Impeller
Encyclopedia
An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.
, usually made of iron, steel, bronze, brass, aluminum or plastic, which transfers energy
from the motor
that drives the pump to the fluid
being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid
radially, and a splined, keyed or threaded bore to accept a drive-shaft.
The impeller made out of cast material in many cases may be called rotor, also. It is cheaper to cast the radial impeller right in the support it is fitted on, which is put in motion by the gearbox from an electric motor, combustion engine or by steam driven turbine. The rotor usually names both the spindle and the impeller when they are mounted by bolts.
s but without the large blades. Among other uses, they are used in water jets to power high speed boats.
Since impellers have no large blades to turn, they can spin at much higher speeds than propellers. The water forced through the impeller is channelled by the housing, creating a water jet that propels the vessel forward. The housing is normally tapered into a nozzle to increase the speed of the water, which also creates a Venturi effect
in which low pressure behind the impeller pulls more water towards the blades, tending to increase the speed.
To work efficiently, there must be a close fit between the impeller and the housing. The housing is normally fitted with a replaceable wear ring which tends to wear as sand
or other particles are thrown against the housing side by the impeller.
Vessels using impellers are normally steered by changing the direction of the water jet.
Compare to propeller
and jet
aircraft
engines.
s in conditions such as temperature or concentration.
There are two types of impellers, depending on the flow regime created (see figure):
Radial flow impellers impose essentially shear stress
to the fluid, and are used, for example, to mix immiscible liquids or in general when there is a deformable interface
to break. Another application of radial flow impellers are the mixing of very viscous fluids.
Axial flow impellers impose essentially bulk motion, and are used on homogenization processes, in which is important to increase fluid volumetric flow rate
.
Impellers can be further classified principally into three sub-types
All these can be discussed immediately after example.
Some constructions of top loading washing machines use impellers to agitate
the laundry during washing.
and many countries of the Commonwealth
use a stylized depiction of an impeller as a rank badge. Officers wear one or more on their epaulette
s or the collar of their firefighting uniform as an equivalent to the "pips" worn by the army
and police
.
engines use an impeller instead of an axial compressor
. For example the Pratt & Whitney Canada PW100
uses a two-stage compressor with a low power impeller discharging air pressure on the high power impeller which compresses the air again into the combustion chamber. The fuel is mixed in at over 200 psi (1,379 kPa) and the mixture burns in the combustion chamber. The reason for using an impeller instead of an axial compressor is that the engine's length can be reduced.
Impellers in pumps
An impeller is a rotating component of a centrifugal pumpCentrifugal pump
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping...
, usually made of iron, steel, bronze, brass, aluminum or plastic, which transfers energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
from the motor
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
that drives the pump to the fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
radially, and a splined, keyed or threaded bore to accept a drive-shaft.
The impeller made out of cast material in many cases may be called rotor, also. It is cheaper to cast the radial impeller right in the support it is fitted on, which is put in motion by the gearbox from an electric motor, combustion engine or by steam driven turbine. The rotor usually names both the spindle and the impeller when they are mounted by bolts.
Impellers in water jets
Some impellers are similar to small propellerPropeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
s but without the large blades. Among other uses, they are used in water jets to power high speed boats.
Since impellers have no large blades to turn, they can spin at much higher speeds than propellers. The water forced through the impeller is channelled by the housing, creating a water jet that propels the vessel forward. The housing is normally tapered into a nozzle to increase the speed of the water, which also creates a Venturi effect
Venturi effect
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi , an Italian physicist.-Background:...
in which low pressure behind the impeller pulls more water towards the blades, tending to increase the speed.
To work efficiently, there must be a close fit between the impeller and the housing. The housing is normally fitted with a replaceable wear ring which tends to wear as sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or other particles are thrown against the housing side by the impeller.
Vessels using impellers are normally steered by changing the direction of the water jet.
Compare to propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
and jet
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
engines.
Impellers in agitated tanks
Impellers in agitated tanks are used to mix fluids or slurry in the tank. This can be used to combine materials in the form of solids, liquids and gas. Mixing the fluids in a tank is very important if there are gradientGradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
s in conditions such as temperature or concentration.
There are two types of impellers, depending on the flow regime created (see figure):
- axial flow impeller
- radial flow impeller.
Radial flow impellers impose essentially shear stress
Shear stress
A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...
to the fluid, and are used, for example, to mix immiscible liquids or in general when there is a deformable interface
Interface (chemistry)
An interface is a surface forming a common boundary among two different phases, such as an insoluble solid and a liquid, two immiscible liquids or a liquid and an insoluble gas. The importance of the interface depends on which type of system is being treated: the bigger the quotient area/volume,...
to break. Another application of radial flow impellers are the mixing of very viscous fluids.
Axial flow impellers impose essentially bulk motion, and are used on homogenization processes, in which is important to increase fluid volumetric flow rate
Volumetric flow rate
The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...
.
Impellers can be further classified principally into three sub-types
- Propellers
- Paddles
- Turbines
All these can be discussed immediately after example.
Example
If one heats a pot of soup on the stove the pot will develop a temperature gradient, (warmest on the bottom and cooler at the surface). Mild agitation will increase the rate of heating by dissipating the heat through the entire pot. See: Law of cooling (which also applies to heating). Even more significant, agitation disturbs the soup directly in contact with the hotter pot surface. Highly turbulent flow at the warming surface is important to good heat transfer. This is the same effect as the "wind chill" factor where moving air and turbulent action on surfaces (like those on people) result in significantly enhanced heat transfer. In unusual circumstances, overly-severe agitation may decrease the rate of heating which defeats the purpose.Propellers
They are axial thrust giving elements. These elements give very high degree of swirling in the vessel. The flow pattern generated in the fluid resembles helix.Impellers in washing machines
Agitator (device)
An agitator is a device or mechanism to put something into motion by shaking or stirring.-Manual agitator:* Manual dishwashers* A rock can be a device used to agitate dirt and other solids from fabric in washing* A stirring rod...
the laundry during washing.
Firefighting rank badge
Fire services in the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and many countries of the Commonwealth
Commonwealth of Nations
The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...
use a stylized depiction of an impeller as a rank badge. Officers wear one or more on their epaulette
Epaulette
Epaulette is a type of ornamental shoulder piece or decoration used as insignia of rank by armed forces and other organizations.Epaulettes are fastened to the shoulder by a shoulder strap or "passant", a small strap parallel to the shoulder seam, and the button near the collar, or by laces on the...
s or the collar of their firefighting uniform as an equivalent to the "pips" worn by the army
Army
An army An army An army (from Latin arma "arms, weapons" via Old French armée, "armed" (feminine), in the broadest sense, is the land-based military of a nation or state. It may also include other branches of the military such as the air force via means of aviation corps...
and police
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...
.
Impellers in gas turbine (turboprop) engines
Some turbopropTurboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
engines use an impeller instead of an axial compressor
Axial compressor
Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...
. For example the Pratt & Whitney Canada PW100
Pratt & Whitney Canada PW100
-External links:*...
uses a two-stage compressor with a low power impeller discharging air pressure on the high power impeller which compresses the air again into the combustion chamber. The fuel is mixed in at over 200 psi (1,379 kPa) and the mixture burns in the combustion chamber. The reason for using an impeller instead of an axial compressor is that the engine's length can be reduced.