fluid note2

8/3/2019 Fluid Note2

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LECTURE 1

FLOW MEASUREMENT

In this module we will illustrate and analyze some of the more common methods for

measuring flow rate in conduits, including the pitot tube, venturi, nozzle, and orificemeters. This is by no means intended to be a comprehensive or exhaustive treatment,

however, as there are a great many other devices in use for measuring flow rate, such as

turbine, vane, Coriolis, ultrasonic, and magnetic flow meters, just to name a few. Theexamples considered here demonstrate the application of the fundamental conservation

principles to the analysis of several of the most common devices. We also consider

control valves in this chapter, because they are frequently employed in conjunction withthe measurement of flow rate to provide a means of controlling flow.

THE PITOT TUBE

As previously discussed, the volumetric flow rate of a fluid through a conduit

can be determined by integrating the local (point) velocity over thecross section of the conduit:

(1)

If the conduit cross section is circular, this becomes

(2)

The pitot tube is a device for measuring vr, the local velocity at a given position in the

conduit, as illustrated in Fig. 1. The measured velocity is then used in Eq. (2) to

determine the flow rate. It consists of a differential pressure measuring device (e.g., amanometer, transducer, or DP cell) that measures the pressure difference between two

tubes. One tube is attached to a hollow probe that can be positioned at any radial location

in the conduit, and the other is attached to the wall of the conduit in the same axial planeas the end of the probe. The local velocity of the streamline that impinges on the end of

the probe is v (r). The fluid element that impacts the open end of the probe must come to

rest at that point, because there is no flow through the probe or the DP cell; this is knownas the stagnation point.

The Bernoulli equation can be applied to the fluid streamline that impacts the probe tip:

(3)

Where, point 1 is in the free stream just upstream of the probe and point 2 is just inside

the open end of the probe (the stagnation point). Since the friction loss is negligible in thefree stream from 1 to 2, and v2 = 0 because the fluid in the probe is stagnant, Eq. (3) can

be solved for v1 to give


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(4)

The measured pressure difference P is the difference between the stagnationpressure in the velocity probe at the point where it connects to the a manometer and the

static pressure at the corresponding point in the tube connected to the wall. Since there

is no flow in the vertical direction, the difference in pressure between any two verticalelevations is strictly hydrostatic. Thus, the pressure difference measured at the DP cell is

the

same as that at the elevation of the probe, because the static head between point 1 and thepressure device is the same as that between point 2 and the pressure device, so that P=P2 - P1.

FIGURE 1 Pitot tube.


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LECTURE 2

THE VENTURI METER

This is other device, however, that can be used to determine the flow rate from a single

measurement. These are sometimes referred to as obstruction meters, because the basic

principle involves introducing an obstruction (e.g., a constriction) into the flowchannel and then measuring the pressure drop across the obstruction that is related to the

flow rate. the venturi meter is , illustrated in Figs. 2. The fluid flows through a reduced

area, which results in an increase in the velocity at that point. The corresponding changein pressure between point 1 upstream of the constriction and point 2 at the position of the

minimum area (maximum velocity) is measured and is then related to the flow rate

through the energy balance. The velocities are related by the continuity equation, and the

Bernoulli equation relates the velocity change to the pressure change:

(5)

FIGURE 2 VENTURI METER


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LECTURE 3

THE ORIFICE METER

The simplest and most common device for measuring flow rate in a pipe is the orifice

meter, illustrated in Fig. 10-7. This is an obstruction meter that consists of a plate with

a hole in it that is inserted into the pipe, and the pressure drop across the plate ismeasured. The major difference between this device and the venturi and nozzle meters is

the fact that the fluid stream leaving the orifice hole contracts to an area considerably

smaller than that ofthe orifice hole itself. This is called the vena contracta, and it occursbecause the fluid has considerable inward radial momentum as it converges into the

orifice hole, which causes it to continue to flow inward for a distance downstream of

the orifice before it starts to expand to fill the pipe. If the pipe diameter is D, the orifice

diameter is d, and the diameter of the vena contracta is d2, the contraction ratio for the

vena contracta is defined as

The complete Bernoulli equation, as applied between point 1 up stream of the orifice

where the diameter is D and point 2 in the vena contracta where the diameter is d2, is

(10)

FIGURE 3 Orifice Meter

As for the other obstruction meters, when the continuity equation is used to eliminate the

upstream velocity from Eq. (10), the resulting expression for the mass flow rate through

the orifice is


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LECTURE 4

ROTAMETERA Rotameter is a device that measures the flow rate of liquid orgas in a closed tube. It

belongs to a class of meters called variable area meters, which measure flow rate by

allowing the cross-sectional area the fluid travels through to vary, causing somemeasurable effect.

