[O-CuK]Marci
New member
Replicated from Cathar's Original Post here: http://www.xtremesystems.org/forums/showthread.php?t=147767
=======================================================
I've been working on a wholistic guide to designing a water-cooling system of late. Using a mix of real-world test data, and calculating pressure drops, I've been able to put together an analysis of the impact of tubing sizes on CPU temperatures.
The radiator and waterblocks are:
Thermochill PA120.2 with 2 x Yate-Loon fans at 12v
Swiftech Apogee GTX
Conroe C2D CPU, overclocked and under load, emitting 100W of heat
2 meters of tubing length
Loop order is pump->radiator->waterblock->pump
Using 1/2" ID tubing and 1/2" OD barbs, I determined the pressure-drop curve for the system. Using Swiftech's published test data for the Apogee GTX, and a flow-performance curve for the PA120.2, we're able to determine the pumping hydraulic power required to push various flow-rates. Using established typical ratios of hydraulic power to actual power draw and heat dump of known real-world pumps, we're able to throw into the mix the amount of pump heat dump required to push any flow rate. We first establish this independently of an actual pump (i.e. determine the theoretical best pump), and then select an actual real-world pump that best suits the theoretical target, and then using the PQ curve of that pump, determine the final flow rate of the system, and hence the correspondent final CPU temperature.
Now in a wholistic model, we're modelling not just the impact of the water-flow rate on the CPU temperature, but the impact of the total heat dump of the cooling system (CPU, pump, radiator fans) has on the room environment, which in turn raises the temperature of the air in the room, and so in turn raises the water temperature because the air-in temperature into the radiator will have warmed up. The effect is very small, but I still model it.
Global temp = 22C
Room C/W = 0.005
Fan Heat Dump = 2.0W
The proposed tubing sizes and fittings we'll be investigating are:
Quick-fit fittings are those similar to those found on the Swiftech MCW50 (http://www.swiftech.com/products/mcw50.asp)
Running the above range of tubing/fitting sizes through the optimal pump power estimator software I wrote, it predicts that the best pump to use is one that's consuming around 10-13W, with optimal pumping efficiency in the ranges of 3-6LPM. I won't go into the intricacies of the pump power estimator. It's not an exact science, suffice to say that it looks at the wholistic scenario given a waterblock, heatload, room C/W, radiator, system restriction, and so on, and puts out a suggestion for where the optimal range of pumping power lies for that setup. This allows us to then pick a real pump that closely matches the suggested pumping characteristics.
Using the Laing data here: http://www.laing.de/file/66 we see that an unmodified DDC1+ (more commonly referred to in forums as the DDC2) is a very good pump fit for our scenario. Another excellent alternative would be the DDC1 with a modded top.
Okay, so our optimised system consists of:
Laing DDC1+ (unmodified)
Thermochill PA120.2 with 2 x Yate-Loon fans at 12v
Conroe C2D CPU, overclocked and under load, emitting 100W of heat
2 meters of tubing length
For the various tubing/fitting sizes, the PQ curves for a full system for each tubing type looks like this:
I overlaid the curves onto the PQ graph for the Laing DDC1+
The flow performance curves for the radiator and waterblock are illustrated on the following graphs:
...and...
The total CPU heat load is 100W. The total system heat load is 114W . We assume a fixed 14W heat dump from pump which was derived from other testing. This does in fact vary a little as we can see by the Laing graph. As flow rates decrease, so does power draw, and therefore the heat-dump as well. For simplicity we'll assume a fixed 14W heat dump for now.
The intersections all are:
Final CPU temperature is ambient (22C) + system load (114W) * radiator C/W + CPU Load (100W) * block C/W
The final CPU temperatures work out to be:
So there we have it. The differences between varying tubing sizes.
Okay, the more astute of you will point out that the block C/W is really the case-to-block C/W, and that the actual CPU-die-to-block C/W is a lot higher. Even if we triple block the C/W (which would be an absolute upper limit based upon older research), we get:
I'll leave it to everyone's own personal value based judgement to determine the relative importance of the differences seen....
It's certainly not the 5C figure that people bandy about. I never expected that it ever would be myself. In my own testing with arbitrarily choking the flow-rate in a test-system, I've always been amazed at the low flow resilience of many setups. Below 2LPM is where things start getting pear shaped quickly for most systems. My recommendation is that even if you're a low-flow fanatic, always ensure that your flow-rates are above 2LPM at the very least, and preferably above 3LPM if at all possible. Still, even when given 1/4" tubing installed with quick-fits and a decent pump like a DDC2, we can see that flow-rates in excess of 4LPM aren't a problem.
