# Degassing Condition in CFX 5.6

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 February 7, 2004, 15:36 Degassing Condition in CFX 5.6 #1 Paresh Jain Guest   Posts: n/a Dear Friends, i m trying to simulate a gas-liquid reaction in a packed bed. Initially, reactor contatins 0.7 volume fraction of liquid and 0.3 volume fraction gas. Now through inlet, i m entering some air. air reacts with gasphase and produces some product. at the same time some of the liquidphase material too undergoes reaction (but within the phase). so essentially there is no reaction between the phases. and also liquid must not leave the system. So as per my knowledge of CFX, when i dont want my liquid to go outside the system, i should specify degassing consition at the outlet so that only gas will leave the system and i will have liquid fraction in the system as 0.7 (i.e. same as it was initially). But i have run a few simulations but output file shows that volume fraction of liquid is reducing with time and even reaching a value close to zero. Can anybody comment on this why liquid is going out of the system ? Please suggeste me some way out. Your replys will surely help me. Thanks & Regards, Paresh Jain IISc, Bangalore

 February 14, 2004, 01:00 Re: Degassing Condition in CFX 5.6 #2 Jeff Guest   Posts: n/a In a fixed volume reactor, if you increase the gas holdup volume, the liquid has to go "somewhere". In CFX I believe it is simply consumed to make room for the gas. Once the system reaches steady state, and the gas leaving the degassing boundary equals the gas being generated, this phenomena should stop. Jeff

 February 14, 2004, 01:27 Re: Degassing Condition in CFX 5.6 #3 Paresh Jain Guest   Posts: n/a Hi Jeff, thanks for ur reply. But what i suppose is the following. as i have gas too present initially (0.3 vol fraction) then when air is entering through the inlet; gas initially present in the domain must leave the domain and the liquid should not. What do you think about this ? because i m running a transient case with initial values of liquid vol fraction 0.7 so this condition has to be satisfied at very small time t->0 waiting for ur comments and suggestions. regards Paresh Jain

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