Thoughts on water pressure & flow rate...

[bigben2k]

Originally posted by Althornin
why in hell would you do this?
Blocks in parallel need MORE flow. (flow is split)
pumps in series provide more head, not more flow.

You can look at it in more than one way

Blocks in parallel *allow* more flow

Pumps in series allow more pressure and, as a result will give you more flow.

But you still have to throttle the blocks so that most of the flow goes through the CPU block.

[Althornin]

Originally posted by bigben2k
You can look at it in more than one way

Blocks in parallel *allow* more flow

Pumps in series allow more pressure and, as a result will give you more flow.

But you still have to throttle the blocks so that most of the flow goes through the CPU block.

this is true.
i just wasnt imagining blocks so restrictive that this would actually be a benificial scenario.

One other thing:
Blocks in Parallel do *allow* more flow - but thats TOTAL flow...so flow per block is not ness. higher.

[sevisehda]

Keep in mind that its not a "rule" only a possibility. A set of unrestrictive blocks would probobly fair well in a series system that wasn't getting close to the max head. However a look at the most modern blocks show a tendency to go toward a high flow rate at the cooling point. This means narrowing the path to increase flow however this also increases resistance.

Its important to either A) do the math on the best setup for your system or B) experiment in your sink/tub to figure what method will work best for you.

My method of testing head resistance is imperfect but its costs nothing and is fast. I hook up my pump(inline or submerged doesn't matter) outside. I make marks on the wall every cm. I connect about 10 feet of hose. Then I raise the hose until the water stalls. I mark this point as Max. Head. Then cut the hose at about a foot and connect that to my test piece and the other 9ft to the outlet. Then I raise it to max head. Take the difference and Bam.

I know this is imperfect because since the flow decreases so does the resistance so then flow increases(makes sense if you think about it). So my number is a little low for each block. I guess I could meause the height at which the pump puts out a gallon per minut(60gallons per hour) which would be closer to my normal flow rate, and hence give me a more accurate number but this would also take alot more time and I'm just to eager to build my sytem and not to test it for hours.

[Since87]

Trying to come up with a general rule of thumb for multiple blocks seems fairly pointless to me. It depends on the blocks and the pump.

Saying that blocks in parallel is always better seems particularly dumb.

Here's a graphs showing some pressure drop vs flowrate curves.

The 'Sim' curves, are graphs of equations that approximate the PQ curves of Iwaki MD20-R and MD20-RZ pumps.

The other four curves show hypothetical cooling loops consisting of a 2-342 heatercore, (single pass, low restriction) 6 feet of 1/2" ID tubing (resistance of the tubing is based on one continous straight piece) and one of the following:

2 White Waters in series
2 White Waters in parallel
2 MCW-5000's in series
2 MCW-5000's in parallel

No attempt is made to account for the added flow resistance of 'tees' or 'wyes' required for a parallel setup.



Two White Waters in parallel have about the same curve as two MCW-5000's in series, so the two curves nearly overlap.

For the Sim20-R, per block flowrate is:
WWS 7
WWP 6.15
MCWS 12.3
MCWP 8.75

For the Sim20-RZ, per block flowrate is:

WWS 8
WWP 5.4
MCWS 10.8
MCWP 6

In all of these cases, series blocks always yields better flowrates through each block. In the high pressure pump case, (similar to cheap pumps in series?) the flowrate advantage of putting the blocks in series is even greater.

Keep in mind that these numbers don't include the flowrate hit for 'wyes' in the parallel cases. Variations in flow resistance in the tubing is not accounted for either.

Looking at the C/W vs flowrate curves for the blocks, it appears that the gain in flowrate would frequently offset the higher water temperature seen by the second block in a series setup. The first block in the series combination would always gain performance from the higher flowrate of course.

References:
Bill Adams' White Water test data.
Bill Adams' MCW-5000 test data.

Edit: This is incorrect. See below.

[Althornin]

The above data matches my thoughts on the matter - which is why i thought that your rule was bass-akwards.
I still do.
I think the "rule" is the exact opposite of what you said, bb2k, and the exception is what you have stated.
However, i guess you need to do some maths and plot some curves to find out whats best for your system.
But i bet you were thinking a WW would have been restrictive enough..but it looks like its not.

[Gooserider]

Seems to make the case stronger for the series blocks, but it probably still makes sense to do testing as well to get the outputs for the setup one is using. This would seem to me like it would be especially applicable in a case like mine where I'm making my own blocks and won't have any reliable reference data to look at.

