Crude oil at 20°c fills the space between two concentric cylinders 250 mm high and with diameters of 150 mm and 156 mm. what torque is required to rotate the inner cylinder at 12 r/min, the outer cylinder rernaining stationary? assume that the viscosity of crude oil is 0.07 poise at 20°c.

Afan that can provide air speeds up to 60 m/s is to be used in a low-speed wind tunnel with atmospheric air at 35 c. if one wishes to use the wind tunnel to study flat-plate boundary layer behavior up to reynolds numbes of re 10, what is the minimum plate length that should be used? at what distance from the leading edge would transition occur if the critical reynolds nurnber were rer,e = 5 × 105?