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An impeller is an important component used in machinery that proficiently moves fluids through energy transfer. It greatly increases the proficiency as well as performance of components such as pumps, compressors, turbines etc. In this blog post we will cover different types of impellers, material they are made from and their application in different industries.
What is an Impeller?
In simple terms an impeller is a rotating mechanical component that uses specially designed blades or vanes to transfer energy to fluids. These components convert rotational force from motor into fluid velocity and pressure, which turns them into important elements of pumps, propulsion setups, mixers etc.
How Does Impeller Work?
The impeller performs its operational process in accordance with certain mechanical principles.
As motor activates the shaft, it also rotates impeller at speed of 500 to 5,000 rpm. This process creates low-pressure area at center (eye) that draws fluid inward.
Then centrifugal force generated by curved vanes moves the fluid outward. After that the expanding volute channel converts this kinetic energy into pressure energy.
Finally fluid exits discharge port with high velocity and pressure which assures constant flow through the system.
Also See: Top 10 Impeller Manufacturers in China
Types of Impellers
Open Impellers
Open impellers are quite simple in design. They are connected to central hub without outer shrouds which makes them easy to maintain & clean. These designs have lower proficiency because of fluid recirculation and are lightweight. Moreover they are suitable for wastewater treatment operations as well as low viscosity fluids.
Closed Impellers
Closed impellers have two shrouds which contain vanes enclosed between them. This design decreases fluid leakage and increases proficiency. That is why these impellers provide outstanding performance despite having more complicated design.
They are good in high pressure applications and handling of viscous fluids. Thus they are mostly used in clean water pumps & HVAC systems.
Semi Open Impellers
Semi-open impellers connect central hub to the backside through single shroud. This design decreases fluid recirculation which in turn improves proficiency.
These impellers work well in medium sized pumps for handling soft solids. But they also produce very high axle thrust loads. Therefore they are normally used in light slurry and food processing operations.
Screw Impellers
Screw impellers use long spiral vane design that has cutting grooves to handle solids. This self-priming configuration, in addition to assuring constant flow rate, also proficiently manages viscous materials.
These impellers provide minimum pulsation along with outstanding suction capability. But their complicated design limits their use in some applications and increases production costs.
Vortex Impellers
Vortex impellers feature recessed design to create stirring motion within fluid. This design permits solids to pass through without damaging impeller⸴ thereby preventing clogging.
These impellers compared to other types show lower efficiency. But they are best suited for handling fluids that contain large debris & solids. Hence these impellers are used for sewage and wastewater treatment.
Also See: What are the Main Differences Between an Open, Semi-Open and Closed Impeller?
Materials Used in Impeller Manufacturing
Stainless Steel
Among stainless steels, types 304 and 316 are prominent for use in aggressive media applications. These types have high tensile strength and outstanding hydraulic performance as well as resistance to corrosion.
Also See: Types of Stainless Steel
Cast Iron
Cast iron shows outstanding performance in high temperature pump applications. It has low thermal expansion coefficient of 6.5 and is easy to machine as well.
Bronze
A combination of tin and copper makes bronze a strong alloy. Because of its good thermal conductivity & non ferromagnetic characteristics, it is perfect for aggressive fluid environments and seawater pumps.
Titanium Alloys
These alloys provide outstanding strength, low weight and better corrosion resistance. They are mostly used in high performance applications which include impellers for medical & aerospace equipment.
Nickel Based Alloys
Nickel based alloys are usually used in oil refining and chemical industry. In corrosive environments & high temperature applications, these materials provide better heat resistance as well as corrosion resistance.
Aluminum Alloys
Grade A 2618 aluminum alloys can keep their structural integrity even at temperatures > 400°C. Moreover these lightweight materials are used in fast speed applications. For example in turbo molecular pumps and supercharger impellers.
See Also: What is an Aluminum Alloy
Non-Metallic Materials
Advanced polymers such as PPS, carbon fiber composites and PEEK provide extraordinary chemical resistance in addition to low weight. These materials operate reliably at temperatures up to 100°C and in acidic environments.
Applications of Impellers
Medical Devices
Blood pumps in the medical industry require special impellers for accurate flow control. Their channel design reduces blood cell damage and keeps flow rate of 1 to 6 L/minute during cardiopulmonary bypass.
