even better than cascade?

[Jabo]

Originally Posted by 8-Ball

Please rephrase to an "imaginary" system with a very low restriction, since the head loss varies with flow rate. It is NOT constant.

The restriction or resistance to flow rate, is a property of a system, however, this also varies with flow rate.

The number of volts applied across an electrical circuit is not a physical property of that circuit is it. It is something we have applied, much like a head loss or pressure drop in a liquid circuit.

8-ball

Hi mate
Btw, check Xtreme thread

WC system is like electrical system with all the 'bits' installed so we are not applyiing anything, all we do is provide different power source (diff pumps) but performance of regular electrical components is linear (guessing here since I am not that conversant with electrics/electronics) and with stronger amps or volts resistor is going to produce the same resistance (hence watts ratings) all the time (lame example?).

Anyways, at diff flows restriction posed by a system as a whole is different, absolutely right. All I am saying is that an assembled system has just one flow-to-head curve dependant only on hardware from which it was made off. Curve doesn't change, values on it do

[Cathar]

Originally Posted by Jabo

This is quite interesting discussion going on here indeed
my 5 pennies:
Lokking at pictures and analyzing decriptions of aformentioned deustch testbed system I came to following conclusions (based on my limited knowledge of fluid mechanics and thermodynamics):

1. Heatload simulating element used (it's size and configuration) produces massive thermal energy density per mm^2. Such setup preffers blocks with thicker base plate (Fourier's law, isotropic heat diffusion etc.), which may in turn explain better performance of Murks block (VERY thick base plate)

Actually cooling performance (in terms of W/m²K) is not affected by the thermal density of the heat-load. The coolant flowing through the block is applying a fixed rate of cooling effect, which is proportional to the rate of thermal convection that's going on inside the block, and since the cooling area is fixed, then the amount that the heat source will warm up by is directly proportional to the heat that it emits.

i.e. a block that cools better at 50W of heat load, will still cool better at 100W or 200W, and in fact will provide increasingly better temperatures.

What a thick base-plate does is determine the amount of thermal spread of the heat by the time that the heat reaches the convectional zones within the block. Stick on a thick base-plate, and all of a sudden you have effectively more surface area for the water convection to work on (presuming that the heat source is initially far smaller than the waterblock).

What we strike here is a balancing act though. The thicker base-plate increases the thermal resistance as well. As the rate of thermal convection is improved (typically through higher flow rates) the thickness of the copper increasingly becomes a barrier to further improvements in cooling performance, as it becomes the predominant source of thermal resistance.

For thin base-plate blocks, these blocks rely on the rate of thermal convection being high enough to overcome the lack of thermal spread. Less convective surface area is available for the coolant to operate on, but the rate of thermal convection is high enough to overcome this drawback. There is the added benefit here that as the thickness of the copper is reduced, this too offers less thermal resistance.

So we have a balancing act. If designing a block for ultra-low flow rates, one would naturally choose a thicker base-plate to offset the reduction in thermal convection by increasing the effective area available to the coolant. If designing a high-flow block, then assuming it's done properly, going down to quite amazingly thin base-plates is exactly what you want.

The amount of heat load of the heat-die has nothing to do with it.

A thin based block will suffer at flow rates below its design balance point in comparison to a thicker based block. A thicker based block will not see any significant gains above its designed flow-rate balance point in comparison to a thinner based block.

Originally Posted by Jabo

2. Taking into account the above and low flow (jet impingement design is based on localized increase of coolant's density/pressure which entails increased thermal capacity maintaining the highest possible dT) it's totally expected that Murks performance is better then Cascade's (sudden 4C drop is simply impossible, unless Tom discovered how to dump excesive heat into another dimenssion or used sth like foamed graphite insert combined with laser beam micro channeling of copper )

Speaking of jet impingement, another important aspect here is the jet power. As flow rate is dropped, so too does the jet power and its ability to impinge on the surface. Higher jet velocities demand a wider cup-jet width ratio as the size of the primary impingement zone increases with velocity. Higher jet velocities also demand that the jet stands off from the base of the cup further, as the increased velocity allows for greater mixing/turbulation of the incoming jet stream without it losing significant power. With lower jet velocities (the result of lower flow rates and pumping pressures) the jets need to be placed closer to the base-plate to offset the loss in impingement "power" that would be experienced if one kept the same parameters as a higher-velocity setup.

i.e. for low flow setups, one would both decrease the jet/cup width ratio, and bring the jets closer to the base of the cups (within 2.5-3.5d).

