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SLK-900 heatsink fan blowing OUT = 13 degrees LOWER temps

By acidosmosis
Apr 7, 2003
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  1. Wow I turned the 80mm heatsink fan around and pointed the air outwards away from the heatsink and now I'm getting about 13'Fahrenheit less than before (now at 107'F when using my PC -- browsing,etc).

    Definately recommend trying this.
     
  2. Arris

    Arris TS Evangelist Posts: 4,552   +97

    I used to run a YS-Tech 4500rpm fan inverted on my SK-6. It gave temperatures in the same range as a non inverted Delta fan at 6000rpm. I'll maybe have to experiment with this on my SLK-800. Thanks for the information. Note that trying any non standard configuration with a HSF are done at the users risk, even though AMD systems now usually have overheating prevention measures in place.
     
  3. Nic

    Nic TechSpot Paladin Posts: 1,928

    Maybe what you are experiencing is a cooler temperature sensor (air rushing in at the sides), rather than a cooler cpu. Sucking air away from the heatsink (as opposed to blowing air at the heatsink) will result in less cool air being directed at the centre of the heatsink - where the cpu core sits - and should result in higher cpu temps. That's the theory anyway, but maybe your particular heatsink acts differently due to its physical shape/design. Interesting results though.
     
  4. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

    Yes, interesting indeed. I tried it awhile ago with the loudest 7200 RPM delta I've ever had the pleasure of listening to - My system overheated. I have an SK6 copper HS.
     
  5. StormBringer

    StormBringer TS Rookie Posts: 2,871

    That theory is not exactly correct Nic. The reason being, the fan doesn't directly cool the CPU at all. It cools the heatsink. The CPU actually cools itself by transfering heat to the heatsink, in turn, the heatsink is cooled by the fan.

    There is a theory that you can cool better by sucking the air from the rather than blowing it away. This theory is based on turbulence. The total case temps (in theory) would lower because of the streamlined airflow. The problem with the theory is that most fans don't pull the air away from the HS near as well as the blow it off of it. this theory has actually been discussed here before. It sounds good and would work if you could move as much air by sucking it away, as you can by blowing it away.

    I would recommend you turn that fan back around.
     
  6. Nic

    Nic TechSpot Paladin Posts: 1,928

    You have some interesting points Storm, but I'm still not conviced.

    Firstly, in order for for a heatsink to be cooled effectively, it needs to come in contact with as much air as possible. Using a fan in reverse results in air taking the shortest route to the fan, thus the air *avoids* contact with the heatsink, especially at the centre where the temps are greatest.

    By blowing air onto the heatsink it is possible to maximise contact so that heat is transfered to the air and then drawn away. This is why all heatsink manufacturers have their fans blowing air onto the heatsink.

    Now imagine trying to cool your hot cup of coffee down so that you can drink it without burning your lips. Do you think that sucking air away, rather than blowing on your coffee, would have much cooling effect. No I don't suppose it would.

    If you take a look at products such as CoolerMaster's new Aero 7, and GlobalWin's CAK4-88T CPU Cooler's you'll find they have tried to maximise the amount of air directed towards the centre of the heasink (plus using micro-fins to maximise air contact), and both have proven to be highly effective, and relatively quiet, coolers.

    However, thats not to say that it isn't possible to produce a device that would work effectively with a sucking fan, but its design would have to be somewhat different to the heasinks that are currently used to cool CPUs.

    Its true that most heat is removed from the CPU by conduction by the heasink, but the greater the temperature gradient at the centre of the heasink, closest to the CPU core, then the more effective the cooling will be. As already mentioned, reversing the heatsink fan will only reduce the temperature gradient, as the tendency will be to cool the outer edges of the heasink, which are already the coldest part.

    Also, I don't feel that reversing the direction of a fan will have any effect on its ability to move air, so it will likely be just as effective regardless of which way round it goes. The important factor is how cool air makes contact with the heasink.

    Although you've raised some good points (storm), I'm still not convinced (yet). :)
     
  7. acidosmosis

    acidosmosis TechSpot Chancellor Topic Starter Posts: 1,574

    Well, it was an experiment and I'm not sure if it worked or not because I don't have a way of directly monitoring the cpu temperatures from inside the cpu core (which would be nice to be able to do). I noticed that when I reversed the fan I felt lots and lots of heat being pulled away because when I put my hand in front of the fan the heat was warm. Although during idle times if I touched the heatsink with my finger and held it there for a second I would notice that the heatsink was hotter than it normally was with the fan pointed towards the heatsink. Though this does not mean the cpu core temperatures were hotter. Since I dont have some high-tech way of monitoring the cpu temperatures other than on-board monitoring I switched the heatsink fan back around the day after I pointed it out. With it pointing towards the heatsink I am getting temperatures of abotu 114 fahrenheit so that is very acceptable.

