Computer host cooling Fan The bigger the better?

fan, for us, are very familiar with, play small from every summer will send bursts of cool breeze, accompany us through the life of every heat. For the computer, the fan is indispensable, whether it is the chassis of the self-release, or Cpu/gpu forced cooling, or a streamer of the visual impact of color, fans have a responsibility.

The fans on the computer are DC fans (this is what the following fans refer to), its operating principle is also very simple, the conductor through the current, the surrounding will produce a magnetic field, if the conductor placed in another magnetic field, will produce suction or repulsion so that objects move, that is, ampere right hand rule, middle school physics have learned, not to detail, This is mainly to look at some common indicators of DC fans, which are used in the selection and use of fans.

On the outside of the fan packaging are generally printed with basic performance indicators

The fan has 4 key parameters from the performance data, that is, air volume, wind pressure, speed and noise, and of course, fan-blade shape, motor bearing and fan frame, etc. A good fan can be sold to large hundreds of, ordinary 30-80, and the cheapest 5 packets of mail are there, visible in the middle is quite exquisite.

Air

Air volume = average wind speed? Over wind area

Air volume is one of the most basic indicators, not limited by the size of the structure, which refers to the unit time through the wind area of air volume, over the wind area is basically equivalent to the fan frame area minus the motor part of the frame area. Air volume generally with cfm (cubic feet per minute, cubic feet/minute) to indicate that there are a few people will use m3/min,12cm fan air volume More in the 30-80cfm room.

Obviously, the average wind speed is certain, the larger the fan diameter, the greater the wind, the greater the amount of air flow, participation in the heat exchange of the more atmosphere, most of the heat dissipation effect is more obvious. But blindly pursue the air volume is also undesirable, because there is a closely related to the "wind pressure" we have to worry about.

Wind pressure

If air volume refers to the total amount of heat exchanged in the unit time, then the wind pressure determines where the air can reach. Accurately speaking, the wind pressure is the outlet and the inlet between the pressure produced by the difference, in layman's terms, the wind pressure defines how far the wind blows, because the pressure difference of the wind pressure description is small, generally in the water column, that is, MMH2O (mm water column), 12cm fan wind pressure in the 0.3-1.0MMH2O between.

The size of the wind pressure depends mainly on the shape, area, height and speed of the fan blades, the impact of the first three is more complex, and the speed of the relationship is very simple, under the same conditions, the faster the speed, the greater the wind pressure.

Schematic diagram of fan wind pressure

Air volume and wind pressure are a mutually restricted relationship, the speed of the same situation, the more wind pressure, the greater the wind pressure, the smaller the amount of air, the degree of control between them depends on the fan blade shape and the overall structure, the following is a typical air flow-wind pressure characteristics diagram.

Air flow-wind pressure characteristic diagram

In our daily applications, the choice of wind volume or the choice of wind pressure fan to rely on the actual situation, for example, chassis front fan more than the choice of wind pressure, so that the cold air can be blown to the inside of the chassis as much as possible, and then the fan can choose to wind large, so that more hot air out of the chassis, such as fins dense or thicker radiator, The matching fan also has certain requirements for the wind pressure.

Speed

Speed refers to the number of fans per minute of the rotation of the circle, the Unit for RPM (Revolutions/minute), the speed of the performance of the fan is enormous, usually the higher the speed of the greater the air flow, wind pressure is higher, but the noise will be even greater.

The fan speed is determined by the motor, the working voltage, the number of fan page, inclination, height, diameter and bearing system. The vast majority of fan speed can be adjusted, this is because their speed will vary with the operating voltage changes, we usually used the governor is actually a small rheostat, and air/wind pressure is different, speed through simple instrument measurement or software view, The speed of the 12cm fan is generally 800-2000rpm.

Fan in the rotation

Noise

Fan noise is when the fan is working, and noise is a direct impact on the user. Noise size by many factors, such as speed, fan size and number, and so on, the nominal fan noise value is less than 17dB noise in the Sound room measurement, 1 meters away from the fan, and the fan shaft along the direction of the fan's intake, using a weighted way.

The general requirements of the fan noise should be as small as possible, and can not be different sound, inferior fan, often the center of gravity of the fan blade is not in the axis, the use of a period of time, the fan bearing gradually wear, will make the vibration increase noise.

Fan Leaf

The design of the fan blades plays a decisive role in the performance of the fans, and the technical foundation of the manufacturers is mostly performed by various blades, and the fan blades have several main parameters affecting the air volume, wind pressure and wind speed.

The greater the curvature of the blade, the greater the amount of air and wind pressure, the greater the resistance of the blades, requiring greater torque of the motor

The larger the blade inclination (the angle with the airflow direction), the greater the wind pressure, but it may produce reflux phenomenon and reduce the fan performance.

Blade spacing too small will flow disturbance, increase surface friction, reduce efficiency, spacing is too large will pressure loss increase wind pressure is insufficient

The blade radian allows the blown airflow to be concentrated in the cylindrical space directly ahead of the outlet, which can increase the wind pressure

In addition, the number of blades also has a great impact, the fan blade number is basically 5, 7, 9, such as odd, this is to balance and avoid resonance, under the same conditions, increase the number of blades, can increase the air volume, but the wind pressure will drop, or, to ensure the same air volume, through the increase in the blade can effectively reduce the speed, thus reducing noise.

In addition to the above indicators, fan bearings are also very important, usually divided into oil bearings, hydraulic bearings, ball bearings and magnetic bearings, different bearings produce a small amount of noise, and their life span is also different. Each of these bearings has different advantages and disadvantages, if the oil bearing cost is low, the noise is small, the technical content is low, the life is also short (5,000-8,000 hours); hydraulic bearings have a long life span (40,000 hours) compared to oil bearing bearings;D iy player's favorite double ball bearings, has a long life, up to 50,000-10 hours, high price , the noise is also large; the magnetic levitation bearing is a synthesis, the technical content is high, the life is also long (50,000 hours), the noise is extremely low, the price is also extremely high.

How do I choose the right fan?

Fan can be simply grouped into three categories, one is the air volume fan, the other is the wind fan, the last one is all balanced fan, the three kinds of fans as the name suggests is some of the air volume is particularly large, some wind pressure is particularly large, some of them are a bit but not small (are very large or very expensive or noisy), and then according to the actual needs of the

It should be said that the wind fan is suitable for most applications, allowing more air to participate in the heat exchange process, such as chassis, upper, side fans can choose the air volume fan, ventilation, chassis front fan can also be used in high wind fans, if the hard disk cage, such as in the vicinity of fans, wind pressure fans will be better, For radiators with fans, if the fins are not very dense radiator is not very thick, or to the main air flow fan, the basic principle is that fans of the exhaust fan more than the use of wind-volume fan, intensive, more resistance to the area of the air blower fan used more high wind pressure, and a prerequisite, noise is small, At least in the dead of night you can't hear it in the rush of joy!