Huh, guess we were both sort of right
I'm kind of surprised that it worked out that way, but it makes some sense now considering the increased surface area. How sensitive is the system to exhaust and atmosphere fluid velocities? I'm having trouble picking out the details of your convection calculations...
It'd be interesting to see where conduction overtakes convection as the surrounding air becomes stagnant (or at least reduces to natural convection).

 

Fat people have more surface area and thicker 'walls', yet the increased surface area is not enough to cancel out the extra heat retention... I have no idea where i'm going with this. goodbye

 

Hey Evil,

If we took air velocity over the pipe into account we would likely see that as Reynolds number/turbulence increases, more heat would be removed through convection making the comparison to conduction even more dramatic.

There's a small error in the calc. I actually meant to use a 1.75" primary diameter, not radius.....So the conduction/convection portion is not apples to apples with the radiant portion. Still ok for showing conduction/convection comparison though.

Fat people don’t have a conduction coefficient like mild steel . Put a real small number in the formula and resistance to HT through a medium goes way up!

-Scott.

 

So you didn't account at all for air velocity then?
Basically what I was saying is it'd be cool to see a heat flow vs air velocity plot - I know the relationship exists, but given how non-linear fluid systems are, I'd like to see the shape of the curve, if you know what I mean...

 

Well I have to look at it again. The convection coef (h) I grabbed from a table. 10-25 seemed like an appropriate value for ambient. I was really hoping to show what would happen with a change in OD only - everything else constant.

I was thinking as well to put this in excel so you could enter pipe-a & pipe-b data and add a coating or heat wrap resistance if you want. Would sure beat doing it long hand for every scenario.

Thanks for your interest!

-Scott.

 

Right, that makes sense since that's what the original discussion was about - increasing wall thickness. I'm kind of shooting off onto a tengent now though, since your calculations show "R3" being so much greater than "R1" and "R2", I'm curious see see how R3 changes with air velocity.