[mark1]

Dear all,
I'm new in Ansys and simulating flowing water temperature change inside copper pipe that's built inside a cladding sheet (the plate covers construction building in future, thats heated up by sun panel).

Please see screenshot from CFX-Pre and arrows in geometry transition between pipes.

I'm having problems: large temperature fluctuations inside pipe, may these arrows (see attachment) be source?

Thanks for any help!

[ghorrocks]

FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

If you want us to help you post an image of your mesh and the results you are getting.

[mark1]

Hi
Thank you for reply.

See result file in attachment 1, where fluid is cooling down in direction inlet->outlet. It should heat up.. Here Water inlet temp: 45 degrees, plate temp: 50 degrees.

In attachment 2, water inlet temp: 40 degrees, plate temp: 50 degrees.

Mesh: 500 110 elements. See individual meshes in attachment.

Thanks for any help!!

[ghorrocks]

I can see your water mesh has got very coarse boundary layer mesh. If you have a Re>200 or so this will be too coarse, if Re>2000 (ie turbulent) then you are miles too coarse. You are going to have to refine this a lot. And your mesh along the length of the pipe is probably too fine. That can probably be coarsened. But all these changes should be done and checked with sensitivity analyses.

Are you modelling the copper pipe as a thin layer? Why are you doing this? It is probably better to model this as a thermal resistance on the interface between the water and the cladding, with no model of the pipe. Note this approach does not take into account the thermal time constants associated with these materials. If you want the correct thermal time response you better directly model the copper pipe.