Two Loops, One radiator

[nikhsub1]

Well of course the 2gpm what confuses me is not that, what confuses me is that lowering the flow of the water by proportion increases the volume of air and vice versa. So if you are only capable of maintaining a certain volume of air wouldn't lowering the volume of water result in decreased temps?

I've read this 4 times and still don't know what you mean. How does water flow affect airflow? They are independent and don't directly affect one another although they must BOTH be taken into consideration for best performance.

[bluehaze]

maybe bluehaze is looking at stationary water boiling in a pot...
bluehaze, the cooling system in your loop does not process in batches, it constantly flows and while if you look at how little amount of heat is absorbed in a block in a given time, you have to take into factor the flow rate...

dunno if this makes sense...

if the loop were to remove temp in batches, then i think the temp of your cpu will spike up and down... also, bigger volume capacity on the blocks would be needed.. no?

No I understand that now because it is a closed loop system the volume of water passing through the rad is directly proportional to the volume of water passing through the blocks so lowering the volume of water through rad while increasing the volume of water through blocks would actually result in less water being cooled and more water being heated.

What I was thinking was that if you had seperate loops you could lower the volume of water passing through the rad thus increasing the volume of air to water.

I don't know though I don't have any education in engineering and only high school science so I am way behind on the learning curve here

[3Z3VH]

As far as the radiator is concerned, it is removing X wattage of heat from the water contained inside it over any given amount of time. Running the water through the radiator twice as fast, only means that you will take half the heat out of twice the volume of water... making the whole issue a wash.

Think of it this way... if you have a light bulb that needs 24 Watts of power to run, and it doesn't care what voltage it is given... Which is more efficient, 240v@0.1Amps or 120v@0.2Amps ? In a perfect world, there is no difference between the two, you are still using 24 Watts. In our less-than-perfect world, the 240v is more efficient since you lose less power in your transport (wires) due to resistance...

Comparing this to watercooling, that resistance is friction from the water running through your tubing and blocks. The more flow you have (much like voltage in a power line) the less effect your resistance will have on the total. No matter what, the radiator will still dissipate the same wattage of heat.

Another thing to consider is, radiators are more efficient the hotter they are. If you leave the water in the radiator too long, you reduce the radiator's efficiency because the water is already cooled by the time it gets to the outlet.

Basically, the difference between the two will be negligible unless you get to extremes, like slowing your flow rate to a crawl... but the higher flow will be slightly better in all cases, due to lower loss to friction in the tubing, and making the radiator operate at a higher efficiency part of it's curve.

[kinghong1970]

No I understand that now because it is a closed loop system the volume of water passing through the rad is directly proportional to the volume of water passing through the blocks so lowering the volume of water through rad while increasing the volume of water through blocks would actually result in less water being cooled and more water being heated.

What I was thinking was that if you had seperate loops you could lower the volume of water passing through the rad thus increasing the volume of air to water.

I don't know though I don't have any education in engineering and only high school science so I am way behind on the learning curve here

bluehaze, correct me if i'm wrong... but i think what you're getting at is looking at figures to increase the efficiency of amount cooled by looking at amount of air flow vs amount of water...

but see, regardless of how much water you have, the loop requires a FIXED amount of water to have a continuous loop with no air bubbles in order to get it to work... if you have more water, it just sits in the reservoir and gets used as needed... if you have too little water, it is basically a T-Line... so there is only so much you can decrease the amount of water...

efficiency of your loop will be dictated more by your flow rate of water and air flow over your radiator...

now i don't know if i make any sense... lol

[bluehaze]

bluehaze, correct me if i'm wrong... but i think what you're getting at is looking at figures to increase the efficiency of amount cooled by looking at amount of air flow vs amount of water...

but see, regardless of how much water you have, the loop requires a FIXED amount of water to have a continuous loop with no air bubbles in order to get it to work... if you have more water, it just sits in the reservoir and gets used as needed... if you have too little water, it is basically a T-Line... so there is only so much you can decrease the amount of water...

efficiency of your loop will be dictated more by your flow rate of water and air flow over your radiator...

now i don't know if i make any sense... lol

LOL Yes you got it, that was the mistake I have been making, being the volume of water is fixed in a closed loop system you cant alter the proportion of air to the proportion of water without increasing or decreasing the air flow. Yay I think I got it now

I guess it's easy to get confused because natural tendency is to consider an open loop with unlimited water supply but when it is a closed loop and your dealing with a fixed volume of water everything changes.