Marine Propulsion
Marine impellers incorporated in waterjet systems are suitable for less deep water operations than conventional propellers which are prone to damage. Apart from that their closed design decreases cavitation at high speeds and uses vectored thrust capabilities to provide outstanding maneuverability.
Industrial Mixing
In chemical processing special impellers are used in industrial agitators to create better flow patterns. Moreover their special blade geometry assures product uniformity as well as good flow distribution in high viscosity fluids.
Food & Beverage Industry
Flexible impeller pumps are used to transfer viscous food products carefully without shear damage. They transfer beverages, fruit pulps and dairy products smoothly because of their special rubber vanes.
Firefighting Equipment
Centrifugal fire pumps use special impellers that have reinforced vanes and double suction head design in order to maintain pressure heads. In emergency firefighting operations, their strong construction guarantees constant water supply through sprinkler and standpipe systems.
Pumping Systems
Impellers are important to transfer fluid in axial and centrifugal flow pumps. Their hydraulic design converts rotational energy into velocity & pressure to provide optimal fluid movement in water management systems.
Wastewater Management
Water treatment plants use free flow impellers to handle wastewater. This wastewater contains complex mixtures of fibers, solids, entrapped gases etc. Their design has large free passages that move sludge and seawage proficiently.
Some Factors That Affect Impeller Performance
Impeller Design Parameters
The hydraulic performance of the impeller depends on important design elements. These are impeller width, diameter and blade outlet angle.
Blade diameter and wrap angle affect pressure generation and flow patterns. Similarly width of impeller determines the level of friction losses and controls flow capacity. Therefore these parameters have to be carefully controlled in order to obtain desired proficiency.
Fluid Properties
Viscosity and density are the main fluid characteristics that determine the performance of impeller. Fluids with higher viscosity require more power to move which can decrease efficiency. Similarly density also affects the power required to move fluid. Higher density values increase load and wear on impeller.
Operating Conditions
These conditions are temperature, rotational speed and pressure which affect the performance of impellers. Higher temperatures decrease fluid viscosity which improves flow but increases the risk of cavitation. Besides that, higher pressures increase stress on impeller blades which causes fatigue and deformation. Consequently this affects operational reliability & hydraulic proficiency.
Hydraulic & Mechanical Efficiency
There are two types of efficiencies that impact performance of impeller.
Mechanical efficiency which includes the evaluation of power losses of seals, couplings and bearings. The second one is hydraulic efficiency in which energy losses are measured that occur between impeller and volute because of liquid friction.
The impeller’s peripheral velocity and vane geometry determine hydraulic performance whereas bearing condition & regular maintenance of its seals impact mechanical performance.
Cavitation
When pressure of fluid becomes lower than vapor pressure, it results in formation of vapor bubbles near impeller which is called cavitation. These bubbles burst with force which causes noise, pitting and lower efficiency. This cavitation damage can be prevented through correct pump design and proper net positive suction head management (NPSH).
To Sum Up
In short impellers are very important components in fluid dynamics that proficiently transfer energy in different applications. Their material selection and design along with operational controls make great difference in reliability and performance.
If you require any kind of custom impeller manufactured with outstanding quality, then RICHCONN is best option. You can contact us anytime.
Related Questions
Can impellers handle fluids with suspended solids?
Yes vortex and screw impellers have special designs to handle fluids with suspended solids. Their large passages prevent clogging and provide smooth flow.
What is the difference between a propeller and an impeller?
A propeller produces thrust for propulsion in open systems such as boats. On the other hand, in closed systems such as pumps, the impeller moves fluid and focuses on controlling flow and pressure.
What is the difference between an agitator and an impeller?
The agitator creates turbulence to mix fluid whereas impellers transfer energy to fluids to create flow or pressure in pump system.
Can impellers be coated to enhance performance?
Yes epoxy and ceramic coatings protect impeller surfaces from chemical and abrasive damage. These coatings increase corrosion resistance and decreases wear in harsh environments.
How does impeller design influence pump efficiency?
Blade angle and curvature in impeller design affect hydraulic efficiency by improving flow paths of fluids and reducing energy losses.
How do impellers differ in submersible pumps compared to standard centrifugal pumps?
Submersible pumps are designed with outstanding sealing and anticorrosion properties for underwater use. On the opposite, standard centrifugal pumps impellers require primary sealing and are used on above ground operations.
