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Originally posted by Joe
Your pump DOES add heat. it may be a very small amount, but you cant deny that the pump transfers some heat to the coolant. Now in a optimum situation, where would you want the coolant to go next? right to the thing that you are trying to cool? or to a heat exchanger to remove that heat before it goes to the thing you want to cool?
Logic would dictate that you would want the lowest temp coolant to go to the object you are cooling, so you should have a heat exchanger right before that object to remove any heat that the system as absorbed in its loop before that.
Also some pumps DO generate a good deal of heat. The Hydrothruster is a good example, as well as a few of the other high end pumps. I did a test a few months ago on my Hydrothruster and at full bore with no fan on the radiator running in a loop with no CPU the water heated up to around 100F in 30 min and would have gone higher, with a small fan on the radiator it dropped 10 DegF to 90F with an ambient temp if 73F. With a 120mm fan the coolant remained at around ambient or a degree or so above.
This shows that the pump CAN put a good amount of heat in the coolant, if you have something that is pre heating the coolant before the core wouldn’t you want to have that coolant cooled off more before it hit the core?
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I'm not disputing that pumps can produce a good deal of heat. The thing is that the heat from the pump does not only heat up the water between it and the heat exchanger!
In a system, heat adding components are the waterblocks and the pumps. Heat loss components are radiators and the lines themselves. Now, the heat loss components are passive, meaning that they don't move heat by doing work like a peltier does, they remove heat by optimizing conditions for convection.
What does all this mean? This means the system must reach a temperature where the heat is lost at the exact same rate as it is gained.
Why is this? This is because the rate of heat gain is constant, but the rate of heat loss is proportionate to the temperature difference between the heat transfer medium and the ambient. That means the hotter the water the faster it will lose heat, given ambient temperatures stay constant.
Now, returning to our problem, what happens is that the pump's added heat requires water in the entire loop to heat up, in order for the rate of heat loss to be able to match the rate of heat gain.
So in summary, if the pump raises the temperature of all the water in the system by an equal amount, what difference does where the pump itself is make?
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As for the radiator ambient temp deal. Isn't the output of the radiator always better if its at ambient or as cool as possible? Yes i know keeping a higher flow rate through the block will give an overall more "averaged" heat up cycle to the coolant, there will be a very small temp increase through the WB, and a very small temp drop through the radiator at a higher flow. But in reality having a radiator output ambient temp coolant to the core is a best case scenario. It all depends on how you tune your system for the right flow rate for the components you are using.
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For a radiator to output air at or near ambient temp, either the quantitiy of heat that it is removing is extremely small, or the flow rate through it is extremely slow. I don't think we even need to address the former case
. In the latter case, the water may enter the waterblock at the lowest temperature. But what temperature does it leave at? The slower the water flows, the more heat each unit of water will have to absorb in its flow through the waterblock. So it may enter somewhat cooler, but if it exits substantially hotter, it means that it will be hotter in some parts of the block, and in these parts the heat removal rate will be lower. On the average, in theory, the results should be about the same.
However, all this does not take into account some factors. Maybe we could discuss them a bit. One factor is the water in over core issue. One could presume that this would work well with lower flow rates where water comes in cooler, but we also know that it will be heated more intensely for longer. What happens as it heats up?
Another factor is the change in properties of the thermal barrier due to increased turbulence at higher flows. So is any gain acheived by "cooler" water entering over the core greater than the loss incurred by the turbulence due to loss in speed?