a stretch, but second only to WW
review up after I move this week (I guess)

8-Ball
correction noted re my inverted phraseology
(using gradient as a magnitude)

Huh? I'm used to tilt being an informal reference to proof by contradiction, but I know that's not what you mean. What do you mean?

pretty sure he was referring to the abuse of a pinball machine :)

He meant that Airsprit's comment is out-of-order (a pinball reference)

The heat being the same, the heat dissipation will also be the same, which means that the water temp will also be the same, so the only thermal gradient that changes, is somewhere between the inside of the core, and the top of the baseplate of the waterblock, just before the heat hits the water.

Hmmm, I agree with the more efficient waterblock leading to warmer water, because of the secondary heat paths. Les is plotting it. I thoerised about it in this thread:

http://forum.oc-forums.com/vb/showth...hreadid=148310

The differences are very minor though. Something that would be near impossible to pick up under normal operation.

pick your premises and stick to them

one can consider a wb's response to a heat load (applied heat warming the coolant)
or
a heat die->TIM joint->wb 'system' (minimal secondary losses, quantified)
or
a CPU->TIM joint->wb 'system' (large secondary losses, rather undefined)

and for each of the 3 there are different considerations, hence different 'answers'

yea, pinball (airspirit was making the same 'bad' moves)

I will try and explain with reference to your example.

You are quite correct that when you turn the soldering iron on, there will be an increase in the surrounding water temperature.

However, this is NOT the equilibrium temperature, as at this point, the thermal energy transferred to the air via evaporation of water will be LESS that the thermal energy transferred from the soldering iron into the water.

Because of this, the thermal energy of the water will continue to rise, (so the temperature will rise), and consequently more thermal energy will be transferred to the atmosphere vie evaporation. The temperature will continue to rise until the transfer of thermal energy via evaporation is the same as the transfer of thermal energy from the soldering iron is the same.

So now we have a situation where there is no NET change in thermal energy in the water. The same amount comes in as goes out. This is the equilibrium condition, which is what would happen if you ran a computer crunching for a couple of hours.

The difference in the temperature between the soldering iron and the water is determined by the convective heat transfer coefficient for the soldering iron surrounded by water. This coefficient gives a value of temperature difference required between the edge of the soldering iron and the water which will cause the transfer of 1W of thermal energy. So supposing it is a 70W soldering iron, the required temperature difference between the soldering iron and the water is the heat load divided by the convective heat transfer coefficient .

Note that regardless of the temperature of the water, 70W WILL be dissipated, PROVIDED that the soldering iron manitains this temperature difference above the water.

This is like the efficiency of the waterblock, but there are more stages to consider in the heat transfer, but it is still a coefficient of efficiency.

Improving the efficiency, (ie a lower C/W) will mean that the same 70W is transferred to the water, but a lower temperature difference is required.

AS SUCH, AT THE EQUILIBRIUM CONDITION, THE CPU WILL BE COOLER, AND NOT THE WATER WILL BE HOTTER.

However, as has been said, this does not take into account the secondary heat paths of a fixed efficiency. Essentially, the total heat output of the cpu is conducted away via a number fo routes, each with varying efficiency. By increasing the efficiency of one of them, you will increas the proportion transferred by this route.

However, I still believe that this was not your understanding of why the water will warm up, VERY slightly, as reinforced by your argument above.

So back to your example, once an equilibrium condition has been reached, changing the efficiency of heat transfer into the water WILL NOT change the water temp. The only way to change the water temp is to change the efficiency of heat transfer from the water to the air, as this would change the temperature difference between water and air, OR change the ambient air temperature.

Supposing we have a fixed ambient air temperature, the efficiency of heat transfer from water to air could be IMPROVED by directing a fan at the surface of the water. This will reduce the temperature difference between water and air, BUT the temperature difference between the water and the soldering will not have changed, though due to the water now being at a lower temperature, the soldering iron will also be at a lower temperature.

So I hope you can see from this that, FOR A GIVEN HEAT LOAD, changing the efficiency of a heat transfer stage will ONLY change the temperature delta of the heat producing component above the heat absorbing component. (by heat producing, I mean the component from which the heat is being transferred, so in a water block, the fins are the heat producing component and the water is the heat absorbing component.)

Does this make sense?

8-ball

Much easier to think of everything as an equalibrium problem. Theres waaay to much calc to be dealing with instantanous conditions when you can be using algebra.

Think of the CPU load as an average value, the radiator performance as an average and the flow rate as an average. That way you can just add componets together without any messy (and unsolvable) differential equations.

Here's a goody:
http://www.bluecooling.com/welcome.htm

Read this thread at sysopt. Some people are just so easily misinformed. :D

"a digital thermistor" :D

that just made my day.

*Lowers and Shakes head*. WTF is that thing. A water block ontop of a HS with a pelt in there? http://www.bluecooling.com/product_BTMS.htm

Patent Pending? Bahahahahaha. They can have it!


Damn, those guys in that forums need to set the crack pipe down for 5 minutes and actual think about how a water cooling system works.

