Helical fin double pipe heat exchanger – Unexpected temperature contour (FLUENT)

- September 1, 2024 at 3:35 pm
  Kanak BUET19
  Subscriber
  I am trying to simulate the fluid flow inside a 1000mm long double pipe heat exchanger with helical fins. After running the simulation, I found that the results were quite unexpected.
  
  The following discrepancies were visible:
- There is a sudden temperature drop in the inlet portion of the hot water.

The outlet temperatures of the water (inner hot fluid) dropped to around 46°C, whereas in the experiment, it should be around 60°C.

I am adding the details of this problem in the following section so that it's easy to navigate the issue. I hope you will be kind enough to address this problem. :))

While defining the boundary condition, I found there were certain walls that were not visible to the actual geometry but they appeared in the boundary section. I cannot even display them with display geometry. I am not sure if they are influencing the results in any way.

Furthermore, after initialising, in the console there was a warning that, there was a interface zone between the hot fluid(water) and cold fluid(air) . I am not entirely sure what it meant because, the fluid zones were defined correctly.

I am adding my simulation setups, mesh and other images for the sake of describing this problem. Can you help me where things could have gone wrong and how will I be able to correct it?

I have used Turbulent realizable K epsilon model with enhanced wall treatment.

Turbulence contour:

Residuals:

unknown wall boundary conditions:

Geometry and mesh :

September 6, 2024 at 12:21 pm

Essence

Ansys Employee

Hello,

Use higher order discretization for higher accuracy and turn ON warped face gradient correction and High order term relaxation (if the case is steady). If you are referring to the shadow faces, then you don't need to worry. In CHT cases, Fluent will automatically create them. I believe you have no inflation layers in air domain. Please add them.

And why are you using mixed BC? You have set zero heat transfer coefficient. Any reason?