1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Cooling So You Want To Watercool Your PC

Discussion in 'Hardware' started by Nexxo, 12 Oct 2005.

  1. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

    Joined:
    23 Oct 2001
    Posts:
    34,079
    Likes Received:
    1,597
    Ever since our ape ancestors picked up the first bone, the first stick, the first flint, turning it over, tentatively weighing it in their hands and examining its potential use as a tool, an important question has haunted us throughout time, and plagued the smartest minds of humanity. That question is:

    “Can I watercool this? And if so, will it perform better?”

    This article aims to inform you of the basic fundamentals of water cooling. This is so you can expand your PC modding horizons, acquire street-cred with the modding crowd, and achieve a Zen-like state of enlightenment. And so you can stop spamming in the Exteme Cooling forums. :)


    The Principle.

    Anyone who has sat in front of a fan knows that moving air cools. This is because the breeze constantly replaces the air around your body, which has been absorbing the heat you radiate, with fresh, cooler air. Heatsinks and fans work in this way: the heatsink absorbs the heat from the CPU, GPU, whatever, and the fan creates a constant breeze of fresh, cooler air to take that heat away from the sink. Of course this process works better when more air can make contact with the surface of the heatsink, so heatsinks are generally built to have as large a surface area as possible. Hence all those fins and spikes.

    The problem is of course, that higher performing hardware has more heat to get rid of, and at some point:

    - air just isn’t cool enough anymore (both literally and figuratively);
    - the heatsink is so large that its weight threatens to snap your motherboard in two (if it will fit at all), causes you massive trauma when you try to lift the case, and requires enough copper for manufacture to supply a medium-sized economy with change;
    - the fan needs to be so powerful that it can lift an Airbus 380, and will shatter your eardrums and turn your insides to pulp with the noise it generates.


    OK, here comes the science bit. Concentrate…

    The issue is one of thermal conductivity, which is expressed in watts per metre-kelvin, or W/(m•K), or simply, k. I won’t bore you with what this all means, because then it gets way too complicated (and believe me, it is). All you need to know is that although a copper heatsink has a thermal conductivity of 385 k, which is good, air (at sea level) only has a thermal conductivity of a piffling 0.025 k. Which is bad --but hey, the heatsink has to lose its heat to something, and radiation just isn’t enough. However water has a thermal conductivity of roughly 0.60 k, which is 24 times better than air.

    Another way of looking at it is in terms of "specific heat". This refers to the amount of heat needed to raise a substance's temperature relative to water. Now air consists (roughly) of 80% nitrogen and 20% oxygen. In the case of nitrogen, its specific heat is approximately 0.25 so nitrogen needs 0.25 times the amount of heat that water needs to raise its temperature by one degree, that is 0.25 calories. In the case of oxygen this figure is about 0.22. So for air as a whole, this figure is roughly 0.24. That’s right, it takes four times as much heat to raise the temperature of water by one degree, as it does air.

    So what do we get? Not only does water conduct heat better, it also can absorb more of it in one pass. So you see the solution: replace air flow over the heatsink with water flow, and presto! Killer cooling.


    Science applied:

    Of course people have known about this for centuries. Back to sitting in front of a fan on a warm summer day: nice, huh? Now take a dip in a swimming pool. Which cools you down quicker? Engineers also know this (but in a much more technical way, involving lots more numbers), and applications of water cooling can be found everywhere, like for instance, in a car engine. We’re going to take a good look at that example because the principle is in fact very similar to what goes on in PC water cooling.

    What you see when you pop the bonnet (or hood, depending on your country of origin) is the following: a header tank containing coolant, traditionally a mixture of water and an anti-corrosive. The anti-corrosive is added to discourage rust and corrosion from forming on the metal components that the coolant gets into contact with. From the header tank tubes lead to a pump (usually driven by the engine, but sometimes also electric) which pushes the coolant through channels in the engine block. This cools the engine. That’s good, but the coolant now needs to get rid of the heat somewhere. As such it carries on to the car radiator, which is exposed to a stream of cool air. The coolant gets cooled down again, and flows from the radiator back to the header tank where the whole cycle starts all over again.