The more restrictive the setup, the more that the setup benefits from a more powerful pump to keep flow-rates up. We're still talking about being slightly more powerful, not massively so. Let's run some figures with a DDC1. It's weaker than the DDC2, so I predict that it'll fall behind the DDC2 a bit for the more restrictive tubing sizes, but close the gap as the tubing opens up. Let's see how it goes eh?
Well, here's the graph of the curves against an unmodified DDC1, which is the other pump I suggested would closely match the simulator's pump prediction. A fair deal weaker pump than the DDC2. Pressure head is in the ballpark of the D5. I don't have the PQ graph for the DDC1 with a modified top, so I'll run with the stock DDC PQ graph. It'll be interesting.
Pump heat dump is 8.5W (measured by me in the past).
The intersections all are:
Final CPU temperature is ambient (22C) + system load (108.5W) * radiator C/W + CPU Load (100W) * block C/W
...or tripling the block C/W
As you can see, the results are very close to the DDC2. With a modified top, I reckon that the DDC1 would be about equal to the DDC2.
The Laing D5 has about the same pressure as the DDC1, but dumps a fair amount more heat into the loop since the D5 is a more highly flowing pump, but that high flowing nature is wasted with a moderately restrictive setup with a Apogee GTX, and so it'll just dump more heat. Without calculating, a top-of-my-head guess is that you'd see results similar to the DDC1, but add on about +0.25C across the board due to the extra pump heat.
Summary
Way back in the day, when many w/c setups were 3/8", and only some were 1/2", we had the super-hot AMD T'bird CPU's, and poorly designed open-flow waterblocks with little internal furniture that demanded that as much flow be rammed through them as possible to perform. Further, most pumps that were available were like the Eheim 1250. High-flow, low-pressure pumps that dumped a fair amount of heat, and radiators taken from cars that also demanded flow rates in excess of 10lpm to get past their performance knee.
i.e. 1/2" ID made sense then. The benefit still wasn't huge over 3/8", but it was noticeable. Tests back then showed that the move from 3/8" to 1/2" meant anything from a 0.2-1.0C improvement, depending on various factors. A 1.0C improvement was enough for most people to make the jump, and so 1/2" tubing got its following. I also feel responsible in part for the jump to the 1/2" band-wagon, since I conducted a fair few tests back then to justify it.
Fast-forwards to today, and we have well designed middling restriction blocks which are more flow agnostic. We have well designed radiators that are more flow-agnostic (both in terms of fan power and liquid flow-rate). We have pumps that are near optimal for PC water-cooling that strike a good balance between pressure, peak-flow, noise, and heat. In short, everything has, quite rightfully, been pegged back from old-school high-flow excess, and tempered with a more balanced approach.
The one thing remaining is tubing size. It's also the thing that seems to cause massive grief. Years back when running tests with the Cascade/Storm designs, I realised that flow rates didn't have to be that high. When I started factoring in pump heat coupled with radiator performance, we learned that there is such a thing as "too much pump". There really is a happy middle ground.
I saw that people loved their low-restriction 1/2" tubing, but people also complained about how big it was. I agreed. 3/4" OD tubing is rather large. People didn't want to give up the idea of the benefits of 1/2" ID tubing, so that's when I investigated and came up with the idea for 7/16"ID|5/8"OD tubing. I ran the tests and the maths. No net difference. The amount of people who adopted the smaller tubing showed just how many people were unhappy with huge tubing. People want small tubing, but that don't want to lose the performance benefits of larger tubing.
Came now to today, with me stuck in the house with injuries, and with all the blocks, pumps, and radiators getting pretty darn close to optimal, I thought it time to revisit the issue of tubing sizes in light of modern developments. Maybe I can atone for convincing so many people to go with 1/2" ID all those years ago, who are still using it, and don't realise that they don't still have to.
Also, I'm just sick of small-bore/big-bore bickering. I've always been a "middle-ground is best and cut-the-crap" kind of guy. Been running tests and for some time now I've even considered converting to 8mm ID tubing with quick-fittings because the differences are so small on modern hardware.
