Since the data derived from the Onset data recorder is in time/rate format, it may be possible to derive the difference between endoergic and isoergic energy requirements. The chart below illustrates the concept. The kiln was fired empty, then using the same profile (up to 1800∞F) with ten pounds of glass in molds. The energy was monitored during both firings. The upper curve represents the energy requirement during the firing with glass in the kiln. The lower curve is the empty kiln. It can be seen how the kiln needed more energy to perform the glass firing.
When the two curves converge, that means that the temperature of the load and the kiln are equal. The load is “done.”
The violet line is energy consumption with load, blue line is energy consumption empty. Left scale is watts, bottom scale is minutes.
The specific heat of the glass with molds is
.22 btu/∞F-pound
Heating glass is an isoergic process, that is, vs. endoergic or exoergic processes, no net energy is either consumed or given off. For ten pounds of glass, the amount of energy expected to heat the glass from 70 to 1832∞F is:
.22 btu/∞F-pound x 10 pounds x (1832-70)∞F = btu = 3876 btu
During actual tests, the empty kiln consumed 6257 watt-hours empty and 7455 watt-hours full. The difference the load in the kiln made was:
7455 – 6257 = 1198 watt-hours x 3.4 btu/watt-hour = 4073 btu.
The predicted value is within 5 percent of the experimental value. This is a remarkable correlation. Even this error may be reduced with a better correlation between the 4-20 milliamp signal and the actual power output from the SCR.
A strategy like this will be used to derive the optimal firing profile for ceramic mixes including recycled glass as a raw material. The final report will be distributed to manufacturers of ceramic products, with the hope that they will consider introducing recycled glass as a raw material.