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Airflow Cooling and CFM

E

EL_BaRTO

Weaksauce
Joined
Sep 16, 2005
Messages
73
Greetings! Well I've decided to "revamp" my airflow for better cooling/temperatures, but I'm trying to gather as much information before I decide how I'll do it. My question:

In regards to negative and positive airflow, is have an increase in CFM on a fan really a big deal on airflow circulation? Let me give an example to clear up my question:

System A: Has total outflow CFM of 1200 and inflow CFM of 600
System B: Has total outflow CFM of 600 and inflow CFM of 300

As you can see both basically have a negative airflow system (more outflow than inflow of air) and same ratio of airflow difference (plz check my math. I suck @ math). My question is: If both have same ratio of airflow difference to be a negative system, does the 1200 cfm benefit the system more than the 600? If system A doesn't give any or little benefit compared to system B, I'd rather choose B cuz it's more quiet and just as effective. Or is system A more efficient cuz it has higher CFM on inflow/outflow of air, even with the same airflow ratio?

Sorry if I'm rambling just want to make sure my question is clear. Lol. I've got a lot of various fans (scythes, panaflos, san aces, etc). Just need to know as much as I can before going all out on airflow. Lol.
 
System A will outperform System B. Quite a number of variables do come into play which will alter just how much difference there will be in performance, but under normal circumstances it's nothing to worry about.
 
The flow rate will have a drop off point where more flow wont benefit you very much, but at what flow rate that happens is dependant on too many things for anyone to guess at, you just have to test it and see what happens. Keeping the same arrangement and same ratio between the fans, a higher CFM will always cool better, the question is how much better it will cool and you can only experiment.

You can't have "negative airflow" or "positive airflow", what flows in must flow out. Conservation of mass and all that jazz. If you have a 1200 CFM fan blowing out and 600CFM blowing in, 600CFM has to be flowing in through gaps and cracks to create a balance in mass flow and/or the 1200CFM fans wont actually run at 1200CFM and/or more than 600CFM will be sucked through the 600CFM fan. Which of those 3 things happen depends on the system and fan layout (and it will likely be some mix of those 3 things)

The most important thing is where you locate the fans, once you've got that sorted you can start playing with flow rates and decide where you want to sit on the flowrate vs noise curve.

The ratio of inflow to outflow is relavant of course, but you can't make guesses on what is best, the fluid dynamics is just too complicated. Simply make a best guess with the arrangement, maybe try a few different arrangements, then test flow rates and ratios of fan speed in and fan speed out.
 
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