Re: Molten Metal
 

sciguy,

your analysis is excellent (esp for an electrical engineer :^)

the only point that doesnt sit right with me is you used the mass of your whole finger (1cm thickness) and if I understand the equation you used then which part of the finger is rasied to 120ºF? the surface of the side in contact with the metal, or the entire mass?

While the finger is in contact with the metal, there will be a temperature gradiant from the contact side to the back side, with the mass of the finger drawing heat away from the contact area.

The reason I ask is your answer seems pretty long - 66mS is only 1/15th of a second. My intuitive basis for this comes from experience, like licking your finger and tapping an clothes iron to see if its hot.

The other question is, what temp can we endure without being burned? 120ºF seems low. Tap water is usually 160 - 180ºF.

Re: Molten Metal
 

I'm assuming that the whole finger is rasied to 120F. There was a couple issues that I couldn't easily resolve. First off, I wasn't sure how to model the heat transfer within the finger. I suspect that if I worked on this long enough, I could probably come up with some differential equation that'll do it. We'd need an equation that describes the rate of temperature rise in the finger at some distance from the surface. I doubt that it would be a very pretty one though. But hey, computers can solve anything.

The other issue was blood. Because it's flowing, it's essentially acting as a coolant. Although, because of the short time, I'm not sure how much it actually does.

Well, I was going off of cooking temperatures. For beef (which I'm assuming is the closest animal to human), medium-rare is 130F. And through the wonder that is Google, here is a handy dandy chart.

Re: Molten Metal
 

the answers to these questions (heat transfer) are learned in college Thermodynamics classes

Its normally taken by mechanical engineering students, after taking 4 semesters of calc and one semester of differential equations, and in many university's its one of the 'weed-out' courses (where D is for Diploma :^)

Re: Molten Metal
 

D isn't for diploma anymore.
It's now C for continuation.

Wetzel

Re: Molten Metal
 

Yup, I'm taking ME113 (Thermodynamics). I don't need it for EE, but I needed some extra units and it looked interesting. It covers topics more along the lines of power generation from heat engines. However, it looks like heat transfer is covered in the other two thermo classes ("heat transfer in electronics" and "thermal engineering"). They both cover heat transfer, but the one I have to take has an emphasis on heat transfer applications in electronics rather than engines and whatnot.

As for math, thermo's prereq is the last semester of calc. The heat transfer classes need differential equations though.

And, according to the course catalog, ME majors need a C- or better in their thermo classes.

Re: Molten Metal
 

This vid is so very obiously fake, lookclosely when he put his hand thru, the video skips from right in front of the metal to the back, not very real

Re: Molten Metal
 

I saw the skipping too. i call fake. metal is ALOT hotter than water or fire or whatever you got.

not with water, it won't. water is a very good conductor of heat. i know from personal experience. long story short, if you have a choice between a wet rag and a dry rag to use as a hot-mitt, go for the dry. avoid burning. and blisters.
water will actually speed up heat transfer in most cases. which, coincidentally, is why water cooling for cars and computers is so much more effective than air. air is an insulater.

Re: Molten Metal
 

I think its real. When you have worked in a place like that for 20 years you learn things instinctively.

it would have been easy for them to experiment, taking a metal rod and hitting the hot flow, and seeing if got warm to the touch.

Heat cannot transfer instantiously, there must be sufficient contact time for the energy to transfer from one material (the molten metal) to the other (flesh).

That being said, I would never try it. Maybe after working with the stuff for 20 years?

Re: Molten Metal
 

I think it was fake but it could be real if he used kevlar... And yes kevlar is used in bulletproof vest but it is also used in firemens suits and cand stand up to 3200 degrees.

Re: Molten Metal
 

Why wait 20 years to lose a hand? If you plan on losing your hand, the sooner you do it, the more time you'll have to learn how to live without it. :)

Re: Molten Metal
 

Right, Water absorbs heat about 240 times faster than air.