# How to control diverging value of temperature

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October 14, 2021, 09:52
How to control diverging value of temperature
#1
Member

L S
Join Date: Apr 2016
Posts: 58
Rep Power: 8
I am trying to simulate subcooled flow boiling with the help of phaseChangeHeatFoam.

The geometry is made 2D representing a pipe flow situation. The case set up is attached with below.

I have been observing during subcooled flow boiling, wherever there is no liquid in contact with the heated wall and only vapor is in contact, the wall temperature keeps rising infinitely like this (see maximum T = 7598.001 K):

Quote:
 MULES: Solving for alpha1 Liquid phase volume fraction = 0.2654015 Min(alpha1) = 1.563196e-09 Max(alpha1) = 1 MULES: Solving for alpha1 Liquid phase volume fraction = 0.2654011 Min(alpha1) = 1.563192e-09 Max(alpha1) = 1 MULES: Solving for alpha1 Liquid phase volume fraction = 0.2654007 Min(alpha1) = 1.563165e-09 Max(alpha1) = 1 MULES: Solving for alpha1 Liquid phase volume fraction = 0.2654003 Min(alpha1) = 1.563161e-09 Max(alpha1) = 1 DILUPBiCG: Solving for Ux, Initial residual = 0.002465843, Final residual = 4.457022e-09, No Iterations 3 DILUPBiCG: Solving for Uz, Initial residual = 0.0008184533, Final residual = 1.029827e-11, No Iterations 5 GAMGPCG: Solving for p_rgh, Initial residual = 0.0001695675, Final residual = 7.185041e-09, No Iterations 9 time step continuity errors : sum local = 9.484659e-06, global = 9.483099e-06, cumulative = 8.552475 GAMGPCG: Solving for p_rgh, Initial residual = 2.088834e-05, Final residual = 8.805387e-09, No Iterations 4 time step continuity errors : sum local = 9.483124e-06, global = 9.483083e-06, cumulative = 8.552485 GAMGPCG: Solving for p_rgh, Initial residual = 1.530388e-05, Final residual = 3.873035e-09, No Iterations 5 time step continuity errors : sum local = 9.483103e-06, global = 9.483038e-06, cumulative = 8.552494 solve TEqn DILUPBiCG: Solving for T, Initial residual = 0.0003295428, Final residual = 3.655628e-12, No Iterations 4 TAve = 1569.162 Min(T) = 48.78237 Max(T) = 7598.001 <- ExecutionTime = 14306.4 s ClockTime = 14333 s Courant Number mean: 0.01276589 max: 0.1493844 Interface Courant Number mean: 0.002812059 max: 0.1287168 deltaT = 2.455655e-07 Time = 1.3642520479467
The non-physical temperature rise results in further rapid evaporation of liquid and slowly the entire liquid evaporated in domain which is incorrect.

How do I control the wall temperature? Is there any way to limit the temperature like some option in fvschemes or fvsolutions? Is there any way to provide minimum and maximum values limit in source code?
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Attached Files
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 October 14, 2021, 11:19 #2 Senior Member   Join Date: Apr 2020 Location: UK Posts: 469 Rep Power: 11 From a quick look at your case, I can see that you are applying a constant gradient (i.e. constant heat flux) boundary condition on T at the wall. This applies whether there is liquid or gas next to the wall. Now think about the physics - is this constant heat flux realistic? The answer is no, and that is why you are ending up with excessive wall temperatures, as the code is trying to achieve your BC. The heat transfer is much less efficient when there is vapour next to the wall, and this should therefore drop your heat flux ... So, can I suggest you have a rethink about your T boundary condition. Good luck, and come back and tell us how/when you have cracked it! silviliril and saidc. like this.

 October 14, 2021, 11:28 Any idea on how to write heat flux? #3 Member   L S Join Date: Apr 2016 Posts: 58 Rep Power: 8 I have been struggling a lot on how to apply the heat flux boundary condition with Scharge or Lee models as most tutorials are using constant wall temperature boundary condition. Do you have any idea on how to effectively apply heat flux boundary condition using groovyBC? I tried using dT/dX = q''/keff; Where keff = alpha*k_L+(1-alpha)*k_V; k_L = Thermal conductivity of liquid and k_V = thermal conductivity of vapour. But, this was worsening the calculation.

 Tags boiling, heat transfer, openfoam, phase change heat foam