F IGURE 4 Rota Meter

A rotameter consists of a tapered tube, typically made of glass, with a float inside that is

pushed up by flow and pulled down by gravity. At a higher flow rate more area (between

the float and the tube) is needed to accommodate the flow, so the float rises. Floats aremade in many different shapes, with spheres and ellipsoids being the most common. The

float is shaped so that it rotates axially as the fluid passes. This allows you to tell if the

float is stuck since it will only rotate if it is free. Readings are usually taken at the top of

the widest part of the float; the center for an ellipsoid, or the top for a cylinder. Some

manufacturers may use a different standard, so it is always best to check thedocumentation provided with the device.

Note that the "float" does not actually float in the fluid: it has to have a higher densitythan the fluid, otherwise it will float to the top even if there is no flow.

Advantages
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A rotameter requires no external power or fuel, it uses only the inherent properties

of the fluid, along with gravity, to measure flow rate.

A rotameter is also a relatively simple device that can be mass manufactured outof cheap materials, allowing for its widespread use.

Disadvantages

Due to its use of gravity, a rotameter must always be vertically oriented and right

way up, with the fluid flowing upward.

Due to its reliance on the ability of the fluid or gas to displace the float,

graduations on a given rotameter will only be accurate for a given substance at a

given temperature. The main property of importance is the density of the fluid;

however, viscosity may also be significant. Floats are ideally designed to beinsensitive to viscosity; however, this is seldom verifiable from manufacturers'

specifications. Either separate rotameters for different densities and viscosities

may be used, or multiple scales on the same rotameter can be used.

Rotameters normally require the use of glass (or other transparent material),otherwise the user cannot see the float. This limits their use in many industries to

benign fluids, such as water.

Rotameters are not easily adapted for reading by machine; although magnetic

floats that drive a follower outside the tube are available.
http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Water


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LECTURE 5

Anemometer

An anemometer is a device for measuring wind speed, and is a common weather stationinstrument. The term is derived from the Greek word anemos, meaning wind.

Anemometers can be divided into two classes: those that measure the wind's speed, and

those that measure the wind's pressure; but as there is a close connection between thepressure and the speed, an anemometer designed for one will give information about

both.

1 . Velocity anemometers

o 1.1 Cup anemometers

o 1.2 Windmill anemometers

o 1.3 Hot-wire anemometerso 1.4 Laser Doppler anemometers

o 1.5 Sonic anemometers

o 1.6 Ping-pong ball anemometers

2 . Pressure anemometers

o 2.1 Plate anemometers

o 2.2 Tube anemometers

o 2.3 Effect of density on measurements
http://en.wikipedia.org/wiki/Weather_stationhttp://en.wikipedia.org/wiki/Anemometer#Velocity_anemometers%23Velocity_anemometershttp://en.wikipedia.org/wiki/Anemometer#Cup_anemometers%23Cup_anemometershttp://en.wikipedia.org/wiki/Anemometer#Windmill_anemometers%23Windmill_anemometershttp://en.wikipedia.org/wiki/Anemometer#Hot-wire_anemometers%23Hot-wire_anemometershttp://en.wikipedia.org/wiki/Anemometer#Laser_Doppler_anemometers%23Laser_Doppler_anemometershttp://en.wikipedia.org/wiki/Anemometer#Sonic_anemometers%23Sonic_anemometershttp://en.wikipedia.org/wiki/Anemometer#Ping-pong_ball_anemometers%23Ping-pong_ball_anemometershttp://en.wikipedia.org/wiki/Anemometer#Pressure_anemometers%23Pressure_anemometershttp://en.wikipedia.org/wiki/Anemometer#Plate_anemometers%23Plate_anemometershttp://en.wikipedia.org/wiki/Anemometer#Tube_anemometers%23Tube_anemometershttp://en.wikipedia.org/wiki/Anemometer#Effect_of_density_on_measurements%23Effect_of_density_on_measurementshttp://en.wikipedia.org/wiki/Weather_stationhttp://en.wikipedia.org/wiki/Anemometer#Velocity_anemometers%23Velocity_anemometershttp://en.wikipedia.org/wiki/Anemometer#Cup_anemometers%23Cup_anemometershttp://en.wikipedia.org/wiki/Anemometer#Windmill_anemometers%23Windmill_anemometershttp://en.wikipedia.org/wiki/Anemometer#Hot-wire_anemometers%23Hot-wire_anemometershttp://en.wikipedia.org/wiki/Anemometer#Laser_Doppler_anemometers%23Laser_Doppler_anemometershttp://en.wikipedia.org/wiki/Anemometer#Sonic_anemometers%23Sonic_anemometershttp://en.wikipedia.org/wiki/Anemometer#Ping-pong_ball_anemometers%23Ping-pong_ball_anemometershttp://en.wikipedia.org/wiki/Anemometer#Pressure_anemometers%23Pressure_anemometershttp://en.wikipedia.org/wiki/Anemometer#Plate_anemometers%23Plate_anemometershttp://en.wikipedia.org/wiki/Anemometer#Tube_anemometers%23Tube_anemometershttp://en.wikipedia.org/wiki/Anemometer#Effect_of_density_on_measurements%23Effect_of_density_on_measurements


