The Incandescent W Experiment
Run 1 - 18AUG98
Description of Apparatus
The cell is a cylindrical glass vessel, 60 mm in diameter and 105 mm tall. It is fitted with a machined G-10 cap that is sealed to the glass with a large O-ring. Passages in the cap allow the W cathode rod and Pt anode wire to enter the cell through O-ring seals. A thermistor temperature probe in a glass jacket also penetrates the cap, again O-ring sealed. A 4th hole in the cap conveys the gases produced by electrolysis out into a small rubber tube.
The cathode is a 1/16" diameter pure W welding rod sleeved with thick-walled Teflon tubing that extends to within 1 cm of the end of the rod. The anode consists of a 0.5 mm dia Pt lead wire that is crimped to a 1 cm2 piece of Pt mesh. The two electrodes are positioned about 2 cm from the bottom of the vessel and are located about 3 cm apart.
The cell was filled with 150 grams of 0.5M K2CO3 solution.
During operation, the cell is contained in a heat exchanger made from ¼" Cu tubing as shown in this photo. This heat exchanger is contained in a sawed-off 600 mL beaker that holds a liquid coupling agent (water) that provides much better thermal coupling between the cell and the Cu tubing than air.
At the very top of this photo you can see four 100 mfd capacitors that are connected in parallel across the cell. These capacitors snub some of the very high frequency currents that occur during the arc discharges in the cell. They also act as bypass capacitors and provide very high currents to the cell when the discharges occur.
Note the space between the coils of Cu tubing near the bottom of the assembly. This space provides a view of the interior of the cell, specifically of the W cathode. It is necessary to view the W cathode during operation in the calorimeter in order to confirm that the proper state of incandescence has been achieved.
Cooling water is circulated through the Cu tubing by an FMI precision metering pump at precisely 4.82 ml/sec. The temperature of this water is measured both before and after passing through these coils by thermistor temperature probes located in Tee fittings that are buried in the thick Styrofoam insulation that surrounds the cell.
The heat output of the cell is obtained simply by multiplying the observed cooling water delta-T by the water flow rate and the specific heat of water.
This photo shows most of the entire system. The cell is inside the rectangular Styrofoam enclosure. The round hole outlined in black on the front of this enclosure is a viewport that looks into the cell. This viewport is thermally insulated with 3 dead-air spaces between 4 plastic panes.
The FMI pump is turquoise-colored and located between the cell enclosure and the computer monitor.
The cylindrical object just below the cell enclosure is a temperature-regulated water bath. Under control of the computer, this bath serves to keep the temperature of the inlet cooling water constant. Since this experiment produces up to 200 watts of heat output, active cooling is required for this bath. This is achieved by valving relatively cool tap water into the bath. The red solenoid valve can be seen just to the left of the water bath.
Just visible in the lower left corner of this photo is the inverted-graduated-cylinder apparatus for measuring the evolving gas flow rate.
Just out of the picture to the right are the Variac-rectifier DC supply and Clarke-Hess 2330 Power Analyzer used to monitor the input power. For this run we used a 250 mfd filter capacitor across the output of the full-wave-bridge rectifier and we also used the 400 mfd capacitor (mentioned above) across the cell inside the calorimeter enclosure. The power analyzer was placed in the line between the filtered DC supply and the calorimeter enclosure. Thus it monitored the filtered DC going into the cell+capacitor located in the calorimeter enclosure.
Here is a close-up of the viewport. You can barely see the Cu-tubing heat exchanger inside.
The cell was not running when this photo was taken.
This photo shows the viewport while the cell is operating in "incandescent mode". (Please excuse the quality of this photo...we had to trick our point-and-shoot into taking this shot.)
This photo shows the used W rod (left) next to a new W rod. As you can see from the data below, this rod ran for several hours in "incandescent mode". The erosion is obvious but not so severe as to prevent accurate calorimetry.
Here are the results of Run 1. The entire time span is only 4 hours and the vertical dotted lines mark each hour. The run begins with about 30 minutes of power-off*. Then about 80 volts was applied to the cell as indicated by the Vcell trace. Cell current (Icell) was about 1.6 amps during this "warm-up" electrolysis period. Cell temperature (Tcell) rose rapidly and leveled off at about 70° C.
After 1 hour you can see that the observed heat output power (Pout) matches closely the measured electrical input power (Pin). Actually, Pout runs about 2 watts less than Pin during this period, consistent with the caloric value of the evolving H2 and O2. A measurement of this gas flow rate at this time yielded only 80% of the flow rate expected from the cell current.
At 1.5 hours, Vcell was increased to about 155 v and the cathode became incandescent. Note that Icell dropped significantly due to the formation of a gas sheath around the cathode. Pin rose somewhat and, unfortunately, became rather erratic. However, for the next hour, Pin stayed in the vicinity of 110 watts and Pout followed it closely, indicating no significant excess heat. During this phase of the run, the measured gas flow rate was about 93% of that expected from the cell current. Note that Tcell runs about 75-80° C during this phase. The double-boiler arrangement in the calorimeter works great!
At 2.7 hours we increased Vcell to 193 v to invoke a regime in which the cell rumbles very loudly and the emitted light becomes "blindingly white". The Pin trace became quite erratic at that point but Pout appears to be following it faithfully and never shows any signs of large excess heat. Tcell reaches about 91° C at the end of this phase. Also during this phase, the measured gas flow rate increased rapidly reaching 2.3 times more than expected from the cell current! Possibly this extra gas was coming from the Teflon insulation around the W cathode which was burning off at a rapid rate at this power level.
The run ended abruptly when the top of the cell popped off (harmlessly)! This happened despite the fact that the cell was vented continuously through the gas flow apparatus!
The results of this run are not encouraging but we plan to go ahead with several more runs in an effort to obtain more definitive calorimetric data. We are preparing a much more robust Teflon insulator for the W rod for the next run.
Comments and suggestions are most welcome
*A plot from an overnight baseline run that preceded this run is available upon request.