A cyclone separator is used to remove sand grains from an airstream at 150C. If the cyclone body is 0.6 m in diameter and the average tangential velocity is 16 m/s, what is the radial velocity near the wall of particles 20 and 40 micrometer in size? How much greater are these values than the terminal velocity in gravity settling? Density of sand is 2196 kg/m3

for this question in step 3/3 why did you substitute with half of the radius values? For a particle size of 20 micrometers (0.00002m), the terminal velocity in gravity setting is: 0.00001 For a particle size of 40 micrometers (0.00004m), the terminal velocity in gravity setting is: 0.00002 ??