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#11
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En el artículo , DK
escribió: When a video driver installation takes 200 MB on a hard drive and is still full of bugs, there is every reason to question designers' competence. Come on. That's software vs. hardware. The engineers may design and build superb hardware, but if the software isn't up to scratch, it's wasted effort. Look at ATi/AMD cards, for instance. Good hardware, lousy drivers. -- (\_/) (='.'=) (")_(") |
#12
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On Aug 18, 7:57 pm, Rheilly Phoull wrote:
Umm, you would not perchance be employed in a government position (spin doctor) ?? If I had my druthers, I'd as rather gainfully, that is contractually and under government auspices, to be on your tax dollar, sic, whereby to impose mandatory interpolation of required observances, forthwith said forthrightly, such that as an agreeable conscientious citizen, I'm sure you are, there could be no other possible meaning given you to mistake my greater schemes. -- 'Within a judicial system, the only worse case scenario, other than a divorce, is a lawyer in full possession and faculty of doctorates both in law and philosophy.' -Socrates, A Known Drinker of Hemlock |
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On Sat, 18 Aug 2012 16:33:13 -0700 (PDT), Flasherly
wrote: On Aug 18, 3:59 pm, John Larkin wrote: I have this theory that the fins of a heat sink should reduce a fan's free-flow rate by 50% for optimum heat transfer. Unless chambered to stop air flowing in for an arbitrary 10-25% reduction of motor shaft speed, equal to chambering outflow, or both chambered, as opposed to an effective vacuum, which might further indicate where motor design is outside operational efficiency, irrelevant of equipment MTBF, and provided there's salience to some residual mean temperature for cooling to be a factor in coincident significance to ascribe at the proposed structural end as an operative upon RPM. Right. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators |
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On Sat, 18 Aug 2012 17:19:48 -0700 (PDT), Robert Macy
wrote: On Aug 18, 12:59*pm, John Larkin wrote: I have this theory that the fins of a heat sink should reduce a fan's free-flow rate by 50% for optimum heat transfer. optimum heat transfer? not sure what the criteria would be, Minimum theta would do. but think instead about the air's thermal mass, thermal resistance form metal to bulk air. and you see you're left with characteristics of the heat sink, not the characteristics of the fan. As a mind argument enfisionone hell of a powerful fan. Now block that to half flow, what do you have? versus an 'underpowered' fan that is blocked to half flow. . If the heat sink doesn't reduce air flow at all, the air is going around the fins, not through them (as Skybuck suggests) and the air does no good. And if you block all the air flow, it does no good. So the amount of airflow restriction that results in the lowest theta must be somewhere between those two extremes. Dead center is a pretty good guess. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators |
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On Sat, 18 Aug 2012 12:59:41 -0700, John Larkin
wrote: I have this theory that the fins of a heat sink should reduce a fan's free-flow rate by 50% for optimum heat transfer. If the input and output temperatures were the same, that might be true. It might also be true if you consider the reduction in free flow rate caused by the back pressure due to the head sink obstructing the air flow. However, air expands when heated, causing an increase in air flow at the exhaust end. That's why the exhaust port for a heat removal system is larger than the intake. My guess(tm) is that the increased exhaust air flow caused by heating is much larger than the reduction in intake air flow caused by the fins getting in the way. On the original assertion, that it's better to suck than to blow, methinks that's wrong. You can demonstrate this with a dirty computer. Take a vacuum cleaner and try to remove the dust by sucking. Most of it will still be in the machine when you're done. Now, put the hose on the same vacuum cleaner exhaust and blow the dust out of the machine. Notice that remaining dust is effectively blown all over the room. It's dispersion versus concentration. When sucking, one pulls air from the sides and from all around the heat sink, including air that does not need cooling. This makes the fan work harder moving excess air, leaving less air flow for between the heatsink fins. Turn the fan around and blow air at the heat sink, and the entire air flow is involved in cooling the fins. Similarly, you can demonstrate the effect by comparing the CPU temperatures with the fan in the normal position (blowing air down towards the heat sink), versus flipping the fan over and sucking air out. I did this with a Pentium 4 dual core. I forgot the measured temperatures, but the difference was substantial. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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On Sat, 18 Aug 2012 17:54:54 -0700 (PDT), Quadibloc
wrote: But a third alternative to setting up a refrigeration system and using chilled water would be using chilled mineral oil. Of course, there, flammability is a problem, although the fractions typically used for such purposes aren't too bad... What you want is immersion cooling: http://images.bit-tech.net/content_images/2009/12/the-hardware-hall-of-fame/hof9.jpg http://www.bit-tech.net/news/2008/10/23/hardcore-computer-launches-immersion-cooled-pcs/1 http://www.maximumpc.com/article/features/hardcorepc_reactor/ http://hackedgadgets.com/wp-content/2/Mineral_Oil_Submerged_Computer_1.jpg http://img.photobucket.com/albums/v53/pinkfloyd33/DSCN2748.jpg http://www.youtube.com/watch?v=PtufuXLvOok http://smallformfactors.com/articles/immersion-form-factor-server-class-systems/ Build a leak proof package, insert computer, fill with fluorinert, mineral oil, anti-freeze, distilled water, or whatever and it will redistribute the heat to a much larger mass and surface area. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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"Jeff Liebermann" wrote:
