Application of Axial Fans

One of the most common applications for axial fans is cooling by transferring heat to ambient air. The process stream to be cooled can be either a liquid or a gas.

The heat exchanger equipment utilized for this heat transfer is divided into three primary categories:

1. Direct Contact Cooling: In this category, the fluid, such as water, is in direct contact with the air and is cooled by sensible and latent heat exchange. This type of equipment includes factory-assembled cooling towers and field-erected cooling towers.
2. Tube Cooling with Water Flow: Here, the liquid or gas within the tubes is cooled or condensed by water flowing over the tubes. The water then comes in direct contact with the air. This type of equipment includes closed-circuit cooling towers and evaporative condensers.
3. Air Cooling of Tubes: In this category, the process liquid or gas inside tubes is cooled or condensed by air passing over the tubes. This type includes air-cooled condensers and air-cooled heat exchangers.

Each of the different product types has different operating and performance characteristics. Consequently, they have varying fan requirements:

Factory-Assembled Cooling Towers

Constructed in a factory and transported by truck to the installation location. They find utility in both HVAC and industrial applications, with fan sizes typically ranging from 4 to 13 feet in diameter. The primary considerations for these applications are corrosion resistance and noise control.

Field-Erected Cooling Towers

Large, custom-designed structures for specific locations and applications. The components are manufactured and shipped to the project location, where the cooling tower is then assembled in the field. These towers find applications in power plants and larger industrial facilities. The fans for this purpose can exceed 40 feet in diameter and have very large drive systems, e.g., 200 - 400 HP (150 - 300 KW). The significant number of components within the cooling tower structure can interact with the fan in various ways, sometimes unexpectedly. Therefore, it is crucial for the fan design to exhibit high structural integrity and a low resonance potential or vibration stability. Corrosion-resistant fan materials are imperative for applications in corrosive environments, such as sea water cooling.

Evaporative Condensers and Closed Circuit Cooling Towers

They find applications in both HVAC and industrial settings. These are predominantly factory-assembled products, transported by truck to the installation location. The fan requirements for this application align closely with those for package cooling towers.

Air-Cooled Heat Exchangers

These serve as devices for cooling or condensing process fluids within finned tubes. Depending on the exchanger's size, they can be transported fully assembled or in components for field assembly. The fans for these applications typically range in size from 4 to 22 feet. In larger units, structural components may interact with the fan, leading to undesirable vibrations. It's crucial for the fan design to have high structural integrity and a low resonance potential or vibration stability.

Air-cooled condensers are often substituted for field-erected cooling towers in power stations where fresh water is limited or nonexistent. These installations can be extensive, consisting of 50 to over 300 fans. The fans used in these applications share similar requirements with those for field-erected cooling towers, except there's generally a reduced need for corrosion-resistant materials. However, due to the size and method of support, vibration control becomes paramount.

Catastrophic failures can lead to expensive corrective action programs. Also, considering the large quantity of fans deployed, fan efficiency and energy consumption become crucial concerns.

Industrial Ventilation

This is a critical application for axial fans. Generally ranging in diameter from 3 to 8 feet, these fans are crucial for applications requiring very high static pressures. Consequently, fans are designed to operate at exceptionally high tip speeds.

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