Study of the Mechanisms of Dust Suspension Generation in a Closed Vessel Under Microgravity Conditions

摘要

An experimental method has been developed to investigate the mechanisms of dust suspension generation in a closed vessel under microgravity conditions. The objective is to characterize the evolution as function of time of the aerodynamic flow field and the dust distribution inside the vessel, in particle concentration conditions representative of actual dust explosions. Cornstarch suspensions in air have been chosen for this purpose. Special adaptation of high frame rate video records with laser sheet tomography allowed performing PIV measurements under microgravity conditions, in the unsteady flow generated during the dispersion process. It was demonstrated that cornstarch particles, in spite of their relatively large size, were suitable to be used as tracers for PIV measurements. Video registrations, at high frame rate (5,000 fps) at discrete instants in the time interval 0-10 s, of the dispersion of cornstarch particles under microgravity conditions allowed to explore the time interval 600 ms to 10 s for which there were no experimental data until now. It appears that after 500 ms, velocity and rms velocity fields become similar for g = 0 and g = 1. For characteristic times beyond 7-8 s, these fields evolve very slowly. Recordings at slower frame rate (125 fps) continuously during the whole process, showed the tendency of particles to become uniformly distributed in the vessel. The variations of particle concentration were followed using the signal of light intensity diffused by the particles. Large fluctuations of the diffused light are detected during the dispersion process. However, for g = 0, the average value of the diffused light intensity remains quasi-constant as function of time, whereas for g = 1, it decreases quickly until approximately 4 s, and then decreases much slowly and becomes slightly smaller than in the case g = 0. To get further information about the subsequent evolution of the suspension, observation of the dispersion process beyond 10 s should be done in future experiments.