    Now there are some important points here and we’ll tackle them one by one.

    - The header tank is there for a good reason. Not only does it make it more convenient to fill the loop, but when coolant warms up, and expands in volume (as warm things do) it has somewhere to expand to. As such you will note that the tank usually has a “maximum” fill level somewhere below the filler cap, which you are not supposed to exceed. The header tank is also useful for trapping air bubbles that may get caught in the loop;

    - The engine block has channels running through it, which conduct the coolant and allow it to carry heat away from the engine. As such the engine block is also a waterblock…

    - Like with a heatsink, the effectiveness of the radiator is determined by its surface area. As such it has a large number of fins to make maximum contact with the cool air stream, but also a large number of long, winding channels to allow warm coolant to make maximum contact with the radiator (so it can pass on the heat to the radiator, which in turn passes it on to the air stream);

    - Normally a car moving forward at a fair clip produces a decent air stream (as any dog with its head out the window can tell you). This is why the radiator generally sits right in the front of the car. However if you drive, you will no doubt know the frustrations of rush hour, during which your car will often not move forward at all, or only very slowly. As such radiators often have a huge thermostat-controlled fan mounted behind them which will kick in and suck air through when the passive air stream by itself just isn’t sufficient.

    Now if you have been reading all this (as I’m sure you have…), you should now realise that a radiator sounds, in fact, just a glorified heatsink, not mounted on the heat source, but away from it, with water acting as a go-between. It is. But it’s a truly huge heatsink, much bigger than what could be created by just slapping some fins onto a rather compact heat source (like the engine, or a CPU). Some engines do, in fact, go that route (think of motorcycle engines or the engines of some propeller airplanes), but if you want efficient cooling that is not restricted by the dimensions or location of the heat source, water cooling is the way to go.
     
    Last edited: 17 Oct 2005
  2. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

    Joined:
    23 Oct 2001
    Posts:
    34,079
    Likes Received:
    1,597
    Science applied to the PC.

    OK, on to the PC. As we said before, the setup is pretty much the same as in a car. Again, we will look at the components in turn and examine their function.


    The reservoir:

    You again get a header tank, except that it is called a reservoir, or more commonly, “res” because people want to sound really l33t, or (more likely) because they don’t know how to spell the word “reservoir”. Another way to avoid spelling mistakes (or if you just have very little space for a reservoir), is to have a “T-line”: you make a vertical split in your tube which ends in a filler cap of some sort. This is a very simple sort of air trap and again allows for easier filling and draining of the system.


    The pump:

    You again get a pump. Now there are many different types of pump: peristaltic, diaphragm, centrifugal… Each has its own particular design, has its own specific applications and its own pros and cons. For PC water cooling you want a pump that is:

    o quiet,
    o reliable
    o delivers a decent amount of flow at a decent pressure (“head”)
    o and will happily run continuously for days on end without interruption (i.e. a “continuous duty” pump).

    Most centrifugal pumps meet those criteria. Usually PC water cooling pumps have been borrowed from another application where reliability and continuous performance is important, like with an aquarium pump or an electric coolant pump found in a car. Lately manufacturers have cottoned on to the PC water cooling scene and are actually designing pumps specifically for the purpose.

    How does a centrifugal pump work? Take a bucket of water, and spin around your axis very fast. You will notice how centrifugal forces want to pull the bucket (and water in it) away from you. Let go of the bucket and it will fly away from you with some force (At this point I should perhaps have mentioned to do this in your garden, not the living-room). A centrifugal pump works the same way. Imagine a round chamber with a propeller in it (in this case called the “impellor”). An electric motor drives this at high speed, causing it to “grab” the water in the chamber and fling it against the outside wall with some force. At one point in the wall is an outlet, and this is where the water escapes.

    As water shoots out of the chamber this way, a vacuum is created inside it, and nature abhors a vacuum... Conveniently, in the center of the chamber above the impellor is an inlet, through which water is sucked in to fill the vacuum, and the whole cycle continues.

