Thoughts on water pressure & flow rate...

[MMZ_TimeLord]

I think I'll stir this up a bit with this question...

If one pump and one loop (basically) in your systems works okay... what if you put TWO loops and join them at a reservior with two different pumps one for the radiator loop and one for the cooling loop (CPU block, GPU block, HD block, etc.)?

Would a differential in flow rates of the two loops to compensate for the different surface areas in each set of thermal transfer devices increase performance?

[TallTxnMo]

Originally posted by murray13
Aren't manifolds bad for pressure drop? (in this situation as described)

Since every abrupt change in diameter causes pressure drop and a manifold has multiple changes in diameter, where would one expect to benefit from using a manifold over using carefully selected components and just running them in series?

I know there are way too many variables to give a difinitive answer but some thoughts on the subject would be nice. Thanks. And hey it's still 'on topic'. [/b]

I'm no engineer, but manifolds wouldn't cause a loss of pressure. In a true closed loop system, pressure would be the same in the entire system, pressure isn't bound by size. A manifold would decrease flow rate. Smaller tube, faster flow rate, bigger tube, slower flow rate. Manifolds can be benificial if used correctly.

[Since87]

Originally posted by TallTxnMo
In a true closed loop system, pressure would be the same in the entire system...

Not true.

[bigben2k]

Originally posted by Since87
Not true.

...and to complete the answer...

The pressure is actually different at every point in the system, and ranges from a low, which may be slightly below atmospheric, to a high, as the pump provides.

*Flow* however, is the same everywhere, except where it is split.

A manifold is indeed *bad*, but only because it adds a little bit of flow resistance. To imagine it, picture a 12" (yes, 1 foot) pipe, with water flowing through it, then imagine 1'000 (1 thousand) infinitely small pipes, that run the exact same flow: which do you think will resist flow the most?

(now it's not really fair for me to put it that way, because I'm not saying anything about having the same cross section either way, but ya'll get it, right?)

Now consider Cathar's latest design, with 50+ mini tubes. The tubes are short enough so that the pressure drop is minimal, and that's the key. In fact, "Cascade" has a lower pressure drop that "White Water"...

[TallTxnMo]

Am I misunderstanding the term "manifold"? Isn't it just a larger container to which you distribute from? It was my understanding that pressure was constant on all sides in a "container" but velocity or flow changed with volume of the container. Look at the attached drawing. Am I wrong? If so, please explain further.

[sevisehda]

Longwinded ideal explanation of pressure inside a system:

Water will exit the pressure at a given pressure say 100rpu(random pressure units). Then it runs through 10 inches of tubing each inch it drops about 0.5rpu so by the time it gets to the rad its at 95rpu. The radiator is a compilation of a very long pipe with plenty of 180 degree bends(horible for flow). So be the time the water exits it at 80rpu. Then it goes through 12 inches of tubing on its way to the cpu. Down to 74. Then it hits a WW which has a very restrictive flow and turbulent area. The drop inside the cpu is 35rpu. So the sytem is now at 39rpu. The WW splits the flow into 2 seperate channles. From now on each branch will receive half the water but the pressure will be 39 at the begining of each loop. One side runs 16 inches to the gpu so its down to 31rpu before the block and 14 after. The other brack runs 8 inches to the NB so its down to 35. After the NB WB the pressure it 16 rpu. Both run back into a resevoir and exit with 10rpu to spare.

That is of course the IDEAL situation. The flow through each branch is related to the resistance in that branch and it would take some effort to eqaulize. Also any bends in the system will resist flow. The hose barbs commonly used also do a fair amount of resisting themselves. There are plenty of small things that complicate the flow inside a system.

I'll admit my model has 1 mistake. The water exits with exesse pressure and I don't think this will happen. I think the pump will compensate for not haveing to push as hard and will push more water.

[TallTxnMo]

Ok, think I understand now. Guess need to put in electrical terms.
Voltage(pressure)=Current(flow) X Resistance(flow restrictions). That makes sense. Guess I was taking the whole system in account. Thanks for the explaination.

[BO(V)BZ]

Redleader: You are off in your calculations. You calculated based on a 1/2 radius tube, not half inch diameter. Assuming everything else is the same, you'd have the second processor being .62*C hotter.

BO(V)BZ

[redleader]

Originally posted by BO(V)BZ
Redleader: You are off in your calculations. You calculated based on a 1/2 radius tube, not half inch diameter. Assuming everything else is the same, you'd have the second processor being .62*C hotter.

BO(V)BZ

Damn. Thanks for the fix

[Gooserider]

quote: Originally posted by BO(V)BZ Redleader: You are off in your calculations. You calculated based on a 1/2 radius tube, not half inch diameter. Assuming everything else is the same, you'd have the second processor being .62*C hotter. BO(V)BZ

Well, that does make the series plumbing for the CPU's a bit less attractive, but I'm still not that worried about it, as it seems to me that other issues might still give bigger differences.

