# warming up gas expansion problem

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 October 8, 2014, 08:25 warming up gas expansion problem #1 Senior Member   Mieszko Młody Join Date: Mar 2009 Location: POLAND, USA Posts: 145 Rep Power: 16 Dear Foamers, I am modeling cold gas injection (5K) into a tunnel filled with warm other gas (300K). I noticed that cold gas is not expanding properly, there is to little of it in the tunnel. did any of you encountered similar problem ? regards mm

 October 8, 2014, 14:36 #2 Senior Member     Marco A. Turcios Join Date: Mar 2009 Location: Vancouver, BC, Canada Posts: 738 Rep Power: 27 What are the boundary conditions of your injection? When you say too little gas, do you mean compared with experiment?

 October 9, 2014, 13:07 #3 Senior Member   Mieszko Młody Join Date: Mar 2009 Location: POLAND, USA Posts: 145 Rep Power: 16 1. inlet/ejection BC is: a) for U - time dependent mass flow of the cold gas1. b) for p - zeroGradient c) for gas1 (cold) - constant = 1 d) for bulk gas2 (warm) - constant = 0 e) for temperature T = 5K 2. yes it is too little comparing to experiment and comparing to fluent results I am using reactinFOAM with chemistry off. Thanks for your interest ! mm

October 9, 2014, 13:23
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Marco A. Turcios
Join Date: Mar 2009
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Rep Power: 27
Quote:
 Originally Posted by ziemowitzima 1. inlet/ejection BC is: a) for U - time dependent mass flow of the cold gas1. b) for p - zeroGradient c) for gas1 (cold) - constant = 1 d) for bulk gas2 (warm) - constant = 0 e) for temperature T = 5K 2. yes it is too little comparing to experiment and comparing to fluent results I am using reactinFOAM with chemistry off. Thanks for your interest ! mm
No problem. I'm not sure about your conditions for c/d, is that the mass fraction? I've found slightly better success with injection when the inlet pressure condition is inletOutlet. Also, what gases are you injecting, and what is the thermo model you are using?

 October 9, 2014, 15:02 #5 Senior Member   Mieszko Młody Join Date: Mar 2009 Location: POLAND, USA Posts: 145 Rep Power: 16 yes, c) and d) are just mass fraction. how would you define inletOutlet condition for pressure ? I do not know the value of the pressure at the eject/inlet. I am injecting Helium, modelled as a perfect gas, but this assumption should be fine, because the same is used in Fluent. for thermo model I use: thermoType { type hePsiThermo; mixture reactingMixture; transport sutherland; thermo janaf; energy sensibleEnthalpy; equationOfState perfectGas; specie specie; } Last edited by ziemowitzima; October 9, 2014 at 15:02. Reason: bug

 October 9, 2014, 16:29 #6 Senior Member     Marco A. Turcios Join Date: Mar 2009 Location: Vancouver, BC, Canada Posts: 738 Rep Power: 27 Well, inletOutlet switches the boundary between being constant value or zeroGradient depending on if the flow is into or out of the domain. Its more a stability helper for me. The extra entry is inletValue, which is the constant value the pressure will be if the flow is into the domain. Try that with some pressure that is close to what you think it should be. Is this gas coming from a resevoir? Also, is the mesh grading similar to what the Fluent simulation used?

 October 10, 2014, 08:30 #7 Senior Member   Mieszko Młody Join Date: Mar 2009 Location: POLAND, USA Posts: 145 Rep Power: 16 Hi, The gas in forcedly ejected in to the tunnel with the mas flow approx 1kg/s. So the flow is always into the domain (because it is inlet). As far as I know, inletOutle BC should be used at the outlet from the domain ?

 Tags cold gas, expansion