BLP Gas-Phase Replication Effort - Run 9….29JAN98 ………………..(best viewed with 1024 pixel display width)
Legend
Total Input Power (electrical)
Output Power (heat)
Chamber Wall Temperature (C)
Gas Temperature (C)
Gas Pressure (torr)
Filament Temperature (° C)
Room Temperature (C)
Inlet water Temperature (C)
Run 9 was another stab at the real thing...and we got a tantalizing result!
The catalyst vial was in the chamber, filled with 0.25 grams of KNO3. Of course we installed a new W filament. For the first 3.6 hours we ran only the cartridge heater with the vacuum system pumping on the chamber. We played with the cartridge heater power a little starting at hour 2.6 to get Pin = Pout sooner than normal. We settled on a "standard" input power level of 32 watts at hour 3.6 and applied 10 watts to the filament, reducing the cartridge heater power as needed to maintain a total input power of 32 watts. We left the filament running in vacuum until hour 4.5 and then filled the chamber with 2 torr of purified H2 gas. Looking for the Press trace to respond made us realize that the pressure signal cable was unplugged so we plugged it in! That explains the sudden appearance of the Press trace descending off the "ceiling".
As before the filament began eroding immediately and we made frequent periodic adjustments to the cartridge heater power in order to keep the total input power constant. To our considerable surprise, the Pout trace gradually separated from the Pin trace showing an apparent excess heat of 1.5-2 watts! The filament lasted until hour 6.5 (only 1 hour). During this time the apparent excess power persisted. Surely, we thought, it will go away when the filament burns out...but it didn't! As soon as the filament burned out, we raised the cartridge heater power to keep the total input power at ~32 watts. The apparent excess heat persisted with no filament until hour 7.7 when we fired up the vacuum pumps to remove the H2 gas from the chamber (the vacuum pumps are typically shut down just after the chamber is filled with H2 because they are no longer needed then).
As luck would have it, the computer crashed just about then and we had to restart the program. The brief interruption in execution of the inlet water temperature regulation algorithm is what caused the bipolar excursions in the Tin and Pout traces. By hour 7.0 the system had recovered and we still had the apparent excess heat signal, now with no filament and no hydrogen.
Finally it occurred to us that the room temperature had changed quite a bit since the early morning hours when the run was started. The TEK THS720 digital scope (the instrument responsible for monitoring the power delivered to the cartridge heater) probably needed to have its Signal Path Compensation routine run. At hour 7.7 we did so and the Pin trace jumped up right on top of the Pout trace (look right at the end of the run). The apparent excess power signal was due to an error in the input power measurement! The Pout trace was correct all along. It was the Pin trace that was erroneously low.
This reinforces an old calorimetry adage: "If it's not one thing causing errors it's another".
Despite the problems we had in this run, there was no sign of the large excess heat signal reported by BLP under similar conditions. In this run our gas temperature ranged from 270-300° C while the filament was operating. BLP gives 280° C as the desired chamber temperature.
We have not disassembled the chamber yet. It will be interesting to see if any of the 0.25 grams of KNO3 has volatized. If not, we'll probably move the KNO3 vial closer to the heaters next time.
P.S. We ordered some K metal from Aldrich for a future run which will have a molten K metal catalyst...a clear departure from the BLP recipe but seemingly worth a try.