Three Phase Eulerian Multiphase (GAS/LIQUID/LIQUID)
 

While modeling three phases in eulerian multiphase, phase "OIL" is asking for diameter. What does that mean?

My case has only one inlet, only air as a dispersed phase having some diameter is entering the fluid domain. Oil is just their in the domain, it is not entering through inlet neither it is exiting the domain.

if you do not use PBM,the oil diameter is the average value(maybe not the real value),and the diamter you used will Influence the result.