High temperature (~950 C) heating blanket

[M_1]

TL;DR

I need to heat up a flat surface in a controlled way from room temperature to approximately 950 C, without combustion heaters.

Hi, I need to heat up a flat surface in a controlled way from room temperature to approximately 950 C. The surface will be some square meters large. Is there any way doing this without combustion, that is using a electric heating blanket? Does anyone know if such blankets exist? (Have already googled with negative result. 950 C seems to be very hot!) Thanks!

 

[davenn]

Summary: I need to heat up a flat surface in a controlled way from room temperature to approximately 950 C, without combustion heaters.

Hi, I need to heat up a flat surface in a controlled way from room temperature to approximately 950 C

why ? that's freakin hot ~ 510 C

you could use nichrome wire as a heater element but the list of suitable materials that it could be wrapped in is going to be very short

Again, what are you wanting to do this for ?

 

[Mark44]

that's freakin hot ~ 510 C

It's even hotter than that. The OP showed 950° C, not a Fahrenheit temperature.

 

[russ_watters]

Hi, I need to heat up a flat surface in a controlled way from room temperature to approximately 950 C. The surface will be some square meters large. Is there any way doing this without combustion, that is using a electric heating blanket? Does anyone know if such blankets exist? (Have already googled with negative result. 950 C seems to be very hot!) Thanks!

This would be a very serious industrial application; expensive, dangerous and using a ton of electricity. May I ask what this is for? There isn't much we can tell you based on that one-liner description.

Note that a 1 square meter object at 950C radiates at upwards of 100 kW.

 

[jrmichler]

Try search term industrial infrared heater. Chromalox is one company that makes electric infrared heaters. Here is a link to one with maximum temperature 1750 deg F (954 deg C): http://www.chromalox.com/en/catalog...hi-high-intensity-quartz-faced-radiant-heater.

I hope that you are aware of the energy involved. I used to work in paper mill that made, as one of their products, a heavy coated paper such as used for new car brochures. Paper coating is similar to thick paint. The paper was coated by applying too much, and scraping off the excess, all at 2500 ft/min. The coating had to be dry before contacting a roll, so they used an infrared dryer. That dryer was about ten feet long. When there was a web break, the paper in the dryer would stop, catch fire, and burn up in about one second. The web break made a BOOM, then about a second later, the flames were gone, leaving only ashes falling. High power infrared needs to be taken very seriously.

 

[Baluncore]

I need to heat up a flat surface

I think you need to identify the material to be heated. How thick is it and what is the thermal capacity. Heat loss will need to be prevented by insulation. Can it be placed in an insulated chamber, or must it be heated while it is fixed in place?
If it is electrically conductive it might be heated by resistance or by induction. Can it be passed through a molten salt bath?
How long must the temperature be maintained?
There are still too many possibilities to answer the question.

 

[davenn]

It's even hotter than that. The OP showed 950° C, not a Fahrenheit temperature.

ohh crap I totally misread
Strangely enough the sentence I deleted now fits well

" Hawai'ian lava fresh out of the volcano isn't much hotter than that -- 950C "

 

[M_1]

Many thanks for all the answers! I want to perform fire testing without a fire! More specifically I would like to test the fire resistance of a wall, say light concrete. According to the so called standard fire curve (ISO 834) the temperatur on the fire exposed side of the wall should be around 950 C after 60 minutes. I'm interested in the temperature development on the non-exposed side of the wall, but not using a combustion furnace.

I understand that a considerable electric power will be required. But the blanket/heater would be attached to the wall surface so there would not be radiation into free space, but still much power required I guess.

 

[Vanadium 50]

I understand that a considerable electric power will be required.

I don't think you do. You're talking several hundred kilowatts for several square meters: about a megawatt. You don't get that much by just plugging into a wall socket. It's equivalent to one stick of dynamite going off every second.

Also, every joule that goes in has to come out again...

 

[Baluncore]

The only realistic way to achieve that heat for any period would be to use an exceptionally well insulated test chamber. I expect you will need ceramic foam tiles. You will also need to control the chamber atmosphere.

