Particle concentration measurements by laser imaging for a turbulent dispersion

K. A. Morrison, D. R. Alexander

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Abstract

A laser imaging system has been developed which can be used for investigating the particle concentration variation in explosive test apparatus such as the Ciba–Geigi and Hartmann Bomb during turbulent dispersions of air–particle mixtures. The pulsed UV (337 nm) laser imaging system using a 500X optical and electronic magnification system has a measurement volume of 900 µm by 675 µm and an in–focus depth of field of 780 µm for a 32 µm diameter particle. Particles in the measurement control volume are imaged every 33 ms during the dispersion process and viewed in real time but stored for later analysis on a video tape system. This paper presents the results of investigating the lycopodium particle concentration variations during the dispersion process of 0.200 grams of lycopodium particles in the Hartmann Bomb explosive test apparatus. Data were taken at the center line and at a radius ratio of 0.5 at a height of 0.102 m (4 inches) above the base of the Hartmann lucite tube. Twenty-five separate dispersions were made at each radius ratio and were based on a reservoir pressure of 103 kPa (15 psig) and 0.200 g of lycopodium powder. The average number of lycopodium particles based upon 25 dispersions at 33 ms intervals in the 473.9 × 106 m3 control volume are reported for a total elapsed time of 15 seconds. The maximum average particle concentration observed was 6.4 particles at 133 ms for r/R = 0.0 and 6.5 particles in 333 ms for r/R = 0.5. Based upon uniform dispersion model for 0.200 g of lycopodium powder, 6.8 particles per control volume, would be expected. The time averaged data followed a Poisson Distribution for each time increment after 0.73 s for both radius ratios of r/R = 0.0 and 0.5 (based upon 95% confidence interval and Kolmogorov-Smirnov test). Data from 0 to 0.73 seconds could not be assigned confidence levels as the data did not follow a Poisson Distribution or any other known statistical distribution. No significant particle agglomeration was observed for the dispersion of lycopodium particles. In any one dispersion the number of lycopodium particles in the control volume was observed to vary widely during each 033 second measurement cycle. To further investigate the particle dispersion, the flow pattern characteristics in the Hartmann dispersion apparatus were studied using flow visualization techniques based upon a matched Reynolds number (3.13 × 106) dispersion of fluorescent dye by turbulent water injection. The matched Reynolds number flow visualization work further indicated the Hartmann Bomb dispersion method produces local pockets of nonuniformly-mixed mixtures during initial stages of the dispersion process, and this work further points out the shortcomings of integrating optical probes.

Original languageEnglish (US)
Pages (from-to)379-395
Number of pages17
JournalParticulate Science and Technology
Volume2
Issue number4
DOIs
Publication statusPublished - Jan 1 1984

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ASJC Scopus subject areas

  • Chemical Engineering(all)

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