High-velocity centrifugal blowers and fans have numerous uses and applications in various industrial fields. They are constant-volume devices that can move a constant volume of air, making them ideal for many applications. But how exactly do high-velocity centrifugal blowers and fans work?
High-velocity centrifugal blowers and fans change the direction of airflow. Air enters in one direction but is usually expelled at a 90° angle perpendicular to the inlet. As the air passes around the impeller, the velocity and air pressure increase, generating a strong flow of air.
There are different kinds of centrifugal blowers and fans, and each can be used in different ways depending on a few factors. Let’s examine high-velocity centrifugal fans and blowers more closely to see how they work and how you can make them work for you.
How High-Velocity Centrifugal Fans And Blowers Work
The working of a high-velocity centrifugal fan is highly dependent on its impeller. (photo)
Impeller Design And Centrifugal Force
The critical component of a centrifugal fan is the impeller. The impeller consists of a set of curved blades, typically arranged in a radial configuration around a central hub. It is connected to a rotating shaft driven by a motor or engine (usually electric). As the motor spins the shaft, the impeller blades also rotate rapidly.
When the impeller rotates, it creates a centrifugal force. This force acts on the air molecules around the blades, pushing them away from the centre of rotation and toward the outer edges of the impeller. The centrifugal force generates a pressure gradient, causing the air to move radially outward.
The amount of air pressure generated is directly related to the speed at which the impeller rotates.
Air Inlet And Flow
The air enters the centrifugal fan through the air inlet at the impeller’s centre. As the impeller rotates and creates centrifugal force, the air is drawn into the impeller from the surroundings. The impeller then accelerates the air outward due to the centrifugal force acting on it.
Diffuser Or Scroll
Once the air leaves the impeller, it enters a diffuser or scroll housing. This housing is designed to guide and direct the high-velocity, low-pressure air from the impeller into a higher-pressure, lower-velocity airflow. The diffuser allows the air to gradually decelerate, converting the kinetic energy gained from the impeller into static pressure.
Velocity Profile And Outlet
The airflow in a centrifugal fan experiences a velocity profile. This means that the air at the outer edge of the outlet has a higher velocity than the air closer to the centre. This velocity profile is a result of the varying centrifugal forces acting on the air particles as they move from the impeller to the outlet.
At the outlet, the airflow is directed at a different angle from the inlet, typically exiting at a 90° angle perpendicular to the inlet, unlike axial flow fans that produce airflow parallel to the impeller’s rotation axis.
The angular output allows the airflow to have higher velocity while maintaining high pressure. This distinct airflow direction makes centrifugal fans suitable for various applications where specific airflow patterns are required.
The Versatility Of High-Velocity Centrifugal Blowers And Fans
By their very nature, high-velocity centrifugal fans and blowers are versatile and can be used in many unique scenarios.
Blowing And Extraction: Dual Functionality
A significant part of a centrifugal fan’s versatility lies in its dual functionality, which is fully reversible. By default, the air inlet will take in air and expel it from the outlet. Still, if you reverse what is considered the standard inlet and outlet, you can turn the fan or blower into a powerful extraction fan to quickly expel air from an environment.
This function can be especially useful in gaseous or chemical-filled environments where it’s of utmost importance to remove contaminated or unsafe air as quickly as possible.
Hot Air Applications
Hot air applications with centrifugal fans are prevalent in numerous industries requiring controlled and efficient heating. The combination of centrifugal fans and process air heaters enables the distribution of heated air to specific areas, making it a versatile solution for a wide range of processes, including:
- Industrial drying. In industrial settings, drying processes are essential for removing moisture from various materials. Centrifugal fans are utilised to blow hot air over wet or damp surfaces, accelerating the evaporation process.
- Space heating. Centrifugal fans are widely used in space heating applications where hot air is distributed throughout a building or a specific area to maintain comfortable temperatures. It can be used in industrial, commercial, or residential areas, but due to the level of noise generated by centrifugal fans, residential uses are mainly limited to large apartment buildings.
- Paint drying and curing. Hot air is used to dry and cure paint or coatings on surfaces in the automotive and furniture industries. Centrifugal fans help evenly distribute the heated air, resulting in faster drying times and improved finish quality.
- Heat treatment processes. Heat treatment is vital in metallurgy, where metal parts are heated to specific temperatures and then cooled to enhance their properties. Depending on the required temperatures, centrifugal fans can aid in heating the furnaces used for heat treatment, ensuring uniform temperature distribution and precise control over the heating process.
- Powder coating. Powder coating is a popular way to apply a protective and decorative finish to various products. Centrifugal fans are used to distribute hot air in the curing ovens, where the powder-coated items are heated, melted, and cured, creating a durable and attractive finish.
- Crop drying. In agricultural practices, particularly in areas with high humidity or during unfavourable weather conditions, centrifugal fans are used to dry harvested crops such as grains, nuts, and seeds. This prevents spoilage and ensures the crops can be stored safely for extended periods.
- Plastic processing. Hot air is employed in plastic welding and thermoforming processes in plastic manufacturing. Centrifugal fans help deliver the required heat to join or mould plastic components effectively.
- Shrinkwrapping. In packaging applications, shrink wrapping involves covering products with a plastic film that contracts and adheres tightly when exposed to heat. Centrifugal fans are used to direct hot air to the wrapped products, creating a sealed and tamper-resistant package.
- Textile drying. In the textile industry, after dyeing or printing fabrics, centrifugal fans assist in drying the textiles quickly and uniformly, improving production efficiency.
- Bakery and food processing. Centrifugal fans are used in baking ovens to circulate hot air evenly, ensuring that the baked goods are cooked thoroughly and achieve the desired texture and appearance.
