View Full Version : Brain teaser fan airflow in case question ...
davidm71
12-15-2009, 09:02 PM
Wondering if you have a radiator, and the top fan is pushing out 50cfm and the bottom fan is pushing in 70cfm, how many cfms come out of the rad? 50 +70? 50? or 70?
Thanks.
My guess is 70?
It depends on how much restriction you get from the radiator. The fan is not a magic machine always producing the same airflow regardless of resistance. Increased flow resistance reduces flow, putting two fans in series pretty much ads the two fan curves, increasing static pressure and hence flow.
It is impossible to have different air flow though two fans in series, unless you somehow removes part of the airflow between the fans.
FireDragon
12-15-2009, 11:29 PM
AFAIK u shouldn't use different fans on one side then the other, they should b the same fans on both sides of the rad, also putting 2 fans in series doesn't increase air flow only pressure like has been said, if there is a high restriction case then 2 fans stacked WOULD give more CFM then a single fan but only because it has more pressure not because it is moving more air vs one fan, understand?
Dragon
Serpentarius
12-15-2009, 11:43 PM
radiator normally cut ~50% cfm on passing
place your hand near the below fan (intake) ... if you felt the some slight air is leaking out from the circular sides, then there's air restriction i.e thick grills or positive pressure
if you're a smoker, could always smoke a cig, blow it to the balloon and release it to see the air movement ..
davidm71
12-16-2009, 05:08 AM
Well lets say the two fans are in a pipe with no restriction? I read that fans are like pumps and that two fans in a pipe will blow out as much cfms that the highest rated fan can push out ??? I think.
On my rad I have three pairs of fans, top and bottom, where the bottom fans are more powerful. Its not ideal but I ran out of fans and thats the best that I had...