Some Interesting/Confusing Data from testing

[Groth]

Ah, yes, it is a bit limiting if you're only looking at complete pipes. :shrug: No playing with coolant or charge or wicking or dimensions. meh.

[Incoherent]

Originally Posted by pHaestus

...wasting lots of Les's and incoherent's time...

Don't feel bad on my account, I absolutely do not consider this a waste of my time, especially considering the amount of time (and effort, and money ...) you are spending obtaining this data for us to pick away at.
I am just happy that the errors are stable enough for them to be detected, a testament to your consistancy.

Heatpipes, and their requirement for a specific heat load. I wonder if these Shuttle SFF CPU coolers take that into account. There appear to be four seperate pipes. Could they all be tuned to different optimum heat loads? in effect creating a "wide band" heatpipe cooler...
It is a shame they are so specific. It's a pretty neat mechanism. I am very curious as to what you are working on Bill.

Cheers

Incoherent

[BillA]

every day is a new lesson, just chuggin' along

[Les]

Originally Posted by pHaestus

The variation in power from last night/this am's data? At very low flow rates it's difficult to perfectly insulate the hoses and I suspect that the 0.5GPM flow number is somewhat suspect for that reason. For the numbers above 2GPM the delta T is so small that better resolution than 0.01C is required (a difference of 0.01C corresponds to nearly 10W). The numbers from 0.75-2GPM are pretty much dead even at 72-74W; not much variation of CPU power with flow in that case.

If you mean the earlier test results then there was a 0.06-0.07C offset in my temperature probes that I didn't catch (but incoherent did).

As for Bill's graph, consider that we are dealing with water inside a heat pipe, and that water has some interesting properties which occur near phase transitions. Solid water floats, for instance.

Yes the sensitivity and the accuracy of the probes is sorely tested by this work.
Notwithstanding,Incoherent's admirable method is a tool to determine the solution. The "0.07c systematic error" suggestion is a the value to give a best fit to an invariable W . The invariable W is questionable.
Using an offset of 0.07c is prejudging that W does not vary with Flow-rate. I don't think this can be done.

I may not be understanding correctly but pHaestus has suggested two evidential values for the systematic error - 0.06/0.07c and 0.02c.
I probably prefer the 0.02c solution which shows an increase of "Heat Absorbed" with increasing flow rate. However, if had to bet, I would choose a value between 0.06/0.07c and 0.02c as giving the true variation of W with flow-rate( this best corresponding with my preconceived notions of the variation of "Heat Absorbed(W)" with "C/W").
Some graphs:




Think will catch up on the Heat Pipe discussion much later. However I imagine that wb's behave similar at a high enough temp when Flow Boiling can be envisaged.

[pHaestus]

Les: 0.02C is the offset in my current setup after moving thermistors around and swapping one out. It is only valid for last night's (Swiftech MCW5000-A) data. In that test run the W varied from 69-75W but I am a bit skeptical of the numbers above 2GPM.

As for the earlier results I don't think much can be done to be conclusive other than repeat tests again. Shouldn't be a big issue though as many more blocks have to be tested and data collection is free.

[Groth]

Originally Posted by Incoherent

Heatpipes, and their requirement for a specific heat load. I wonder if these Shuttle SFF CPU coolers take that into account. There appear to be four seperate pipes. Could they all be tuned to different optimum heat loads? in effect creating a "wide band" heatpipe cooler...

I wondered about that, too. Plus, a heatpipe will have optimal temperature range. How wide? How does that range relate to coolant and charge? How much will the thermal impedance vs. heatload curves change over the temperature range? Could using two coolants with different boiling points give a wide-band cooler in a single pipe?

[Brians256]

Originally Posted by Groth

I wondered about that, too. Plus, a heatpipe will have optimal temperature range. How wide? How does that range relate to coolant and charge? How much will the thermal impedance vs. heatload curves change over the temperature range? Could using two coolants with different boiling points give a wide-band cooler in a single pipe?

