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Old 10-27-2007
lin lin is offline
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Default front panel fan generates warm air?

Hi I would like to know what you guys think.

Recently, I placed a fan at the front panel in hope that it will help to reduce the hdd temperature. The fan spinning quite well and I can feel the air being blown.

Unfortunately, it didn't produce a single drop in temperature. So I opened up the pc side panel and tried to feel the air being blown out by the front panel fan. It felt warm. I think this could be because of the fan motor and after spinning for sometime, it get warmed.

Does it happened to all the fans? Or in your opinion, it's this particular fan that I am using that generates warm air more easily than others. I had another fan which I placed it at the side panel but it doesn't produce such warm air like the front panel fan.

I am very puzzled because the purpose of placing a front panel fan was to reduce my hdd temperature.

Appreciate your views as to whether there is a need to get another fan instead.

Thanks.
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Old 10-27-2007
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mpilchfamily mpilchfamily is offline
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What fan is it? Different fans work differently. Most fans are brush less and don't generate a whole lot of heat. But they will all generate a bit of heat due to friction. Shouldn't bee too noticeable though. Are you sure you weren't feeling the heat off the drives?

There is also the possibility that the HDDs where already getting plenty of airflow and the added fan wasn't cooling them any better. But that is unlikely the case.
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Old 10-27-2007
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Quote:
Originally Posted by mpilchfamily View Post
What fan is it? Different fans work differently. Most fans are brush less and don't generate a whole lot of heat. But they will all generate a bit of heat due to friction. Shouldn't bee too noticeable though. Are you sure you weren't feeling the heat off the drives?

There is also the possibility that the HDDs where already getting plenty of airflow and the added fan wasn't cooling them any better. But that is unlikely the case.
Both the front panel fan and side panel fan are just ordinary fans.
The front panel is AVC Brushless Ball Bearing 120mm. The Side Panel is just an ordinary fan which could be sleeve bearing.

I think you have a point about the heat dissipates off from the drives with the fan blowing.

So I remove my hdd and just feel the air that was generated by the front panel fan. Notice that it was not so warm as before. But the air wasn't 'cooling' compared to my side panel fan.

Everyone, I wonder is the air blown by your fan slightly 'cooling' or not at all? Yes, the airflow might be 'windy' but is it a bit 'cooling'?

Last edited by lin; 10-27-2007 at 02:29 AM.
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Old 10-27-2007
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The air blown by the fan is only as cool as the air temp in the room. A fan doesn't cool the air it just moves it. The only reason a fan feels cool when blowing on you is that its helping your body to cool down by evaporating your sweat and pulling the heat away from your skin.

For whatever reason people think that by adding fans you get more cooling. Well there reaches a point when you have maximized the cooling your going to get. You reach a point where the air moving threw the system is removing the heat as fast as your HS can dissipate it into the air. Anything more then that is just producing more noise and not aiding in cooling at all.
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Old 10-27-2007
cypherpunks cypherpunks is offline
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*Sigh*. There is a limit, but no maximum. Convective heat transfer, especially with turbulence, is a bit more complicated, but for now assume that every time you double the amount of air, you halve the thermal resistance between the surface of the heat sink and the inlet air temperature. That's not quite right, but it's very close.

So my inlet air is 25 C, my heat sink surface is 33 C, and my outlet air is 29 C. Then I double the air flow. Now the heat sink surface is 29 C and my outlet air is 27 C.

Then I double it again. Heat sink surface is 27 C and outlet air is 26 C.

You can keep going, and the heat sink surface will approach, but never reach, the limit of 25 C, and in the meantime you're sharing a computer with an F-16 on full afterburner.

(Actually, there will come an air flow level when the energy lost due to air friction inside the case actually heats it to more than the inlet temperature, but let's assume for now that we come to our senses and stop before things go supersonic. Air pressure will also rip a standard sheet metal case to bits after a certain point. As I said, it's an approximation that gets the point across.)

But in addition to the air cooling effect, the heat sink itself has a thermal resistance, and adding more air won't change that. So even if the heat sink's outer surface can be frozen at 25 C, the chip will be warmer than that.

There is indeed a point of diminishing returns, but more air doesn't actually reduce the cooling until you get to ridiculous (> 100 mph) levels. All that happens is that the improvements get so small as to be unmeasurable.

It's like most things in life: there are multiple bottlenecks. Once you've found and fixed the first problem, something else becomes the limiting factor. You can make a car go a bit faster by improving the engine, but after a while more power just spins the tires. Then you need new tires, then a stiffer suspension to hold them on the road, then a stronger clutch to carry the force, then an improved transmission, then better brakes so you can avoid killing yourself, and on it goes...

As for a fan heating the air, indeed all fans do that; they consume power, which they dissipate as hear, and that heat goes into the air stream. But it's usually piddling compared to the extra cooling. Although, again, if you take it to sufficiently ridiculous extremes, the extra power consumption from the fans can overwhelm the cooling benefit.
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Old 10-28-2007
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Yes. Also, drawing air from devices with tight clearances between surfaces will not remove as much heat as blowing/forcing cool air over. This is because of the complex physics that happens with things like HD bays with lots of drives close together or Heat Sinks with fins close together: Less cool air will flow where it needs to if you suck versus blow.

Now if you can design an HD rack that seals and channels the air under pressure using a fan that has good back pressure characteristics (fans that push well even when there is resistance) you will cool better, but I haven't seen cases that are designed with discreet air channels that direct air, it would be nice though...
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Old 10-31-2007
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Hi thanks for replying. I guess like what u all said, it comes to a point where that is the 'maximum' or 'how much limit' cooling i can get. The ordinary fans I got, I think they did pretty well. I can feel some air blown out at a distance of 14 cm/ 140 mm and they spins fast enough to be moving some air without being too noisy.

As these are ordinary fans, I couldn't get any speed sensor or was there any spec to say how much cfm or at what speed are they rotating. Even if I get an adapter cable, I doubt I can get any sensor reading of the speed because the fan connected on 4-pin molex only comes with red (believe it's the 12v) and black (ground) wires. There is a missing third wire for speed sensor reading. Previously I kept wondering if those slightly expensive or better brand fans make a big difference in temperature drop since I have never them tried out.

I think I should learn to be satisfied with my temperature since they are not very high.

Thanks again everyone for all the above feedback.
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Old 10-31-2007
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Well, do remember that CFM and dB is only part of the metric list to consider. Static Pressure (what I was referring to earilier partly) and the real world auditory response of *your* human ears, versus the dB value, are other metrics. Sadly, few fans sold for computer geeks are sold with such metrics, though some are.

You can assume, however, that larger diameter, slower moving fans and deeper fans and fans with special rotor designs may prove to be more effective in various ways.
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Old 12-31-2007
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My antec case has a HD rack with fan that attaches directly to the front..not super sealed but pretty good airflow across my Raptors and my storage drive...

I got 4 year old EARLY 36 Raptors and they still run perfect.. many have had those fail....


Derr in other words that warm air is a sign your drives are cool.....so its a good thing...

yes your case flow will have to process it.
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Old 01-18-2008
IAmATeaf IAmATeaf is offline
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Is this newly installed front fan blowing air into the case or drawing air from the case out? If the later then this would/could account for why you can feel warm air. For me the front fans are always set to suck air into the case over the HDDs, you then let the rear fan and fan vent the air inside the case out through the back of the case.
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