[millertime359]

As far as the radiator is concerned, it is removing X wattage of heat from the water contained inside it over any given amount of time. Running the water through the radiator twice as fast, only means that you will take half the heat out of twice the volume of water... making the whole issue a wash.

Think of it this way... if you have a light bulb that needs 24 Watts of power to run, and it doesn't care what voltage it is given... Which is more efficient, 240v@0.1Amps or 120v@0.2Amps ? In a perfect world, there is no difference between the two, you are still using 24 Watts. In our less-than-perfect world, the 240v is more efficient since you lose less power in your transport (wires) due to resistance...

Comparing this to watercooling, that resistance is friction from the water running through your tubing and blocks. The more flow you have (much like voltage in a power line) the less effect your resistance will have on the total. No matter what, the radiator will still dissipate the same wattage of heat.

Another thing to consider is, radiators are more efficient the hotter they are. If you leave the water in the radiator too long, you reduce the radiator's efficiency because the water is already cooled by the time it gets to the outlet.

Basically, the difference between the two will be negligible unless you get to extremes, like slowing your flow rate to a crawl... but the higher flow will be slightly better in all cases, due to lower loss to friction in the tubing, and making the radiator operate at a higher efficiency part of it's curve.

Great description.

[kinghong1970]

LOL Yes you got it, that was the mistake I have been making, being the volume of water is fixed in a closed loop system you cant alter the proportion of air to the proportion of water without increasing or decreasing the air flow. Yay I think I got it now

I guess it's easy to get confused because natural tendency is to consider an open loop with unlimited water supply but when it is a closed loop and your dealing with a fixed volume of water everything changes.

he he he...

1) hook up your loop to tap water and drain out your toilet...
2) fixed/closed loop

if the following is fixed:
a) temp of water
b) air flow over rad
c) flow rate in loop

then i think your resulting temp will be the same... except, choice 1 will give you bigger water bill...

[bluehaze]

he he he...

1) hook up your loop to tap water and drain out your toilet...
2) fixed/closed loop

if the following is fixed:
a) temp of water
b) air flow over rad
c) flow rate in loop

then i think your resulting temp will be the same... except, choice 1 will give you bigger water bill...

Right but see that's where the confusion came in, plan was to have 2 pumps so you could have lower flow through rad and higher flow through blocks.

[Kuntz]

As far as the radiator is concerned, it is removing X wattage of heat from the water contained inside it over any given amount of time. Running the water through the radiator twice as fast, only means that you will take half the heat out of twice the volume of water... making the whole issue a wash.

Think of it this way... if you have a light bulb that needs 24 Watts of power to run, and it doesn't care what voltage it is given... Which is more efficient, 240v@0.1Amps or 120v@0.2Amps ? In a perfect world, there is no difference between the two, you are still using 24 Watts. In our less-than-perfect world, the 240v is more efficient since you lose less power in your transport (wires) due to resistance...

Comparing this to watercooling, that resistance is friction from the water running through your tubing and blocks. The more flow you have (much like voltage in a power line) the less effect your resistance will have on the total. No matter what, the radiator will still dissipate the same wattage of heat.

Another thing to consider is, radiators are more efficient the hotter they are. If you leave the water in the radiator too long, you reduce the radiator's efficiency because the water is already cooled by the time it gets to the outlet.

Basically, the difference between the two will be negligible unless you get to extremes, like slowing your flow rate to a crawl... but the higher flow will be slightly better in all cases, due to lower loss to friction in the tubing, and making the radiator operate at a higher efficiency part of it's curve.

^Metaphor of the century^

And another way to look at it is:

If you increase flow, the water spends less time in the radiator getting cooled off, but it also spends less time in the CPU block getting heated up. If you decrease flow, your water will spend a lot of time in the radiator getting cooled off, but it will also spend even more time in the CPU block getting boiled! It all balances itself out for the most part.

[nikhsub1]

As far as the radiator is concerned, it is removing X wattage of heat from the water contained inside it over any given amount of time. Running the water through the radiator twice as fast, only means that you will take half the heat out of twice the volume of water... making the whole issue a wash.

Not really. The flow rate of the water and the air will determine how efficient the rad is, it will not be a wash, it will be very different at different flow rates.

Another thing to consider is, radiators are more efficient the hotter they are. If you leave the water in the radiator too long, you reduce the radiator's efficiency because the water is already cooled by the time it gets to the outlet.

Your first sentence here is misleading. Radiators are most efficient when there is a large liquid to air temp differential. If the rad's water is at 50C and so is the air, the rad won't be efficient at all. If the air was 25C it would be. The second sentence makes no sense. This would apply to serial rads where the first rad in the loop would be more efficient than the second because the first rad already cooled the water some.

