Mahalakshmi Engineering College

96 Pages·2014·7.78 MB·English

MAHALAKSHMI
ENGINEERING COLLEGE
TIRUCHIRAPALLI – 621213
QUESTION BANK
DEPARTMENT : MECHANICAL SEMESTER : III
SUBJECT: FLUID MECHANICS & MACHINERY SUBJECT CODE: ME2204

UNIT I- INTRODUCTION
PART – A (2 Marks)
01. Why are some fluids classified as Newtonian fluid? Give examples to Newtonian fluids.
(NOV’2)
Newtonian fluids are the simplest mathematical models of fluids that account for viscosity. While
no real fluid fits the definition perfectly, many common liquids and gases, such as water and air,
can be assumed to be Newtonian for practical calculations under ordinary conditions.

02. What is specific gravity? How is it related to density? (Apr’08)
The ratio of the density of a substance to the density of a standard, usually water for a liquid or
solid, and air for a gas

03. Define the term pressure .What are its units? (Dec’05)
The continuous physical force exerted on or against an object by something in contact with it.

04. State Pascal’s law? (Dec’05 & Dec’08)
Pascal's law or the principle of transmission of fluid-pressure is a principle in fluid mechanics
that states that pressure exerted anywhere in a confined incompressible fluid is transmitted
equally in all directions throughout the fluid such that the pressure ratio (initial difference)
remains the same

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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05. What is meant by stagnation pressure? (Dec’08)
In fluid dynamics, stagnation pressure (or pitot pressure) is the static pressure at a
stagnation point in a fluid flow. At a stagnation point the fluid velocity is zero and all
kinetic energy has been converted into pressure energy (isentropically). Stagnation
pressure is equal to the sum of the free-stream dynamic pressure and free-stream static
pressure. Stagnation pressure is sometimes referred to as pitot
pressure because it is measured using a pitot tube.

06. What is the difference between gauge pressure and absolute pressure? (Dec’07)
 Gauge pressure is zero-referenced against ambient air pressure, so it is equal to
absolute pressure minus atmospheric pressure. Negative signs are usually omitted. To
distinguish a negative pressure, the value may be appended with the word "vacuum" or
the gauge may be labeled a "vacuum gauge."
 Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge
pressure plus atmospheric pressure

07. Define compressibility and viscosity of a fluid? (Apr’05)
 Compressibility is a measure of the relative volume change of a fluid or solid as a
response to a pressure (or mean stress) change.
 The viscosity of a fluid is a measure of its resistance to gradual deformation by shear
stress or tensile stress. For liquids, it corresponds to the informal notion of "thickness".
For example, honey has a higher viscosity than water.

08. State the Newton’s law of viscosity? (Apr’04)
Newton's law of viscosity defines the action of some fluids under a restricted range of conditions
and such fluids are referred to as Newton's fluids. The law states that when a shear stress is
applied to a fluid, the velocity gradient that it yields in the direction perpendicular to the stress is
proportional to the applied shear stress. The resultant velocity decreases with distance from a
plane over which the shear stress is applied to.

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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09. What is the effect of temperature on viscosity of water and that of air? (Nov’04)
where is a constant for the gas.

Let μ = dynamic viscosity in (Pa·s) at input temperature T,
μ0 = reference viscosity in (Pa·s) at reference temperature T0,
T = input temperature in kelvins,
T0 = reference temperature in Kelvin,
C = Sutherland's constant for the gaseous material in question.

10. Define capillarity? (Dec’05)
Capillary action (sometimes capillarity, capillary motion, or wicking) is the ability of a liquid to
flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity.
The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin
tube, in porous materials such as paper, in some non-porous materials such as liquefied carbon
fiber, or in a cell. It occurs because of intermolecular forces between the liquid and solid
surrounding surfaces. If the diameter of the tube is sufficiently small, then the combination of
surface tension (which is caused by cohesion within the liquid) and adhesive forces between the
liquid and container act to lift the liquid

11. Explain the effect of property of capillarity (Nov’04)
The liquid rise is known as capillary rise. And the liquid drop is nothing but capillary depression.

12. What are the three major assumptions made in the derivation of the Bernoulli’s equation?
(Apr’03)
 The fluid is incompressible and non viscous.
 There is no energy loss due to friction between the fluid and the wall of the pipe.
 There is no heat energy transferred across the boundaries of the pipe to the fluid as
either a heat gain or loss.
 There are no pumps in the section of pipe under consideration.
 The fluid flow is laminar and steady state.

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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13. Mention any three applications of bernouills equation? (Apr’05)
1. pitot tube
2. Pitot static tube
3. Venture meter
4. Orifice meter
5. Notches and weirs

PART-B ( 16 Marks )
01. Calculate the specific weight, density, and specific gravity of 1 litre of a liquid which weighs
7N. (APR-03)

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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02. State and prove Pascal’s law.

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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03. Calculate the capillary rise in glass tube of 2.5mm dia when immersed in mercury take the
surface tension and angle of contact of mercury as 0.52N/m and 130⁰ respectively .Also
determine the minimum size of the glass tube, if it is immersed in water, given that the
surface tension of water is 0.0725N/m and the capillary rise in the tube is not to exceed
0.5mm. (NOV-03)

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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04. Derive from the first principles, the Euler’s equation of motion for a steady flow along a
stream line. Hence derive Bernoulli’s equation. State the various assumptions involved in
the above derivation.

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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05. A 15 cm vertical cylinder rotates concentrically inside another cylinder of diameter 15.10cm.
Both cylinders are 25 mm high. The space between the cylinders is filled with a liquid
whose viscosity is unknown. If a torque of 12 Nm is required to rotate the inner cylinder at
100 r.pm, determine the viscosity of the fluid (DEC-08)

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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06. An oil film of thickness 10mm is used for lubrication between the two square parallel plates
of size 0.9m×0.9m each, in which the upper plate moves at 2m/s required a force of 100N
to maintain this speed. Determine,
1. Dynamic viscosity of oil 2. Kinematic viscosity of oil If the specific gravity of the oil is
0.95 (NOV-03)
Given:
A = 0.9 x 0.9 m = 0.81 m2 dy = 10 mm u= 2 m/s
F = 100 N S = 0.95
Solution:
(i) Dynamic viscosity of oil :-
Shear stress = = F/A = µ du/dy
Force / area = 100/0.81 = 123.456
123.456 = µ (2/0.01)
µ = 0.61728 Ns/m2
(ii) Kinematic viscosity of oil If the specific gravity of the oil is 0.95: -
K = µ/ρ
The value of µ is 0.61728 Ns/m2
K = 0.61728 / ρ
Value of ρ is determining from S = ρ of oil / ρ of water
0.95 = ρ of oil / 1000
ρ = 950 kg/m3
oil
Therefore, K = 0.61728/950 = 6.5 x 10-5

Prepared by A.Bovas Herbert Bejaxhin Asst. Prof / MECHANICAL, MEC
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