Spherical particles of density 2500 kg/m³ and in the size range 20–100 µm are fed continuously into a stream of water (density, 1000 kg/m³ and viscosity, 0.001 Pa s) flowing upwards in a vertical,...

Extracted text: Spherical particles of density 2500 kg/m³ and in the size range 20–100 µm are fed continuously into a stream of water (density, 1000 kg/m³ and viscosity, 0.001 Pa s) flowing upwards in a vertical, large diameter pipe. What maximum water velocity is required to ensure that no particles of diameter greater than 60 µm are carried upwards with water?