Study of Fluids

Presented By:

Sadhana Singh

Outlines

• Introduction

• Classes of Fluids

• Properties of Fluids

• Types of Fluids Flow

• Fluids in Motion

• Applications of Fluids

• Conclusions

• References

12/4/2014 2Fluids

Introduction

• A fluid is anything that flows, usually a liquid or a gas

• Fluids are treated as continuous media, and theirmotion and state can be specified in terms of thevelocity u, pressure p, density ρ , etc evaluated atevery point in space x and time t

• A fluid cannot resist a shear stress by a static deflection and it moves and deforms continuously as longas the shear stress is applied

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Cont’d…

• Fluid mechanics is the study of fluids either in motion

(fluid dynamics) or at rest (fluid statics)

• Both liquids and gases are classified as fluids

• If the fluids are at rest, the study of them is called

fluid statics

• If the fluids are in motion, the study of them is called

fluid dynamics

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Cont’d…

• The science and technology of the mechanical

properties of liquids is called hydraulics

• Similarly, the science and technology of the

mechanical properties of air and other gases is called

pneumatics

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Cont’d…

• The Fluid density is defined as:

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Cont’d…

• The science and technology of the mechanical

properties of liquids is called Hydraulics.

• Similarly, the science and technology of the

mechanical properties of air and other gases is called

pneumatic.

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Figure 1: Fluid

Cont’d…

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Figure 2: Effects of Viscosity and shape on the fluid flow

Classes of Fluids

• Two classes of Fluids are:

Liquids

Are composed of relatively close‐packed molecules

with strong cohesive forces

Liquids have constant volume

Will form a free surface in a gravitational field if

unconfined from above

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Cont’d…

• In a liquid, the particles move fast enough that they

can’t stay in a rigid structure but they still want to

stay close by.

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Figure 3: Liquid crystals

Cont’d…

Gases

Molecules are widely spaced with negligible cohesive

forces

A gas is free to expand until it encounters confining

walls

A gas has no definite volume, and it forms an atmosp

here when it is not confined

Gravitational effects are rarely concerned

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Cont’d…

• In a gas, however, the particles are moving even

faster and fly by each other, bouncing off the edges

of the container.

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Evaporation: a liquid

molecule becoming a gas

molecule

Figure 4: Gas molecule

Solids

• In a solid, the particles are moving slowly enough

that this attraction keeps them in a rigid structure.

• Has definite volume

• Has definite shape

• Molecules are held in specific locations

by electrical forces

• vibrate about equilibrium positions

• Can be modeled as springs connecting molecules

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Cont’d…

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Figure 5: Both are solids

Properties of Fluids

• Density or Mass Density:

Density or mass density of a fluid is defined as ratio

of the mass of a fluids to its volume. Thus mass per

unit volume of a fluid is called density.

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Thus unit of density in S.I. is kg/m3

Cont’d…

• Specific weight or weight density:

Specific weight or weight density of a fluid is defined

as ratio between the weights of fluids and to its

volume. Thus weight per unit volume of a fluid is

called weight density.

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Thus unit of specific weight in S.I. is N/m3

Cont’d…

• Specific Volume:

Specific volume of a fluid is defined as volume of a

fluid occupied by a unit mass or volume per unit mass

of a fluid.

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Thus specific volume is the reciprocal of mass

density. It is expressed as m3/kg. It is commonly

applied to gases.

Cont’d…

• Specific gravity:

Specific gravity is defined as the ratio of weight

density of a fluid to the weight density of a standard

fluid.

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Types of Fluids Flow

• Fluid evenness: Steady or unsteady flow

• Fluid squeezability: Compressible or incompressible

flow

• Fluid thickness: Viscous or nonviscous flow

• Fluid spinning: Rotational or irrotational flow

• Division of flows with respect to distance

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Fluid evenness: Steady or unsteady flow

• Fluid flow can be steady or unsteady, depending on

the fluid’s velocity:

• Steady. In steady fluid flow, the velocity of the fluid

is constant at any point.

• Unsteady. When the flow is unsteady, the fluid’s

velocity can differ between any two points.

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Fluid squeezability: Compressible or

incompressible flow

• Fluid flow can

be compressible or incompressible, depending on

whether you can easily compress the fluid.

• Liquids are usually nearly impossible to compress,

whereas gases (also considered. a fluid) are very

compressible.

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Fluid thickness: Viscous or nonviscous

flow

• Liquid flow can be viscous or nonviscous. Viscosity is

a measure of the thickness of a fluid, and very gloppy

fluids such as motor oil or shampoo are called viscous

fluids.

• Viscosity is actually a measure of friction in the fluid.

When a fluid flows, the layers of fluid rub against one

another, and in very viscous fluids, the friction is so

great that the layers of flow pull against one other and

hamper that flow.

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Fluid spinning: Rotational or irrotational

flow

• Fluid flow can be rotational or irrotational. If, as you

travel in a closed loop, you add up all the components

of the fluid velocity vectors along your path and the

end result is not zero, then the flow is rotational.

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Division of flows with respect to distance

• Uniform flow – constant section area along flow path

• Non-uniform flow – variable section area

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Laminar Flow

Flow along parallel paths

Shear stress proportional to velocity gradient

(τ = μ⋅du/dy)

• Disturbances in the flow are rapidly damped by

viscous action

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Turbulent Flow

Fluid particles moves in a random manner and not in

layers

Length scales >> molecular scales in laminar flow

Rapid continuous mixing

Inertia forces and viscous forces of importance

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Figure 6: Turbulent Flow

Fluids in Motion

• All fluids are assumed in this treatment to exhibit

streamline flow.

• Streamline flow is the motion of a fluid in which

every particle in the fluid follows the same path past a

particular point as that followed by previous particles.

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Figure 7: Streamline flow

Fluid System And Control Volume

• Fluid system: Specified mass of fluid within a closed

surface

• Control volume: Fix region in space that can’t be

moved or change shape. Its surface is called control

surface.

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Applications

• Fluids is extremely important in many areas ofengineering and science. Examples are:

Biomechanics

Blood flow through arteries

Meteorology and Ocean Engineering

Movements of air currents and water currents

Chemical Engineering

Design of chemical processing equipment

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Cont’d…

Mechanical Engineering

Design of pumps, turbines, air-conditioningequipment, pollution-control equipment, etc.

Civil Engineering

Transport of river sediments

Pollution of air and water

Design of piping systems

Flood control systems

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Conclusions

• A fluid is a substance that continually deforms(flows)

under an applied shear stress.

• Fluids are a subset of the phases of matter and

include liquids, gases, plasmas and, to some

extent, plastic solids.

• Fluids can be defined as substances which have

zero shear modulus or in simpler terms a fluid is

a substance which cannot resist any shear

force applied to it.

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References

• http://www.dummies.com/how-to/content/the-different-types-

of-fluid-flow.html

• Genick Bar Meir, “ Basics of fluid mechanics”, July 25, 2013.

• M. Bahrami, “Introduction and properties of fluids”, Spring

2009.

• T. J. Pedley, “Introduction to Fluid dynamics”, LECTURES

ON PLANKTON AND TURBULENCE. C. MARRASÉ, E.

SAIZ and J.M. REDONDO (eds.), 1997.

• Bird, Byron; Stewart, Warren & Lightfoot, Edward

(2007). Transport Phenomena. New York: Wiley, Second

Edition. p. 912. ISBN 0-471-41077-2.

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