    This is why centrifugal pumps do not like restrictions of the inlet. At the outlet water comes out with considerable speed and pressure, but if the vacuum cannot be filled quickly enough, the pump is starved of water and the flow stalls. Just as pressure is created at the outlet, underpressure is created at the inlet. If, due to an inlet restriction, this becomes too big, water in the chamber starts to become gaseous and you get cavitation: a rattling and foaming of the coolant that is bad for your pump and bad for your ears…

    You also want your centrifugal pump to be a magnetic drive pump. This means that rather than there being a shaft connecting the motor with the impellor in the chamber (which requires a water-tight seal, which will wear and cause leaks) there is a spinning magnet at the motor end, the pump chamber wall, and a spinning magnet at the impellor end. This is so no direct connection between the pump motor and impellor exists (and so that no liquid can leak from pump chamber into the motor housing).

    The radiator:

    You get a radiator (also called “rad”). In design it is basically much the same as the one you find in a car (only smaller). It is so similar, in fact, that some PC water cooling radiators are simply car “heatercores”. Heatercores are like small radiators tucked behind the car dashboard except that the air passing through them is heated up by hot engine coolant to provide cabin heating. Because of their compact design they work a treat in PCs also, this time to cool water down.

    Because a PC will not barrel down the highway at 60mph, but generally stays stationary on or under your desk (don’t let the wheels on a Lian-Li V1100 case fool you), there is no unassisted (“passive”) air flow through the radiator at the best of times, so generally you also get a case fan mounted behind the radiator to suck the air through, thus creating a constant air flow. In between the fan and the radiator should ideally be a shroud. This is because the fan has a “dead spot” right over the hub of the propeller. As such, putting your fan right on top of the radiator would mean that about 11% of the radiator surface does not get airflow, which is rather a waste of good cooling potential. Moreover you can get more turbulence and noise.


    The waterblocks:

    You get one to several waterblocks (also simply called “blocks”) to mount on the heat sources (the CPU, GPU and any other chips you may wish to cool); This, of course, is the water cooling equivalent of a heatsink which now needs to be a closed unit (because water spilling all over the inside of your PC is bad, mmmokay?). It consists of at least two parts, made of aluminium or copper which join together to form the block with a channel running through it. The channel is usually in a spiral or zig-zag pattern to allow it to have a large surface area for heat to transfer, while impeding the flow of water as little as possible, but sometimes the insides simply consists of a hollow chamber in which you can see suspiciously heatsink-like structures like fins or pins. The underside of the block looks pretty much like a heatsink also. Installation of a water block is similar to that of a heatsink also, with a thermal pad or thermal grease placed between it and the chip being cooled to aid heat transfer.


    Tubing:

    You get some tubing to connect the lot. This comes in three main flavours: silicone, PVC or Tygon.

    - Sillicone is soft and flexible, but does not look that great. Moreover it is slightly porous and water will evaporate through its walls in the long term;

    - PVC looks prettier, but kinks easily when it is forced in a tight curve (and kinks are restrictions, and restrictions are bad, mmmokay?). It also tends to yellow with age. Put some nice UV CCFLs in your case and this process is accelerated;

    - Tygon is the daddy of all tubing. It looks good, is flexible, curves around pretty tight bends without kinking, does not yellow and it is not porous. The reason why it is so good is because it was created for laboratory applications. This makes it rather good stuff, but also rather expensive.

    For those who balk at that sort of expense, there now is also Clearflex: a sort of “I can’t believe it’s not Tygon” substitute. It is a fancy form of PVC with most of the advantages of Tygon but none of the cost.

    Tubing is connected to the in- and outlets (the “barbs”) of the components in different ways, depending on the type of barbs. We will come back to this later.


    Coolant:

    Last but not least you get the coolant—again water with an anti-corrosive, except that the water here is distilled or de-ionised water. Tap water has too many impurities in it: limescale, algae spores, bacteria… although our digestive tract manages (but then again it manages cola), PC water cooling components are not as forgiving. What you basically have is water that warms up to a pleasant temperature as it cools your PC. Add to that a window, and/or some UV light sources, and you create an interesting incubation environment for algae and anaerobic bacteria to grow in. This then creates an interesting gunk which in the end will clog up your system. That’s why it is better to stick with distilled or de-ionised water.

