The principle of a cooling fan
Cooling fans, English name: Cooling fans. The technology and performance of the cooling fan have fully reached a mature stage, and new technologies are constantly emerging. Fan specifications range from 15mm to 280mm, with voltages ranging from 5V, 12V, 24V, 48V, 110V, 220V, 380V, and shapes in square, circular, olive, and other shapes.
Cooling Fan - Principle of Cooling Fan
The working principle of a cooling fan is achieved through energy conversion, namely: 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.
Cooling Fan - Classification and Characteristics of Cooling Fans
1、 Axial flow fan
The blades of an axial fan drive air to flow in the same direction as the shaft. The impeller and propeller of an axial fan are somewhat similar. When it operates, the majority of the airflow flows parallel to the axis, in other words, along the axis direction. When the inlet airflow of an axial fan is free air with zero static pressure, its power consumption is the lowest. When operating, the power consumption will also increase with the increase of the airflow back pressure. Axial fans are usually installed on electrical equipment cabinets and sometimes integrated into motors. Due to their compact structure, they can save a lot of space and are easy to install, making them widely used.
Its characteristics: high flow rate, moderate wind pressure
2、 Centrifugal fan
When a centrifugal fan is in operation, the blades push the air to flow in a direction perpendicular to the axis (i.e. radial). The intake is along the axis direction, while the outlet is perpendicular to the axis direction. In most cases, using an axial fan can achieve cooling effects. However, sometimes centrifugal fans must be used if the airflow needs to rotate 90 degrees to discharge or when a large air pressure is required. Strictly speaking, fans also belong to centrifugal fans.
Its characteristics: limited flow rate, high wind pressure
3、 Mixed flow fan
A mixed flow fan, also known as a diagonal flow fan, is not much different from an axial flow fan at first glance. In fact, the inlet of a mixed flow fan is along the axis, while the outlet is along the diagonal direction of the axis and vertical axis. This type of fan, due to its conical blades and outer cover, results in higher wind pressure. Compared to axial fans, centrifugal fans have lower noise at the same size and other comparable performance.
Its characteristics include high flow rate and relatively high wind pressure
4、 Through flow fan
Through flow airflow can generate a large area of airflow and is usually used to cool large surfaces of equipment. The inlet and outlet of this fan are both perpendicular to the axis (as shown in the figure on the right). A through flow fan uses a relatively long cylindrical fan impeller for operation. The diameter of these cylindrical fan blades is relatively large, which allows for the use of lower speeds while ensuring overall air circulation, thereby reducing noise caused by high-speed operation.
Its characteristics: low flow rate, low wind pressure
Cooling Fan - Common Bearing Structures for Cooling Fans
Common bearings for cooling fans include ball bearings, oil bearings, and magnetic levitation bearings.
Ball bearings
Ball bearings have changed the friction mode of bearings by using rolling friction. There are some steel balls or columns between the two iron rings, supplemented by some grease lubrication. This method is more effective in reducing friction between bearing surfaces, effectively improving the service life of fan bearings, and thus reducing the heat generation of the radiator, extending its service life. The disadvantage is that the process is more complex, leading to increased costs and higher work noise.
Oil bearing
Sleeve Bearing is a sleeve bearing that uses sliding friction and lubricating oil as a lubricant and drag reducer. It can be said that it is the most common bearing technology in the current market. Due to its low cost and simple manufacturing, many products, including well-known brands, are still in use. Its advantages are quietness, low noise, and low price during initial use.
magnetic bearing
The motor of Magnetic Bearing adopts a 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 magnetic levitation line, and the shaft core is parallel to the magnetic levitation line, so the weight of the rotor is fixed on the running track. The almost unloaded shaft core is used to support the anti magnetic levitation line direction, forming the entire rotor suspended on the fixed running track. Compared with traditional ball bearings and oil bearings, magnetic bearings do not have mechanical contact and the rotor can operate at high speeds. They have advantages such as 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 environments. Magnetic levitation is actually just an auxiliary function, not an independent bearing form. Specific applications also need to be combined with other bearing forms, such as magnetic levitation+ball bearing, magnetic levitation+oil bearing, magnetic levitation+vaporization bearing, and so on.
Cooling Fan - Common Technical Indicators for Cooling Fans
Air volume
Air volume refers to the total volume of air discharged or incorporated by the 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 air volume unit commonly used for cooling fans is CFM (approximately 0.028 cubic meters per minute).
Air volume is the most important indicator to measure the heat dissipation capacity of a cooling fan. Obviously, the larger the air flow, 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 per unit time can carry away more heat. Of course, under the same air volume, the heat dissipation effect is related to the flow mode of the wind.
wind pressure
Wind pressure and air volume are two relative concepts. Generally speaking, in order for manufacturers to save costs, designing fans with high air volume requires sacrificing some air pressure. If the fan can drive a large amount of air flow, but the wind pressure is small, the wind cannot blow to the bottom of the radiator (which is why some fans have high speeds and large air volume, but the heat dissipation effect is not good). On the contrary, if the wind pressure is high, it 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, working voltage, number of fan blades, inclination angle, height, diameter, and bearing system. There is no necessary connection between speed and fan quality. The speed of the fan can be measured through internal speed signals or externally.
As the application situation and environmental temperature change, different speed fans are sometimes required to meet the demand. Some manufacturers have specially designed cooling fans with adjustable fan speeds, available in both manual and automatic modes. The main purpose of manual operation is to allow users to use low RPM for low noise in winter and high RPM for good heat dissipation in summer. Automatic temperature regulating radiators generally come with a temperature control sensor that can automatically control the fan speed based on the current working temperature. If the temperature is high, the speed will increase, and if the temperature is low, the speed will decrease to achieve a dynamic balance, thus maintaining the best combination of wind noise and heat dissipation effect.
