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Popularization of cooling fans


Author : adminViews : 465 Time : 2018-08-18

        Cooling fan, English name: Cooling fans. The technical and performance aspects of the cooling fan have reached a mature stage, and new technologies are constantly emerging. The fan size ranges from 8mm to 280mm, and the voltage is 5V, 12V, 24V, 48V, 110V, 220V, 380V. The shape is square, round, olive and so on.


       The working principle of the cooling fan is realized by energy conversion, namely: electric energy→electromagnetic energy→mechanical energy→kinetic energy. The circuit principle is generally divided into various forms, the circuit used is different, and the performance of the fan will be different.


classification


Axial fan


        The blades of the axial fan push the air in the same direction as the shaft. The impeller of the axial fan is somewhat similar to the propeller. When it is in operation, most of the airflow is parallel to the axis, in other words, along the axis. The axial flow fan has the lowest power consumption when the inlet airflow is 0 static air, and the power consumption increases as the airflow back pressure rises during operation. Axial fans are usually installed in the cabinet of electrical equipment, and sometimes integrated into the motor. Due to the compact structure of the axial fan, it can save a lot of space and is easy to install, so it is widely used.


        Its characteristics: high flow rate, medium wind pressure


Centrifugal fan


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


        The intake air is in the direction of the axis, while the outgas is perpendicular to the axis. In most cases, an axial fan can be used to achieve cooling. However, sometimes a centrifugal fan must be used if the airflow needs to be rotated 90 degrees or if a large wind pressure is required. Strictly speaking, fans are also centrifugal fans.


        Its characteristics: limited flow rate, high wind pressure


Mixed flow fan


        The mixed flow fan is also called the diagonal flow fan. At first glance, the mixed flow fan and the axial flow fan are no different. In fact, the intake air of the mixed flow fan is along the axis, but the outflow is the diagonal direction along the axis and the vertical axis. This type of fan has a conical shape due to the blade and the outer casing, resulting in a higher wind pressure. The centrifugal fan has lower noise than the axial fan in the same size and other comparable performance.


        Its characteristics: high flow rate and relatively high wind pressure


Cross flow fan


        Tubular airflow produces a large area of wind flow and is typically used to cool large surfaces of equipment. This kind of wind


        The intake and exhaust of the fan are perpendicular to the axis (as shown on the right). The cross-flow fan is operated by a relatively long barrel-shaped fan blade. The diameter of the barrel-shaped fan blade is relatively large. Because of the large diameter, a relatively low speed can be used on the basis of ensuring the overall air circulation amount. Reduce the noise caused by high-speed operation.


Bearing structure


Introduction


Common bearings for cooling fans are: ball bearings, oil-impregnated bearings, magnetic bearings.


Ball bearing


        Ball Bearing changes the friction of the bearing. Rolling friction is used. There are some steel balls or steel columns in the middle of the two iron rings, supplemented by some grease lubrication. This method is more effective in reducing the friction between the bearing surfaces, effectively improving the service life of the fan bearing, and thus reducing the heat generation of the radiator and prolonging the service life. The disadvantage is that the process is more complicated, resulting in higher costs and higher operating noise.


Oil bearing


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


Magnetic suspension bearing


        The magnetic bearing (Magnetic Bearing) motor is designed by magnetic system (MS). It 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 floating line, and the axial core and the magnetic floating line are parallel, so the weight of the rotor is fixed on the running track, and the almost unloaded axial core is struts in the direction of the antimagnetic floating line to form the whole. The rotor is suspended and is on a fixed running track. Compared with traditional ball bearings and oil-impregnated bearings, the magnetic bearings do not have mechanical contact. The rotor can run to very high speeds, with low mechanical wear, low energy consumption, low noise, long life, no lubrication, no oil pollution, etc. It is especially suitable for special environments such as high speed, vacuum and ultra-clean. Magnetic levitation is actually only an auxiliary function, not a separate bearing form. The specific application has to match other bearing forms, such as magnetic suspension + ball bearings, magnetic suspension + oil bearing, magnetic suspension + vaporized bearings and so on.