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LECTURE 6

Force on Immersed BodiesIntroduction:

In engineering fields there are various problems which involve the fluid around the

submersed bodies. In such problems either a fluid may be flowing around

submerged stationary body or body may be flowing through a large mass of

stationary fluid.Examples:

Motion of very small objects such as sand particles in air or water.

Large bodies such as airplane, submarines, automobiles, ships etc moving through airor water

Structure such as buildings and bridges etc which are submerged in air or water.

Force Exerted by a Flowing Fluid on a Body:

Whenever there is relative motion between a real fluid and a body, the fluid exerts a

force on a body and the body exerts equal and opposite force on the fluid. A bodyfully immersed in a real fluid may be subjected to two kinds of forces called drag

force and lift force.

Drag force: The component of force in the direction of flow on a submerged body is

called drag force (FD).

Lift force: The component of force in the perpendicular to the flow is called the lift

force (FL).

In the symmetrical body moving through an ideal fluid (no viscosity) at a uniform

velocity, the pressure distribution around a body is symmetrical and hence theresultant force acting on the body is zero. However real fluids such as air, water,

posses viscosity and if it is moved through these fluid at a uniform velocity, the

body experiences a resistance to motion.For the symmetrical body such as sphere and cylinder facing the flow is

symmetrical, there is no lift force. For the production of lift force there must be

asymmetry of flow, but drag force exists always. It is possible to create dragwithout lift but impossible to create lift without drag.

The fluid viscosity affects the flow around the body causing the force on the body

accordingly. At low Reynolds' Number the fluid is deformed in very wide zone

The relative wind acting on the airplane produces a certain amount of force which iscalled (unsurprisingly) the total aerodynamic force. This force can be resolved into

components, called lift and drag, as shown in figure 1.
http://www.av8n.com/how/htm/4forces.html#fig-lift+drag%23fig-lift+draghttp://www.av8n.com/how/htm/4forces.html#fig-lift+drag%23fig-lift+drag


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Figure 1: Total Aerodynamic Force = Lift + Drag

Here are the official, conventional definitions of the so-called four forces:

Liftis the component of aerodynamic force perpendicular to the relative wind.

Dragis the component of aerodynamic force parallel to the relative wind.

Weightis the force directed downward from the center of mass of the airplanetowards the center of the earth. It is proportional to the mass of the airplane times

the strength of the gravitational field.

Thrustis the force produced by the engine. It is directed forward along the axis of

the engine.

It is ironic that according to convention, the total aerodynamic force is not listed among

the four forces.

Figure 2: The Four Forces Low Speed Descent
http://www.av8n.com/how/htm/4forces.html#fig-lift+drag%23fig-lift+draghttp://www.av8n.com/how/htm/4forces.html#fig-four-slow-descent%23fig-four-slow-descenthttp://www.av8n.com/how/htm/4forces.html#fig-lift+drag%23fig-lift+draghttp://www.av8n.com/how/htm/4forces.html#fig-four-slow-descent%23fig-four-slow-descent


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LECTURE 7

Stokes' Law is written as,

where Fd is the drag force of the fluid on a sphere, m is the fluid viscosity, V is the

velocity of the sphere relative to the fluid, and dis the diameter of the sphere. Using thisequation, along with other well-known principle of physics, we can write an expression

that describes the rate at which the sphere falls through a quiescent, viscous fluid.

We must draw a free body diagram (FBD) of the sphere. That is we must sketch thesphere and all of the internal and external forces acting on the sphere as it is dropped into

the fluid. Figure below shows a sketch of the entire system (sphere dropping through a

column of liquid). The FBD is the dashed cross-section that has been removed andexploded in the left portion of this figure.