My head is starting to hurt again......

Hehe. I've got a lot more where that came from. :rolleyes:

I just remembered the BTMS because someone asked about it on the overclockers.com forum. Even the boys at the [H]ard thought that thing was horrible. :D

Don't really want to drag this thread up, but what the hey!

Enjoy

8-ball

I like the instant calculus in my head thingy. I think that is where much of the confusion is coming from here. The more efficient the block is, the more heat that will be transferred to the water rather than dumped through other means (air, board, etc). That is the meaning of that graph. If you dump a larger percentage of the identical heat load into the water (see above), the water will be warmer. Though the radiator will work more efficiently because of the larger dT, it will NOT cool the water to below the temp of the lower heat input. Therefore, you will have warmer water. Not a big difference, but a difference nonetheless.

I don't think any of what I said qualifies as a "tilt". Theory is only as good as what it's applied to. As far as heat travelling from higher to lower regions, that still applies. The die is hotter than the water, which is then hotter than the rad. Everything fits. A more efficient block will assist the heat in taking the path of least resistance: the path to the water. This is just like reducing the restriction on a parallel circuit: it will cause more energy to flow through that particular branch. Since more of that thermal energy will be sent to the water as opposed to other distribution sources (passive cooling), more energy will go to the water. This phenomenon can not be disputed as it holds perfectly to all the theory out there. Plus, it doesn't magically make heat disappear, unlike some of the other ideas being thrown about.

I respect your expertise, guys, but I think you're wrong this time.

That's true, but you're going on about it as if the best performing blocks fare better because they have a greater secondary heat loss, and that's just not the case.

The way my simplified mind see's it is the water temp is produced by the temp of the block(CPU), so a cooler CPU is going to create cooler(or not hotter) water...

The water is at 'X' temperature because of the temperature of the block/CPU, not because it carries 'X~BTU's per cubic~CM'...

Am I wrong in thinking this?...

The water is at X temperature because of the heat load of the cpu. The temperature of the cpu is because of the required temperature difference across the whole cooling setup.

8-ball

airspirit,

the reason there is dispute is largely the way you explained it.

I agree that a more efficient block will result in warmer water as the heat dissipated through the watercooling will be slightly greater, so the temperature difference between the water and the air will have to be slightly greater.

However, the way you tried to justify yourself was flawed, and it was more that that I was trying correct than the statement that a more efficient block will result in a greater percentage of the heat load being dissipated by the watercooling.

8-ball

So, I guess it gets back to my first post on the subject:

"That is a really murky statement. If you can assume that heat is being pulled more efficiently into the water via the block (like a WW when compared to a Senfu), then naturally the water will be a little warmer, and this would cause the radiator to transfer more heat. How they stated it, though, is really stupid, and is a case of making alot of noise about nothing ... and stating it backwards perhaps to deliberately confuse the customer and hopefully gaining a sale because of the long-winded description that means that it has to be good ... right? They should have summed it up as "a more efficient water block.""

While the change in water temperature doesn't matter to any measurable degree, it is still there. That manufacturer/retailer was trying to explain why their part was the shiznit because of the warmer water statement. I was basically trying to say that going into that level of irrelevant detail doesn't serve the customer well, and in the end the whole thing could be summed up as: a more efficient block.

We've now gone full circle. *sigh*

And I've been trying to bend my head around why it's not warmer! :cry: :shrug: ...












:D

Wet and chilly chips

Read the blurb in the center. below the competition. I like the cooling myths in particular.

8-ball

LOL

"So why use 3/8 tubing its unsightly and not necessary on this system."

I like how they try to excuse their sucky crap in comparison to other manufacturers' superior products by saying "it's not like you're cooling a Chevy V8!" It's like saying that the stock AMD heatsink is outstanding because it can theoretically keep the chip running ... just not as cool as other products. But hey, who wants a cool chip anyway?

I find the 10C over ambient claim to be far more noteworthy than the drivel about copper and flow rates being un-necessary. Lets play along, and agree that flow, and good materials are for suckers. Then, we have only to establish how they get that genuince CPU die temperature of 30C in a 20C room. Assuming the CPU is roughly 70W, then that would mean that the Wet and Willy Block has a C/W of about .14 with thermal interface material. That ain't half bad. It's crap but it's impressive ain't it.

off topic -

Wait a minute, you guys are going to tell me that there is no Santa Claus, no Easter bunnie, Clinton didn't inhale, and Gore didn't invent the internet. Ch*ist is there nothing sacred to you scientist and engineers???

.... There is a free lunch...tickets still available....send $5 cash (no checks, credit cards or money orders) to
Ralph's Save the World Fund
PO Box 1663
Santa Fe, NM, USA
- tax deductable
- discounts for groups so call your friiends and family
- water cooling door prizes for the first 100 folks
- AND if we receive your money within the next 2 weeks you will be entered in the grand prize drawing (a Cray YMP just taken out of service by LANL, winner responsible for power supply, power backup system and cooling)

If ignorance were dope, 95% of the world would OD.



PS. I don't wanta hear the money is in the mail Bill!