Waterblocks effectiveness in terms of power dissipation

[bigben2k]

I've had that dP kindly calculated for me (see details in Radius thread). I can share this formulae with you (or try to post it here, PM me).

Calculations were based on fluid properties, flow rate, and nozzle size. Results include dP (and speed?).

I was also kindly reminded to look into hypersonic (or was it supersonic) flow speeds... (I was assuming 4 gpm ).

[bigben2k]

Originally posted by SysCrusher
The pump may well do a 14 foot head but try to get a 14 foot head with a 3/16 id hose. Does that pump have the required pressure to push the water now in the same distance? It's the limitation of the impeller called back pressure.

I'm assuming that you're not trying to imply that the pump's behavior does not correspond to it's curve.

I simply used a bucket of water at the inlet. Granted that there was a 1 foot rise, but I honestly expected the water to shoot up 15 feet, not 10. I have to revisit that test sometime, and see how I can get it right . I know that my previous calculations were wrong.

[SysCrusher]

Originally posted by Les
Without accurate data would not like to add to further to my "evasion".
Have found trying to estimate dP in different ID nozzles beyond me.
Will leave the "evasion" posted - graphs quite pretty(and maybe informative




Would be most interested in any links to any of this work.All are intuitively attractive.

That's ok Les, I understand. I'm not here to belittle anyones education or way of thinking but to discuss and learn something new from what data that is present.

Here's some links.
An impingement database but you have to pay. Why? So I can't link to any information.
http://www.eevl.ac.uk/jet/index.htm

Various links I collected.
http://www.electronics-cooling.com/h...01_may_a2.html

http://home.icpf.cas.cz/vejrazka/web...ew_booklet.pdf

http://web.cvut.cz/cp1250/fme/k212/p...ta/h06%5Ea.htm

http://www.stanford.edu/~xzm/Research/Reno2003.pdf

http://widget.ecn.purdue.edu/~eclweb/jet_benchmark/

http://fcl6.kaist.ac.kr/people/phd/pts/article.pdf

http://216.239.57.100/search?q=cache...n&ie=UTF-8</a>

Calc to calculate heat transfer of impingement. No idea how accurate it is.
http://www.coolingzone.com/Content/D...as/fcalc10.htm

Then there is the libraries but you have to pay for each copy of an article. Their more informative than these links. What ever happened to free imformation via the internet for the people?

[Les]

Ben.
Thanks for the offer.For the moment, further dP sums are not on my agenda so will give a miss.

SysCrusher.
Thanks. 50% are new to me.
As you are aware, I have used and abused the the Flomerics calculator for both Cathar's WW* and the Switech462**.
I do get reasonable( my opinion) , if accidental, agreement with Billa's test data.

* http://forum.oc-forums.com/vb/showth...hreadid=161563
** http://forum.oc-forums.com/vb/showth...hreadid=161124

[murray13]

Originally posted by SysCrusher
Les, that's true if the id stays the same. Sure, you will lose velocity and pressure the more .25 id holes you have. If you smaller holes to equal the same pressure and velocity of one .25 id hole, their the same not including geometry.

No, not quite. If the ID stays the same and you add more holes of the same D then the pressure drop will be the SAME. The flow rate (gph) will increase.

You can NOT decrease the diameter of the opening with the same pressure.

[SysCrusher]

Originally posted by murray13
No, not quite. If the ID stays the same and you add more holes of the same D then the pressure drop will be the SAME. The flow rate (gph) will increase.

You can NOT decrease the diameter of the opening with the same pressure.

I'll chew on this one for awhile. I "think" I see your point but still I don't see the logic in it.

[SysCrusher]

Originally posted by Les

SysCrusher.
Thanks. 50% are new to me.
As you are aware, I have used and abused the the Flomerics calculator for both Cathar's WW* and the Switech462**.
I do get reasonable( my opinion) , if accidental, agreement with Billa's test data.

* http://forum.oc-forums.com/vb/showth...hreadid=161563
** http://forum.oc-forums.com/vb/showth...hreadid=161124

Here's another link Les. It challenges what I said about multiple jets in a previous post. I just might try it once more and see what results I get. I'm quite interested in this impingement. I believe with a well designed impingement one will get results that rival micro-channels.

http://micromachine.stanford.edu/~lian/jetcooler.html

[gone_fishin]

Here is a cut and paste from a publication. The author is in the paste so it should be alright to post it here.

