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.
Laser induced phosphorescence imaging for the investigation of evaporating liquid flows
The phosphorescence properties of liquid and gaseous acetone, following excitation at 308 nm, are studied and utilized in order to overcome two main challenges of two-phase flow laser induced fluorescence imaging: the large fluorescence intensity disparity between the two phases and the ensuing effect of halation. This is achieved on account of the different phosphorescence decay rates of the liquid and vapour phases, which allow for a more favourable signal ratio to be obtained. The benefits of visualizing the phosphorescence emission, instead of the fluorescence, are demonstrated by droplet stream experiments set up in different bath gases, at 1 atm and 297 K. The liquid–vapour interface can be accurately located, while the vapour surrounding the droplets is clearly visualized without any halation interference. The vapour phase phosphorescence signal was calibrated in order to quantify the vapour concentration around an evaporating droplet stream, and the results are compared to laser induced fluorescence images collected in the present study and results found in the literature. The effect of halation in the fluorescence images is shown to extend as far as 10 droplet diameters away from the interface for 161 μm droplets, resulting in a significant overprediction of acetone vapour mole fractions in that region. The vapour profile obtained by laser induced phosphorescence (LIP) imaging agrees with data found in the literature, for which a halation correction on fluorescence images was successfully performed. The demonstrated LIP technique for simultaneous vapour and liquid phase visualisation is only applicable to oxygen-free environments, as even trace quantities of oxygen completely quench the vapour phase phosphorescence emission.
Enzymic Reactor/Room-Temperature Phosphorescence Sensor System for Cholesterol Determination in Organic Solvents
The development and evaluation of a novel cholesteral oxidase reactor/room-temperature phosphorimetric (RTP) sensor system, operating in a continuous organic flowing stream, for cholesterol determination in food samples is presented. The organic carrier es a mixture of hexane/5% (v/v) chlroform. Cholesterol oxidase is physically retained onto controlled pore glass beads to form the bioactive material. Oxygen consumption during the enzymatic reaction is followed via the changes in the RTP of an oxygen-sensitive metal chelate retained on an anion-exchange resin