G H PATEL COLLEGE OF ENGINEERING AND TECHNOLOGY FLUID POWER ENGINEERING (2151903) CENTRIFUGAL PUMP PREPARED BY:- DEV MAKATI(130110119026) KEVAL MAKWANA(130110119027) MOHIT MIRCHANDANI(130110119028) *DHRUMIL NIZAMA(130110119029) HARDIK PANCHAL(130110119030)

Introduction to pump What is pump? The pump is mechanical device which conveys liquid from one place to another place. It can also be defined as hydraulic machine which converts the mechanical energy into hydraulic energy(pressure energy of fluid).

Purpose of pumps The purpose of pumps may be increasing the pressure energy, imparting kinetic energy, lifting and circulating, exhausting or extracting liquids etc. APPLICATION Thermal engineering 1)to feed water into boiler 2)to circulate water in condensor Agriculture and Irrigation Chemical industries Municipal water works Drainage system Hydraulic control system

Positive displacement There are two main categories of pump: Rotodynamic pumps. Positive displacement pumps. PUMP Rotodynamic Positive displacement Centrifugal Rotary Reciprocating Axial flow Mixed flow Gear Piston Turbine Lobe Diaphragm Sliding Vane Plunger Screw 2

Why use a centrifugal pump?? Available in a wide range of sizes – discharges from 1” to 12ft and bigger Handle a wide range of head and flow conditions. Limitations: cannot handle entrained air – 3% max. cannot handle viscous liquids.

Pump types Centrifugal pumps come in a wide variety of styles. end suction. split case. in-line. double suction. vertical multistage. horizontal multistage. submersible. self-priming. axial-flow. regenerative.

Centrifugal Pumps: centrifugal pumps have a rotating impeller, also known as a blade, that is immersed in the liquid. Liquid enters the pump near the axis of the impeller, and the rotating impeller sweeps the liquid out toward the ends of the impeller blades at high pressure. For low flows and high pressures, the action of the impeller is largely radial.

Positive-displacement Pumps: A variety of positive-displacement pumps are also available, generally consisting of a rotating member with a number of lobes that move in a close-fitting casing. The liquid is trapped in the spaces between the lobes and then discharged into a region of higher pressure. A common device of this type is the gear pump, which consists of a pair of meshing gears. The lobes in this case are the gear teeth

What is the main difference between kinetic and positive displacement pumps ? The main difference between kinetic and positive displacement pumps lies in the method of fluid transfer.  A kinetic pump imparts velocity energy to the fluid, which is converted to pressure energy upon exiting the pump casing A positive displacement pump moves a fixed volume of fluid within the pump casing by applying a force to moveable boundaries containing the fluid volume.  4

Main parts of centrifugal pump Impellar (rotating part) Casing (air tight passage) Suction pipe Delivery pipe

Components of centrifugal pump IMPELLER:It is a wheel or rotor which is provided with a series of backward curved blades or vanes. It is mounted on a shaft which is coupled to an external source of energy (usually an electric motor) which imparts the required energy to the impeller thereby making it to rotate. CASING:It is an airtight chamber which surrounds the impeller. It is similar to the casing of a reaction turbine. The different types of casings that are commonly adopted are described later.

CONTI……… SUCTION PIPE: It is a pipe which is connected at its upper end to the inlet of the pump or to the center of the impeller which is commonly known as eye. The lower end of the suction pipe dips into liquid in a suction tank or a sump from which the liquid is to be pumped or lifted up. DELIVERY PIPE: It is a pipe which is connected at its lower end to the outlet of .the pump and it delivers the liquid to the required height. Just near the outlet of the pump on the delivery pipe a delivery valve is invariably provided. A delivery valve is a regulating valve which is of sluice type and is required to be provided in order to control the flow from the pump into delivery pipe.

casing Volute type

IMPELLAR Axial flow Radial flow Mixed flow Three main categories of centrifugal pumps exist Axial flow Radial flow Mixed flow 7

Type of Impeller There are three main categories of impeller due type of impeller’s vane, which are used in the centrifugal pumps as; Radial vanes, Fig. (a). Backward vanes, Fig. (b). Forward vanes, Fig. (c). 12

Cont.. The tips of the blades are sometimes covered by another flat disc to give shrouded blades , otherwise the blade tips are left open and the casing of the pump itself forms the solid outer wall of the blade passages. The advantage of the shrouded blade is that flow is prevented from leaking across the blade tips from one passage to another.

