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Really understand the air volume and pressure of the cooling fan
2024-07-15 14:32:22
On the introduction of cooling fan air volume and wind pressure, the Internet has long been a search of a large number, is also a commonplace problem, but in the circle can make this problem clear really is very few, after all, professional is not the same, such as separated mountains. Recently, I have been studying the test device of air volume and wind pressure, and I have made up a lot of lessons. I suddenly feel that my previous understanding of air volume and wind pressure is really superficial, and it is necessary to talk about this old topic again.
The reason why the air can flow must be because there is an energy difference in the system, and in our common DC cooling fans, the air obtains energy from the rotating blades, thus forming air flow. The energy in the air flow is usually expressed in the form of pressure (of course, there is internal energy in the form of heat), and at any point in the air flow, it exists in the form of static pressure energy, kinetic energy and potential energy, which can be represented by static pressure, dynamic pressure and potential pressure respectively. In the daily state, due to the limited space and the small density of air, the potential pressure can be ignored. The static pressure and the dynamic pressure in between are closely related to today's topic. Why is the wind pressure low when the air volume is high?
The cooling fan converts electrical energy into electromagnetic energy, which is then converted into mechanical energy of the blade, and then transferred to the air, which is converted into static pressure and dynamic pressure. Static pressure is commonly known as wind pressure (this is not standardized, because the wind pressure also contains dynamic pressure), and the air volume is the most intuitive expression of dynamic pressure, and there is a formula between them to calculate each other (air volume = coefficient * dynamic pressure 1/2), for a cooling fan, its air power (the energy converted by the fan blade) is:
Fan air power = k * air volume * air pressure
What does that mean? For the designed fan, its maximum air power is subject to the motor power and conversion efficiency, so when the air volume increases, the wind pressure must be reduced, and when the wind pressure is increased, the air volume must be smaller. However, air power is also closely related to the working environment, and the size of air volume and wind pressure is not a simple negative linear relationship.
This is from the macro to explain this problem, in fact, at every point in the wind flow, the wind volume and wind pressure are also rising, in order to better explain this problem and the needs of the following, let's first look at Bernoulli's principle.