[Albigger]

If you want to know the heat ouptput from a cpu, measuring the dT water in-out of the block is not too practical (I gather) for the reasons stated above.
Either of these seem practical?

1)slow the flow rate so there is a larger dT that can be measured with more confidence. Problems: at slow flow rates 'our' meters become inaccurate (would have to buy a new low flow meter probably) and as flow slows, the block heats up and more heat is lost to secondary sources (mobo) and so this wattage would underestimate the heat output under normal flow conditions.

2) How about making a 'thermal bath' - insulate the entire loop and pump water through the processor into some reservoir (recirculate the water) and keep measuring the temp increase. Need to be careful - many variables, also pump power input.
3) Better yet to put a copper slug with a round tube full of water (think the LN2 containers the benchers use but with less mass) to rest on top of the cpu die. keep sides and top well-insulated, with a stirring stick and temp probe and measure increase in temp of copper slug and water - caculate wattage.

--Jay