heat transfer in an annulus

[corus]

In the site

http://www.cheresources.com/convection.shtml#annular

it refers to the nominal Nu.tube but which tube of the annulus is it referring to? The outer tube diamter Do, or the hydraulic diameter, Dh = Do-Di ?

corus

 

[Montemayor]

Corus:

If you notice, the reference for the equations given is: Petukhov and Roizen. That is where you should start looking in order to find the logic and the algorithm employed to come up with the equations.

If it is argued that the presentation of the equation and it's explanation is flawed, I have to agree whole-heartedly. However, that is another forum and the only way to get a full version of what the equation represents is to go to the referenced sources.

 

[siretb]

It refers to the Hydraulic diameter Do - Di

 

[corus]

Thanks siretb, though without the actual paper for refernce I was thinking that the 'tube' referred to the boundary condition, ie. for the outer wall insulated then it would be the inner tube, and vice versa. For heat loss from both tubes then it would be the hydraulic diameter. A comparison of values using different tube sizes doesn't give a significant difference in values in my case anyway though I will check the actual reference paper to see if there is a clearer definition.


corus