Popularize the definition of cooling fan

Cooling fans, English name: Cooling fans. The technology and performance of cooling fans have fully reached a mature stage, and new technologies continue to emerge. The fan specifications range from 8mm to 280mm, with voltages of 5V, 12V, 24V, 48V, 110V, 220V, 380V, and shapes such as square, circular, and olive.

The working principle of a cooling fan is achieved through energy conversion, that is, electrical energy → electromagnetic energy → mechanical energy → kinetic energy. The circuit principle is generally divided into various forms, and the performance of the fan will vary depending on the circuit used.

axial fan

The blades of an axial fan push air to flow in the same direction as the shaft. The impeller and propeller of an axial fan are somewhat similar. During operation, the majority of the airflow flows parallel to the shaft, in other words, along the axis direction. Axial flow fans have the lowest power consumption when the inlet airflow is free air with zero static pressure, and their power consumption increases with the increase of airflow backpressure during operation. Axial fans are usually installed in electrical equipment cabinets and sometimes integrated into motors. Due to their compact structure, axial fans can save a lot of space and are easy to install, making them widely used.

Its characteristics: high flow rate, moderate wind pressure

Centrifugal fan

When a centrifugal fan is working, the blades push the air to flow in a direction perpendicular to the axis (i.e., radially),

The intake is along the axis direction, while the exhaust is perpendicular to the axis direction. In most cases, using an axial flow fan can achieve cooling effect. However, sometimes if a 90 degree rotation of the airflow is required or a large air pressure is needed, a centrifugal fan must be selected. Strictly speaking, fans also belong to centrifugal fans.

Its characteristics: limited flow rate, high wind pressure

Mixed flow fan

Mixed flow fan, also known as diagonal flow fan, at first glance, mixed flow fan and axial flow fan are not much different. In fact, the intake of mixed flow fan is along the axis, while the exhaust is along the diagonal direction of the axis and vertical axis. Due to the conical shape of the blades and outer casing, this type of fan results in higher air pressure. Compared to axial fans, centrifugal fans have lower noise levels at the same size and other comparable performance.

Its characteristics: high flow rate and relatively high wind pressure

Cross flow fan

Cross flow airflow can generate large areas of airflow and is typically used to cool large surfaces of equipment. This kind of wind

The intake and exhaust of the fan are both perpendicular to the axis (as shown in the figure on the right). A cross flow fan uses a relatively long cylindrical fan blade for operation. The diameter of this cylindrical fan blade is relatively large, which allows for the use of lower speeds while ensuring overall air circulation, thereby reducing noise caused by high-speed operation.

Bearing structure

Introduction

Common bearings for cooling fans include ball bearings, oil impregnated bearings, and magnetic levitation bearings.

ball bearing

Ball bearings change the friction mode of bearings by using rolling friction, with some steel balls or columns between two iron rings, supplemented by some grease lubrication. This method more effectively reduces the friction phenomenon between the bearing surfaces, effectively improves the service life of the fan bearings, and thus reduces the heat generation of the radiator, extending its service life. The disadvantage is that the process is more complex, resulting in increased costs and higher work noise.

oil-impregnated bearing

Sleeve Bearing is a sleeve bearing that uses sliding friction and lubricating oil as a lubricant and drag reducer. It can be said to be the most common bearing technology on the market now. Due to its low cost and simple manufacturing, many products, including well-known brands, are still in use. Its advantages are quiet during initial use, low noise, and affordable price.

magnetic bearing 

The motor of Magnetic Bearing adopts Magnetic System (MS) design, which uses magnetic force to suspend the rotor in the air, so that there is no mechanical contact between the rotor and the stator. The principle is that the magnetic induction line is perpendicular to the maglev line, and the axis core is parallel to the maglev line, so the weight of the rotor is fixed on the running track. The almost unloaded axis core is used to support the rotor in the opposite direction of the maglev line, forming the entire rotor suspended on the fixed running track. Compared with traditional ball bearings and oil containing bearings, magnetic bearings do not have mechanical contact, and the rotor can operate at high speeds. They have the advantages of low mechanical wear, low energy consumption, low noise, long service life, no need for lubrication, and no oil pollution. They are particularly suitable for special environments such as high speed, vacuum, and ultra clean. Magnetic levitation is actually just an auxiliary function, not an independent form of bearing. Specific applications also need to be combined with other forms of bearings, such as magnetic levitation+ball bearings, magnetic levitation+oil containing bearings, magnetic levitation+vaporization bearings, and so on.

