Supercritical Fluid analysis in ansys fluent

AKandwal · March 4, 2023, 08:46

I am trying to do heat transfer analysis for Supercritical fluid flow. But currently I am not able tp figure out how to define fluid property for Supercritical fluid after selecting water from fluent database.

Please help in this regard since material for Supercritical water analysis in Fluent is very rare.

LoGaL · March 4, 2023, 13:20

You do not impose a fluid to be supercritical, it is simply an outocome of the pressure and temperature at which it is. The equation of state you use ( the rule you select under " density") has to be capable of correctly predicting the supercritical behaviour.

So in the specific, you select water as material and then choose a "density rule" i.e. an equation of state which is appropriate for the regime.

AKandwal · March 4, 2023, 13:28

So my doubt is that very point that what is that density rule and how to find it?

LoGaL · March 4, 2023, 15:47

some nice literature research will help you. It may also help give you an idea of what you are trying to model. I would start reading the fluent manual in the "real gas models" section.

AKandwal · March 5, 2023, 00:39

What should be operating pressure for supercritical water?
I have attached the screenshot where it is required

AKandwal · March 5, 2023, 01:17

WARNING: Invalid cp (-7.155988e+45 J/kgK) for water-liquid at temperature 0.000002 K

Can someone explain the cause of the above warning. I am unable to initialise my solution due to this.

Also earlier to this I was getting

Warning: For compressible (ideal and real) gas models with buoyancy,
it is recommended that you use a specified operating density value of zero:
After which I set operating pressure as 0.

What to do with these two warnings?

LuckyTran · March 5, 2023, 13:54

Fluent has calculated a negative value for Cp at a temperature of 0.000002 K. This could mean that the equation of state you use is not good for this temperature if you truly meant to initialize your simulation with a very low temperature. But more than likely your initial temperature is just too low. Water isn't supercritical at the micro Kelvin temperatures so I'm guessing mistakes have been made.

Certain buoyancy models require the operating pressure to be zero. Just listen to Fluent. If you want to learn more about it, you can dig into how the buoyancy forces are formulated for the models you are using.

March 4, 2023, 08:46	Supercritical Fluid analysis in ansys fluent	#1
AKandwal New Member Abhishek Kandwal Join Date: Mar 2023 Posts: 4 Rep Power: 3	I am trying to do heat transfer analysis for Supercritical fluid flow. But currently I am not able tp figure out how to define fluid property for Supercritical fluid after selecting water from fluent database. Please help in this regard since material for Supercritical water analysis in Fluent is very rare.

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March 4, 2023, 13:20		#2
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	You do not impose a fluid to be supercritical, it is simply an outocome of the pressure and temperature at which it is. The equation of state you use ( the rule you select under " density") has to be capable of correctly predicting the supercritical behaviour. So in the specific, you select water as material and then choose a "density rule" i.e. an equation of state which is appropriate for the regime.

March 4, 2023, 13:28		#3
AKandwal New Member Abhishek Kandwal Join Date: Mar 2023 Posts: 4 Rep Power: 3	So my doubt is that very point that what is that density rule and how to find it?

March 4, 2023, 15:47		#4
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	some nice literature research will help you. It may also help give you an idea of what you are trying to model. I would start reading the fluent manual in the "real gas models" section.

March 5, 2023, 00:39		#5
AKandwal New Member Abhishek Kandwal Join Date: Mar 2023 Posts: 4 Rep Power: 3	What should be operating pressure for supercritical water? I have attached the screenshot where it is required

March 5, 2023, 01:17		#6
AKandwal New Member Abhishek Kandwal Join Date: Mar 2023 Posts: 4 Rep Power: 3	WARNING: Invalid cp (-7.155988e+45 J/kgK) for water-liquid at temperature 0.000002 K Can someone explain the cause of the above warning. I am unable to initialise my solution due to this. Also earlier to this I was getting Warning: For compressible (ideal and real) gas models with buoyancy, it is recommended that you use a specified operating density value of zero: After which I set operating pressure as 0. What to do with these two warnings?

March 5, 2023, 13:54		#7
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Fluent has calculated a negative value for Cp at a temperature of 0.000002 K. This could mean that the equation of state you use is not good for this temperature if you truly meant to initialize your simulation with a very low temperature. But more than likely your initial temperature is just too low. Water isn't supercritical at the micro Kelvin temperatures so I'm guessing mistakes have been made. Certain buoyancy models require the operating pressure to be zero. Just listen to Fluent. If you want to learn more about it, you can dig into how the buoyancy forces are formulated for the models you are using.