Figure : Free-body diagram of a sphere in a quiescent fluid.


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LECTURE 9

The hydraulic diameter or equivalent,DH, is a commonly used term when handling

flow in noncircular tubes and channels. Using this term one can calculate many things inthe same way as for a round tube.

Definition : hydraulic radius rH= A/P

DH=4A/P,

whereA is the wetted cross sectional area andPis the wetted perimeterof the cross-

section.

Porosity orvoid fraction is a measure of the void spaces in a material, and is a fraction

of the volume of voids over the total volume, between 01, or as apercentagebetween 0100%. The term is used in multiple fields includingpharmaceutics,ceramics, metallurgy,materials, manufacturing, earth sciences and construction.

Sphericity is a measure of how spherical (round) an object is. As such, it is a specific

example of a compactness measure of a shape. Defined by Wadell in 1935, thesphericity, , of a particle is the ratio of the surface area of a sphere (with the same

volume as the given particle) to the surface area of the particle.
http://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Calculatehttp://en.wikipedia.org/wiki/Circlehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Wetted_perimeterhttp://en.wikipedia.org/wiki/Percentagehttp://en.wikipedia.org/wiki/Pharmaceuticshttp://en.wikipedia.org/wiki/Ceramicshttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Materialshttp://en.wikipedia.org/wiki/Manufacturinghttp://en.wikipedia.org/wiki/Earth_scienceshttp://en.wikipedia.org/wiki/Constructionhttp://en.wikipedia.org/wiki/Compactness_measure_of_a_shapehttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Spherehttp://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Calculatehttp://en.wikipedia.org/wiki/Circlehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Wetted_perimeterhttp://en.wikipedia.org/wiki/Percentagehttp://en.wikipedia.org/wiki/Pharmaceuticshttp://en.wikipedia.org/wiki/Ceramicshttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Materialshttp://en.wikipedia.org/wiki/Manufacturinghttp://en.wikipedia.org/wiki/Earth_scienceshttp://en.wikipedia.org/wiki/Constructionhttp://en.wikipedia.org/wiki/Compactness_measure_of_a_shapehttp://en.wikipedia.org/wiki/Surface_areahttp://en.wikipedia.org/wiki/Spherehttp://en.wikipedia.org/wiki/Volume


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LECTURE 10

Flow through a packed bed

Flow through a packed bed is dependent on the Reynolds number, similar to the flow

through a straight pipe. For a packed bed, the Reynolds number is dependent on not onlythe four normal properties, density, , viscosity,, velocity, v, and the equivalent

spherical diameter,Dp, but it is also dependent on the void fraction,

(1)The Ergun equation is a combination of both the Kozeny-Carmen and Burke-Plumber

equations, which both look at energy losses due to flow through a packed bed. The

Kozeny-Carmen equation models laminar flow through a packed bed, taking into accountthe energy losses due to viscosity. At low flow rates, viscosity will be most important in

fluid flow. Therefore, in situations of laminar flow, the timing of fluidization would also

depend on viscous forces. The Kozeny-Carmen equation, seen below, is valid forNRe,p< 10

(2)

where p is the pressure drop from the top to the bottom of the column. Also, there is a

strong dependence on the void fraction, . Experimentally, this parameter must bedetermined accurately in order to yield accurate results about the pressure drop.

The Burke-Plummer equation examines turbulent flow through a packed bed and

accounts for kinetic energy losses such as wall effects rather than viscous energy losses.When the flow rate of a fluid increases from laminar to turbulent, the viscosity of a fluid

decreases and becomes negligible at high flow rates. Here, there is a larger dependenceon the velocity, while the dependence on the void fraction is still large .

(3)Also, L is the depth of the packing material. This model is valid for turbulent flow, such

thatNeR,p > 1000.Prior to Ergun, experimenters did not how these two resistances were related to each

other and how flow through a packed bed was modeled in the transition zone between

laminar and turbulent flow. Ergun determined experimentally that the two resistancescould simply be summed, such that

(4)


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Fluidization is defined as

-- an operation through which fine solids are transformed into a fluid like state

through contact with either a gas or a liquid.

Under the fluidized state, the gravitational pull on granular solid particles is offset by thefluid drag on them. Thus the particles remain in a semi-suspended condition. A fluidized

bed displays characteristics similar to those of a liquid, as explained below with the help

of Figure below.

Figure A fluidized bed demonstrates all the characteristics of a fluid.

