Heat transfer problem - not given tube thickness

[CatRunner]

Homework Statement

We have 5 cm of external diametre tubing with 200*C of superficial temperature. The boundary temperature is 20*C and the convective heat transfer coefficient is 3.0 W/m^2*C

What is the heat loss

Homework Equations

q = U*A*(T1-T2)

1/U = 1/h1 + [r1 * ln (r2/r1)]/k1 + r1/r2*h2

The Attempt at a Solution

Okay, my problem is that I don't have a k value for the tubing, nor do I have the thickness of the tubing (or alternately, an inside and outside diametre). The only information I have is given (outside diametre, two temperatures, and the convective heat transfer coefficient).

I just have no idea how to tackle this without a k value or a tube/pipe thickness.

Thanks for any assistance

 

[morrobay]

Homework Statement

We have 5 cm of external diametre tubing with 200*C of superficial temperature. The boundary temperature is 20*C and the convective heat transfer coefficient is 3.0 W/m^2*C

What is the heat loss

Homework Equations

q = U*A*(T1-T2)

1/U = 1/h1 + [r1 * ln (r2/r1)]/k1 + r1/r2*h2

The Attempt at a Solution

Okay, my problem is that I don't have a k value for the tubing, nor do I have the thickness of the tubing (or alternately, an inside and outside diametre). The only information I have is given (outside diametre, two temperatures, and the convective heat transfer coefficient).

I just have no idea how to tackle this without a k value or a tube/pipe thickness.

Thanks for any assistance

You have all you need to solve this with the Heat Transfer Coefficient value for copper (h)
h = q / A* delta T

h = cal/sec/M² * C
q = cal /sec
A = external surface area
delta T
So q = h * A * delta T

 

[edgepflow]

This problem brings up a good practical point. For most (but not all) heat transfer problems involving pipes (especially metal pipes), the conduction resistance of the pipe or tube wall is small compared to the convection resistance inside and outside the tube and may be ignored.

Ofter, the interior heat transfer is forced convection and the exterior is natural convection and you can apply suitable correlations. In addition, if the temperatures are high, insulation is added and radiation heat transfer is important. Other times, the pipe is sitting in the sun and you account for the energy absorbed.

Anyway, this will all make more sense as you study heat transfer. It is an interesting and practical subject.