I think you have hit the nail on the head, as those have been the questions in the back of my mind for quite some. time. However, I have not seen any information about this in public literature. So, if the answers exist, they are either in proprietary care or they are in expensive books that are not in my library or on the internet.

I do think that using a multiple coolant heatpipe would greatly widen the effective sweet spot. I also think that even a single coolant heatpipe would probably have a wider sweet spot than we fear. For example, Bill's heatpipe data shows that it works fairly well for a ten to twenty watt range in heat input.

[BillA]

Les
just poking at the semantics here

"The invariable W is questionable." WRT pHaestus' testing, that W (net to wb) is variable is certain, only the rate of change is in question.

"Using an offset of 0.07c is prejudging that W does not vary with Flow-rate. I don't think this can be done." In a strictly absolute sense you are probably correct, at least with anything my setup can document. More loosely speaking however, I can and have repeatedly demonstrated that within 'reasonable' limits the device C/W is independent of the applied load (but NOT for heat pipes).

Once I have a testing 'peer' (get with it pHaestus !), I will be better able to identify the slight 'apparent' influence that changes in the applied power may induce. One needs multiple benches to verify that an 'effect' is not an artifact just of that particular bench.

pHaestus
I observe a very slight increase in the coolant temp rise (at the lowest flow rates where such is most visible, 0.01 to 0.02°C) between wbs with a high C/W as compared to others with a lower C/W. In these cases the bp is at a higher temp, which implies a different energy 'load'. Be interested to see if you see the same.

Groth
and you haven't even touched on wicking structures and fabrication methods, lol

[Les]

Originally Posted by unregistered

Les
just poking at the semantics here
.....
More loosely speaking however, I can and have repeatedly demonstrated that within 'reasonable' limits the device C/W is independent of the applied load (but NOT for heat pipes).
.......

Not my intention to suggest a device's "C/W" is changing with heat load. A device,here, is considered to be a particular wb with a particular coolant flow.Each point on the "Watts Absorbed" v "C/W" graphs are separate devices with different "C/W"s.

[BillA]

ah, ok
was looking at the 'set' of points, rather than individually

[pHaestus]

A practical observation:

When I remount the MCW5000-A (using one hand to hold clips onto lugs and other to work the screwdriver) the mobo's power circuitry is both very close and very hot. It's hard to imagine that at least a little of this heat doesn't make its way into the waterblock via the baseplate and top. And the amount would be pretty wb dependent (the Swiftechs are a lot closer to these parts whereas the long 4 hole wbs are instead closer to the northbridge).

[BillA]

and . . . . .
is this too not part of the reason for bench testing ?

are we testing the system (of which the mobo is a part), or the wb (independent of the effects of the other parts)?

perhaps I've not been paying attention, but why are you not using your heat die ?

[pHaestus]

heat die still involves sinking substantial dollars into it (need 2 good DMMs, PSU, insulation, etc etc). Time and money, time and money.

Plus I am a bit of a masochist; can't you tell from my hobbies?

[Groth]

pHaestus, have you seen those cones veterinarians put on dogs? How 'bout using a similar approach - blow some significant air on your voltage-regulators and northbridge to minimize the extraneous heat, but protect the CPU/block from spurious, non-reproducible air currents.

Bill,
Wicking? All the possibilities of material, fiber shape/size, weave (or not), bonding, thickness, and how all of those interact with all the other variables. It makes water look easy and friendly. When can we expect your data?

[joemac]

PH would it be possible to drill into the blocks you have to obtain a temperature reading. This would allow you to easily insulate a small hole rather then trying to control a larger environment. I don’t know how feasible this would be on some blocks but I think it would provide a real insight to what the temperatures look like between the heat source and the transfer medium.

[TerraMex]

Doesnt WW, Cascade and RBX blocks have a very very thin base ?
If it could be done:
Wouldnt that influence the blocks performance...?

