The characteristics used as parameters in the fan law are:
- Fan diameter (D).
- Fan speed (N)
- Static air pressure (P)
- Airflow (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 lets us know how much noise it generates, ideal in this case if we want to have a system that is as quiet as possible.
volume of air
Air speed is directly proportional to air volume 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 switch to a 140mm fan then we will see the air volume increased by 1.6 times.
This is important when deciding whether to go for a slightly larger or smaller fan. So a 120mm fan at 1600 rpm will receive the same volume of airflow 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 fan speed, 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 the density of the air, 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 an open-concept system is created. On the other hand, it is common in a system that the fan speed fluctuates depending on the internal temperature level, so the air pressure when running 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, 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 these.
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 selected. It is a detail that manufacturers usually do not specify and therefore we have to deduce said specification through other technical specifications.
fan noise
We must 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 rotational speed of a fan, we not only generate more volume in the air , but also much more noise. However, we cannot directly measure fan noise, as it is derived from a calculation between pressure and sound intensity.
However, there is an easy to understand relationship and that is that the larger the diameter of a fan, the more noise it will make when moving at high revolutions per minute. The disadvantage is that placing a smaller fan means reducing the heat dissipation capacity it can give us.
Fan performance in parallel or in series
It is common in PC cases to see two or three fans placed in a row, so fan performance will not be the same. We must 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 they are installed in series, the opposite occurs since it is the air pressure which is added but not the volume of air.
Por lo que no es lo mismo colocar dos ventiladores delante que colocar uno delante y otro atrás, podemos pensar por desconocimiento que al haber dos ventiladores en ambos casos su rendimiento a la hora de renovar el aire de dentro de la caja será similar, cuando realmente It is not like that.
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