Heat Transfer ? - Steel Tube/Duct

[somarp]

Duct is a 8” x 8” steel square tube with 0.3125” wall thickness, 200” long.
Duct weight 742 lbs.

One end is capped off and the other end is capped off except it has a 4" OD inlet opening.

An external heat source will be used to pump heated air through 4" OD opening in the tube.

The duct is placed in -40 degrees F outside still air.

Determine overall BTu's per hour to heat the steel from inside to out to bring the outer surface from the -40 to 32F
Determine the required forced air temperature of heat source on inside of duct to maintain outer surface at 32F

 

[berkshire]

Student Question?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[somarp]

No, not a student. I am mechanical designer, but have been tasked with this problem and it has been quite a while since my Thermo and Heat Transfer days. I am just looking for some advice/assistance on how to get this started.

 

[berkshire]

This is Roymech who have very useful tables, see if this will give you a start.
B.E.

http://www.roymech.co.uk/Related/Thermos/Thermos_HeatTransfer.html

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[somarp]

Thanks, but I already went there. I use that site alot.

 

[IRstuff]

And why would you not be using the information on that site, considering that your problem seems to be perfectly apropos for a convection calculation?

I'm assuming that since you've been here a while, you'd have to be a super-senior times 3 to still be a student, yet your problem statement is couched precisely the way homework problems would be formulated.

TTFN
faq731-376

 

[LCeballos]

I am agree with my colleagues berkshire and IRstuff. This is a student question (convection heat transfer).

 

[dvd]

This does seem to be a more academically-slanted problem. I would like to know what the practical application really is. Also curious what maximum pressure is possible, since it only allows in-flow: is the flow driven by a fan, blower, or compressor? Does not appear that there will be very thorough mixing of the warm gases inside of the vessel, and, thus, rather uneven surface temperature.