How to choose the mean diameter value for dispersed fluid?
Hi everyone,
I am simulating twophase flow consisting of one continuous phase and one dispersed fluid phase (Here Argon gas is injected into a vessel consisting of molten steel from nozzle located at bottom). Here I am considering Argon gas as dispersed fluid and molten steel as continuous phase. In CFXPre under Fluid details tab it was asking for mean diameter of dispersed fluid (Argon gas), Can any one please tell me how to choose the value of mean diameter of dispersed fluid. In CFX manual it has mentioned "Mean Diameter For a Dispersed Solid or Dispersed Fluid, you must supply the mean diameter of the dispersed particles, droplets or bubbles constituting the phase. The mean diameter is the actual diameter for spherical particles. For nonspherical particles, you should provide the Sauter mean diameter, that is, the diameter of a sphere possessing the same volume as the particles." But I am not getting how to choose the right value for mean diameter. FLUID: Argon gas FLUID MODELS: FLUID BUOYANCY MODEL: Option = Density Difference END MORPHOLOGY: Mean Diameter = 0.68 [m] Option = Dispersed Fluid END TURBULENCE MODEL: Option = Dispersed Phase Zero Equation END END END FLUID: Molten Steel FLUID MODELS: FLUID BUOYANCY MODEL: Option = Density Difference END MORPHOLOGY: Option = Continuous Fluid END Looking forward for reply. Thanks & Regards, Niranjan Reddy. 
The bubble diameter is a function of the flow conditions and therefore you must specify it. Hopefully you know it from experimental results. If not, you can estimate it from the argon nozzle diameter and look in the literature for gas bubble size from a nozzle.

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