    In a car, this is not an issue because the coolant there easily heats up to near-boiling point. Nothing survives that (well, nothing does that lives in tap water. There are actually plenty of algae and bacteria living near underwater volcanic vents that feel quite happy in boiling temperatures).
     
  3. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

    Joined:
    23 Oct 2001
    Posts:
    34,079
    Likes Received:
    1,597
    The water cooling process in the PC:

    The cycle is pretty much the same as in a car engine. Coolant is sucked from the reservoir into the pump, which pushes it through the waterblocks (where it warms up) and subsequently through the radiator (where it cools down) before it returns to the reservoir where the whole cycle repeats itself. As with a car engine, it does not really matter much whether the coolant goes to the radiator first or to the waterblocks first (or even in what order it visits those waterblocks), as long as it does at some stage, before returning to the reservoir. Simple, no?

    Just as with the car, PC water cooling is a solution designed to mount the heatsink away from heat sources which are too small, and in too awkward a place to enable slapping on a massive heatsink with a huge surface area exposed to plenty of cool air locally. Instead the “heatsink” (now the radiator) is put in a different place where there is plenty of room, and plenty access to cool air, with water as the go-between.


    But hang on, water in a PC?!?

    At this stage someone usually pipes up that they learned somewhere that water and electricity don’t mix. They would not be wrong: putting your hairdryer in your bathtub does NOT make a nice Jacuzzi. So water in a PC?... Well, it depends, really. For those of you who have an electrically heated shower at home, have you never considered that somehow both water and on average 9000 Watts of electricity come together inside that plastic box to generate the warm water that comes out of the shower head? And you’re standing in it? The reason that no-one has ever been electrocuted by these quite ubiquitous showers is that despite their flimsy appearance on the outside, they are really well designed on the inside. There is no way that water and high-voltage electricity can ever meet. With PC water cooling it is the same; build it well, test it thoroughly and it should work just fine.

    However Charles Dickens once wrote that the biggest scourges of mankind were Ignorance and Want. This is also the case with PC water cooling: everyone Wants to do it, but many people approach it with a staggering amount of Ignorance… Cock it up and be assured to lose a few thousand of pounds hardware, instantly (cock up really badly and stand to lose your life, or at least your eyebrows). Be careful. Be thorough. Be informed. This ride is not for the ignorant. But if all the other modders out there can do it, then with a bit of common sense, so can you.


    The Why of PC Water cooling:

    So why do it? We already examined some of the reasons above. Hardware is getting more powerful, but as a result also more power hungry. As a result of that, it gets hotter and needs more efficient cooling. Another reason not addressed earlier is the “Will it perform better?” question. That is a lot harder to answer.


    The power, the power!

    One way to squeeze more out of your PC is to overclock the hardware beyond its specifications. A direct consequence of this is that it also runs hotter, and it is important to have more efficient cooling to compensate for this extra heat. This does not mean however that cooler chips necessarily means faster chips (not unless you think of superconduction at temperatures of -270C which, unfortunately, is just outside of the reach of technology which basically consists of a radiator, some tubing and an aquarium pump). First, there are many other factors which impose limits on an overclock, of which temperature is but one (there is also signal noise to consider for instance, voltage limits, other components in the PC creating a bottleneck etc.). So once a CPU has reached its maximum stable clock speed, it doesn’t much matter whether it runs at 30C or 60C. It’s nice to have some headroom for those really hot summer days or if you want to throttle down the radiator fan to reduce noise, but beyond that it’s just bragging rights.

    Here it is important to remember that with PC water cooling, you will never get your CPU below room temperature anyway (in practice rather a bit higher than that). If you get, say, 35C you are doing really well. This is, basically, because heat always flows from a warmer object to a cooler object, and if your CPU were cooler than room temperature, the water would have to be cooler than room temperature, and consequently, so would the radiator. In that state of affairs, heat would actually flow from the surrounding air to the radiator and warm the coolant up. So it ain’t gonna happen, is it? Moreover, speed of heat transfer depends on difference in temperature. The hotter the CPU/radiator, the faster it will transfer that heat to the water/air, but as this difference gets smaller, you get diminishing returns. At some point bigger radiators and more powerful fans just won’t make a difference anymore. But that’s OK, because once your CPU has reached its overclock limit, it does not matter whether it runs at room temperature or 10 degrees below zero.

