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Water Flow Rate

post #1 of 3
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Do water flow rate can determine the temp?

because before this i run my mcp665 pump at full speed, no.5. the idle temp i got is 34'c and prime full load 75'c at 5Ghz.

now i turn the pump speed to no.2, and my temp is lower, 28'c on idle and prime full load barely reach 70'c. only 65'c

can someone enlighten me about this

tq..
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Mopiko Laila
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post #2 of 3
Flow rate does determine the heat transfer rate up to a point. As the flow rate increases you get turbulent flow which is better for heat transfer. At lower flow rates you get lamina flow, which isn't so good (I can provide a more detailed explanation if you want). In between turbulent and lamina flow there is a period called transitional flow, which is a mix of both. In most modern blocks the transition flow rate is somewhere in the region of 0.6-1GPM.


The point where flow rate no longer affects the heat transfer rate so much is where you have fully developed turbulent flow (>1GPM in most blocks). Once you go over that then the benefits reduce.

Another thing to consider is the heat dump from the pump. The faster you run the pump the more energy it is putting into the fluid. Since pumps are not 100% efficient some of this energy ends up as heat in the liquid. Therefore the harder you run your pump the more you heat your loop.

This means that there is a sweet spot between pump heat dump and flow rate which will vary from loop to loop. You might have found yours.

I have to say though that 5-10°C is a little large for this effect. What is more likely is that either your ambient changed between these tests, your loop had some air trapped in it for the previous test or something changed with the test.

If I am wrong and it is consistently lower then well done, you have found a good point to run your loop at.
Edited by GingerJohn - 10/22/11 at 10:47am
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post #3 of 3
Quote:
Originally Posted by GingerJohn;15409051 
Flow rate does determine the heat transfer rate up to a point. As the flow rate increases you get turbulent flow which is better for heat transfer. At lower flow rates you get lamina flow, which isn't so good (I can provide a more detailed explanation if you want). In between turbulent and lamina flow there is a period called transitional flow, which is a mix of both. In most modern blocks the transition flow rate is somewhere in the region of 0.6-1GPM.


The point where flow rate no longer affects the heat transfer rate so much is where you have fully developed turbulent flow (>1GPM in most blocks). Once you go over that then the benefits reduce.

Another thing to consider is the heat dump from the pump. The faster you run the pump the more energy it is putting into the fluid. Since pumps are not 100% efficient some of this energy ends up as heat in the liquid. Therefore the harder you run your pump the more you heat your loop.

This means that there is a sweet spot between pump heat dump and flow rate which will vary from loop to loop. You might have found yours.

I have to say though that 5-10°C is a little large for this effect. What is more likely is that either your ambient changed between these tests, your loop had some air trapped in it for the previous test or something changed with the test.

If I am wrong and it is consistently lower then well done, you have found a good point to run your loop at.

+rep here.

MCP655's/D5's dump a lot of extra heat into a loop running at full speed. In a CPU only loop, running the pump at a lower speed like 2-4 will be more beneficial than the highest speed since the extra amount heat being dumped into the loop will negate any cooling benefits. Seeing how you're on an EK HF, there really isn't any need to run that pump higher than the 3 setting since it's such a low restriction water block.
    
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