determining direction of fan airflow

[wm]

I'm building a PC and I don't have an available power supply yet, so I'd
like to know if there's a way to determine which way a fan will blow. I
noticed that the fan blades are all curved. With my limited knowledge
of aerodynamics I believe the fans will blow in the direction of the
convexity of the fan blades. In other words, the radius of the
curvature will be on the side where air blows away. I wish I could
explain it in better words. Can anyone confirm this, or let me know of
a better way to determine?

~wm

 

[Martin]

I'm building a PC and I don't have an available power supply yet, so
I'd like to know if there's a way to determine which way a fan will
blow. I noticed that the fan blades are all curved. With my limited
knowledge of aerodynamics I believe the fans will blow in the
direction of the convexity of the fan blades. In other words, the
radius of the curvature will be on the side where air blows away. I
wish I could explain it in better words. Can anyone confirm this, or
let me know of a better way to determine?

~wm

Yup, look on the side of the fan for a little arrow. With my limited
knowledge of archery, I have concluded that the air blows in the direction
of the arrow!

;>)

Martin

 

[Jon Danniken]

Yup, look on the side of the fan for a little arrow. With my limited
knowledge of archery, I have concluded that the air blows in the direction
of the arrow!

Another method is to look for where the opening for the motor is; that is always faces towards
output side.

Jon

 

[ric]

I'm building a PC and I don't have an available power supply yet, so I'd
like to know if there's a way to determine which way a fan will blow. I
noticed that the fan blades are all curved. With my limited knowledge
of aerodynamics I believe the fans will blow in the direction of the
convexity of the fan blades. In other words, the radius of the
curvature will be on the side where air blows away. I wish I could
explain it in better words. Can anyone confirm this, or let me know of
a better way to determine?

Other than look at the arrow on the fan's casing?

Imagine the fan's blades as a spoon. The air flows out of the section
of the spoon that would hold the cereal.

( airflow is ->

 

[tweak]

Other than look at the arrow on the fan's casing?

Imagine the fan's blades as a spoon. The air flows out of the section
of the spoon that would hold the cereal.

( airflow is ->

In layman's terms the airflow is out of the power supply..
Common sense says you don't want it sucking air into the case, all
that dust. So a it blows out and a vent is located somewhere on the
front?side of the tower case to allow for cross flow.

 

[DaveW]

PSU suck air up into the unit's bottom fan and blow it out the back of the
case. This describes the action of 90% of the PSU's out there.

 

[wm]

Yup, look on the side of the fan for a little arrow. With my limited
knowledge of archery, I have concluded that the air blows in the direction
of the arrow!

;>)

Martin

Well color me jackass! I can't believe I missed something so obvious.
And here I was trying to remember physics to figure this one out. =/
Thanks a bunch.

~wm

 

[jeffc]

Imagine the fan's blades as a spoon. The air flows out of the section
of the spoon that would hold the cereal.

( airflow is ->

Thinking of ice cream rather than cereal usually gives more accurate results
for me.

 

[Martin]

Well color me jackass! I can't believe I missed something so obvious.
And here I was trying to remember physics to figure this one out. =/
Thanks a bunch.

~wm

If it's any consolation, I did exactly the same as you once. I had to post
to a NG to get the answer too..... (and I'm not just saying that to make you
feel better).

Martin

 

[Kevin Lawton]

| PSU suck air up into the unit's bottom fan and blow it out the back
| of the case. This describes the action of 90% of the PSU's out there.

Except for the majority of PSUs which only have one fan

 

[Phisherman]

I'm building a PC and I don't have an available power supply yet, so I'd
like to know if there's a way to determine which way a fan will blow. I
noticed that the fan blades are all curved. With my limited knowledge
of aerodynamics I believe the fans will blow in the direction of the
convexity of the fan blades. In other words, the radius of the
curvature will be on the side where air blows away. I wish I could
explain it in better words. Can anyone confirm this, or let me know of
a better way to determine?

~wm

On many fans there is an arrow engraved in the plastic case on the
side. This show the direction of the airflow, provided you hook up
the fan properly. Since the fan is DC, you can cross the the input
wires and the fan will blow in the reverse direction.

 

[ric]

Since the fan is DC, you can cross the the input
wires and the fan will blow in the reverse direction.

You have been told many times that this is RUBBISH! DC fans for PCs
spin in ONE direction only. Reverse the wires and the fan WON'T SPIN.
Why do you keep repeating this misinformation?

Credibility meter: * \ *

 

[jeffc]

| PSU suck air up into the unit's bottom fan and blow it out the back
| of the case. This describes the action of 90% of the PSU's out there.

Except for the majority of PSUs which only have one fan

I think he was merely describing air direction - up into the unit's bottom
and out the back. That probably describes more than 90% of the PSUs out
there.

 

[wm]

I think he was merely describing air direction - up into the unit's bottom
and out the back. That probably describes more than 90% of the PSUs out
there.

Uhm....90%? Are there actually PSUs out there that blow air IN to the
case? That wouldn't work too well seeing as the power supply actually
heats the air passing through it....

~wm

 

[wm]

Thinking of ice cream rather than cereal usually gives more accurate results
for me.

Dammit man! Now you made me hungry...

~wm

 

[Gary Tait]

On many fans there is an arrow engraved in the plastic case on the
side. This show the direction of the airflow, provided you hook up
the fan properly. Since the fan is DC, you can cross the the input
wires and the fan will blow in the reverse direction.

It isn't stictly DC. It is a two-phase electronically coomutated
motor. With that, it will work with power connected one way only.

 

[jeffc]

Uhm....90%?

I said more than 90%

Are there actually PSUs out there that blow air IN to the
case? That wouldn't work too well seeing as the power supply actually
heats the air passing through it....

But there are also the cases where you can suck air in the bottom of the PSU
and out the top (not back) of the PC, suck air through the sides (not
bottom) of the PSU and out the back of the PC, etc. There have been cases
where the PSU blows in, but I haven't seen one like that in a long time.

 

[jeffc]

You have been told many times that this is RUBBISH! DC fans for PCs
spin in ONE direction only. Reverse the wires and the fan WON'T SPIN.
Why do you keep repeating this misinformation?

I believe this was not always the case. It could be lingering memories. I
know I've seen fans spin in both directions, but I don't remember which fans
or how long ago it was. Until corrected last year on this forum, I thought
the same thing Phish did.

 

[Sooky Grumper]

I'm building a PC and I don't have an available power supply yet, so I'd
like to know if there's a way to determine which way a fan will blow. I
noticed that the fan blades are all curved. With my limited knowledge
of aerodynamics I believe the fans will blow in the direction of the
convexity of the fan blades. In other words, the radius of the
curvature will be on the side where air blows away. I wish I could
explain it in better words. Can anyone confirm this, or let me know of
a better way to determine?

~wm

Look on the black plastic housing around the fan. On one side, it'll
have two arrows in the plastic, perpendicular to each other. One is
blade rotation direction, the other is airflow direction.

 

[Andy]

Uhm....90%? Are there actually PSUs out there that blow air IN to the
case? That wouldn't work too well seeing as the power supply actually
heats the air passing through it....

~wm

Yes, that was the original ATX design specs. Theory was to push more air to
the CPU.

As we all know nearly everyone quickly ignored that part of it but I still
have a couple of original ATX supplies that I had to reverse the fan on.

Andy