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Chapter: Mechanical - Fluid Mechanics And Machinery - Fluid Properties and Flow Characteristics

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Important Answers and Solved Problems: Fluid Properties and Flow Characteristics

Mechanical - Fluid Mechanics And Machinery - Fluid Properties and Flow Characteristics

FLUID PROPERTIES AND FLOW CHARACTERISTICS

 

PART A

 

1.  Define fluids.

 

Fluid may be defined as a substance which is capable of flowing. It has no definite shape of its own, but confirms to the shape of the containing vessel.

 

2. What are the properties of ideal fluid?

 

Ideal fluids have following properties i)It is incompressible

 

ii)    It has zero viscosity

iii)   Shear force is zero

 

3.   What are the properties of real fluid?

 

Real fluids have following properties i)It is compressible

 

ii)    They are viscous in nature

iii)   Shear force exists always in such fluids.

 

4. Explain the Density

 

Density or mass density is defined as the ratio of the mass of the fluid to its volume. Thus mass per unit volume of a fluid is called density. It is denoted by the symbol (ρ).

Density = Mass of the fluid (kg) / Volume of the fluid (m3)

5. Explain the Specific weight or weight density

 

Specific weight or weight density of a fluid is the ratio between the weight of a fluid to its volume. Thus weight per uint volume of a fluid is called weight density and is denoted by the symbol (W).

 

(W) = Weight of the fluid / Volume of fluid 

= Mass x Acceleration due to gravity / Volume of fluid

W = pg

6. Explain the Specific volume

 

Specific volume of a fluid is defined as the volume of the fluid occupied by a unit Mass or volume per unit mass of a fluid is called specific volume.

Specific volume = Volume / Mass  = m3 /kg = l/p

7. Explain the Specific gravity

 

Specific gravity is defined as the ratio of weight density of a fluid to the weight density of a standard fluid. For liquid, standard fluid is water and for gases, it is air.

 

Specific gravity = Weight density of any liquid or gas Weight / density of standard liquid or gas

8.Define Viscosity.

 

It is defined as the property of a liquid due to which it offers resistance to the movement of one layer of liquid over another adjacent layer.

 

9. Define kinematic viscosity.

It is defined as the ratio of dynamic viscosity to mass density. (m²/sec)

 

10. Define Relative or Specific viscosity.

 

It is the ratio of dynamic viscosity of fluid to dynamic viscosity of water at 20°C.

 

11. State Newton's law of viscosity and give examples.

 

Newton's law states that the shear stress ( ) on a fluid element layer is directly proportional to the rate of shear strain. The constant of proportionality is called co-

 

efficient of viscosity.

r = μ du / dy

 

12.            Give the importance of viscosity on fluid motion and its effect on temperature.

 

Viscosity is the property of a fluid which offers resistance to the movement of one layer of fluid over another adjacent layer of the fluid. The viscosity is an important property which offers the fluid motion.

 

The viscosity of liquid decreases with increase in temperature and for gas it Increases with increase in temperature.

 

13.            Explain the Newtonian fluid

The fluid which obeys the Newton's law of viscosity i.e., the shear stress is directly

 

proportional to the rate of shear strain, is called Newtonian

fluid. r = μ du / dy

14. Explain the Non-Newtonian fluid

 

The fluids which does not obey the Newton's law of viscosity i.e., the shear stress is not directly proportional to the ratio of shear strain, is called non-Newtonian fluid.

 

15. Define compressibility.

 

Compressibility is the reciprocal of bulk modulus of elasticity, k which is defined as the ratio of compressive stress to volume strain.

k        =       Increase of pressure / Volume strain

Compressibility = 1       / k               =                 Volume of strain  / Increase of pressure

16. Define surface tension.

 

Surface tension is defined as the tensile force acting on the surface of a liquid in Contact with a gas or on the surface between two immiscible liquids such that contact surface behaves like a membrane under tension.

 

17. Define Capillarity.

Capillary is a phenomenon of rise or fall of liquid surface relative to the adjacent general level of liquid.

 

18. What is cohesion and adhesion in fluids?

 

Cohesion is due to the force of attraction between the molecules of the same liquid. Adhesion is due to the force of attraction between the molecules of two different Liquids or between the molecules of the liquid and molecules of the solid boundary surface.

 

19. State momentum of momentum equation?

 

It states that the resulting torque acting on a rotating fluid is equal to the rate of change of moment of momentum.

 

20. What is momentum equation

 

It is based on the law of conservation of momentum or on the momentum principle It states that,the net force acting on a fluid mass is equal to the change in momentum of flow per unit time in that direction.

 

21. What is Euler's equation of motion

 

This is the equation of motion in which forces due to gravity and pressure are taken into consideration. This is derived by considering the motion of a fluid element along a stream line.

 

 

22. What is venturi meter?

 

Venturi meter is a device for measuring the rate of fluid flow of a flowing fluid through a pipe. It consisits of three parts.

 

a. A short converging part b. Throat c.Diverging part. It is based on the principle of Bernoalli's equation.

 

23. What is an orifice meter?

 

Orifice meter is the device used for measuring the rate of flow of a fluid through a pipe. it is a cheaper device as compared to venturi meter. it also works on the priniciple as that of venturi meter. It consists of a flat circular plate which has a circular sharp edged hole called orifice.

 

24. What is a pitot tube?

 

Pitot tube is a device for measuring the velocity of a flow at any point in a pipe or a channel. It is based on the principle that if the velocity of flow at a point becomes zero, the pressure there is increased due to the conversion of kinetic energy into pressure energy.

.  What are the types of fluid flow?

 

Steady & unsteady fluid flow Uniform & Non-uniform flow

One dimensional, two-dimensional & three-dimensional flows Rotational & Irrotational flow

 

25. State the application of Bernouillies equation ?

 

It has the application on the following measuring devices.

1.Orifice meter.

 

2.Venturimeter.

3.Pitot tube.

 











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