help about the fluent degas boundary

ggbaby

I have some qustion about the de-gas boundary of multiphase. In my research, the oil droplet come into a container and separate with the gas. after separation the oil droplet will fall down and leave the container. So I want to set a outlet boundary to let the leave, but gas couldn't pass through this outlet. The left oil droplet and gas will leave another pressure outlet. I have downloaded the de-gas UDF of fluent in fluentuser.com. However I met some problem because I couldn't not understand this very well.

Usage instructions:

- Setup your multiphase flow problem using Mixture model or Euler/Euler.

finished. - Make sure you've introduced a pressure inlet or outlet somewhere, with (backflow) boundary condition so that LIQUID may enter here.This is probably UNnecessary (or perhaps even nocuous!) if you are(despite all caveats) simulating a bubble column in steady state...

Finished

- At the free liquid surface, you must define a symmetry boundary.

Finished. Why I have to set a symmetry boundary not a outlet?

- The Zone ID of that symmetry zone must be assigned to the RP variable "degas-symmetry-zone-id" -- cf. above!

I should set the symmetry boudary name to degas-symmetry-zone-id?

- The Domain ID of the dispersed gas bubble phase must also be assigned to an RP variable -- cf. above again. I should set all the domain's name as degas-bbl-phs-domn-id? And how to set it?

- Please do even introduce the three other RP variables listed above...

??????????? how to understand this line?