The characteristics that are used as parameters in the fan law are:
- Fan diameter (D).
- Fan speed (N)
- Static air pressure (P)
- Air volume (Q)
- Air power (W)
- Noise(LW)
- Air density (p)
These parameters are used for three formulas: the first gives us the volume of the air, the second its pressure and the third the power. A fourth can also be derived that allows us to know how much noise it generates, ideal in this case if we want to have a system that is as quiet as possible.
air volume
The air speed is directly proportional to the volume of air and, therefore, is related to the diameter or size of the fan, measured in millimeters, and its speed, which is given in revolutions per minute. So, if we have a 120mm 2000 RPM fan, it will have double the air volume of a 1000 RPM fan of the same size, but if for example we go to a 140mm fan then we will see the air volume increased by 1, 6 times.
This is important for when we decide to go for a slightly larger or smaller fan. So a 120mm fan at 1600 RPM will get the same volume of air as a 140mm fan at 1000 RPM.
air pressure
The relationship between fan speed and air pressure is exponentially quadratic. This means that if we double the speed of the fan then we will generate four times the air pressure. This relationship is not only given with the speed of the fan, but also with its diameter. In addition to being proportional to air density, but given that inside a PC tower this parameter does not vary, it is not very fundamental, yes, it must be taken into account if we create an open concept system. On the other hand, it is common in a system that the speed of the fan fluctuates depending on the internal temperature level, so the air pressure when it works at half speed also decreases quadratically.
wind power
The relationship between wind power and speed is not quadratic, but cubic. This means that if we increase its speed twice then the power will increase 8 times. Since 8 is 2 cubed. This formula is the combination between the formulas of the two previous ones and, therefore, it is a combination of them.
The power of the wind helps us to know the efficiency of a fan when it comes to cooling its environment, so the fans with the highest wind power will be the best, but the quality will depend on the motor that the manufacturer has chosen. This is a detail that manufacturers do not usually specify and, therefore, we must deduce said specification through other technical specifications.
fan noise
We have to start from the concept that the volume of the air is directly related to the existing heat dissipation capacity, the problem is that if we increase the speed of rotation of a fan we not only generate more volume in the air, but also much more noise . However, we cannot measure fan noise directly, as it is derived from a calculation between pressure and sound intensity.
However, there is an easy to understand relationship and it is none other than the larger the diameter of a fan, the more noise it will make when it moves at high revolutions per minute. The downside is that placing a smaller fan means reducing the heat dissipation capacity it can give us.
Fan performance in parallel or series
It is common in PC cases to see a couple or three of fans placed in a row, so the performance of the fan will not be the same. We have to take into account that the air pressure does not vary with the amount of the same that we have installed in our PC, instead the volume of the air is added. On the other hand, if we install them in series, the opposite happens, since it is the air pressure that is added but not the volume of the air.
Therefore, it is not the same to place two fans in front than to place one in front and one in the back, we can think out of ignorance that since there are two fans in both cases, their performance when it comes to renewing the air inside the box will be similar, when really It is not like this.
