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#1
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Case fan as CPU cooler?
I've seen a couple of articles for adapting an 80mm fan to a 60mm
heatsink, but it seems to me that the most effective way to do this would be to turn a rear fan around and duct the air flow to the heatsink. It seems to me that this setup would supply more air and cooler air to the sink. It also seems to me that there must be a good reason why this isn't a common setup because I'm not the sharpest tool in the shed and others must have tried this before and there must be a reason why it doesn't work. So, why not? Thanks. |
#2
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"Dave Smith" wrote in message news I've seen a couple of articles for adapting an 80mm fan to a 60mm heatsink, but it seems to me that the most effective way to do this would be to turn a rear fan around and duct the air flow to the heatsink. It seems to me that this setup would supply more air and cooler air to the sink. It also seems to me that there must be a good reason why this isn't a common setup because I'm not the sharpest tool in the shed and others must have tried this before and there must be a reason why it doesn't work. So, why not? Where is all this air going to go once past the heatsink? You still need a decent exhaust fan someplace. I was considering something similar, except leave the back fan exhausting. Suck the case air through the heatsink and out the back of the PC. |
#3
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On Sat, 27 Sep 2003 00:53:25 GMT, "Phrederik"
wrote: "Dave Smith" wrote in message news I've seen a couple of articles for adapting an 80mm fan to a 60mm heatsink, but it seems to me that the most effective way to do this would be to turn a rear fan around and duct the air flow to the heatsink. It seems to me that this setup would supply more air and cooler air to the sink. It also seems to me that there must be a good reason why this isn't a common setup because I'm not the sharpest tool in the shed and others must have tried this before and there must be a reason why it doesn't work. So, why not? Where is all this air going to go once past the heatsink? You still need a decent exhaust fan someplace. I was considering something similar, except leave the back fan exhausting. Suck the case air through the heatsink and out the back of the PC. My case has two rear exhaust fans. I figured to reverse one of them and maybe move the other to the front. There's also the power supply fan, though it doesn't seem to move much air. |
#4
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The fan in power supply is typically more than sufficient to
exhaust case air. Case air temperature relative to room air temperature is a function of chassis fan CFM. Bottleneck in CPU cooling is not interior case temperature. Bottleneck is mostly where thermal conductors change medium. For example, CPU to thermal compound. Thermal compound to heatsink. Heatsink to air. As airflow drastically increases, heatsink cooling improvements become marginal. Most heatsink cooling is with almost no airflow. As airflow increases, the overall improvement in cooling decreases exponentially. As airflow increases, then heatsink cools better, but not by that much more. Therefore almost as much cooling is obtained blowing air across heatsink as when driving airflow into heatsink (as determined by how heatsink fins are designed for that airflow). Heatsink cooling is more affected by LFM across heatsink and not by massive CFM increases of interior to external chassis airflow. AFter the first 80 mm fan, that additional cooling fans provide only marginal advantage. Direction of airflow across heatsink also is irrelevant. Why not mount a bigger fan on heatsink? A maximum weight spec limits how much can be attached to CPU. Too much weight can mean less cooling by compromising another thermal bottleneck. CPU to heatsink interface is degraded by too much weight and vibration. Dave Smith wrote: My case has two rear exhaust fans. I figured to reverse one of them and maybe move the other to the front. There's also the power supply fan, though it doesn't seem to move much air. |
#5
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On Fri, 26 Sep 2003 23:24:16 -0400, w_tom wrote:
The fan in power supply is typically more than sufficient to exhaust case air. Case air temperature relative to room air temperature is a function of chassis fan CFM. Bottleneck in CPU cooling is not interior case temperature. Bottleneck is mostly where thermal conductors change medium. For example, CPU to thermal compound. Thermal compound to heatsink. Heatsink to air. As airflow drastically increases, heatsink cooling improvements become marginal. Most heatsink cooling is with almost no airflow. As airflow increases, the overall improvement in cooling decreases exponentially. As airflow increases, then heatsink cools better, but not by that much more. Therefore almost as much cooling is obtained blowing air across heatsink as when driving airflow into heatsink (as determined by how heatsink fins are designed for that airflow). Heatsink cooling is more affected by LFM across heatsink and not by massive CFM increases of interior to external chassis airflow. AFter the first 80 mm fan, that additional cooling fans provide only marginal advantage. Direction of airflow across heatsink also is irrelevant. Why not mount a bigger fan on heatsink? A maximum weight spec limits how much can be attached to CPU. Too much weight can mean less cooling by compromising another thermal bottleneck. CPU to heatsink interface is degraded by too much weight and vibration. Thanks very much for your input. If I read your reply correctly, ducting air from outside the case VIA an 80mm fan for CPU cooling would work, but would not provida a significant cooling advantage. I also was hoping to reduce noise as low RPM case fans are quieter than typical 5000 RPM CPU fans. Is there anything inherently wrong with this approach? Dave Smith wrote: My case has two rear exhaust fans. I figured to reverse one of them and maybe move the other to the front. There's also the power supply fan, though it doesn't seem to move much air. |
