Re: Replacement power supply and CPU fan/thermal cooler?

[Maurice Hilarius <maurice harddata com>]

With regards to your message at 12:20 PM 2/18/02, Alan Young. Where you stated:
> Do you know what the rating (CFM or RPM) of a fan for a LX 533 needs to be?
>
> Have you had any experience with a 80mm fan and a CPU funnel
> similar to this http://www.coolerguys.com/cpucool/filtersguard.shtml ?
>
> Thanks,
> Alan
Unfortunately cfm airflow is only part of the info.
Airflow against resistance is usually more important.
Specified cfm is measured with the fan unimpeded, that is to say not 
directly attached to a heatsink.
Actual airflow is severely diminished simply by putting it next to a flow 
resistance.
Most axial fans do not perform well against an adjacent resistance, usually 
dropping airflow by 50% or more.
A lot of these guys using a bigger and slower rpm fan are fooling 
themselves. They read the rating for cfm of a fan and say "cool, this fan 
moves more air, so all I have to do is adapt it down to the heatsink".
What they are ignoring is that when you put a restriction on a fan like 
this the airflow drops off severely.
To counter that fans need to be used that are designed to provide flow 
under resistive conditions.
Fans like that usually have more blades, and or deeper/taller designs.
Indications of flow capability are usually expressed in terms of inches of 
water they will raise.
Here is a very good example of what I am talking about. This line of fans 
is specifically designed to run against a high resistance.

http://www.deltaww.com/products/dcfans/pdf/FFB606038.pdf

Here is a listing for a comparably sized "conventional" design high-flow fan.
Note that the figure for inches of water is about half that of the previous 
example.


Ideally a blower can be used, as the perform much better in this application.
Unfortunately it is much hard to fit a blower over a heatsink effectively.
I think the stock fan is likely to be as good as you are going to find in 
terms of actual airflow.
Anything that produces better flow is likely to be turning at higher rpm, 
and WILL be much louder.
Anything more quiet will almost certainly produce less airflow.

We have done testing using 80mm fans with adapters on athlons, and in every 
case the actual airflow on a ducted  80mm fan was much lower than the 60mm 
higher rpm versions.
To get back to the same airflow we had to use a higher rpm fan, and then it 
was not any quieter.

Some references on fans from the manufacturers:
http://www.deltaww.com/products/dcfans/default.htm
http://www.nidec.com/fans.html
http://www.globalwin.com.tw/
http://www.sunon.com.tw/index_en.htm

Anyway, I still feel there is little to be gained in your case, unless you 
are prepared to use a high capacity blower and fabricate a duct for it..
A lot of work..


With our best regards,

Maurice W. Hilarius       Telephone: 01-780-456-9771
Hard Data Ltd.               FAX:       01-780-456-9772
11060 - 166 Avenue        mailto:maurice@harddata.com
Edmonton, AB, Canada      http://www.harddata.com/
   T5X 1Y3

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