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- Jun 17, 2010
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- Marietta, GA
I resisted the urge to break out calculus for an example equation...someone needs to get radeon28 in here, isn't he in thermodynamic engineering?
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1) Ambient + cwdT + awdT = chip temp. If you can make your cwdT smaller then, for the same ambient temp, you will get lower chip temps.
... you've seen how a bad cpu mount can affect temps right? Well that actually DECREASES your water temp as well (albeit very little) a good cpu mount will increase your water temp (once again, nominally).
As I did some testing recently I have the figures for the system in my sig to hand although my sensors aren't particular sensitive but have been 'calibrated' with a known accurate one.
evolvedpc - Thank you, I also understand that now.
As I did some testing recently I have the figures for the system in my sig to hand although my sensors aren't particular sensitive but have been 'calibrated' with a known accurate one. With GPU at idle I get:
Ambient = 23ºC
Load Water temp = 28ºC
CPU Load temp = 63ºC
This was after cleaning my loop and is roughly a degree cooler than it was.
After a point, this all becomes very academic because of the temperature ranges we typically see and can measure cheaply. Personally, I think we need much better temp measurement before any hard conclusions can be made. So we tend to use trial and error or at least educated guesses for our systme sizing etc. Still I suppose good enough to get a general idea what to troubleshoot.
I know in my case it's unlikely to be a problem with the block. I've switched mine round, firstly to see the effect of lapping a block (before and after) and also to see how an old block compared to a recent one (badly, although not as bad as I expected). I'm assuming it's my particular CPU.
I agree. As you said each system is different, but I think the over all approach you have is sound.Yeah - the trouble with this stuff is that there are a huge number of variables to take into account. Comparisons between different systems will not be nearly so useful as comparisons between different iterations of the same system. (e.g. Did that remounted block lower my temps, any?)
However, having an idea of what makes a good value for awdT and cwdT is one thing that we should be able to compare. That will at least give us an indication of whether we've mounted our blocks properly, which is worth knowing!
I agree. As you said each system is different, but I think the over all approach you have is sound.
I've used C/W ratios in the past - C here is usually waterblock or heatsink temp but we tend to use die temp and W is in CPU wattage. Getting a "true" wattage of a CPU is tough when overclocking and overvolting. And not many of us have instrumented our waterblocks so CPU temp is used instead.
I agree that we need to use as similar of methods/data points as possible. I have found that similar to what you stated water temp in and out of the rad is very close. We'd need temperature measurements with a .01 C resoluiton (or better) to really see the inlet to outlet difference. Again another reason to use CPU temp to ambient as you suggest.That raises an interesting point, actually. Each of my loops has 2 in-line temp sensors in it. They tend to read within 0.5C of each other at all times, so I have a pretty good idea of my water temp. As my flow rate decreases, I start to see differences between water in and water out of my rads. Which water temp should we use for our dT values?
I suspect that water in/out of any given block will be so close as to make the question irrelevant for any loop with a workable flow-rate, but for a big rad, with a low (but still workable) flow rate and a high awdT, there is going to be a difference between water in/out. Which should we use for awdT? Is one more correct? Maybe it doesn't actually matter, so long as we are consistent, but if we are comparing my figures to yours, then we need to make sure we are comparing apples with apples.
That raises an interesting point, actually. Each of my loops has 2 in-line temp sensors in it. They tend to read within 0.5C of each other at all times, so I have a pretty good idea of my water temp. As my flow rate decreases, I start to see differences between water in and water out of my rads. Which water temp should we use for our dT values?
I suspect that water in/out of any given block will be so close as to make the question irrelevant for any loop with a workable flow-rate, but for a big rad, with a low (but still workable) flow rate and a high awdT, there is going to be a difference between water in/out. Which should we use for awdT? Is one more correct? Maybe it doesn't actually matter, so long as we are consistent, but if we are comparing my figures to yours, then we need to make sure we are comparing apples with apples.
I would hate to recommend fluid dynamics or heat transfer, cause that involves calculus, diff eq, and tables which will scare people away. Basic thermodynamics can be tackled though with nothing more than Algebra, so its not to scary.
One of these days I might write a "mini-textbook" for watercoolers, which will give all the thermo, HT science, and math they need to understand their systems better, but still make the math simple so heads don't explode... i smell a sticky in my future haha.
Solid Mechanics is that like Continuum Mechanics? My favorite ME course was Computational Fluid Dynamics, but I'll stick with my Thermalhydraulics. Double the phases, double your fun! But I digress.That's a rare statement, someone asking for calculus (even in the engineering community). I'll reserve my math response until my finals are over on the 16th (Solid Mechanics and Design... worthless class imo) and then I promise I'll break out calculus lol...
Not sure your curriculum equivalence but I had incompressible (mostly water/liquids) and compressible fluid dynamics (gas flow shock waves etc) which may be like the Fluid Mechanics I and II? CFD is actually taking the formulae from these "Fluids" courses and developing computer codes to model them. Although mostly moot in todays world as there are off the shelf software codes to do all of this.I don't wanna super hijack this thread, but Solid Mechanics is more along the lines of studying the moments and forces that occur within an object under load or torsion. I'm glad to hear you enjoyed fluid mechanics, cause I'm taking Fluid Dynamics II this fall.
Maybe once I get a "math explanation thread going" I can run the math and theories by you and m0r7if3r... I want it to encompass fluid dynamics, heat transfer, and thermodynamcis, as well as little things as to why, with mathematical backup, stacking radiators don't work and other common questions that can only be truly explained through some math.