Fans, blowers and compressors are differentiated by the method used to move the air, and by the system pressure they must operate against. American Society of Mechanical Engineers (ASME) defines fans, blowers, and compressors using the specific ratio, which is the ratio of discharge pressure to suction pressure.
Fans: A fan is a powered machine with rotating blades, typically made of plastic or metal, that create air flow through a fan. The rotating assembly of blades and hub is known as an impeller, rotor, or runner.
Blowers: Blowers are mechanical devices used to move air or gas by creating a flow of air through a system. Blowers generate continuous flow of air or gas at specific volume and velocity, unlike compressors that increase pressure.
Compressors: A compressor is a mechanical device or equipment used to increase the pressure of a gas or vapor by reducing its volume. In simple terms, it takes in a low-pressure gas and compresses it into a smaller volume, thereby raising its pressure.
Types of Fans
Fans fall into two general categories: centrifugal fans and axial fans:
Centrifugal fans, also known as centrifugal blowers, are a type of mechanical device used to move air or gas through a system by using the principles of centrifugal force. Fan housing draws air, directing it outward at a perpendicular angle to the incoming air direction. As the air moves outward, it gains velocity due to the centrifugal force generated by the rotating impeller blades.
Axial fans are a type of mechanical device used to move air or gas through a system by creating a flow of air in the same direction as the fan’s axis of rotation. These fans consist of a series of blades, known as propeller blades, mounted on a central hub. Fan blades rotate around hub, drawing air parallel to rotation axis and pushing it out in the same direction.
Centrifugal fan : types
Radial Blade Centrifugal Fan: This type features blades that are straight and extend radially from the hub. Radial blade fans are capable of handling particulate-laden air. These fans are industrial workhorses because of their high static pressures (upto 1400 mm WC) and ability to handle heavily contaminated airstreams. Because of their simple design, radial fans are well suited for high temperatures and medium blade tip speeds.
Forward-Curved Centrifugal Fan: In this type, the blades curve forward against the direction of rotation. They are used in clean environments and operate at lower temperatures. They are well suited for low tip speed and high-airflow work – they are best suited for moving large volumes of air against relatively low pressures.
Backward-Curved Centrifugal Fan: In contrast to forward-curved blades, the blades in this type curve backward against the direction of rotation. Backward-inclined fans are more efficient than forward-curved fans. These fans reach their peak power consumption and then power demand drops off well within their useable airflow range. Backward-inclined fans are known as “non-overloading” because changes in static pressure do not overload the motor.
Axial Fans: Types
The major types of axial flow fans are: tube axial, vane axial and propeller:
Tube axial fans are designed to move air or gases within a cylindrical duct or tube. They have a tubular housing that encases the fan blades and helps to direct the airflow. Tube axial fans have a wheel inside a cylindrical housing, with close clearance between blade and housing to improve airflow efficiency. The wheel turn faster than propeller fans, enabling operation under high-pressures 250 – 400 mm WC. The efficiency is up to 65%.
Vane axial fans feature guide vanes or stator blades positioned in front of the fan blades. These vanes help to improve efficiency and airflow direction control. Vane axial fans are similar to tube axials, but with addition of guide vanes that improve efficiency by directing and straightening the flow. As a result, they have a higher static pressure with less dependence on the duct static pressure. Such fans are used generally for pressures upto 500 mmWC. Vane axials are typically the most energy-efficient fans available and should be used whenever possible.
Propeller axial fan: This is the simplest type of axial fan, consisting of a set of blades mounted on a hub. The blades are typically flat and arranged in a circular pattern around the hub. Propeller fans usually run at low speeds and moderate temperatures. They experience a large change in airflow with small changes in static pressure. They handle large volumes of air at low pressure or free delivery. Propeller fans are often used indoors as exhaust fans. Outdoor applications include air-cooled condensers and cooling towers. Efficiency is low – approximately 50% or less.
Types of Blowers
Centrifugal Blower: Centrifugal blowers, also known as centrifugal fans, use an impeller with backward-curved, forward-curved, or radial blades to create a centrifugal force that accelerates the air or gas outward. Blowers are utilized in HVAC systems, industrial ventilation, and air pollution control for moderate to high pressure and low airflow volumes.
Axial Flow Blower: Axial flow blowers, similar to axial fans, move air parallel to the blower’s axis of rotation. They consist of propeller-like blades that generate a high volume of airflow at low to moderate pressures. These blowers are used in applications like cooling electronics, exhaust ventilation, and air circulation.
Positive Displacement Blower: Positive displacement blowers, also known as rotary lobe blowers or Roots blowers, use a pair of counter-rotating lobes to trap and transport air or gas from the inlet to the outlet. Blowers ensure consistent airflow in pneumatic conveying, wastewater treatment, and aeration applications.
Types of Compressors
Positive displacement compressors are a type of compressor that work by trapping a specific volume of gas and then reducing the volume to increase its pressure. These compressors operate using mechanical components that move gas in a cyclic manner, resulting in compression.
Dynamic compressors are a type of compressor that work by imparting kinetic energy to gas and then converting that kinetic energy into pressure. These compressors operate by continuously adding velocity to the gas and then slowing it down to raise its pressure.
