Indicates the velocity of mobile phase through the column.
where
ν = flow velocity (cm/s)
F = flow rate (mL/min)
d = inner diameter of column (mm)
ε = void fraction
Whereas flow rate is the volume of eluent moving through the column per unit time, the flow velocity is the distance traveled by eluent moving through the column per unit time. It is dependent on the flow rate, column diameter, column length, and void fraction.