Quote
"Article number: 1321
Title: Effect of nozzle geometry on impingement heat transfer distribution from jet arrays
Author: Owens,R.D. and Liburdy,J.A.
Year: USA, 6-8 August, Vol. 1, ASME HTD 303, 3-10
Abstract: Heat transfer distributions were determined for flat surfaces using three different 3 x 3 jet-impingement arrays. Each array used a different jet orifice cross sectional geometry, either circles, triangles, or ellipses. For each geometry, the jet-to-jet spacing divided by the hydraulic diameter, was three. Five flow rates were tested with Reynolds numbers ranging from 268 to 1557. For each flow rate, the four jet array height-to-jet spacings (H/D) of 2, 3, 4, and 5 were tested. All of the parameters presented, such as the Reynolds and Nusselt numbers, were based on the orifice hydraulic diameter. In order to determine the heat transfer distributions for each condition tested, thermochromic liquid crystals were used as part of a transient heating test method. In the majority of the tests, the ellipse array performed the best, with the triangular orifice close behind. Also, of the three orifice geometries, the ellipse had the lowest pressure drop. The heat transfer improvement was especially predominant at low Reynolds number.
Publication: Proc. 30th 1995 National Heat Transfer Conf., Portland,"
End quote

Click to jet impingement database search engine

I'll dig some more. I recall reading a strange phenomena with the ellipse. It (the jet profile) will invert itself on the impingement surface at the right conditions for a benefit in heat transfer.

[bigben2k]

Originally posted by unregistered
Les
I think Ben is a masochist

ok Ben
wtf you talkin' about ?
2 - 12 is enough spread to cover an ocean
SysCrusher was referring to a 462-B, and you ?

ahh, I see your latest post
so what does a java calculator have to do with your determination of "best" ?

this is drivel
why do you need to add such tripe to your already inflated post-count ?

get serious Ben

All right.

I found my other source of "confusion".

When designing/calculating a nozzle within a pipe, the formulaes used assume that the distance passed the nozzle is at a minimum of 10d.

So I now conclude (incorrectly?) that the pressure drop in a jet inpingement configuration is composed of 2 things:

a)pressure drop across the nozzle

b) pressure drop caused by the jet striking the baseplate.

Now is there actually a pressure drop from [b], or is this configuration merely affecting the nozzle's performance, throwing off any calculations? If there is a pressure drop, is it calculable?

[myv65]

Originally posted by bigben2k
[b]b) pressure drop caused by the jet striking the baseplate.

Now is there actually a pressure drop from , or is this configuration merely affecting the nozzle's performance, throwing off any calculations? If there is a pressure drop, is it calculable?

The easy answer is that "yes", the baseplate will have an effect at the velocities and gaps we operate within. The tough answer is determining the effect. There is no analytical solution, only simulations. Accurate testing is the best bet.

[SysCrusher]

Originally posted by myv65
The easy answer is that "yes", the baseplate will have an effect at the velocities and gaps we operate within. The tough answer is determining the effect. There is no analytical solution, only simulations. Accurate testing is the best bet.

The velocity at which it strikes the baseplate stays the same. Only after it strikes the plate does velocity drop because of surface geometry, friction, surface tension(think the last is correct). In the case of submerged, surrounding water effects velocity also which I found out the hard way. As you get further out in diameter from the stagnation area and up to the ouside diameter of the impingement wall the greater heat transfer. So the base plate in it self can effect the results of the impingement.

This is the question I keep running through my mind. If there is micro-channels or any surface geometry that causes enough pressure drop, will it render the jet impingement useless? I'm leaning towards the answer of "yes".

[SysCrusher]

Originally posted by gone_fishin
Here is a cut and paste from a publication. The author is in the paste so it should be alright to post it here.

Quote
"Article number: 1321
Title: Effect of nozzle geometry on impingement heat transfer distribution from jet arrays

I have seen those. Their should be another about ellipse. If you find that one I like to have it. I lost it some where between my links, papers and a kid.

I seen one about how the angle at which the ellipse jet was orientated to the plate performed well.

[Cathar]

Originally posted by SysCrusher
This is the question I keep running through my mind. If there is micro-channels or any surface geometry that causes enough pressure drop, will it render the jet impingement useless? I'm leaning towards the answer of "yes".

As a guy who somewhat surprisingly doesn't know the full theory behind it (the 90% rule here) my answer goes like this.