However, doing this will then impact higher flow performance. One won't see quite the gains that is possible at higher flow rates.

Co-incidentally, the Murks 3.1, from what I can see of it, does just what I'm highlighting as issues for low-flow/pressure setups.

Originally Posted by Jabo

3. Results are just numbers and like with all statistics one reading it has to know very well how to interpret results or not be suprissed arriving at incorrect conclusions.

To summarize, as Cathar stated above, there are no universal designs and every piece of h'ware shows it's potential only if used within it's design perameters.

Exactly. Waterblock design is a game of trade-offs. For myself, I focus on the highest possible design performance, accepting that in doing so I am sacrificing low flow performance.

I do still believe though that the results with the Cascade at WCP are at the very least between 1-2C worse than I would have expected, but given that the block had been modified by the user with no guarantees of anything after that event, then I guess anything is possible. The Cascade as it ships is still a very powerful low-flow performer, but I happily accept that had I been focussing on lower-flow performance then it could be made to perform better in that scenario.

Changing the base-plate to 2.5-3mm thickness, dropping the jet/cup ratio to 2d (presently above that), dropping the jet standoff distance to 3d (presently significantly above that), and increasing inter-cup area ratio slightly, would yield a design that at 100W would probably pick up 1-2C or so at 1-2LPM flow rates, but we'd see much flatter performance curve beyond 4LPM at which point the present Cascade design would overtake it.

Horses for courses.

[freeloadingbum]

Changing the base-plate to 2.5-3mm thickness, dropping the jet/cup ratio to 2d (presently above that), dropping the jet standoff distance to 3d (presently significantly above that), and increasing inter-cup area ratio slightly, would yield a design that at 100W would probably pick up 1-2C or so at 1-2LPM flow rates, but we'd see much flatter performance curve beyond 4LPM at which point the present Cascade design would overtake it.

Why would increasing the baseplate thickness help when it seems that the overall jet grid area isn't being increased? Would this design have more jets as well?

[Cathar]

Originally Posted by freeloadingbum

Why would increasing the baseplate thickness help when it seems that the overall jet grid area isn't being increased? Would this design have more jets as well?

Well the jetted area on the Cascade is larger than any core is presently, and this is to cater for large cores that may be covered by an IHS.

As it stands, the heat of say, a Barton die underneath the shipping Cascade really only engages about 35% of the block's jetted area. The other 65% is basically cooling nothing.

By making the base-plate thicker, the heat will spread to a wider area, engaging more of the jetted area in the act of cooling the heat. By making the base-plate thicker, the thermal resistance inherent in the copper's conduction is also increased.

As I was saying, there is a trade-off point for the base-plate thickness on the basis of the rate of convectional cooling being applied.

[freeloadingbum]

As it stands, the heat of say, a Barton die underneath the shipping Cascade really only engages about 35% of the block's jetted area. The other 65% is basically cooling nothing.

Wow! That makes the cascade's performance even more impressive when you consider it has a "Whole lotta nothing goin on"

[Cathar]

Originally Posted by freeloadingbum

Wow! That makes the cascade's performance even more impressive when you consider it has a "Whole lotta nothing goin on"

If it were economically viable to produce a block that is explicitly tuned for a particular CPU die, and not worry about when people upgrade their CPU's, then it would be possible to do even substantially better than what the Cascade is doing.

That is another trade-off that I admittedly made.

This is another aspect to consider when people start tuning around a test-bed. It's like certain graphics companies that go around tuning their drivers for a specific benchmark, cutting corners and removing absolutely anything at all that is superfluous to the demands of the testbed/benchmark.

There can undoubtedly be a situation of something performing brilliantly under a single very tightly defined scenario and significantly less well for other test cases vs a case of performing almost as well across a wide range of scenarios.

Speaking of which - my machinists just informed me that the Cascade XXX (with customisable cooling zones) has been coded up and they're about to run it on the CNC mill pending my approval, for which I'm about to head out the door and have a look...*clicks heels*

[pHaestus]

XXX eh? Surprised it doesn't carry the "FX" or "XP" moniker

[jaydee]

Originally Posted by Cathar

Well the jetted area on the Cascade is larger than any core is presently, and this is to cater for large cores that may be covered by an IHS.