I have another question I'm wanting to ask which is somewhat off topic, so I'm starting a new thread here:
http://forums.procooling.com/vbb/sho...&threadid=7079
At least part of it is somewhat related, in that I was wondering if anyone had data about how long it would take the CPU's to overheat if a pump failed so there was no longer water circulating in a system (No pelts or extreme cooling, just normal WC to ambient setup)

Assuming I had a flow detector that would detect the failure and send a signal to the system, would there be time for a graceful shutdown (ie 'shutdown -h now') or would I be safer to have the sensor trigger a relay that killed the power and slammed the system off (and worry about any resulting data problems later...)

I know that there are many variables, but lets assume a medium to bad scenario - Athlon, stock to moderate overclock (80-100 watts?) small to medium size copper WB, some airflow, but just what you might get from 1 80mm and the PSU, not enough to significantly cool things down. The shutdown must be fast enough to prevent damage to any hardware so that you could just replace the pump and power things back up.

[Gooserider]

Another quick question; I've seen comments to the effect that a 'rotor type' flowmeter is "highly restrictive", but no data as to 'how bad' it really is.

Can anyone post or point me at a source for data as to just how much restriction they really offer?

My understanding is that those units are the least expensive way to get data on flow in a format that can be handled by a digi-doc or mobo fan sensor.

Are there other alternatives that are comparable in cost and less restrictive?

I want to have some way of monitoring flow status in my system, at the bare MINIMUM I want 'flow / no flow' detection, ideally I would like some idea of how much flow is happening at a given momemt. (reference my prior post on disaster prevention)

Thanks,

Gooserider

[sevisehda]

Unless your over curious don't bother. Keep in mind that if the rad should fail the water will slowly increase in temp. There are plenty of hardpoint to add a thermal probe. If I were to put a probe anywhere it would be on the top of the CPU cooler(only possible on an all copper block, plexi is to insulative). This spot should be the same temp as the coolant inside the cpu block. If you have a fan failure the temps will rise slowly then you could shutoff your comp. Or if the pump fails the water inside the block will rise somewhat quickly and the probe would also detect this and shutdown your comp.

[Gooserider]

sevisehda: Unless your over curious don't bother. Keep in mind that if the rad should fail the water will slowly increase in temp. There are plenty of hardpoint to add a thermal probe. If I were to put a probe anywhere it would be on the top of the CPU cooler

This is an interesting approach, I had thought of doing temperature based alarming, but thought flow based would be better (plus it gives me an excuse to get a flowmeter ) My reasoning was that I wanted as much of an early failure warning as possible, so that I would have time to do a graceful shutdown as opposed to having to slam the power.

You seem to at least imply that there would be a slow enough rise to allow for a graceful shutdown regardless of failure mode. Assuming the pump does a total crapout, do you know if there are any kind of numbers as to how long from failure to melt down?

As a second thought - In a dual CPU setup, would it be necessary to put failure detection on BOTH CPU's? Or would doing one be enough on the theory that the temperature is going to go up at about the same rate on both?

Gooserider

[bigben2k]

Calculating the pressure drop of two CPU blocks in parallel seems rather pointless to me.

The actual application would be composed of a CPU block, and a GPU and/or NB block, both of which should be far less restrictive, which dictates the use of a valve. I'll admit however, that the GPU and NB should be in series.

As I said, this also requires taking a look at the pump, because the "rule of thumb" isn't always right. Would like to see the same graphs with an Eheim 1250, which is more typical, and in line with the kinds of pumps that most water coolers use.

[Skulemate]

Originally posted by bigben2k
... Would like to see the same graphs with an Eheim 1250, which is more typical, and in line with the kinds of pumps that most water coolers use.

If you look at the curves for a second, it looks like you can substitute pretty much any centrifugal pump curve for the Iwakis... you're going to have different flow results, but the conclusions should be the same. I'd guess that the Eheim results are similar in character to the Iwaki 20R results... i.e. a less pronounced advantage to having the blocks in series, but an advantage none the less.

[sevisehda]

Some people have modded there pumps to have a small res right at the intake. The theory is centrifugal pumps need a large source to pump most effiecently. However since the pump output would equal input in a loop does this make sense? Does attaching a res directly to the pumps intake really increase flow or is it just a space saver?

[Since87]

[Edit]
The graph in this post is incorrect. See below.
[/Edit]

Originally posted by bigben2k
Calculating the pressure drop of two CPU blocks in parallel seems rather pointless to me.

I don't know. I've seen the subject come up several times from people with dually boards.

Originally posted by bigben2k
The actual application would be composed of a CPU block, and a GPU and/or NB block, both of which should be far less restrictive, which dictates the use of a valve. I'll admit however, that the GPU and NB should be in series.

