Minimum distance of wall from inlet of PC axial fans?

[iamoni]

I am planning on using pc axial fans for better air circulation inside a grow box I am designing.
What could be the minimum distance I need from the wall to the inlet of the fan so I am not obstructing air flow?

 

[algreenery]

i dont know exactly what centimeters or inches you are going to need but if you are placing your hand behind the exhaust you can feel the air pressure. if the air pressure is to hard when it hits the wall try to give it some more space until you find the perfect distance. It all depends on how much air your exhaust is pulling i guess.
Check the temps at the same time too!

 

[Jhhnn]

Imagine a cylinder between the inlet and the wall, same diameter as the inlet. The surface area of the cylinder should at least equal the area of the inlet for full flow. Making the distance from the wall the same as the inlet diameter is a safe bet.

 

[iamoni]

Wow! Now here's something I can work with, this makes so much sense.
Let's see, the formula for the area of a circle is pi × r2.
For the cylinder, we will imagine it as a rectangular plane. I will not include the area for the two circular plane since those are the fan inlet and the wall

The fan's diameter is 11.5 cm, so it's inlet surface area is
r= 5.75
pi = 3.14
area = 103.8 cm2.

For the cylinder's area, the height is equal to the distance of the fan from the wall. The length is equal to the fan inlet circumference.
Circumference is pi x diameter
diameter= 11.5 cm
pi = 3.14
circumference is 36.11 cm

So the height of the cylinder will be, the area of the inlet divided by its circumference
103.8 cm2 / 36.11 cm = 2.8748 cm or I can round it to 2.88 cm for safes.

I have done some Googling recommending the distance of 10% - 15% of the inlets diameter for axial fans. That equals to 1.15cm to 1.575cm. Supposedly distances less than these will create noise or a reduce in function.

 

[Jhhnn]

Sure, iamoni. What I offered is an old rule of thumb for hvac techs. It works, for sure. Less distance may work, too.