Normal speed value for particles at inlet
 

Dear all
I am working on a venturi scrubber and there are three phase i.e. air, water and particles. So at inlet i have defined the volume fraction for air as 1 and water as 0 so for particles i have to define the normal speed in a fluid values tab. Can any one tell me how to calculate the normal speed of the particle at inlet. I shall be very thankful if someone help me in this.
Thanks you
Regards,
Ibadullah Safdar