# Unrealistic wall temperatures in boiling flows

Member Posts: 1
edited April 4 in Fluids

I am getting very high and unrealistic wall temperatures (going up to 5000K) for my case while attempting the simulation of flow boiling through a mini-channel (Diameter=2.1mm).

Also, somehow temperature in some other parts of the domain seems to reduce for some reason I am unable to figure this out exactly.

One of the possible reasons that I feel is that I am applying a wall thickness (t=1.5mm) comparable to the channel diameter in: -

Boundary conditions -> wall -> Thermal -> Wall Thickness

• Posts: 949Member

can you show geometry and residuals?

Are you using Lee model?

• Posts: 7Member

Thanks for the response. Here is the geometry, it is a 2D planar case for a simple pipe as specified earlier.

Here are the residuals

Also as far as I'm aware I'm not using the Lee model (If I remember correctly this is a part of Eulerian multiphase modelling). I am using the VOF model for multiphase modelling.

• Posts: 949Member

How did you turn on boiling? is it through phase_interaction - mass_transfer _ evaporating and condensation? if yes, this is Lee model.

I don't think you have deep convergence ... Can you increase the number of iterations per time step and see if you have a difference

• Posts: 7Member

Additionally, here is a picture of the temperature shooting up, it happens near the top wall only. I forgot to mention that the heat flux given is about 80kW/m^2 (at both the upper and lower walls) and this shooting up begins in about 10 milli-seconds which is also very unrealistic

• Posts: 949Member

Because your dimensions are very small, your time step must be very small as well. Try smaller time step and larger number of iterations per time step

• Posts: 7Member

Yes it is the Lee model. Thanks for the info I'll try to reduce the timestep and work with it.

• Posts: 7Member

I really cannot understand how but reducing the timestep seems to instantly end up in the divergence of the solution.

• Posts: 949Member

? strange!

Go to methods, and make everything First order when applicable. Then go to controls and reduce the under relaxation factors. Specially the energy

• Posts: 7Member

Ok, I will try that. Also, I would like to know whether a subcooled wall boiling model is implementable in the VOF model?

• Posts: 949Member

There is a mechanistic boiling model. I never used it but check the guide ... I think it has many limitations, so it is better to upgrade to the latest version if you plan to use it