    There are ways, of course, to get your chips below room temperature (“below ambient” as it is also called), but this involves esoteric devices like Peltiers, which we will not discuss here. This is about the basics of water cooling, and if you need to read this you are not yet ready for extreme water cooling.


    The bells, the bells!

    Of course, water cooling being efficient means that you can cut down on those tiny 60mm heatsink fans that scream away like a sawmill. Instead you can slap one or two slower, more efficient 120mm fans on the radiator, which produce more airflow for their RPM and an altogether more agreeable, lower pitch hum. If you have a really big radiator, you can do away with fans altogether and rely on convection only, i.e. the principle that warm air rises and thus creates a slow, vertical breeze over your radiator all by itself. In short, PC water cooling is not only more efficient, but also quieter and stops your PC from being a complicated sort of vacuum cleaner (i.e. makes lots of noise and sucks up lots of dust).
     
  4. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

    Joined:
    23 Oct 2001
    Posts:
    34,079
    Likes Received:
    1,597
    Choosing the components:

    The first question everyone asks is: “what do I need?” You shouldn’t have to, however, if you have read the above, because it tells you there. If you are asking that question, then either you skipped the above and have started reading right here, or you read the above but not quite absorbed it all. Either way you should stop here NOW and read all the stuff you just skipped (or didn’t absorb). You can’t get down to the doing before you have the understanding.
    You need:

    - one or more blocks (one for each component that you intend to cool);

    - a reservoir or T-line;

    - a pump;

    - a radiator;

    - one or more fans for the radiator, preferably with a shroud;

    - tubing and tubing fasteners/clips;

    - coolant;

    - know-how.

    What you do NOT need is:

    - the biggest-ass pump you can find;

    - multiple reservoirs;

    - more than (the equivalent of) a 3x120mm radiator (I mean, really);

    - to watercool absolutely everything in your case. Choose wisely. Some things, like the NB or harddisks manage fine with a good passive heatsink or some airflow;

    - a loop more complex than an industrial beer brewery.

    I'm not saying that you might not want to have these things, you just don't need them. Elegance is key...


    to be continued...
     
    boiled_elephant likes this.
  5. M_D_K

    M_D_K Active Member

    Joined:
    3 Apr 2002
    Posts:
    6,184
    Likes Received:
    23
    Dude your a legend :) lets hope this brings down the silly questions, anyway of highlighting it so it stands out more from the other stickies ?? or make it flash PINK lol



    morgan.
     
  6. Marvt74

    Marvt74 New Member

    Joined:
    29 Mar 2004
    Posts:
    199
    Likes Received:
    1
    Great post dude :)
     
  7. hughwi

    hughwi Well-Known Member

    Joined:
    23 Dec 2003
    Posts:
    1,584
    Likes Received:
    36
    That... is amazing! Informative but not in a condescending way.
     
  8. kiljoi

    kiljoi I *am* a computer king.

    Joined:
    13 Oct 2003
    Posts:
    2,301
    Likes Received:
    0
    Cheers Nexxo! :thumb:
    Being a WC n00b myself, this is a great read. Now I fee like I can at least have a foot to stand on when I start to WC my rig (hopefully soon).
     
  9. Shadowed_fury

    Shadowed_fury Active Member

    Joined:
    21 Nov 2003
    Posts:
    7,506
    Likes Received:
    21
    Great post ;) Typical nexxo style too!
     
  10. nookie

    nookie New Member

    Joined:
    28 Mar 2005
    Posts:
    34
    Likes Received:
    0
    This is very interesting post but even if you don't learn something new its worth to read it as it is writen in a very amusing way. Bravo! :D
     
  11. hitman012

    hitman012 Active Member

    Joined:
    6 May 2005
    Posts:
    4,877
    Likes Received:
    19
    Excellent post, very well written.
     
  12. lbreevesii

    lbreevesii New Member

    Joined:
    18 Oct 2005
    Posts:
    26
    Likes Received:
    0
    great thread. Can't wait to read more.
     
