Unexpected results - higher flow = higher temps

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10-23-2006, 10:06 AM
Vikodemous

Quote:

Originally Posted by MaxxxRacer

Please go read the guides before you say such nonesense.

Thats your explanation Mr. Darth Water? With him running Dual rads let's hear your Brilliant Deduction then...

P.S. It's spelled nonsense.
10-23-2006, 10:10 AM
Hound53

Quote:

Originally Posted by virtualrain

So here is the problem with my flow meter that may or may not be related to this issue... Keep in mind this could be a red-herring as it could be a faulty flow meter or the Aquaero mis-behaving.

According to spec, the Remag flow meter generates 700 imp/l. I have noticed that if I set the Aquaero to this value and then run the pumps at full speed, the flow reported is way off... it's 0.6lpm. If I run the pumps at lower voltage, the flow meter seems more accurate...

However, if i set the imp/l on the Aquaero to 70 imp/l, I get what seem like more accurate flow ratings of 6lpm at full speed and 3lpm at 7V.

Here's the flow meter output at different pump speeds for the rated 700imp/l. Note that 0% = 7V and 100% = 12V due to the voltage divider I'm using...

10% = 1.5lpm
20% = 1.9lpm
30% = 2.2lpm
40% = 2.6lpm
50% = 2.9lpm
60% = 0.1lpm (very erratic)
70% = 0.4lpm (now it's off by about an order of magnitude!)
80% = 0.6lpm
90% = 0.6lpm (no change)
100% = 0.6lpm

Note that I tested the loop with buckets and both pumps running at max and the flow was 6lpm! So again, I say this may be a red-herring and it could be a faulty flow meter or Aquaero.

No I think I swas suffering from a case of anal cranial inversion and forgot all about efficiency curves. Most pumps operate most efficiently between 70%and 90% of their rated head. 90% being at the top of the scale and 70% being a cheap pond pump. Keep in mind that I am just a shade tree mechanic, and we really need to get a real engineer in here to settle this.
10-23-2006, 10:40 AM
Reinvented

Quote:

Originally Posted by Vikodemous

Thats your explanation Mr. Darth Water? With him running Dual rads let's hear your Brilliant Deduction then...

P.S. It's spelled nonsense.

Please, do US ALL a favor and THINK before you post...
10-23-2006, 10:47 AM
Fairydust

Check out this brilliant pump review, it explains a lot of the basics (horrible robotranslation sorry). You see the improved block/radiator performance from increased flowrate is often not enough to offset the increased water temperature from higher heatdump of the more powerfull pump.
10-23-2006, 11:39 AM
Firelord-OCHW

Why have you got the rads infront of the cpu block? Surely the Apogee would benefit from being right after the pump for max flow and then the rad after before it hits back round
10-23-2006, 11:40 AM
virtualrain

Quote:

Originally Posted by Fairydust

Check out this brilliant pump review, it explains a lot of the basics (horrible robotranslation sorry). You see the improved block/radiator performance from increased flowrate is often not enough to offset the increased water temperature from higher heatdump of the more powerfull pump.

Interesting find!!! At first glance, their findings with dual DDC's vs. a single DDC is consistent with my own. I gather that running both my DDC's at 7V is equivalent to just a bit more than a single DDC at 12V.

I guess I have a few options...
1. Get rid of one pump and run the other at full speed for the same results.
2. Keep both pumps as is running at 7V (they are very quiet at 7V)
3. Add more restriction (i.e. my GPU and possibly a Storm) to take advantage of the over-kill in pump power.

I'm obviusly leaning towards #3 and possibly using #2 during idle periods. Since I've already invested in the extra pump (which I purchased also for redundancy and to eliminate down-time in the event of an RMA) I may as well just keep it as is... no real point to ripping it out of the loop.

What do you think?

Question... would I benefit much from higher flow fans?
10-23-2006, 11:41 AM
virtualrain

Quote:

Originally Posted by Firelord-OCHW

Why have you got the rads infront of the cpu block? Surely the Apogee would benefit from being right after the pump for max flow and then the rad after before it hits back round

I think common lore is to have the CPU block directly after the rads for coolest water. Flow is the same at all points throughout the loop.
10-23-2006, 11:43 AM
Vikodemous

Quote:

Originally Posted by Reinvented

Gee, I wonder why...

