EarthTech BLP Replication Effort:….Run 3 - without KNO3………10JAN98

LEGEND:

Vertical scales are noted in parentheses after each color-coded digital display in the upper portion of the screen. For example, Pin and Pout are plotted on a scale that runs from -10 to 40, which makes each vertical division 5 watts (a horizontal gray line denotes P=0 for these two traces). Most of the other traces have zero at the bottom of the graph….except room temperature which was deliberately run from 12 to 22 ° C to move the trace out of the way.

The runs starts with all input power turned off to establish a baseline for the calorimetry. Also the chamber was evacuated at the start of the run (the non-zero pressure indication is due to a noise problem in the data acquisition of the mV pressure signal which we are working on…actual chamber pressure was ~10^-6 torr). About 1 hour into the run, we filled the chamber with 2 torr of H₂ gas. About 2 hours into the run, after the Pout trace had settled within +/-0.5 watts of zero, we applied 30 watts of power to the cartridge heater in the chamber. This input power was maintained until about 8 hours into the run. At the end of this period, the Pout trace had risen to match the Pin trace very closely (within +/- 1 watt). Note that the chamber pressure rose steadily during this period from 2 torr to about 7 torr. This about twice what is predicted by the ideal gas law due to the chamber's rise from room temperature to ~250° C.

At the 8 hour point, we applied 30 watts of power to the tungsten filament and turned off the cartridge heater completely (causing a spike in the Pin trace). The filament temperature, Tfil, jumped up to about 2100° C and the chamber pressure rose dramatically to ~12 torr. A constant voltage was maintained across the filament until hour 12. During this period the filament power decreased slightly and the filament temperature increased slightly…perhaps an indication that the filament was eroding away and its resistance increasing. By hour 12 the chamber pressure had reached ~13.5 torr!

At hour 12 the filament power was turned off. Over the next 12 hours, the system returned to baseline conditions demonstrating again that Pout is satisfactorily close (within +/- 0.5 watts) to zero when Pin=0.

At the end of this run, when everything was cooled down to the 40° C baseline temperature imposed by the calorimeter, the chamber pressure was about 9 torr! Obviously something in the chamber is outgassing significantly, especially when the tungsten filament is operating. What could it be?

Here's a picture of the present filament arrangement just to refresh your memory. The stainless cylinder houses the cartridge heater, the threaded rod is a 6-32 stud which provides structural support and electrical ground for the filament. The ceramic item in the background is a made-for-the-purpose 4-passage tube which houses the chromel and alumel wires leading up to the K thermocouple that senses the gas temperature.

The chamber and it's contents are entirely metallic except for the ceramic tube.