Surface Tension and Capillarity

Q1. Explain from microscopic point of view the concept of viscosity and momentum transfer. Explain how viscosity of liquids and gases behave with temperature. Q2. Define kinematic viscosity and explain the significance of the same. Q3. Derive an expression for the torque and power required to overcome the viscous drag for a shaft running at a particular rpm. Q4. Two large planes are parallel to each other and are inclined at 30° to the horizontal with the space between them filled with a fluid of viscosity 20 cp. A small thin plate of 0.125 m square slides parallel and midway between the planes and reaches a constant velocity of 2 m/s. The weight of the plate is 1 N. Determine the distance between the plates. Answer: (5 mm) Q5. A hydraulic lift shaft of 500 mm dia moves in a cylindrical sleeve the length of engagement being 2 m. The interface is filled with oil of kinematic viscosity of 2.4 × 10–4 m2/s and density of 888 kg/m3 . The drag resistance when the shaft moves at 0.2 m/s is 267.81 N. Determine the ID of the cylinder. Q6. A shaft of 150 mm dia rotates in bearings with a uniform oil film of thickness 0.8 mm. Two bearings of 15 cm width are used. The viscosity of the oil is 22 cP. Determine the torque if the speed is 210 rpm. Answer: (10.58 Nm)