Testing waterblocks vs pumping power
 

Been thinking on this problem a bit and attempting to find a way to convey to an everyday user what waterblock performance is like.

The problem with flow vs C/W graphs is that they do not convey any pressure based information. One can look at a graph of two blocks of two vastly different levels of restriction, and performance per LPM may be higher than the less restrictive block, but the less restrictice block will perform better per unit of pressure drop.

Then we get to the issue of a pressure drop vs C/W graph, where real world pumps do not provide a constant pressure drop as flow rate varies. So while in the example above the second block performs better per unit of pressure drop, it will also be allowing a higher flow rate due to its lower restriction, and so any centrifugal pump that is applied to it will apply less pressure to that block, than to the first more restrictive block.

Ideally we have to present both graphs for a full picture, and the reader needs to analyse and understand both graphs.

That's how it should be done, but it's requires substantial work to glean an overall picture from 4 graphs (flow vs C/W, pressure vs C/W, block pressure vs flow, pump PQ curve). In order to present a composite picture of block performance vs pumping power, then how about the possibility of displaying a graph that is just that? Basically a graph of waterblock C/W vs Pumping Wattage?

So I was thinking about how to present such in an easier to understand picture, and thought that DC pumps presented one possible answer. Using a variable voltage power supply, and tracking the current that flows through to the pump, one can measure how much pumping power is being applied to the cooling loop. On top of the other charts, plot a C/W vs Pump Wattage chart.

There are some drawbacks to this approach though, and primarily it falls down to the test loop's resistance. Pumping power gets spent overcoming all the restrictions in the test loop, and we would not test loop resistance to be terribly high. The way around this though would be to calibrate it. Plot a graph of the test loop's pump power vs flow rate curve with no waterblock in the test loop. Then when plotting data points for a tested waterblock with a certain amount of pumping power, adjust the pumping power by subtracting the test loop's required power at whatever flow rate is being measured. In this manner I believe that the pumping power vs performance curve can be easily calibrated to remove the test loop's characteristics from being an influence.

The second drawback, which is perhaps more serious, is what to exactly use as a pumping model. There are high-head/low-flow pumps (Laing DCC), and high-flow/low-head pumps (Eheim 1250), and there are pumps that fit somewhat in the middle and offer both (Laing D4). We would probably be after a middling sort of DC pump that offers up to ~20LPM of peak flow for the ultra low flow resistance blocks, and up to 10mH2O of pressure head for the ultra high head favored blocks.

That could be achieve in one of two ways. Either by putting 2 x Laing D4's in series, or by using a pump like an Iwaki RD-30 which at 24v offers 10mH2O head and 20LPM flow. Both types of pumps do support running at very low electrical powers (through decreased voltage). The D4's in particular can run as low as 1W each before failing to turn any longer, and can handle being run at up to 15v easily (for 5mH2O pressure head, or 10mH2O for two pumps in series), or at about 25W of pumping power each.

Thoughts? Would this be an appropriate way to present an easier to understand mosaic of waterblock performance that encompasses a good approximation of real world pumping characteristics with varying pumping power in a single easy to present graphing format that the layman can look at and determine which blocks are good for which pumping power scenarios, and for any given pumping power, which encompasses both flow and pressure, what to expect?

[Corrected some statements that were missing adverbs]

I've always believed that it should be acomplished in the easiest way:
1-run the performance test, using either flow or pressure

2-run a pressure versus flow test. (no performance measurement there)

The two data sets can be used to interpret the results in one way or another.



I think your real question is more about how a reader can use the info. The WB performance graph that pH is using now is pretty nice; if there was a way to do the same thing by overlaying pump curve, that's be interesting, but it wouldn't account for the rad, nor any of the fittings/tubing. Fitting/tubing info is easy to obtain, but the rad is still a big black spot in the WC community but then, the same graph becomes really, really complicated.

In MY opinion, the solution is to produce C/W vs flow data and dP vs flow data for waterblocks and a few common radiator/fan combos. Then to use that data along with the other components in the loop and the pump P-Q curves to predict a final C/W for the system. That is what groth was going for here:

http://pages.sbcglobal.net/water.gro...20process1.htm

The interface would have to be simplified a lot and it's awaiting my dP vs flow data...

It's waiting on my dP vs flow numbers to be generated; that's next up after this Alphacool nexxos XP review is done

The one curve that I would like to see for blocks is flow through the block vs pressure. The way I see to get that info would be to set the block up in a loop with a powerful pump like the md30rz with a valve on the outlet folowed by a flow meter and then a accurate pressure gauge. That way tou could plot the flow vs pressure of each block just by varrying the valve and take the flow and pressure reradings. I have always been curious on what the flow in my system is and have thought about putting in a 0~5psi guage on the outlet on mine. That way as long as the pq curve of my pump is accurate I could get the flow by plotting the pressure reading to my pq curve.

