Impeller & Propeller

http://en.wikipedia.org/wiki/Impeller

http://en.wikipedia.org/wiki/propeller

Thanks Rosy

The two are used quite interchangably in the fluid mixing industry. Essentially though a propeller in mixing is usually a cast impeller with variable angle and variable width blades. It essentially looks very much like a boat propeller.

An impeller on the other hand tends to be fabricated so is available in a large range of sizes, and to large diameters without too much of a weight penalty (which means the agitator becomes impractical). Fabricated impeller tend to be fixed width bent or straight sheets of steel.

I have to say that the wikipedia articles are rather strange as they give a definition, then examples that don't comply with the definition. The joys of wikipedia I suppose.

HI! I've read other replies, they seem rather cumbersome. I've copy/pasted for u the following:

im-pel-ler (im pel'uhr) n.
1. a person or thing that impels.
2. a rotor for transmitting motion, as in a
centrifugal pump, blower, turbine, or
fluid coupling.
[1675-85]

pro-pel-ler (pruh pel'uhr) n.
1. a device having a revolving hub with
radiating blades, for propelling an
airplane, ship, etc.
2. a person or thing that propels.
3. the bladed rotor of a pump that drives
the fluid axially.
4. a wind-driven, usu. three-bladed device
that provides mechanical energy, as for
driving an electric alternator in wind
plants.
[1770-80]

SOURCE: Random House Webster's

So far my understanding an Impeller is surrounded by a housing (and the housing design important for the equipment function). Means, the impeller forces the medium (gas, fluid) but the housing is directing the effect from energized medium. Examples: big air fan, water jet drive. You can see, with an impeller arrangement you can "propel" a ship or an airplane - the design and its effect are two different things and should not be mixed up. Impellers most often creating a radial flow (but is not a must).

A propeller is an open running device - its function directly is creating the effect (usally a thrust force --> where the word propelling is derived from and which might be one reason of confusions). Sometimes you see a propeller surrounded by a short tube. Now it becomes difficult to decide whether we have an impeller or an propeller. If the tube-like surrounding is made to protect the environment against side effects from enrgizing the media (like protecting the harbour ground against impact from fluid flow turbulences; similar for an hoover-craft drive) we still have an propeller. If such arrangement significantly is bringing up the efficiency of the whole arrangement we may have an impeller.

Practically the word impeller merely is used for pumps and fans, sometimes turbines rotor. Moving boats. planes, vehicles the word propeller will be used (however, for a jet like driver we should talk about an impeller or turbine runner...).

Albert

Dear sir,

Impeller of ,say,a pump:

Kinetic energy is given by the impeller to the fluid,and then trasferred to pressure energy via a volute or diffuser to allow for fluid flowing.

Pump casing is fixed.

This process consumes electric energy.

Propeller of,say,a hydraulic turbine:

Potential energy is given by the fluid to the propeller to generate electric power.

Turbine casing is fixed.

Propeller of,say,a ship or boat:

Kinetic energy is given by the impeller to the fluid.

The created thrust is used here to move the ship or the boat.

Regards,

Sayed Sarhan.

Actually, a PROpeller does exactly what the name implies; it propells. That is, it has blades that are at various angles relative to the shaft or centerline of the device. As the propeller turns, the angle of the blade to the shaft pushes the medium being moved in a forward direction. The greater the angle, the more medium is propelled. The same action causes the propeller to pull in the other direction because as the propeller pushes the medium because of its angle to the shaft, the back side of the blade "grabs" the medium and pulls against it. This causes the force to be in the opposite direction and causes the shaft to be drawn in that direction.

The IMpeller, on the other hand operates in a completely different mode. The rotation of the impeller causes the liquid to be thrown off the blades. As the blades rotate, the medium is drawn into the "eye" if the impeller. Then it is "thrown" off the impeller by centrifugal force against the pump volute. As it travels oround the inside of the volute, it is "stripped" from the impeller by the "cutwater" where it exits the pump.

The principle behind the action of the impeller is, as stated above, centrifugal force. The force (pressure) that the pump will deliver is controlled by the "tip speed" of the impeller. The faster it travels, the more it will pump and the greater pressure it will produce. Tip speed can by controlled by two things: the diameter of the spinning impeller and the actual rotative speed of the impeller.

I hope this helps you.

Then what are the blades of a wind generator called?

It looks like a propellor, but I hope it does not "Propel' the generator from it's tower.

Joe

Good question!! The propellers of a wind generator are not propellers in the true sense of the word. They are actually operating the same as propellers, but the energy is expended in the opposite direction. In other words, the energy is being applied to the propeller of the wind generator by the wind, whereas the energy of the propeller on a fan, for instance, is being generated by the turning of the propeller via a motor or other means.

This brings up another point. The propeller is actually causing the wind or air around it to be propelled; not the device to which it is attached. The device attached to the propeller, in the case of a fan, is housing the motor that drives the propeller which in turn propells the air passing through it. In the wind generator, the propeller is being turned by the wind itself and the resulting energy is turning the generator armature to produce the electricity.

This is the major difference between the propeller and the impeller, getting back to the original question. The propeller, having blades that are at an acute angle to its shaft, impart, or as in the case of your wind generator, consume energy in a rotary direction. The impeller, consumes rotary energy but imparts the energy via centrifugal force since its blades are at right angles to its shaft and they are curved backwards to take advantage of the centrifugal energy the spinning impeller uses to move its pumped medium.

You may recall as a kid, having a string with some object tied to the end and spinning the string to build up speed and then letting go of the string. The object tied to the string would fly in the direction it was last headed when spinning. That is centrifugal force. The cutwater I mentioned before is the element that causes the pumped medium to be "cut loose" from the spinning impeller and it travels out the nozzle of the pump.

This is a thumbnail sketch of the theory. Hope it's not too confusing.

does direction of rotor blades(CW or CCW)makes any difference in impeeler and propeller????smetimes i hav a doubt dat if a fan is rotating CW it acts as propeller but if rotation is in CCW then it is impeller....???i m very confused...

waitin fr ur reply sir/madam........

thanks a lot.

sails

The basic difference between the two according to me is:

A propeller can be equated to like an Axial fan. Where, due to its rotation the wind passes over the blades and exits axially to its rotational axis by which a thrust can be generated which is parallal to axis of rotation.

An Impeller is like a radial fan and provides a centrifugal force to the liquid which then produces a 'HEAD' or in other words, increases the pressure at discharge.

How the effects are put to use depends on application.

Impeller draws/pulls/sucks in air, water or gas while propeller does the opposite:push out. Let's say in laymens term: I impell liquid through my mouth(i drink) and i propelled gas out thorugh my anus.