Tube bank head loss

[dianad]

Hi,

I'm calculating a superheater, and i was faced with the following problem.

when we calculate the external (gas) head loss, we have the following expression: dP=2*f*G^2*N/density
In this equation, we have the value G, that represents: "mass velocity at minimum flow area" (extracted from Holman). This "G" value is = mass flowrate/minimum area. My problem is related with this minimum area. Not many books refer what is this "minimum flow are", not eaven Steam (Babcock). A bigger problem, is when we find several books with different calculations for this area.
Because of this now i'm starting to wonder if my idea of this "minimum area" is correct.

can anyone help me on this?
Thanks!

 

[KernOily]

Well one thing you can do is use all the available formulae you have found thus far and calculate the head loss using the formulae. This will give you a range of values, or a 'bracketed' solution. You can then apply judgment and the red-face factor to see how realsitic you think your bracketed solutions are.

Also look in a shell-and-tube heat exchanger book to see how they calculate the shellside dP across the outside of a tube bank for flow perpendicular to the tubes. If there is a formula for a shellside dP in gas flow you are in business. This will give you an idea of the hf = kQ^2 relationship. Might want to ask your question over in the pressure vessel forum or the chemical engr forum. (Is there a heat exchanger forum? I dunno.) Hope this helps! Pete