PDF27 has it right: your temp probes should be measuring temps at the water block inlet and outlet.
What's not obvious here, is that the wattage that your going to calculate as a result, is achieved at a state of balance (i.e. the loop has been running stable temps for a while), and that wattage is what's actually dissipated by your cooling solution. If your cooling solution were more efficient for some reason (like turning up the fan), your measurements would be different.
As PDF27 also pointed out, it's not easy to measure this. We're talking about temp differences in the order of 0.1 and less, especially at higher flow rates. Because of that, it's really critical that all your measurements, including flow, are as accurate as they can be.
I'm opting to use Platinum RTD, and I'm shooting for 0.001 deg C resolution, which should give me a narrow enough margin to make a somewhat accurate measurement. I haven't picked the flow meter yet, but I'm leaning towards a magnetic unit. Anything that can give me 1% accuracy or better, but isn't outrageously expensive.
PDF27: you need to look into the WBTA (in my sig): you'd be a welcome member! (end shameless plug)
|