nice neat at least semi industrially polished product hah. I will def add that to the list to look into after rough prototype is done here. Ty so much gang

 

Thank you bud. Kanthal is rated well over my temp and the fiberglass heat tape I have is rated at over 1400f continuous operation. Nither my heat Element or shield will be over 50% of their max tolera

You should watch those vids I linked bud. And I appreciate your concern. So much mixed information out there

Np. Yeah in the video by nurd rage he BARLEY covers his 100ml flask coiling 4ft of wire. So I did the mafs that if a 2.5" rbf needs 4' of tape to cover it, my 1lrbf that is roughly 5" base would need roughly twice the length. 8feet.(case you don't have time for those vids)
@shortbus
And @MisterBill2 I like that design idea. It may be to much work for me initially here and I def don't have the materials or anything for that but end goal here would be to have a very nice neat at least semi industrially polished product hah. I will def add that to the list to look into after rough prototype is done here. Ty so much gang

OK, it seems that others are involved. I had guessed that this was a one-off maker project, evidently not. The need for appearance does add more requirements.
What is going to be cooking in that flask? it could be a metal alloy with that temperature. Or is it a top secret sort of project??

 

OK, it seems that others are involved. I had guessed that this was a one-off maker project, evidently not. The need for appearance does add more requirements.
What is going to be cooking in that flask? it could be a metal alloy with that temperature. Or is it a top secret sort of project??

Oh no I only need one rn but I may need more down the road. An I just like my stuff now. An only me, just I was using those two vids for my guidelines. And I just want to be covered for my chemistry carrier and not need more heating down the road. I tried a hot plate and it broke within a week. Sick of buying stuff that doesn't work an the stuff that does is so far out of my price range it myswell be a fantasy being a poor working class in America. So making it myself the best I can to meet my needs is what I'm doing =] so no worries about that jus doing best I can here lol

 

I would love to get this figured out ASAP tho so I can just get back to my projects. Miss chemistry an haven't done any since hotplate broke.
Who knows trying to figure out a coiled piece of kanthal would take me weeks and every internet forum known to man XP still no answer. I seriously underestimated how hard the equation is. I thought I was just dumb but seems no one else can figure it out it either so feel a lil better haha

 

So then your plan is to wrap the flask clear to the top? Not like any of the mantles in your video or the one I posted. They only go to the midpoint of the ball part of the flask.

You say no one can figure the amount of wire you need, but you don't want to believe the videos. Draw a 5" circle on paper. Draw a mid line and then lines every 1/2" down to the bottom of the circle. The measure the center distance of those lines(1/4" from the line you drew) and multiply those by. That will give you the circumference for each wrap of heat tape or wire.

Kanthal also has free help on their website. https://www.kanthal.com/en/products/furnace-products/electric-heating-elements/

 

So then your plan is to wrap the flask clear to the top? Not like any of the mantles in your video or the one I posted. They only go to the midpoint of the ball part of the flask.

You say no one can figure the amount of wire you need, but you don't want to believe the videos. Draw a 5" circle on paper. Draw a mid line and then lines every 1/2" down to the bottom of the circle. The measure the center distance of those lines(1/4" from the line you drew) and multiply those by. That will give you the circumference for each wrap of heat tape or wire.

Kanthal also has free help on their website. https://www.kanthal.com/en/products/furnace-products/electric-heating-elements/

Yeah. I'm finding premade heat flask inserts to that are pretty price friendly and would really simplify my needs, but none that are for 1l rbf with 450c capabilities yet. Well that aren't 200 bux. They got like 380cs 20 to 30 bucks or so. I'm giving up on this probably unless someone who knows the equations comes out an is like hey I did the math this is what you need lol

 

For a cheating trick to discover the length of heater wire required, get a roll of either insulated wire or plastic clothesline rope the diameter of the coiled heating cord you intend to produce. Then wrap it around the flask you are intending to use, in the arrangement you are planning to use. When it looks like what you want to create, mark the end, unwind it, and measure the length. That will give you a close measure of the element length. Then decide the spacing between turns, and calculate the number of turns wrapped around your selected core diameter. That will allow you to calculate the number of wraps.
Then calculate the length of one wrap around the core. Multiply that by the number of wraps and you will have close to the length to wrap around the core. That will give the total length of resistance wire wrapped around the core.
add a foot at each end and you have your total required length, based on actual measurements. No need for any formula.