I just wanted to share what I've been seeing in private tests, and provide the theory behind it as well. After running the maths I've decided:
3/8" ID | 1/2" OD into 1/2" ID push-fittings is ideal
Caveat: Where very tight radii are needed, can use 5/16" ID tubing instead for those short sections. 5/16"ID|1/2"OD tubing has a 1" bend radius.
It's not small-bore, and it's not big-bore. It's the middle-ground and for the loss of ~0.05C, it's perfectly acceptable. As we add the extra restriction of GPU blocks it becomes even more justifiable.
Yeah, Swiftech have had 3/8" systems for ages now and had stuck by it in the face of a rampant 1/2" market. They were right to do so.
Stew Forster (aka Cathar)
=======================================================
I've been working on a wholistic guide to designing a water-cooling system of late. Using a mix of real-world test data, and calculating pressure drops, I've been able to put together an analysis of the impact of tubing sizes on CPU temperatures.
The radiator and waterblocks are:
Thermochill PA120.2 with 2 x Yate-Loon fans at 12v
Swiftech Apogee GTX
Conroe C2D CPU, overclocked and under load, emitting 100W of heat
2 meters of tubing length
Loop order is pump->radiator->waterblock->pump
Using 1/2" ID tubing and 1/2" OD barbs, I determined the pressure-drop curve for the system. Using Swiftech's published test data for the Apogee GTX, and a flow-performance curve for the PA120.2, we're able to determine the pumping hydraulic power required to push various flow-rates. Using established typical ratios of hydraulic power to actual power draw and heat dump of known real-world pumps, we're able to throw into the mix the amount of pump heat dump required to push any flow rate. We first establish this independently of an actual pump (i.e. determine the theoretical best pump), and then select an actual real-world pump that best suits the theoretical target, and then using the PQ curve of that pump, determine the final flow rate of the system, and hence the correspondent final CPU temperature.
Now in a wholistic model, we're modelling not just the impact of the water-flow rate on the CPU temperature, but the impact of the total heat dump of the cooling system (CPU, pump, radiator fans) has on the room environment, which in turn raises the temperature of the air in the room, and so in turn raises the water temperature because the air-in temperature into the radiator will have warmed up. The effect is very small, but I still model it.
Global temp = 22C
Room C/W = 0.005
Fan Heat Dump = 2.0W
The proposed tubing sizes and fittings we'll be investigating are:
- 6.35 (1/4") ID tubing with quick-fit fittings
- 8mm (5/16") ID tubing over 6mmID|8mmOD barbs
- 8mm (5/16") ID tubing with quick-fit fittings
- 9.6mm (3/8") ID tubing over 7.5mmID|3/8"OD barbs
- 9.6mm (3/8") ID tubing with quick-fit fittings
- 11.1mm (7/16") ID tubing stretched over 10.5mmID|1/2"OD barbs
- 12.7mm (1/2") ID tubing over 10.5mmID|1/2"OD barbs
Quick-fit fittings are those similar to those found on the Swiftech MCW50 (http://www.swiftech.com/products/mcw50.asp)
Running the above range of tubing/fitting sizes through the optimal pump power estimator software I wrote, it predicts that the best pump to use is one that's consuming around 10-13W, with optimal pumping efficiency in the ranges of 3-6LPM. I won't go into the intricacies of the pump power estimator. It's not an exact science, suffice to say that it looks at the wholistic scenario given a waterblock, heatload, room C/W, radiator, system restriction, and so on, and puts out a suggestion for where the optimal range of pumping power lies for that setup. This allows us to then pick a real pump that closely matches the suggested pumping characteristics.
Using the Laing data here: http://www.laing.de/file/66 we see that an unmodified DDC1+ (more commonly referred to in forums as the DDC2) is a very good pump fit for our scenario. Another excellent alternative would be the DDC1 with a modded top.
Okay, so our optimised system consists of:
Laing DDC1+ (unmodified)
Thermochill PA120.2 with 2 x Yate-Loon fans at 12v
Conroe C2D CPU, overclocked and under load, emitting 100W of heat
2 meters of tubing length
For the various tubing/fitting sizes, the PQ curves for a full system for each tubing type looks like this:
I overlaid the curves onto the PQ graph for the Laing DDC1+
The flow performance curves for the radiator and waterblock are illustrated on the following graphs:
...and...
