Question

The kinematic viscosity of oil of specific gravity .8 is .0005 .This oil is used for lubrication of shaft of diameter .4 m and rotates at 190 rpm. Calculate the power lost in the bearing for a sleeve length of 90mm. The thickness of the oil film is 1.5mm.

(a) 477.65 Watts

(b) 955.31 Watts

(c) 238.83 Watts

(d) None of the mentioned

The question was asked during an online interview.

The question is from Viscosity in chapter Properties of Fluids of Fluid Mechanics

Answer 1

Correct choice is (a) 477.65 Watts

For explanation: Power lost=  torque * angular velocity

                                     =  force* radius* angular velocity

                                     =  shear stress * area* radius* angular velocity

                     Shear Stress = viscosity* velocity gradient

                     Power lost= 0.0005*0.8*1000* 2*3.142*190/60*0.2*3.142*0.23 * 190/60

                                     = 477.65 Watts.