It's either 3 or 5 blades, why do electric fan blades have to be an odd number?

Audit expert: Zhao Liangyu

Associate Professor, Flight Control Department, School of Aeronautics and Astronautics, Beijing Institute of Technology

Although it is the beginning of autumn, the hot weather in many parts of the country has not subsided at all, but has become more and more severe. "The hot summer is so sweet with you", when this familiar Internet buzzword spreads, it is definitely not only the beautiful love and the crisp watermelon that make people "sweet" on hot days, but also the "electric fan" that saves people from the heat.

Source: News Photo

As a family heat relief device, air conditioners have saved many workers from disasters. In areas where air conditioners are not available, electric fans bring a moment of coolness to countless people. So how does this simple-looking, affordable appliance bring "wind", and why are its blades always odd in number?

How does an electric fan blow air?

Regardless of the shape of the electric fan, whether it is tall or short, old-fashioned or novel, the electric fans used in general households are composed of main parts such as plugs, fan blades, motors and outer covers. When people plug in the plug and turn on the power, the motor consumes electrical energy and converts it into mechanical energy through rotation, driving the fan blades to rotate rapidly.

Source: News Photo

The rotating fan blades do not create wind, but they bring cool breezes to people who are afraid of heat by driving air flow. This is because when the fan blades rotate at high speed, the flow speed of the surrounding air increases, forming wind. The reason why people can feel cool in the "windy" environment is that the passing of wind accelerates the evaporation of sweat on the surface of the human body.

Are the number of blades on electric fans always odd?

I wonder if you have ever observed the blades of an electric fan . In fact, their structure is not a wild imagination, nor is it a spontaneous creation. Most of the blades of electric fans have the same or similar appearance: slanted blades with a certain angle, and the number of blades is mostly odd numbers such as 3 or 5.

For a qualified electric fan, the air volume is very important, and this factor is determined by the spatial structure of the fan blades. People have found through experiments that compared with the combination of even-numbered fan blades such as 4 or 6 blades, the advantages of odd-numbered fan blades are more obvious.

Source: pixabay

First of all, odd-numbered blades are more stable and avoid shaking during operation. Even-numbered blades make it more difficult for the fan to maintain balance and are more likely to cause resonance problems. When the blades are in frequent resonance, they may break because they cannot withstand excessive vibration energy. For manufacturers, the resulting after-sales maintenance problems are also quite tricky.

Relatively speaking, an odd number of blades can avoid this problem. Arranging the blades in an asymmetrical shape can effectively reduce noise and self-jitter.

Source: pixabay

Secondly, electric fans with odd numbers of blades are more environmentally friendly and more in line with public expectations in terms of energy saving and power saving. Taking a three-blade electric fan as an example, its structure can form a reasonable dynamic force with each other in terms of mechanics. In other words, as long as two blades are in a potential energy state, they can drive the other blade that does not have dynamic potential energy to rotate together, thus saving electricity and energy.

Therefore, we can find that most household electric fans have three blades. This design can ensure a larger flow rate and meet people's cooling needs on the one hand; on the other hand, it conforms to the principles of fluid mechanics and better exerts the "power" of electric fans. At the same time, it avoids noise and unexplained shaking problems, reduces bearing loss, and increases service life. Therefore, not only electric fans, but also many blade mechanical systems have adopted this design concept, such as some propeller helicopters also have an odd number of blades.

Source: News Photo

Of course, in real life, the saying that "fan blades are always odd numbers" is not absolute . For example, helicopters also have 2-blade and 4-blade propellers, and some small electric fans also use 4-blade designs. Whether to use an even number of blades in product design depends more on the actual situation of the aircraft.

Are these new electric fans really effective?

In addition to bladed electric fans, many new types of electric fans have also begun to enter thousands of households in recent years, among which bladeless electric fans, tower fans, air flow fans and air conditioning fans are the most representative.

The bladeless electric fan is the invention of British scientist James Dyson. Since the first bladeless electric fan appeared on October 12, 2009, it has won the favor of the public with its novel and simple design. The design without blades improves safety and solves the hidden danger of people (mainly young children) being injured by the blades.

The bladeless electric fan, which consists of a ring and a bracket base, has become a tool for creating a sense of technology and modernity in many home environments with its simple and smooth lines. The bladeless electric fan is not only beautiful, but also powerful. It can adjust the pitch angle and remote control of ordinary electric fans, and at the same time use the turbocharging principle to achieve "blowing".

Source: News Photo

The shape of the tower fan is very distinctive. As the name suggests, most of the fans are cylindrical, and some can be as high as 1 meter. For urban families, this slender shape and design effectively saves space. At the same time, its narrow air outlet makes the "wind" more gentle, giving people the comfort of natural wind. The extremely low noise is also one of its advantages, which is especially suitable for families with elderly people and children. Due to market demand, many tower fans will also add an aromatherapy box design to make the wind have its own fragrance, adding a romantic atmosphere.

The air conditioning fan is the largest among the three new types of fans, but it does not have a compressor like an air conditioner. Its functions are somewhat similar to those of a tower fan, except that it comes with an ice-adding function and has the advantage of humidifying the air.

The air conditioning fan is additionally equipped with a water tank and an air filter . Users can choose to add water or ice to the water tank. The built-in water pump circulates the water in the machine continuously, cooling the surrounding air, and moistening the air while cooling it. Although this cooling method is relatively primitive and the air supply is relatively limited, it cannot cool down as quickly as air conditioning, but it is a good choice for the elderly and children who are weak and afraid of air conditioning sickness.

Source: A shopping website

The dog days are over, but the "autumn tiger" is still lurking. Many areas in my country have entered a period of continuous high temperatures, so it is important to take precautions against heatstroke and cool down when going out. The most down-to-earth leaf electric fans are still bringing coolness to countless busy people. However, remember not to use the fan too hard after strenuous exercise or heavy sweating.