Arc temperature / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Arc temperature

Move Thread

LAN_403

Clive Hansen

Mon Dec 03 2007, 09:47PM

Registered Member #1149 Joined: Wed Nov 28 2007, 09:30PM
Location: Christchurch, Canterbury, New Zealand
Posts: 9

Hello,
Does anybody know the rough temperature of the arc from a 15/30 nst? Is there a formula for calculating this? I am trying to measure the arc temperature from my jacobs ladder but it is out of range of my thermometer.

-Clive

Mates

Mon Dec 03 2007, 10:32PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Clive Hansen wrote ...

Hello,
Does anybody know the rough temperature of the arc from a 15/30 nst? Is there a formula for calculating this? I am trying to measure the arc temperature from my jacobs ladder but it is out of range of my thermometer.

-Clive

I think it should be around 6000 C (K). You can estimate the temp by the color (temp) of the emited light (problem is you that you never see the whole spectrum, but there are sensors which can). Anyway, once the emitted light from an object is very bright white-blue the source of the light should be around 6000K (but this not valid for all light sources, for example the wolfram makes a shift which makes the clasical bulb brighter then it should be)

BTW: there is nothing like a probe which can measure these temperatures directly...

Clive Hansen

Mon Dec 03 2007, 11:02PM

Registered Member #1149 Joined: Wed Nov 28 2007, 09:30PM
Location: Christchurch, Canterbury, New Zealand
Posts: 9

Is there a formula for arc temperature?

Shaun

Tue Dec 04 2007, 12:02AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

No, there is no formula for this. What I would do to get a rough estimate of temperature is see what it can melt. Maybe a tungsten lamp filament. If it can melt this (it probably will), suffice to say that its pretty damn hot.

Other than that...if you knew the exact volume of the arc, maybe you could use the power it is dissipating (450W) to find a temperature? just thinking out loud here.

Oh and BTW "...it is out of range of my thermometer"
O rly? lol

MOT_man

Tue Dec 04 2007, 06:10AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

You can theoretically say that a plasma arc - at its very core would have to be at least 6000 degrees C ---but remember this is a very microscopic core - the flame that surround the core is much cooler and that is what we typically see... I'd estimate the cooler flame to be 1000 C- 1500 C.
If you pull an arc with a MOT --- the snappy flaming filament is mostly cooler gases that are being produced by a super heated core. It snaps and pops because the air is expanding so rapidly it causes local disturbances to form.

Chris

Tue Dec 04 2007, 08:11AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

I think the short answer has been found; at least 6000K in the core of a typical arc, but this is just a tiny strand. It is difficult to define an exact border of the arc, and therefore difficult to define an "average temperature" in the arc, since the farther you get from the very center the cooler it gets, and how much you see glowing depends largely on incandescence, which has no cutoff limit at all. You and I and every object around us are glowing with incandescence at lower RF bands because of our lower temperature. The visible part of the arc is more or less just part of a temperature gradient or bell curve from the core to the ambient temperature, the magnitude of which depends on its current. Some part of that temperature gradient will be at 6000K, some part will be at 3000K, some part will be at only 500K, and I am not aware of any all-inclusive formula for finding the temperature at any given point. The Stefan-Boltzmann equation could be used for a rough estimate under ideal conditions, but other factors like conduction and convection in ambient temperature will come into play to throw it off much like those ideal problems and stuff you see in high school physics.

What I would do to get a rough estimate of temperature is see what it can melt. Maybe a tungsten lamp filament.

Sorry, but that's one of the more bogus means of measuring arc or flame temperature that I have heard. The ability of an arc or flame to melt stuff depends on the power of the arc just as much as the temperature inside. Any arc will have a core temperature of at least around 6000K, even more under other conditions, and this is more than hot enough to melt, in fact usually boil, any material that does or can theoretically exist. Obviously you can't melt a significant piece of metal with an NST though because the heat is conducted or radiated away quickly from the piece and it cannot even approach the arc's core temperature unless it is very tiny. Tungsten lamp filaments don't have to be melted to make them disappear, either. You probably know that if you break a hot lightbulb, the filament is gone almost instantly, not because it got so hot it melted away, but because it oxidized in the air.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob