|
|
General Liquid/Water Cooling Discussion For discussion about Full Cooling System kits, or general cooling topics. Keep specific cooling items like pumps, radiators, etc... in their specific forums. |
Thread Tools |
08-16-2004, 09:36 PM | #1 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
Water Cooling Myths
Watercooling Myths Exposed
Written by Greenman100 (Tim Elmore) edited by members at ProCooling. Disclaimer: The following is the work of a team of technically minded individuals who worked together to make the facts as correct as possible. However, one should not believe everything they read on the internet blindly, and if you have evidence that contradicts the information presented here, fell free to voice your thoughts. Myths about Water and Flow Myth: Water must slow down to fully absorb heat. Reality: In a closed loop, a given water molecule actually spends the same amount of time in the radiator no matter how fast it is moving, as long as the water is indeed moving. If this is a difficult concept to understand, think about a racecar on a track. If the track is 1 mile (5280 ft) long and the car is driving at 60 mph, the car will spend about 1 second in a 100 ft stretch. Think of the 100 ft stretch as the radiator. Now, if the speed is doubled, the car only spends ½ a second in the 100ft section, but it passes through that same section twice a minute, so it spends a total of 1 second in the 100ft section per minute. If this is unclear, please post. Myth: Order of components makes a significant impact on temps. (e.g. radiator must be before CPU) Reality: Order of components makes a difference of less than .5C in most watercooling systems. The physics: pump---->radiator---->CPU---->pump pump---->CPU---->radiator---->pump There is only one difference, and that is the position of the pump in the loop, be ir before it after the CPU. Assuming the pump dumps about 50w of heat into the water, and flow rate is 1GPM (very reasonable): Water has a thermal capacity of 4186J/Kg-C at 22C, and a density of about 1g/mL With a flowrate of 1GPM, that’s ~3.75LitersPM. 3.75LPM/60 seconds= 0.0625Liters or Kilograms through the waterblocks per second. 4186*0.0625=261.625W/C So that's 1C warmer for every 261W But only 50 watts of heat are present, so: 50/261.625=.19C So, there is a .19C difference in water temperature between the inlet and outlet of the pump. This does not mean the water is only .19C warmer than air, that is an entirely different calculation. And that’s with 50 watts. If you’re running a smaller pump, like the D4, you're looking at 15w or so. So, do what allows for the simplest tubing runs, tubing length/kinking will have a greater impact on temps. Myth: Pump power consumption makes a significant impact on temps Reality: It is difficult to know exactly how much heat a pump dumps into water, but a good rule of thumb is the following: An inline pump generally dumps 70-90% of its heat into the water. A submerged pump dumps 100% of its heat into the water. A dual 120mm radiator with a decent fan is good for about .03C/W, with a decent pair of 120mm fans. That is, the water temps will rise 1C for every 33 watts in the water. So, if your pump dumps 33 watts into the water, water temps will rise 1C. Therefore, the difference between a Mag3 at 40w and an Iwaki WMD-30 at 90 watts is fairly insignificant; 32w into water versus 72w, so about 1.1C. Note that the performance of a waterblock will improve with diminishing returns as the pressure increases. Myth: A pump's flowrate is the only consideration to make when choosing a pump Reality: A pump's maximum head pressure is just as, if not more important. Waterblocks are relatively restrictive, and many aquarium pumps are not made for that kind of restriction. In order to estimate one's flowrate, Calculate all pressure drops, then overlay on top of the pump's P/Q curve. In other words, it's not easy, but consider head pressure, too. Myth: A t-line must be at the top of the system or water will leak out when you take the top off. Reality: If the water were to leak out, air would have to replace the water. Since the entire rest of the system is sealed, air can’t get in to replace the water. Thus, no water will leak out of an opened t-line, unless there is a leak in the top of your loop Myths About Materials/Coolants Myth: Aluminum absorbs/dissipates heat faster than copper Reality: All thermal properties of copper are better than aluminum. The only advantage to aluminum is that is lighter. So, if one were given a pound of copper and a pound of aluminum, you could make a better performing heatsink with the aluminum. However, this is not directly applicable to watercooling, as weight is very rarely a factor. Myth: Gold is the best thermal conductor. Reality: Diamond (6-50w/cm-k, dependent on purity) is actually best, but too cost prohibitive. Silver (4.173w/cm-k ) is second, and copper (3.937w/cm-k) is a close third. Gold’s thermal conductivity is 2.913w/cm-k. It’s primary use is its electrical conductivity, and resistance to corrosion. The reason for this is that gold is largely chemically inert, and thus will withstand many harsh environments. Graphite has many different thermal conductivity values, ranging from .6-10 w/cm-k, dependent on the formulation. Sources: http://www.ai.mit.edu/people/tk/tks/tcon.html http://www.pyrographite.com/pyrogr.htm Myth: Mercury would make a good coolant. Reality: Mercury is way too environmentally unfriendly to be used in a non-industrial cooling system. In fact, engineers studied using mercury to cool a power plant. If mercury is too unsafe for workers working around a controlled nuclear reaction, it probably has no business in the home PC. Speaking of the home PC, if you ever did have a leak, liquid mercury is a very good electrical conductor, and would leave you with a dead motherboard rather quickly. Mercury vapor is poisonous. Myth: Antifreeze improves the thermal properties of water Reality: Antifreeze is actually makes the thermal properties of water worse, and is 18 times thicker at room temperature, resulting in more backpressure and slightly lower flow. However, in a multiple metal loop (like aluminum and copper) antifreeze or some other anticorrosive is needed to keep metals from galvanic ally reacting, resulting in corrosion. Antifreeze is good at raising the boiling point of water and lowering the freezing point. Unless you are boiling your CPU (not recommended) or running below ambient (see condensation myth) then you are not in need of those two characteristics. Myth: Bleach is a good coolant additive. Reality: Bleach is actually very corrosive, as indicated by both its datasheets and ionic makeup. The chemical formula for bleach is NaOCl, Which is ionic and in water becomes Na+ and OCl-. Ions in solution will lead to galvanic corrosion, as previously noted, as well as bleach's natural tendency to corrode. Source: http://www.fact-index.com/s/so/sodium_hypochlorite.html Myths About Temperatures and Measurement Myth: On-board temeprature sensors are accurate. Reality: You shouldn't even ask what someone else's temps are. This is one of the biggest problems i see in forums. YOUR temps are not even accurate relative to your own system, much less someone else’s. Let me elaborate. Just because your board reads 41C does not mean that if the temps drop 5C in real life the board will read 36C. Motherboards are not "absolutely accurate", nor are they "relatively" accurate. This is even worse with in-socket monitoring while watercooling. It is quite possible for the area around the socket to heat up to 50-60C, and influence the temperature measurements of the in-socket thermistor. Myth: Digidoc5/ThermalTake/Vantec temperature monitors are accurate Reality: While generally not as easily influenced by other factors, generally these sensors are off by more than +-3C. that means if your sensor is reading 3C high, and your friends is reading 3C low, you could be off by 6C on your comparison. More accurate sensors are available, the questions is whether that is important to you. The point is, do not believe onboard/digidoc temps. You shouldn't even tell other people what they are, they are so inaccurate. Tell them your overclock. There is very little inaccuracy in mhz measurements. Myth: Condensation will form when watercooling. Reality: The water in a watercooling cannot get any lower than the temperature of the air around the watercooling system/flowing through the radiator. In order to make th water colder than the surrounding air, energy must be applied either in the form of a compressor system or a thermoelectric device, both of which will cool the water, sometimes below ambient. The temperature point at which water condenses is a function of both temperature and humidity. Myths About Waterblocks Myth: If a block is shiny, it will conduct heat better. Reality: In reality the flatness of the block is what counts. Flatness ensures maximal contact with the CPU and minimal TIM necessary to bridge the gap between. Shiny just looks nice. It is also of note that hand lapping a flat machined base will only make the base worse, if the base was fairly flat from the factory. Myth: You can tell how a waterblock will perform just by looking at it. Reality: The only way to know for sure is to run a highly calibrated test with a well thought out method. Thanks to: Cathar for the racetrack analogy, and several corrections and comments. Crimedog for doing a search on OCers for me when I was unable to. nikhsub1, Etacovda, Razor6, AngryAlpaca, and DrMemory for corrections and comments. All of those not names previously who have given me an education in the field of watercooling in general. Add any i missed, and correct me where I'm wrong I'm thinking of submitting to pH and OCers
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp Last edited by greenman100; 08-17-2004 at 09:13 PM. |
08-16-2004, 09:47 PM | #2 |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
As an update to the ordering of components myth, the only difference between:
pump->cpu->radiator vs pump->radiator->cpu is the additional pump heat as the water flows through the pump before it gets to the inlet of the CPU block. The size of the difference is therefore a calculation based upon the heat that the pump adds to the water, and not the CPU. For almost all pumps and blocks that are in common use, the difference is actually substantially less than 0.1C if the math is done. More commonly down around the 0.05C mark. |
08-16-2004, 09:53 PM | #3 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
good point cathar, I was goign with more of a difference between hottest and coldest, but that doesn't address the myth
also, you will be credited for the racetrack analogy in the final version, because that's where I got it from any other comments?
