Fine silt is to be continuously separated from crude $($an oil$/$water emulsion$)$ in a centrifugal sedimentation tank. The flow rate of crude is $5m^3{h}^{-1},$ its specific gravity $=0\mathrm{.}9$ and its viscosity $=12cP.$ The particle size analysis of silt shows that the particle size ranges from $8$ to $100m.$ The density of silt is $2400kg*m^3.$ A centrifugal bowl of $600mm$ diameter and $500mm$ is available to this aim. The oil $-$ silt suspension is continuously delivered through a slotted vertical shaft of $150mm$ diameter. Specify the required speed of revolution to perform full separation of silt. Note: angular speed $()=2N$ where $N$ is the number of rotations per second.