even better than cascade?

[Cathar]

Originally Posted by 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

Yeah. It's a little gnarly. There were some minor differences between different revisions of the Cascade. The one tested at WCP, being from the first batch at 0.5GPM (1.88LPM) would have had an Re down around 850 or so. For the second batch, Re would be around 900. For the 3rd/4th batches, up around 950. For the SS, up over 1000. This reflects the fine tuning of the production process over time to allow for tighter tolerances.

[WAJ_UK]

I must have been using the dimensions for the later batches at 2 lpm.
I'm not sure when I'll be able to get to a scanner so I took a photo of it with my phone. Sorry for the poor quality but it is just about readable

[Jabo]

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.

Thats what I meant exactly
You chaps obviously have to much time on your hands to post so much or are hopless addicts as I am


Discussion about jet sizing and distancing pontificates over 'How to obtain trully turbulent flow' age old cooling dilema.
Reynolds number tells us if liquid flowing over surface (pipes in our cases) is turbulent or laminar. We want truly turbulent. Reynolds number is proprtional to Velocity and specific lenght L (pipe diameter here). We obviously cannot increase pipe diameter as much as coolant's velocity so we go for the latter.
To obtain truly turbulent flow we need Reynolds >4000 (
reference here ).
The whole reason for turbulent flow is to make as many water molcules get in contact with 'sticky' layer as possible and to reduce boundary layer thickness to minimum (Fourier's Law of conduction Q= k*A*dT*time/d, where d here is thickness of boudary layer and Q energy transferred).
Jet impigement system substitutes for larger heat transferr area limited by dimensional constrains here.

Does it make any snense?

[WAJ_UK]

Today I have too much time on my hands and I'm a hopeless addict I've been sitting around all day taking far too many temp measurements. I have 9 different combinations of blocks to test and I'm almost halfway, after pretty much a solid week of testing. I don't have any lectures at uni on a friday so I've spent all day sitting at the laptop updating my spreadsheets as my test continues.

There is a bit more to water jet impingement than whether or not the flow is turbulent. It is highly likely that the flow is turbulant anyway at lower reynolds numbers. You need quite a long, extremely smooth pipe for the flow to become turbulant as high as 4000. As soon as the jet exits into the surrounding water it will become increasingly turbulant the further it travels through the surrounding water. However the centerline velocity of the jet reduces the further the jet travels through the surrounding water.
These two elements (turbulence and centerline velocity) are the key ingredients to impingement cooling. So basically, the further the nozzle exit from the base plate, the greater the turbulence and the closer it is the greater the jet velocity. So it is a case of balancing the two components to give the optimum heat transfer.

But now I'm off to the pub

Typical student

[SysCrusher]

Originally Posted by 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.

I understand all that and your correct in this. To close and performance drops because of the stagnation area but that's not what I was getting at.

Originally Posted by Cathar

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.

This is why I made my last post before this. I might of misread your post but I took it that you were saying further away then what you have now was better. I don't know the cascade in it's real form but from my understanding your jet tubes are just about level with the rims of the cups which I would consider optimal as this is what I was doing with my cone shaped design - though inferior to the cup or spherical shape. There is a point were further becomes worse and there is a fine line inbetween good and bad with our flow rates/pressure. Diameter also influences the optimal distance. Being submerged complicates the situation more as the surrounding fluid acts as a restriction. In a low flow situation your about to lose the game as the surrounding warmer liquid could actually heat the incoming liquid or restricts it to the point it never reaches the base. It's a balancing act just to get some where in the middle of the two situations - low/high flow. But then, we're assumming there is no restriction after that where the restriction is greater then the block or equal to it. Though I doubt we would see that.

Originally Posted by Cathar

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.

The math I'v seen has been a bit different from one study to another. But as you say, they do provide a good reference point to start with. But as you know, that's with a flat plate in mind. Throw in furniture, base plate thickness and a different heat source, all that changes. I missed the paper you linked but going to take a look after this.

