## Fluids

#### how to find the frequencys of evaporation and condensation in lee model?

• nagesh56
Subscriber

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
Ansys Employee

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
Subscriber

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

• DrAmine
Ansys Employee

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

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
Subscriber

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
Ansys Employee

See previous posts.

• Nitin_Bansal
Subscriber
hello
are you able to come over to your problem?