PC fans - everything you need to know

If you are here it is because you do not underestimate the importance of fans on your PC. Some elements that we only remember when they start to fail and make noise. But nothing further from reality, the quality and performance of the fans could depend on the proper functioning of our PC , and precisely that is what we will try to make clear here.

We will see and explain practically everything there is to know about a fan to always succeed in our purchase. The use of this is very clear, they are elements that, thanks to the rotation of a propeller and its high revolutions, generate a forced current of air that directly affects a hot metal surface. Due to a temperature difference between the air and the element, part of the heat will be transferred to the flow, thus decreasing the temperature of the heatsink and consequently the CPU, RAM, graphics card or where we have placed it.

Index of contents

How important are the fans on a PC

Well, the good cooling of the components will depend in part on them. It goes without saying that electronic components work at high frequencies and with strong current intensities. This, together with a minimum surface, causes the temperatures in them to rise, thus requiring heat sinks. In turn, these heatsinks are able to take all the heat generated by the chip and distribute it in an innumerable amount of copper or aluminum fins in them. What are so many fins for? Well, so that a forced air flow enters them and takes all the heat possible into the environment.

If there are no fans, the heat will still be in the heatsink, and will only go into the calm air around it in much less amount due to natural convection. In this way, the chip continues to accumulate temperature, and the system to protect it drastically lowers the voltage, which we call Thermal Throttling, in order to control the heat it generates. So the result is a slower, hotter computer with less life expectancy. Convinced of the importance of fans?

The Joule Thomson effect

Surely you have placed a fan in front of your face once, and you will notice that the air that comes out of it, is a little cooler than that of the environment. In fact, the higher the speed of it, the colder it will seem to us. This is due to the Joule-Thomson effect.

This physical phenomenon explains the process in which the air temperature decreases or increases due to its spontaneous expansion or compression at constant enthalpy. Enthalpy is basically the energy that the system (air) exchanges with the rest of the environment. If the air compresses, then it increases in temperature, while if it expands, it decreases. This can be proved very easily: open your mouth and blow air into your hand, you will see that it is hot (around 36.5⁰C if you do not have a fever). Now do the same with your mouth almost closed, you will see that the air comes out much colder, even more than the ambient air. !! Congratulations!! The Joule Thomson effect is with you.

In a fan we have both phenomena; as it passes through the propellers, the air compresses and increases its temperature slightly, while being expelled it decreases. The more air flow a fan has, the more cooling capacity it will have, since the more energy it will exchange with the environment (the heatsink).

Diameters and types

Diameters

A very important factor in choosing a fan will be its diameter and its configuration or type of operation.

They are two very easy factors to understand. The first refers to how big the fan is, the more diameter, the larger its blades will be and consequently, the greater the air flow it generates. We are not going to go into technical aspects like flow type, laminar or turbulent, but we do know that a large slow fan will cool much better than a small faster one.

At this point what really interests us users is that the fan we buy enters our chassis or our heatsink for it, what we will have to do is simply go to the specifications of our chassis and see the diameters of the fans. that admits. They can be basically three sizes: 120 mm, 140 mm and 200 mm. They are the standard measurements and those currently used except for custom configurations. Please do not use 80mm fans, they are very old, basic and only make noise.

As for the types of fans, we have the following:

• Centrifuges or turbines: these fans are the ones used in blower type heatsinks. The fins that collect the air are placed totally vertical to the axis of rotation, so the air flow is generated in a direction of 90 ^o with respect to the inlet (it enters horizontally and exits from the front). In general they are quieter and more efficient fans, but in electronics this is not the most recommended configuration, since the air comes out at less speed and at lower pressure, so it collects little heat.

Turbine fan

• Axial: these are the fans of all life, their blades placed at an angle leave the rotor directly to generate a flow perpendicular to them and without changing the trajectory. They are noisier, and require more power, but the air pressure and flow are higher, so they are more effective on finned heatsinks.