As it stands, the heat of say, a Barton die underneath the shipping Cascade really only engages about 35% of the block's jetted area. The other 65% is basically cooling nothing.

By making the base-plate thicker, the heat will spread to a wider area, engaging more of the jetted area in the act of cooling the heat. By making the base-plate thicker, the thermal resistance inherent in the copper's conduction is also increased.

As I was saying, there is a trade-off point for the base-plate thickness on the basis of the rate of convectional cooling being applied.

Sounds like an experiment! Take the Cascade and plug some of the outer holes and see what happens. Theoretically if the pump is decent it should cause an increase in velocity in the remaining unplugged jets and may cause a performance increase eh?

[Cathar]

Originally Posted by pHaestus

XXX eh? Surprised it doesn't carry the "FX" or "XP" moniker

It's pure water-block porn.

Really though - approaching 3x the jets/cups in about the same area - hence XXX.

If I got it right - it should be quite a deal better than the Cascade right across the board.

[Cathar]

Originally Posted by jaydee116

Sounds like an experiment! Take the Cascade and plug some of the outer holes and see what happens. Theoretically if the pump is decent it should cause an increase in velocity in the remaining unplugged jets and may cause a performance increase eh?

Have already made the cutouts for it a week ago. Haven't had the time to plug it in yet.

[pHaestus]

xxx is x^3 not 3x though

[jaydee]

Originally Posted by Cathar

Have already made the cutouts for it a week ago. Haven't had the time to plug it in yet.

I would have just put some silicone in the bottom of the cups, put the jets peice in, let it dry and fire it up but your way sounds more professional!

[Cathar]

Originally Posted by pHaestus

xxx is x^3 not 3x though

LOL. C'mon. Work with me here!

It's a reduction of the Cascade design in all 3-dimensions. It is, in essence, a direct cubic relationship between the Cascade and the XXX.

Every 2.8mm² of CPU real-estate will have its own jet/cup.

There. Is that better?

I'm outta here. Back a few hours...

[SysCrusher]

You guys need to think outside of the box a bit more.

I like the tunable jets Cathar. Maybe add the ability to raise or lower them according to the flow.

Honestly though. I don't know why you would want the jet tubes any higher. The closer they are to the plate the better, until you restrict flow anyways. That will be anywhere around 1mm with those jets you use. Of course higher flow/pressure always allows for them being further away but from what I seen and the math Nusselt number will tell you the closer the better. Use Nusselt average over the area, the distance from the stagnation point.

Nu=hD/k

Re=VD/v

I'm missing a few variables as I don't know how to enter them in using a keyboard.

D=diameter
V=velocity
v=kinematic viscosity
k= thermal conductivity
h= average heat transfer

Of course the shape of the jet changes all that then it gets more complicated. Basically a different shape will allow a bigger cooling area.

[Wildfrogman]

I cant wait to see the new Cascade XXX. Announces like a movie "Come and see the new feature block Cascade XXX showing in a procooling forum near you, dont miss it!" Anyways...its bound to attract attention thats for sure.

[pHaestus]

syscrusher you can't simply post a basic equation and then back away. DO model the double impingement mathematically and produce optimum design as a function of water velocity and baseplate thickness. Especially with nothing more than a calc of those two numbers

Hint: it isn't a currently solvable problem mathematically

[Cathar]

Syscrusher. In a nutshell as to why you want the jet to be stood off slightly can be explained in the following way.

When the jet is really close to the surface, the what happens is the water just squirts out the side of the jet tube, but in the middle of the tube it doesn't really move at all. i.e. the point of central stagnation is fairly large. Imagine filling a glass with water and sticking a flat piece of something on it and turning it upside down. Now lift the glass slightly away from the surface. The water that flows out mostly flows out the small gap, but the water in the middle is barely moving at all, i.e. the stagnation region.

Now do the same experiment but lift the glass away quickly and all the water pours out and strikes the whole area under the glass, rather than merely leaking out the sides.

By standing the jet off a certain distance we greatly reduce that central stagnation effect where the water is barely moving at all. The actual best distance to stand the jet off by is linked to the velocity of the jet stream, as one can well imagine. It gets a little more complicated in submerged jet scenarios where the jet loses power as it moves through the liquid around it, but also gains added turbulence as a bit of a bonus.

