DROPLET BREAKUP PHENOMENA IN FLOWS WITH VELOCITY LAG

摘要

Available experimental data on droplet disintegration have been reviewed with due regard for modern knowledge of the phenomenon. Disintegration processes are known to be induced in flows with velocity lag between a continuous medium and dispersed particles. The disintegration process results in a drastic decrease in the characteristic size of particles. The formation of fine fog promotes evaporation processes and enhances processes of gasdynamic relaxation. The droplet breakup phenomena play an important role in various applications: shock, blast, compression and rarefaction waves in two-phase flows; two-phase flows in convergent/divergent nozzles; liquid jets and sprays in diesel engines; and supersonic flight in rainy conditions or in a dusty atmosphere. The critical conditions of droplet disintegration have been reviewed comprehensively and spatial and temporal characteristics of the phenomenon have been described quantitatively. Possible breakup modes are classified, specifying the ranges of their existence in terms of governing parameters. Also reviewed are the available data on breakup of non-Newtonian liquid and slurry. Of particular interest is knowledge of the effect produced by neighboring particles on the disintegrating droplet. Specific features of breakup phenomena in dense sprays have been discussed. Experimental data on superheated liquid drop disintegration are also presented. An attempt is undertaken to find similarities between the droplet breakup processes in various systems: (1) liquid drop—gaseous flow, (2) dense liquid drop—light liquid flow. Available data have been collected in order to address specific features of drop acceleration and deformation. The data presented allow comparison of characteristic times of chemical reactions in premixed combustible mixtures with characteristic times of atomization and evaporation in two-phase systems consisting of full drops and gaseous oxidant.