[.............] On the original assertion, that it's better to suck than to blow, methinks that's wrong. ..... Given the same mass/sec flow of air over the fins of a heatsink, the best heat transfer is by blowing due to the greater turbulence - which disturbs the boundary layer of air that lies in contact with the fins and puts more flowing air in direct contact with the surface of the fins. In the case where the fins rise up away from the source of the heat, it's best to blow downward from the ends of the fins toward the source of the heat. IOW, the air should move in a direction opposite to the heat flow. This principle is not only used in heat transfer systems, but also in biological systems in oxygen transfer through membranes - as in fish gills where the blood moves across the gill membrane in a direction opposite to the flow of water. The basis of this principle lies in the finite heat (or gas) capacity of a fluid and that greatest heat (or gas) flow occurs as a linear function of the difference of temperature (or gas concentration) between 2 bodies. Apply a little calculus, and the principle of opposing flows results. This design principle was recently seen when I opened up the case of a friend's PC to clean it out: The cooling fins for the CPU rose up from the CPU, and the cooling fan blew air down along the fins toward the CPU. Obviously, the designer had paid attention during college freshman physics. *TimDaniels* |
#18
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"Timothy Daniels" wrote in message
... This design principle was recently seen when I opened up the case of a friend's PC to clean it out: The cooling fins for the CPU rose up from the CPU, and the cooling fan blew air down along the fins toward the CPU. Obviously, the designer had paid attention during college freshman physics. Oddly, my new, stock heatsink is designed with fins arranged not-quite-radial, in an X pattern around the center. It looks like extrusion oriented axially (axis normal to the processor face), rather than transverse. The fan blows air over the center and fins. At 100% CPU I get 42C tops, so it seems to be doing its job. Nothing special, a dual core 3.2GHz Athalon II. It's also entirely possible AMD (or whoever they contracted to make them) doesn't know their physics. Note that heat transfer by volume isn't usually the goal, so much as minimum temperature is. In a counterflow setup, the hottest part of the heatsink is cooled by the hottest air. If you flip it around, the hottest part of the heatsink gets cooled by the coolest air, achieving the highest heat flux for a given surface area and temperature difference -- more power density, at some expense to mass flow and pumping loss. You might avoid this, for example, if you had to use pure nitrogen (or helium, for that matter) for some process, minimizing the gas flow to keep operating cost down. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
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On Sat, 18 Aug 2012 22:05:11 -0700, Jeff Liebermann
wrote: However, air expands when heated, causing an increase in air flow at the exhaust end. That's why the exhaust port for a heat removal system is larger than the intake. My guess(tm) is that the increased exhaust air flow caused by heating is much larger than the reduction in intake air flow caused by the fins getting in the way. The air density drops from 1.2 kg/m³ at +25 C to about 0.6 kg/m³ at +325 C, so yes, it might make sense to double the exhaust cross section area. However, for practical semiconductor cooling applications, with intake temperature at +25 C and exhaust temperatures below +60 C, air density is about 1.07 kg/m³, an expansion is only about 10 %. I doubt it would make much sense to try to optimize exhaust areas. |
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On Sun, 19 Aug 2012 01:56:38 -0500, "Tim Williams"
wrote: Note that heat transfer by volume isn't usually the goal, so much as minimum temperature is. In a counterflow setup, the hottest part of the heatsink is cooled by the hottest air. If you flip it around, the hottest part of the heatsink gets cooled by the coolest air, achieving the highest heat flux for a given surface area and temperature difference -- more power density, at some expense to mass flow and pumping loss. You might avoid this, for example, if you had to use pure nitrogen (or helium, for that matter) for some process, minimizing the gas flow to keep operating cost down. Why not use compressed/expanded air for this purpose ? Using a piston compressor to compress the air to a few bars, the air gets quite hot, then let it go through a heat exchanger to get rid of most of the heat and cool the pressurized air closer to ambient temperature. Let the air expand to normal ambient pressure and the air temperature is now well below ambient temperature and let it flow through semiconductor heatsinks to the environment. To avoid problems with dust and condensation, a closed loop might make sense, but of course, now the heat exchanger would also have to dissipate the heat from the semiconductor. However, the heat exchanger can be remotely located and it can have much higher temperatures than the semiconductors, getting rid of the heat into the environment would be easier. |
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