Very low steam fraction RPI boiling

PierreLCV · May 26, 2023, 11:23

Dear All,

I am currently working on my first CFD boiling simulation using RPI model and I face an issue I can not fix. I have started with a very straightforward steady state situation, vertical tube 20mm diameter and 2000mm length. Water inlet at the bottom at 20°C, 1 bar and 1m/s.
I have imposed a heat flux on the wall which i increase gradually simulation after simulation. It appears that the monophasic situation works very well. I activate the multiphase model when the temperature on the wall is about to reach the saturation temperature and that's where the problem start. Indeed, whatever the heat flux imposed, the steam volume fraction remains very low (i can not reach more than e-5). I have tried to increase a lot the heat flux but the solver diverge then...
Briefly, my simulation is working very well in monophasic state (even when the multiphase option is activated when the heat flux is low enough) but when the heat flux is high enough to create steam, the fraction remains very low whatever the flux.
As it is my first RPI boiling simulation, i am using the "default" values for all the RPI model parameters adviced by Fluent Manual.
I precise that I have activated the gravity...

Any idea ?

Thank you for your help !

Pierre

gulab1708 · November 13, 2024, 13:22

i also want answer for the same. have you got the solution?

PierreLCV · November 13, 2024, 15:29

Dear gulab1708,
This post is quite old now, but I am still working on this subject, so maybe I can help

. I do not know exactly what is your issue but if the situation is close to mine in May 2023 I suggest you to start from the Bartolomei validation case (you will find it on the Ansys Help site).
If you have specific question please do not hesitate to ask I will try to help you on this difficult but passionating subject !

You can also send me directly a message/email

Best regards,
Pierre

May 26, 2023, 11:23	Very low steam fraction RPI boiling	#1
PierreLCV Member Pierre LECHEVALIER Join Date: Mar 2023 Posts: 31 Rep Power: 3	Dear All, I am currently working on my first CFD boiling simulation using RPI model and I face an issue I can not fix. I have started with a very straightforward steady state situation, vertical tube 20mm diameter and 2000mm length. Water inlet at the bottom at 20°C, 1 bar and 1m/s. I have imposed a heat flux on the wall which i increase gradually simulation after simulation. It appears that the monophasic situation works very well. I activate the multiphase model when the temperature on the wall is about to reach the saturation temperature and that's where the problem start. Indeed, whatever the heat flux imposed, the steam volume fraction remains very low (i can not reach more than e-5). I have tried to increase a lot the heat flux but the solver diverge then... Briefly, my simulation is working very well in monophasic state (even when the multiphase option is activated when the heat flux is low enough) but when the heat flux is high enough to create steam, the fraction remains very low whatever the flux. As it is my first RPI boiling simulation, i am using the "default" values for all the RPI model parameters adviced by Fluent Manual. I precise that I have activated the gravity... Any idea ? Thank you for your help ! Pierre

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November 13, 2024, 13:22		#2
gulab1708 New Member gulab verma Join Date: Feb 2023 Posts: 2 Rep Power: 0	i also want answer for the same. have you got the solution?

November 13, 2024, 15:29		#3
PierreLCV Member Pierre LECHEVALIER Join Date: Mar 2023 Posts: 31 Rep Power: 3	Dear gulab1708, This post is quite old now, but I am still working on this subject, so maybe I can help . I do not know exactly what is your issue but if the situation is close to mine in May 2023 I suggest you to start from the Bartolomei validation case (you will find it on the Ansys Help site). If you have specific question please do not hesitate to ask I will try to help you on this difficult but passionating subject ! You can also send me directly a message/email Best regards, Pierre