Cooling fans are used in a variety of applications. Just to give two or three examples, they can be installed in air cooled heat exchangers or air cooled condensers to keep appliances from overheating. Or they can be incorporated into cooling towers for power stations.
For whatever application, you want your cooling fan to be durable, powerful, efficient and to provide a minimum of noise.
Some cooling fans come with individually adjustable blades. This can allow you to adjust the pitch of each blade so that the fan provides as much cooling as you need while placing a minimum of load on the motor. Look for a fan that is engineered to be low noise. Some will even come with the description very low noise for an extra measure of quiet.
Super low noise cooling fans are also available. Typically, these fans will have an advanced, aerodynamic blade design. That means it is not just the motor thats being quiet. Blades can be specially designed to produce a minimum of turbulence, making the air flow as quiet as possible as well. These designs can help you to meet noise abatement requirements without skimping on the cooling.
Not every fan needs to have adjustable blades. If you are using the fan for a cooling tower or in an air cooled condenser, a fan with fixed pitch blades is all you need. In fact, you are better off with fixed pitch blades if they are suitable for your application. Assembled at the factory and firmly fixed in place, these blades dont go out of kilter or require fine tuning.
If your application is a field erected cooling tower or an air-cooled steam condenser, look for a fan that represents itself as specifically designed to operate at peak efficiency in those environments.
Fan blades can be made out of aluminum or fiberglass reinforced polyester. Either type should be able to withstand a fair amount of heat and stay rigid and properly directed. The blades can range in size from under 2 1/2 feet to over 6 1/2 feet in length. Somewhere in that range, you should be able to find a fan that fits your needs.