The actual math of all that is the subject of a large number of research papers into impingement and its effects. I won't pretend that I could construct a mathematical answer for any scenario, and in fact I don't think that many researchers could either, but the theory that's out there does provide guidelines for good starting points, and unless your jet velocity is extremely low, having the jet really close (<2d) often turns out to be worse.

Have a poke through that paper I linked to above for more information.

[WAJ_UK]

I've looked into it a bit. I found some useful info but it is mainly experimental data with submerged jets. The only conditions where nozzle plate spacing becomes less important seems to be when the reynolds number is below 800 which means very low water velocities. I'm basing this on some experiments carried out by Elison and webb mentioned in "Advances in Heat Transfer" volume 26. I would recommend it for anyone interested in jet impingement as it goes into lots of detail about nozzle plate spacing, modified impingement surface, wall roughness, jet splattering, jet pulsation, motion of the impingement surface, all from 180 different references and technical papers. Should keep anyone busy for a while

[Cathar]

Originally Posted by WAJ_UK

I've looked into it a bit. I found some useful info but it is mainly experimental data with submerged jets. The only conditions where nozzle plate spacing seems to be when the reynolds number is below 800 which means very low water velocities.

At 2LPM, the (per-tube) Reynold's number on the Cascade is about 1000, which basically means that, yes, it is very close to the level you're talking about. I stand by my statement that once you get down to the ~0.5GPM (<2LPM) flow rates that the WCP testbed tests at, then you're into the realm of where altering the jet standoff distance actually becomes important. At 4-10LPM flow-rates, the Cascade is seeing Re numbers of ~2000-5000, and the z/d ratio has been set for that sort of range.

[WAJ_UK]

sorry Cather, I just reread my message. I missed a bit out of my sentence, it was supposed to be in agreement with you. The nozzle plate spacing is very important to the heat transfer coefficient at reynolds numbers above 800. I have a graph here from a document called "Local characteristics of convective heat transfer from simulated microelectronic chips to impinging submerged round water jets". Unfortunately I don't have the whole document as I'm sure it would be very informative. It appears that the higher the reynolds number the more critical the nozzle plate spacing is. If I can get access to a scanner I'll scan the graph in, it might be useful for people who want to experiment

[Cathar]

Originally Posted by WAJ_UK

sorry Cather, I just reread my message. I missed a bit out of my sentence, it was supposed to be in agreement with you

My apologies too as I didn't mean my response to come across that way. I was just backing up what you were reporting with an actual Re number for a certain flow rate with the Cascade.

[Les]

Oh.
I thought you were disagreeing:
WAJ UK "The only conditions where nozzle plate spacing becomes less important seems to be when the reynolds number is below 800 which means very low water velocities"
and "The nozzle plate spacing is very important to the heat transfer coefficient at reynolds numbers above 800"
Cathar " once you get down to the ~0.5GPM (<2LPM) flow rates that the WCP testbed tests at, then you're into the realm of where altering the jet standoff distance actually becomes important"

No matter

[WAJ_UK]

I was just working out the reynolds number for cascade couldn't figure out why I was getting such a huge number. I forgot to change jet diameter to metres. I made it 1020.22598

[WAJ_UK]

yeah I know Les, I've confused myself now. All I have is bits of paper with other people's results on. Cather has done all the hard work of experimenting with different possibilities so his comments are probably more valid

[Cathar]

Originally Posted by Les

Oh.
I thought you were disagreeing:
WAJ UK "The only conditions where nozzle plate spacing becomes less important seems to be when the reynolds number is below 800 which means very low water velocities"
and "The nozzle plate spacing is very important to the heat transfer coefficient at reynolds numbers above 800"
Cathar " once you get down to the ~0.5GPM (<2LPM) flow rates that the WCP testbed tests at, then you're into the realm of where altering the jet standoff distance actually becomes important"

No matter

Sorry - should've made myself clearer.

From a mix of emperical testing and research. Very roughly:

Re = 2000 => z/d optimally about 4
Re = 20000 => z/d optimally about 5
Re = 200000 => z/d optimally about 6

At Re < 1000, we're pretty close to the region where that pattern starts to break down, and we may as well stick z/d at anywhere between 1 and 2 and be happy.

At Re=1000, z/d should be somewhere between 2.5-3.5, hence somewhat away from the >4 value that the Cascade uses.

Poorly worded. My apologies.

I'd be interested to see the graph WAJ_UK, especially to see if it correlates to the above from my understanding of it all.