Reply
 
Thread Tools Display Modes
  #1  
Old 10-27-2011, 05:48 PM
Incubus is offline
BANNED
 
Join Date: Apr 2002
Location: California
Posts: 5,891

How much radiant heat does molten steel give off?


I was watching sky captain and in one scene a dex fires a 1920s death ray at a steel plate and admires his handywork. It got me wondering just how close you could stand next to molten steel before the radiant heat burns you.
  #2  
Old 10-27-2011, 07:00 PM
engineer_comp_geek's Avatar
engineer_comp_geek is online now
Robot Mod in Beta Testing
Moderator
 
Join Date: Mar 2001
Location: Pennsylvania
Posts: 25,583
I've done a lot of work in steel mills. I've stood right next to slabs of steel that were just barely cool enough to keep their shape. It's a wee bit warm. When you get close to the flowing molten steel it feels a lot like someone blasting you in the face with a hair dryer set on high (only without the windy part) but you can get pretty close to it without getting burned.
  #3  
Old 10-27-2011, 07:11 PM
engineer_comp_geek's Avatar
engineer_comp_geek is online now
Robot Mod in Beta Testing
Moderator
 
Join Date: Mar 2001
Location: Pennsylvania
Posts: 25,583
This isn't a plant I've been to, but I have been to plants that look very similar to this. Note the bridge going across the molten steel. I've stood on a bridge like that (yes, it's a bit warm up there).
http://www.nzsteel.co.nz/images/Stan...lant-hires.jpg

Again, not the same plant I've been to, but I've stood right next to slabs like this while troubleshooting a high precision laser device that measured the slab width for quality control purposes.
http://www.rksteel.com.pk/images/574505.jpg
  #4  
Old 10-27-2011, 07:18 PM
sweeteviljesus is offline
Guest
 
Join Date: Mar 2006
Posts: 2,405
The quantity of molten steel matters a lot here. It's just like standing next to an ice cube versus a glacier, or a bonfire versus a match.

Rob
  #5  
Old 10-27-2011, 07:20 PM
Boyo Jim is offline
Member
 
Join Date: Nov 2001
Location: Madison, WI
Posts: 36,997
I'm not sure what an upward limit there would be. Is vaporized steel still "molten"? I would guess that steel liquifies at some point, and vaporizes at some higher point. And maybe becomes plasma at some still higher point? And presumably, the higher the temperature the steel is, the more heat it also radiates.
  #6  
Old 10-27-2011, 08:57 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 85,825
It varies a bit from one alloy to another, but it looks like the melting point of steel is around 1500 C. That's about a third the temperature of the Sun, and heat radiated is proportional to the fourth power of temperature, so a lump of molten steel at such a distance that it has an angular area 81 times that of the Sun would provide you about the same amount of heat. That'd mean a ball (or disk, face-on) of steel about 1.5 degrees in diameter would warm you up about as much as the Sun does on a clear day.
  #7  
Old 10-27-2011, 10:03 PM
JWT Kottekoe is offline
Guest
 
Join Date: Apr 2003
Location: California
Posts: 1,017
As you can see from Chronos' answer, it depends on two things, the temperature to the fourth power and the angular area (a.k.a. solid angle) to the first power. If you were completely surrounded by molten steel, it doesn't matter how far away it is, you'll be cooked, just like you would if you were one foot away from a gigantic bonfire. Movies and video games get this wrong all the time, with people surrounded by flames or molten lava.

The only other factor that matters is the emmissivity, which depends somewhat on the material and the temperature, but for molten steel is probably not too far from 100%
  #8  
Old 10-27-2011, 10:45 PM
ZenBeam is offline
Guest
 
Join Date: Oct 1999
Location: I'm right here!
Posts: 8,858
Quote:
Originally Posted by Chronos View Post
It varies a bit from one alloy to another, but it looks like the melting point of steel is around 1500 C. That's about a third the temperature of the Sun, and heat radiated is proportional to the fourth power of temperature, so a lump of molten steel at such a distance that it has an angular area 81 times that of the Sun would provide you about the same amount of heat. That'd mean a ball (or disk, face-on) of steel about 1.5 degrees in diameter would warm you up about as much as the Sun does on a clear day.
1.5 degrees would only be 9 times the area. You'd need 4.5 degrees.
  #9  
Old 10-27-2011, 11:00 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 85,825
Thanks, I knew I was screwing up somewhere there.
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 09:58 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@straightdope.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Copyright 2019 STM Reader, LLC.

 
Copyright © 2017