Suck or blow

[CarlD]

I'v asked a few people this question but i would like other peoples opinions..

i have 3 120mm fans that will be going on my new rad and i would like to no if i should get the fans to suck the air or make the fans blow air across the rad?

(rad will be mounted outside the case)

 

[nick_lerwill]

"Suck or blow" different name for same thing lol

 

[CarlD]

pfft im too tired to explain fully You no what i mean


/\ /\ /\ /\
--------------------- - suck
---------------------


\/ \/ \/ \/
---------------------
--------------------- - blow

---- = rad
/\ = air flow direction

/\ = suck
\/ = blow

tbh i dont think that helped at all.

 

[Felix Da Housecat]

Blow

 

[CarlD]

Lol thanks.. ahh im laughing at my post now

 

[Felix Da Housecat]

Lol thanks.. ahh im laughing at my post now

but it's ok to suck too i guess



Taxi

 

[CarlD]

Lol =]]]

 

[Mr-White]

blow always has given me better temps, the only time i used suck was when i had 6x 120mm fans on my thermochill he120.3

MW

 

[nippynoo]

Definitely blow - because sucking draws in air from all 180 degrees (including sideways!) so if there's any gaps on the side, thats where the easiest air flow is from. Blowing is a focussed jet.

Its how our nostrils work - ie its why we dont die from breating in the air we just breathed out.

 

[SteveOBHave]

Blow as it allows you to control where the air is coming into the machine and means you won't be sucking dust in through all the little gaps in the case.

 

[xrob]

why dont you just test it yourself? will more than likely depend on the airflow of the fans output, and the what the rad is designed for. just try it both ways and see which ones gives the best performance although i really dout you will see much difference.

Blow as it allows you to control where the air is coming into the machine and means you won't be sucking dust in through all the little gaps in the case.

with watercooling on rads thats not true because you can just mount them on the opposite side, i have 3 YS-TECH FD1238 120mm Fan on my PA120X3 sucking out the top of my Lian-Li PC V1000 PLUS.

 

[harris1986]

here's a quick question for you which hopefully should see you figure out the answer to this question!

if you are hot and switch on a fan are you sat infront of the fan so the air is blowing at you or are you sat behind the fan so it is sucking air?

answers on a postcard people - a milkyway bar on it's way to the first correct answer!

 

[welshtom]

I think most old school watercoolers (including me) will say suck. But i dont think there is much difference at all.

Tom

 

[Marci]

S'all about positive and negative pressures, and which assists in getting better air dispersal over the entire core surface area... and pull (suck) has been tested to win in the majority of cases for the majority of rads with the majority of fans.

 

[FrostedNipple]

theve brought out 2 different types of fans, they either spit or swallow, aaahahahaha

but in a more serious retrospective ( :S is tht a word) i would have them blowing on the rad cuz u sit infront of the fan(can i have the milkyway bar now, you can email to me )

 

[fornowagain]

here's a quick question for you which hopefully should see you figure out the answer to this question!

if you are hot and switch on a fan are you sat infront of the fan so the air is blowing at you or are you sat behind the fan so it is sucking air?

answers on a postcard people - a milkyway bar on it's way to the first correct answer!

Take the same fan, stick it in a tube and put you head at either end. Its the same air flow rate m3/s at either end, same cooling ability. The main difference in the example is the highly turbulent air flow after the fan compared to the semi-laminar before it. Assuming the fan is sealed at the sides to reduce pressure loss. Then I'd say blow because turbulent airflow gives better surface cooling than laminar which is good for less noise and friction. Turbulent flow is known to mix any static air at the convection surface. Practically, if its sealed then the difference would be tiny.

 

[joeyjojo]

Didn't read the op properly, but my rad works better with fans sucking through it. Also, makes dust removal easier as you can just vacuum the non-fan side, if blowing you have fans in the way. Words of wisdom those

 

[Cir108]

In fluid dynamics, the study of the movement of fluids, blowing will cause turbulent [or uncontrolled] flow whereas sucking will effect a laminar [or controlled] flow. This means that blowing is better if you want cooling in an uncontrolled fashion which is more applicable to a HSF [or water block] for the aim is to disturb the movement of air “all over” the cooling surface. Sucking is more applicable to a “smooth” flow over the cooling surface where you need to manupilate the fluid [air in this instance] flow to achieve various parameters like pressure, velocity, lift, etc, for various technical goals.

In the case of a fan blowing into a HSF array of fins, the fan will supply the pressure to maintain the turbulence in order to reach the surface of the cooling fins. In contrast, when air is sucked through the cooling fins, there is almost zero air movement on the actual surface of of the fins [called the sub-laminar layer] and this will result in less cooling.

 

[Dist]

not owning i water cooling system myself i dont know what the rads look like up close, but can you put a fan on one side to blow, and a fan on the other side too so that one fan blows cool air onto the rad, and the fan on the other side sucks that now hot air and blows it away?

 

[fornowagain]

snip

Would you care to express that as a dimensionless number? Only kidding.

Boundary layers? Been awhile, there an intermediate buffer layer as well if I remember correctly? Anyway one point, I doubt that the flow of air so close to the fan inlet (i.e rad matrix) will remain entirely laminar, certainly within the velocity gradient. It brings to mind the minimum length to diameter ratios needed in wind tunnels for laminar flow. IIRC based on the Reynolds number.