When installing an axial fan, it is important to consider several factors relating to how it is mounted to the application. Ideally, when we choose an axial fan we could allow for lots of room on both the suction side and exhaust side of the fan to promote an even airflow into the fan and a controlled dispersal of the air on the exhaust side of the fan. Unfortunately, this may not always be possible to achieve and a compromise must be reached.
As a rule of thumb, the clearance (x) on the suction side and the exhaust side of the fan before an obstruction is reached should be at least 1/3rd of the diameter of the fan.
X >= diameter D x 0.33
e.g. For an axial fan of 450mm diameter, there should be at least 150mm of clearance between the fan and an obstruction to flow (Coil, Filter, wall etc…)
Mounting considerations – position of the fan in the system
The position of an axial fan in the application will affect its operating conditions. In the example below the choice for cooling an enclosure containing electronics dissipating a heat load is shown…
As mentioned above, the components of an axial fan are designed to promote a smooth laminar flow of air on to the impeller blade. A laminar flow will maximise the efficiency of imparting a force on the air to move it from the suction to the exhaust side of the impeller blade. On the exhaust side of the impeller blade, the flow will become random and turbulent if flow straightening devices are not used.
Placing the fan at the inlet and blowing into the enclosure is one option to consider. We can use the turbulent exhaust of the fan to spread the air around the enclosure. This will ensure that all surfaces of the components within the enclosure will encounter some of the cool supply air. Being turbulent the random air path will create more pressure in the system as the air makes its way towards the exhaust. More pressure in the system will create more noise from the fan and require more power to deliver the required airflow.
On the other hand, we could place the fan at the exhaust which will change the system characteristic. The air will follow the path of least resistance which means that some of the components will experience less cooling. The pressure in the system will be lower resulting in quieter operation and lower power consumption. The fan will see a higher operation temperature as the air passing over the motor will have an increased temperature caused by the dissipation of heat from the components inside the enclosure.
