What is High Temperature Blower and Why Do We Use Them?

Posted by Sam Pelonis | Apr 20, 12:12:40 AM 0 Comments

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Both fans and blowers are commonly used equipment for cooling and providing air circulation throughout buildings, internal spaces, outdoor environments, and more. They're also vital components in HVAC systems. While 'fans' and 'blowers' are often considered synonymous, they each have different functionalities, advantages, and applications.

Fans vs. Blowers

Because fans and blowers are used as interchangeable terms, it's important to be clear about what you need for your specific application. Consider how the two differ in terms of functionality, common applications, and unique benefits.

Function

Blowers are electromechanical systems that direct air to a certain point or in a particular direction by means of a fan and controlled channels. Fans themselves are electrical devices that move the air. Fans can also exist separately from blowers to circulate air throughout a space without a specific destination for the air. Picture a blower as a whole assembly with a channel, or an inlet and outlet, that surrounds the fan so large volumes of air can be pumped in a specific direction. The interior fan has small blades and uses centrifugal force to push the air outward; blowers also provide some degree of air pressurization to drive it out and forward. A fan, on the other hand, consists of blades arranged around a central point and a motor that powers the fan and drives the blade motion. Fans are generally powered by electric motors, but some models can use internal combustion engines or hydraulic motors. When you're determining whether you need a fan or blower based on functionality, keep these two rules in mind:

1. Blowers operate at moderate pressure, with an air pressure ratio of 1:1.1 to 1:1.2, and fans move large volumes of air with little to no change in air pressure.
2. Blowers direct air in a specific direction, while fans circulate air throughout a defined space.

Applications

Fans and blowers are used for very different applications. The two common applications of fans are:

• Cooling areas by moving the air
• Ventilating spaces, such as living areas

The common applications of blowers are:

• Drying goods and surfaces by forcefully directing air toward it
• Cleaning surfaces and areas, like a leaf blower
• Increasing the size of a fire

Benefits

Both assemblies have key benefits that will make them useful in your facility. The unique advantage of selecting a fan is its energy efficiency. They use less electricity than blowers that move the equivalent amount of air. Blowers, on the other hand, are advantageous because of the direct airflow and power they provide. Blowers also have a lower initial purchase price.

Should You Use a Fan or a Blower?

Now that you know more about the different uses and advantages of fans and blowers, you can better select the right fit for your needs. Consider these factors:

• Pressure:
  • If you need a tool that increases air pressure, choose a blower.
  • If you need air pressure to remain the same, choose a fan.
• Power Source and Availability:
  • If you have more power available, you can choose a blower.
  • If you have less power available, choose a fan.
• Air Flow Requirements:
  • If you need to direct air in a specific direction, choose a blower.
  • If you need indirect airflow throughout a space, choose a fan.

Based on the particular functions and capabilities you need, there are multiple different fans and blowers to choose from. Fans come in axial, centrifugal, and cross-flow fans, each of which provides different types of air motion; blowers are available in centrifugal and positive displacement models, which use different types of force to move the air from the inlet through the outlet and in a specific direction.

Fans and Blowers From Pelonis Technologies

At Pelonis Technologies, we provide standard and customized fan and blower systems for commercial and industrial clients. For over 25 years, we've been delivering innovative air movement solutions, and we’re here to help you choose the best option for your needs. Contact us today to learn more about our capabilities, or request a quote to get started.

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By Aaron Saldanha, Howden 

This article appeared in the edition of AMCA inmotion magazine.

In a high-temperature manufacturing environment, failure of a fan can have a devastating effect on operations. To specify a fan for maximum service life, it is important to understand factors influencing fan design and construction.

Whether it is optimizing the mix and temperature of a chemical composition in a petrochemical plant, regulating process conditions in a metal furnace, or simply circulating hot air through an industrial bakery oven, fans play a critical role in many manufacturing operations. It should come as no surprise, then, that failure of these fans can have dire consequences. This is especially true with high-temperature applications, given that, when a fan fails, the system typically needs to be shut down. Once a replacement fan is installed, the system may take a few days to reach its optimum temperature, resulting in significant productivity loss.

The key to ensuring proper selection and construction of a fan for a high-temperature environment is good communication between the consulting engineer or end user and the manufacturer by way of the specification. This article will discuss important considerations that go into the selection and construction of a fan for a high-temperature environment.

For temperatures greater than 1,550°F (843°C), many manufacturers use special casting alloys to reduce welding and mitigate issues caused by thermal creep. Often, this increases both costs and lead time.

There is no formal definition of high-temperature fan. Most industrial-fan manufacturers, however, consider a high-temperature fan to be a fan capable of withstanding operating air-stream temperatures 250°F (approximately 120°C) and higher. Air-stream temperature is the temperature of air/gas inside of a fan; it is different from ambient temperature, or the temperature of the air surrounding the motor, bearings, and external accessories of a fan (Figure 1). It is important to understand how these two temperatures impact the design of a fan.

High-Temperature Air Streams, Continuous Operation

A high-temperature fan can fail in a number of ways.

Wheel failure. Wheel failure can be evidenced by not only breakage, but distortion. One of the main contributing factors is thermal creep. Fan manufacturers account for thermal creep through proper selection of the materials of construction of air-stream components (Table 1).