For a fine-channel (I say fine - because the term "micro" is open to subjective interpretation) setup given a particular channel width, I believe that there is a pretty tight range of values that specifies the "optimal" fin width and height. This implies a direct relationship between channel width and fin height.

Now given a particular range of operable pumping pressures, say 2-4PSI for the pumps that people typically use, this then (in my mind) places a lower bound on the usable channel width before the pressure drop becomes so high that the pump can't pump enough appreciable volume through the channels, and this will result in a performance loss as the water itself heats up too much because there is not enough heat mass in the liquid.

What I'm saying is that problem is self-balancing. The point at which the jet impingement would begin to suffer would also be the point at which the micro-channel implementation would begin to suffer as well, that is, it is possible to make the channel so fine and restrictive to "damage" the jet impingement action, but in doing so you will be losing performance in other places as well, so the problem as you describe is self-defeating given a correctly ratioed fin/channel width/height micro-channel system.

The question then becomes one of "what is then the smallest micro-channel dimensions that you can use effectively with a 2-4PSI pump". I already have a fair idea of the answer to that question, but it is also tempered with the need for secondary blocks in the system to not have their performance hampered in a significant fashion by a singular restrictive block in the system, so the answer suddenly takes on a new perspective.

[SysCrusher]

Originally posted by Cathar

The question then becomes one of "what is then the smallest micro-channel dimensions that you can use effectively with a 2-4PSI pump". I already have a fair idea of the answer to that question, but it is also tempered with the need for secondary blocks in the system to not have their performance hampered in a significant fashion by a singular restrictive block in the system, so the answer suddenly takes on a new perspective.

I have an idea as well but no experience to back it up. I failed to realize the thought of extra blocks in the system. Thanks for the new sudden perspective.

I fully understand what you saying. It is a delicate balancing act and finding that balance is the key without the expense of effecting something else in the chain. Atleast, not to much. You ever try something with a 50 PSI and decent flow rate? To bad I can't find a pump like that.

I'm still going to try the total impingement design. If anything to learn even if it doesn't perform as expected or as I thought.

[Since87]

Originally posted by airspirit
I think Ben's first post was on the mark 100%. This is NOT measuring the cooling power at all.

An easy way to describe this would be to take two blocks, one of high resistance, and one of low resistance. Looking at the original equations, you would raise W by increasing the resistance of the block. Raising the resistance of the block would lower the flow rate. Lowering the flow rate decreases the efficiency of the block, and you get higher temps.

Conversely, with a low resistance block, you get more flow, and more efficiency, and while W goes down, temps lower as well.

The perfect waterblock would draw heat from the die in the most efficient manner possible while providing the least amount of resistance to flow. Increasing the resistance of a block and thereby increasing the amount of time a slug of coolant remains in it will NOT lead to better temps. While I commend you on the effort, I think you are measuring a different type of force, not the cooling potential of the block.

If I thought that just dissipating power in a waterblock would cool my CPU, I'd simply set up my watercooling system out in the garage and wouldn't bother mounting the waterblock on the CPU.

You think I'm suggesting that increasing the power dissipation in a water block is good, in and of itself? Not even close.

The fact of the matter is, for any given block, there is a relationship between the hydraulic power applied to the block, and the thermal resistance of the block. Within limits, the thermal resistance of the block decreases as more hydraulic power is applied. Because a waterblock is part of a system including (usually) a centrifigual pump, considering issues related to transferring power from the pump to the block is important. (It's not necessary to look at the system in terms of power transfer to determine how well it will cool, there may not even be any particular benefit to doing so, it's just a viewpoint that comes 'naturally' to me, and I find it interesting to consider watercooling systems in these terms.)

Because I'm an electrical engineer, I tend to think about a lot of this stuff in electrical analogies. One tool from electrical engineering that appears somewhat relevant is The Maximum Power Transfer Theorem. In short, it says that if I have a voltage source with a resistor permanently attached to one of its output leads, then to get the maximum power into the load, I need to connect a load with the same resistance as the permanently attached resistor.

This would be more directly applicable to watercooling systems if flow resistances behaved akin to Ohm's Law or:

dP = Rf * Q

Where:
dP is pressure drop
Rf is flow resistance
Q is flow rate

Instead, flow resistances generally behave as:

dP = Rf * Q^2

Because centrifugal pumps behave somewhat like ideal pressure sources in series with an inherent flow resistance, a modified version of the Maximum Power Transfer Theorem may be applicable enough to be useful. From the very limited number crunching I've done so far, it appears that the maximum power will be transferred to the load, when the load resistance is twice the inherent resistance of the (idealized) pump. I'll let someone who's had a math class much more recently than I, attempt to prove or disprove this.

