Forums > Technical Discussion > heat condutivity?

Posted: 24th Mar 2003
Oooo... a physics question! Yeay, I finally get to use my Ph.D. for something!!!

I take it your staff is a metal pipe and the wood previously employed was like a cork that accepted the screws?

I will also assume your bolts go all the way through so that basically 1 bolt does the job of 2 screws, and that the wicks are still roughly the same size (or course bigger wicks mean more heat).

let's look at it this way. If the bolts are the same diameter as the screws, then they have the same suface area contact with the metal staff. If they are twice the diameter, then they have twice the contact area and will conduct twice as much heat as the screws if they are of the same material.

However, if you had brass screws and steel bolts, then (since iron is a better conductor than brass as I recall - I dont actually have a CRC handbook available right now) then perhaps the steel bolts that are twice as big conduct perhaps 4 times as much heat as the brass screws.

But this surface area of the bolts contacting the staff is trivial compared to the surface area of the metal staff exposed to flame. The area under the wick is pretty well insulated, especially if you are using kevlar, so that doesn't count when you have the wood in there corking the end up. that leaves the part of the staff just inboard of the wick and the very tip. Take the wood out, as you have with the new arrangement, and you have suddenly doubled the effective area of the staff exposed to the flame since one can reasonably expect the flame to billow as much into the end of the staff as it does at the inboard end of the wick - probably even more because convection almost certainly takes lots of hot air up the inside of the staff in almost any position.

In fact, I bet it is the convection of hot air up the center of the staff that is your primary culprit, particularly if your staff is made of some aluminum alloy like say electrical conduit piping is (Aluminum has a very high conductivity).

Cork the ends and I bet you will find your problem is solved, in addition to adding more nice weight at the ends for a more favorable moment of inertia.An alternate solution would be to move the wicks inboard slightly, moving the flam away from the tip so that you don't get that convection effect, but this will have a detrimental effect on your preferred moment of inertia.

I could be wrong, but I doubt it.

-v-

Wiederstand ist Zwecklos!

Posted: 24th Mar 2003
sounds about right to me!!!

Posted: 26th Mar 2003
kewl,

sounds right, ill give it a go, thanks vanize.

N?

This is a post by tom, all spelling is deleberate
-><- Kallisti

Posted: 26th Mar 2003
This almost exactly answered my question "Why do people put a bit of dowel in the end of their staff?"

Excellent.

--Luke

Posted: 27th Mar 2003
my pleasure. I get a perverse satisfaction from using my arcane knowledge.

-v-

Wiederstand ist Zwecklos!