Measurements of Acetone Fluorescence and Phosphorescence at High Pressures and Temperatures
Laser-induced fluorescence and phosphorescence signals of liquid acetone at pressures from 1 to 15 atm were measured and analyzed. Liquid acetone, which was preprocessed to minimize any dissolved oxygen, was injected as a low velocity jet into a pressurized chamber with either an air or nitrogen co-flow. The actone was excited at 266 nm. The laser-induced fluorescence intensity from the liquid was found to be invariant with pressure and co-flow conditions. The measured phosphorescence lifetimes were also found to independent of pressure, for both nitrogen and air environments. The phosphorescence lifetime for the liquid was measured to be ~1 μs, which is significantly smaller than the lifetime for acetone vapor (200 μs). This is likely due to self-quenching by acetone. The effect is further seen in the phosphorescence to fluorescence (P/F) ratio comparison between the liquid and vapor. The P/F ratio for liquid is 0.012, which is much smaller than the vapor value of 9.0. The overall phosphorescence intensities, however, were seen to decrease in the air co-flow cases compared to the nitrogen co-flow. Diffusion of oxygen into the liquid jet was observed, and the estimated concentration was found to be a few orders of magnitude less than the saturated concentration.
A novel method for instantaneous, quantitative measurement of molecular mixing in gaseous flows
Abstract. We describe a novel method for making instantaneous, quantitative, planar measurements of fluid mixed at the molecular level in gaseous flows. The method relies on the effective oxygen quenching of the phosphorescence of luminescent tracers, such as acetone and biacetyl. The tracer's fluorescence emission is used to obtain information about the passive scalar, regardless of its molecular mixing state, whereas the phosphorescence emission from the same tracer displays mixing-state-dependant behavior and reveals the presence of molecularly unmixed fluid. By combining the information from both fluorescence and phosphorescence signals, the instantaneous, quantitative measurements of molecularly mixed fluid fraction can be obtained at each pixel of the detector. This method accomplishes the same objectives as previous dual-tracer LIF methods, but with a single tracer and a much-reduced burden on the instrumentation and the experimental setup. The new technique is demonstrated in a study of mixing in a forced acetone-seeded nitrogen jet discharging into ambient air. The instantaneous spatial maps of molecularly mixed jet fluid fraction and jet fluid mixing efficiency are presented. The capability of the present technique to identify stirring at sub-resolution scale is also demonstrated.
Optical rotatory dispersion and absolute configuration—III
Abstract Optical rotatory dispersion measurements on pyrrolidine, piperidine, and tetrahydro-isoquinoline alkaloids indicate that the absolute configuration of the α-asymmetric center may be assigned directly from the dispersion curve, provided either that the nitrogen atom is not protonated, or that the compound contains a chromophore absorbing above 200 mμ.