[SysCrusher]

Originally Posted by 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

LOL ok pHaestus. My humble apologies for the little girl remark. I'll admit, that I was a bit rude on my part. But I still stand in my opinions and everyone has one.

I have modeled the impingement mathematically and have been over it and over it. I won't sit here and go through it with you just for your proof as I assume your just as well versed in it as I am. Neither will I play the "Who's smarter or better" game. Base plate thickness is just another variable in the "whole picture of the block" that one can tailor to benefit the impingement you have. Design the impingement based on the flow/velocity/pressure and use baseplate/furniture to benefit that. With all the different systems and flow rates, the problem becomes unsolvable mathematically - I agree. What it can do is get you somewhere close with the constants you have as a reference point to work from.

[Jabo]

I've just found this
I think it presents all basic theory in quite simple way.

I am spawnig some ideas of how to improve jet design but atm most o them are too expensive to produce (to complicated to machine.

I am off to produce some 3D models to show you

[SysCrusher]

Originally Posted by Cathar

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

Looks like we're somewhat on the same page. I'v seen this one and used it to base my block on also. Though quite different from your cascade design, performs just as good.

What would be interesting is to try a capillary tube design in an array that would benefit pelts but be interchangable plates to use in a IHS design. Machining that would be a nightmare though. I'v got a decent design in the works using that idea but you can forget using any pump less than a L30 or equivilent as it restricts flow to much. Not to the mention the amount of drill bits I killed. Now if i had access to a laser.

Intel has a good white paper you might be interested in also. If I can dig it up again from them I'll post a link to it. It's an interesting read.

[SysCrusher]

Here's something that migh catch your eye Cathar. Check out the chapter called "MICROPROCESSOR POWER AND HEAT FLUX TRENDS"

http://www.intel.com/technology/itj/...cles/art_4.htm

[Cathar]

Ignore this

[Jabo]

Originally Posted by WAJ_UK

There is a bit more to water jet impingement than whether or not the flow is turbulent. It is highly likely that the flow is turbulant anyway at lower reynolds numbers. You need quite a long, extremely smooth pipe for the flow to become turbulant as high as 4000.
But now I'm off to the pub

Typical student

He He He I hope you managed to get yourself properly pi$$ed m8
I used to have my best ideas after two,three tumblers of 18 year old highland single malt

Anyways, what I meant in my post was that turbulence and turbulent flow causes boundary layer to thin down. Jetted water stream is exerting additional localized high pressure causing further thinning of boundary layer over small area (cup). The overall goal is to make boundary layer as thin as possible to achieve otherwise unimaginable conductive heat transfer coeficient (sp?). Optimal distance between cup and nozzle is dependant on nozzle diameter and jet stream velocity. Water exisiting nozzle is shapad like paraboloid function graph due to simple fact that middle of the stream is the highest velocity and the closer to nozzle wals the slower water travels beacuse of friction (viscous) forces (again boundary layer effect). Adjusting distance tries to aim 'peak' of the jet before it starts to turbulate (jet is and must be as laminar in it's flow as possible to obtain the highest speed). The biggest problem with jet design is that it's peak working paremeters windows is quite narrow and that's why Cathar is designing his blocks for certain flow range adjusting z/d accordingly. Imho that's all what could be possibly done in this area.
Looking at the equation I wrote earlier one can clearly see that the next step is to fight for bigger surface area and this is the biggest challange here. Production costs (there are many designs which are MUCH more effective but are exorbitantly more expensive) versus performance ratio is the killer here. Who in his right mind would pay £500 for water block???
I only spent 15 mins on 3D model and it's not yet presentable but I just thought about a clever way to make it feasible to mass produce.
Unfortunately it is going to be yet more expensive than Cather's baby...
T'nite I hope to post my model for you guys to check out and beat the living daylights out of my design

[Jabo]

