I am currently running a transient multi phase simulation using a step size of 0.001 for a period of 5 to 10 s flow time to achieve a steady time-averaged gas holdup value. Which boundary condition is more appropriate at the sparger inlet which can be applicable for various gas flow rates and increasing fluid viscosity?

1) Slip Velocity = 0

2) Slip Velocity = 1

Your insights is much appreciated,

Thank you!