Finding heat transfer coefficient "h" at tube bundle surface help!
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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, komega 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: Areaweighted 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. Can you please help me where I am doing wrong? Thank you in advance, bluejojoba 
anyone guys? I am really desperate.

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