Centrifugal Pump Alfred Franklin

Session – 2 Working Principle of Centrifugal Pump Alfred Franklin V Cell Number: 9965370082

Course: B.E/B.Tech (First Year)-common to all Branches. Subject: Basic Civil and Mechanical Engineering. University: Anna University Tirunelveli.

Session Objectives At the end of this session, the learner will be able to: • • • • • •

Define pump Classification Pumps Describe the working principle. Understand about the Multi stage pumps. Know priming and Cavitation. List the Applications.

Teaching Learning Material • • •

Black Board and Chalk PPT Animation

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Centrifugal pump St.Xavier’s Catholic college of Engg

Session Plan Time (in min)

10

5

Content

Introduction to Pumps

Pump Classification & Components

Learning Aid and Methodology

Brain storming

PPT

Faculty Approach

Facilitates

Explains

Typical Student Activity

Participates

Listens

Skill and Competency Developed Remembering/ Knowledge Understanding/ Comprehension Interpersonal

Remembering/ Knowledge Understanding/ Comprehension

Remembering/ Knowledge Understanding/ Comprehension

10

Working Principle

PPT

Explains

Listens

15

Velocity triangle& Work done

Chalk and Talk

Explains

Listens

Understanding/ Comprehension LogicalMathematical

10

Multistage Pumps

Demonstration/ ppt

interaction

participate

Remembering Understanding Linguistic

5

Priming , Cavitation & Application

PPT

Explains

Listens

Understanding/ Comprehension LogicalMathematical

5

Conclusion

Pick & speak

Conducts & Facilitates

Participates

Comprehension Interpersonal/ intrapersonal

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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Session Inputs Introduction to Pump The learners may have some basic understanding of pump, as it is a general term. Therefore, It would be a good idea to conduct a brain storming session so as to know what they know about the term ‘pump’. Suggested Activity: Brainstorming Brainstorming is carried out by posing the question: 1. What is pump? 2. What is the need for pumps? 3. How pumps can be classified? Responses from the learners can be listed on the board. 1. A device to pump water. A device to pump fluids 2. Lift water, pump water, bring water to tank, etc.. 3. Mono block 1hp, Submericible pump, jet pump. The unrelated words are to be removed by explaining why they are not relevant. After removing the irrelevant words, the definition is tried from the remaining words on the board.

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Centrifugal pump St.Xavier’s Catholic college of Engg

What is a pump? • Hydraulic machine converts mechanical energy into hydraulic energy. The objective of pumping system are: • Transfer liquid from source to destination • Circulate liquid around a system How pumps are classified?

Pumps

Others (e.g. Impulse, Buoyancy)

Dynamic

Centrifugal

Special effect

Internal gear

Positive Displacement

Rotary

External gear

Reciprocating

Lobe

Slide vane

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 • Used for pumping fluids • Reciprocating pump -Displacement by reciprocation of piston plunger

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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-Used 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

Components of Centrifugal pump Before explaining the working principle of centrifugal pump we have to explain the components so that the students can understand the operation of pump quickly. The components of centrifugal pump are :

a)Casing b) Impeller c) Suction Pipe d) Delivery Pipe.

Casing --It is an air tight Passage. 1. Volute Casing

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Centrifugal pump St.Xavier’s Catholic college of Engg

2. Vortex Casing 3. Casing with guide vanes

Impeller -Rotating part of pump is called impeller

Working Principle:

After explaining the components of centrifugal pump, the students can understand the working principle quickly. The following two figures are used for explaining the working principle. The working principle is explained below by showing more images.

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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A centrifugal pump is one of the simplest pieces of equipment in any process plant. Its purpose is to convert energy of a prime mover (a electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped. The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diffuser. The impeller is the rotating part that converts driver energy into the kinetic energy. The volute or diffuser is the stationary part that converts the kinetic energy into pressure energy. Note: All of the forms of energy involved in a liquid flow system are expressed in terms of meter of liquid i.e. head. Generation of Centrifugal Force The process liquid enters the suction nozzle and then into eye (center) of a revolving device known as an impeller. When the impeller rotates, it spins the liquid sitting in the cavities between the vanes outward and provides centrifugal acceleration. As liquid leaves the eye of the impeller a low-pressure area is created causing more liquid to flow toward the inlet. Because the impeller blades are curved, the fluid is pushed in a tangential and radial direction by the centrifugal force. This force acting inside the pump s the same one that keeps water inside a bucket that is rotating at the end of a string.

A centrifugal pump will pump fluid at the point where the system curve intersects the pump curve.

