An impeller is a rotor used to increase the pressure and flow of a fluid. The velocity achieved by the impeller transfers into pressure when the movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an inlet to accept incoming fluid, vanes to push the fluid radially. 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, the rotor usually names both the spindle and the impeller when they are mounted by bolts. In a failing heart, mechanical circulatory devices often utilize a continuous axial-flow impeller pump design, open impeller Semi-open impeller Closed or shrouded impeller The main part of a centrifugal compressor is the impeller. An open impeller has no cover, therefore it can work at higher speeds, a compressor with a covered impeller can have more stages than one that has an open impeller. Some impellers are similar to small propellers 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. To work efficiently, there must be a fit between the impeller and the housing. The housing is 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. Impellers in agitated tanks are used to mix fluids or slurry in the tank and this can be used to combine materials in the form of solids, liquids and gas. Mixing the fluids in a tank is important if there are gradients in conditions such as temperature or concentration. 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 increased fluid volumetric flow rate is important. Impellers can be further classified principally into three sub-types Propellers Paddles Turbines All these can be discussed immediately after example, if one heats a pot of soup on the stove the pot will develop a temperature gradient. Mild agitation will increase the rate of heating by dissipating the heat through the entire pot, even more significant, agitation disturbs the soup directly in contact with the hotter pot surface. Highly turbulent flow at the surface is important to good heat transfer
An impeller for a dam turbine generator
Several different types of pump impellers
Flexible impeller of cooling system pump of an outboard engine. (Coin for comparison, diameter 16.25 mm.)
Axial flow impeller (left) and radial flow impeller (right).