# gas cylinder filling

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 November 23, 2005, 09:53 gas cylinder filling #1 Farrukh Guest   Posts: n/a I want to simulate a transient problem in which a cylinder is filling with the gas and i have to measure the pressure inside the cylinder at diffrent time instants. Can any one help me in selecting the boundary conditions and give me some hints abut solution of this problem Regards M.Farrukh

 November 26, 2005, 03:38 Re: gas cylinder filling #2 Ali Guest   Posts: n/a hi, Actually i'm modeling a gas cylinder emptying case. There is not so much difference between these two cases. You should use a transient method with some small timesteps and in each timestep you need to calculate the pressure and temperature inside the cylinder and set the B.C. of the inlet of the cylinder by using a UDF in each timestep.

 November 26, 2005, 13:57 Re: gas cylinder filling #3 Farrukh Guest   Posts: n/a Hi Ali Thanx for your kind attention towards my problem The last line of your message i.e. set the B.C. of the inlet of the cylinder by using a UDF in each timestep is not clear to me Please explain it to me briefly and if possible you send me the copy of your "udf" and "cas & dat" file. Regards M.Farrukh

 November 27, 2005, 06:41 Re: gas cylinder filling #4 Ali Guest   Posts: n/a Hi Farrukh, If you want to calculate the time of cylinder filling you only need to model the connecting pipe to the cylinder which the outlet of the pipe is the inlet of the cylinder with different pressures and temperatures as a B.C. in each timestep. But if you want to model the cylinder too, you should model it seperately with a mass flow rate B.C. at the inlet of the cylinder which varies with time and you need to define it in a UDF by using the mass flow rate data you have already obtained by solving the connecting pipe model. I'm developing my UDF and the models and still don't reach to the final results. Also, my problem is different from yours but i'll give it to you when i reach to a solution. Sincerely

 November 27, 2005, 10:24 Re: gas cylinder filling #5 Farrukh Guest   Posts: n/a OK ali i m waiting for your results in the mean time i will try to do it myself and if it will be done than i share it to u. Regards M.Farrukh

 November 30, 2005, 18:42 Re: gas cylinder filling #6 Paul Guest   Posts: n/a Hello, I am looking at a similar problem, modeling loss of vacuum accidents. In this case there is simply a tank with a hole through which ambient air rushes in. It seems like this should be simple to set up and run (only need to specify pressure inside and at the breach), but I can't get anything to work. Obviously I am not very familiar with fluent... any help is appreciated. Paul

 December 1, 2005, 10:31 Re: gas cylinder filling #7 Paul Guest   Posts: n/a Update: I think I see what you mean now about modeling the inlet and tank separately, and then specifying the tank inlet as a mass flow inlet. Otherwise, there is a large discontinuity in pressure there.

 December 2, 2005, 11:41 Re: gas cylinder filling #8 Ali Guest   Posts: n/a Hi Paul, Actually im working on an emtying case instead of filling case and i have so much trouble with it! In my problem the pressure is too high. so, the gas isnt ideal and unfortunately fluent real gas model is just a library data files which i couldnt get any result from them! It always gives an error message in finding and interpolating the properties of the gas from the real gas library file.

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