A stirred tank reactor 3 ft in diameter with a 12-in. flat-blade turbine has been used for a batch reaction in which the blending time of added reagents is considered critical. Satisfactory results were obtained with a stirrer speed of 400 r/min. The same reaction is to be carried out in a tank 7 ft in diameter, for which a 3-ft standard turbine is available. 

(a) What conditions would give the same blending time in the larger tank?

(b) What would be the percentage change in the power per unit volume? Density ρ = 60 lb/ft³; viscosity μ = 5cP.