SimScale CAE Forum

Always getting an error on my conjugate heat transfer case


#1

I have successfully run conjugate heat transfer cases in the past but now I am trying to simulate 3 U shaped heating elements in a body of water using conjugate heat transfer and the simulation returns an error every time (it just says error without giving more information). I have set the heat elements as absolute power sources. As for other conditions, I’ve tried leaving the external walls without boundary conditions, tried using wall heat transfer boundaries on the external walls, tried using zero temperature gradient on the external walls, tried changing mesh density, using a turbulence model and even manually defined the contact between the heating elements and fluid (even though the mesh log said they were resolved successfully) but nothing seems to work. The error always comes up very early on in the run. In the log it says ”error::printStack(Foam::Ostream&)” which according to google may be a division by zero error.

Project link https://www.simscale.com/projects/roy_g/heater/

I am considering trying to alter the CAD model so that the heating elements are completely covered by the water but I am not sure why it should be an issue if they are not covered, as long as they have the right boundary conditions.


#2

Hi Roy!

Could you first be specify what exactly you want to do here?

Some obvious issues are the material definition ‘equation of state’ to be rhoConst. and then numerics between the ranges of liquid density (notes by my colleague Sam).

Cheers!

Jousef


#3

Ok I have changed the equation of state and have changed the min and max density in the numerics to 500 and 2000. I am rerunning and will let you know.

I am trying to simulate the heating of the water (transient) by the heating element, nothing special in mind i’m just doing it for practice


#4

Hi @jousefm

Your previous suggestion did not solve the problem (though it seems like the correct thing to do and may explain why I had some unexplained density changes in a previous simulation), but what did help was increasing the size of the water volume to completely cover the heating elements. Once I did this the simulation ran but after a short while I get an error that the maximum courant number has been exceeded. Looking at the plot, it rises very suddenly to an insanely high number so this is not a question of simply reducing the time step etc. Do you have any idea what may be wrong? The project link is as before.

thanks

Roy


#5

Hello @roy_g,

Please have a look into the following project
https://www.simscale.com/projects/sjesu_rajendra/heater/

There is one steady-state case and one transient run which can be used as reference for your future studies. For the transient analysis I made some numerics changes to make it more stable. Basically you have to start with a very small time step to make sure we get stable results. The auto-time step option then increases this value based on the CFL criterion.

I hope this helps moving forward with the project.

Best,
Sam


#6

Hi @sjesu_rajendra

Thank you for running my simulation. The steady state result looks good but I feel that the transient result is not correct as the entire temperature field is uniform which would no t happen, certainly not in such a short time. Are there any transient conjugate heat transfer projects you know of which you could share a link to

thanks

Roy


#7

Hi @roy_g,

The trial simulation was run for a very short time. Note that I have initialized the regions with higher temperatures, hence you see the different values. For transient simulations it is best to specify initial conditions so that the convergence is faster. Unfortunately I don’t have any model of transient CHT that you can use as template. Due to the expensive nature of analysis it is best to run a steady state CHT or approximate to structural heat transfer case. I hope this should give us reliable results.

Regards,
Sam