simple multi-phase simulation ...... help please!

Tim

Hi,

I am currently attempting a simple multiphase simulation in which I have a straight height of tube, inlet at top of 0.2 (volume fraction) solid dispersed particles and 0.8 air. The simulation completes ok to 1e-4 convergence, with the particles speeding up under the influence of gravity as you would expect. However, when I inspect the volume fractions at the inlet for the solution it says the volume fraction of the solid particles is like 0.5% and 99.5% for the air. Why is this the case? i.e. the solid particles volume solid fraction should be much higher at 20% rather than 0.5%.

Thanks, Tim.