Originally Posted by SysCrusher

Here's something that migh catch your eye Cathar. Check out the chapter called "MICROPROCESSOR POWER AND HEAT FLUX TRENDS"

http://www.intel.com/technology/itj/...cles/art_4.htm

Yeah, it's like with HP's idea of direct die open air evsporstive CPU die cooling using their piko droplet technology and ultra clear coolants leaving no residues over the hottest parts of silicone. Strangely enough nobody ever heard of it again

The coldet spots are cache areas (memory as we all know do not heat up much). The rest is a mixture of controllers and logic arrays.
Well, the best idea would be to have silicone sandwiching layer through which w could pass veru low energy atoms on much smaller than copper size creating effectively in-die nano cooling solution (quite similiar to Peltier Effect )

[Les]

Originally Posted by Jabo

He He He I hope you managed to get yourself properly pi$$ed m8
I used to have my best ideas after two,three tumblers of 18 year old highland single malt

Anyways, what I meant in my post was that turbulence and turbulent flow causes boundary layer to thin down. Jetted water stream is exerting additional localized high pressure causing further thinning of boundary layer over small area (cup). The overall goal is to make boundary layer as thin as possible to achieve otherwise unimaginable conductive heat transfer coeficient (sp?). Optimal distance between cup and nozzle is dependant on nozzle diameter and jet stream velocity. Water exisiting nozzle is shapad like paraboloid function graph due to simple fact that middle of the stream is the highest velocity and the closer to nozzle wals the slower water travels beacuse of friction (viscous) forces (again boundary layer effect). Adjusting distance tries to aim 'peak' of the jet before it starts to turbulate (jet is and must be as laminar in it's flow as possible to obtain the highest speed). The biggest problem with jet design is that it's peak working paremeters windows is quite narrow and that's why Cathar is designing his blocks for certain flow range adjusting z/d accordingly. Imho that's all what could be possibly done in this area.
Looking at the equation I wrote earlier one can clearly see that the next step is to fight for bigger surface area and this is the biggest challange here. Production costs (there are many designs which are MUCH more effective but are exorbitantly more expensive) versus performance ratio is the killer here. Who in his right mind would pay £500 for water block???
I only spent 15 mins on 3D model and it's not yet presentable but I just thought about a clever way to make it feasible to mass produce.
Unfortunately it is going to be yet more expensive than Cather's baby...
T'nite I hope to post my model for you guys to check out and beat the living daylights out of my design

Would possibly suggest*
h=151.44Re^0.623
for calculating a convection coefficient for 1mm nozzles in a dashpot(bowl or channel urinal).
This generic suggestion is most probably incorrect.However finding an alternative may be difficult and without a reliable estimate of h all CFD(or any other) modeling is completely useless.

* From here




Edit(very late): Mis-read my own graph.
Corrected h=263.66Re^0.643 to h=151.44Re^0.623

[Cathar]

Les, when stating h, and the area associated with it, what are you defining as the area? The area of the heat source? The convectional area? The "net effective" convectional area?

[Les]

Originally Posted by Cathar

Les, when stating h, and the area associated with it, what are you defining as the area? The area of the heat source? The convectional area? The "net effective" convectional area?

Would describe as the average h within a distance of d/5(ish) of a vectorial(terminology?) change in velocity.
Edit. In the WW case the considered area is within d/5(ish, ish) of the die area.
Would tentatively suggest that Impingement is only a special case of a vectorial change in coolant velocity.

[Jabo]

As promised some piccies and explanation.
What I was aiming at was increase of area and actually some increase in pressure (velocity) due to maintained (roughly) cross sectional area after stream leaves nozzle.
Apologies for crappy quality of renderings due to lack of time...

It's only schematic for starters. Red stuff represents blocks base, blue are nozzles and greyish bits represent my 'innovation'.




TOP VIEW


LEVEL VIEW


Last One


The only problem is in manufactruing the damn thing. One could machine it form one piece of copper but costs probably would be greatly prohibitive. Then I thought about drilling hole for each pin. If nozzle is 1mm dia and is spaced by 2mm from each other then pins could be 2.5mm in dia if conoidal or 2.5 square base tapering to a point, which is much easier to make - just take 2.5mm dia hard copper or brass wire , grind it to shape leaving around 3mm for thread at one end, cut thread and screw it into ready threaded hole in baseplate.

