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Ch_18_(853-944).pdf

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18

CHAPTER

18.1

HYDRAULIC

MACHINES — TURBINES

INTRODUCTION

Hydraulic machines are defined as those machines which convert either hydraulic energy (energy possessed by water) into mechanical energy (which is further converted into electrical energy ) or mechanical energy into hydraulic energy. The hydraulic machines, which convert the hydraulic energy into mechanical energy, are called turbines while the hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps. Thus the study of hydraulic machines consists of study of turbines and pumps. Turbines consists of mainly study of Pelton turbine, Francis Turbine and

Kaplan Turbine while pumps consist of study of centrifugal pump and reciprocating pumps.

18.2

TURBINES

Turbines are defined as the hydraulic machines which convert hydraulic energy into mechanical energy. This mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine. Thus the mechanical energy is converted into electrical energy. The electric power which is obtained from the hydraulic energy (energy of water) is known as Hydroelectric power.

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Ch_6_(256-316).pdf

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6

CHAPTER

6.1

DYNAMICS OF FLUID

FLOW

INTRODUCTION

In the previous chapter, we studied the velocity and acceleration at a point in a fluid flow, without taking into consideration the forces causing the flow. This chapter includes the study of forces causing fluid flow. Thus dynamics of fluid flow is the study of fluid motion with the forces causing flow. The dynamic behaviour of the fluid flow is analysed by the Newton’s second law of motion, which relates the acceleration with the forces. The fluid is assumed to be incompressible and non-viscous.

6.2

EQUATIONS OF MOTION

According to Newton’s second law of motion, the net force Fx acting on a fluid element in the direction of x is equal to mass m of the fluid element multiplied by the acceleration ax in the x-direction.

Thus mathematically,

Fx = m.ax

...(6.1)

In the fluid flow, the following forces are present :

(i) Fg, gravity force.

(ii) Fp, the pressure force.

(iii) Fv, force due to viscosity.

(iv) Ft, force due to turbulence.

(v) Fc, force due to compressibility.

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Ch_7_(317_354).pdf

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7

CHAPTER

7.1

ORIFICES AND

MOUTHPIECES

INTRODUCTION

Orifice is a small opening of any cross-section (such as circular, triangular, rectangular etc.) on the side or at the bottom of a tank, through which a fluid is flowing. A mouthpiece is a short length of a pipe which is two to three times its diameter in length, fitted in a tank or vessel containing the fluid.

Orifices as well as mouthpieces are used for measuring the rate of flow of fluid.

7.2

CLASSIFICATIONS OF ORIFICES

The orifices are classified on the basis of their size, shape, nature of discharge and shape of the upstream edge. The following are the important classifications :

1. The orifices are classified as small orifice or large orifice depending upon the size of orifice and head of liquid from the centre of the orifice. If the head of liquid from the centre of orifice is more than five times the depth of orifice, the orifice is called small orifice. And if the head of liquids is less than five times the depth of orifice, it is known as large orifice.

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Ch_15_(683-736).pdf

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15

COMPRESSIBLE FLOW

CHAPTER

15.1

INTRODUCTION

Compressible flow is defined as that flow in which the density of the fluid does not remain constant during flow. This means that the density changes from point to point in compressible flow. But in case of incompressible flow, the density of the fluid is assumed to be constant. In the previous chapters, the fluid was assumed incompressible, and the basic equations such as equation of continuity, Bernoulli’s equation and impulse momentum equations were derived on the assumption that fluid is incompressible. This assumption is true for flow of liquids, which are incompressible fluids. But in case of flow of fluids, such as

(i) flow of gases through orifices and nozzles,

(ii) flow of gases in machines such as compressors, and

(iii) projectiles and airplanes flying at high altitude with high velocities, the density of the fluid changes during the flow. The change in density of a fluid is accompanied by the changes in pressure and temperature and hence the thermodynamic behaviour of the fluids will have to be taken into account.

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Ch_16_(737-802).pdf

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16

CHAPTER

16.1

FLOW IN OPEN

CHANNELS

INTRODUCTION

Flow in open channels is defined as the flow of a liquid with a free surface. A free surface is a surface having constant pressure such as atmospheric pressure. Thus a liquid flowing at atmospheric pressure through a passage is known as flow in open channels. In most of cases, the liquid is taken as water. Hence flow of water through a passage under atmospheric pressure is called flow in open channels. The flow of water through pipes at atmospheric pressure or when the level of water in the pipe is below the top of the pipe, is also classified as open channel flow.

In case of open channel flow, as the pressure is atmospheric, the flow takes place under the force of gravity which means the flow takes place due to the slope of the bed of the channel only. The hydraulic gradient line coincides with the free surface of water.

16.2

CLASSIFICATION OF FLOW IN CHANNELS

The flow in open channel is classified into the following types :

1. Steady flow and unsteady flow,

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