Basic definitions:

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Centrifugal pump St.Xavier’s Catholic college of Engg

1. Suction head (hs) It is the vertical height of free surface of water in the sump to the centre of pump. 2. Delivery head (hd)

It is the vertical height of free surface of water in the overhead tank to the centre of pump. 3. Manometric head (Hm)

The head against which the centrifugal pump has to work is known as manometric head.

Velocity triangle

The derivation of work done by the pump is explained with the help of velocity triangle. The various components of velocities should be explained. The velocity components at inlet and exit are explained as below.

At Inlet: Fluid enters at absolute velocity v1 through a cylindrical surface of radius r1 at an angle α. v1 vf1 vwl vrl u1 α θ

= = = = = = =

absolute velocity vector flow velocity whirl velocity relative velocity with respect to impeller blades tangential velocity of impeller angle between absolute velocity and tangential velocity. inlet blade angle

At Outlet: Fluid exits at absolute velocity v2 through a cylindrical surface of radius r2 at an angle α 2 . v2 vf2 vw2 vr2 u2 β φ

= = = = = = =

absolute velocity vector radial flow velocity two components whirl velocity of v2 relative velocity with respect to impeller blades tangential velocity of impeller angle between absolute velocity and tangential velocity outlet blade angle

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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• •

Mass flow rate = ρ Q =(Volume flow rate)(fluid density) Discharge (Q) = π D2 B2 Vf2 = π D1 B1 Vf1

Work done per second (E1) = T ω = m’ u2 Vw2

Watts

Work done per second by the impeller on the fluid = rate of energy transfer Euler’s Equation Euler Head = E = (1/g) ( ( v w 2 u 2 − v w1u1 ) in units of meters (m) This equation applies to both pumps and turbines. For turbines vw1u1>vw2u2 and thus E is negative and indicates that the energy transfer is in the opposite direction.

Multistage Pumps

Having discussed the working of centrifugal pump, let us now discuss the multi staging of centrifugal pumps to handle critical situations where high head or discharge being required. The images will help the students self explanatory. Centrifugal pumps can be arranged in: 1. Series. 2. Parallel.

Pumps (impellers) in series

- The pumps can be arranged in series where the fluid is lifted to a higher level.

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Centrifugal pump St.Xavier’s Catholic college of Engg

-Here Discharge remains constant. Q1 = Q 2 - Total head is equal to sum of individual head of all impellers. Htotal = H1+H2+-----+Hn

be the requirement of discharge is more.

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

Pumps in Parallel - The pumps can arranged parallel where

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- Head remains constant. H1= H2 - Total Discharge is equal to sum of individual Discharge of all pumps. Qtotal = Q1 + Q2 + Q3+-----+ Qn Priming & Cavitations: Before explaining the working principle of centrifugal pump we have to explain the components so that the students can understand it easily.

Priming The process of filling the suction pipe, casing and the portion of delivery pipe up to delivery valve with the fluid is known as priming.

Cavitation Very destructive phenomena that occur when the pressure of the fluid drops below vaporization point. The result is the formation of tiny bubbles that collapses when pressure increase on the impeller. Those implosions work as small “explosions” on the impeller that will destroy it. It’ll happen mainly for 3 reasons: • Bad system design. • Clogging of pre-filters. • Valves closed on the suction side.

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Centrifugal pump St.Xavier’s Catholic college of Engg

Applications: 1. Domestic. 2. Irrigation. 3. Industrial applications. Conclusion: To conclude this session, we can do a pick and speak activity Suggested Activity: Pick & Speak The keywords from this topic are written on some chit and put it on a bowl. Then the learners are asked to take it one by one and they have to talk about the key word that they took. The key words are: 1. Impeller 2. Casing 3. Priming 4.Cavitation 5. Multi staging. 6. Head

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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Summary In this session, we learnt to: • • • • • •

Define a pump Classify Pumps Describe the working principle. Compare pumps in parallel and Series. Understand priming and Cavitations. List the Applications.

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Centrifugal pump St.Xavier’s Catholic college of Engg

References BOOKS

1. Frank. M. White, Fluid Mechanics, McGraw Hill, Singapore, 1999. 2. J. E. Huguenin and J. Colt, Design and operating guide for aquaculture seawater systems, Elsevier, Netherland, 1992. 3. George Fischer , Industrial Piping Systems- Planning Fundamentals, Georg Fischer AG, Schweiz, 2002. 4.

Bansal, Fluid Mechanics and Publications, New delhi ,2008.

Machinery,

Laxmi

WEBSITES http:/www.pumpworld.com/ http:/Imoneng.com/ www.images.google.com

Topic Name: Working Principle of Centrifugal Pump Author Name: Alfred Franklin.V

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Centrifugal pump St.Xavier’s Catholic college of Engg