Advance Devlopment in Flow System

8/7/2019 Advance Devlopment in Flow System

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ADVANCE DEVLOPMENT IN FLOW SYSTEM

GUIDED BY : PREPARED BY:Dr H R Patel Ronak Shah

Roll no : 16


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Defination

A flow is a process that deforms

continuously under the action of a

shearing force.

Shear () = F/A


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Factors Affecting flow

* Physical properties which affect the flow are

PressureTemperature

Viscosity

Density


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Viscosity

Measure of internal friction of fluid particles

Molecular cohesiveness

Resistance fluid has to shear (or flow)

Dynamic viscosity = = shear stress/rate of change

of with time

/du dy

XQ !

= velocity gradient = Shear Stress


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Kinematic Viscosity

vQ

V!

Viscosity constant at given T; doesnt depend ontype of shearing stress or duration of stress Newtonian Fluid

T

Kinematic viscosity determines extent to which fluidflow exhibits turbulence

= viscosity

= density


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Stokes Law : The drag force acts in

the direction oppositethe objects velocity (itopposes motion).

The drag force equalsthe product of aconstant (6 for asphere), the radius rofthe object, the speed vof the object (or therelative speed

between the objectand fluid), and thefluids viscosity :


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Types of Fluid Flow

Laminar Flow flow persists as unidirectionalmovement Molecules flow parallel

Movement up and down by diffusion

Turbulent Flow highly distorted flow Large scale flow perpendicular to direction of flow

Transfer of movement up and down by macroscaleprocesses

Turbulence = irregular and random component offluid motion

Eddies = highly turbulent water masses


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Laminar vs Turbulent Flow

Laminar flow velocity constant at a point over time

Turbulence

Most flows = turbulent

Slow settling velocity upward motion of water particles

Increases effectiveness of fluid in eroding and entraining

particles from the bed; but less efficient transport agent

Velocity measured at a point over time tends towards an

average value; but varies from instant to instant

Resists distortion to much greater degree than laminar

flow

Apparent viscosity = eddy viscosity


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Shear Stress:

Laminar vs Turbulent Flow

du

dyX

Add apparent viscosity or eddy viscosity () toturbulent flow shear stress equation

Turbulence exerts larger shear stress onadjacent fluids than laminar

( )du

dyX Q L!

Laminar Flow Turbulent Flow


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Reynolds Number

Balance between inertial forces (cause turbulence)

and viscous forces (suppress turbulence) Laminar: Re < 1000 viscous dominate; shallow

depth or low velocity Turbulent: Re >1000 inertial forces dominate;

deep or fast flow

Re = UR/ = UR/

U = mean flow velocity = density

R = hydraulic radius (A/P) = viscosity

= kinematic viscosity (/)


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Steady or Unsteady Fluid Flow

In steadyflowthe velocity of the fluid particles at any point is

constant as time passes.

Unsteadyflowexists whenever the velocity at a point in the fluidchanges as time passes.


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Compressible or Incompressible Fluid

Flow

Most liquids are nearly incompressible; that is, the density of a

liquid remains almost constant as the pressure changes.

To a good approximation, then, liquids flow in anincompressible manner.

In contrast, gases are highly compressible. However, there are

situations in which the density of a flowing gas remains

constant enough that the flow can be considered

incompressible.


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Viscous or Nonviscous Fluid Flow

A viscous fluid, such as honey, does not flow readily and is

said to have a large viscosity.

In contrast, water is less viscous and flows more readily;

water has a smaller viscosity than honey.

The flow of a viscous fluid is an energy-dissipating process.

A fluid with zero viscosity flows in an unhindered manner

with no dissipation of energy.

Although no real fluid has zero viscosity at normal

temperatures, some fluids have negligibly small viscosities.

An incompressible, nonviscous fluid is called an ideal fluid.


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Streamline Flow

When the flow is steady, streamlines are often used to represent the trajectories of the

fluid particles.

A streamline is a line drawn in the fluid such that a tangent to the streamline at any

point is parallel to the fluid velocity at that point.Steady flow is often called streamline flow.


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Flow Measurement Technique

Recently three methods are in use to measure the flowof fluids

1 Variable Area Flow Meter

2 Rota Meter

3 Ultrasonic Doppler Flowmeter


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Variable area flowmeter

Variable area flowmeters are very versatile

and useful to measure flow of all types of

liquid, gases & steam.

They operate on variable area where they

changes the position of float, Piston or vane to

open larger area for fluid flow.

The position of float, Piston or vane is used to

give direct visual indication of flow rate.


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Variable area flowmeter, has a

float that moves up or down in

a tapered tube. The distance itmoves is proportional to the

liquid flowrate and the annular

area between the float and the

tube well.


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Various features and advantages ofvariable area flowmeter

Flowrate Meters and Controllers

Measurement of Liquids and Gases

Direct Visual Indication Low Pressure Drop

6 to 76 mm (14 to 3") Typical Size

Visual, Transmitting and Alarm Models

Up to 2% of Reading Accuracy


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Up to 14% of Reading Repeatability

Simple to Install and Maintain

No Up- or Downstream Piping Limitations

Broad Range ability Glass, Plastic and Metal Tube Designs

Especially Suited for Low Flowrate Metering

Piston and Vane Units Can Be Mounted in Any

position


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Rota Meter

It is an industrial flowmeter used to measure flow of

liquid & gases.

Rotameter working on same principle of variable

area flowmeter where height of float is praportionalto flowrate.

In liquid float is raised by combination of buoyancy of

liquid & velocity head of fluid while in gases

responds to only velocity head.

Float moves is praportional to fluid flowrate as well

annular area between float & tube wall.


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Advantages

Linear scale, Long measurement range and Low

Pressure drop.

Simple to install & maintain.

Compatible with variety of construction material like

glass tube, plastic tube & metal tube.

Compansate with wide range of Pressure &

Temprature. Float response to flowrate changes linearly as well

pressure remain constant.


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Limitation

Constant pressure require during

measurement of flowrate with float system.

Float position is gravity dependant sorotameter vertically oriented & mounted

require.

Repeatability of flowrate is % of instataneous

flowrate which resemble for operator to reset

while in variable area flowmeter it can done

with the help of valve system.


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Ultrasonic Doppler Flowmeter

It is mainly measure the flowrate of fluids, slurries with

suspended particles and gaseous bubbles flow.

Operating principle is change in frequency of Ultrasonic signal

when it comes to contact with suspended particle or gasbubbles.

Ultrasonic signal is transmitted simaltaneousaly with fluid

flow due to discontinuties signal reflected lead to change in

frequency observed which is directly praportional to the

flowrate of liquid.

These frequency shift phenomena also called as Doppler

effect.


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Advantages and Limitation

Advantages

No pressure drop

created due to that

suitable for measuringflowrate of slurries &

gas bubbles.

Flow measurement

accuracy with field

calibration is +/- 1%.

Limitation

Flowrate of liquid

sample to be measure it

must contain 100 ppmconcentration with 100

micron size suspended

particle in solution.


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Documents

Advance Devlopment in Flow System