[boogle]

Not really. The flow rate of the water and the air will determine how efficient the rad is, it will not be a wash, it will be very different at different flow rates.

You're kidding right? It's a CLOSED loop, flow rate will have little affect outside of extreme highs and lows. To make it simple:

A train follows a circular track that loops in on itself - like many basic trainsets. Put the station at one point. If the train does 1 lap every 10 seconds, it'll spend 1 second travelling through the station each lap.

Now if the train does 1 lap every 20 seconds, it'll spend 2 seconds travelling through the station each lap.

But here's the rub, in the first instance if you increase the time measured to 20 seconds, then it spends exactly the same amount of time in the station as the second loop.

Numbers only:
1 lap every 20secs, 2 secs in station per 20sec
1 lap every 10secs, 2 secs in station per 20sec

Ultimately the flowrate doesn't make a major difference to the time water spends in the radiator, which is why flowrate doesn't make a difference.

Flowrate makes a difference with waterblocks, not radiators.

[Adamantine]

Lower flow doesn't help make a radiator perform better. The most important part of cooling is being ignored here, how the heat is transfered in the first place: Turbulence. Higher flow means more turbulence.

Can't use data from an actual loops, it'd have to be just a test loop where the only variable is the flow rate.

[Kuntz]

Lower flow doesn't help make a radiator perform better. The most important part of cooling is being ignored here, how the heat is transfered in the first place: Turbulence. Higher flow means more turbulence.

Can't use data from an actual loops, it'd have to be just a test loop where the only variable is the flow rate.

I'd tend to think that too, more turbulence in the radiator translates into better transporting of heat to the radiator fins. If you stir a pot of water, does it come to a boil much faster than if you just leave it sit? I live in a Dorm and can't test this.

[nikhsub1]

You're kidding right? It's a CLOSED loop, flow rate will have little affect outside of extreme highs and lows. To make it simple:

A train follows a circular track that loops in on itself - like many basic trainsets. Put the station at one point. If the train does 1 lap every 10 seconds, it'll spend 1 second travelling through the station each lap.

Now if the train does 1 lap every 20 seconds, it'll spend 2 seconds travelling through the station each lap.

But here's the rub, in the first instance if you increase the time measured to 20 seconds, then it spends exactly the same amount of time in the station as the second loop.

Numbers only:
1 lap every 20secs, 2 secs in station per 20sec
1 lap every 10secs, 2 secs in station per 20sec

Ultimately the flowrate doesn't make a major difference to the time water spends in the radiator, which is why flowrate doesn't make a difference.

Flowrate makes a difference with waterblocks, not radiators.

I think you need to do some reading too. Step 1, reread what I wrote and what I was referring to. You asked me if I was kidding? Closed loop? Yes the assumption is a closed loop. And flow rate DOES make a difference in radiators. Please check your facts.

[troelsm]

I'd tend to think that too, more turbulence in the radiator translates into better transporting of heat to the radiator fins. If you stir a pot of water, does it come to a boil much faster than if you just leave it sit? I live in a Dorm and can't test this.

That is not easy to test that way. The reason (atleast thats what i think) why more turbulence = better heat transfer is because much more of the water is touching radiator.

I guess a good way to describe it is to try and look at the water from a molecular point of way and "travel distance".

Say we have two loops that both have a flow rate of 2 gpm. One has no turbulence (i know this is not possible but it's only to make the argument easier to understand) the other has a lot of turbulence.

Now they both have the same flowrate but the molecules in the one with turbulence would travel a much greater distance in one passing of the entire loop than one molecule in the non-torbulent loop would, since it would travel in a "straight" line. This means that the turbolent molecules would travel at a much greater velocity.

Therefore the molecules in the turbulent loop would touch the actual radiator more and thereby increase heat transfer.

I hope this is as understandable to people who read it as it is in my head

Edit2: Which in the end means that more flow = more torbulence = better heat transfer. This doesn't mean you can just add something to your loop to create torbulence and you'll see better numbers. The more torbuelence you got in the loop the more pumping power it takes to keep the same flow rate.

[[XC] riptide]

http://www.xtremesystems.org/forums/...d.php?t=226199

Bluehaze and everyone else that wonders. Read the above thread. Its a good one. It answers even more than you are asking.

