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measuring gas holdup

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Old   February 15, 2012, 14:48
Question measuring gas holdup
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hemen khaled
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I want to simulate a bubble column in cfx. How can I measure gas holdup in cfx post?please help me.
thanks.
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Old   June 16, 2012, 17:34
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very simple. you must to monitoring the gas volume fraction. If you are modelling air -water, the air is a dispersed phase. so you shold measure the air volume fraction. I suggest you measure time average gas holdup
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Old   April 29, 2015, 23:44
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how to measure the time average gas holdup.
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Old   April 30, 2015, 01:13
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you need to créate a transient simulation and add in the output a aritmetic average to account for thr "Time or Trnavg" for each timestep
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Old   April 30, 2015, 02:31
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Glenn Horrocks
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There is a neat way of doing this which does not require a transient simulation . You create an additional variable with units of time. You make the variable have a convection equation (but not diffusion), and start at the inlet with time = 0. You then put a source term on additional variable on the entire domain of 1 [1/s].

This creates an additional variable which moves around with the fluid and the source term makes it increment by time. By the time it reaches the outlet it has incremented to the residence time.

(I may have details of the implementation wrong, hopefully somebody will correct me if this is the case. But I know the approach works.)
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Old   April 30, 2015, 02:36
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Hi, I think the additional variable helps if you want to track the particles as a residence time distribution, but if you need to know the "gas volumen fraction(time averaged) I suggest create TRNAVG variables in the output or create a PERL routine instead automatic aritmetic average in each timesteps.....regards
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