Couple of (probably stupid) fan questions

[Wej]

My heatsink (a ridiculously sounding Norse name that I've temporarily forgotten) has a side mounted fan.

Firstly, how do I know which side sucks and which side blows? One side the fins curve away (sort of convex), the other side curve towards (i.e. sort of concave).

Secondly, should a fan blow or suck on a CPU heatsink?

I know these questions are probably noobtabulous, but there you go!

 

[Zefan]

You can work out which way a fan will blow by using common sense.... think about it!

Whether you should fit it to blow or suck is debatable and dependent on the rest of your case airflow/position of your heatsink with relation to case fans. I'll let others answer that.

 

[Wej]

Well my case has a shedload of fans all over the place. I have a degree (albeit a rubbish 3rd) in Physics and I'm not sure my knowledge of fluid dynamics is good enough to work out the airflow inside.

As for the fan thing, I'm being stupid. Trouble is it's been a long day and I was trying to take a shortcut rather than thinking. Which is a bit hypocritical as it annoys me when other people do it!

I would imagine sucking is better (so to speak) as at least you then know that the warm air is coming out in a relatively ordered fashion, whereas if it's blown through the heatsink surely the fins would 'diffuse' the resultant hot air, making it harder to deal with?

 

[martian_aphid]

If you can't work it out by inspecting the blades there are couple of things to do: first look for some arrows on the sides of the fan housing - one pointing through the fan [direction of airflow] and the other showing which way is upright. I have usually found the side with the sticker on the centre to be the side that draws air, though I don't know if this is a rule. The last step would be to just plug the fan in and see which way blows air in your face!

I've usually had my fans blowing air through my heatsink but that's because I have an exhaust fan at the back which draws this air out of the case.

 

[j.col]

usually you have the fan blowing through the heatsink.
back of case <- rear case fan / heatsink <- fan
<- being air flow
is usually the best way

just plug the fan into a mobo header and feel the breeze and note which way its blowing

 

[BrianB]

The flat frame is always at the back of the fan. Fans look best facing you. Air always blows out the back.

The idea of heat sink fan is to have high static pressure (CFM for unrestricted fans), it can blow the fresh air through the fins as they radiate the heat which is more effective than trying to spin at such high rpm as to create a vacuum to remove the heat. Also one fan at the back pulling looks backwards.