Axial Fan

• Helical: it is a variant of axial fans in which the blades, instead of being straight, are curved on themselves. These fans generate a large air flow at lower pressure, making them quieter. They are ideal for getting air in and out of the chassis.

Helical Fan

Fan performance and characteristics

Now let's take a closer look at the main characteristics of PC fans, as they will be important for its durability and performance.

Blade design and number

We have already seen how axial and helical fans are very similar, and it is only a matter of differentiating the design of their blades. These are in charge of making the air move in the indicated direction and in this way there is an acceleration of the air that translates into noise, which the manufacturers try to eliminate at all costs.

Most of these have custom bladed fans in their arsenal, including ribs on the inside or spoilers on the back to prevent air turbulence from translating into noise. The number of them will also be important, since the more we have, the more air they can move at lower revolutions, so you always have to find a balance between them.

Bearings

Bearings or bearings are the mechanism responsible for allowing the movement of a fan through the motor. In these very small fans, the axis of rotation and the electrical coils or stators, are normally separated, normally the latter are fixed. This is just the opposite of a normal motor, for example, those who use toys. With this formula, what is achieved is that the axis has less inertia when the coils are fixed and we can put fluid inside it to eliminate the sound and maximize durability.

These are the bearings most used in PC fans:

• Sleeve or plain bearing: The fan shaft has a plain bearing with lubrication and lubrication to facilitate rotation. The coils form an outer ring of 4 or 6 depending on the manufacturer. They are fairly quiet, easy to manufacture, and last pretty well for around 25, 000-30000 hours before their lubrication wears out, their weakest point. Lubricated balls are placed to improve and eliminate this wear on the previous bearing, in order to ensure contact with the turning cylinder. They offer greater durability and withstand higher temperatures, but are somewhat noisier due to the friction of the balls, which after a blow could move and fail. Fluid dynaminc bearing: Finally, we have the most complex of all, the one that uses a pressurized oil pre-chamber around the bearing to maximize durability and lubrication. They are also very quiet and offer an average life of 150, 000 hours. These are widely used by Noctua.

RPM

These are the revolutions per minute at which a fan rotates. Each revolution is a complete turn of it, so the more turns there are in a minute, the faster it will go and the more air flow it will generate.

Type of electrical connection

The way to connect the fan to our PC is also very important. Perhaps you have noticed that the fans do not always bring the same power connector, some do it through a 3-pin header, others with a 4-pin header and even the most basic ones have a two-pin connector next to a MOLEX.

• Molex or LP4 connection: it is the most basic, two conductors, positive and negative, will be connected to the part of the head of the corresponding motherboard or directly to a MOLEX head of the PSU. These receive a constant electrical signal, 5V or 12V, so they always rotate at their maximum RPM. DC connection: this is very common for mid-range fans that come integrated into the chassis or connected to basic microcontrollers. This time we have three pins instead of two, adding a rotation speed control depending on the percentage of tension that enters the motor. Control is done analogically and allows user interaction if the controller is compatible. PWM connection: finally we have the most complete of all, using 4 pins, it is possible to control the motor rotation by means of pulse width modulation (PWM). The voltage is generated by a digital signal formed by pulses, the higher the pulse density, the higher the average output voltage, and the faster it will rotate. This system is very useful to control the CFM of the fan based on the power consumed.

Air flow and static pressure Which is better?

After looking at the basic features and construction, it's time to look at the different performance measurements of the fans. Those that most appear without a doubt are the air flow and its static pressure.

Air flow or flow is the amount of air circulating through the fan. In fluid mechanics it is measured in the form of flow (Q), being proportional to the section of the duct (S) and to the speed of the air (V), Q = S * V. There is another measure that is widely used for this type of digital fans, the CFM or Cubit Feet per Minute or cubic feet per minute, a British measure. In this case, the air flow through a section per unit of time is measured.