[joemac]

Originally Posted by TerraMex

Doesnt WW, Cascade and RBX blocks have a very very thin base ?
If it could be done:
Wouldnt that influence the blocks performance...?

I don’t think the base is thin through out the entire block. I think the only thin part of the RBX and the WW is over the core in which case the probe hole can be made to be stop just outside the valley of the block. This should prevent affecting the performance reading of the block (most user only care about the reading above the core). Frankly without the proper insulation on the test, this should remove more variables than it introduces.

[prandtl]

Originally Posted by joemac

I don’t think the base is thin through out the entire block. I think the only thin part of the RBX and the WW is over the core in which case the probe hole can be made to be stop just outside the valley of the block. This should prevent affecting the performance reading of the block (most user only care about the reading above the core). Frankly without the proper insulation on the test, this should remove more variables than it introduces.

IF something like this was to be done, it would mean the temperature probe will not be at the same position (in respect to the core) for all wbs, wich will make any datas useless for any wb to wb comparison.

[pHaestus]

joemac:

Not sure how to back calculate "W" from a baseplate temperature? The insulation is definitely a problem for the 3 barb blocks, but honestly I am not so interested in this now that I found out that weird results were operator error

I will, if there is interest, run tests as function of MHz and Vcore using whatever block is on my testbed this week (it's the aquajoe atm). There's a catch though. Can get someone (Les? Incoherent? Groth?) to use results to come up with better radiate-style equations for CPU power using my data?

[Les]

Originally Posted by pHaestus

1) ... but honestly I am not so interested in this now that I found out that weird results were operator error
..........
1) Can get someone (Les? Incoherent? Groth?) to use results to come up with better radiate-style equations for CPU power using my data?

1) Suggest that for the MCW5000A the relatively small increase of Wwb with increasing Flow rate is,perhaps, a consequence of only a small change of "C/W" with flow rate.


or as I insist on plotting ( I share Bill's unease but ....)


Think it is a little early to judge the issue.

2) I only do beer-mat sums not computer equations.

[bigben2k]

Nice. How about power vs flow, for the last 4 blocks tested? I'd just like to see the variation in the power. I see what you mean pHaestus. Would you foresee any benefit in having 3 decimal resolution, I mean, do you think that it would be practical?


From my limited understanding of heatpipes, they are designed to work at a specific temperature, i.e. the boiling point of the liquid inside the pipe. So as a cooling solution, you have to take into account the gradient, between the liquid and the CPU, and it is going to depend on the power being supplied, as well as all the usual variables (TIM joint, notably). Bill's graph is representative indeed: the heatpipe relies heavily on the latent heat (energy from the change of phase) of the liquid being "boiled", so if the temperature is outside of that range, the performance relies strictly on the conduction/convection of the remaining metal assembly, which will be poorer. Many more variables... Testing these involves a different approach than for WBs (as Bill demonstrated). I've had the chance to think about that particular one, ever since I was asked to test one a few months back (had to turn it down: not ready to test yet!). It's a real nightmare, but one I suspect may become part of future cooling products, under one form or another.

[Incoherent]

Originally Posted by pHaestus

joemac:

I will, if there is interest, run tests as function of MHz and Vcore using whatever block is on my testbed this week (it's the aquajoe atm). There's a catch though. Can get someone (Les? Incoherent? Groth?) to use results to come up with better radiate-style equations for CPU power using my data?

pHaestus, if you come up with the data, I would certainly be happy to give it a shot. I am not a programmer though so it would only be a set of functions which fits your data, in Excel sheet format, not a radiate style program.
Of course this is assuming that we are able to identify and account for all the dominant parameters, at best it would be a "typical" value in a typical system, presented as "CPU power output minus secondary losses" Data at a range of water temperatures would be interesting. I would expect to see a Power/Temperature curve upon which the true CPU power output would lie somewhere.

