Learning Forum

[nagesh56]

I am trying to simulate the two-phase thermosyphon heat pipe by using the lee model of evaporation and condensation in the how to fix the values of evaporation and condensation frequencies.I  left it as default and done the simulation but at the condenser, it is rejecting more heat compared to the heat input given at evaporator section. I don't know how to fix this problem it this is the reason for more rejection at condenser or any other parameters I need to check?

 

Edit: rwoolhou. Move to Fluids. 

[Rob]

Check for convergence too: you may find that you've not got an accurate calculation. This assumes the mesh is also sufficiently resolved to give a good result. Re those defaults, you'd need to decide whether they're suitable for your model. 

[nagesh56]

yes, I created a fine mesh of 40K elements. and all my boundary conditions are fine, still, I am finding this problem.

[DrAmine]

The coefficients are not derived from principles. You need to have some references, experimental data or machine learning to find the best suitable coefficients. have a fun!

[nagesh56]

Atleast tell us how to guess the values depending on our operating conditions. As of now we don't have any experimental results.

[DrAmine]

If you do not know anything then it is hard. It is case dependent. Generally the evap frequency can bet set 10 times larger the condensation one but as I said it requires tuning from your side as it is a "MODEL" and not the "REALITY".

[nagesh56]

my operating conditions are operating pressure  20kpa  and corresponding saturation temperature is 60 C, the heater is at a constant temperature of 340 K and condenser is at a constant temperature of 300 K. So for these conditions can you suggest some  guess values.  

[DrAmine]

See previous posts.

[Nitin_Bansal]

hello
are you able to come over to your problem?
if yes then please help me out because i am facing the same problem .
thanks

[Karthik R]

If your question is related to the coefficients in the Lee model, please refer to the literature to understand what range of values are applicable for the working fluid as well as the conditions you are attempting to model. As mentioned by this is a tuning parameter and generally needs to come from experiments.
If you are having modeling issues, please create a new post and provide some details about these issues and we'll help you.
Thanks.
Karthik

[Rob]

As you've already done https://forum.ansys.com/discussion/23790/lee-model-implementation-for-different-fluid#latest
Locking current thread.