Are all HSF's Badly designed

[dazza b]

Please bare with me while i try to explain this.

We all know that the most important things with a HSF are:

1) The velocity of the air coming out of the fan onto the HS
2) The difference between the temperature of the air being pulled throught the fans and the temperature of the HS itself.

Well, almost all HSF's have the fan positioned directly ontop of the HS .... this sounds like a good idea but due to the actual motor on the fan there is a dead spot of air directly in the center of the fan. If that makes sence.

So therefore the center of the fan does not create a high air velocity and there is less difference between the air temperatures. Now on a CPU which area is the hottest?? Its the Core which is in the middle of the chip and therefore in the middle of the HSF which is getting far less fast moving cold air being blown onto it ......... This to me sounds stupid.

So what can you do ???

Well if you raise the fan above the HS anout 1-2 inches the dead spot will have dissapeared by the time it reaches the HS as the walls of air which are blown from the fan willspread out and bring air in from the sides, sort of covering up the dead spot.


Does this make sence ????


W.O.R.D
Dazza B

[Darthtanion]

Lets consider something here. What happens with the airflow when it finishes the downsloping travel and colides with the heatsink? Does it die off and become moot?

Nope. It spreads outward to the outer edges of the sink so that it can escape, drawing out the heat from the base in the process. It cannot bounce back upward because of the continuous downward force of additional airflow. It cannot continue downward because of the base of the heatsink creating a block. So it spreads outward.

Also consider that the forced air is not all directly going in a 90 degree angle straight down from the fan.

Two other things to consider in your formula are the mass and weight of the heatsink. Material should also be considered. All added together, the modern heatsinks are both cool and effective. :)

[dazza b]

ahhh but, when the air hits the heatsink, it straight away increases in temperature due to it taking the heat away from the heatsink. Then it spreads out, so walm air is passing over the center of the HS and will therefore not take as much heat away as cool air could.

Also due to convection currents the air blown onto the HS will not spread to the centre of the HS (warmest part) it will be blown off to the sides.

2x 60 mm fans blowing at about a 45 degree angle onto the HS would be far more effective.

[ReSpAwN DeMoN]

That does sound logical but lets consider something else here. The cool air being blown on the HS from the fan however warm because it passed through the entire heatsink is FAR cooler then the heat just sitting there. Also the "cool" air being thrown out the sides of the heatsink will create a vacuum affect in the middle pulling all the hot air our. Plus when you have a fan moving 38CFM or 50?CFM trust me that middle part is not gonna sit there untouched especially when you about 2 inches worth of heatsink sitting above it.

[JealousMidget]

You mentioned convection, but just as important is conduction. When you cool the outer part of the HS, that draws heat from the center/warmer part of the HS. So that conduction is likely the driving method of cooling the center of the HS. I think the two fans at 45 degrees would be worse than the conventional setup. You would likelystill end up with a pretty good dead spot in the middle. Ideally, parallell to the surface would be best, in theory. Keep in mind that the fin layout of the HS is going to ultimately control how the air moves away from the center.

[Darthtanion]

There was a company not too long ago that created a heatsink like you suggest. I think the company name was Brown... something or other and they called their cooler the V-8. It used a pair of 60mm fans sitting at a 45 degree angle. I never got the chance to get my hands on one, but they were basically a flop.

Also, unless you placed some sort of divider between the two fan flows, you would do nothing more than create a terrible turbulence where the two flows met. This normally doesn't lend itself to effective cooling.

But hey... you go ahead and put that divider in place to counter the turbulence effect. Now you have a spot right above the central part of the heatsink that won't be directly hit by the air due to the divider being there.

Most of the bigger name heatsink manufacturers have put an awful lot of time and money into R&D when it comes to cooling. Their end result comes up as today's coolers. Why? Because they work and are about the best setup currently available.

[JealousMidget]

I think I vaguely remember someone trying the 45 degree angle. I don't remember hearing a lot of good things about it, probably for the reasons that you mentioned. I also remember last year, that a company tried the parallell flow idea that I mentioned. That didn't go over well either, but I think that was a flaw in the retention design. People were cracking their CPUs trying to put the thing on. I did see a couple reviews that said it was actually an adequate cooler - not stellar, but adequate. But it was such a pain to install, that even the reviewers that thought it cooled okay, didn't recommend it. The name of that particular cooler escapes me know, but there was a bit of a buzz, when it first became available.

[smokie]

Taken from General Fan Performance Guide:

In some instances, raising the fan slightly above the heat sink results in lower temperatures. One reason for this is the extra air that gets pulled in by the moving air stream. The other reason is that all fans have a dead spot in the center of flow immediately following the fan. This dead spot is cause by the central hub of the fan. This dead spot disappears after a short distance. Since the center of the heat sink has the highest temperature, the dead spot can cause elevated temperatures.


http://www.amdmb.com/article-display.php?ArticleID=132

[dazza b]

:D :rolleyes: :rolleyes: :D :rolleyes: :rolleyes: :D

I thank-you ..... for once i was right

[Wiggo]

Actually most HSF's have the fan raised slightly above the heatsink itself just for that purpose. ;)
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