Les, your C/W vs W chart is very disturbing, I do not like it. I can not imagine a situation where power output is dependent on anything but CPU temperature, applied voltage, speed and load level so I do not want to see anything but noise in such a chart where the above parameters are constant. Flowrate is irrelevant. Anything else, any trend, linear or curve in such data says that there's either a measurement error or in fact one or more parameters are changing. Although of course, in reality all these parameters will change within a certain range, maybe predictably.

Thinking.

Cheers

Incoherent

[Les]

Originally Posted by Incoherent

....
Les, your C/W vs W chart is very disturbing, I do not like it. I can not imagine a situation where power output is dependent on anything but CPU temperature, applied voltage, speed and load level so I do not want to see anything but noise in such a chart where the above parameters are constant. Flowrate is irrelevant. Anything else, any trend, linear or curve in such data says that there's either a measurement error or in fact one or more parameters are changing. Although of course, in reality all these parameters will change within a certain range, maybe predictably.

Thinking.

Cheers

Incoherent

Some wordage:
1) The inputs are sources' heat and paths' resistances.
Varying the flow rate changes the resistance of the "die>contact area >water" path. Changing a path's resistance will effect the source's temperature.Would expect increase in heat through the "die>contact area >water" path as its resistance is lowered.
"C/W" is the "die>contact area >water" resistance.
"Heat absorbed" refers to the heat absorbed by the water.
2) IF heat only reaches the water by the "die >contact area>water" path then the plotted "C/W" is the "C/W" and "Heat absorbed" is the Heat passing through the "die>contact area >water" path.

Plotting measured "C/W" v measured "Heat absorbed" explores both 1) and 2)

[Incoherent]

Some more incoherent ramblings

Originally Posted by Les

Some wordage:
1) The inputs are sources' heat and paths' resistances.
Varying the flow rate changes the resistance of the "die>contact area >water" path. Changing a path's resistance will effect the source's temperature.Would expect increase in heat through the "die>contact area >water" path as its resistance is lowered.

If the die temperature decreases (which it does). Then the loss via secondary paths is reduced. More heat is flowing via die>contact area>water path. Agreed.

Originally Posted by Les

"C/W" is the "die>contact area >water" resistance.

Also in Fouriers equation Q=k.A.dT/L, dT/Q or C/W, is equal to L/kA. I prefer to think of it in those terms, changing flowrate changes the effective L or A or k or all of them. These are physical parameters, if they are changing then your statement about the points in the chart being like individual waterblocks is a good one. I guess C/W is convenient.

Originally Posted by Les

"Heat absorbed" refers to the heat absorbed by the water.
2) IF heat only reaches the water by the "die >contact area>water" path then the plotted "C/W" is the "C/W" and "Heat absorbed" is the Heat passing through the "die>contact area >water" path.
Plotting measured "C/W" v measured explores both 1) and 2)

If we adjusted the water temp to maintain a constant die temperature at the different flowrates, the secondary path gradient would remain unaltered, even though the primary "die >contact area>water" path C/W's changed with flowrate. The "Heat absorbed" is constant. If you plot this again at several temperatures I am not sure there would be any relationship except the "Heat absorbed" changing with temperature. Point being, I think the C/W vs W chart is only a few points in a chart that is filled with data points, ie every C/W can have any W so there is no trend to be gleaned.

I'll keep thinking, I am a little muddled here.

Cheers

Incoherent

[BillA]

"If we adjusted the water temp to maintain a constant die temperature at the different flowrates, the secondary path gradient would remain unaltered, even though the primary "die >contact area>water" path C/W's changed with flowrate. The "Heat absorbed" is constant. If you plot this again at several temperatures I am not sure there would be any relationship except the "Heat absorbed" changing with temperature."

interesting
I can do this both on an insulated heat die, and a ttv (~mobo + CPU)
will report - eventually