Another possibility is the conduction of alumina. Alan has measured the electrical conductivity of alumina to increase rapidly above 900C. The heater coils are wound directly on the mullite reactor tube and they are covered with thick alumina tubes. When the outer cover alumina tube is over 900C, it can develop a conductivity to where the outer alumina touches the heater coils. Then this couples a small AC current directly to the thermocouple. The resistance through the alumina can be in the 20k-100k range. When the AC heater voltage is coupled to the TC, it adds a common mode signal to the TC input at the DAQ and causes a large noise, and can cause offset. The AC voltage wrt DAQ ground can be higher for one side of the series coil-pair than the other.
In the latest measurements, noise is being seen in the active side more than the null side (but seen in both). Could the offset be a similar ratio as the noise? The noise seems to be varying faster than the thermal time constant of the system, suggesting it is electrical noise. The additional danger is that when it cools, the conductivity of the alumina will go away and any offset caused by AC common mode at the DAQ could disappear, making it look as though the TC was "OK". On Sat, Apr 16, 2016 at 10:32 AM, Jones Beene <[email protected]> wrote: > Another strange possibility to consider – with which to account for lower > than expected performance on the active side, and in fact the null side > being slightly warmer for a unexpected proportion of the time is this: the > null side could be active as well in a lower temperature range. > > > > Otherwise, both sides should be almost identical. If hydrogen, even in > trace amounts, collects on the so-called null side, and if the SPP modality > is playing a role in excess heat, then both sides can be gainful under > different parameters - since a metal catalyst per se is not needed – or > stated another way, the dielectric/gas interface on the null sides > functions as the catalyst for SPP formation. > > > > This possibility becomes far more relevant if there was anomalous > radiation, as seems to be the case. > > > > *From:* Craig Haynie > > > > Here is a video, queued to the time shortly after the green (active) > thermocouple became hotter than the purple (control) thermocouple. The > control had been running a couple of degrees hotter, previously. The > change-over occurred shortly after raising the power to the point where the > temperature went above 1020c. The timing couldn't really have been much > better. This occurred at 2016-04-16 02:00 UTC. > > https://www.youtube.com/watch?v=xUyWnN--u7M&feature=youtu.be&t=13188 > > Craig > > On 04/16/2016 11:27 AM, Jones Beene wrote: > > This temperature differential is more meaningful than it seems since some > of the excess heat on the active side goes to heat the null side. > > > > The basic concept of comparative calorimetry is good, and this ceramic is > not a great conductor of heat, but there is a conductive pathway between > the two sides, which could possibly have been made less in an improved > design. Actually the heater wire itself could be part of the heat transfer > problem. > > > > *From:* Craig Haynie > > > > The optical imager is typically reading between an 18c and 20c difference. > > Craig > > Eric Walker wrote: > > Interesting. I hope a post-run calibration shows that when the fuel is > removed, the active and null outside temperatures return to one another to > within experimental uncertainty. This will be critical to show before > concluding anything. > > > > Eric > > > > > > > > On Sat, Apr 16, 2016 at 9:58 AM, Craig Haynie <[email protected]> > wrote: > > 60c on the latest... > > https://youtu.be/VLK19pllG9g?t=6278 > > > > On 04/16/2016 10:53 AM, Eric Walker wrote: > > On Sat, Apr 16, 2016 at 2:01 AM, CB Sites <[email protected]> wrote: > > > > I have to say. This one is pretty fascinating. At 1000+C they had a > delta T of 30C between a fueled and unfueled cell that lasted for hours, > until I gave up. > > > > At what time in the video did you see this? When I skipped through the > video, I always saw the "Outside heater active" (the green line) slightly > lower than the "Outside heater null" (purple line). Perhaps you're > referring to a delta between different numbers than these? > > > > Eric > > > > > > > > > > >