I'd guess that a GPU block in series with a NB block, may well be more restrictive than a MCW5000. What's your basis for saying they, "should be far less restrictive"?

Originally posted by bigben2k
Would like to see the same graphs with an Eheim 1250, which is more typical, and in line with the kinds of pumps that most water coolers use.

[Gooserider]

bigben2k: Calculating the pressure drop of two CPU blocks in parallel seems rather pointless to me.

Only if you don't HAVE two CPU blocks! The system I'm working on will have a Tyan 2468UGN (Thunder K7) mobo. This is a dual Athlon MP based board, so I will have two CPU's to deal with...

The actual application would be composed of a CPU block, and a GPU and/or NB block,

Sorry BB2k, you need to go back up and re-read my original posts again. Perhaps I wasn't clear enough, though others seem to have gotten it.

The ACTUAL application I was asking about will consist of TWO CPU blocks, and several smaller blocks (exact number unknown as yet) for hard drives, possibly NB, probably not GPU (I'm not into fancy video, so won't have a GPU that needs it).

I was asking about putting the CPU blocks on one or two loops, with the small blocks on an additional loop. I only had one loop in mind for the small blocks, but if that doesn't work well, I might split them up a bit (probably 3-4 small blocks per small block loop)

both of which should be far less restrictive, which dictates the use of a valve. I'll admit however, that the GPU and NB should be in series.

What makes you think the smaller blocks would be less restrictive? I am assuming, and basing my design setup on the idea that they would be far MORE restrictive!

Here's why:

• My CPU blocks will use 1/2" plumbing. My small blocks will use 1/4" or 3/8" plumbing.
• The loop(s) for the CPU blocks will be as short as I can easily manage. The loop(s) for the small blocks will be far longer.
• The CPU blocks may end up in series or parallel, but they will be the only items in their loop. The small blocks will probably all end up in one or two loops depending on how many of them there are. (If I split them into smaller loops, there will still be 2-3 blocks / loop.)
• The CPU blocks I'm planning to make with passage cross sections (1/2") at least as large as the plumbing for low restriction. The small blocks will likely be made with 1/4" copper tubing, and lots of bends.

I can't see ANYTHING that would make my small block loop less restrictive than the CPU blocks!

Gooserider

[bigben2k]

Since you'll be making your own NB and GPU block, the actual flow resistance isn't known, but in what's commonly available, it isn't hard to see that even a DD Z-chip block would be less restrictive than a lot of waterblocks. If you design your NB and GPU blocks specifically to be restrictive, then that'll change everything.

I don't see 2 * Eheim 1250 in series, on that last graph, but I can see that Since87 did account for a certain loss, in the "serial" application, which is correct.

Otherwise, I have to agree: in a dual setup, putting the CPU blocks in series appears to be best.

You could run some flow/pressure tests on those blocks you're making, and recalculate what would perform best.

[Since87]

Originally posted by bigben2k
I don't see 2 * Eheim 1250 in series, on that last graph, but I can see that Since87 did account for a certain loss, in the "serial" application, which is correct.

WTF? Did you expect to see 2 1250's in series on that graph for some reason?

I have no idea what, certain loss, in the "serial" application you think I accounted for. The cooling loop curves are the same I graphed earlier, and are based on the same 'idealized' setup.

[bigben2k]

I suppose that two pumps aren't relevant at this point... I must be loosing track of this thread! The first graph you posted shows Sim20R and Sim20RZ, I thought they were about the same pump, for some reason. I understood that putting pumps in series does not result in a full doubling of the pressure: am I off my rocker? Nah, just OT, sorry.

From both graphs you've posted, I'm inclined to believe that blocks in series work best!:shrug:

[sevisehda]

Failure recovery.
If your flow slows to lets say half more than likely your temps would rise X amount and level off at some point. If your pump were to fail then the time would be dependent on the thermal mass of the WB and the water inside it. So a small cooler would die faster a large one would give you more time. Without doing any math I'd guess you'd have about 10-20 seconds. I read a article about a guy who forgot to turn on his pump(same as a failure basically) the water boiled and the steam blew out the block and the rest is obvious.

Parallel vs Series
I'd go with series 90% of the time but if your nearing your pumps max head then going parallel will get you more flow through each block.

[jaydee]

Originally posted by sevisehda


Parallel vs Series
I'd go with series 90% of the time but if your nearing your pumps max head then going parallel will get you more flow through each block.

Couldn't you just make a bypass valve around the rad to keep flow going. Kinda what aspirit did with his rack mount deal. Kill two birds with one stone. More flow rate through the blocks without giving up serial routing. Wonder if the loss of cooling would defeat the purpose. Of course the pump may not be working as hard either and add less heat to the water......

