Session – 2
Working Principle of Centrifugal Pump
Alfred Franklin VCell Number: 9965370082
Course: B.E/B.Tech (First Year)-common to all Branches.Subject: Basic Civil and Mechanical Engineering.University: Anna University Tirunelveli.
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Session Objectives
At the end of this session, the learner will be able to:
Define pumpClassification PumpsDescribe the working principle.Understand about the Multi stage pumps.Know priming and Cavitation.List the Applications.
Teaching Learning Material
Black Board and ChalkPPTAnimation
Topic Name: Working Principle of Centrifugal Pump Page 3Author Name: Alfred Franklin.V College Name: St. Xavier’s Catholic College of Engineering
Session Plan
Time(in min) Content
Learning Aid and
Methodology
Faculty Approach
Typical Student Activity
Skill andCompetency Developed
10 Introduction to Pumps Brain storming Facilitates Participates
Remembering/KnowledgeUnderstanding/ComprehensionInterpersonal
5 Pump Classification & Components PPT Explains Listens
Remembering/KnowledgeUnderstanding/Comprehension
10 Working Principle PPT Explains Listens
Remembering/KnowledgeUnderstanding/Comprehension
15 Velocity triangle& Work done Chalk and Talk Explains Listens
Understanding/ComprehensionLogical-Mathematical
10 Multistage Pumps Demonstration/ppt interaction participate
RememberingUnderstandingLinguistic
5Priming , Cavitation & Application
PPT Explains Listens
Understanding/ComprehensionLogical-Mathematical
5 Conclusion Pick & speak Conducts & Facilitates Participates
ComprehensionInterpersonal/ intrapersonal
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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 fluids2. 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.
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?
Topic Name: Working Principle of Centrifugal Pump Page 5Author Name: Alfred Franklin.V College Name: St. Xavier’s Catholic College of Engineering
DynamicPositive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal gear
External gear
LobeSlide vane
Others (e.g. Impulse, Buoyancy)
Pumps
DynamicPositive
Displacement
Centrifugal Special effect Rotary Reciprocating
Internal gear
External gear
LobeSlide vane
Others (e.g. Impulse, Buoyancy)
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
• Used for pumping fluids
• Reciprocating pump-Displacement by reciprocation of piston plunger-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
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-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) Impellerc) Suction Piped) Delivery Pipe.
Casing--It is an air tight Passage.
1. Volute Casing2. Vortex Casing 3. Casing with guide vanes
Topic Name: Working Principle of Centrifugal Pump Page 7Author Name: Alfred Franklin.V College Name: St. Xavier’s Catholic College of Engineering
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.
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
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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:
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
Topic Name: Working Principle of Centrifugal Pump Page 9Author Name: Alfred Franklin.V College Name: St. Xavier’s Catholic College of Engineering
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 = absolute velocity vector vf1 = flow velocityvwl = whirl velocity vrl = relative velocity with respect to impeller bladesu1 = tangential velocity of impellerα = angle between absolute velocity and tangential velocity.θ = inlet blade angle
At Outlet:Fluid exits at absolute velocity v2 through a cylindrical surface of radius r2 at an angle .
v2 = absolute velocity vector vf2 = radial flow velocity two componentsvw2 = whirl velocity of v2
vr2 = relative velocity with respect to impeller bladesu2 = tangential velocity of impeller
= angle between absolute velocity and tangential velocityφ = outlet blade angle
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 = m’ u2 Vw2 Watts
Work done per second by the impeller on the fluid = rate of energy transfer
Euler’s Equation
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Euler Head = E = (1/g) ( 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 PumpsHaving 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.
Topic Name: Working Principle of Centrifugal Pump Page 11Author Name: Alfred Franklin.V College Name: St. Xavier’s Catholic College of Engineering
-Here Discharge remains constant. Q1 = Q2
- Total head is equal to sum of individual head of all impellers.Htotal = H1+H2+-----+Hn
Pumps in Parallel- The pumps can be arranged parallel where the
requirement of discharge is more.
- Head remains constant.H1= H2
- Total Discharge is equal to sum of individual Discharge of all pumps.
Qtotal = Q1 + Q2 + Q3+-----+ Qn
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Priming & Cavitations:
Before explaining the working principle of centrifugal pump we have to explain the components so that the students can understand it easily.
PrimingThe 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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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
Summary
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In this session, we learnt to:
Define a pumpClassify PumpsDescribe the working principle.Compare pumps in parallel and Series.Understand priming and Cavitations.List the Applications.
References
BOOKS1. Frank. M. White, Fluid Mechanics, McGraw Hill,
Singapore, 1999.
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2. J. E. Huguenin and J. Colt, Design and operating guide for aquaculture seawater systems, Elsevier, Netherland, 1992.
3. George Fischer , Industrial Piping Systems- PlanningFundamentals, Georg Fischer AG, Schweiz, 2002.
4. Bansal, Fluid Mechanics and Machinery, Laxmi Publications, New delhi ,2008.
WEBSITEShttp:/www.pumpworld.com/http:/Imoneng.com/www.images.google.com
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