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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. |
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10-22-2004, 05:52 PM | #1 |
Cooling Neophyte
Join Date: Oct 2004
Location: Texas
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Inlet and outlet temps = no difference. How can that be?
Seems like when you think you are starting to understand something, a cold fish slaps you in the kisser to keep you humble.
I added another thermistor on my outlet so as to have one on inlet and outlet. Before that I made sure both agreed when exposed to several different temps. Basically, and I am really confused about this, there is no difference between inlet and outlet. If I really throw serious VCore like 2.2 at it there is a 1C difference. How could this be? Gee, I actually thought I was starting to understand this stuff. Would really appreciate some comment and help to understand this. |
10-22-2004, 06:00 PM | #2 |
Put up or Shut Up
Join Date: Dec 2001
Location: Spokane WA
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In and out temps only very by .5C or less. Probably not enough accuracy in the equipment to measure it. Hence the difficulties to properly test blocks.
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10-22-2004, 06:27 PM | #3 |
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Yep.
http://www.nordichardware.com/articl...vattenkylning/ Go to page 2 for the formulae: P*t/(C*m)=DT Where: P=power t=time C=constant 4190 J/(kg*K) m=mass of water DT=temp difference |
10-22-2004, 07:23 PM | #4 |
Thermophile
Join Date: Jun 2001
Location: The deserts of Tucson, Az
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Water has an astronomical specific heat capacity. The change in temperature is simply too miniscule for your equipment to detect.
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10-22-2004, 07:55 PM | #5 |
Cooling Neophyte
Join Date: Dec 2003
Location: Rochester, NY
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Hurrah for the laws of heat transfer and thermodynamics.
Now if I could only figure out how to solve those damn differential equations.....
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10-22-2004, 08:59 PM | #6 | |
Cooling Neophyte
Join Date: Oct 2004
Location: Texas
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Quote:
Along those lines, and since I have liberally applied the butter, have you run across any in depth testing of the popular pumps where the the amount of heat dumped into the circuit was measured in lab or semi-lab conditions? I'm particularly interested in the 12 volts pumps where the cooling effects of flow changes, via overvolting or undervolting, might be negated by changes in the waste heat. My question may not be clearly stated, so let me clarify a little. If you increase flow via overvolting, you would also increase the heat dumped into the system which may negate any cooling gains. Inversely, lowering the voltage might decrease flow but also decrease heat dump. I'm basically trying to find the X spot. People talk about using 2 Swiftech pumps in series, yet they consume 25 watts each so that is 50 watts. Since I don't know how much heat is dissipated from the case to air and how much is dumped into the loop, it is hard to judge whether that would be a good idea. 50 watts into the loop seems self defeating? I'm sensitive to this because I installed a groundloop and added a larger pump rated at 70 watts to replace my 10 watt fountain pump. It increased my flow like crazy, yet drove up cpu and inlet temps. That was a real eye opened and I don't think I would have noticed if I did not have the constant temp of the groundloop constantly monitored in front of me. Any information you can point me to would be appreciated. Last edited by DDogg; 10-22-2004 at 09:08 PM. Reason: clarification and spelling |
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10-22-2004, 09:12 PM | #7 |
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The heat added is relatively negligeable, and IMO, poorly understood. Myv65 and I had a lengthy discussion on this, some time ago.
Let me know if digging up the thread would help: I'll be more than happy to look it up. |
10-22-2004, 09:33 PM | #8 | |
Cooling Neophyte
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10-22-2004, 10:31 PM | #9 | |
Thermophile
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Quote:
Furthermore relatively little energy is added by the pump. 10 or 20 watts means very little when a CPU is putting out 100, and a GPU 60. Combine the excess radiator capacity with low heat input, and the result is generally a negligable change in temps in all but the most extreme cases. |
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10-22-2004, 11:35 PM | #10 | |
Cooling Neophyte
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Location: Texas
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Quote:
10, 20, or 50 watts is just that - watts. Heat is heat, isn't it? Each system has an ability to sink a certain amount of heat. If you add more the system has to compensate by finding a higher temp to achieve equilibrium again, so I think it could be said that the potential extra heat dumped into a system by a pump could cause that shift in equilibrium. Let's look at it in another way. When you increase VCore you are increasing heat output. What? 10 watts maybe per .1 increment (just pulling that completely out of the air to illustrate the point). If a pump dumps just 10 watts into a system, in effect it would be the same as increasing VCore by .X At that stage it is not insignificant anymore because it is actually costing you higher VCore potential. At least that is how it strikes me as an OC'er. As said, I'm no pro or engineer. Just a country boy tinkerer, but I wonder if this is not a subject that could bear further scrutiny by those that do have this stuff down cold from a proper math and engineering standpoint (and hopefully those that do not lovingly embrace the concept of "conventional wisdom"). /Add: BTW, redleader, that is not a barb directed at you. Rather one directed at the general BS that gets handed back and around over and over. This subject may not be one of those, but then, it may be. Something I can say from absolute certainty. There is not one member of this forum who would not appreciate all pumps being reviewed with the added information of how much fluid temp is increased above ambient in a closed loop for a 10 hour cycle, or something similar. Then you could make a better buying decision by knowing: Pump A is 450 GPH 14 ft head - 11C rise on closed loop cycle/ 55 watts Pump B is 350 GPH 12 ft head - 2C rise on closed loop cycle/ 12 watts I know I would sure not be interested in Pump A, would you? BTW2: I don't have a radiator, I have an external fixed ground loop/sink. I can't turn up the fan to make it better. Last edited by DDogg; 10-22-2004 at 11:59 PM. |
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10-23-2004, 02:41 PM | #11 |
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10-23-2004, 08:18 PM | #12 | |
Cooling Neophyte
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Location: Texas
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Quote:
I'm coming to really appreciate the Swiftech's performance on 25 watts. Given the specs of the pump, it must be very efficient. I suspect the pump that gave me trouble was a very inefficient one, Heck, like I said, you could not hold it. Literally, it would have burned your fingers after 5 seconds or so. I wonder how much heat the MAG5 pumps dump into the loop. People may not be getting the great deal they think they are. |
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10-23-2004, 10:50 PM | #13 | |||||
Thermophile
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Sort of the whole big piece of a small pie or small piece of big pie thing. Quote:
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Edit: Sorry I had to leave the library I was typeing this post in and walk a few blocks to another building with a computer. Hence the edit. Last edited by redleader; 10-23-2004 at 11:07 PM. |
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10-24-2004, 12:10 PM | #14 | |||
Cooling Neophyte
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Given that, isn't it then factual to say the amount of heat put into a loop by the pump directly effects the inlet temp which directly effects the CPU temp? Quote:
Presently my inlet temp from the gloop is 28C. VCore/CPU Temp= 2.03/48C, 2.06/50C, 2.075/52C, 2.10/53C, 2.125/54C, 2.150/56C So yes I have measure it to a point. Nothing real scientific. IIRC, when I was on the radbox and opened the window on a chilly morning where ambient air to the rad was around 20C, I could run 2.125/48C. I did not have the inlet sensor installed at that point so I can't quote inlet temp directly. Quote:
Remember my semi-rant (sorry for that) started when many good and knowledgeable people insisted that more flow would be better without ever mentioning the negative effects of pump heat dump. This is a glaring omission in my book and one that should be considered as important as GPH and Head. I grabbed a 300 GPH pond pump and flow increased very substantially, yet inlet temps and the corresponding CPU temps increased. I think the pump I tried was particularly inefficient and so effected my temps more than if I had bought a proper pump more designed for our use. I have a feeling I monitor my inlet temps a little more intensely than many. Because of this I picked up on the problem quickly. I do wonder how many folks are out there that thought, like I, that a pump is just a pump and that it was all about GPH and Head. That is clearly not so. Pump heat dump is an important part of the equation and I don't think that can be disputed. I'm thinking there may be a lot of folks that may actually have higher CPU temps because of buying low efficient pumps. My central point is that GPH and Pump Head, without the corresponding information on heat dump, makes it impossible to evaluate a pump purchase. There is certainly a point where the increased flow can not offset the increased heat input into the loop by an inefficient pump. That's just an indisputable fact, I believe. Without factual information on the pump efficiency/ heat gain, one is just taking a potshot at when buying a no name pump. |
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10-24-2004, 12:18 PM | #15 |
Cooling Savant
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Your new, higher flow pump offered higher temperatures because of the higher heat. Estimates put the heat output (inline) from a pump to be 50-60% of the power drawn. Try your overclock with the big pump that offers higher temperature. It may in fact be better despite higher temperatures.
Since the energy is constantly being transferred, we're talking joules, not watts. Joules are for one time things, like combustion. |
10-24-2004, 12:56 PM | #16 | ||||
Cooling Neophyte
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10-24-2004, 01:16 PM | #17 | ||||
Cooling Savant
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It should be, "Since the energy is constantly being transferred, we're talking watts, not joules. Joules are for one time things, like combustion. |
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10-24-2004, 01:37 PM | #18 | |
Cooling Neophyte
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Quote:
I think you are speaking of the pinprick hot-spot stuff that I read about somewhere a while back. It made the point that while CPU temps may not increase, lower flow allowed 'mini-pockets' or 'pinpricks' of heat to develop in the die surface. These mini-pockets of heat buildup were not enough to raise the CPU temp noticeably, but they would cause CPU failure due to 'junction failure', or something like that. Makes some sense I guess. :-) Got a direct link laying about for Cathar's stuff you mentioned? If not, maybe I can find it. Thanks. |
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