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Is a stronger pump better? - Page 3

post #21 of 25
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post #22 of 25
I think there is a sweet spot (speed) where the heat will transferred to the water which is passing thru the block. It's where the block's heat and water's heat get balanced.

Let's say the block gets 55C hot and the water coming from the rad is 19C. If the water passes too slow, block and water will get balanced first (say they balanced at 28C) and than both will keep increasing after balanced because the water is not passing thru fast enough.

When the flow is too fast, then the system won't have enough time to get balanced. For example the water temprature will increase to 25C and the block will decrease to 32C (not balanced) The water still have the capacity to gain more energy but it already left the block.

I am not good in physics but this is how i think.
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post #23 of 25
I thought about this again and asked myself; what happens next, after the unbalanced water leaves the block :

Another amount of 19C follows and now the block is at 32C and the balanced system should be lower than 28C. So This means faster pump will get us to lower tempratures (can't go lower than 19C tho)

Man this stuff confuses me everytime
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post #24 of 25
Quote:
Originally Posted by 3xtr3m3 View Post
I think there is a sweet spot (speed) where the heat will transferred to the water which is passing thru the block. It's where the block's heat and water's heat get balanced.
You’re aint kiddin...this stuff is confusing! But many times it’s confusing because some of our most basic presumptions are wrong. Once those get straightened out, other things usually start to clear up.

For example, in your description you start with a block at 55 C and then theorize that it gets cooler as the water gets hotter because heat is going from one to the other. At some point they’re the same (balance.) This is your first incorrect presumption. There is definitely heat, but the temperature of the block is maintained by the energy output from the CPU. That is because these components don’t operate at temperature levels...they operate at energy output levels.

Just as tubing transfers water, the block acts like tubing for energy. Energy simply flows through the block, like water flows through tubing. And as water has a constant rate of flow determined by the pump, the energy has a constant rate of flow as well, determined by the CPU.

Remember that the definition of heat is the transfer of energy. The source of this energy is the CPU. So if you’re folding and your CPU is using 70 watts of energy then you have a constant 70 watts of energy to move into the water (and get rid of in the radiator.) So there’s never a balance point such as the one you described...if the temperature of the block is 55 C, then it is always at 55 C. Why? Because the constant flow of energy keeps it hot.

Quote:
Originally Posted by 3xtr3m3 View Post
Another amount of 19C follows and now the block is at 32C and the balanced system should be lower than 28C. So This means faster pump will get us to lower tempratures (can't go lower than 19C tho)
What you’re describing here is Wind Chill. You’re standing out in the cold and you’re okay with a slight breeze but then a big gust comes along and freezes your butt. The temperature of the air didn’t change, but for some reason the wind made you feel colder. The reason you feel colder is because, sure enough, the wind caused more heat to get sucked out of you.

This phenomenon has caused more confusion than any other, the first being the belief that faster flow cools faster. This is wrong. You don’t feel colder because the air molecules are moving faster across your body. You feel colder because MORE AIR moved across your body during the gust that it did in the breeze. It’s all about volume...not speed. If, somehow, the same volume of air could be moved across your body at a slower speed, you would feel just as cold.

But let’s give speed its due. Faster flow causes more turbulence, which helps with heat transfer. However, when it comes to modern waterblocks, the flow is already turbulent at low flow rates...and more turbulence than you need isn’t necessarily better. With turbulence, there’s such a thing as too much of a good thing.

But back to volume and your description. In your description you send in more water at 19 C. This is your second incorrect presumption. When you’re standing out in the cold, there’s lots and lots of cold air available to zip by you. The air temperature is independent of your body temperature. If the speed of the air changes, its temperature stays the same. But in water-cooling the temperature of the water is very closely related to the energy output of the CPU. If the speed of the water changes, then the temperature of the water changes. So your faster water may not be at 19 C any more. It might be at 19.5 C.

This is why the Wind Chill analogy doesn’t work that well. Air temperature isn’t closely tied to the energy that your body burns. In water-cooling, water temperature IS closely tied to the energy that the CPU burns.

Think about that for a while
post #25 of 25
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In order for there to be a middle ground (local maxima) for the heat transfer to be the highest you could need productive forces that increase the heat flow, and counterproductive forces that decrease the heat flow as coolant flow rate increases. There is no counterproductive force (something that reduced heat flow), therefore, there will be no local maxima.
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