technical indicators

air volume

Air volume refers to the total volume of air discharged or contained by a cooling fan per minute. If calculated in cubic feet, the unit of air volume is CFM; If calculated in cubic meters, it is CMM. The commonly used air volume unit for cooling fans is CFM (approximately 0.028 cubic meters per minute).

Airflow is the most important indicator for measuring the heat dissipation capacity of a cooling fan. Obviously, the larger the air volume, the higher the heat dissipation capacity of the cooling fan. This is because the heat capacity ratio of air is constant, and a larger air volume means that more air can take away more heat per unit time. Of course, the heat dissipation effect is related to the flow of wind under the same air volume.

wind pressure

Wind pressure and air volume are two relative concepts. Generally speaking, in order for manufacturers to save costs, they need to sacrifice some wind pressure when designing fans with high air volume. If a fan can drive a large amount of air flow, but the wind pressure is low, the wind cannot reach the bottom of the radiator (which is why some fans have high speed and large air volume, but the heat dissipation effect is poor). On the contrary, a high wind pressure often means that the air volume is small, and there is not enough cold air to exchange heat with the heat sink, which can also cause poor heat dissipation effect.

fan speed

Fan speed refers to the number of times the fan blades rotate per minute, measured in rpm. The fan speed is determined by the number of turns of the coil inside the motor, the operating voltage, the number, inclination angle, height, diameter, and bearing system of the fan blades. The speed and fan quality are not necessarily related. The speed of the fan can be measured through internal speed signals or external measurements.

As the application situation and environmental temperature change, sometimes different speed fans are needed to meet the requirements. Some manufacturers have specifically designed cooling fans with adjustable fan speed, available in both manual and automatic modes. The manual mode mainly allows users to use low speed in winter to achieve low noise, and use high speed in summer to achieve good heat dissipation effect. Automatic temperature control radiators generally come with a temperature sensor that can automatically control the fan speed based on the current operating temperature. When the temperature is high, the speed is increased, and when the temperature is low, the speed is decreased to achieve a dynamic balance, thus maintaining the best combination of wind noise and heat dissipation effect.

Fan noise

In addition to the heat dissipation effect, the working noise of fans is also a common concern for people. Fan noise refers to the amount of noise generated by a fan during operation, which is influenced by various factors and measured in decibels (dB). When measuring the noise of a fan, it is necessary to conduct the measurement in a soundproof chamber with a noise level of less than 17dB, one meter away from the fan, and align it with the air inlet of the fan along the direction of the fan shaft. The measurement is carried out using A-weighted method. The spectral characteristics of fan noise are also important, so it is necessary to use a spectrometer to record the frequency distribution of fan noise. Generally, it is required that the noise of the fan be as small as possible and there should be no abnormal noise.

Fan noise is related to friction and air flow. The higher the fan speed and air volume, the greater the noise caused. In addition, the vibration of the fan itself cannot be ignored. Of course, high-quality fans have minimal self vibration, but the first two are difficult to overcome. To solve this problem, we can try using larger fans. Under the same air volume, the working noise of a large fan at lower speeds should be lower than that of a small fan at higher speeds. Another factor that we tend to overlook is the bearings of the fan. Due to the friction and collision between the shaft and bearings during high-speed rotation of the fan, it is also a major source of fan noise.

application

Widely used in traditional or modern instruments and equipment such as computers, communication products, optoelectronic products, consumer electronics products, automotive electronic equipment, switches, medical equipment, heaters, air conditioners, frequency converters, teller machines, automotive refrigerators, welding machines, induction cookers, audio equipment, environmental protection equipment, refrigeration equipment, etc.