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Incoherent · 12-08-2003, 06:33 PM

I have removed the heat current block first to test this and then totally removed watercooling for my impending move from Texas back to Sweden. Meanwhile I have become totally distracted by pH's data. Wrestling with it I think it might be possible to characterise the secondary losses.
Assuming measurements are correct three assumptions must be made;
1. That the real CPU power output is unchanged throughout the measurements,
2. That the real CPU power output equals the sum of measured power output, secondary (via mb and air) losses and hose losses. i.e. MB is cooler than CPU and we are not adding heat from other sources and therefore measured/calculated W must always be less than real CPU W.
3. The properties of the heat paths (primary and secondary) are not changing throughout the measurements i.e. conductivities, lengths, surface areas.

Predicted dTs can be calculated for different wattages and compared to the measured data:

From this chart and obeying 2. above I have interpolated that actual power output is 88W. This number is based on the fact that we should always measure less power than the CPU is producing no matter what the flowrate, if the motherboard T is less than the CPU. It is an estimate. That said, even if it is wrong the behaviour is valid I think.
The difference between ideal and measured is the dT error caused by the sum of all losses (MB and outlet probe position)

By using the measured power vs flowrate values and the measured CPU/inlet water dT we can generate a curve representing the lengths of an equivalent piece of copper (or any material) which would behave the same as the CPUdiode/silicon/TIM/WB/water path. Assuming that the properties of this path are constant (3 above), it is possible to extrapolate a value for the length and hence the apparent Q and thereby from the real "known" W the secondary path loss and Outlet sensor error (hose losses) which does not violate 2 above. (measured W+ 2nd loss+Outlet sensor error= "known" or real CPU power output.)

A bit flakey I know, but some of the results look right to me. It's hugely dependent on the assumed value of W. pHaestus, if you manage to replumb your setup it will show whether I am in the ballpark or off chasing wild geese.

Cheers

Inc

Edit: Oops, killed the charts. I will reinstate them tomorrow.
Edit 2, replaced the pics after an unfortunate FTP mouse click
Edit 3, corrected a mistake, "real CPU power" was "measured CPU power".

12-08-2003, 06:33 PM	#67
Incoherent Cooling Savant Join Date: Sep 2003 Location: Vallentuna, Sweden Posts: 410	I have removed the heat current block first to test this and then totally removed watercooling for my impending move from Texas back to Sweden. Meanwhile I have become totally distracted by pH's data. Wrestling with it I think it might be possible to characterise the secondary losses. Assuming measurements are correct three assumptions must be made; 1. That the real CPU power output is unchanged throughout the measurements, 2. That the real CPU power output equals the sum of measured power output, secondary (via mb and air) losses and hose losses. i.e. MB is cooler than CPU and we are not adding heat from other sources and therefore measured/calculated W must always be less than real CPU W. 3. The properties of the heat paths (primary and secondary) are not changing throughout the measurements i.e. conductivities, lengths, surface areas. Predicted dTs can be calculated for different wattages and compared to the measured data: From this chart and obeying 2. above I have interpolated that actual power output is 88W. This number is based on the fact that we should always measure less power than the CPU is producing no matter what the flowrate, if the motherboard T is less than the CPU. It is an estimate. That said, even if it is wrong the behaviour is valid I think. The difference between ideal and measured is the dT error caused by the sum of all losses (MB and outlet probe position) By using the measured power vs flowrate values and the measured CPU/inlet water dT we can generate a curve representing the lengths of an equivalent piece of copper (or any material) which would behave the same as the CPUdiode/silicon/TIM/WB/water path. Assuming that the properties of this path are constant (3 above), it is possible to extrapolate a value for the length and hence the apparent Q and thereby from the real "known" W the secondary path loss and Outlet sensor error (hose losses) which does not violate 2 above. (measured W+ 2nd loss+Outlet sensor error= "known" or real CPU power output.) A bit flakey I know, but some of the results look right to me. It's hugely dependent on the assumed value of W. pHaestus, if you manage to replumb your setup it will show whether I am in the ballpark or off chasing wild geese. Cheers Inc Edit: Oops, killed the charts. I will reinstate them tomorrow. Edit 2, replaced the pics after an unfortunate FTP mouse click Edit 3, corrected a mistake, "real CPU power" was "measured CPU power". Last edited by Incoherent; 12-09-2003 at 08:31 PM.