# Finding heat transfer coefficient "h" at tube bundle surface -help!-

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April 22, 2013, 04:08
Finding heat transfer coefficient "h" at tube bundle surface -help!-
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Burak
Join Date: Apr 2013
Posts: 4
Rep Power: 5
Hello guys!

I am trying to find the "h" coefficient of a tube bundle in a duct. You can see the geometry as attached.

Problem conditions are:
Tubes are at 90C constant.
Fluid is water at 10C with 0,5 m/s inlet.

The steps I followed on FLUENT are:

1- Models: energy equation, k-omega standart & enhanced wall treatment
2- Materials: conditions of water at 10C
3- Cell zone conditions: changed to water as described above
4- Boundary conditions: Inlet 0,5 m/s at 283 K with 1% turbulent intensity and hyraulic dia. of the duct
Outlet is outflow
Tubes are walls at 363 K constant
Duct walls are walls and insulated, thus no heat flux
5- Reference Values: Compute from "inlet"
6- Monitors: Area-weighted average & surface heat transf. coeff. of tubes
7- Solution Initialization: standard initialization compute from "inlet"

After 1000 iterations, I adapt boundary and region twice and run another 1000 iterations, and I get these values:

h = ~7300 w/m2K
Nu = 11242
dT= 2,75K

But if I do a manual calculation according to Zhukauskas' equation for staggered heat exchangers this is what I get: (please see Empirical Calculation.pdf)

h = 11388 w/m2K
Nu= 290,3
dT= 4,5 K

Why I get that different solutions? I am new at CFD and I tried a lot of different ways in FLUENT such as different meshing, different turbulent intensity or models but i still don't get what I should be getting.

bluejojoba
Attached Images
 HX geometry.jpg (48.3 KB, 17 views)
Attached Files
 Empirical Calculation.pdf (86.6 KB, 28 views)

 April 24, 2013, 20:17 #2 New Member   Burak Join Date: Apr 2013 Posts: 4 Rep Power: 5 anyone guys? I am really desperate.

 Tags coefficient, forced convection, heat exchanger

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