Bah! Probably a higly ignorant post....

[Gooserider]

bigben2k: Since you'll be making your own NB and GPU block, the actual flow resistance isn't known, but in what's commonly available, it isn't hard to see that even a DD Z-chip block would be less restrictive than a lot of waterblocks. If you design your NB and GPU blocks specifically to be restrictive, then that'll change everything.

Well, I'm designing my CPU blocks to be non-restrictive actually. While I'm not specifically trying to make the NB and hard drive blocks restrictive, I don't see how they couldn't be to a fairly large degree - I'm going to be making them with 1/4" ID tube, (CPU's get 1/2") with fairly long passages that will have as many bends as I can figure out how to fit on the drive plate (I'm going for simplicity - bend tubing into a maze, solder the maze onto a 1/8" x hard drive sized plate. No milling, no seams, should be no leaks, efficient enough to cool the drive.) I am guessing each plate will have between 1 and 2 feet of tubing, and there will be at least 3 plates, and possibly an NB block (which would be relatively restrictive internally, but still use 1/4" plumbing)

sevisehda: Failure recovery. If your flow slows to lets say half more than likely your temps would rise X amount and level off at some point. If your pump were to fail then the time would be dependent on the thermal mass of the WB and the water inside it. So a small cooler would die faster a large one would give you more time. Without doing any math I'd guess you'd have about 10-20 seconds.

Thanks for the input on failure recovery, it is somewhat reassuring. Big is relative, but I think I'll be on the heavy side of that set of numbers. I might do a limited simulation test once I get things built to get more definite information.

A minor planning concern I just had - I haven't dealt with one of the modern ATX type power supplies from user space yet. Do you know how it behaves when the AC input line is interrupted and then restored? Obviously it goes off when the power does, but when the power comes back does it turn back on and try to bring the PC back up?

I'm planning on implementing a 'last chance kill' relay that would interrupt power to the PC and pump if it triggered. If the supply stays off, then I only need a momentary relay. IF it trys to come back up, I would need a latching relay that would keep the power disconnected until I reset it.

jaydee116: Couldn't you just make a bypass valve around the rad to keep flow going. Kinda what aspirit did with his rack mount deal. Kill two birds with one stone. More flow rate through the blocks without giving up serial routing. Wonder if the loss of cooling would defeat the purpose.

Depends on what your purpose is If it's to get lots of flow, it would probably work. If it's to cool the system, it seems rather pointless to bypass the cooling loop. I haven't seen Aspirit's setup, but if its a rackmount (presumably w/ multiple processing boards) I'd suspect the function of his bypass valve is to isolate a part so that it can be serviced without having to shut down the entire rack. At least if *I* were doing something like that (and I used to work on high reliability rackmount setups for telcos) it is the kind of thing I'd do.

Gooserider

[Since87]

I'm resurrecting this old thread because I figured out today that the two graphs and accompanying information above is wrong.

My calculations for systems with paralleled blocks were wrong. The following are corrected graphs.





For the Sim20-R, per block flowrate is:

WWS 7.5
WWP 7.8

MCWS 12.3
MCWP 9.6

For the Sim20-RZ, per block flowrate is:

WWS 8.5
WWP 5.8

MCWS 10.8
MCWP 6.2

So, for restrictive blocks combined with a pump with a 'general purpose' PQ curve, per block flowrate may be better with a parallel setup. (The resistance of the rad and tubing have an impact on whether parallel or series is best.) With a pump designed for 'high' pressure, series is still best though.

Of course, all this assumes I've got my maths right this time.

[Les]

Oh dear.
My old graphs do not agrree with either versions.
http://forum.oc-forums.com/vb/showth...hreadid=183841



Will check*

* Edit:Will checklater.

[Cathar]

Well Les, I can say from practical experience that an MD-30RZ (50Hz) model does indeed push about 12LPM through a single WW, and just over 7LPM with an Eheim 1250, and over 5.5LPM with an Eheim 1048. Will lose a little bit with a radiator attached, but the PD of a radiator is fairly low in comparison so long as the fittings are largish.

[Since87]

Originally posted by Les
Oh dear.
My old graphs do not agrree with either versions.

LOL, had me worried there for a moment.

My graphs have a radiator and tubing figured in as well. I believe that is the difference. My graphs would be consistant with yours if those terms were removed.

[Les]

Originally posted by Since87
LOL, had me worried there for a moment.

My graphs have a radiator and tubing figured in as well. I believe that is the difference. My graphs would be consistant with yours if those terms were removed.

Also had me worried.
Like yourself I do not like posting misinformation or wrong calculations.
However all looks sweet.