Quote:
Originally posted by bigben2k
Whoa! I never meant to imply that a thicker base would spread the heat quicker! The purpose of a thicker base is to spread the heat, so that the deltaT is at a point where the water can pick it up better.
|
Yes, sorry. Didn't mean to imply you, or anyone specific in that comment. I've just seen the idea tossed out in various places.
Quote:
Originally posted by bigben2k
Think about an extreme: if the source heat was say 300 degC (assume a 1500W source), the water would pick up a lot of energy, but it certainly wouldn't pick it up fast enough to lower the temp back down anywhere near 20 or 30 deg C.
I think that's where your thinking is at. Yes, a higher temp will transfer more heat, but you're also allowing your source to remain hot.
There is an optimal set of conditions at which the water will transfer the most amount of heat, a.k.a. a maximum efficiency point. You're just shooting for maximum heat, without considering the efficiency of the heat transfer. That's what's biting you in the rear end!
|
Ah!! Methinks you're mixing your apples with your oranges
You've introduced a factor that is independent of block design.
Inside the block, water is being heated. However, that water is also moving. Any given gram of water is being heated only for the short time it remains in the block. The quicker the water is removed, the less heat it will absorb. This sounds bad. *BUT*, the quicker you remove that gram of heated water, the quicker you can get in a *fresh* gram of water that is starting off at the base temperature. This is good. This is the simple reason why increased flow cools faster.
So, to your comment I would answer "it depends on the flow rate." Thinking extremes, At flowrate = infinity, heat transfer = infinity, and the copper touching the water would be at the water's initial temperature all the time and all heat would be absorbed by the water. (Yes, in the real world friction would be a problem. But lets stay in the fake world for a while
) The temperature of the CPU die would be limited only by the thermal conductivity of the copper. Start slowing down the water, and now the water has time to heat up, which slows heat transfer through the copper...the CPU die heats up. So you simply slow down the rate to the point that gives you the cooling you're looking for. This will be true, regardless of the size of the heat source or size of the surface area. Of course, you could end up needing a google of gallons per minute for a given situation, but you will get the cooling you want.
Instead of saying that there is an optimal set of conditions at which the water will transfer the most amount of heat, I would put it as there is an optimal set of conditions at which a particular water cooling configuration will transfer the most amount of heat. I would say this because BillA has already demonstrated what physics says should happen...increase flow rate makes a water block work better. So flow rate must be considered, but the radiator's ability to get rid of that heat must also be considered, as that is the true limiting factor to how much heat can ultimately be removed.
I'm looking at a temp reading right now of 41C on a processor that is known to run really hot (early 2200+) that's running at full load. And this is with a crappy rad and pump. I really can't complain. This block is working well (at least, that's what I'd like to think!
)
And I didn't even lap the base! Just rubbed it on some 400 to clean it up.