Post-processing Pressure in a boiling simulation

soumitra2102 · December 24, 2018, 15:19

In a subcooled pool boiling simulation under normal atmospheric pressure, am I expected to see rise in pressure level of the liquid phase with time (transient simulation).

I set reference pressure in Pres-processing (ANSYS CFX- Pre) for the domain to be 1 atm and initial condition to be 0atm pressure, still in post processing (ANSYS CFD-Post), I see Pressure contour variable rise ~ 9atm throughout the domain.

ghorrocks · December 25, 2018, 06:46

I do not understand your question.

I think the first line of your question says you expect to see the pressure rise as the liquid boils - this makes sense if it is boiling in a constant volume container.

I think the second line of your question says that the pressure has risen to 9 atm. So isn't that what you expect? It does sound like a very big pressure rise, you must have a large heat flux to get that much pressure.

soumitra2102 · December 25, 2018, 10:53

Oh sorry,my bad.

The first line is actually a question. Am I expected a pressure rise in the liquid phase for a subcooled pool boiling under normal atmospheric condition?

The pool boiling tank is open to atmosphere from it's top wall (it's a free liquid water surface in contact with atmospheric air (and this atm. pressure)). So it is not a constant volume boiling (also, in simulation, I put Outlet boundary condition with 0 relative pressure).

And yes, the is huge flux, because the temperature of the heating medium is about 240 C. (It's is conjugate heat transfer problem).

ghorrocks · December 26, 2018, 04:45

If the thing is open to atmosphere then the pressure will remain near atmospheric, with some hydrostatic component and a small effect from and fluid motion generated.

If it is open to the atmosphere but you are generating huge pressures then it sounds like something is wrong.

December 24, 2018, 15:19	Post-processing Pressure in a boiling simulation	#1
soumitra2102 Member Soumitra Vadnerkar Join Date: Aug 2018 Posts: 70 Rep Power: 8	In a subcooled pool boiling simulation under normal atmospheric pressure, am I expected to see rise in pressure level of the liquid phase with time (transient simulation). I set reference pressure in Pres-processing (ANSYS CFX- Pre) for the domain to be 1 atm and initial condition to be 0atm pressure, still in post processing (ANSYS CFD-Post), I see Pressure contour variable rise ~ 9atm throughout the domain.

December 25, 2018, 06:46		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	I do not understand your question. I think the first line of your question says you expect to see the pressure rise as the liquid boils - this makes sense if it is boiling in a constant volume container. I think the second line of your question says that the pressure has risen to 9 atm. So isn't that what you expect? It does sound like a very big pressure rise, you must have a large heat flux to get that much pressure. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

December 26, 2018, 04:45		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	If the thing is open to atmosphere then the pressure will remain near atmospheric, with some hydrostatic component and a small effect from and fluid motion generated. If it is open to the atmosphere but you are generating huge pressures then it sounds like something is wrong. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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December 25, 2018, 10:53		#3
soumitra2102 Member Soumitra Vadnerkar Join Date: Aug 2018 Posts: 70 Rep Power: 8	Oh sorry,my bad. The first line is actually a question. Am I expected a pressure rise in the liquid phase for a subcooled pool boiling under normal atmospheric condition? The pool boiling tank is open to atmosphere from it's top wall (it's a free liquid water surface in contact with atmospheric air (and this atm. pressure)). So it is not a constant volume boiling (also, in simulation, I put Outlet boundary condition with 0 relative pressure). And yes, the is huge flux, because the temperature of the heating medium is about 240 C. (It's is conjugate heat transfer problem).