As a junior field engineer, you have been asked to assist the contractor on your job in resolving the following problem. A 4.9 kW motor and gear drive rated at 175 rpm has been shipped with the four impellers described below. The baffled rapid mix tank into which it is to be installed is 3.0 m ³ in volume (1.56 m diameter by 1.56 m deep). Which impeller should be used? Assume a water temperature of 10 ^o C, a G  = 1,000 s ^{– 1} , a water density of 1,000 kg/m ³ , and that the motor power to water power efficiency is 80%. Show the calculations to justify your decision.

Impellers

A.  Propeller, pitch of 2, 3 blades, diameter = 0.48 m, N _p   = 1.0

B.  Propeller, pitch of 2, 3 blades, diameter = 0.61 m, N _p   = 1.0

C.  Turbine, 6 flat blades, vaned disc, diameter = 0.48 m, N _p   = 6.3

D.  Turbine, 6 flat blades, vaned disc, diameter = 0.61 m, N _p   = 6.3