7v means less heat dump into the water, as opposed to 12v... get the picture?

Doesn't take a damn rocket scientist to figure that one out..

Your right, I should have said something charming Like you did. You reply to his post like it's a burden. Lord forbid I try to give someone some sort of explanation to his having lower temps with lower flow rate.

And your absolutely right, "water that is no longer under constant heat won't cool"<-- I hope this statement makes you feel better.
10-23-2006, 11:54 AM
Senater_Cache

Quote:

Originally Posted by Vikodemous

The lower Flow rate is giving the water more time to cool through the rad before it goes back to the CPU.

better run and hide man.

Quote:

Originally Posted by Vikodemous

Lord forbid I try to give someone some sort of explanation to his having lower temps with lower flow rate.

you did nothing but spread misinformation. You did more harm to his grasp on watercooling than you did good.

Quote:

Originally Posted by Vikodemous

"water that is no longer under constant heat won't cool"

thats not quite the idea behind a radiator nor a block...think about convection rate and how its better at higher temperature differences between 2 materials.
10-23-2006, 11:56 AM
[XC]Atomicpineapple

Quote:

Originally Posted by Vikodemous

The lower Flow rate is giving the water more time to cool through the rad before it goes back to the CPU.

Small problem there. The water takes a time t to traverse the waterblock. During that time its temperature increases as it absorbs heat energy from the CPU. As its temperature increases the temperature difference (or 'delta') between the CPU and the water inside the block decreases, thus heat transfer rates drop.

If the flow rate is increased time t taken to traverse the block is decreased. Therefore each unit (molecule) of water absorbs less heat energy so its temperature remains lower. Thus the temperature differential is maintained and the heat transfer rates stay as high as possible. Now youre thinking 'ah-ha less heat transfered to water, means higher CPU temps at higher flow'. Um, no, because the higher flow rate will mean that more water molecules traverse the block in a given time period.

However as others have pointed out this increase in flowrate means more heat energy is dumped into the water by the pump(s). This can raise temperatures.

Thinking aloud now because I'm not sure where this will go........ The smaller time t also applies to the radiator. This means that the water has less time to remove its heat energy across a temperature delta, but as heat transfer rates grow exponentialy with temperature difference the decrease in t will perhaps have little to no effect on the radiator exit water temp as the decrease in time t would, in effect, be removing the section of the heat energy removal graph that relates to low temperature deltas, thus being the section of the graph where temperatures are least affected.
10-23-2006, 11:57 AM
Nanometer

:horse: I never understood what this smiley meant. Anyone want to explain?
10-23-2006, 11:57 AM
Reinvented

Quote:

Originally Posted by Vikodemous

Your right, I should have said something charming Like you did. You reply to his post like it's a burden. Lord forbid I try to give someone some sort of explanation to his having lower temps with lower flow rate.

And your absolutely right, "water that is no longer under constant heat won't cool"<-- I hope this statement makes you feel better.

Actually, maybe you should. And while your at it bud, read the stickies, and educate yourself a bit more...
10-23-2006, 12:01 PM
Modzilla

radiator placement is less important than some people think, if using a radiator that is about the size of a heater core (like most watercooling rads). what really matters is the heat absorbtion and dispersion capacity of the system as a whole. with a decent flowrate, the temperature of the water at any given point in the loop will be within a couple degrees F of the temp at any other point in the loop. it takes time for the water to absorb the heat and disperse it to the rad, and for the rad to disperse it to the air. its that steady state achieved by the system, after accounting for heat input and heat dispersion.
10-23-2006, 12:04 PM
virtualrain

Quote:

Originally Posted by Modzilla

radiator placement is less important than some people think, if using a radiator that is about the size of a heater core (like most watercooling rads). what really matters is the heat absorbtion and dispersion capacity of the system as a whole. with a decent flowrate, the temperature of the water at any given point in the loop will be within a couple degrees F of the temp at any other point in the loop. it takes time for the water to absorb the heat and disperse it to the rad, and for the rad to disperse it to the air. its that steady state achieved by the system, after accounting for heat input and heat dispersion.

