SimScale CAE Forum

Tutorial U-Tube Heat Exchanger CHT - different result

Hello,

i was working on the Tutorial: Conjugate Heat Transfer in a U-Tube Heat Exchanger. I’ve done every mentioned step but i could not achieve the same result as depicted on the website. This is what my result looks like including a cutting plane:

It seems like there is no heat transfer from the hotter fluid to the colder fluid in my simulation.

This is the link to my project: https://www.simscale.com/workbench/?pid=782841440043491799&rru=789e952e-c7a5-42b2-9536-9d59a1067881&ci=38dab482-3b16-41f0-abb8-1b795499a525&ct=SOLUTION_FIELD&mt=SIMULATION_RESULT

This is the link to the SimScale tutorial: https://www.simscale.com/docs/tutorials/cht-heat-exchanger/
The actual result is shown down below.

I’m happy for any advice.

Greatings
swagler

Hi there!
Thank you for pointing this out. Actually you are using the correct properties for water, and in the tutorial air properties are used instead. This has an effect on the results of course. Other than that your project setup is just fine, only the tutorial needs an update :slight_smile:

Best regards,
Fillia

Hi Swagler and Tsite

I noticed the sample problem as Swagler. When the fluid density is assumed to be constant the results do not me sense to me.
The picture below shows the temperature profile for the inner fluid (water) entering at 35oC. According to this picture, the fluid warms up and then leaves the tubes almost at the same temp as the inlet, which makes no sense to me.

Tsite, could you please help me to understand why that is happening?

I changed the the equation of state to perfect gas instead of constant density and the results make more sense to me, see picture below. The water enters at 35oc and leaves the tubes at about 39oc, which makes sense. Looking forward to hearing from you. Thanks.

@swagler and @tsite, sorry, I forgot to mention your names in my previous post.
Regards,
Fernando

Hi Fernando, thank you for sharing! Can you also include a link to your project please?

Hi Tsite (@tsite)
Please find the link below:

Please check the simulations called “Control” and “ConstDens”

Thank you very much for your help,
Fernando

Hi again Fernando,

Have a look here, under the 'Check Fluid Properties’ section: https://www.simscale.com/knowledge-base/cht-simulation/

If you are applying a gas (e.g., air), then you can use the ‘Perfect gas’ equation.
If you are using a liquid (e.g., water), then choose the ‘Rho constant equation of state fluids constant transport’ option and specify the fluid density manually.

As mentioned above, the original document has an error, as it uses the properties of air, that should be treated as a perfect gas.

Another approach is to apply water properties to the cooling stream, and air properties to the hot stream, have a look at the corresponding results here:


You can still see that the cold stream is not affected a lot, but by introducing different conditions and material properties, there could be a significant difference :slight_smile:

Best regards,
Fillia

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@tsite Hi Fillia
Thank you very much for your help and for all your suggestions :slight_smile:
Have a nice day.
Fernando

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