BLP Gas-Phase Replication Effort - Run 5….15JAN98 ………………..(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 Resistance (ohms)
Room Temperature (C)
Inlet water Temperature (C)
Something really strange is going on with the hot tungsten filament in the hydrogen atmosphere! This run started at 9:00 AM with a new filament and 0.1 grams of KNO3 in the chamber. A good vacuum was established in the chamber (<10-6 torr) and, thirty minutes later, the cartridge heater and the filament were each set to 15 watts. About 3.5 hours into the run, the cartridge heater power was adjusted to 25 watts and the filament power was lowered to 5 watts…to preserve the filament as much as possible. About 5.1 hours into the run, the filament was turned off completely and the cartridge heater was raised to 30 watts. By this time, Pout was reading about 29 watts…we were nearing thermal equilibrium. At about 6 hours into the run, we filled the chamber with 2 torr of purified H2 gas. We let that sit for almost 1 hour and then switched the cartridge heater off entirely and applied a full 30 watts to the filament. Initial filament temperature was about 2200°C but apparently the filament was attacked rapidly because the resistance starting climbing steeply (see the Tfil curve). As in Run 4, this necessitated manual adjustment of the filament voltage to keep the filament power about constant and we didn't do a superb job of it. However, we did manage to keep Pin at about 30 watts for the remainder of the filament's life…which was about 45 minutes. During this time there was no sign of a large excess heat generation in the chamber. The small positive "bobble" in the Pout trace that occurred right after we switched the filament on is probably a disequilibrium signal due to the thermal redistribution…however we cannot be sure of that with this sketchy data.
The filament problems are worse than we thought. The filament was in good shape this time when we energized it in the H2 atmosphere. Apparently it is being consumed rapidly by the H2 gas. As you can see from the flat pressure trace we have eliminated the gaseous species that were causing the dramatic pressure increases in the earlier runs. The problem could still be due to residual levels of other gases present in the chamber but this now seems unlikely.
More equipment problems: During the brief life of the filament in the hydrogen atmosphere we started having problems with the thermocouple-analog converters responsible for the Twall and Tgas signals. Those temps did not actually fluctuate wildly during that period as indicated. They stayed about 270°C and 260°C respectively.
As usual, comments and suggestions are most welcome.
P.S. The only thing we ever bought from Omega and were dissatisfied with is the TAC80B-K Temperature-to-Analog Converter on p. K-84 of Vol. 29 Temperature Handbook. To put it bluntly, it is a real piece of crap.