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 09:55 PM | #4 |
Cooling Neophyte
Join Date: May 2004
Location: Tuscaloosa, AL
Posts: 53
|
Cool. What about using pums in series. Does this make for better cooling?
__________________
SYSTEM: A64 3000+ @2.42Ghz w/CO stepping | Chaintech VNF3-250 | Sapphire 9600 Pro | 2x512MB Corsair PC3200 | Enermax 460w PS | 2x80 gig IDE HD | WATER COOLING: DangerDen Maze 4 CPU waterblock | Hydor L20 waterpump |Homemade reservior | Heater core| biketour.blogspot.com |
08-16-2004, 09:56 PM | #5 |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
Other points of note, a single 120mm radiator with a fan of tolerable noise level has a C/W of more like 0.05, rather than 0.02. Significantly alters the complexion of the pump heat maths. Lots and lots of variables on this one, but a fairly dumb rule of thumb of the pump not having more than about 20W of rated nominal power draw per 12x12cm area of radiator space actually works pretty well.
The only basis of the aluminium vs copper dissipation myth is that based solely upon weight. It is possible to construct an aluminium heatsink that weighs less than a copper heatsink, and dissipate heat better. If we ignore weight and just keep all dimensions equal, copper always wins. The real clincher here though to bring the point home is that the commonly accepted formulas for either passive or forced convectional heat transfer is not dependent upon the properties of the surface of convention, other than the area of that surface. Since aluminium, all sizes being equal, is more costly to conduct heat from somewhere else to that surface than copper, then this is why aluminium is typically worse. Last edited by Cathar; 08-16-2004 at 10:02 PM. |
08-16-2004, 10:06 PM | #6 |
c00ling p00n
Join Date: Jun 2002
Location: L.A.
Posts: 758
|
Never heard anyone think gold was the best metal for heat conduction. Never the less, Silver is the best metal as you have stated, you did forget graphite which is just under diamond. You may want to put using bleach as an additive is horrible, I have seen it all too often. I would also state in the component routing that one is better off with the least amount of bends and tubing and it should designate what order the components go in. Looks good, now let's see if we can get the ignorant to actually believe the truth.
Oh, the last myth should be: MYTH; you can tell a blocks performance by just looking at it I actually got that one the other day
__________________
*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:* E6700 @ 3.65Ghz / P5W DH Deluxe / 2GB 667 TeamGroup / 1900XTX PC Power & Cooling Turbo 510 Deluxe Mountain Mods U2-UFO Cube Storm G5 --> MP-01 --> PA 120.3 --> 2x DDC Ultras in Series --> Custom Clear Res "Artificial intelligence is no match for natural stupidity." 1,223,460+ Ghz Folding@Home aNonForums *:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:* |
08-16-2004, 10:08 PM | #7 |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
Maybe extend the description of gold being that it is the best heat conductor that is largely chemically inert and not prone to tarnishing, even in harsh environments. This is why gold gets used for various thermal and/or electrical applications. It is, as you've explained, not the best conductor of heat/electricity though - it's just the best that is most stable for a wide range of harsh environments.
|
08-16-2004, 10:08 PM | #8 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
edit2: tweaked pump myth to use AC pumps and more realistic C/W figure
edit3: added to cu/alu myth, added graphite, added bleach nikhsub1, I've seen it, I'm sure others have too
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 10:11 PM | #9 |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
Mercury was once originally considered as a coolant for nuclear power plants. Upon extensive studies and tests, it was eventually decided that it was far too dangerous and toxic to use, and this is even for the fission nuclear energy crew. If these guys think it's too toxic and dangerous to consider using it while sitting atop a controlled nuclear explosion, the average home user has no real right to think that perhaps they know better.
|
08-16-2004, 10:20 PM | #10 |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
Anti-freeze (ethylene glycol) is actually about 18x thicker than water at or around 20-30C. Anti-freeze does two major things - it lowers the freeze point of water for people who live in snow-bound countries, it raises the boiling point of water which under pressure allows cars engines to run at optimal temperatures.
