What are the Maximum Air Flow and Maximum Static Pressure of Fans?

In this column, we will introduce the maximum air flow and maximum static pressure of a fan in an easy-to-understand manner using models of each condition.

• 

  Ms. Ori, can I ask you something?

• 

  What is it, Vex?

• 

  A customer had a question about cooling fans, and asked what the "maximum air flow" and "maximum static pressure" in the catalog are…
  I can kind of imagine it, but I can't really explain it...

• 

  You're right, it's certainly difficult. Let's start to consider with the air flow.
  The unit for air flow is [m³/min]. For example, 1 [m³/min] means that a volume of 1 m³ of air can be blown per minute.
  In other words, air flow is the amount of air flowing.

• 

  I see what you mean. Then how should I think about static pressure?

• 

  The unit for static pressure is [Pa], which refers to the pressure of air.
  The relationship between the air flow of a fan and static pressure can be shown in the air flow - static pressure characteristics graph below, so I'll use this to explain briefly.

  

  ① is when the outlet of the box is fully open and there is nothing to block the fan's airflow. So all the wind that is inhaled will be exhaled.
  This is called the maximum air flow, and the static pressure is 0 [Pa].

  

  For ③, the pressure inside the box will increase if the air is pumped in while the box's exhaust outlet is completely blocked. If this continues, even rotating the fan will not produce airflow any more. This is called the maximum static pressure, and the air flow rate is 0 [m³/min].

  

• 

  Oh, so that's how it is. I now properly understand maximum air flow and maximum static pressure. Then what is the state of ②?

• 

  For ②, as the outlet is narrower than the intake, it is difficult for the air to flow, and air flow will be less than maximum air flow. Instead, the pressure of the air inside will increase, so the static pressure will increase.

  

• 

  So that's how the relationship between air flow and static pressure works.
  Axial flow fans are often used to cool the insides of control cabinets, but I think it would be better to have a large outlet.

• 

  That must be the case. But, be careful even if the outlet is enough, maximum air flow may not flow through.

• 

  Huh? What does that mean?

• 

  If you're thinking about cooling the inside of a control cabinet, mounting density is also an important point.

• 

  The mounting density inside the control cabinet?

• 

  For example, if there are fewer components in the control cabinet, the air flow path is wider, so the air flow is easier and similar to ①.

  

  On the other hand, if there are too many components, the airflow path in the control cabinet will be narrower. The wind becomes difficult to flow, so the situation will be similar to ②.

  

• 

  I see, so I have to consider not only the size of the outlet, but also how much there is in the control cabinet that will obstruct the wind flow.

• 

  Yes! For cooling the inside of a control cabinet, it's better to choose a fan with about twice the air flow required, considering that the actual air flow will be about half of the maximum air flow.
  By the way, Vex. Isn't it difficult to explain the air flow like this?

• 

  Yes. It's because it's something we can't see.

• 

  That's right. But, there’s actually a video that uses smoke to visualize the wind flow.
  You can see how the air flow changes depending on the size of the intake, whether there is a divider plate or not. Knowing all of these will help you use the fan effectively.

• 

  I didn't know about this... Thank you very much.
  When we receive inquiries about wind flow, I will proactively introduce these videos to the customers.

• April 15, 2022  Updated with the latest information.

Related Content

e-learning "Basics of Cooling Fans"

Technical Document "Relationship between Air Flow, Static Pressure, and Equipment Cooling Efficiency"

Related Products

View More About Cooling Fans

Cooling Fans