What do you think?

[Jabo]

Les, I always thought that we are dealing here with conductive energy transfer, not convectional (vector oriented, usually in static flow, or totally static conditions, in liquids that is) thermal energy transfer.
I may be totally wrong here since I only atrted doing this stuff recently

[Les]

Originally Posted by Jabo

Les, I always thought that we are dealing here with conductive energy transfer, not convectional (vector oriented, usually in static flow, or totally static conditions, in liquids that is) thermal energy transfer.
I may be totally wrong here since I only atrted doing this stuff recently

Think again and again.

[bigben2k]

Nice design indeed.

The pins act as the required fins, and there's still an inpingement effect on the baseplate and, to some extend, up the sides of the pins.

But the proportion of those pins leave a much smaller "fin equivalent". The "Cascade" being the reverse design, the fins are more massive, in higher proportion, and most important: connected.

I'm sure it would be an excellent performer, but I wouldn't bet that it would beat a Cascade just yet.

The main issue I see is that by reversing the design, you have the incoming flow interfere with the second inpingement effect, and adding an almost useless laminar flow parallel to the pins. The secondary inpingement may also end up forming on a plane perpendicular to the baseplate, between the pins, which would be another loss of pressure, without any thermal benefit.

On a scale so small, I'd consider press fitting the copper pins into the baseplate. Got an Enermax around the shop?

[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?

Made a cut-out that is about 1.5mm larger on each edge over the Barton AthlonXP core size (i.e. an 17x10mm rectangle). It effectively blocks off about half of the tubes. The blocked off tubes do receive a small amount of flow as the water flows through the chamfers between the jet intakes.

After some testing, I'm seeing basically at least a full 0.5C improvement with the Iwaki MD30-RZ pump, which I guess is about as much as I would expect.

Re: the XXX. The program is written up and I fixed/tweaked a few things. The machinists won't get time to run until about 10 days away, and even then it's a "maybe". They are being pretty nice to me with the prices they're charging so I can't complain too loudly if higher paying customer jobs hold things up a bit.

[freeloadingbum]

Originally Posted by Cathar

Made a cut-out that is about 1.5mm larger on each edge over the Barton AthlonXP core size (i.e. an 17x10mm rectangle). It effectively blocks off about half of the tubes. The blocked off tubes do receive a small amount of flow as the water flows through the chamfers between the jet intakes.

After some testing, I'm seeing basically at least a full 0.5C improvement with the Iwaki MD30-RZ pump, which I guess is about as much as I would expect..

Blocking off 50% of the jets should make even a bigger difference at lower flow rates. You should get double the velocity at the same flow rate so the cascade may give near the same performance at .5 gpm that it does at 1 gpm without the blockage. This would amount to 1C according to pHaestus' results

[Cathar]

Originally Posted by freeloadingbum

Blocking off 50% of the jets should make even a bigger difference at lower flow rates. You should get double the velocity at the same flow rate so the cascade may give near the same performance at .5 gpm that it does at 1 gpm without the blockage. This would amount to 1C according to pHaestus' results

No, not quite. Blocking off 50% of the jets results in close to double the restriction. Given the way that mag-drive pumps work this would equate to maybe 25% less total flow rates, or about a 50% increase in jet velocity.

Mind you, the MD30-RZ was already pushing about 10LPM (~2.65GPM) through the complete system without the restriction plate, so there's not much correlation that could be drawn with Phaestus's results.

[freeloadingbum]

No, not quite. Blocking off 50% of the jets results in close to double the restriction. Given the way that mag-drive pumps work this would equate to maybe 25% less total flow rates, or about a 50% increase in jet velocity.

I wasn't refering to how it would perform with a specific pump, but how it would plot on a graph which shows performance at specific flow rates.