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Old   September 25, 2006, 13:14
Default temperature 1K- 5000K
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aga
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HI We are trying to simulate an evaporation and boiling process. Everything seems to be OK. Mass bilans is OK but the problem is with temperature. In our simulation temperature of liquid phase is OK but the temperature of vapor phase isn`t OK. At the begining of simulation temperature is 320K (set up by me), after few iteration t starts to decrease to 1K (meanwhile liquid temperature rise to 375 K - we have boiling), after few hours of calculations temperature increase to 5000K. We`ve heard that this is normal problem but how to solve it?? Some guy from Poland told me that we should change boundary conditions. I`ve tried....no resultes. Can you help us with this.
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Old   September 25, 2006, 22:56
Default Re: temperature 1K- 5000K
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Ahmed
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When intermediate temperature computations produce negative absolute temperatures, the solver takes care of this situation by adjusting the temperature to a positive value. Reduce your under relaxation parameters (this is the first recommendation) but you ought to give more about your simulation, what solver are you using, is it a unsteady simulation, etc Good Luck
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Old   September 28, 2006, 17:02
Default Re: temperature 1K- 5000K
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aga
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I`m using unstady solver, VOF model, viscosity k-epsilon,, 2 phase,water - vapour, gravity, heat and mass transfer (from vapour to water and from water to vapour) UDf; BC are: pressure outlet and 3 walls. under relaxation factors between 0,5-0,7. Iteration time steps=0,0005s. Are you able to tell me more now????
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Old   September 28, 2006, 18:10
Default Re: temperature 1K- 5000K
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Ahmed
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1- How did you calculate your time step (The time step should be less than the characteristic time of your flow, if you cannot define that parameter, reduce to 1e-6s and increase as the solution proceeds 2- Under Relaxation factors, reduce them, specially the momentum and pressure (I would go for 0.1 or less for some 25-50 iterations and as the solution proceeds you can increase them but gradually 3- Can you upload or send me your mesh file

Good Luck
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Old   September 29, 2006, 03:12
Default Re: temperature 1K- 5000K
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aga
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give me please your email address aga
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Old   October 2, 2006, 03:02
Default Re: temperature 1K- 5000K
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Ahmed
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Use the <send email> button, it is not a good idea to post any email address on a public forum.
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