A centrifugal fan pulls air in at the centre and throws it out sideways into a spiral casing. Use the view to look inside and follow the air from the inlet eye, around the impeller, into the scroll and out of the outlet.
A centrifugal fan moves air the way a centrifugal pump moves water. Air is drawn into the centre of a spinning wheel with many short blades, then thrown outward into a casing shaped like a spiral. Because the spiral passage widens, the fast-moving air slows and builds pressure, so the fan can push air through long ducts rather than just stirring it.
From outside it is just a box with an inlet and an outlet. The wheel, the blades and the spiral casing that actually move the air are all hidden inside, so a cutaway is the only way to see how the spin and the scroll work together to build a useful airflow.
The spinning impeller lowers the pressure at its centre. Outside air is then pushed in through the round inlet eye, flowing straight into the middle of the wheel.
Short blades around the rim catch the air and throw it outward at high speed. This is where the wheel gives the air its energy โ like a pump impeller throwing water, it adds speed, not pressure.
Air leaves the impeller all around its rim. The spiral casing gathers all of it and steers it round in one direction toward the outlet.
As the scroll wraps around, its passage gets steadily wider. The fast air is forced to slow down, and the energy it loses as speed is converted into pressure โ the useful push that moves air down the ducts.
A motor turns the impeller through a shaft. The faster and larger the wheel, the more air it moves and the more pressure it can build.
The spiral, called a scroll, gets steadily wider as it wraps around the wheel. Air leaves the impeller fast, and the widening passage slows it down and turns that speed into pressure โ just like the volute of a pump.
A propeller pushes air straight through in an axial direction. A centrifugal fan pulls air in at the centre and throws it out sideways, so the scroll can build real pressure โ which is why it is used to push air through long ducts.
Air enters axially through the round eye at the centre of the wheel, then leaves radially around the rim and is guided to the rectangular outlet. That is why the inlet and outlet point in different directions.
The wheel speed and its size. A faster, larger impeller moves more air and can build more pressure, but it also needs more motor power and makes more noise.
Yes. Forward-curved blades give more airflow for a given speed, while backward-curved blades are more efficient and quieter. The blade shape is chosen to match the job.