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#31
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
"Martin Brown" wrote in message
... 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. But also very probably wrong. The volume of air going through the heat sink is proportional to the amount of cooling you get for a given design so there is a definite bias towards not blocking off half the free air flow. I would guess at something more like allowing 2/3 to 3/4 of free airflow as about the best depending on the exact heatsink geometry. It could easily be higher - easy enough to do the experiment. Indeed, and add to that the fact that fans are not "resistive" air sources. The peak power point (pressure * flow) occurs at a pressure of about 25% of maximum (fully blocked) pressure. You can't operate very far from this condition or your flow will be too slow. If you include dynamic pressure (mass flow), fans are even more nonlinear. Next time you have a squirrel cage type laying around, hook it up and play with it. Put your hand over the outlet. You'll find the velocity is great until about 1-2 diameters away, where you start feeling the force of ram air. Within about 0.5 to 0.25 diameters, pressure is maximum, because flow hasn't gone to zero yet, meanwhile static pressure is building. Put your hand all the way up to block it, and static pressure goes to maximum, but velocity goes to zero, so the power you're feeling drops sharply. BTW, I use the example of a squirrel cage because they provide more pressure, making a more illustrative example. Regular axial fans do as well, and manufacturers typically provide comparable graphs. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |
#32
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck,don't blow ! heatfins direction)
But also very probably wrong. The volume of air going through the heat sink is proportional to the amount of cooling you get for a given design so there is a definite bias towards not blocking off half the free air flow. I would guess at something more like allowing 2/3 to 3/4 of free airflow as about the best depending on the exact heatsink geometry. It could easily be higher - easy enough to do the experiment. I suspect the perfect shape for an optimum heatsink is rather more complex than the typical fins we get but the designs used at present are good enough and much easier to engineer. Heat pipes have helped enormously with the latest generation of quiet heatsinks. It is a sobering thought that high performance CPUs often have a heat output per unit area that exceeds the tip of a soldering iron. Nope, no theta modules presently marketed, just a couple squirrel cages and extant circular Zalman takes from a fairy good run given a premium to pricing structures. Mass seems the byword, now-a-days, massive as a restriction only limited by standardization among case manufacturers. Had one recently, the typical behemoth of 7- to 1155 sockets, I picked for a proverberial song & dance, which barely missed a nonstandard case construction I do own, within designer case specifications by a mere 1/4", (yes, I simply had to measure it), as opposed to a standard, however exact fit, such as Rosewill's understudy of Antec cases. Excepting the fan -- I'd as well be veritably ecstatic over results obtained within a reality of present heatwick technology -- as it is, the size of an exterior case fan ported and packaged to that CPU HS is at best, safer to defer for a project to rewire its connection off the MB current draw and onto a PS lead, proper. As mentioned aside by similar instances of a P4 or AMD X2, a benefit not only set to 107F (and lower, I reside at as low as 100F respective to ambient temperatures), is a backtest of their efficiency to approach flash computational processes conceivably closer to these "soldering tips" of 130F, for as much in as least time possible then to regain steady state 107F operational status. It's my own personal theory, fwtw, that case designs importantly conducive to achieving such good results, are at much an impasse the last generation of P4s encountered before heading into nonlinear modes of augmented, multicore processing. Extensively drilled, variously meshed and screened, the approach has effectively advanced to a breadboard construct from a standpoint of free air. |
#33
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
On Sun, 19 Aug 2012 09:25:59 -0700, John Larkin
wrote: On Sun, 19 Aug 2012 08:47:26 -0700 (PDT), Flasherly wrote: On Aug 19, 12:12 am, John Larkin wrote: Right. I've bought about every heatsink or fan imaginable, given and within, as another mentioned, an axiomatic engineering construct concept -- 'if it's done right [in the first place], it's time to [attempt] an improvement, [if and while not in need of entirely new construction concepts]';- time simply follows, technologically speaking, to march upon and then past any R&D Dept., in failure aptly to communicate, if at least not uniquely, then an underlying implementation of adequacy pertaining to key hard and software, constructional elements coming in, daily, across so broad a field as computers. Where, specifically, I see you for a fit is at a coincident juncture of heatsink fins and augmented airflow, both being common terms to common acceptance for pragmatic practice. The argument you have placed to ally yourself as well follows true to the same axiom: that being one, effectively, of a quest for perpetual motion: for so long as the key component of design efficiency is established, widely employed to a common basis of underlying industrial acceptance, the cost factor, then, is effectively one which requires of me nothing more, out of my pocket, than to advance a better sense of encouragement that such benefit, you have chosen to propose, indeed, is of worthier consideration. Stop by anytime if you'd like to talk, John. My office is at the top of the stairs. Are you really John Fields? Or DimBulb. It's sometimes hard to tell them apart. |
#34
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
[................]