MULTI-STAGE CENTRIFUGAL PUMPS. When a centrifugal pump consist of two or more impellers the pump is know as a multistage centrifugal pump. The important functions of a multistage centrifugal pump are; (i) To produce high head (pumps in series) (ii) To deliver or discharge large quantities of a liquid (pumps in parallel)

PUMPS IN SERIES. It is an arrangement made by mounting a number of impellers on the shaft of a motor as shown. Such an arrangement is useful when the liquid has to be pumped to large heights keeping the discharge constant. If, Hm is the head developed by one impeller n= number of impellers. Then, nxHm= total head developed by the pump Q=discharge through the pump.

PUMPS IN PARALLEL. It is an arrangement made by connecting a number of pumps in parallel as shown. Such an arrangement is useful when a large quantity of liquid is to be pumped to a particular height. If Q=discharge from one pump N=identical number pumps. Then, nxQ= total discharge delivered by the pump Hm is the head developed by the pump.

Working As the impeller rotates, the fluid is drawn into the blade passage at the impeller eye, the centre of the impeller. The inlet pipe is axial and therefore fluid enters the impeller with very little whirl or tangential component of velocity and flows outwards in the direction of the blades. The fluid receives energy from the impeller while flowing through it and is discharged with increased pressure and velocity into the casing. To convert the kinetic energy or fluid at the impeller outlet gradually into pressure energy, diffuser blades mounted on a diffuser ring are used. The stationary blade passages so formed have an increasing cross-sectional area which reduces the flow velocity and hence increases the static pressure of the fluid. Finally, the fluid moves from the diffuser blades into the volute casing which is a passage of gradually increasing cross-section and also serves to reduce the velocity of fluid and to convert some of the velocity head into static head. Sometimes pumps have only volute casing without any diffuser.

Priming in centrifugal pump Most centrifugal pumps are not self-priming. In other words, the pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. If the pump casing becomes filled with vapors or gases, the pump impeller becomes gas-bound and incapable of pumping. To ensure that a centrifugal pump remains primed and does not become gas-bound, most centrifugal pumps are located below the level of the source from which the pump is to take its suction. The same effect can be gained by supplying liquid to the pump suction under pressure supplied by another pump placed in the suction line.

Additionally, a centrifugal pump should not be operated until it has been filled with fluid. Should the pump run without fluid, there is the danger of damage to critical lubricated internal components. There are several methods to properly vent a air or gas from a pump. The process of filling the pump with liquid to called priming. In some systems, the pump is primed by utilizing a priming pump controlled by a float switch. Priming the pump and venting the pump casing during system startup should prevent gas buildup.

CENTRIFUGAL PUMP ADVANTAGES DISADVANTAGES Simple in construction and cheap Handle liquid with large amounts of solids No metal to metal fits No valves involved in pump operation Maintenance costs are lower. Cannot handle highly viscous fluids efficiently Cannot be operated at high heads Maximum efficiency holds over a narrow range of conditions.

General Pumping System and the Net Head Developed by a Pump

The total head at any point comprises pressure head, velocity head and elevation head. For the lower reservoir, the total head at the free surface is HA and is equal to the elevation of the free surface above the datum line since the velocity and static pressure at A are zero. Similarly the total head at the free surface in the higher reservoir is (HA+HS ) and is equal to the elevation of the free surface of the reservoir above the reference datum. The liquid enters the intake pipe causing a head loss hin  for which the total energy line drops to point B corresponding to a location just after the entrance to intake pipe. The total head at B can be written as

Let, Z1= pump elevation at inlet hf1=other losses due to friction at inlet Z2= pump elevation at outlet hf2=other losses due to friction at outlet he=exit losses at E Total inlet head to the pump =  Total outlet head of the pump =  Where  V1 and V2  are the velocities in suction and delivery pipes respectively. Therefore, the total head developed by the pump,

 The vertical distance between the two levels in the reservoirs Hs  is known as static head or static lift. Relationship between , the static head Hs and H , the head developed can be found out by applying Bernoulli's equation between A and C and between D and F as follows: And between D and F, substituting HA, we can write

Velocity triangles for centrifugal pump Impeller

Let β1 be the angle made by the blade at inlet, with the tangent to the inlet radius, while  β2 is the blade angle with the tangent at outlet V1 and V2 are the absolute velocities of fluid at inlet an outlet respectively, while Vr1 andVr2 are the relative velocities (with respect to blade velocity) at inlet and outlet respectively. Therefore, Work done on the fluid per unit weight =   considering the operation under design conditions, the inlet whirl Vw1velocity  and accordingly the inlet angular momentum of the fluid entering the impeller is set to zero. Therefore, Work done on the fluid per unit weight = manometric efficiency:- it is the ratio of the manometric head to the head actually generated by the impeller.