For those who want to pass it to units of the international system this is the equivalence:

Static pressure on the other hand is the force that air is capable of exerting on an object, let's say it is the power at which air leaves the fan. The higher the static pressure, the more difficult it will be to break the air flow. It is measured in mmH2O or millimeter of water.

Now comes the important thing for the user, do we want more flow or more pressure? Well that depends, but it is best to have both. In the market there are specific fans for each type of measurement, those with more blades (9 or more) have a higher CFM, while those with less blades, but wider (8 or less) are specialized in mmH2O. When in a brand, for example Corsair, you see the SP or AF series it will mean that they are "Static Pressure" or "Air Flow".

AF fans are more oriented to their use in the chassis to get air in and out, since greater flow allows us to renew more air inside the cabin. On the other hand, SP fans recommend them for heatsinks and radiators for being able to remove more heat from the surface. Practice says that the higher the two parameters, the better the fan will be, so with CFM equal, take the fan with the highest mmH2O, and if the mmH2O varies only one unit, take the one with the highest flow. For example:

Corsair SP120 RGB	Corsair AF120 LED
1.45 mmH2O 52 CFM € 17.9	0.75 mmH2o 52.19 CFM € 22.90
Worst option	Better option

Noise

The noise generated by a fan depends in part on the above parameters and also on the type of internal bearing it has. The more RPM, the more noise because more air circulates. Oil-bearing fans are the quietest.

The noise generated is measured in Decibels (dB), although we normally see it with an A in front (dBA). This means that the value has been weighted to fit human hearing ability. The dB covers all the available sound frequencies, while the dBA adjusts to the range of 20 - 20, 000 Hz that the human being hears.

RGB-lit fans

Already a fundamental part of the fans is the inclusion of RGB lighting systems. Of course having RGB dramatically increases all the performance of the fan (kidding). In any case, we cannot deny that we are all struck by RGB, and we want our chassis to be the best of all.

In the current scenario, almost all manufacturers have their own lighting technologies, with LEDs that are capable of giving up to 16.7 million colors. The most important thing is to have a system that allows us to customize it through software, so we must make sure that they are ARGB (Addressable RGB) with 4-pin headers.

How to get the best air flow in a chassis

Finally we will study quickly and give some tips on how to get the best air flow in a chassis. Many times it is not about the quantity of fans, but rather their quality or how well they are placed. Essentially we can generate three types of air flows in a chassis; horizontal flow, vertical flow, and mixed flow. Let's always keep in mind that hot air weighs less than cold, so it will always tend to go up.

Vertical flow

We create it by drawing air from the base of the chassis and taking it out from above. This would be the most optimal flow of all since we facilitate air circulation to the maximum. The problem is that few chassis are open underneath, because they carry the PSU covers that isolate it from the central compartment. The important thing is to know that the upper fans always have to draw air, and the lower fans have to get it.

Horizontal flow

On the other hand, we have the towers that are closed both below and above. In this case there is a panel of fans on the front that will be open or semi open. These we must always place them to put air in, while in the back we will have another fan that takes all this air out.

Ideally, fans with a large CFM will be used so that hot air does not get stuck in the upper part, especially the rear.

Mixed flow

These chassis are by far the most common today. They have the bottom area closed with the PSU cover, but both the front and the top are open, as well as the back.

Again, the ideal will be to put fans that put air in the front, and leave the back and top to expel the hot air. It is a horizontal flow but aided by a super very open part and ideal for liquid cooling radiators.

Conclusion and guide with the best fans for PC

If you thought that buying a fan did not have many secrets, here we have shown you that it also has its crumb. We should not underestimate its importance in a PC, especially if we have very powerful hardware or we have a poor quality chassis. High temperatures can wreak havoc on our components. Now we leave you with our guide.

How many fans do you use in your chassis and how big are they? Have you ever stopped to think why there are so many fan models on the market?