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 The goal is maximum heat transfer per gram of air for the flow provided by the fan, or calories/gm/sec. IOW, you want the most heat transferred for the mass of air that the fan can move through the fins. (Note that the volume of the air changes as it heats up, so mass is used in the calculations instead of volume.) And yes, in a counterflow situation (i.e. heat flowing through the fins in a direction opposite to the flow of air), the coolest air contacts the coolest portion of the fins, and the hotest air contacts the hotest part of the fins. Since the highest heat transfer occurs where the temperature difference is greatest, one might think that the greatest heat transfer would occur for parallel flow situation. But no, it's the opposite when one does the calculus. The reason is that the heat transfer in the counterflow situation works over a longer period of time since the temperatures of the 2 media (i.e. fins and air) remain different throughout the time of transit. In the parallel flow situation, the greatest transfer occurs at the beginning when the 2 media have the greatest temperature difference, but the temperature difference falls of rapidly as the air flows toward the cooler part of the fins and the heat transfer falls off as well. For overclocking, where adequate cooling becomes vital, I'd go with water cooling for the CPU. That would leave more room inside the case for air cooling of the other components. But... that's an added expense that one may not want to bear. *TimDaniels* |
#35
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
On Sun, 19 Aug 2012 14:34:23 -0400, "
wrote: Or DimBulb. It's sometimes hard to tell them apart. You and Larkin are both idiots. |
#36
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
On Sun, 19 Aug 2012 13:05:25 -0700, TheGlimmerMan
wrote: On Sun, 19 Aug 2012 14:34:23 -0400, " wrote: Or DimBulb. It's sometimes hard to tell them apart. You and Larkin are both idiots. From you, AlwayWrong, that's some compliment. |
#37
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck,don't blow ! heatfins direction)
On Aug 18, 11:17*pm, Jeff Liebermann wrote:
What you want is immersion cooling: I did a Google search after my post, and found that all the references to the use of mineral oil were to immersion cooling. However, I have also seen it noted that mineral oil could damage some parts of present- day computers. I was thinking in terms of avoiding immersion, but using a forced flow. John Savard |
#38
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck,don't blow ! heatfins direction)
On 2012-08-19, Tim Williams wrote:
"Martin Brown" wrote in message ... 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. But also very probably wrong. The volume of air going through the heat sink is proportional to the amount of cooling you get for a given design so there is a definite bias towards not blocking off half the free air flow. I would guess at something more like allowing 2/3 to 3/4 of free airflow as about the best depending on the exact heatsink geometry. It could easily be higher - easy enough to do the experiment. Indeed, and add to that the fact that fans are not "resistive" air sources. The peak power point (pressure * flow) occurs at a pressure of about 25% of maximum (fully blocked) pressure. You can't operate very far from this condition or your flow will be too slow. If you include dynamic pressure (mass flow), fans are even more nonlinear. Next time you have a squirrel cage type laying around, hook it up and play with it. Put your hand over the outlet. You'll find the velocity is great until about 1-2 diameters away, where you start feeling the force of ram air. Within about 0.5 to 0.25 diameters, pressure is maximum, because flow hasn't gone to zero yet, meanwhile static pressure is building. Put your hand all the way up to block it, and static pressure goes to maximum, but velocity goes to zero, so the power you're feeling drops sharply. BTW, I use the example of a squirrel cage because they provide more pressure, making a more illustrative example. Regular axial fans do as well, and manufacturers typically provide comparable graphs. I've observed this too, I first observed it playing with a squirrel-cage fan driven by a 1200W series universal motor (Electrolux :-) ) The universal motor made it more obvious because these motors respond more to load changes. Modern cooling fans often have a pulse output that indicates fan speed, but monitoring software seems to only alarm on a low speed, where a high speed should possibly also be alerted as it may indicate a clogged heatsink. The fans with a PWM input would be harder to handle as the pwm to speed relationship would need to be compared -- ⚂⚃ 100% natural --- Posted via news://freenews.netfront.net/ - Complaints to --- |
#39
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck,don't blow ! heatfins direction)
On Sat, 18 Aug 2012 17:54:54 -0700, Quadibloc wrote:
On Aug 18, 11:19Â*am, "Skybuck Flying" wrote: Place the heatsink fins 90 degrees turned so that the overflow must go OVER the heatsink fins and not in between. All of you are responding to a known troll and idiot, Skyduck Farting. |
#40
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(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)
On Sun, 19 Aug 2012 10:22:54 +0100, Martin Brown
wrote: On 19/08/2012 05:18, John Larkin wrote: 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 More to the point if the heatsink fins are not thick enough to conduct heat away from the thing being cooled it doesn't matter how easily you can push air through them. Equally it is no good if you get perfect laminar airflow since then only the air touching the surface warms up and the core air remains cool. So you have to have some turbulence and opposition to free flow but the tricky question is how much is enough? Something like this might be close : ====o ====o ====o ====o ====o ====o ====o ====o (slightly tighter together than ASCII art will allow) Airflow from left to right with a blob on the end to mix the air up. 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. But also very probably wrong. The volume of air going through the heat sink is proportional to the amount of cooling you get for a given design It's not. Look at a heatsink theta-versus-air-flow curve. There's also cooling at zero flow. so there is a definite bias towards not blocking off half the free air flow. I would guess at something more like allowing 2/3 to 3/4 of free airflow as about the best depending on the exact heatsink geometry. It could easily be higher - easy enough to do the experiment. I don't think the experiment is easy. With the same fan, you'd have to vary the airflow resistance, like the pin or fin density or something, and keep the remaining geometry the same. This would matter in a case like deciding between two heatsinks that are the same overall dimensions but have different fin densities, cooled by the same fan. Heatsink data sheets give you half the information you need (theta vs flow) but not the other half (backpressure vs flow). I suspect the perfect shape for an optimum heatsink is rather more complex than the typical fins we get but the designs used at present are good enough and much easier to engineer. Heat pipes have helped enormously with the latest generation of quiet heatsinks. It is a sobering thought that high performance CPUs often have a heat output per unit area that exceeds the tip of a soldering iron. I wonder if CPU chip layouts include hot-spot distribution, like putting the hottest bits into the corners or something. |
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