The following graph shows the PQ curve for an Eheim 1048 pump as well as the following equation as some indication of how accurate a simple simulation of a pump might be.

dP = 1.5 - 0.015 * Q^2 (1.5 is the max head, and 0.015 is the inherent flow resistance)



It's getting too late at night to go on with this now. Some examples of looking at watercooling systems in terms of power transfer tomorrow night.

[myv65]

Originally posted by SysCrusher
The velocity at which it strikes the baseplate stays the same.

Only if the flowrate remains constant. You would find that as the gap became smaller, the flow would also drop. The generic answer is that "downstream" stuff affects "upstream" stuff if the flow velocity is less than the speed of sound within the medium. Our velocities are much, much less than the speed of sound in water. So the question becomes, "How big must the gap be given the jet size, speed, etc., before changing the gap has no appreciable effect?" I suspect the answer would be single-digit millimeters, but that's merely a hunch.

[airspirit]

Maybe this is a boob thing to say, but here goes:

Isn't the benefit of the nozzle realized in the increased flow velocity over the point in the block where most of the heat is concentrated, thereby allowing more efficient heat transfer in the liquid? In other words, the coldest fluid is pounded against the hottest surface to get maximum heat transfer, while still allowing the exiting water to absorb some more heat from the rest of the block (where the microchannel portion comes into play, increasing the surface area thereby making heat absorbtion easier).

The jet allows you to replace the fluid on the "hot spot" at a faster clip, and turbulates the coolant directly on that spot. Without the nozzle, you would have more of the coolant slipping across the top of the channel, not cooling the hot spot as effectively, requiring it to spill more heat laterally across the block before it is absorbed rather than allowing a larger portion of it to be immediately absorbed into the coolant.

Microchannels are nice, especially at distributed heat transfer, and jet impingement is nice to reduce the necessary size of the block. I think the effective use of both is why Cathar's block works so well.

[bigben2k]

Yes...

In order to improve the heat transfer to the coolant, we have to try to reach a high Reynolds number (aka turbulent flow). Since 99.9% of us can't do that, because it requires a veri high pressure pump, we use jet inpingement to "throw" the coolant at the baseplate, which results in a turbulent area, similar to the above. Turbulent flow, without the high pressure pump.

Add fins, whose purpose is to spread the heat further, from the baseplate, and you'll reduce the resulting CPU's temp.

Combine both (above) and you've got an ideal waterblock. That's what Cathar did, yes.

But it can still be improved

[SysCrusher]

Originally posted by myv65
Only if the flowrate remains constant. You would find that as the gap became smaller, the flow would also drop. The generic answer is that "downstream" stuff affects "upstream" stuff if the flow velocity is less than the speed of sound within the medium. Our velocities are much, much less than the speed of sound in water. So the question becomes, "How big must the gap be given the jet size, speed, etc., before changing the gap has no appreciable effect?" I suspect the answer would be single-digit millimeters, but that's merely a hunch.

This is true, only if flow rate is constant and concure that the smaller the gap the less flow. I done tried it. Your hunch is right though. With our low pressure pumps, anywhere between 2 - 6mm depending on the size of the jet being used.

Couple of interesting thoughts. How much of an effect the angle of the jet and the actual shape of the base plate play a role? It's quite surprising.

[Cathar]

Another thing to consider here is the width of the jetted area.

The WW design doesn't really care how wide a heat source is that straddles the fins. It effectively "slices" that heat source up, and treats it as a series of elongated strips that run the length of the channels. This is a simplistic view of things, but given the thin base-plate, isn't too bad of an approximation. This basically means that a heat source under a channel can be effectively viewed as a 8-12mm long strip that needs to be cooled. This means that our useful jet impingement region needs to hopefully be around the 12mm wide mark within the channel.

Now myv65 was onto something when he talks about what I call diminishing returns with respect to making the nozzle smaller than a small number of millimeters. For a 3PSI pump like an Eheim 1250, the smaller the nozzle is made, the higher the water velocity, but to a point. Eventually you reach a stage where the water velocity goes up VERY slowly as the nozzle is decreased in size. A bit like plotting a hyperbola.