1. The static pressure at any height is approximately equal to the weight of bed

solids per unit cross section above that level.

2. The bed surface maintains a horizontal level, irrespective of how the bed is titled;also the bed assumes the shape of the vessel.

3. The solids from the bed may be drained like a liquid through an orifice at the

bottom or on the side.4. An object denser than the bulk of the bed will sink, while one lighter than the bed

will float. Thus, a steel ball sinks in the bed, while a light shuttlecock floats on the

surface.5. Particles are well mixed, and the bed maintains a nearly uniform temperature

throughout its body when heated.

An increase in the gas velocity through a bed of granular solids brings about changes in

the mode of gas-solid contact in many ways. With changes in gas velocity the bed movesfrom one state or regime to another.

Fluidized beds are used as a technical process which has the ability to promote high

levels of contact between gases and solids. In a fluidized bed a characteristic set of basic

properties can be utilised, indispensable to modern process and chemical engineering,these properties include:

Extremely high surface area contact between fluid and solid per unit bed volume

High relative velocities between the fluid and the dispersed solid phase.

High levels of intermixing of the particulate phase.

Frequent particle-particle and particle-wall collisions.


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Basic model

When the packed bed has a fluid passed over it, the pressure drop of the fluid is

approximately proportional to the fluid's superficial velocity. In order to transition from apacked bed to a fluidized condition, the gas velocity is continually raised. For a free-

standing bed there will exist a point, known as the minimum or incipient fluidisationpoint, whereby the bed's mass is suspended directly by the flow of the fluid stream. The

corresponding fluid velocity, known as the "minimum fluidization velocity", umf.

Beyond the minimum fluidization velocity (), the bed material will be suspended by thegas-stream and further increases in the velocity will have a reduced effect on the

pressure, owing to sufficientpercolation of the gas flow. Thus the pressure drop from for

u > umfis relatively constant.

At the base of the vessel the apparent pressure drop multiplied by the cross-section area

of the bed can be equated to the force of the weight of the solid particles (less the

buoyancy of the solid in the fluid).

pw =Hw(1 w)(s f)g

Fig. A diagram of a fluidized bed
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LECTURE 1

What is the Pump?

Transferring the Fluids by increasing the pressure

Classification

Reciprocating displacement

Rotary displacement

Centrifugal

Air displacement

How we can select a pump?

Amount of the fluid

The fluid properties

Head required Type of the flow

Power supply

Cost compared to efficiency

Pump Classification

Classified by operating principle

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gearLobe

Slide

vane

Others (e.g.Impulse, Buoyancy)

Pumps

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gearLobe

Slide

vane

Others (e.g.Impulse, Buoyancy)

Pumps


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Non-Mechanical Pumps

A, steam jet ejector is a pump-like device that uses the Venturi effect of a converging-

diverging nozzle to convert the pressure energy of a motive fluid to velocity energywhich creates a low pressure zone that draws in and entrains a suction fluid. After passing

through the throat of the injector, the mixed fluid expands and the velocity is reduced

which results in recompressing the mixed fluids by converting velocity energy back intopressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained

suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream.

The adjacent diagram depicts a typical modern ejector. It consists of a motive fluid inlet

nozzle and a converging-diverging outlet nozzle. Water, air, steam, or any other fluid athigh pressure provides the motive force at the inlet.

An injector is a more complex device containing at least three cones. That used fordelivering water to a steam locomotive boiler takes advantage of the release of the energy

contained within the latent heat of evaporation to increase the pressure to above thatwithin the boiler.

The Venturi effect, a particular case ofBernoulli's principle, applies to the operation of

this device. Fluid under high pressure is converted into a high-velocity jet at the throat of

the convergent-divergent nozzle which creates a low pressure at that point. The lowpressure draws the suction fluid into the convergent-divergent nozzle where it mixes with

the motive fluid.

In essence, the pressure energy of the inlet motive fluid is converted to kinetic energy inthe form of velocity head at the throat of the convergent-divergent nozzle. As the mixedfluid then expands in the divergent diffuser, the kinetic energy is converted back to

pressure energy at the diffuser outlet in accordance with Bernoulli's principle.
http://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Venturi_effecthttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Latent_heathttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Venturi_effecthttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/De_Laval_nozzlehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Latent_heathttp://en.wikipedia.org/wiki/Bernoulli's_principlehttp://en.wikipedia.org/wiki/Kinetic_energy


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An airlift pump is a simplepump which is powered by compressed air. The only energy

required is air. This air is usually compressed by a compressoror a blower. The air is

injected in the lower part of a pipe that transports a liquid. It usually bubbles into anotherlarger diameter pipe. Bybuoyancy the air, which has a lowerdensity than the liquid, rises

quickly. By fluid pressure, the liquid is taken in the ascendant air flow and moves in the

same direction as the air. The calculation of the volume flow of the liquid is possiblethanks to the physics oftwo-phase flow.

