pumps (lecture 3)

Industrial Pharmacy 1Third lecture

Dr. Heba Gad, PhD.

Lecturer of Pharmaceutics and Industrial Pharmacy

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Fluid flow (Cont.)

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Fluid flow in pipes

The rate of flow R is defined as the volume V of a fluid that passes a certain cross-section Aper unit of time t

Rate = Area * length / time

Velocity = length /timeRate = Area * velocity

For an incompressible fluid, the velocity increases when the cross-section decreases:

A1

A2

R = A1v1 = A2v2

v1

v2

v2

2 2

1 1 2 2v d v d1 1 2 2R v A v A

Bernoulli’s Principle

• He observed that the water level at the centreis the lowest.

• He made some assumptions:a) As fluid moves from a wider pipe to a

narrower one, the speed of water flow will beincrease.

b) As the speed of water flow increase, thepressure will decrease and the water cannot goup the upside of pipe easily.

• Hence Bernoulli's conclusion: the slower therate of flow, the higher the pressure, and thefaster the rate of flow, the lower the pressure.

Pumps

• The pump is mechanical device which conveys liquid from one place to another place.

• It can be defined as a hydraulic machines which converts the mechanical energy into hydraulic energy.

• Classification:

• Positive displacement pumps

• Roto - dynamic pumps

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Positive displacement pumps

• A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe.

• Most commonly used for the discharge of relatively small quantities of fluid against relatively large heads.

• Positive displacement pumps, theoretically can produce the same flow at a given speed no matter what the discharge pressure.

• Thus, positive displacement pumps are constant flow machines.

• However, a slight increase in internal leakage as the pressure increases prevents a truly constant flow rate.

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Positive displacement pumps

• Types

A positive displacement pump can be further classified according to the mechanism used to move the fluid:

• Reciprocating-type positive displacement

• Rotary-type positive displacement

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Reciprocating-type positive displacement

• Reciprocating pumps move the fluid using one or more oscillating pistons, or diaphragms, while valves restrict fluid motion to the desired direction.

• Single acting Reciprocating pump

• The fluid is drawn into a cylinder through an inlet valve by movement of the piston to the right.

• The stroke in the opposite direction drives fluid through the out

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• Double acting reciprocating pump

• Cessation of pumping on the return stroke is overcome in the double-acting piston pump by utilizing the volume on both sides of the piston.

• Fluid is drawn in on one side by a stroke that delivers the fluid on the other

• In both pumps, delivery fluctuates

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• A modification, known as the diaphragm pump, is constructed so that reciprocating parts do not contact the pumped liquid

• A flexible disk, fixed at the periphery, expands and contracts the pumping chamber, drawing in and discharging liquid through valves.

• Diaphragm valves are used to pump hazardous and toxic fluids.

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Advantages• Operation is simple and efficient.

• Widely used in gas compressors.

• In pumping liquids, no priming is necessary

because the pump will effectively discharge air

present in the pump or feed lines.

Rotary-type positive displacement

• Positive displacement rotary pumps move fluid using a rotating mechanism that captures and draws in the liquid

• Both liquids and gases are discharged so that priming is not necessary.

• Rotary positive displacement pumps fall into three main types:

• Gear pump (a)

• Lobe pump (b)

• Sliding vanes (c)

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• The gear pumps

the liquid is conveyed in the spacesformed between a case and theconsecutive teeth of two gears thatintermesh at the center of the pumpto prevent return of the liquid to theinlet.

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• The lobe pump

• widely used as a liquid pump and as a blower, operates in a similar manner.

• Each impeller carries two or three lobes that interact with very small clearance to convey fluid from inlet to outlet.


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• The sliding vanes (c), • these have a cylindrical rotor encased in a similarly

shaped housing. • The rotor is maintained in contact with the case by

centrifugal force • As the rotor orbits, the vanes trap fluid between the

rotor and the casing, drawing the fluid through the pump.

• Fluid is drawn into the chamber createdby two vanes at the inlet.


• Advantages: very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually.

• Drawbacks: The nature of the pump demands very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed.

• The small clearance between moving parts precludes the pumping of abrasive slurries.

• If rotary pumps are operated at high speeds, the fluids cause erosion, which eventually causes enlarged clearances that liquid can pass through, which reduces efficiency

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Roto - dynamic pump

• Centrifugal Impeller Pumps• The centrifugal impeller pump is the type

most widely used in the chemical industry.

• This machine consists of an impellerrotating within a case

• The impeller consists of a number of vanes, usually curved backward from the direction of rotation.

• The vanes may be open or, more commonly, closed between one or two supporting plates. This reduces swirl and increases efficiency.

Centrifugal Impeller Pumps

• The impeller is rotated at high speeds, imparting radial and tangential momenta to a liquid that is fed axially to the center.

• Liquid directed into the center of the rotating impeller is picked up by the impeller’s vanes and accelerated to a higher velocity by the rotation of the impeller and discharged by centrifugal force into the case.

• Disadvantage

• To begin pumping, the impeller must be primed with the liquid to be pumped.

• Uses:

• To pump slurries and corrosive liquid, steadily delivering large volumes against moderately large heads.

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