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Wall thickness affects heat transfer rate

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Old   March 16, 2018, 10:21
Default Wall thickness affects heat transfer rate
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Michal
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Hello everybody,

I am simulating case with spherical object cooled by an impingement water jet (single phase axisymmetric solution, object is immersed).
In my case I want to calculate heat transfer coefficient and heat transfer rate.
Water has got constant parameters, its temperature is moreless constant within the domain, sphere surface temperature is (for now) also constant.
I am modeling only the fluid domain, object interior is not included into the domain. Turbulence model is k-omega SST with low Re correction.

I have set wall boudary condition with constant temperature.
After comparing my results with analytical solution and the literature, it turned out that my heat transfer rate is 2x bigger than I should obtain.

I tried to change many parameters, the only one that affected my solution wass the wall thickness in wall BC.

I am a little bit confused... My wall has fixed temperature, all the time I was sure that the wall thickness should affect the solution.
While increasing the wall thickness, my heat transfer rate decreases.

Could somebody give me some idea what's going on? I would appriciate every suggestions.

Best regards,
michal.s
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Old   March 16, 2018, 13:11
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The wall thickness should be 0.

The wall thickness simulates a contact resistance, which you should not need. Setting a wall thickness adds a layer of conduction resistance which reduces heat transfer.

Quote:
Originally Posted by michal.s View Post
I have set wall boudary condition with constant temperature.
After comparing my results with analytical solution and the literature, it turned out that my heat transfer rate is 2x bigger than I should obtain.
Analytical solution... Is that for a laminar flow? If so why are you using a turbulence model?
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Old   March 18, 2018, 10:19
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Quote:
Originally Posted by LuckyTran View Post
Analytical solution... Is that for a laminar flow? If so why are you using a turbulence model?
It's turbulent flow.
I have found formula for Nusselt number for that kind of flow.
Then I've calculated heat transfer coefficient and having fluid mean temperature, surface temperature and the surface area, I've calculated total heat transfer rate that I should expect.

I guess that Wall Thickness is for giving temperature behind the wall. I was suprised that the difference in my results is so big.

Still looking for the source of my problem :/
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boudary condition, heat transfer, temperature, wall

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