Either way, for reasons I mentioned earlier, I will still be splitting the output of my pump into multiple circuits, and perhaps the question should be rephrased....

Given that ANY kind of plumbing fixture will have a negative impact on flow rate, which of the following is WORSE?

The Manifold (note output number and placement is only a guess for illustration purpose only, I might put in several outlets)
............_______________________________
...........|...............................|
...........|........Manifold chamber.......|
-----------|....(approx 1.5" d X 3" L......|
IN (1/2"d or larger).......................|
____________...............................|
...........|...............................|
...........|...............................|
...........------|......|-------|...|------|
.................|..out.|.......|out|
.................|.1/2".|.......|1/4"|

Or the T fitting:

--------------------------------------------
IN (1/2"d)..........................OUT (1/2"d)

------------------|....|----------------------
..................|out.|
..................|1/4"|

Bonus question: What if there are several T fittings in a row?

Now I will be the first to admit my understanding of flow dynamics is not great. However my take on it is that the manifold is better, especially if there are multiple outlets.

To (mis)use the electrical analogy here, I see the manifold chamber acting in some ways like a battery or capacitor, it takes the flow from the pump and 'charges' to the pump pressure, then acts in it's own right as the pressure source that supplies the different outlets, where as the "T" fitting is like a spliced junction in an electrical wire that just pulls power off the main line, and adds some impedance losses.

Does what I say make any sense, or is my understanding full of bovine byproduct???

Gooserider

[sevisehda]

'T' fittings suck because the flow has to make a 90 degree bend. This isn't natural for water to do and causes a great deal of turbulence, loss of energy. The waters momentum wants to maintain is forward velocity. I've actually seen water flow through an open T in 2.5in PVC and not spray out because the flow rate was so great. Keep in mind how water will flow through the pipes of your system. A large manifold will slow the rate down so its *probobly* the best solution. A series of 'T's will kill your flow rate and the flow will be different in each branch.

My solution was to build a CPU block with 1/2 intake an 4 x 3/8 exausts. This way the block itself is a manifold. If you are cooling a dual system them Y the intakes.

[MMZ_TimeLord]

Y blocks are almost always better because you are keeping the water as close to a straight line path as possible.

Manifolds, unless they actually have an open area like a hollow waterblock are just as bad as multiple T fittings, because most times manifolds are one large bore with smaller splits at 90°, like so...

______________
              |
_____   ____  |      <-- Basic Hydraulic Manifold 
     | |    | |         (only concern is transferring pressure)

What we want for smooth water flow is a Y splitter, like so...

[redleader]

Well, that does make the series plumbing for the CPU's a bit less attractive, but I'm still not that worried about it, as it seems to me that other issues might still give bigger differences.

Not really. Performance drops off exponetially at lower flowrates while the heat from a second CPU is linear. Take a look at BillA's data. Unless you have amazing flow, splitting is going to take a lot more then .6C off.

And if you had such flow, then you'd have such a high coolant velocity that the .6C figure would be much less anyway. theres really no reason to ever split CPU flow.

[Gooserider]

Well, I guess that did stir things up a bit, kicked over onto another page and everything

Lets see...

MMZ_TimeLord: Y blocks are almost always better because you are keeping the water as close to a straight line path as possible.

True, but the local hardware store has PVC galore, I haven't seen any "Y" fittings. I find I like to have my hands on the hardware when I'm buying things.

Manifolds, unless they actually have an open area like a hollow waterblock are just as bad as multiple T fittings, because most times manifolds are one large bore with smaller splits at 90°, like so...

The manifolds I'm planning will have a LARGE open space. What I'm planning is a piece of 1.5" PVC pipe, 3-4 inches long, capped on one end and plugged on the other (in case I need to clean it out). The inlet will be whatever size comes off the Rad (probably 3/4") and probably come in via the cap end. The outlets will be around the sides, located to make the best shots at the target devices. The exact configuration will have to wait until I have the hardware in hand. However it sounds like I'm meeting your description of a 'good' manifold.

I am planning to do a high flow rate system, I am thinking in terms of an Eheim 1250 pump or equivalent. (I'm looking at a Danner Pondmaster "Pond-Mag 5" which claims higher flow, better head, slightly smaller size and similiar wattage. Anyone have any experience with these?)

sevisehda: A large manifold will slow the rate down so its *probobly* the best solution. A series of 'T's will kill your flow rate and the flow will be different in each branch. My solution was to build a CPU block with 1/2 intake an 4 x 3/8 exausts.

