Axial Fans for Cooling Towers, Air-Cooled Condensers and Heat Exchangers

Cooling is the largest single use of axial fans in industry. Every cooling tower, closed-circuit cooler, air-cooled condenser, and air-cooled heat exchanger uses fans to move air across a surface that rejects heat. These duties are ideal for axial fans, with high volumes at low resistance, but they are hard on equipment: wet, corrosive, hot, and often outdoors year-round. This page explains how airflow relates to heat rejection, what is different about wet and dry cooling, and where our range fits, since the biggest cooling-tower fans are far larger than we build.

Where Axial Fans Fit

Equipment	How the fan is used	Notes
Cooling towers (small and medium)	Induced or forced draught through fill	Wet, corrosive, drift
Closed-circuit coolers	Air over a coil, with spray	Wet and sometimes hot
Air-cooled heat exchangers (dry coolers)	Air across finned tubes	Dry, outdoors
Air-cooled condensers	Air across condenser coils	Dry, large installations
Very large industrial cooling towers	Very large fan diameters	Outside our range

Fan diameter is the key limit. Our fans reach 1,600 mm. Small towers, closed-circuit coolers, and dry coolers built from banks of modest fans suit that range well. Very large towers and large air-cooled condensers use much larger fans, and we do not cover them.

From Heat Load to Airflow: A Worked Example

For a dry cooler or air-cooled heat exchanger, the sensible heat carried away by the air is:

Airflow = heat load ÷ (air density × specific heat × air temperature rise)

Example. A dry cooler must reject 1,500 kW. The air is allowed to warm by 12 K as it passes through the coil. Ambient air is 40 °C at sea level, with a density of 1.127 kg/m³.

Airflow = 1,500 ÷ (1.127 × 1.006 × 12) = 110.3 m³/s, or about 396,900 m³/h.

This is not one fan. A bank of three fans of about 132,300 m³/h each fits within our range, each at about 72% of the range maximum, with room for staged control. Wet cooling towers work differently, since evaporation carries most of the heat, but the principle of relating airflow to duty and splitting it across fans holds. See how to size an axial fan.

Design Ambient and Recirculation

Cooling performance depends on the outside air temperature, and equipment is sized for a design ambient. Hot climates reduce capacity because the air is warmer and thinner. At 45 °C at sea level, density is about 92% of standard, so a fan of a given speed moves the same volume but a lower mass of air. Check capacity at the highest ambient the plant will see.

Hot air recirculation is a real and common problem. When hot discharge air is pulled back into the inlet, for example because of wind, nearby walls, or another cooler, the effective inlet temperature rises and capacity falls. Layout, spacing, and discharge velocity matter as much as the fan.

Wet Duty and Corrosion

Cooling towers and closed-circuit coolers put fans in humid, wet air with chemically treated water, sometimes with drift and salt. Fan materials and coatings must suit that: corrosion-resistant metals, protective coatings, or fibre-reinforced plastic, with attention to fasteners and to the motor. Motors in wet duty need high ingress protection and suitable sealing. See corrosion-resistant axial fans.

Control and Energy

Cooling loads vary with the weather and process, and fans run for thousands of hours a year, so control matters more here than almost anywhere. Speed control follows the load with the cube-law saving, and staged operation of several fans adds redundancy. Because the fans are outdoors and long-running, energy is usually the largest cost. See adjustable pitch versus VFD control and fan laws explained.

Noise

Cooling equipment often runs at night near communities, and boundary noise limits commonly apply. Fan tip speed is a strong driver of noise, so larger fans at lower speed, attenuators, and sensible layout all help. See axial fan noise.

Vibration, Blade Tip Clearance, and Protection

Fans on cooling equipment are often protected by vibration switches that trip the fan if it becomes unbalanced, for example from ice, damage, or a lost weight. Blade tip clearance to the shroud affects efficiency and noise, and thermal and structural movement can change it. Routine inspection of blades, hubs, and supports, and vibration trend monitoring, prevent failures. See axial fan vibration, balancing and maintenance.

Where Our Range Fits

NextAir Systems manufactures axial fans with impeller diameters up to 1,600 mm, static pressure up to 2,400 Pa, and air volume up to 185,000 m³/h. That covers small towers, closed-circuit coolers, dry coolers, and air-cooled heat exchanger bays built from fans of that size. Very large cooling-tower fans and large air-cooled condenser fans are outside what we build, and we will say so early instead of forcing a selection.

What to Specify

1. Heat load and the air-side temperature rise, or the manufacturer’s required airflow.
2. Design ambient temperature, altitude, and humidity.
3. Wet or dry duty, and water chemistry for wet duty.
4. Fan diameter limits, number of fans, and layout.
5. Control approach and redundancy.
6. Corrosion, coastal, and noise conditions.
7. Vibration protection and monitoring.

Get a Fan Selection for Your Cooling Equipment

Send your heat load, design ambient, and layout, and we’ll size the fans and confirm the arrangement. Contact us for a free quote.

Frequently Asked Questions