    Oh well, maybe I can play with this experiment later on sometime :).
     
  8. Nic

    Nic TechSpot Paladin Posts: 1,928

    Well of course it would be warm as it has just been heated and then concentrated by the fan. This is how hair dryers work.:D

    Yes, I'm afraid is does mean that the CPU core was hotter since this is the only heat source present. I can't imagine the heatsink being hotter than the CPU to which it is attached. I guess you've just confirmed the temperature gradient argument:p
     
  9. StormBringer

    StormBringer TS Rookie Posts: 2,871

    Nic, you completely missed my point, which was that although the theory is there, the requirements for the theory to work are not. It would require a specialized fan, I only mentioned that to illustrate the reason why it will not work.
     
  10. Nic

    Nic TechSpot Paladin Posts: 1,928

    Ok, I think I see where you're coming from storm.;)

    Its good to have a lively discussion every once in a while, and its good to have opposing views also, otherwise there would be no discussion. So don't hesitate to make any points you feel will help make things clearer, even if you don't necessarily agree with them. And as I already said, you do make some very good points/observations (storm), but its not always obvious where you are coming from.:)

    PS: I guess this discussions has now pettered out.
     
  11. acidosmosis

    acidosmosis TechSpot Chancellor Topic Starter Posts: 1,574

    Na I didn't mean the heatsink was hotter than the CPU core lol...
     
     
  12. Nic

    Nic TechSpot Paladin Posts: 1,928

    Here's an interesting link I came across today ...

    GlobalWinUSA
     
  13. Arris

    Arris TS Evangelist Posts: 4,552   +97

    But you have to take airflow into consideration. Cool air comes in the front, gets sucked through the fins of the heatsink and then out the exhaust and/or blowhole. This is still achieved with the fan going either direction, although blowing air at the heatsink surely will cool the heatsink somewhat itself rathern than just pulling air through it. Oh I don't know... just confused myself. But I guess that the manufacturers will all have tried this. With the number of heatsinks out there that are configured in the standard blowing down on the heatsink configuration, they can't all be wrong ;)
     
  14. StormBringer

    StormBringer TS Rookie Posts: 2,871

    The theory of sucking the air off of the HS was devised to reduce turbulence and to streamline airflow through the case. This was in the effort to make the overall case temp cooler. the problem is that while it can lower the case temps, by reducing turbulence, it has yet to be effective in being better, or even as good in cooling the CPU itself.
     
  15. smith

    smith TS Rookie

    blowing sucks

    Now hear this: I also reversed my fan and achieved a 6 degrees lower cpu temperature. I believe that the reason for this is that my enermax psu has an outtake directly (<5mm) above the cpu fan. Now, if the cpu fan blows downwards, while the psu sucks upwards, they both use a lot of energy doing opposite things. When the cpu fan is reversed, the airflow is streamlined from the bottom front of the case towards the cpu fan cooling the fins of the heatsink, and directly out of the case through the psu. Temps blowing: idle 56 load 64, sucking: idle 50 load 58
     
  16. Didou

    Didou Bowtie extraordinair! Posts: 5,899

    My Alpha 6035 & my Alpha 8045 both have the fan blowing air away from the heatsink. That's how they were designed to work & I actually installed the fan the same way on my SLK-800.

    Guess I was used to having the fan remove the hot air from the heatsink so that it can get sucked out by the two rear exhaust fans.
     
  17. Nic

    Nic TechSpot Paladin Posts: 1,928

    Maybe checking the cpu 'core' temp would give a better idea as to which method works best with a particular heatsink. Reversed fans on heatsinks tend to cause cool air to rush in at the sides of the heatsink, which would affect the temperature sensor underneath the cpu socket, and result in a temp reading that is lower than the true cpu temp.
     
  18. Godataloss

    Godataloss TS Rookie Posts: 501

    I dont think it matters which direction the fan points- what matters is the amount and temperature of air being introduced to the convection area of the HS. When the fan blows away from the HS it isnt blowing the 'heat' away. It is creating a vacume behind itself that draws air across the HS's induction volume. If this air is cooler and of a sufficient volume, it will cool the HS faster than the it would blowing directly onto the HS. I imagine there is a cfm rate at which the HS cannot conduct heat away from the cpu fast enough to cool it unless the air introduced into the HS's induction volume is cooled thereby increasing the temperature gradient and the potential convection.
     
  19. Well well well

    This is all new to me and about 6 months ago I put the fan on the side of the CPU heatsink so the air would blow thru it and between the PCI card as they are close together and I imagined that as hot air rises the card would stop it rising so blow air in there would help. Was stock and reliable 333 cyrix and I must fix the bios one day. over + out :wave:
     
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