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Air pressure, heatsinks.

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March 14, 2011 4:15:51 AM

I am getting slightly varying results about cfm versus air pressure of fans from the internet articles I have been finding. I want to see what you guys say. But here is what I think I know:

-cfm and ap are important on heatsinks
-the denser the fins are on the heatink or radiator, the more need of higher ap
-cfm is more the cause of noise, so low noise (probably achieved through less cfm and other sound dampening tweaks) high ap fans are ideal choices for cpu fans (Like xtraflo, blade master, and excalibur from CM)
-cfm is more important for case fans, ap is more important for heatsinks
-ap and fan turbulence are the same thing



What fans do you all use for your heatsinks and why? Got any corrections for me?

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
bought one of these, second one is on its way ^_^ I've read their ap is over 10!

More about : air pressure heatsinks

a b K Overclocking
March 14, 2011 4:37:45 PM

This involves Fluid Dynamics.

Consider flow of water through a pipe. There is water flow and also water pressure. A higher water pressure will result in more water as well well as more flow of water.

For heatsinks, the greater the air flow, the greater the heat transfer. Of course, greater air pressure will create greater air flow (all other things held constant).

CFM is one of the factors affecting noise. Others include bearings design and type, vibrations, resonant frequencies, and turbulence.

Air pressure and turbulence are not the same thing. If they were, then there would be no need for two separate descriptions. Turbulence (or lack of laminar flow) may happen at high air pressures, low air pressures, and in between. It is a function of airfoil (fan blades in this case) design, and whether the tip velocity is near or exceeds Mach1.

Now leave Fluid Dynamics aside, look for fans based on pricing, specs., >60 CFM, and pick the ones that have the lowest DbA rating. Try one or two different well known brands.

The fan you picked has an excellent CFM rating, ideal for cooling fins.
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March 14, 2011 5:14:57 PM

Ubrales is correct....it sounds like you are looking for a magic bullet - one fan that is the best. They dont exist.

Every fan is a compromise between airflow and noise and is complicated by the case airflow - and if you push too much air thru the cpu cooler relative to the case exhaust, the heated air will loop back around to the input of the cpu cooler decreasing efficiency.

Most people try to maximize airflow while keeping the sound down. This is why you see a fan on both sides of the cpu cooler. High CFM, low noise, low RPM.
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a b K Overclocking
March 14, 2011 10:02:06 PM

vvhocare5 said:
Ubrales is correct....it sounds like you are looking for a magic bullet - one fan that is the best. They dont exist.

Every fan is a compromise between airflow and noise and is complicated by the case airflow - and if you push too much air thru the cpu cooler relative to the case exhaust, the heated air will loop back around to the input of the cpu cooler decreasing efficiency.

Most people try to maximize airflow while keeping the sound down. This is why you see a fan on both sides of the cpu cooler. High CFM, low noise, low RPM.

^1 vvhocare5! A gentle breeze as opposed to a tornado!

Paying attention to the temps while changing ONE variable at a time will help achieve good results.

For the adventurous who want to achieve the correct combinations of fans, CFM, low noise, etc., there is DOE (Design Of Experiments). DOE is a multi-variables matrix solution that will solve for maximum (or minimum as the case may be) value of the objective function in just a few experiments. This is especially effective when the interactions among the variables is unknown. Also in instances where the solution has only one optimum value (when the variables are increased in value, the output decreases or vice versa).

More information in this technique, read this: http://www.jmp.com/support/downloads/pdf/jmp_design_of_...
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March 15, 2011 2:26:58 AM

Oh yeah, but I don't care about noise really. I want lower temps. As long as it is under 65dba, I don't really mind. Anyway, I'm mostly after air pressure versus cfm on heatsinks. Especially denser ones like mine.
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a b K Overclocking
March 15, 2011 10:45:46 AM

sparkle_ftw said:
Oh yeah, but I don't care about noise really. I want lower temps. As long as it is under 65dba, I don't really mind. Anyway, I'm mostly after air pressure versus cfm on heatsinks. Especially denser ones like mine.

The fan you picked has a great air flow (CFM) and would be my personal choice too. In fact, I have added it to my wish list!
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a b K Overclocking
March 15, 2011 6:36:43 PM

Sparkle - There's a lot of information missing.

Which heatsink is the fan for - cpu, gpu, or a chipset?
Which brand and model cpu/gpu/chipset are you trying to cool?
Which brand and model cpu/gpu/chipset heatsink do you have?
Which brand and version thermal compound do you use?
Which brand and model gpu do you have?
Which brand and model pc case do you have?
Did you install additional case fans?
Do you overclock the cpu and gpu?
Do you use power management to control fans?
What is the ambient air temperature in the room where the pc is located?

These are all important questions. For example, there is no point in using a 3,400 rpm fan on a cpu heatsink when the heatsink was designed for optimal performance with a 1,600 rpm fan. It would help quite a bit if you posted answers to the questions.
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March 16, 2011 5:18:40 AM

I'm not really looking for help, I've got my temps covered... I was just trying to see if you guys knew about cfm/ap on heatsinks and what is a good ratio for optimal performance or whatever. I was also looking to see what other OCers used on their heatsinks and radiators. Mine:

Cooler master V6 with dual Delta AFC1212D-PWM (kept the cool red fan it came with though)
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a b K Overclocking
March 16, 2011 10:34:04 AM

I still use my original Coolermaster Hyper 212 (not 212+) cpu heatsink with one Scythe S-Flex 120mm 1,600 rpm fan and IC Diamond 7 Carat Thermal Compound. It works for me. I experimented with two case fans on the heatsink but it did not make a difference. The fan on the rear of the heatsink was too close to the case fan at the top of the rear panel. Even though the fans were identical they were out of sync which caused too much turbulence for optimal airflow and cooling.

I also use the Scythe S-Flex 120mm, 1,600rpm fans as case fans in my Lian Li/Lancool Dragon Lord Case. I mounted one fan in the top three drive bays using a Coolermaster 4-in-3 drive bay device. That top front fan, the cpu heatsink fan, and the fan at the top of the rear panel all line up to form a wind tunnel effect.

Over the years there have been quite a few discussions about air pressure but they were usually about air pressure inside a pc case rather than fan air pressure. Some individuals advocated positive air pressure while others advocated negative air pressure. Personally I just go for a balanced approach. I use two intake fans and two exhaust fans.

A long long time ago when Intel first started making cpu's that ran hot we didn't care about noise. We used heavy duty Delta and Panaflo fans. They sounded like jet fighters at full throttle. Things have changed.
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March 16, 2011 1:03:03 PM

Noise will change over time as the bearings need oil or start to wear out.
When they wear out, they will make a grinding noise and finally lock up.
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