One for Martin.

[Bond Number]

Martin,
I have question concerning your heat dump test versus an in situ test, where one measures temperatures before and after the water block and the flow rate with an inline meter.

Are you worried about the accuracy of the flow meter? I see this and the performance decrease of an inline flow meter as the biggest drawbacks. However one would be able to log heat dump as a function of cpu load during their daily use. This might be useful data for people who do not run their cpu at full load. Also one could look at how heat dump varies with temperature, i.e. for the same operation what is the efficiency of the processor (how much current leakage) at different temperatures.

Also in your current setup what is the flow pattern? If you let the hot water enter the bottom of the thermos it would help to eliminate any temperature gradients. But from you picture it looks like the flow is pretty turbulent so the gradient should be small.

[Martinm210]

Martin,
I have question concerning your heat dump test versus an in situ test, where one measures temperatures before and after the water block and the flow rate with an inline meter.

Are you worried about the accuracy of the flow meter? I see this and the performance decrease of an inline flow meter as the biggest drawbacks. However one would be able to log heat dump as a function of cpu load during their daily use. This might be useful data for people who do not run their cpu at full load. Also one could look at how heat dump varies with temperature, i.e. for the same operation what is the efficiency of the processor (how much current leakage) at different temperatures.

Also in your current setup what is the flow pattern? If you let the hot water enter the bottom of the thermos it would help to eliminate any temperature gradients. But from you picture it looks like the flow is pretty turbulent so the gradient should be small.

You theoretically could measure the heat in watts by measuring flow rate and temperature delta, but the problem quickly becomes the resolution of the tools. To do that you would really need inline temperature probes with a resolution and relative accuracy down to .001C which takes some high dollar lab grade tools. The crystalfontz is only good to about .2C depending on the temp range, so it's not good enough. You may be able to get better than that using multiple probes and averaging logged data, but I'm still not sure it would be good enough.

I think it requires something like 350 watts if I remember right to make a 1.5GPM flow rate change 1 degree, so most of the time the temperature differential is nearly as much as the error in the probes. You might be able to improve the temperature resolution by adding restriction and slowing flow rates way down, but then you'd need a higher resolution flow meter.

The $3 thermos is pretty cheap in comparison and more accurate than what I have on hand. It's too bad though because measuring heat dump or loss by having some really high resolution probes would be the ideal way to measure both heat dump as well as measure radiator performance because it's really cut's down the time to test and eliminates any error of other heat losses that are outside those two points of temperature measurement.

The coolingmasters guys over in France did just that when they did their radiator testing, so I know the tools are out there. You just need temp probes with a relative accuracy of .001C to do it, which they did.

It doesn't matter what the flow pattern is. At 1.5+ GPM the flow is so turbulent and so highly recycled the temperature is virtually constant throughout the loop with the exception of the very slight .1C jump across the block and pump. You can see that in the logged chart. The blue line is actually data points that were collected by the crystalfontz on 1 second intervals across the entire test, so temperature is very much a natural slope. The curvature is error from the system losses, that's why I averaged it with a straight line trendline to account for it.

[Bond Number]

Thanks

Me and friend were thinking of doing so experiemnting over the next couple of months, so thanks for the insight.

[relttem]

Martin,
I have question concerning your heat dump test versus an in situ test, where one measures temperatures before and after the water block and the flow rate with an inline meter.

Are you worried about the accuracy of the flow meter? I see this and the performance decrease of an inline flow meter as the biggest drawbacks. However one would be able to log heat dump as a function of cpu load during their daily use. This might be useful data for people who do not run their cpu at full load. Also one could look at how heat dump varies with temperature, i.e. for the same operation what is the efficiency of the processor (how much current leakage) at different temperatures.

Also in your current setup what is the flow pattern? If you let the hot water enter the bottom of the thermos it would help to eliminate any temperature gradients. But from you picture it looks like the flow is pretty turbulent so the gradient should be small.

You really need to calibrate everything if you want to get accurate results. I have seen thermocouple (high end) that are off by a degree. Thermocouple accuracy is usually a function of the temperature you are reading and the temperatures that the thermocouple is made for. There are all types of thermocouples - some for liquids, some for air..etc etc. We always calibrated our flow meters using a gram scale. We would simply pump the fluid out of a large container into a smaller container that was on a gram scale for a specified amt of time. We would do that a few times and take an average. We use the equation:

Q = mdot Cp dT to calculate how much heat our water is pulling from the chip.

knowing the mdot you can calculate the Reynolds number:

Re = 4*mdot/(mu*D)

mu is the viscosity of water, which you can look up online
D is the diameter. This gets tricky when flowing through a water block - you have to compute a hydraulic diameter, which is going to be different for every block. But, the Reynolds number will let you know if the flow is turbulent - more or less if Reynolds > 4000. But, if the Re is below 4000 it can be made turbulent which would be the case in water blocks.
Turbulence increase the convective coefficient, which is important in heat transfer involving a moving liquid (air, water, etc), but the trade off is higher pressure drop, which means you need a stronger pump.