 

[russ_watters]

I understand that a considerable electric power will be required. But the blanket/heater would be attached to the wall surface so there would not be radiation into free space, but still much power required I guess.

Keeping the gap small reduces loss and keeps the power input from INCREASING beyond 100 kW per square meter (actually it's 125 without insulation). That's the MINIMUM initial power input, but after the wall started heating and acted as insulation it would start to drop.

950C is a lot hotter than wood burns, though; do you really need it that hot?

 

[anorlunda]

Would you consider a plasma torch combustion?

 

[Tom.G]

Would you consider a plasma torch combustion?

Unfortunately, same power requirement, VERY high design/engineering cost for that size!

 

[anorlunda]

Unfortunately, same power requirement, VERY high design/engineering cost for that size!

Yes, same power, or even more than by direct heating.

But an array of multiple plasma torches could do it. Electric plasma torches can be purchased commercially.

 

[gmax137]

is it really necessary for the sample material to be several square meters? why can't the test be on a small sample in a kiln or heat treat oven?

 

[cjl]

Keeping the gap small reduces loss and keeps the power input from INCREASING beyond 100 kW per square meter (actually it's 125 without insulation). That's the MINIMUM initial power input, but after the wall started heating and acted as insulation it would start to drop.

950C is a lot hotter than wood burns, though; do you really need it that hot?

No, that's not the minimum. You could do it for significantly less than that if you had insulation on the other side of the heater (so you had wall on one side of the heater and insulation on the other). Yes, it will radiate 100kW/m^2, but the insulation will radiate that same amount back into the wall/heater once it reaches thermal equilibrium at 950C.

Electric kilns reach this temp and higher all the time, and yet a kiln like this with about 1.2 by 0.8m opening (and by my calculations somewhere around 4 square meters of internal capacity) only requires ~24kW to reach 1150C, even though the radiated power at 1150C is 232kW/m^2 (and thus the entire inside of the kiln is radiating something like a megawatt).

 

[russ_watters]

No, that's not the minimum. You could do it for significantly less than that if you had insulation on the other side of the heater (so you had wall on one side of the heater and insulation on the other). Yes, it will radiate 100kW/m^2, but the insulation will radiate that same amount back into the wall/heater once it reaches thermal equilibrium at 950C.

[emphasis added]

I did say "initial". I don't think this would accurately represent a fire against the wall if it starts relatively cool and slowly warms up. Fire resistance tends to be measured with time, so that could defeat the purpose of the test.

 

[cjl]

A fire won't heat the wall to 950C instantly either though. If you wanted to simulate the fire, you'd really need to figure out what power input the fire would be providing, and match that.

Also, even with the correction/clarification, you're still incorrect. Initial required power will depend entirely on the heat capacity of the wall, the thermal conductivity, and how fast you want to heat it up. If you want to heat to that temperature instantly, power will be infinite. On the other hand, if both the wall and the insulating surface behind the heater are made of very low heat capacity, strongly insulating materials, the power level to reach 950c could be very low, even if you wanted to achieve it quickly. A good example of this would be a heating element sandwiched between a pair of the ceramic insulating tiles from the space shuttle TPS. As long as you have another insulating surface behind the heater though, the radiation is irrelevant.

 

[russ_watters]

A fire won't heat the wall to 950C instantly either though.

I'm not saying it would, in fact I'm saying the opposite: the initial radiation is against a room temperature background, so a 950C radiator emits 125kW.

If you wanted to simulate the fire, you'd really need to figure out what power input the fire would be providing, and match that.

Agreed. This isn't my research but I was figuring a rapidly growing fire. Since "rapidly" is hard to define, I was figuring an essentially instant ramp up in power output.

Also, even with the correction/clarification, you're still incorrect. Initial required power will depend entirely on the heat capacity of the wall, the thermal conductivity, and how fast you want to heat it up.

No, that's not how it works. The starting point is what you have before any of those effects take hold. The surface temperature - indeed the entire structure temperature - is room temperature at T=0.

If you want to heat to that temperature instantly, power will be infinite.

No, I am not suggesting that.

