# water in piston whose volume doesn't change

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 November 7, 2010, 09:18 water in piston whose volume doesn't change #1 New Member   Ki-hwan Jun Join Date: Jul 2009 Posts: 9 Rep Power: 9 Hi, I want to question about a matter of water's temperature change in a piston whose volume doesn't change with pressure increasing. There is a piston which is filled with water. This piston is pressured and the pressure is increasing. The volume of the piston doesn't change, so I think that the water's temperature will increase. I wonder whether this matter can be modelled by FLUENT code. And if possible, I want you to tell the detail contents, such as boundary conditions, and any thing else related with this problem. And if you know the examples related with my question, please help me find them. If impossible, I will be thankful if you reply the reason, please. My e-mail adress is york49@snu.ac.kr Then, have a nice week~. Last edited by junbbung; November 7, 2010 at 10:41.

 November 7, 2010, 11:04 Piston or Cylinder #2 Member   Anonymous Join Date: Jun 2009 Posts: 55 Rep Power: 9 Do you mean Piston or do you mean a cylinder? Anyway, I assume it's just a constant volume container. And from one side, something is trying to compress it. However, the volume change will be negligible. And this is not a fluid flow problem, so, forget about Fluent. It's more of thermodynamics. Better try to find out the best Equation of State for liquid in question and apply it to a particular process, in your case it could be adiabatic.

 November 7, 2010, 11:18 #3 New Member   Ki-hwan Jun Join Date: Jul 2009 Posts: 9 Rep Power: 9 Dear vinerm. Thank you for your reply. I did the same question to the supply company in my contry, and the engineer told me that it is possible to model. But I had no confidence about the possibility, so I made out this thread. I understand your explanation. thank you! But if there is a fluent user who think that it's possible to model with FLUENT for my subject, then please reply! Thank you!!

 November 7, 2010, 12:33 It's possible #4 Member   Anonymous Join Date: Jun 2009 Posts: 55 Rep Power: 9 There is no issue with modeling such a scenario using Fluent but it may not be useful. Fluent is supposed to solve Navier-Stokes along with Energy or just Energy balance and as add-ons you have reacting flows, discrete phases, etc. However, here the problem is of stationary fluid that is being compressed. If you want to model in Fluent, may be you would like to consider the natural convection part of it for better distribution of energy. Or if you neglect that, you can specify a boundary condition at one face of container to be of increasing pressure with time, you will have to write a simple UDF or you can use transient profile as BC. Secondly, you will have to use a particular EoS for water. I have never checked but in Fluent's documentation you can find out which ones are available and which one is most suitable for water

 November 7, 2010, 13:07 #5 New Member   Ki-hwan Jun Join Date: Jul 2009 Posts: 9 Rep Power: 9 Dear vinerm, I'm really appreciated for your kindness and smartness. I study more about the subject because I know it's not possible. I'm very sorry but I want to question one more. The cylinder's volume doesn't change, so I will make a rectangular for 2d simulation, and the bottom will be conditioned as pressure inlet, and the other three line of the rectangular will be conditioned as wall. If I give these boundary condition, there's no way for the water flow out. Does this make sense? I wonder your opinion. Thank you very much!

 November 8, 2010, 12:02 #6 Member   Anonymous Join Date: Jun 2009 Posts: 55 Rep Power: 9 That's what you want. Don't you? You want the pressure to increase but you don't want the water to go in or come out. And therefore, you will have three sides as walls, as you mentioned. But the fourth side, which you have mentioned as pressure inlet will also be wall. Pressure inlet means you are adding water with some pressure. And this will stop as soon as the pressure balances. However, I think what you want is to increase the pressure slowly. For that you have to assume a moving wall, just like a piston going for a compression stroke in a reciprocating engine.

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