 


Technical indicators


Air volume


        The air volume refers to the total volume of air discharged or included in the cooling fan per minute. If calculated in cubic feet, the air volume unit is CFM; if it is calculated in cubic meters, it is CMM. The unit of air volume that is often used by cooling fans is CFM (approximately 0.028 cubic meters per minute).


        Air volume is the most important indicator to measure the cooling capacity of a cooling fan. Obviously, the larger the air volume, the higher the heat dissipation capability of the cooling fan. This is because the heat capacity ratio of air is constant, and the larger air volume, that is, more air per unit time can take more heat. Of course, in the case of the same amount of wind, the heat dissipation effect is related to the way the wind flows.


Wind pressure


        Wind pressure and air volume are two relative concepts. Generally speaking, under the consideration of the manufacturer's cost saving, it is necessary to sacrifice some wind pressure to design a fan with a large amount of wind. If the fan can drive a large amount of air flow, but the wind pressure is small, the wind will not blow to the bottom of the radiator (this is why some fans have high speed and large air volume, but it is the reason for poor heat dissipation). Conversely, Large wind pressures often mean that the air volume is small, and there is not enough cold air to exchange heat with the heat sink, which will also cause poor heat dissipation.


speed of the fan


        Fan speed is the number of times the fan blades rotate per minute, in rpm. The fan speed is determined by the number of turns in the motor, the operating voltage, the number of fan blades, the angle of inclination, the height, the diameter, and the bearing system. There is no necessary connection between speed and fan quality. The speed of the fan can be measured by the internal speed signal or by external measurement.


        As the application conditions and ambient temperature change, different speed fans are sometimes required to meet the demand. Some manufacturers have deliberately designed a cooling fan that can adjust the fan speed, both manual and automatic. The main purpose of the manual is to allow users to use low speed for low noise in winter and high speed for good heat dissipation in summer. The automatic temperature-regulating radiator usually has a temperature-controlled sensor, which can automatically control the speed of the fan according to the current working temperature. When the temperature is high, the speed is increased, and when the temperature is low, the speed is reduced to achieve a dynamic balance, thereby making the wind noise. Maintain an optimal combination of heat dissipation.


Fan noise


        In addition to the heat dissipation effect, the working noise of the fan is also a common concern. Fan noise is the size of the noise generated by the fan when it is working. It is affected by many factors and the unit is decibel (dB). Measuring the noise of the fan needs to be carried out in a silencing chamber with a noise of less than 17 dB, one meter away from the fan, and aligned with the air inlet of the fan in the direction of the fan shaft, and measured by A-weighting. The spectral characteristics of the fan noise are also important. Therefore, it is also necessary to use a spectrum analyzer to record the noise frequency distribution of the fan. Generally, the noise of the fan is required to be as small as possible, and no abnormal sound can exist.


       Fan noise is related to friction and air flow. The higher the fan speed and the larger the air volume, the greater the noise caused. In addition, the vibration of the fan itself is a factor that cannot be ignored. Of course, the high-quality fan's own vibration will be small, but the first two are difficult to overcome. To solve this problem, we can try to use a larger fan. The operating noise of a large fan at a lower speed should be less than the operating noise of a small fan at a high speed when the air volume is the same. Another factor that we easily overlook is the fan's bearings. It is also a major source of fan noise due to the frictional collision between the shaft and the bearing when the fan rotates at high speed.


 


application


        Widely used in computers, communication products, optoelectronic products, consumer electronics, automotive electronics, switches, medical equipment, heaters, air conditioners, inverters, teller machines, car refrigerators, welding machines, induction cookers, audio equipment, environmental protection equipment, Traditional or modern instruments such as refrigeration equipment.


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