| OCR Text |
Show emissivity can be below 0.3 at 2,000°F, fire clay emissivity is above 0.7. An intermediate value of 0.44 was chosen. Again the waterwall model is not extremely sensitive to the choice. The greater the insulation value of the refractory, the less sensitive the heat transfer is to the refractory emissivity. The refractory conductivity factor, Kp>, was chosen to agree with that of ref. 4. The soot mass loading was arbitrarily fixed at 5 x 10"4 g/g. Finally, the flame diameter was taken from visual observation to be 2.0 ft at an oil pressure of 45 psig, and 2.3 ft at 80 psig. The relationship was assumed to be linear in between. Figure 13 shows a comparison between the model and several experimental results. The experimental bulk temperature values are calculated as the weighted average of seven radial measurements. There is good agreement for a range of postflame temperatures of 900°C (1,600°F). The comparisons include several firing rates and stoichiometrics, as well as tests with and without waterwalls in place. The experimental temperature measurements do not correspond to steady-state conditions. The zone energy balance has no time-dependent term. It would be expected, therefore, that the model predicts temperatures in excess of the measured values. This is indeed the case at the high-temperature conditions. 2,750 | - • Axial position (ft) Figure 13. Comparison of Model (Solid Line) to Experimental Bulk Gas Temperature Data 5.5.26 |