I don't see using the block as a manifold as being a good solution in my case - I want the blocks to be as identical as I can make them, and it would be a challenge to balance the flows so as to make them all even at best. I'd probably have to many branches as well. Also I plan on making the 'drive loop' from much smaller ID tubing than the CPU loop, so putting that in series with the CPU would impose serious restrictions.
Lastly, the mobo I'll be using doesn't have the holes to do a 4 bolt mount, so I have to do a clip-on. This cuts into the amount of real estate I have to put barbs into, so I don't think it's on.

FWIW dept, I am planning to make a high flow block with I/O at opposite corners, doing a serpentine maze with a wider center section containing lots of turbulence pins. Sort of a cross between a Swiftech and a DD Maze 3. I know this looses the benefit of direct jet impingement, but I think it will work OK anyways.

This way the block itself is a manifold. If you are cooling a dual system them Y the intakes.

This sounds like you are suggesting I SHOULD plumb the CPU's in parallel, which appears to be the opposite of what redleader is saying - I feel confused

theres really no reason to ever split CPU flow.

FWIW again, 3rotor on his website seems to be running his dual rig in parallel though it is hard to be certain from the pictures.

Gooserider

[sevisehda]

Every system is different so to say you should do something 1 way all the time is not productive. Try mocking your system up in a sink with the blocks in parallel then in series. Measure the flow you get each way. The best way to optimize any system is to experiment with it then fix the problems.

If your pump can generate enough pressure by all means run them in series to get the max flow through each block. But chances are that 2 blocks are too much resistance for most pumps and will cut the flow too much. At first it may seem running in parallel may cut the flow in half. But since the systems resistance will be lower the pump will push more water increasing flow. So in actuality you may see some drop in flow for each branch but the overall system will have more flow. What works for you though will be whatever your experimentation leads you too.

[Skulemate]

Originally posted by sevisehda
... So in actuality you may see some drop in flow for each branch but the overall system will have more flow. ...

The problem with this is that you do not have the highest flow rate where it counts... namely through the waterblock.

[Gooserider]

sevisehda: Every system is different so to say you should do something 1 way all the time is not productive. Try mocking your system up in a sink with the blocks in parallel then in series.

Makes sense, though I'll probably use the tub since it has better capacity for flood control

The big question as I see it is that the simulation would lack the thermal input from the processors, so it might be a challenge to figure out how much of an increased total flow volume from running parallel it would take to compensate for the decreased volume going through each individual block.

To save typing;
Op = total output of parallel hookup/time;
Os = Total output of series/time;
Bp = volume through ONE block in parrallel/time;
Bs = volume through either block in series/time;

Now correct me if I'm wrong, but Bs = Os in a single branch system as I understand it.

In a parallel system, Bp = OP/# branches, assuming that all branches have equal flow resistance. I.e. in a two branch system, each block would see 1/2 the total volume pumped in a given time.

Also, within diminishing return limits, the higher the volume flowing through an individual block, the more heat it will remove from the block. However, the hotter the water is entering the block the less heat it will remove per unit of volume.

The issue is mostly a question of in a series setup how much hotter the water going into the second block would be on account of it's trip through the first block, and thus how much hotter the second CPU will run. In addition there is a question of how much the flow would be reduced by having all the water having to pass through both blocks.

The series advocates maintain that the temperature difference between the two blocks would be nominal since each volume of water would only be picking up a little heat in the first block. In addition they feel that making all the water pass through both blocks means that each block will see more volume and be cooled more than the flow would be increased with the lower resistance parallel setup.

The parallel advocates maintain that the greater total flow due to lowered resistance will make up for the fact that each block will only see part of the total.

Now, boundary conditions...

Case 1: Op < Os - The series folks win clearly, as there is no increase in flow with the parallel setup, and Bp = 1/2 Bs, which would obviously mean less cooling.

Case 2: Op > 2 x Os - in this case the parallel folks have it easily, since the flow through each block would be the same or better than the series flow, and the increased volume should mean the whole system runs cooler.

I would be suprised to see EITHER of these cases, but would expect to see something in between, where Op = 1.? x Os. This leads to the main question, how does one estimate the point where one crosses from case 1 to case 2?

I know I've been talking about having an additional low flow branch for the hard drives, etc. I think it is safe to leave that out of the overall calculation since it would be the same in either hookup. (actually it might get LESS flow in the parallel setup since the lowered resistance of the main branches would make the high resistance side branch less 'attractive'...)

Skulemate: The problem with this is that you do not have the highest flow rate where it counts... namely through the waterblock.

I don't quite get your point Skulemate, there will be two blocks, and I don't know where else the water would go besides through them (barring leaks ) I am NOT talking about having a 'no cooling bypass loop'! If I split the flow, I would be splitting the cooling loads as well.

Gooserider

[sevisehda]

I wrote up a really long explanation with RHUs(Random Heat Units) and RVU(Random Volume Units)s but realized it was way to complicated to make much sence so I found a power curve chart. Lets imagine for a second the Maze 4 equals a foot of head. So figuring everything else in your loop equals 1.5 feet of head and you have an Eheim1048.