#6
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On Fri, 26 Sep 2003 22:11:59 -0700, Dave Smith
wrote: Thanks very much for your input. If I read your reply correctly, ducting air from outside the case VIA an 80mm fan for CPU cooling would work, but would not provida a significant cooling advantage. I also was hoping to reduce noise as low RPM case fans are quieter than typical 5000 RPM CPU fans. Is there anything inherently wrong with this approach? If you reverse that fan to cool the CPU you need to reassess the entire chassis cooling, since having the air intake there completely alters chassis airflow. You'll have less air intake in the front and even if you added a fan in front, you then have a singular point of air entry instead of an even flow across many components. "Sometimes" this single-point can be advantageous, if it's a fan in front of the HDD bay, and even better if the air also has an unimpeded path towards the video card, but on the other hand you still decrease airflow around CDRW drive... some run hot and others don't. Also a front fan "can" be the one most easily heard in an otherwise quiet system, especially if that system is sitting under a desk. Only you can test each change and note the results, but don't just look at the CPU temp sensor and assume it's better. Blowing air towards a part with a temp sensor on it will seem to help, but it only tells you what that single point temp reading is, and that part, the CPU in this situation, is designed to tolerate a little heat. By having all fans in the rear blowing out you maximize the airflow though the chassis. If you really need a cooler or quieter CPU then you might consider buying a better heatsink, it is the time-tested and proven course of action, and should help even if you did end up running that rear fan reversed. Dave |
#7
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"Dave Smith" wrote in message news I've seen a couple of articles for adapting an 80mm fan to a 60mm heatsink, but it seems to me that the most effective way to do this would be to turn a rear fan around and duct the air flow to the heatsink. It seems to me that this setup would supply more air and cooler air to the sink. It also seems to me that there must be a good reason why this isn't a common setup because I'm not the sharpest tool in the shed and others must have tried this before and there must be a reason why it doesn't work. So, why not? Thanks. i've built quite a few machines using a smaller case fan as a cou cooler with excellent results. it only takes a few minutes to make a mounting bracket and i;ve been able to keep the cpu relatively cool... plus the larger fans tend to be quite a bit quieter |
#8
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Larger, less noisy 80 mm fans will move more air across the
heatsink. But they are heavier. Therefore they cannot be mounted on CPU. All the better. If they blow air across heatsink, then they are not mounted on heatsink and CPU, and if fan fails, the heatsink still provides cooling. Less cooling, but heatsink still cools CPU. 80 mm fans come in normal noise and lower noise versions, with lower noise versions moving less air. An 80 mm fan manufacturer may have between 10 and 20 different fans in that same form factor. Each moving different amounts of air (CFM) and making different levels of noise (dB). Dave Smith wrote: Thanks very much for your input. If I read your reply correctly, ducting air from outside the case VIA an 80mm fan for CPU cooling would work, but would not provida a significant cooling advantage. I also was hoping to reduce noise as low RPM case fans are quieter than typical 5000 RPM CPU fans. Is there anything inherently wrong with this approach? |
#9
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Examples of 80 mm fans just from one company:
http://www.comairrotron.com/DCFans/Flight80.htm http://www.comairrotron.com/DCFans/SprintDC.htm http://www.comairrotron.com/DCFans/SpriteDC.htm Dave Smith wrote: Thanks very much for your input. If I read your reply correctly, ducting air from outside the case VIA an 80mm fan for CPU cooling would work, but would not provida a significant cooling advantage. I also was hoping to reduce noise as low RPM case fans are quieter than typical 5000 RPM CPU fans. Is there anything inherently wrong with this approach? |
#10
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On Sat, 27 Sep 2003 08:35:56 -0500, In this world we created "philo"
NONphiloNONplazaearthNONcomNON wrote : "Dave Smith" wrote in message news I've seen a couple of articles for adapting an 80mm fan to a 60mm heatsink, but it seems to me that the most effective way to do this would be to turn a rear fan around and duct the air flow to the heatsink. It seems to me that this setup would supply more air and cooler air to the sink. It also seems to me that there must be a good reason why this isn't a common setup because I'm not the sharpest tool in the shed and others must have tried this before and there must be a reason why it doesn't work. So, why not? Thanks. i've built quite a few machines using a smaller case fan as a cou cooler with excellent results. it only takes a few minutes to make a mounting bracket and i;ve been able to keep the cpu relatively cool... plus the larger fans tend to be quite a bit quieter I've been using this way for near 2 years on my O/C XP1800, http://superfan.freewebspace.com/ Not the,"Mummy" version.Quiet and cheap.Max under load temps just over 50 Deg C :P -- Free Windows/PC help, It's a G not a J in jmx to reply http://www.geocities.com/sheppola/trouble.html Free songs download, http://artists.mp3s.com/artists/17/sheppard.html |
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