  13. pdf27

    pdf27 New Member

    Joined:
    6 Jul 2006
    Posts:
    169
    Likes Received:
    1
    What do I need to cool xxxxx?

    One of the common questions on the forum is along the lines of "how much do I need to cool system xxxxxxxx". It's actually quite a simple question to answer, but requires a small amount of thermodynamics.

    First of all, we need the temperature difference between water and silicon. This is defined by two things - the design of your waterblock and how fast you can pump water through it. Contrary to popular myth, there is no such thing as a waterblock "optimised for low flow" - all waterblocks will work better with higher flows through them (see following post). Some waterblocks will suffer less badly than others from low flow, however.
    A general rule of thumb is that pressure head is more important than peak flow in choosing a pump. As for water blocks, ask around on the forums - ProCooling used to produce good test data, but they're no longer testing the latest blocks so are out of date nowadays. For a good system, depending on exactly how hot it is you're looking at a temperature difference of between 5°C and 15°C.

    The next stage is the difference between the water flowing through the radiator and the air leaving the radiator. This is generally pretty small - for a modern radiator such as the Thermochill PA series you're looking at 1-2°C in almost all cases.

    The final stage is the difference between the ambient air entering the radiator and the hot air leaving it. This is actually the easiest place to improve system performance, and the one that is IMHO most often ignored.

    So, to recap, CPU temperature = (silicon-water temperature difference) + (radiator water-outlet air temperature difference) + (radiator inlet air-outlet air temperature difference). For the rest of this article, to simplify things I'm going to assume that outlet air temperature is the same as the water temperature.

    Conservation of energy of course means that the power dissipated by the radiator is equal to the amount of heat being dumped into the system - usually the TDP of the water cooled components plus the power draw of the pump (10W or so).

    (TDP + pump power) = (mass flow of air per second in kg) x 1010 x (Temperature difference between air and water in °C)
    Where 1010 is the specific heat capacity of air at constant pressure in J/Kg.

    One cubic foot of air has a mass of 0.034 kg, so the above formula can be simplified to

    (TDP + pump power) = (CFM of Fan) x 0.572 x (Temperature difference between air and water in °C)

    So what does this leave us with?

    CPU temperature = (silicon-water temperature difference) + (TDP + 10)/(CFM of Fan x 0.572)
    Assuming that the pump draws 10W, which is pretty typical of most current watercooling pumps.

    A final cautionary note on the CFM of the fan - this is NOT the rated CFM of the fan, but rather the amount of air it can push through your radiator.
    Like pumps, fans have two important values - the maximum flow of air they can push for no pressure difference across them, and the maximum pressure difference they can sustain across them for no flow. If you plot a graph of pressure against flow, these two points will typically be joined by some sort of flow.
    Your radiator will have a similar characteristic, but in reverse - the more air you want to push through it, the higher the pressure drop across it is needed. You can plot the two curves on the same graph, and the point where they cross is the operating point for that fan on that radiator.
    Unfortunately, this isn't terribly helpful - while some fan manufacturers like Sunon publish these curves, most don't and even when they do it's hard to find the data. Worse, radiator manufacturers rarely publish anything at all. However, it does give us some idea of what to look for and what to expect:
    1) Radiators with wide open fins, or ones with a larger than average surface area per fan are a good thing for getting better air flow per fan.
    2) Thicker fans are a good thing for radiators - 120x38mm fans will have the same flow rate but a higher peak pressure compared to 120x25mm fans.
    3) As a rule of thumb you can probably only expect to get half the rated CFM of a fan actually pulled through a radiator - less if your radiator gets clogged up with dust.

    So that leaves us with something along the lines of:
    CPU temperature = (silicon-water temperature difference) + ((TDP + 10)/(Rated CFM of Radiator Fan(s) x 0.28)) + (Room Temperature)
     
    Last edited: 7 Jun 2007
  14. pdf27

    pdf27 New Member

    Joined:
    6 Jul 2006
    Posts:
    169
    Likes Received:
    1
    Of Pumps and Boundary Layers...

    One of the problems people commonly have in understanding waterblock design and implementation is the concept of the boundary layer. It's pretty fundamental to all fluid dynamics - and relatively simple to understand - so I thought I'd explain it here.

