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serdar April 27, 2005 13:20

thermal phase change
dear all: I have a problem. my problem is as follow: i have a pressure tank and at the bottom of the tank (in the tank temperature 180 celcius and pressure 1mpa saturated water) there is a pipe which is opened to atmospehere. in case of any accident the pipe is activated and water is discharged. but in the pipe water becomes two-phase flow. i have only pressure and temperature as inlet condition. i want to calculate pressure, temperature mass fraction of vapor and water, velocity and other thermodynamic and thermalhydrolic properties. before i did not use cfx but i have some friends they use cfx. if anyone know how to simulate the two phase(thermal phase change) or cavitation please help me. many thanks serdar

Bart Prast April 28, 2005 07:22

Re: thermal phase change
what's in the tank: -liquid water with water vapour on top? -just water vapour (steam)? -Other components (in liquid and vapour) as well?

You might not be able to do this with standard CFD. We have a customized version of CFX5 to do aspects of this problem (and no, you cannot have the code for free) as we do calculations on condensing gas/vapour mixtures and cavitation for our own research.

look at

serdar April 28, 2005 08:42

Re: thermal phase change
there is only water liquid and vapour on top. but during discharge the pressure is constant(assumption) in the tank. at least i want to calculate the nozzle exit pressure mass fraction ,velocity and other thermodynamic and thermalhydroulic quantities.and in the inlet i know the temperature and the pressure (they are constant, assumption ).

if i use only a pipe (with no tank) at the inlet i know tempereture and pressure and at the exit i need the quantities. how can i simulate with cfx

in this case if you help me to calculate the quantitties with cfx (i know cfx is not so good for this purpose) i will be greatful. at least i can use this value as initial value for my other subject. best regards serdar piroglu

Bart Prast May 3, 2005 06:50

Re: thermal phase change
What you can do is probably the following: Model the vessel as a constant (total) pressure nozzle inlet (with large radius compared to the pipe diameter). In principle you have a boiling liquid (or thermal cavitation if you wish). You can do that in CFX (cavitation model with temperature dependend water vapour pressure). Only problem is is that the liquid in your tank will also be boiling so a priori you have a problem in defining there the vapour volume fraction (bouyance will play a role in the tank, in the pipe much less). This will give you the values you want but I'm not sure how accurate. Maybe you should contact CFX on the best approach here.

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