1 Maze4 115GPH Total Loss 2.5ft
2 Maze4s Ser. 85GPH Total Loss 3.5ft
2 Maze4s Par. 125GPH Total Loss 2.0ft
62.5GPH per loop

Cut the flow for the parallel system in half and you get 62.5GPH through each loop. A difference of 22.5 from series. Now I choose 1 ft of loss for the Maze4 at random. It would be a close call at this point what would do better parallel or series. Lets take this further through.

Lets say I decide I need a bigger radiator and now my base head loss is 2.0ft instead of my previous 1.5ft. So my new numbers are.

1 Maze4 100GPH Total Loss 3.0ft
2 Maze4s Ser. 62GPH Total Loss 4.0ft
2 Maze4s Par. 115GPH Total Loss 2.5ft
57.5GPH per loop

Now that the curve is flattening out we see a huge drop in flow for a highly restrictive system. The difference is a mere 4.5GPH. A little more restriction and the parallel may actually get more flow. Given the great increase in flow with parallel I choose it simply because now I have 53 more gallons per hour to cool other parts of my computer.

I've figured out 2 things in the past 5 minuts. Its crucial to check the curves for figuring out the layout of a system. And it would be freakin awesome if places posted numbers on headloss through their blocks.

[bigben2k]

Good show, Sevisehda.

Most pumps are used at the far end of the curve, but it's different for everyone. The average frow rate for a typical rig is ~60 gph.

With blocks in CPU you still want most of the flow to go through the CPU block, and that means throttling the flow to other blocks. By doing so, the total pressure should end up being slightly less than if the CPU block was by itself, which will result in a bit more flow, but still split.

Blocks in series put the pump further out of their energy efficiency range: gph for head, you end up loosing further than you already have.

I ran the calcs once for LiquidRulez, for pressure drops of a nozzle, and found that the rad/heatercore alone will create a significant pressure drop, throwing anything else way up on the curve.

[Skulemate]

Your RUA (random unit analysis) is a bit bogus, since the flow resistance of the various components will be dependent on the flow rate through the system.

And Ben, running a pump on one extreme end of the curve or the other means that it wasn't chosen properly in the first place

[bigben2k]

True.

I'm gonna stick to the old rule of thumb: pumps in series, blocks in parallel, but the pump has to be considered in the equation.

[Althornin]

Originally posted by bigben2k
True.

I'm gonna stick to the old rule of thumb: pumps in series, blocks in parallel, but the pump has to be considered in the equation.

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.

[sevisehda]

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.

Did you miss my last post. Sometimes more head means more flow.

2 pumps may push alot of coolant in parallel but in a restrictive system both will be held back severely. Placing them in series will allow them to 'throttle up' and push more water.

Your RUA (random unit analysis) is a bit bogus, since the flow resistance of the various components will be dependent on the flow rate through the system.

There just for explantions sake. Perfect Units for a perfect world.

Now I'm not a MechE but I've seen some formulas for drag and I take it the formulas for resistance will be somewhat similar. So since headloss is related to flow they could provide a graph simlar to the pumps power curve.

[Althornin]

Originally posted by sevisehda
Did you miss my last post. Sometimes more head means more flow.

2 pumps may push alot of coolant in parallel but in a restrictive system both will be held back severely. Placing them in series will allow them to 'throttle up' and push more water.

I'm not an idiot, but he implies it is a "rule of thumb" - in fact, it is more the exception to said rule

[Gooserider]

Good discussion sevisehda, your examples make sense, and look like reasonable real world numbers. I suspect (can't prove yet) that I'll be able to get higher flows than your example, but I think your reasoning still holds.

Pump - I'm currently planning on a Danner PondMag 3. It is smaller and less expensive than an Eheim 1250, and has better flow rate and head numbers if one is to believe the advertisements. I've searched the forums here, and haven't found anything really bad said about it.

Blocks - I'm going to make my own, but I'm planning to go for a very high flow design (at least as I understand how to get high flows) to get good cooling via 'brute force' of lots of volume, rather than fancy flow juggling tricks (like Cathar & Co.)

Rad - From the reviews I've read, discussions, etc. I've gathered the impression that most of the WC purpose designed rads have pretty high restrictions, and tend to be on the small side. I'm planning to use a heater core (supposedly less restrictive) big enough to put at least 2 92mm fans side by side blowing through it. I've just ordered an AMS CK1100B 20 bay cube case from Servercase.com, (195.00 w/o PSU) and figure on hanging the rad off the back of the case which I'll mod to have the two case exhaust fans blowing through it.

I'm thinking now that testing for comparative flow volumes with the hardware I'm actually using will be my only way of knowing for sure what will work best, and that will have to wait a while until I get it in hand.

Gooserider