In my case, the water temperature as measured just before the rads is often only 0.3 degrees C warmer than the water temp after the rads.
10-23-2006, 12:06 PM
Senater_Cache

Quote:

Originally Posted by Nanometer

:horse: I never understood what this smiley meant. Anyone want to explain?

lol...yep.

But it will never end. and with chaps like vikedemous running rampant spreading the gospel its only gonna get worse.
watercooling, soon to be mainstream and completely misunderstood.
10-23-2006, 12:25 PM
nikhsub1

Quote:

Originally Posted by virtualrain

I think common lore is to have the CPU block directly after the rads for coolest water. Flow is the same at all points throughout the loop.

Careful how you word that. While overall system flowrate is constant, PRESSURE IS NOT. You will get the greatest pressure right after the pump, pressure goes down as it goes through each piece in the loop.
10-23-2006, 12:34 PM
Radical_53

Quote:

Originally Posted by Modzilla

radiator placement is less important than some people think, if using a radiator that is about the size of a heater core (like most watercooling rads). what really matters is the heat absorbtion and dispersion capacity of the system as a whole. with a decent flowrate, the temperature of the water at any given point in the loop will be within a couple degrees F of the temp at any other point in the loop. it takes time for the water to absorb the heat and disperse it to the rad, and for the rad to disperse it to the air. its that steady state achieved by the system, after accounting for heat input and heat dispersion.

Depends on what you mean with "radiator placement". Where it is on the loop, you're right. Where it is in your case, definitely not. Makes a huge difference if there's not enough space for the air to get in or out.

@fairydust: You're right about that review, there was something from Cathar on a topic like that too:

http://forums.procooling.com/vbb/sho...light=storm+g7

Generally spoken, a too small pump will give you low performance because the flow rate is low, but a too big pump will give low performance too, as the heat dump is too high.
Somewhere in the middle you'd find the "perfect pump" for your setup. One reason why I dumped the second DDC+ on my loop, as it doubled pump heat dump but only gave me ~15-25% higher flow rates. It didn't show a real improvement, so why hassle around with it.
10-23-2006, 12:35 PM
Fairydust

Quote:

Originally Posted by virtualrain

Question... would I benefit much from higher flow fans?

If your radiator performance increases and °C/W drops (more powerfull fans or radiator, bigger area) the impact on water temperature of the raised heatdump of a more powerfull pump will shrink. If the impact of the heatdump is smaller than the increase in block performance due to increased flowrate, temps will drop. If this will happen in your particular setup I do not know.
10-23-2006, 12:36 PM
Modzilla

I meant where the rad is in the loop. For my posts, Im assuming that the rad has adequate air-flow.
10-23-2006, 12:39 PM
Radical_53

Ok, my fault ;) Then I totally agree with you. I've seen differences of up to 1°C before and after the rad, but that depends a lot on the rad used and how much air is going through the rad. On a "good" setup, definitely nothing to even think about.
10-23-2006, 12:40 PM
nikhsub1

Quote:

Originally Posted by Radical_53

One reason why I dumped the second DDC+ on my loop, as it doubled pump heat dump but only gave me ~15-25% higher flow rates. It didn't show a real improvement, so why hassle around with it.

Actually it will give you ~35% improvement in flowrate.
10-23-2006, 12:46 PM
Herr Brun

Quote:

Originally Posted by nikhsub1

Careful how you word that. While overall system flowrate is constant, PRESSURE IS NOT. You will get the greatest pressure right after the pump, pressure goes down as it goes through each piece in the loop.

But that doesn't matter, if I understand correctly? Pressure does not matter, flowrate does? Or is it different with impingement (sp) style blocks?
10-23-2006, 12:54 PM
nikhsub1

Quote:

Originally Posted by Herr Brun

But that doesn't matter, if I understand correctly? Pressure does not matter, flowrate does? Or is it different with impingement (sp) style blocks?

There is no way to correctly answer that question. Yes sometimes it does matter, how much? Another guess. If pressure didn't matter we'd all be running pumps with 1 inch of max head...
10-23-2006, 12:55 PM
JoeBar

And Tt would be the king of wc'ing... :lol2:

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