Type of PumpsType of Pumps

Positive Displacement Pumps

For each pump revolution

Fixed amount of liquid taken from one end

Positively discharged at other end

If pipe blocked

Pressure rises

Can damage pump
http://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Gas_compressorhttp://en.wikipedia.org/wiki/Blowerhttp://en.wikipedia.org/wiki/Buoyancyhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Two-phase_flowhttp://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Gas_compressorhttp://en.wikipedia.org/wiki/Blowerhttp://en.wikipedia.org/wiki/Buoyancyhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Fluid_pressurehttp://en.wikipedia.org/wiki/Two-phase_flow


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Used for pumping fluids other than water

Reciprocating pump

Displacement by reciprocation of piston plunger

Used only for viscous fluids and oil wells

Rotary pump

Displacement by rotary action of gear, cam or vanes

Several sub-types

Used for special services in industry

Dynamic pumps

Mode of operation

Rotating impeller converts kinetic energy into pressure or velocity to

pump the fluid

Two types Centrifugal pumps: pumping water in industry 75% of pumps

installed

Special effect pumps: specialized conditions


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Piston pump

A piston pump is a type ofpositive displacement pump where the high-pressure seal

reciprocates with the piston.[1] Piston pumps can be used to move liquids or compressgases.

A plunger pump is a type of positive displacement pump where the high-pressure seal isstationary and a smooth cylindrical plunger slides though the seal. This makes them

different frompiston pumps and allows them to be used at high pressures. This type of

pump is often used to transfer municipal and industrial sewage.

A diaphragm pump is a positive displacement pump that uses a combination of the

reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable non-

return check valves to pump a fluid. Sometimes this type of pump is also called a

membrane pump.
http://en.wikipedia.org/wiki/Positive_displacement_pumphttp://en.wikipedia.org/wiki/Piston_pump#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Piston_pumphttp://en.wikipedia.org/wiki/Pump#Positive_displacement_pumpshttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Polytetrafluoroethylenehttp://en.wikipedia.org/wiki/Diaphragm_(mechanics)http://en.wikipedia.org/wiki/Check_valvehttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Positive_displacement_pumphttp://en.wikipedia.org/wiki/Piston_pump#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Piston_pumphttp://en.wikipedia.org/wiki/Pump#Positive_displacement_pumpshttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Polytetrafluoroethylenehttp://en.wikipedia.org/wiki/Diaphragm_(mechanics)http://en.wikipedia.org/wiki/Check_valvehttp://en.wikipedia.org/wiki/Fluid


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A gear pump uses the meshing of gears to pump fluid by displacement.[1] They are one

of the most common types ofpumps forhydraulic fluid powerapplications. Gear pumpsare also widely used in chemical installations to pump fluid with a certain viscosity.

There are two main variations; external gear pumps which use two external spur gears,and internal gear pumps which use an external and an internal spur gear. Gear pumps arepositive displacement(orfixed displacement), meaning they pump a constant amount of

fluid for each revolution. Some gear pumps are designed to function as either a motoror

a pump.

Fig. External gear pump design forhydraulic powerapplications.
http://en.wikipedia.org/wiki/Gear_pump#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Hydraulic_machineryhttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Positive_displacement_pumphttp://en.wikipedia.org/wiki/Hydraulic_motorhttp://en.wikipedia.org/wiki/Hydraulic_machineryhttp://en.wikipedia.org/wiki/Gear_pump#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Hydraulic_machineryhttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Positive_displacement_pumphttp://en.wikipedia.org/wiki/Hydraulic_motorhttp://en.wikipedia.org/wiki/Hydraulic_machinery


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Fig. Internal gear (Gerotor) pump design for high viscosity fluids.

Generally used in:

1. PETROCHEMICALS: Pure or filled bitumen, pitch, diesel oil, crude oil, lube oil etc.

2. CHEMICALS: Sodium silicate, acids, plastics, mixed chemicals, isocyanates etc.

3. PAINT & INK.

4. RESINS & ADHESIVES.

5. PULP & PAPER: acid, soap, lye, black liquor, kaolin, lime, latex, sludge etc.

6. FOOD: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, molasses, animal

food etc.

