How it Works?
An axial fan blade works on the same principle as how an aircraft wing generates lift. The wing of an aircraft has an aerofoil shape which as it is propelled forwards the air is diverted above and below the wing. The air above the wing has farther to travel than the air under the wing which results in a difference in air velocity above and below the wing. The higher velocity air stream above the wing has a higher dynamic force which results in a lower static pressure. Below the wing, the air is moving slower which means it has a lower dynamic force and higher static pressure. The difference in higher pressure below the wing and lower pressure above it generates lift.
In the case of a fan we use an impeller blade like an aerofoil however instead of generating lift we keep the fan blades rotating in a stable axis and this creates airflow. This follows Newton’s third law of motion that for each action there is an equal and opposite reaction. The air above the aerofoil is drawn into the fan by the reduction in static pressure and pushed out through the fan creating a positive pressure area.
To direct the airflow and obtain optimum performance, we use a mounting plate with a bell-mouth shaped inlet cone to create a smooth laminar flow into the suction side of the fan. The fan is held centrally in the mounting plate by the mounting guard which maintains a small tip clearance between the fan and bell-mouth.
There are other methods of mounting an axial fan including placing it in a plain diaphragm hole or in a short radius, however, these mounting methods compromise performance. Using a full bell-mouth mounting plate will ensure that optimum performance from the fan will be achieved.