Pump pulling from CPU does it make a difference?

[Martinm210]

I agree with Vapor on this one:

Pressure

Pressure does vary through the loop, it is at it's highest behind the pump and lowest right before the pump.

Pressure however has no impact to thermal performance, because liquids are incompressible at least in the sense of our tiny little pressures we're dealing with. If the fluid is not compressed, there no density change to the fluid, and it results in no performance difference.

Pressure Drop. Remember pressure drop is a "DIFFERENCE" in pressure, it is the pressure difference of the inlet vs. the outlet and it doesn't matter where in the system that component is. If the pressure drop was 5PSI at 1GPM, it would always be 5PSI. It could have 20PSI at the inlet, but it it was flowing 1GPM, the outlet would be 15PSI. Or it could be 7PSI at the inlet and 2PSI at the outlet.

Flow Rate
Flow rate is constant throughout the loop.

Velocity
Velocity is NOT constant throughout the loop, and to no suprise...velocity is the key to increased thermal performance. Because flow rate has to be constant throughout the loop, when an opening gets smaller, the fluid has to go faster. Nozzles and small channels are designed for one thing, to increase velocity where heat transfer occurs. The more velocity, the more turbulent the fluid and the more likely more of the fluid comes in contact with the heat transfering surfaces.

Loop Order
-The coldest water is located directly behind the radiator, but the differential is extremely small and almost always less than a degree and often only a few tenths of a degree cooler. The question you have to ask is, is this .2C worth the plumbing arrangement needed for that setup. For some the answer is yes, for many no. If the DTS sensor resolution is 1C, chances are you'd never be able to measure the difference.

-The only thing that really matters is having the reservoir or T-line before the pump so you can adequately fill the loop without the pump running dry at startup. After filling it really doesn't matter.

THIS WHOLE PUMP BEFORE THE BLOCK

HAS NEVER BEEN DOCUMENTED AS A BENEFIT. There's no scientific basis or reasoning that supports it. Sure blocks with high pressure drop often perform well, but it's not because of pressure. It's because of high velocities and the scrubbing that occurrs and that will be the same no matter where the pump is in the system

Don't believe me, you convinced it's "PRESSURE" that increases performance? Try this. You can add static pressure to a system by simply extending a T-line or fillport up the wall next to your PC and fill that tube completely up, you've just added static pressure to the whole system by that extra elevation. If pressure in itself makes a difference, this little trick by added pressure to the system should also improve performance.

But it simply won't because pressure by itself has no net benefit to thermal performance of water blocks. Velocity and forcing the water to impact those surfaces is really the only liquid property that provides benefit.

For most people loop order is insignificant enough not to worry about other than placing a res/t-line before the pump so they can fill the system. I still go with the common Rad>Block>Res>Pump scenario because I want that extra .2C, but I wouldn't bother if it screwed up tubing routing. I'd probably pay more attention though if you were running a TEC or a tri-SLI type of setup. If you had enough heat, you could start seeing more than a degree difference around the loop, but that would be pretty rare.