Hot Air Recirculation
In some cases, and where it’s deemed safe after careful design consideration, it’s possible to recirculate hot air back into the centrifugal fan’s inlet to be used again. This improves a company’s energy efficiency since it’s not always necessary to reheat air, which also cuts operating costs.
Typical Applications For Centrifugal Fans/Blowers
Apart from their various uses with heating and drying systems mentioned before, high-velocity centrifugal fans are also used in many other applications.
Water Aeration
In aquaculture and fish farming, water aeration is crucial to maintain adequate oxygen levels in the water. Those who operate fish farms often use centrifugal fans to create bubbles or agitation on the water’s surface, which increases oxygen transfer and promotes a healthier environment for aquatic life.
Heating Components
As we’ve already seen, centrifugal fans are integral components in various heating systems, including space heaters, industrial furnaces, and HVAC systems. They distribute heated air effectively, ensuring uniform temperatures in both residential and industrial settings.
Cooling
Though centrifugal fans work differently from axial flow fans, they are still fans. Because of this, centrifugal fans play a vital role in cooling applications, especially in air conditioning units, refrigeration systems, and radiators. They draw in ambient air and propel it over cooling coils or heat exchangers to dissipate heat and lower temperatures.
The uses for this can range across many industries, primarily industrial applications. However, they can also be used in air conditioning, though not commonly for residential purposes due to the high level of noise centrifugal fans can generate.
Ventilation
Adequate ventilation is essential in buildings, mines, tunnels, and confined spaces to maintain proper air circulation and remove pollutants or stale air. Centrifugal fans are commonly used in ventilation systems, ensuring fresh air exchange and improving indoor air quality.
Again, due to the noise level, residential applications of centrifugal fans for ventilation are mainly limited to large apartment buildings, not houses or smaller structures.
Industrial Drying
Centrifugal fans aid in drying processes in manufacturing and processing industries, such as food processing, pharmaceuticals, and chemicals. They accelerate the evaporation of moisture from products, ingredients, or materials, leading to improved efficiency and reduced production times.
For drying systems, centrifugal fans can be combined with heating systems or used without them, depending on the specific requirements of the products that require drying.
Dust And Gas Extraction
Industries that produce dust, fumes, or harmful gases need efficient extraction systems to maintain a safe and clean working environment.
This is where the reversible nature of centrifugal fans comes in very handy. Centrifugal fans are employed in dust collectors and gas extraction systems to remove contaminants like dust, chemicals, or smoke from work areas and filter or expel them outside. This is vital for ensuring a healthy working environment and preventing cross-contamination in some industries.
Gas Boosting
One of the primary benefits of a centrifugal fan is its capability to create stable air pressure. In applications where low-pressure gases must be compressed or boosted to higher pressures, centrifugal fans can be utilised to achieve the desired pressure levels. This is commonly seen in natural gas pipelines and other gas distribution systems.
Pneumatic Conveying
Some industries use industrial blowers as conveying systems to transport solid materials through pipelines. They are called pneumatic conveying systems, and these blowers use centrifugal fans. The centrifugal fan creates the necessary air pressure to propel the materials from one point to another efficiently, which cannot usually be done with axial flow fans.
Air Pollution Control
Most industries have strict environmental regulations these days since most countries have employed strategies and legislation to reduce their carbon footprint. Companies often use centrifugal fans in air pollution control systems such as scrubbers and catalytic converters in such industries.
These systems effectively capture, filter, and process contaminants before releasing exhaust gases into the atmosphere. Centrifugal fans can provide the required pressure to ensure these systems work as they should.
Fume Hoods And Laboratory Exhaust Systems
In laboratories and chemical processing facilities, fume hoods and exhaust systems are utilised to protect workers from harmful fumes and chemicals. These contaminants must be taken out of the facility as quickly as possible to prevent poisoning or other harm, and the best way to ensure quick removal is a high-pressure system.
That’s why centrifugal fans (in reverse configurations, acting as extractor fans) are critical components in these setups because they ensure that the fumes are captured and vented away from the workspace quickly and efficiently.
Grain Handling
We’ve already seen how the agriculture sector often uses centrifugal fans to dry crops in adverse weather conditions, but their uses aren’t limited based on the weather. Centrifugal fans can also be used in grain handling and storage facilities to aerate and cool stored grains.
Proper aeration helps prevent spoilage and maintains grain quality during storage, lengthening the grain’s storage life and ensuring that it can be sold and used for longer than it could without the use of centrifugal fans.
Material Handling
Centrifugal fans aid in material handling processes, such as pneumatic transport in cement plants, sawdust collection in woodworking facilities, and handling various bulk materials in industrial settings.
Sewage Aeration
Aeration is an essential aspect of sewage treatment because it boosts the aerobic biodegradation of organic materials, speeding up the sewage treatment process. Centrifugal fans are the logical solution because sewage aeration systems require consistent high air pressure levels.
Conclusion
High-velocity centrifugal fans (or blowers) are powerful devices that can boost air pressure and maintain it at a consistent level, which depends on the speed of the fan’s rotation. They work by passing the air through an impeller and expelling it at a different angle from the inlet, which is usually 90 degrees perpendicular to the inlet airflow.
These fans have numerous industrial, commercial, and even residential uses. Still, they benefit industries that face requirements like air purification, pressure stabilisation, pneumatic conveyors, and aeration of any liquid. With that list, there’s no doubt that almost any industry will require centrifugal fans at some point.
References
https://www.sciencedirect.com/topics/engineering/centrifugal-fan
https://www.dynamicfan.com/what-is-a-centrifugal-fan-used-for/
https://uk.rs-online.com/web/content/discovery/ideas-and-advice/centrifugal-fans-guide
https://secomak.com/wp-content/uploads/2022/08/Secomak_Model-575-1_14-02_23web.pdf
