Instructor: Dr. Bishara Abu-Ghannam

Homework No. 1 and its solution (Fluid Properties)

1.2 Classify the following substances (maintained at a constant temperature):

a)

du/dy, rad/s 0 3 4 6 5 4τ, kPa 2 4 6 8 6 4

b)du/dy, rad/s 0 0.5 1.1 1.8τ, kPa 0 2 4 6

c)du/dy, rad/s 0 0.3 0.6 0.9 1.2τ, kPa 0 2 4 6 8

Solution:a) Non Newtonian, Hystresis suggests thixotropyb) Non Newtonian.c) Newtonian; μ = 6.667 N.s/m2

1.5 A Newtonian fluid is in the clearance between a shaft and a concentric sleeve. When a force of 500N is applied to the sleeve parallel to the shaft, the sleeve attains a speed of 1m/s. If a 1500-N force is applied, what speed will the sleeve attain? The temperature of the sleeve remains constant.

BIRZEIT UNIVERSITYDepartment of Mechanical Engineering

Fluid Mechanics I – ME335

Solution:

1.14 A plate, 0.5mm distance from a fixed plate, moves at 0.25m/s and requires a force per unit area of 2 Pa to maintain this speed. Determine the viscosity of the substance between the plates.

Solution:

1.21 A fluid has a relative density of 0.78. For a kinematic viscosity of 1.0x10-6m2/s, determine the viscosity.

Solution:

1.22 A body with a gravity force of 500N with a flat surface area of 0.2m2 slides down a lubricated inclined plane making a 30o angle with the horizontal. For viscosity of 0.1 Pa.s and body speed of 1 m/s, determine the lubricant film thickness.

Solution:

1.23 What is the viscosity of gasoline at 25oC?

Solution:

From Figure C.1 page 536:Viscosity of gasoline at 25 oC ≈ 2.9 10-4 Pa.s

1.24 Determine the kinematic viscosity of benzene at 27 oC.

Solution:

From Figure C.2 page 537:Kinematic viscosity of benzene at 27 oC ≈ 7 10-7 m2/s.

1.35 Express the bulk modulus of elasticity in terms of density change rather than volume change.

Solution:

1.38 For K = 2.2 GPa for bulk modulus of elasticity of water what pressure is required to reduce its volume by 0.5 percent?

1.41 At what pressure can cavitation be expected at the inlet of a pump that is handling water at 20 oC?

Solution:Cavitation occurs when internal pressure drops to vapor pressure. From table C-2, vapor pressure of water at 20 oC = 2.5 kPa.

1.47 A method for determining the surface tension of a liquid is to find the force needed to pull a platinum wire ring from the surface. Estimate the force necessary to remove a 20-mm-diameter ring from the surface of water at 20 oC. Why is platinum used as the material for the ring?

Solution:

Let D be the ring diameter. Wire diameter is not important. Assume that the surface is vertical at the breaking point A

(σ from table 1.2)