As a family summer refuge, air conditioning can be said to have saved many migrant workers from fire and water. In areas that are not covered by air conditioning, the presence of electric fans brings a moment of coolness to countless people.
If you look closely, you can see that most of the fans have an odd number of blades, and the most common ones are electric fans with 3 and 5 blades. Why don't we seem to have seen a fan with 2 or 4 leaves? What is the impact of different blade numbers? Today, we're going to talk about the secrets behind fan blades!
We know that the electric fan is driven by the motor to rotate the fan blades to generate forward wind, but its own heating is not cooling, but through the wind blowing out to accelerate the cooling of the human body.
Generally, the electric fan used in the home is composed of the main components such as the plug, fan blades, motor and cover. When people plug in the plug and turn on the power supply, the motor begins to consume electric energy, and converts the electrical energy into mechanical energy by rotating, driving the fan blades of the electric fan to rotate rapidly. When the fan blades rotate at high speed, the flow of the surrounding air increases, and wind is formed. The reason why people can feel cool in a windy environment is because the passage of wind will accelerate the evaporation of sweat on the surface of the human body.
So why do electric fans use more odd blades in their design?
First of all, odd-numbered blades are more stable.
When the number of blades of the fan is even, the blades will flutter when rotating at high speeds due to the uneven quality of the material itself and the error in installation. If the blades are designed to be even, a symmetrical arrangement is formed. Due to the symmetry, the jitter of one blade conducts to the opposite blade, which is prone to resonance, resulting in fracture due to the fact that it cannot withstand the energy generated by the resonance for a long time.
This problem can be avoided when the fan has an odd number of blades, as it can be arranged in an asymmetrical shape, effectively reducing noise and jitter.
Symmetrical shape of even-numbered blades (top) Odd-numbered blades are more balanced (bottom)
Secondly, from the perspective of energy saving, the three-piece fan is more cost-effective and relatively energy-saving.
Because the three fans can form an asymmetrical reasonable mechanical power, when one blade does not have the power potential energy, the other two are in the state of potential energy, and the two potential energy blades can naturally easily drive a blade that does not have potential energy temporarily, so as to save electricity and energy.
Some friends may be curious, is it better to have more fan blades or less?
I believe we have all noticed that most of the old-fashioned fans are three-bladed electric fans, with strong wind, but at the same time, they also have the shortcomings of loud noise, relatively direct wind, relatively hard, and poor comfort to the human body, and with the progress of materials and technology, the household electric fans we see now are more five-bladed, seven-leaf or even more leaf fans, the increase of blades needs to be matched with the update of materials and the improvement of motor technology. The wind is softer and less noisy. This is due to the fact that, with the speed basically the same, an appropriate increase in the number of fan blades can reduce the volume of air cut by a single blade, resulting in a softer wind and less noise.
The design concept of singular blades is not only applicable to fans, but also to a certain extent in the design of some propeller helicopters.
In addition, for the axial fan of the radiator, because the actual heat dissipation effect of the radiator largely depends on the design of the number of blades, the manufacturer usually adopts the method of increasing the number of blades to ensure a certain air volume and air pressure, but no matter what the number of blades of the axial fan is, most of the blade structures are also composed of odd numbers such as 7, 9, and 11, and the same reason is also true.
Radiator blades
Helicopter propellers
Windmill blades for power generation
Source: Popular Science China