    At a molecular level, every surface is extremely rough. That means when a surface is exposed to a fluid, the fluid next to it will stick to it and won't move relative to it. A long way from the surface, of course, the fluid will be moving at speed. This layer of stagnant fluid is known as the boundary layer, and is absolutely critical to fluid mechanics.
    It's pretty easy to see this effect in action for yourself. Stand out in a wide open space on a windy day, and feel the wind on you. Now lie down on the ground, and feel the wind at ground level - it will be massively less, and right next to the ground itself it will be gone altogether.

    The reason a boundary layer is so important to us is that stagnant water is a very poor conductor of heat - so the bigger the boundary layer, the worse your cooling system will work. Water blocks deal with this in two common ways - turbulence and impingement.

    Turbulence is the most common way - and until recently the only way. If water is turbulent - swirling in all directions randomly - it mixes very well. It will tend to mix with the top of the boundary layer, increasing the speed of the fluid in it and so making the boundary layer as a whole thinner.
    There are two major ways of creating turbulence - increasing the flow speed (for example by running the water through thin channels), or by "tripping" the flow - maybe by using small pins or serrated edges. Most GPU blocks use this method in one form or another.

    Impingement is a more modern method, and is only used in some blocks (e.g. the Little River series of blocks, Danger-Den TDX, etc.). In reality it's a way of creating very intense turbulence in a particular place controlled by your design.
    What happens is that the surface you want to create the impingement on is blasted by a jet of high velocity fluid. This penetrates vertically into the boundary layer, where it creates intense turbulence. This both blasts away and increases the velocity of the water in the boundary layer, making it drastically thinner and thus improving performance.

    How does this affect pumps? Well, a block that uses the impingement method will probably never reach particularly high flow rates for most pumps - at high flow rates, it will take a massive pressure to force the water through, more than the pump can supply. Thus, peak head is really the only number to worry about for this type of block.
    For blocks that use the turbulence method - particularly those using channel flow - you need a more balanced pump. Peak head is still important because ultimately it's pressure that drives your flow rate, but peak flow starts to become more important. This is because the total pressure drop in your blocks will be substantially lower, thus you will be further to the right on the pressure/flow graph and more affected by the peak flow of the pump.
     
  15. pdf27

    pdf27 New Member

    Joined:
    6 Jul 2006
    Posts:
    169
    Likes Received:
    1
    Comments/questions? I'll try and add some suitable graphs/pictures tonight if I get time (babysitting a vacuum pump at work at the moment, so can't find the right pictures). My writing style could probably use a lot of improvement, but hopefully it's understandable enough.
     
  16. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

    Joined:
    23 Oct 2001
    Posts:
    34,079
    Likes Received:
    1,597
    Great contribution, pdf27! Vital information and some really useful formulas. Your writing style is clear and spot-on. :thumb:
     
    Last edited: 7 Jun 2007
  17. M_D_K

    M_D_K Active Member

    Joined:
    3 Apr 2002
    Posts:
    6,184
    Likes Received:
    23
    Just to keep it at the top of the page :) great addition pdf27 :).

    Also read through your posts again Nexxo and am chuckling to myself about the Res/Reservoir thing lol and other whitting digs.
     
  18. airchie

    airchie New Member

    Joined:
    22 Mar 2005
    Posts:
    2,136
    Likes Received:
    2
    Excellent info Nexxo and pdf.

    I suggest to the Bit staff that they stick some pretty images in it and make it an article on the front page.. :)
     
  19. Krikkit

    Krikkit All glory to the hypnotoad! Super Moderator

    Joined:
    21 Jan 2003
    Posts:
    23,453
    Likes Received:
    368
    Nice info pdf27, just what we needed. :)

    I vote for immediate stickification. :thumb:
     
  20. pdf27

    pdf27 New Member

    Joined:
    6 Jul 2006
    Posts:
    169
    Likes Received:
    1
    Anything else people would like me to cover?
    <still babysitting the same vacuum pump - it's only tried to blow itself up once so far today, and I'm getting very bored>
     
Tags:

Share This Page