The total CPU heat load is 100W. The total system heat load is 114W . We assume a fixed 14W heat dump from pump which was derived from other testing. This does in fact vary a little as we can see by the Laing graph. As flow rates decrease, so does power draw, and therefore the heat-dump as well. For simplicity we'll assume a fixed 14W heat dump for now.
The intersections all are:
- 6.35mm quick fit = 4.45LPM flow, 0.0795 block c/w, 0.0374 rad c/w
- 8mm barbed = 4.75LPM, 0.0783 block c/w, 0.0373 rad c/w
- 8mm quick fit = 5.6LPM, 0.0770 block c/w, 0.0369 rad c/w
- 9.6mm barbed = 5.7LPM, 0.0768 block c/w, 0.0369 rad c/w
- 9.6mm quick fit = 6.2LPM, 0.0762 block c/w, 0.0367 rad c/w
- 11.1mm barbed = 6.3LPM, 0.0761 block c/w, 0.0367 rad c/w
- 12.7mm barbed = 6.35LPM, 0.0760 block c/w, 0.0366 rad c/w
Final CPU temperature is ambient (22C) + system load (114W) * radiator C/W + CPU Load (100W) * block C/W
The final CPU temperatures work out to be:
- 6.35mm quick fit = 34.21C
- 8mm barbed = 34.08C
- 8mm quick fit = 33.91C
- 9.6mm barbed = 33.89C
- 9.6mm quick fit = 33.80C
- 11.1mm barbed = 33.79C
- 12.7mm barbed = 33.77C
So there we have it. The differences between varying tubing sizes.
Okay, the more astute of you will point out that the block C/W is really the case-to-block C/W, and that the actual CPU-die-to-block C/W is a lot higher. Even if we triple block the C/W (which would be an absolute upper limit based upon older research), we get:
- 6.35mm quick fit = 50.11C
- 8mm barbed = 49.74C
- 8mm quick fit = 49.31
- 9.6mm barbed = 49.25C
- 9.6mm quick fit = 49.04C
- 11.1mm barbed = 49.01C
- 12.7mm barbed = 49.00C
I'll leave it to everyone's own personal value based judgement to determine the relative importance of the differences seen....
It's certainly not the 5C figure that people bandy about. I never expected that it ever would be myself. In my own testing with arbitrarily choking the flow-rate in a test-system, I've always been amazed at the low flow resilience of many setups. Below 2LPM is where things start getting pear shaped quickly for most systems. My recommendation is that even if you're a low-flow fanatic, always ensure that your flow-rates are above 2LPM at the very least, and preferably above 3LPM if at all possible. Still, even when given 1/4" tubing installed with quick-fits and a decent pump like a DDC2, we can see that flow-rates in excess of 4LPM aren't a problem.
name='MetalZone' said:
The more restrictive the setup, the more that the setup benefits from a more powerful pump to keep flow-rates up. We're still talking about being slightly more powerful, not massively so. Let's run some figures with a DDC1. It's weaker than the DDC2, so I predict that it'll fall behind the DDC2 a bit for the more restrictive tubing sizes, but close the gap as the tubing opens up. Let's see how it goes eh?
Well, here's the graph of the curves against an unmodified DDC1, which is the other pump I suggested would closely match the simulator's pump prediction. A fair deal weaker pump than the DDC2. Pressure head is in the ballpark of the D5. I don't have the PQ graph for the DDC1 with a modified top, so I'll run with the stock DDC PQ graph. It'll be interesting.
Pump heat dump is 8.5W (measured by me in the past).
The intersections all are:
- 6.35mm quick fit = 3.9LPM flow, 0.0812 block c/w, 0.0378 rad c/w
- 8mm barbed = 4.2LPM, 0.0805 block c/w, 0.0376 rad c/w
- 8mm quick fit = 4.95LPM, 0.0782 block c/w, 0.0372 rad c/w
- 9.6mm barbed = 5.0LPM, 0.0781 block c/w, 0.0372 rad c/w
- 9.6mm quick fit = 5.4LPM, 0.0774 block c/w, 0.0370 rad c/w
- 11.1mm barbed = 5.55LPM, 0.0771 block c/w, 0.0369 rad c/w
- 12.7mm barbed = 5.6LPM, 0.0770 block c/w, 0.0369 rad c/w
Final CPU temperature is ambient (22C) + system load (108.5W) * radiator C/W + CPU Load (100W) * block C/W
- 6.35mm quick fit = 34.22C
- 8mm barbed = 34.13C
- 8mm quick fit = 33.86C
- 9.6mm barbed = 33.85C
- 9.6mm quick fit = 33.75C
- 11.1mm barbed = 33.71C
- 12.7mm barbed = 33.70C
...or tripling the block C/W
- 6.35mm quick fit = 50.46C
- 8mm barbed = 50.23C
- 8mm quick fit = 49.50C
- 9.6mm barbed = 49.47C
- 9.6mm quick fit = 49.23C
- 11.1mm barbed = 49.13C
- 12.7mm barbed = 49.10C
As you can see, the results are very close to the DDC2. With a modified top, I reckon that the DDC1 would be about equal to the DDC2.