Now there are a few things going on here that need to be balanced. As the nozzle is reduced, so does volumetric flow. It's pretty easy to plot the raw C/W of water vs volumetric flow. Short of phase changing the water, it's impossible to get a better C/W than that line - you can only ever hope to be as close to it as possible. So as we reduce volumetric flow rate through a smaller nozzle, we can reach a point where the volumetric flow decrease overwhelms the gain from the marginally higher water velocity.

There's a second effect that happens here too. The width of the nozzle also dictates the width of the jet impingement region. The higher the volumetric flow rate, the wider the jet region. Also, the wider the nozzle, the wider the region - to an extent - if the nozzle is made too wide then no real jet region forms and the water just mashes out the side and never really hits the base hard where we want it.

So here it can be seen that there is again a fine balance point. I spent a lot of time, theory and practise behind the scenes away from any public discussions tracking down what I believed to be the optimal nozzle width for standard pump applications with the White Water.

It's easy to think that making the nozzle smaller will boost velocity and hence performance, but the reality is that it's not that simple. There are many things to consider here, and it's not all that obvious at first glance.

[SysCrusher]

Originally posted by Cathar

Now myv65 was onto something when he talks about what I call diminishing returns with respect to making the nozzle smaller than a small number of millimeters. For a 3PSI pump like an Eheim 1250, the smaller the nozzle is made, the higher the water velocity, but to a point. Eventually you reach a stage where the water velocity goes up VERY slowly as the nozzle is decreased in size. A bit like plotting a hyperbola.

Depends on what your block design is and it's surface geometry. Throw in micro channels and too small of a nozzle size will kill the flow rate to the point your channels no longer function as intended. Your right. Can only make the nozzle diameter so small till the point that velocity levels off and then drops along with flow rate.

Originally posted by Cathar

It's easy to think that making the nozzle smaller will boost velocity and hence performance, but the reality is that it's not that simple. There are many things to consider here, and it's not all that obvious at first glance.

I found that out also. Making it smaller will just kill the flow rate to the point the impingement is useless. Shape of the nozzle effects the impingement region also which I find interesting. The circlular impingement is actually the worst compared to an ellipse, triangle, the square in that order. Have to consider the shape to work with in your design and take advantage of it. There is alot of variables to keep in mind. One will effect the other and there is a balance in it all. Impingement by it's self I believe can be very promising.

[Cathar]

Originally posted by SysCrusher
Impingement by it's self I believe can be very promising.

Totally agreed - the question I guess is how promising it is given 3PSI pressures that people use?

Given 50PSI pressures, it's definitely the way to go.

The old theory vs practicality thing. Then again, I guess that if we all had 50PSI pumps, then we'd be looking for more still.

Ever considered using one of those high-pressure jet-sprayers that are used for cleaning mud and crap off cars and engines? I've always been curious if the rapid pulsing effect of the flow would create favorable turbulence by rapidly increasing and decreasing the jet impingement radius, and the pumps can typically push up to 600PSI or so. It'd be a "cheapish", if rather noisy, way to conduct the experiment, and when you're done with it, you get to clean your car too.

[Since87]

Originally posted by Cathar

There's a second effect that happens here too. The width of the nozzle also dictates the width of the jet impingement region. The higher the volumetric flow rate, the wider the jet region. Also, the wider the nozzle, the wider the region - to an extent - if the nozzle is made too wide then no real jet region forms and the water just mashes out the side and never really hits the base hard where we want it.

I think you can see an example of this in BillA's MCW462-H vs MCW462-UH data.

One can compare the thermal resistance of the two blocks at operating points with equal inlet nozzle velocity. Even though the MCW462-UH is has a greater volumetric (and mass) flowrate at the same inlet velocity, the MCW462-H still has lower thermal resistance.

[BillA]

and there is also data on different internal surfaces in the 462-B modding article

[gone_fishin]

Originally posted by Cathar
Totally agreed - the question I guess is how promising it is given 3PSI pressures that people use?

Given 50PSI pressures, it's definitely the way to go.

The old theory vs practicality thing. Then again, I guess that if we all had 50PSI pumps, then we'd be looking for more still.

Ever considered using one of those high-pressure jet-sprayers that are used for cleaning mud and crap off cars and engines? I've always been curious if the rapid pulsing effect of the flow would create favorable turbulence by rapidly increasing and decreasing the jet impingement radius, and the pumps can typically push up to 600PSI or so. It'd be a "cheapish", if rather noisy, way to conduct the experiment, and when you're done with it, you get to clean your car too.

Or you could use one of them sewage line cleaners Just don't get your hand in the way or it's a quick amputation.