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hemenkhaled February 15, 2012 14:48

measuring gas holdup
I want to simulate a bubble column in cfx. How can I measure gas holdup in cfx post?please help me.

zolrack June 16, 2012 17:34

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 :):)

omar.rahul April 29, 2015 23:44

how to measure the time average gas holdup.

zolrack April 30, 2015 01:13

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

ghorrocks April 30, 2015 02:31

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.)

zolrack April 30, 2015 02:36

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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