On the other hand, if both the wall and the insulating surface behind the heater are made of very low heat capacity, strongly insulating materials, the power level to reach 950c could be very low, even if you wanted to achieve it quickly. A good example of this would be a heating element sandwiched between a pair of the ceramic insulating tiles from the space shuttle TPS.

Yes, I was thinking about calculating that. I agree it probably wouldn't take long.

As long as you have another insulating surface behind the heater though, the radiation is irrelevant.

No, essentially all of the heat transfer from a radiant heater is radiant.

 

[cjl]

Who said anything about a radiant heater? Heating blanket to me implies a contact heater heating the wall directly through conduction.

EDIT: Also, even if you are using a radiant heater, a radiant heater between a pair of insulators will heat up as the surfaces do, so you still only need 100kW/m^2 if you want to deliver 100kW/m^2 to the surface (and you'd actually need twice that, since only one side of the radiator is facing the surface to be heated)

 

[anorlunda]

A fire won't heat the wall to 950C instantly either though. If you wanted to simulate the fire, you'd really need to figure out what power input the fire would be providing, and match that.

That makes me think more on the problem. If you really want the test to accurately simulate fire, there's more than temperature and power to consider. Are you sure you don't want combustion and actual fire?

No matter what you choose, make sure that whatever parties will read the test results report will accept your testing methods as valid. If they don't, the whole test is pointless.

Have you checked with the NFPA? They might have published standards for fire resistance testing, or they might have helpful advice.

 

[gmax137]

According to the so called standard fire curve (ISO 834) the temperatur on the fire exposed side of the wall should be around 950 C after 60 minutes.

It looks like the OP has some kind of standard to be followed.

 

[russ_watters]

Who said anything about a radiant heater? Heating blanket to me implies a contact heater heating the wall directly through conduction.

It's in post #5, and I ran with it as it would seem like a good fire simulator. I can't even imagine what a "heating blanket" would look like/be made of that is capable of 950C.

EDIT: Also, even if you are using a radiant heater, a radiant heater between a pair of insulators will heat up as the surfaces do, so you still only need 100kW/m^2 if you want to deliver 100kW/m^2 to the surface (and you'd actually need twice that, since only one side of the radiator is facing the surface to be heated)

Yes, I would assume at least the back side of the radiant heater would be insulated.

 

[Baluncore]

Put two fire doors face to face, with insulated spacers around the edges. Heat the air between them. The heat would have to escape through the doors. That would be a realistic test.
You could almost halve the heat loss by replacing one door with a well insulated wall.

 

[trurle]

Many thanks for all the answers! I want to perform fire testing without a fire! More specifically I would like to test the fire resistance of a wall, say light concrete. According to the so called standard fire curve (ISO 834) the temperatur on the fire exposed side of the wall should be around 950 C after 60 minutes. I'm interested in the temperature development on the non-exposed side of the wall, but not using a combustion furnace.

I understand that a considerable electric power will be required. But the blanket/heater would be attached to the wall surface so there would not be radiation into free space, but still much power required I guess.

According to ISO 834, the acceptable yet relatively low cost test method is to use a fire resistance furnace.
For example:
https://www.fire-testing.com/horizontal-fire-resistance-test-furnace/
I used a similar one to test aircraft black boxes. Equipment complexity is definitely not a DIY level - best option may be to rent an existing hardware, unless you are a factory owner and have to make such tests regularly.

 

[Hal Jordan]

This is actually very simple - as a former SkunkWorks guy, like mentioned above there are rigs...but such a device is actually quite simple to build - - -it ain’t rocket science. Just trapped heat.

If you take Combustion out of the equation, and have a closed box the O2 will be used up very quickly. Just four sides, one being the material you want to test. The key is insulation of the box. Make it airtight and well insulated and put a in a NiChrome rod with an electrical source. Add a thermostat that is good to the desired temp (that may be your biggest problem to surmount) and flip the ON switch. You might be able to do this with a common clothes iron (with a 1750F thermostat mod) if get a cheap one w/o any modern electronics or sensors and too much plastic.

PS - DO NOT give the modified iron to the local Thrift Shop when you are done, destroy the beast!