Centrifugal Pumps

How do they work?

Liquid forced into impeller Vanes pass kinetic energy to liquid: liquid rotates and leaves impeller

Volute casing converts kinetic energy into pressure energy
http://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Viscosity


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Rotating and stationary components

Impeller

Main rotating part that provides centrifugal acceleration to the fluid Number of impellers = number of pump stages

Impeller classification: direction of flow, suction type and shape/mechanical

construction

Shaft

Transfers torque from motor to impeller during pump start up and

operation

Casings

Functions

Enclose impeller as pressure vessel Support and bearing for shaft and impeller

Volute case

Impellers inside casings Balances hydraulic pressure on pump shaft

Circular casing Vanes surrounds impeller Used for multi-stage pumps


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Assessment of pumpsAssessment of pumps

How to Calculate Pump Performance

Pump shaft power (Ps) is actual horsepower delivered to the pump shaft

Pump shaft power (Ps):

Ps = Hydraulic power Hp / pump efficiency Pump

Pump Efficiency (Pump):

Pump = Hydraulic Power / Pump Shaft Power

Pump output/Hydraulic/Water horsepower (Hp) is the liquid horsepower

delivered by the pump

Hydraulic power (Hp):

Hp = Q (m3/s) x Total head, hd - hs (m) x (kg/m3) x g (m/s2) / 1000

hd = discharge head hs = suction head, = density of the fluid g = acceleration due to gravity

CAVITATION

A centrifugal pump increases the fluid pressure by first imparting angular momentum (or

kinetic energy) to the fluid, which is converted to pressure in the diffuser or volute

section. Hence, the fluid velocity in and around the impeller is much higher than thateither entering or leaving the pump, and the pressure is the lowest where the velocity ishighest. The minimum pressure at which a pump will operate properly must be above the

vapor pressure of the fluid; otherwise the fluid will vaporize (or boil), a condition

known as cavitation. Obviously, the higher the temperature the higher the vapor pressureand the more likely that this condition will occur. When a centrifugal pump contains a

gas or vapor it will still develop the same head, but because the pressure is proportional

to the fluid density it will be several orders of magnitude lower than the pressure for a


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liquid at the same head. This condition (when the pump is filled with a gas or vapor) is

known as vapor lock, and the pump will not function when this occurs. However,

cavitation may result in an even more serious condition than vapor lock. When thepressure at any point within the pump drops below

the vapor pressure of the liquid, vapor bubbles will form at that point (this generally

occurs on or near the impeller). These bubbles will then be transported to another regionin the fluid where the pressure is greater than the vapor pressure, at which point they will

collapse. This formation and collapse of bubbles occurs very rapidly and can create local

shock waves, which can cause erosion and serious damage to the impeller or pump.

NPSH

To prevent cavitation, it is necessary that the pressure at the pump suction be sufficiently

high that the minimum pressure anywhere in the pump will be above the vapor pressure.

This required minimum suction pressure (in excess of the vapor pressure) depends upon

the pump design, impeller size and speed, and flow rate and is called the minimumrequired net positive suction head (NPSH). Values of the minimum required NPSH for

the pump in Fig. 8-2 are shown as dashed lines. The NPSH is almost independent ofimpeller diameter at low flow rates and increases with flow rate as well as with impeller

diameter r at higher flow rates. A distinction is

sometimes made between the minimum NPSH required to prevent cavitation(sometimes termed the NPSHR) and the actual head (e.g., pressure) available at the

pump suction (NPSHA). A pump will not cavitate if NPSHA > (NPSHR + vapor pressure

head).

Priming in Centrifugal Pump

All centrifugal pumps must be primed by filling them with water before they can operate.

The objective of priming is to remove a sufficient amount of air from the pump and

suction line to permit atmospheric pressure and submergence pressure to cause water toflow into the pump when pressure at the eye of the impeller is reduced below

atmospheric as the impeller rotates.

When axial-flow and mixed-flow pumps are mounted with the propellers submerged,

there is normally no problem with re priming of these pumps because the submergence

pressure causes water to refill the pumps as long as air can readily be displaced. On theother hand, radial-flow pumps are often located above the water source, and they can lose

prime. Often, loss of prime occurs due to an air leak on the suction side of the pump.

Volute or diffuser pumps may lose prime when water contains even small amounts of airor vapor. Prime will not be lost in a radial-flow pump if the water source is above the eye

of the impeller and flow of water into the pump is unrestricted.

