How do different fan mesh patterns affect fan and chassis airflow ?

 
Is your chassis still equipped with this old style exhaust fan mesh? How about replacing a better one to improve performance?
 
The cooling performance of chassis is not only determined by fan size, the number of fans, and the airflow layout, but also by the type of exhaust fan grille/mesh that the fan is attached to. It is impossible to reach the maximum air flow in a computer system because the components inside the chassis cause resistance, which prevents fans from achieving their maximum air flow capability (please refer to the previous article: What is air pressure?). To understand how we can achieve more efficient air flow by using the right fan grille/mesh, we need to calculate the ratio of the opening. The higher the exhaust ratio is, the lower the air resistance and therefore, resulting in higher maximum air flow from the fans.
 
Why lower area ratio of exhaust air will result in higher air flow resistance and noise?
 
When the ratio of exhaust air is lower, more air flow produced by the fan is pressing against the grille/mesh, resulting is higher energy loss. Therefore, the higher the ratio of exhaust air, the better air flow performance becomes.
 
The following table is a comparison of different styles of fan grille/mesh. This data retrieved from all grille/mesh are conducted under identical condition.  The results clearly show that wire grille has the best performance of all fan grille/mesh solutions.

 

Fan grille /
mesh style

Picture

Exhaust Air Ratio

Speed
(testing with FN121)

Speed Ratio
(based on free open air)

No grille/mesh

100%

3.1 m/s

100%

Wire grille

71%

2.6 m/s

84%

Hexagonal Venting holes

72%

2.4 m/s

77%

Square venting holes

60%

2.2 m/s

71%

Round venting holes

29%

1.1 m/s

35%

 
Why wire grille can result in lower noise?
 
Stamped out mesh pattern found on many chassis, regardless of the venting holes shape, have areas that sits vertical to the air flow path.  This results in air bouncing back from non-vented area of the mesh, creating small pockets of air swirls and turbulence.  Air turbulence such as these is a major contributor to chassis noise.  With wire grille, the air flows more smoothly due to the rounded shape of the grille so the noise is significantly lower.

 

The air flow line of wire grille section

 

The air flow line of mesh venting holes section

 
Since 2005, nearly all mainstream and premium SilverStone chassis models have implemented wire grilles as standard equipment.