Positive Displacement Compressors: Types
Rotary Compressor: A rotary compressor is a type of compressor that uses a rotating mechanism to compress gas or air. The design of rotary compressors allows for continuous and smooth compression, making them efficient and suitable for various applications.
Reciprocating Compressor: A reciprocating compressor is a type of positive displacement compressor that uses a reciprocating piston mechanism to compress gas or air. Compressor draws gas into cylinder during intake stroke, compresses it as piston moves back and forth.
Rotary Compressor: Types
Rotary Vane Compressor: Rotary vane compressors consist of a rotor with sliding vanes that move along the inner surface of a cylindrical chamber. Rotor turns, gas enters expanding volume, compressed as volume decreases, causing expansion and compression. These compressors are known for their reliability and quiet operation and are used in applications with moderate pressure requirements.
Rotary Screw Compressor: Rotary screw compressors use two interlocking helical rotors to compress gas. The rotors rotate in opposite directions, and gas is trapped in the space between them and the compressor housing. As the rotors mesh, gas is compressed as the available volume decreases. These compressors are commonly used for generating compressed air in industries like manufacturing, construction, and automotive.
Scroll Compressor: Scroll compressors use two spiral-shaped scrolls—one stationary and the other orbiting—to compress gas. Gas is drawn into the outer regions of the spirals and then trapped and compressed as the scrolls move closer together. Compact compressors offer efficiency, smooth operation, and are commonly used in air conditioning, refrigeration, and heat pump systems.
Reciprocating Compressor: Types
Single-Acting Reciprocating Compressor: In this type, gas is compressed on only one side of the piston during each stroke. Intake, compression, and exhaust strokes occur on the same piston side, while the opposite stroke occurs on the opposite side. Single-acting compressors are simpler in design and are often used for low to moderate pressure applications.
Double-Acting Reciprocating Compressor: In this type, gas is compressed on both sides of the piston during each stroke. Both sides of the piston have intake, compression, and exhaust strokes. Double-acting compressors are more efficient and can handle higher pressures compared to single-acting compressors.
Diaphragm Reciprocating Compressor: Diaphragm compressors use flexible diaphragms instead of pistons to compress gas. The diaphragms move back and forth to create pressure differentials that compress the gas. Compressors prioritize gas purity with diaphragms for separation between compressed gas and mechanical components.
Dynamic Compressor: Types
Centrifugal Compressor: A centrifugal compressor consists of an impeller with curved blades that rotates within a casing. Gas enters impeller, propelled outward by centrifugal force from high-speed rotation. Gas moves outward, increases velocity, enters diffuser, converts kinetic energy into pressure. Centrifugal compressors handle high flow rates and pressures in industrial processes, HVAC systems, and gas pipelines.
Axial Compressor: Axial compressor uses rotating and stationary blades to accelerate gas in an axial direction. The gas passes through multiple stages of rotating and stationary blades, with each stage contributing to a higher pressure rise. The kinetic energy imparted to the gas is gradually converted into pressure as it moves through these stages. Axial compressors are essential in jet engines, gas turbines, and power generation for high efficiency and power output.
Applications of Fans, Blowers, Compressors
Fans, compressors, and blowers have diverse applications across various industries due to their ability to move air and gases. Here are some common applications for each:Fans:
- Ventilation and Air Conditioning: Fans are extensively used for general ventilation in buildings, homes, and industrial facilities. They also play a crucial role in air conditioning systems by distributing conditioned air throughout spaces.
- Cooling Systems: Fans are used in radiators and heat exchangers to dissipate heat from engines, electronics, and industrial machinery.
- HVAC Air Distribution: Fans are used to circulate air within HVAC ductwork to ensure even distribution of conditioned air.
- Industrial Processes: Fans control temperatures, remove fumes, and provide ventilation in industrial processes like manufacturing, welding, and chemical production.
- Drying and Dehumidification: Fans are employed to facilitate drying processes in industries such as food processing, paper manufacturing, and textiles.
Blowers:
- Industrial Ventilation: Blowers are used to provide fresh air and remove pollutants in industrial environments like factories and chemical plants.
- Wastewater Treatment: Blowers provide air for aeration processes in wastewater treatment plants, aiding in the breakdown of organic matter.
- Pneumatic Conveying: Blowers transport bulk materials in food processing and agriculture industries using pneumatic systems for efficient transportation.
- Biogas Generation: Blowers are used in biogas production systems to maintain proper airflow for anaerobic digestion.
- Aquaculture: Blowers supply oxygen to water in fish farms and aquaculture systems to support aquatic life.
Compressors:
- Industrial Processes: Compressors increase gas or air pressure in industries for processes like pneumatic conveying and material handling.
- Oil and Gas: Compressors are used in oil refineries and natural gas processing to transport and compress gases for distribution.
- Air Compression: Compressors are used to provide compressed air for power tools, machinery, and pneumatic systems in manufacturing and construction.
- Refrigeration: Compressors are a core component of refrigeration systems, compressing refrigerant gases to facilitate heat exchange and cooling.
- Aerospace: Jet engines and aviation systems use compressors to compress air before combustion for efficient propulsion.
Fans, compressors, and blowers serve various industries, ensuring indoor air quality, enabling processes, and transporting materials, showcasing their diverse functions.