In Which Direction Fan Rotates? Know The Science Behind It

Do you know that most of the fans rotate in the clockwise direction?

Whenever fans are used, there is always need for preferred air conditioning to be achieved, whether hot or cool. While the direction of motion of the fan would really not matter, its rotation is actually set according to the design of the blade and its orientation in which it is mounted on the rotor.  There are different types of fans, serving different purposes and consequently their direction of rotation must also be consistent with what the user intends to achieve. Such types include:

  • Ceiling fans
  • Pedestal
  • Tower
  • Window
  • Bladeless
  • Desk/Table
Figure 1: fan rotating in clockwise direction

All fans are designed such that they suck and push the air from behind to the front or vice versa depending on the design of the blades. Out of all the listed fans, most window and desk fans rotate in the clockwise direction. The idea is for the blades to suck cool air from behind and push it to the front for maximum cooling effect.

The fan design (Table fan)

The figure below is an illustration of a desk fan showing how the blade orientation necessarily requires that the fan must rotate clockwise

Figure 2-Table fan with an illustration of how the blade is designed to maximize the volume of air displaced.

The figure below is an illustration of a desk fan showing how the blade orientation necessarily requires that the fan must rotate clockwise.

The science behind the sleek fan design

Both table and window fans are designed to allow cool air currents to flow in from behind the fans to the front. And this process is predicated on specific and scientific reasoning that borrows heavily from the Bernoulli Principle in physics which states that;

“As the speed of a fluid (liquid or gas) increases, the pressure of the fluid decreases and vice versa”

In application of this principle, the fan blades are designed in an L shaped and a backward slanting manner to maximize the amount of air being displaced in the front of the fan. This is achieved through creating a more turbulent interaction between the blade and the air particles in front. Relatively, since the back end of the blades is nearly smooth, there is a less turbulent air flow at the back of the fan.

Because of this variance in the turbulence of the air currents, the Bernoulli’s Principle therefore accounts for faster air speed in front of the blades compared to the back side. This thus creates more static pressure behind the blades and less in the front side. This state thus causes the higher pressure at the back of the blades to push the cooler air to the front of the blades and consequently displace the warm air particles occupying the low pressure zone at the front of the blade.

Why clockwise rotation only?

Given the fixed design of this type of fan, were it to rotate in anticlockwise direction, it would still achieve the desired result but with much less efficiency since the air displaced by the blades will not be optimized.  This way, the fan would end up consuming the same amount of electrical energy but with less effect ultimately.

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