Drive arrangement. ANSI/AMCA Standard 99 | Standards Handbook prescribes drive configurations for different types of fans. With high-temperature fans, the bearings must be outside of the air stream. For these fans, then, Drive Arrangement 1 (two bearings mounted on a pedestal and the wheel overhung to one side), 2 (similar to Arrangement 1, except the bearing pedestal is supported by the fan housing), 8 (similar to Arrangement 1, but with a smaller “outrigger” motor or turbine base connected to the bearing pedestal), or 9 (similar to Arrangement 1, but with the motor mounted on the fan, rather than on the “floor”) typically is recommended. For double-width fans or applications requiring Drive Arrangement 3 (a bearing bracket-mounted on each side of the housing or wheel), an inlet box with the bearings outside of the air stream is recommended (Figure 8). The extended shaft length needed to account for the inlet boxes often presents a design challenge, however.

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Drive Arrangement 4 (the wheel directly mounted on the motor’s shaft and bearings) is restricted by the maximum allowable temperature at the motor shaft, which usually corresponds to an air-stream temperature of 250°F (approximately 120°C). Some manufacturers use a custom motor to achieve air-stream temperatures of 450°F (approximately 230°C) for a Drive Arrangement 4 fan. For certain high-temperature applications, such as tunnel ventilation, axial fans with the motor in the air stream are used. These are rated for use for only a short period (i.e., 1.5 to 2 hr), however. This will be covered further in the “Applications of High-Temperature Fans” section.

Housing design. Expansion of housing material needs to be accounted for in housing design. With centrifugal fans, this is particularly important in defining the axial and radial gap between wheel and inlet. With axial fans, tip gap (Figure 9) is increased to account for thermal growth attributed to elevated temperature. When these fans are run at standard temperature, their efficiency will be lower, as the higher the tip gap, the lower the efficiency.

Sealing/semi-gastight construction. Although, depending on their size and method of construction, many fans cannot be made 100-percent gastight, precautions can be taken during design to reduce the impact of hot-gas leakage. For higher temperatures, use of a mechanical shaft seal is recommended. The body and internal components of the seal must be designed to handle the air-stream temperature. In many cases, a carbon ring seal with nitrogen purge (Figure 12) is used not just to improve sealing efficiency, but to cool the seal.

When using a gasket on a high-temperature fan, ensure the gasket is rated for the air-stream temperature. This is especially important when replacing gaskets during fan maintenance.

Motors and VFDs. In many cases, there is a power-saving advantage to using a variable-frequency drive (VFD) on a high-temperature fan. Consider, for example, a requirement to move 33,000 cfm (15.57 m3/s) of air with 10.2 in. w.c. (2,538 Pa) of static pressure at an air-stream temperature of 450°F (232°C), which corresponds to an operating density of 0.044 lb/ft3 (0.705 kg/m3). At this operating condition and density, a 40.2-in.- (1,021 mm) diameter centrifugal fan operating at 1,770 RPM would absorb 67 hp (50 kW) of power and require a 75-hp (55 kW) motor if used with a VFD. The fan would start at approximately 30 Hz when the system is at ambient temperature (70°F/20°C) and slowly speed up as the system temperature increased. At the rated operating temperature, the fan speed would be the rated speed of 1,770 RPM (Figure 13). If a VFD were not used, the power needed to start the fan when the system is at ambient temperature would be 114 hp (85 kW), and a 125-hp (93 kW) motor would be required. Apart from the motor cost, the owner would need to invest in panels/cables rated for 125 hp, as opposed to 75 hp. In many cases, this would be more expensive than a VFD. That being the case, it always is beneficial to do a cost-benefit analysis when investing in a high-temperature fan.

High-Temperature Ambient Conditions, Continuous Operation

As mentioned earlier, the temperature of the air surrounding motors, bearings, belts (drive arrangements 1, 3, 9, and 10), and all other outside-the-air-stream accessories requires precautions.

Motors. The temperature of the air surrounding a totally enclosed, fan-cooled motor should not exceed the temperature for which the motor was rated. If it does, the motor’s temperature can be lowered through the use of a water jacket or an external cooling system. Ensure the motor’s bearings and lubrication are designed for the temperature requirement.

Bearings. In many high-temperature applications, an oil-circulation system is used to ensure bearing temperatures are maintained (Figure 14).

Applications of High-Temperature Fans

Depending on a fan’s intended use, the amount of time the fan can be expected to be exposed to high-temperature air can vary. Thus, a fan can be rated for a short, defined duration or it can be rated for continuous operation.

Take, for example, main ventilation fans and jet fans used in a roadway or transit tunnel. Because their purpose is to evacuate air in the event of a fire, these fans are rated for a short duration, normally 1 or 2 hr. Most other fans, such as those for petrochemical processing and those for forced circulation or recirculation of air or gas in furnaces, ovens, kilns, and dryers, are rated for continuous operation.

Conclusion

Most high-temperature applications have unique requirements that can make fan specification complicated. The key is identifying the system information the fan manufacturer needs to design and supply a product optimized for the application.

Are you interested in learning more about High Temperature Blower? Contact us today to secure an expert consultation!