I have a Rosemount dP xmitter and a 5.5 digit DMM. I just haven't had the time to make it happen. This weekend I hope it will be time. I don't have enough space downstairs to set up that test loop without dismantling part of the existing one. I think we're at a break between wb releases though so this is a good time.

That IS the correct way to do things, but it involves work on behalf of the reader, and work that many are unwilling to even learn to understand what they need to do to interpret the results properly.

The issue that I am attempting to confront here is that of reader laziness. As in a approach of "Okay, so all this technical stuff just flew over your head? That's cool. If there's one graph which you should read, try to understand, and take away with you as an approximated summary of the results seen, it would be this graph".

Why not just provide C/W per dP graphs? Given that, are C/W verses flow graphs even relevent? Its not like most people have any way to gauge flow, while their pump max head is published, and you can make educated guesses about what a radiator does to that figure.

...because pumping pressure is not constant as flow rate varies...

For direct comparison between blocks, I think that using C/W vs Power is a good idea. I'm not so sure about the methodology of using a real pumps' input power though.
Why not use Hydraulic Power, or more simply Flow*Pressure? (based on P/Q data AND C/W vs flow)

As suggested and explored by Since87 here in post 26.

Not quite(?) Unless I misread it...
(I find Since87's graphs rather confusing)
Will try and codge something up in Excel to illustrate (see if it works?!)

Edit:

http://img103.exs.cx/img103/5748/nexxosxp.gif

I only have Cathars graphs to work off for the PQ data, so unforetunately the inclusion of the 1/2" tubing + rad is going to mess things up somewhat. (I would have liked to plot 2 or 3 blocs on this graph to compare)

My understanding was he was suggesting plotting C/W v dP*Q .

Indeed, I remember that now too. Definitely a better approach by using hydraulic power, rather than pump input power. A "unified" approach to cooling performance assessment?

Thanks for the link Les. Will go over it, hopefully with a clear head.

Edit: Just saw lolito_fr's graph above. Yes - that's pretty much exactly the sort of thing I was hoping for.

Bingo.

http://img105.exs.cx/img105/4841/nexxos-mcw6000.gif

no less than 6 pages of excel!!! (more work than I bargained for)
usual disclaimer - GIGO (+fair chance of rounding errors, etc)
Not to mention the involuntary inclusion of pipe losses and rad losses, however I think this is a pretty good illustration of Cathars idea:)

lolito_fr
Yes, I like your graph and yes not quite the same as suggested by Since87.
Will also investigate(slowly) further when head clears

Thanks lolito_fr.

One possible improvement to the graph to clarity sake may be to make the power axis logarithmic. 1W of hydraulic power goes a long way and there's an awful lot of information contained in the 0.01 to 1W range, and somewhat less in the 1W to 10W range. Would seem to me that a logarithmic power scale might space out the plots a little better for comparison layout purposes.

Sorry Les, that graph is way out - have just edited my post.
As suspected, too much haste + head not sufficiently cleared.

Cathar, yes, will try a log scale when I get this little prob sorted out :)

lolito
Good.
Was just about to embark on a data check - saved me the trouble.
Will still do, but will postpone till after todays pub

It is a problem when posting calculations made "on the hoof"
I am constantly having to correct my own mis-calculations.

I was able to re-use data that I had input from my simulator thing and wrote a custom perl script to munge it into a usable data set. I removed the rad + tubing effects. This is the graph that I arrived at. Re: the logarithmic thing - given Phaestus's data it would appear that since the flow rates don't go down low enough that 0.3W is where the graph starts from anyway. Where this will get gnarly though is for blocks like the DangerDen Maze4 which have a very low pressure drop, and 0.3W of hydraulic power equates to around 8.5LPM flow rates.

http://www.employees.org/~slf/curves...stormg4pwr.png

[Edit: Oops - corrected the axis labels - reload page to see correct labels]

Cheers Cathar. I now need to remove the rad+tube effects!!
No Perl scripts here unforetunately:(

Here is a log version of the above corrected graph

http://img105.exs.cx/img105/7176/nexxos-mcw6000-log.gif

enjoy!

the Nexxos seems to be holding up surprisingly well (even against the G4) ...
but of course the rad will play a part :p

Oh, now THAT is interesting isn't it?!

Well if you are referring to the straight lines, my dT vs Power graphs are both best matched by power functions:
y = 10.08115*(x^-0.03524) for the MCW
y = 9.52474288*(x^-0.08522324) for the Nexxos

Other than that, then yes the Nexxos seems to whip butt :D

Here's what I managed to work out, with log axis:

Edit: Graph deleted due to computational error

Quite frankly I find the near straight lines most fascinating.

Edit: I was plotting the G4 line from the Procooling test results graph page, and noticed that it is different from the separate line graph that Phaestus posted. I will need to confirm with him tomorrow as to what's up there.

Cathar
You seem to be having a good day with your arithmetic(or perl thingy -whatever that is).

Edit Removed wrong comment.