Why are fan wings slightly curved?

Fan wings, also called blades, are curved for optimum air circulation which is determined by solidity ratio which is the ratio of the area of the blades to the area of the disc swept by them.

 If a flat plate is used as a blade, it will provide air circulation no doubt but the volumetric flow rate will be less compared to a blade which is suitably curved based on aerodynamic principles.

The cross-section of a blade is in the form of a circular arc and is called camber. It will vary from the root of the blade to its tip. One can see the blade twisted from the root to the tip.

The angle of attack (angle between the chord of the aerofoil and flow direction) will vary from the root to the tip. Engineers optimize these Para-meters, now-a-days using computer modeling, so that as the fan rotates there is enough air flow. The flow disc varies with rotational speed.

            The numbers of blades in fans vary between 2 and 4. Accordingly, their shapes differ some are slender and long while others are broad and short.