Anti-freeze has a specific thermal capacity about 1/3rd that of water, meaning that it heats up more per unit of energy, and its added viscosity increases the effort required to reach turbulent flow conditions, effectively lowering the Reynold's number for any given flow rate resulting in lower thermal transfer. Glycol becomes substantially more "runny" at the ~120C operating temperature range for car engines, and this coupled with increasing the boiling point of water is why it "helps to cool a car engine more efficiently". It only "improves" the thermal properties of water in its alteration of water's freezing and boiling points, thereby extending the useful operational temperature range of water. It does not actually make water a better conductor of heat. |
08-16-2004, 10:25 PM | #11 |
Cooling Savant
Join Date: Feb 2004
Location: Dunedin NZ
Posts: 735
|
Even basics such as "You'll get condensation with watercooling" would be good.
A bit on temperatures is probably the most needed (the amount of people that swear black and blue that their onboard sensors are correct is pretty amazing) |
08-16-2004, 10:30 PM | #12 |
Cooling Savant
Join Date: Apr 2002
Location: Houston, TX
Posts: 192
|
So if you doubled your heat from say 100w to 200w, say by adding a gpu and chipset block, the temperature of the water would not go up by even 1c? Since in real life the flow would drop as a result of more blocks being added, for the question assume the flowrate stayed the same through the loop.
|
08-16-2004, 10:33 PM | #13 | |
Thermophile
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 2,538
|
Quote:
|
|
08-16-2004, 10:35 PM | #14 | |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
Quote:
at point 1: ok at point 2: I'm trying to keep this watercooling oriented....comments have been made over AIM by others about TEC myths....lets take on one battle at a time
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
|
08-16-2004, 10:40 PM | #15 |
Cooling Savant
Join Date: Jan 2004
Location: Alberta
Posts: 631
|
Greenman, the sensors read higher if there is no fan involved, so with watercooling it's frequently higher than with technically warmer aircooling. It's relevant. On that note, though, I suppose that something about lapping doesn't apply.
|
08-16-2004, 10:45 PM | #16 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
cathar, will clarify pump myth
angry, this is only true for insocket temps, but by popular request, will add I take it me spending this time is a good thing?
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 10:46 PM | #17 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
and angry, what myth would you have to dispell about lapping?
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 10:47 PM | #18 |
Cooling Savant
Join Date: Jun 2004
Location: Dallas, TX
Posts: 101
|
Mercury is also an excellent electrical conductor and even a very small leak could lead to a dead motherboard.
|
08-16-2004, 10:49 PM | #19 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
haha, will add, drmemory
though that would be the least of my worries if a leak developed.
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 10:55 PM | #20 | |
Cooling Savant
Join Date: Apr 2002
Location: Houston, TX
Posts: 192
|
Quote:
|
|
08-16-2004, 10:58 PM | #21 | |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
Quote:
understood here, yes go spend some time at OCers, you will see the light (or darkness?)
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
|
08-16-2004, 11:07 PM | #22 | |
Cooling Savant
Join Date: Jan 2004
Location: Alberta
Posts: 631
|
Many people that improving the finish by lapping will increase performance, while lapping will make the base less flat and so worse contact is had. Bill Adams supports this opinion, apparently,
Quote:
|
|
08-16-2004, 11:12 PM | #23 | |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
Quote:
ok, way not true maybe a myth for your myth? if a base is indeed not flat, lapping will help speaking of Bill Adams: "I still have the TC4 I tested, after days of lapping" emphasis all his http://www.ocforums.com/showpost.php...4&postcount=26 are you saying he lapped it to worsen performance? again if not flat, handlapping will help
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
|
08-16-2004, 11:14 PM | #24 |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
not a good idea to spread misinformation though a "myths exposed" article.
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
08-16-2004, 11:16 PM | #25 | |
Cooling Savant
Join Date: Jun 2004
Location: Florida
Posts: 414
|
Quote:
haha, I saw that
__________________
"Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." --Socrates "greenman100 = obnoxious ass hole"-gazorp |
|
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
|
|