The Laing D5 has about the same pressure as the DDC1, but dumps a fair amount more heat into the loop since the D5 is a more highly flowing pump, but that high flowing nature is wasted with a moderately restrictive setup with a Apogee GTX, and so it'll just dump more heat. Without calculating, a top-of-my-head guess is that you'd see results similar to the DDC1, but add on about +0.25C across the board due to the extra pump heat.
Summary
Way back in the day, when many w/c setups were 3/8", and only some were 1/2", we had the super-hot AMD T'bird CPU's, and poorly designed open-flow waterblocks with little internal furniture that demanded that as much flow be rammed through them as possible to perform. Further, most pumps that were available were like the Eheim 1250. High-flow, low-pressure pumps that dumped a fair amount of heat, and radiators taken from cars that also demanded flow rates in excess of 10lpm to get past their performance knee.
i.e. 1/2" ID made sense then. The benefit still wasn't huge over 3/8", but it was noticeable. Tests back then showed that the move from 3/8" to 1/2" meant anything from a 0.2-1.0C improvement, depending on various factors. A 1.0C improvement was enough for most people to make the jump, and so 1/2" tubing got its following. I also feel responsible in part for the jump to the 1/2" band-wagon, since I conducted a fair few tests back then to justify it.
Fast-forwards to today, and we have well designed middling restriction blocks which are more flow agnostic. We have well designed radiators that are more flow-agnostic (both in terms of fan power and liquid flow-rate). We have pumps that are near optimal for PC water-cooling that strike a good balance between pressure, peak-flow, noise, and heat. In short, everything has, quite rightfully, been pegged back from old-school high-flow excess, and tempered with a more balanced approach.
The one thing remaining is tubing size. It's also the thing that seems to cause massive grief. Years back when running tests with the Cascade/Storm designs, I realised that flow rates didn't have to be that high. When I started factoring in pump heat coupled with radiator performance, we learned that there is such a thing as "too much pump". There really is a happy middle ground.
I saw that people loved their low-restriction 1/2" tubing, but people also complained about how big it was. I agreed. 3/4" OD tubing is rather large. People didn't want to give up the idea of the benefits of 1/2" ID tubing, so that's when I investigated and came up with the idea for 7/16"ID|5/8"OD tubing. I ran the tests and the maths. No net difference. The amount of people who adopted the smaller tubing showed just how many people were unhappy with huge tubing. People want small tubing, but that don't want to lose the performance benefits of larger tubing.
Came now to today, with me stuck in the house with injuries, and with all the blocks, pumps, and radiators getting pretty darn close to optimal, I thought it time to revisit the issue of tubing sizes in light of modern developments. Maybe I can atone for convincing so many people to go with 1/2" ID all those years ago, who are still using it, and don't realise that they don't still have to.
Also, I'm just sick of small-bore/big-bore bickering. I've always been a "middle-ground is best and cut-the-crap" kind of guy. Been running tests and for some time now I've even considered converting to 8mm ID tubing with quick-fittings because the differences are so small on modern hardware.
I just wanted to share what I've been seeing in private tests, and provide the theory behind it as well. After running the maths I've decided:
3/8" ID | 1/2" OD into 1/2" ID push-fittings is ideal
Caveat: Where very tight radii are needed, can use 5/16" ID tubing instead for those short sections. 5/16"ID|1/2"OD tubing has a 1" bend radius.
It's not small-bore, and it's not big-bore. It's the middle-ground and for the loss of ~0.05C, it's perfectly acceptable. As we add the extra restriction of GPU blocks it becomes even more justifiable.
Yeah, Swiftech have had 3/8" systems for ages now and had stuck by it in the face of a rampant 1/2" market. They were right to do so.
Stew Forster (aka Cathar)