[eth0s]

First of all let's remember what the purpose of water cooling is: to move the heat from the hot parts of the computer to the outside of the case. We cannot destroy the heat, we can only move it. How is this accomplished? First we use a small amount of water to absorb the heat produced by the cpu in the cpu block. Then we move this quantum of water to the radiator where the heat is transferred through the fins of the radiator into the air. This cools the water back down. Now we send this same quantum of less hot water back to the cpu block to absorb more heat. And we do this over and over again. The faster we do it, the better. The more times per minute that you heat up the quantum of water and cool it off again the more cooling capacity your loop will have. Just like the fact that the faster the air is passing over the radiator the more heat will be transferred to the air. This situation is not analogous to trains, unless you have the trains loading and unloading passengers. Now the total passengers you load and unload over a full day, is a more analogous, if still inapt, to water cooling. Further the voltage in a light bulb is analogous to the head pressure of the pump, not the flow rate, which is analogous to the current in the wires. And finally, radiators do more work when there is more flow, and do less work when there is less flow. You would never want to slow the water down in a radiator, this would never provide you any benefit (in terms of cooling).

[troelsm]

First of all let's remember what the purpose of water cooling is: to move the heat from the hot parts of the computer to the outside of the case. We cannot destroy the heat, we can only move it. How is this accomplished? First we use a small amount of water to absorb the heat produced by the cpu in the cpu block. Then we move this quantum of water to the radiator where the heat is transferred through the fins of the radiator into the air. This cools the water back down. Now we send this same quantum of less hot water back to the cpu block to absorb more heat. And we do this over and over again. The faster we do it, the better. The more times per minute that you heat up the quantum of water and cool it off again the more cooling capacity your loop will have. Just like the fact that the faster the air is passing over the radiator the more heat will be transferred to the air. This situation is not analogous to trains, unless you have the trains loading and unloading passengers. Now the total passengers you load and unload over a full day, is a more analogous, if still inapt, to water cooling. Further the voltage in a light bulb is analogous to the head pressure of the pump, not the flow rate, which is analogous to the current in the wires. And finally, radiators do more work when there is more flow, and do less work when there is less flow. You would never want to slow the water down in a radiator, this would never provide you any benefit (in terms of cooling).

I agree 100% with you that less flow will never achieve better temperatures. Though air over the radiator isn't a very good analogy to the water flowing through the radiator. This is because the air over radiator is an open system, and therefore it's all about how much air you can get over the radiator. In the case of the water, if it wasn't for the turbulence created by more flow the heat transfer curve would've flatten out at very low gpm because it's a closed system.

This is if we look away from turbulence for a second: I think the problem with your example is that (if i read it right) you seem to imply that more flow means that the blocks will heat up the quantum of water more times per minute. In a sense this is true but the problem in a closed system is that it wouldn't heat each quantum up as much as they would if the flow had been slower.. ie. the water goes through twice as fast but only moving half the heat each passing.

All this is cancelled by the turbulence the flow creates though. Just wanted to try and explain why you can't really compare it to fans on a radiator.

[bluehaze]

http://www.xtremesystems.org/forums/...d.php?t=226199

Bluehaze and everyone else that wonders. Read the above thread. Its a good one. It answers even more than you are asking.

Thanks for the link! Just briefly scanned the thread so far but it is easy to see why this all gets so confusing. Most everything with a closed loop system is so counter intuitive to the natural thought process. It seems to me if they are isolating temp drop accross the radiator only that it is not an accurate method of measurement as lower flow will definitely decrease temps in this measurement, that is what I was trying to say before with lowering the flow of water is equivalent to increasing the flow of the air accross the radiator only.

It would seem the best way to get realistic temp data would be to just plunk a meter in the res and measure during a certain time period of a sustained heat load. As if you try to measure at any 2 points you are eliminating a portion of the loop which plays a part in overall temps.

[3Z3VH]

Not really. The flow rate of the water and the air will determine how efficient the rad is, it will not be a wash, it will be very different at different flow rates.


Your first sentence here is misleading. Radiators are most efficient when there is a large liquid to air temp differential. If the rad's water is at 50C and so is the air, the rad won't be efficient at all. If the air was 25C it would be. The second sentence makes no sense. This would apply to serial rads where the first rad in the loop would be more efficient than the second because the first rad already cooled the water some.

Stop worrying about the flow rate of the air. We are assuming the air flow rate is a constant, because no matter how fast/slow the water is passing through the loop, it will not make your fans spin faster. So the air flow rate is a constant.

Also, my sentence isn't misleading. I agree with you, they get more efficient as the delta between ambient and water temps increases. Now, when you are given a constant value as your ambient temperature, what is the only variable that will increase the delta between ambient and water temps ? That's right, the temperature of the water... meaning, the hotter the water, the more efficient the radiator will be, since the ambient is considered a constant (for the purposes of this conversation). Now read my sentence again, considering that the ambient temp is a constant.... The hotter the radiator is (due to water temps) the more efficient it is. Seems true to me !