In some cases pumps are primed by manually displacing the air in them with water everytime the pump is restarted. Often, by using a foot valve or a check valve at the entrance to


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the suction pipe, pumps can be kept full of water and primed when not operating. If prime

is lost, the water must be replaced manually, or a vacuum pump can be used to remove

air and draw water into the pump.

A self-priming pump is one that will clear its passages of air and resume delivery of

liquid without outside attention. Centrifugal pumps are not truly self-priming. So calledself-priming centrifugal pumps are provided with an air separator in the form of a large

chamber or reservoir on the discharge side of the pump. This separator allows the air to

escape from the pump discharge and entraps the residual liquid necessary during repriming. Automatic priming of a pump is achieved by the use of a recirculation chamber

which recycles water through the impeller until the pump is primed, or by the use of a

small positive displacement pump which supplies water to the impeller.

Pumping equipment for gases

Essentially the same basic types of mechanical equipment are used for handling gases

and liquids, though the construction may be very different in two cases. Under the normalrange of operating pressures, the density of a gas is considerably less than that of a liquid

so that higher speeds of operation can be employed and lighter valves fitted to thedelivery and suction lines. Because of the lower viscosity of a gas there is a greater

tendency for leak to occur, and therefore gas compressors are designed with smaller

clearances between the moving parts. Since a large proportion of the energy ofcompression appears as heat in the gas, there will normally be a considerable increase in

temperature which may limit the operation of the compressor unless suitable cooling can

be effected. For this reason, gas compression is often carried out in a number of stages

and the gas is cooled between each stage.

Fans, Blowers, and Compressors

Machinery for compressing and moving gases is conveniently considered from the

standpoint of pressure difference produced in the equipment. This order is fans, blowers,compressors.

Fans:

The commonest method of moving gases under moderate pressures is by means of some

type of fan. These are effective for pressures from 2 or 3 inch of water up to about 0.5

psi. Large fans are usually centrifugal, operating on exactly the same principle as

centrifugal pumps. Their impeller blades, however, may be curved forward; this wouldlead to instability in a pump, but not in a fan. Since the change in density in a fan is

small, the incompressible flow equations used in centrifugal pump calculations are often

adequate.

The fans may be classified into three types: the propeller type, the plate fan, and the

multi-blade type.


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The propeller type is represented by the familiar electric fan and is of no great importance

for moving gases in plant practice.

Plate fan consists of plate steel blades on radial arms inside a casing. These fans aresatisfactory for pressures from 0 to 5 inch of water, have from 8 to 12 blades. Another

variation of the steel-plate fan has blades curved like the vanes of centrifugal pumpimpellers and can be used for pressures up to 27 inch of water.

The multi-blade fans are useful for pressures of from 0 to 5 inch of water. It is claimedthat they have much higher efficiencies than the steel-plate fan. These fans will deliver

much larger volumes for a given size of drum than steel-plate fans.

Blowers:

Any pump of the rotary type can be used as a blower. When so used they generally have

only two or three lobes on the rotating parts. These blowers are used for pressures from

0.5 to 10 psi. Such blowers are often used for services where very large volumes must bedelivered against pressures too high for a fan. They are being replaced in many cases by

centrifugal blowers.

The appearance of centrifugal blower resembles a centrifugal pump, except that thecasing is narrower and larger impeller diameter. The operating speed is high, 3000 rpm or

more. The reason for the high speed and large impeller diameter is that very high heads,

measured in meters of low-density fluid, are needed to generate moderate pressure ratios.

Compressors:

Centrifugal compressors are multistage units containing a series of impellers on a singleshaft, rotating at high speeds in a massive casing. These machines compress enormous

volumes of air or process gas - up to 100 m3/sec at the inlet - to an outlet pressure of 20atm. Smaller capacity machines discharge at pressures up to several hundred

atmospheres. Interstage cooling is needed on the high pressure units.

Axial flow machines handle even larger volumes of gas, up to 300 m3/sec, but at a lower

discharge pressures of 2 to 10 atm. In these units the rotor vanes propel the gas axiallyfrom one set of vanes directly to the next. Interstage cooling is normally not required.

Rotary positive displacement compressors can be used for discharge pressures to about 6

atm.

Most compressors operating at discharge pressures above 3 atm are reciprocating positive

displacement machines. When the required compression ratio is greater than that can beachieved in one cylinder, multistage compressors are used. The maximum pressure ratio

normally obtained in a single cylinder is 10 but values above 6 are unusual.

fluid note2

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