The overall efficiency :- It is the ratio of the work done by the pump in lifting water against gravity and friction in the pipes to the energy supplied by the motor. mechanical efficiency:- It is the ratio of the impeller power to the power of the motor or the prime mover. So that,

POWER AND EFFICIENCY Power supplied by the pump: Power delivered to the fluid: From above two equations, Where m=mass flow rate, kg/s H= total discharge head, N.m/kg =efficiency …………(1)

Effect of blade outlet angle a) when β2 > 90o, the Forwards curved vanes of the impeller. b) when β2 = 90o , the radial curved vanes of the impeller. c) when β2 < 90o, the Backwards curved vanes of the impeller. where : V = absolute velocity of the water. U = Tangential velocity of impeller (peripheral velocity). Vr = relative velocity of water to the wheel. Vf = velocity flow. N = Speed of impeller in (rpm). 13

Cavitation in centrifugal pumps Cavitation is likely to occur at the inlet to the pump, since the pressure there is the minimum and is lower than the atmospheric pressure by an amount that equals the vertical height above which the pump is situated from the supply reservoir (known as sump) plus the velocity head and frictional losses in the suction pipe. Applying the Bernoulli's equation between the surface of the liquid in the sump and the entry to the impeller, we have

where, Pi  is the pressure at the impeller inlet and  PA  is the pressure at the liquid surface in the sump which is usually the atmospheric pressure, Z1 is the vertical height of the impeller inlet from the liquid surface in the sump, Hf is the loss of head in the suction pipe. Strainers and non-return valves are commonly fitted to intake pipes. The term  Hf must therefore include the losses occurring past these devices, in addition to losses caused by pipe friction and by bends in the pipe. In the similar way as described in case of a reaction turbine, the net positive suction head 'NPSH' in case of a pump is defined as the available suction head (inclusive of both static and dynamic heads) at pump inlet above the head corresponding to vapor pressure.

Therefore Again, we can write

Example 1 The impeller of a centrifugal pump is 0.5m in diameter and rotates at 1200 rpm. Blades are curved back to an angle of 30 ° to the tangent at outlet tip. If the measured velocity of flow at outlet is 5 m/s, find the work input per kg of water per second. Find the theoretical maximum lift to which the water can be raised if the pump is provided with whirlpool chamber which reduces the velocity of water by 50%.

Solution: 1) The peripheral speed at impeller outlet (given) Work input per unit weight of  Water = =72.78m Under ideal condition (without loss), the total head developed by the pump = 72.78 m  

Absolute velocity of water at the outlet At the whirlpool chamber, The velocity of water at delivery = 0.5 *23.28m/s Therefore the pressure head at impeller outlet =72.78 -  = 65.87m Hence, we theoretical maximum lift = 65.87m

A centrifugal pump has a 100 mm diameter suction pipe and a 75 mm diameter delivery pipe. When discharging 15 l/s of water, the inlet water mercury manometer with one limb exposed to the atmosphere recorded a vacuum deflection of 198 mm; the mercury level on the suction side was 100 mm below the pipe centerline. The delivery pressure gauge, 200 mm above the pump inlet, recorded a pressure of 0.95 bar. The measured in put power was 3.2 kW. Calculate the pump efficiency.

Manometric head = rise in total head

Example 2 Two identical pumps having the tabulated characteristics are to be installed in a pumping station to deliver sewage to a settling tank through a 200 mm uPVC pipeline 2.5 km long. The static lift is 15 m. Allowing for minor head losses of 10.0V2/2g and assuming an effective roughness of 0.15 mm calculate the discharge and power consumption if the pumps were to be connected: (a) in parallel, and (b) in series.

Solution: The ‘system curve’ is computed as in the previous examples; this is, of course , independent of the pump characteristics. Calculated system heads (H) are tabulated below for discrete discharges (Q)

Parallel operation The predicted head v. discharge curve for dual pump operation in parallel mode is obtained as described,. i.e. by doubling she discharge over the range of heads (since the pumps are identical in this case). The system and efficiency curves are added. From the intersection of the characteristic and system curves the following results are obtained: Single pimp operation; Q = 22.5 l/S; Hm = 24 m ;  = 0.58 Power consumption = 9.13 kW Parallel operation, Q = 28.5 l/S; Hm = 26 m ;  = 0.51 (Corresponding with 14.25 l/s per pump) Power input = 14.11 kW

Parallel operation

Series operation Plotting the dual-pump characteristic curve, intersection with the system curve yields Series operation

Q=32.5 l/S; Hm = 28 m ;  = 0.41 Power input = 21.77kW Note that for this particular pipe system, comparing the relative power consumptions the parallel operation is more efficient in producing an increase in discharge than the series operation.

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