Your radiator, with a constant air flow over it, using a constant ambient temp, will give a predictable cooling capacity, represented by wattage, which will look like a curve on a graph of liquid temp vs. heat dissipated. The higher the temp of the liquid, the more capacity your radiator has to dissipate it.

Thus, my oversimplified statement "The hotter the radiator is, the more efficient it is" is true for purposes of this conversation. And you only proved my point by your statement about the differential... if you let the water sit in the rad for, say, an hour it should get pretty close to ambient temp... do you think the radiator is still radiating warm air ? Nope. That is because it is no longer removing as much heat from the water. If you let the water temp get too close to ambient, the radiator will not be as efficient. Thus, the slower the water, the more time it has to get closer to ambient, thus, the less efficient your radiator will be. All the water that is waiting to get pumped through the radiator is getting hotter and hotter waiting for its turn to go through the radiator at such a slow rate.

I'd tend to think that too, more turbulence in the radiator translates into better transporting of heat to the radiator fins. If you stir a pot of water, does it come to a boil much faster than if you just leave it sit? I live in a Dorm and can't test this.

Actually if you stir a pot, it will boil slower, but it is not due to turbulence. It is because you are letting ambient air into the liquid, which cools down what you are stirring. A pot that is not being stirred, still has natural convection to spread the heat around to all the liquid quickly.

I think you need to do some reading too. Step 1, reread what I wrote and what I was referring to. You asked me if I was kidding? Closed loop? Yes the assumption is a closed loop. And flow rate DOES make a difference in radiators. Please check your facts.

Please show us a benchmark of how flowrate through a radiator affects temps in a closed system.

[nikhsub1]

Also, my sentence isn't misleading. I agree with you, they get more efficient as the delta between ambient and water temps increases. Now, when you are given a constant value as your ambient temperature, what is the only variable that will increase the delta between ambient and water temps ? That's right, the temperature of the water... meaning, the hotter the water, the more efficient the radiator will be, since the ambient is considered a constant (for the purposes of this conversation). Now read my sentence again, considering that the ambient temp is a constant.... The hotter the radiator is (due to water temps) the more efficient it is. Seems true to me !

I knew what you meant, however when you say the hotter the rad is that could mean hot ambient with cool liquids or vice versa. No matter, we are just arguing semantics.

Please show us a benchmark of how flowrate through a radiator affects temps in a closed system.

http://swiftnets.com/Technical/Asses...erformance.pdf

[3Z3VH]

I knew what you meant, however when you say the hotter the rad is that could mean hot ambient with cool liquids or vice versa. No matter, we are just arguing semantics.


http://swiftnets.com/Technical/Asses...erformance.pdf

Except my semantics were relevant to the conversation, and yours were not.

Also, every graph in that link shows that the higher velocity of your water, the more heat gets dissipated. You'll even notice, that as the flow rate gets critically low, the heat dissipated becomes exponentially smaller. This supports my argument, not yours.

[[XC] riptide]

Except my semantics were relevant to the conversation, and yours were not.

Also, every graph in that link shows that the higher velocity of your water, the more heat gets dissipated. You'll even notice, that as the flow rate gets critically low, the heat dissipated becomes exponentially smaller. This supports my argument, not yours.

Actually.

Running the water through the radiator twice as fast, only means that you will take half the heat out of twice the volume of water... making the whole issue a wash.

and

Basically, the difference between the two will be negligible unless you get to extremes

is wrong. But you seem to have tried to turn the tables.

In nikhsub1 link the diff between .5 and 4gpm is about 40% increase and is hardly "negligible"

[nikhsub1]

Thank you [XC] riptide, I was beginning to think I lost my mind for a second. He says that flow rates won't make a difference, I say otherwise. He then asks me for proof (as if I have no idea what I'm talking about ), I provide it, then it proves my point and he says he is right and I am wrong. Wow.

[3Z3VH]

My argument was that the higher the flow, the more heat a radiator dissipates. I was correct. I also stated that the hotter a radiator is, the more heat it dissipates, I am still correct, as shown by the graphs YOU presented.

Also, I said "unless you get to extremes"... as you will read from MANY sources, here and elsewhere, anything below 1.5GPM you should start worrying about how to increase flow rate... meaning 0.5GPM is an extreme.

Again, you have lost sight of the argument you were trying to make, and are now arguing semantics.

Show me proof that lower flow rates are more efficient in a radiator than higher flow rates, because you still have not done so.