Common Technical Indexes of a Fan motor
Common Technical Indexes of a Fan motor
The common technical indicators of heat dissipation fans are air volume, air pressure, fan speed and fan noise.
Air volume refers to the total volume of air discharged or incorporated by a cooling fan every minute. If calculated in cubic feet, the unit of air volume is CFM; if calculated in cubic meters, it is CMM. CFM (about 0.028 cubic meters per minute) is the most commonly used unit of air volume for heat dissipation fans. Air volume is the most important index to measure the heat dissipation capacity of heat dissipation fans. 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 certain, larger air volume, that is, more air can take more heat per unit time. Of course, under the same air volume, the heat dissipation effect is related to the flow mode of the wind.
In order to conduct normal ventilation, it is necessary to overcome the resistance in the fan's ventilation stroke. The fan must produce pressure to overcome the supply resistance. The change of pressure measured is called static pressure, i.e. the difference between maximum static pressure and atmospheric pressure. It is the pressure of gas acting on the surface parallel to the object, and the static pressure is measured through holes perpendicular to the surface. It is called dynamic pressure that the kinetic energy needed in gas flow is transformed into pressure. In order to achieve the purpose of air supply, static and dynamic pressure are needed. Total pressure is the algebraic sum of static pressure and dynamic pressure. Total pressure refers to the increment of total pressure given by the fan, that is, the difference of total pressure between the outlet and the inlet of the fan. The higher the air pressure, the stronger the fan's ability to supply air. In practical application, the nominal maximum air volume is not the actual air supply from the radiator. The large air volume does not mean that the ventilation capacity is strong. When the air flows, the airflow will encounter the obstruction of the radiator fins in its flow path, and its impedance will restrict the free flow of air. That is to say, when the air volume increases, the wind pressure will decrease. Therefore, there must be an optimal operating point, that is, the intersection point of fan performance curve and wind resistance curve. At the rework point, the slope of fan characteristic curve is the smallest, while the change rate of system characteristic groove is the lowest. Note that the static efficiency of the fan (air volume X, air pressure/power consumption) is the best at this time.
The fan speed refers to the number of rotations per minute of the fan blade in rpm. The fan speed is determined by the number of turns in the coil, the working voltage, the number of fan blades, the inclination, the height, the diameter and the bearing system. There is no necessary relationship between speed and fan quality. The speed of the fan can be measured either by internal speed signal or by external speed signal. With the change of application and environment temperature, different speed fans are sometimes needed to meet the demand. Some manufacturers have specially designed heat dissipation fans that can adjust the speed of fans. They are manual and automatic. Manual is mainly to allow users to use low speed in winter to achieve low noise, high speed in summer to achieve good heat dissipation effect. The automatic temperature-regulating radiator usually has a temperature-controlled inductor, which can automatically control the speed of the fan according to the current working temperature. The higher the temperature, the higher the speed, and the lower the temperature, the lower the speed, so as to achieve a dynamic balance, so as to keep the best combination of wind noise and heat dissipation effect.
In addition to the heat dissipation effect, the working noise of fans is also a common concern. Fan noise is the size of noise generated by the fan when it works, in decibels (dB). The measurement of fan noise needs to be carried out in a muffler with noise less than 17 dB, one meter away from the fan, and aligned with the fan inlet along the direction of the fan rotation axis. The frequency spectrum characteristics of fan noise are also very important, so it is necessary to record the frequency distribution of fan noise with a spectrum analyzer. Generally, the noise of fan should be as small as possible, and there can be no abnormal sound. Fan noise is related to friction and air flow. The higher the speed of the fan and the larger the volume of the fan, the greater the noise will be. In addition, the vibration of the fan itself is also a factor that can not be ignored. Of course, the self-vibration of high-quality fans will be very small, but the first two are difficult to overcome. To solve this problem, we can try to use larger fans. In the case of the same air flow, the working noise of large size fan at low speed is smaller than that of small size fan at high speed. Another factor that we can easily overlook is the bearing of the fan. Because of friction and collision between shaft and bearing when fan rotates at high speed, it is also a main source of fan noise.