(NVIDIA) Fan-Based-Heatsink Designs are probably wrong. (suck, don't blow ! heatfins direction)

The amount of heat power removed is directly proportional to mass flow, temperature rise and specific heat. With the exhaust temperature fixed due to the semiconductors, the heat removal can increased only by reducing the inlet temperature or increasing the mass flow.

If the maximum exhaust temperature is +60 C, dropping the inlet temperature from +30 C to -30 C will triple the amount of heat that can be removed. For air, the specific heat is about 1 kJ/kg/K and air density of 1 kg/kg, 1 m³/s of air flow will remove 1 kW with 1 C temperature increase. With 1 l /s (1000 cm³/s) and 30 C temperature increase, 30 W can be removed. If the allowed temperature increase is

90 C (from -30 C to +60 C), 90 W can be removed. With 5 m/s air speed, the duct cross section would have to be 2 cm².

Of course, there are practical problems of transferring the heat to the mass flow.

This is of course true, no argument about that.

The problem is arranging the liquid cooling on a crowded PCB and the consequences of any leakage.

Of course, if heat pipes are used and then the heat exchanger is cooled by tap water outside the box, will simplify things.

Raised floors and building cooling are used because it's too expensive to individually cool each computer individually and because the heat has to be move to the outside of the building somehow.

ISP's and data centers have the same problem. Thousands of small fans on individual machines blowing hot air to nowhere. So, if you can't cool the machine, and cooling the entire building is too inefficient, then perhaps just cooling the racks. There are a multitude of schemes but most use liquid cooling inside the racks.

For those with blade servers, there is individually immersive liquid cooling packaging for each server: Air has a very low specific heat. Liquids are much better.

Yep.

Sorta. The problem is that the heat source has to be hot enough to convert the fluid to vapor. If the aluminum or copper heat sink doesn't get hot enough to vaporize the water, you'll lose efficiency. For example, the heat sink would need to be above 100C in order to vaporize the water. Unfortunately, it also works both ways. If the hot water vapor hits something cold on its way out of the computah case, it will condense the water and leave a puddle.

Over the years, I've had other adventures in computer cooling. The goal was not to design the worlds most efficient cooling system. Rather, it was to get rid of the noisy fan(s). I've tried heat pipes, bolting heat sinks on the back of machines, giant blocks of aluminum, water cooling, anti-freeze cooling, immersion cooling, and heat sequestering (bucket of water thermal sink). All of these worked, but they also had problems. For example, the heat sink on the back of the machine was enough to burn my hands. The smell of burning dust was also unpleasant. I've though of using the heat to run a coffee cup heater but haven't tried it. All of the liquid coolers either leaked or stunk. Can't win.

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Or DimBulb. It's sometimes hard to tell them apart.

Sure, but the point is that far from what was stated, "Using refrigerated air for heat sink cooling is ridiculous.", it's commonly done. It's done both by separate air handlers and by integral heat exchangers.

Refrigerating *air*, which is used to cool the heatsinks.

If you need it, you're wasting too much energy. ;-)

So you simply choose something else. Ether boils well enough to use in dunky birds. ;-)

Water is a very poor choice, as noted. Fortunately, it isn't the only liquid available. There are all sorts of CFCs that can be tailored to pretty much whatever boiling point you wish.

If you use the coffee cup, it has to remain full. ;-)

That is under normal atmospheric pressure (1 bar).

Connect a vacuum pump and drop the pressure to 0.1 bar and the water boils at 50 C.

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*

You and Larkin are both idiots.

From you, AlwayWrong, that's some compliment.

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

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

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All of you are responding to a known troll and idiot, Skyduck Farting.

It's not. Look at a heatsink theta-versus-air-flow curve. There's also cooling at zero flow.

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 wonder if CPU chip layouts include hot-spot distribution, like putting the hottest bits into the corners or something.

Actually, you find out that in this sort of system, the humidity increases the efficiency of the operation, since you now have a phase change step in operation. A design to use this type of cooling for automotive use actually added a supply of water to spray into the intake after they tested during a thunderstorm and saw the marked increase in performance!

Charlie

I wouldn't as generally implemented within a more direct approach ostensibly to remove added abstractions through dynamic modeling practices as gate clocking and fetch latches contingent upon sensor relays. Labeled under a safety badge to ensure another preventative layer against failure conditions, the intent is established in advantage to saving the core processor when a $2 heatsink or fan malfunctions or improperly is manipulated outside provisional intents by which they're packaged and distributed.

Word salad. You must be AlwaysWrong.

Lex parsimoniae -- irrespective of older processors I do own, to have attributed heat as randomness to an ordering of chip density cannot either wrong or right, whether suspect or implicit in indulgence, much as application [more correctly] negates relevancy by dint of simple apparency;- well, almost. . .I did elect not to turn on heat throttling in my CMOS.

" On the original assertion, that it's better to suck than to blow, methinks that's wrong. "

I will draw a more detailed drawing for you what I ment with "suck". There is also some "blow" involved.

Side view of proposed heat sink design by skybuck:

+--------------------------------------+

" 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. "

I'd love to see simulation that actually includes dust particles and hair to see how much effectiveness remains for this theory.

I suspect the simulation software used at the time did not include these factors, and therefore all designs might be totally wrong for dusty/hairy environments.

Bye, Skybuck.

" 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. "

I like this idea of a closed air system very much...

Maybe a case which is build entirely out of "heatsinks" or something... to get rid of as much heat from inside the case to the outside... without actually sucking in any dust/hair.

Bye, Skybuck.