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Show N18b- t .... ,.,..' ..... ......... - H When the windowless entrainment chamber ~=~;~~~;-" was employed, the high-temperature oxidant passed through a 38.1 nun-thick Zirconia porous cylinder (see Fig. 3). The windowed entrainment chamber midsection had three large openings, 150 nun in width and 190 nun in height, arrayed about the chamber circumference at 900 intervals. Quartz windows having a thickness of 12.7 nun were employed over these openings. When the Fig. 3. Schematic diagram (typical) of the windowed entrainment chamber was used, the jet entrainment region associated with the high-temperature surrounding gas passed bench-scale apparatus. through a 50.8 nun thick, 102 nun inner-diameter, 406 nun outer-diameter Zirconia porous disk (see Fig. 2). For each different test condition, the surrounding gas composition in the entrainment chamber was measured. More specifically, the gas samples were withdrawn using a water-cooled stainless steel probe and a vacuum-pump based sampling system. After the water was removed from the gas sample, the sample was sent to a Servomex 570A O2 analyzer, a Horiba VIA-510 CO2 analyzer, a Lira MSA CO analyzer and a UTI l00c mass spectrometer. The amount of water in the gas sample was calculated from a hydrogen atom balance. The most successful technique tested to measure a jet's mass entrainment capacity was an acetylene torch method. Recall that Ricou and Spalding [2] used a differential pressure method to measure the mass entrainment rate of turbulent jets. Here, a 3.18 nun outer-diameter stainless steel tube distributed a low flow rate of acetylene at the exit of the entrainment chamber (see Fig. 3). Once ignited, the acetylene-based flame would either be pushed away from the exit or drawn into the entrainment chamber depending on the jet and surrounding-gas mass flow rates supplied. If the entrainment capacity of the jet was not satisfied by the surrounding-gas mass flow rate, then outside air would be drawn into the entrainment chamber, thus pulling the acetylene-based flame towards the entrainment chamber. Conversely, if the surrounding-gas mass flow rate overwhelmed the jet's entrainment capacity, the excess surrounding gas flow resulted in the acetylene-based flame being forced away from the entrainment chamber. When the flame appeared balanced between the interior and exterior of the entrainment chamber, the mass flow rates of the jet and surrounding gas were measured and used to calculate the mass entrainment ratio. This technique, albeit simple, seemed to best indicate the jet entrainment rate, and yielded results in a timely manner. A disadvantage of the method, however, was that it required an interpretation of the status of the acetylene flame. Note that the differential pressure method used by Ricou and Spalding [2] to measure mass entrainment was attempted, but the measurement was often biased by radiant heat transfer to the pressure pickup probes. Eliminating these biasing effects is the subject of current work. The lift-off distance , h , was defmed as the distance from the injector exit to the luminous base of the flame. Note that the flame was observed against a "cold" background to achieve sufficient contrast with the flame luminosity. The measurements were made using a 6 |
