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PostPosted: Tue Sep 04, 2007 1:54 am 
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in theory, a rad with more widely spaced fins presents less backpressure to the fan, so airflow is higher. however there is reduced surface area, so one has to ask if the increase in airflow can compensate for the decrease in surface area; according to chylld's experience, clearly not. :wink: however the papst fans are known for having good pressure characterisics, so one should maybe not generalise that all fans will handle dense rads so well.


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PostPosted: Tue Sep 04, 2007 2:05 am 
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Location: Sydney, Australia
jaganath wrote:
in theory, a rad with more widely spaced fins presents less backpressure to the fan, so airflow is higher. however there is reduced surface area, so one has to ask if the increase in airflow can compensate for the decrease in surface area; according to chylld's experience, clearly not. :wink: however the papst fans are known for having good pressure characterisics, so one should maybe not generalise that all fans will handle dense rads so well.


very true... apparently the smallest difference in fan blade geometry can make a big change.

one thing that i forgot to mention in my last post, was that i am running my fans in a 'pull' configuration; which for me at this airflow with this heatercore, works 3-5 degrees C better than a 'push' configuration. i also have a good 2-3" between the fans and the radiator which helps to reduce the effect of any dead zones (e.g. the areas immediately behind the fan's hub)

i think (someone correct me if i am wrong) that airflow is more turbulent leaving a fan than it is entering a fan, i.e. in the case of rotary case fans, the airflow is 'smoother' as it speeds up, but 'rougher' as it slows down. this might explain why you can get such good performance using low speed fans in a pull configuration.


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PostPosted: Tue Sep 04, 2007 3:00 am 
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Quote:
airflow is more turbulent leaving a fan than it is entering a fan


absolutely bang on:

http://www.ebmpapst-ad.com/features/art ... rt006.html

Quote:
This is largely because the flow of air into a fan is usually laminar and smooth, while the exhausted air is much more turbulent.


most axial fans emit a hollow rotating "ring" of airflow, although fans with a substantially different gemoetry (e.g. Noctua) seem to have a very different airflow pattern.


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 Post subject: Fin spacing
PostPosted: Tue Sep 04, 2007 5:00 am 
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Food for thought. I thought I'd seen somewhere that the Ninja air cooled heatsink worked so well because teh fins were more widely spaced than other models. but those are also usually set up as "push" systems when used with a fan.

Maybe I'll rework my system this weekend. I'm using a push system with a one inch shroud. I think I'll just turn that around and use it as a pull and see what happens.


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PostPosted: Thu Sep 06, 2007 1:13 pm 
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with well designed radiators the fins per an inch doesn't mean much because rad with low FPI would just be made thicker while a rad with a lot a FPI would be thin eithier way you would end up with same surface area. Something to consider is with a higher FPI your going to catch alot more dust unless air is some how filtered


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PostPosted: Thu Sep 06, 2007 2:06 pm 
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Location: Sydney, Australia
res0r9lm wrote:
Something to consider is with a higher FPI your going to catch alot more dust unless air is some how filtered


dust? what dust? :D

Image

unbelievably my airflow and temps weren't affected much by the dust... probably due to the pull configuration.


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