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The results of experimental studies of the conditions of loss of stability of the shape of a single dispersed-phase inclusion (droplet and bubble) during its motion in a viscous fluid at low Reynolds numbers are presented. It is shown that in the conditions considered the deformation of an initially spherical inclusion occurs due to the development of the Rayleigh-Taylor instability, as a critical value of the Bond number is attained. It is found that the onset of deformation of the phase interface and the instability mechanism depend strongly on the particle motion regime. A range of critical Reynolds numbers, corresponding to the boundaries of the regions of the Rayleigh-Taylor and Kelvin-Helmholtz instabilities, is determined.An interest in the physics of phenomena occurring in disperse media is associated with their decisive role in a number of applications related to two-phase flows in power plants, the formation of atmospheric precipitations, heat transfer in boiling, cavitation, underwater acoustics, atomization of liquids, flotation, and other engineering processes. In these applications, important factors are the size and the shape of droplets/bubbles, the regimes of their motion, and the mechanisms of instability leading to deformation and fragmentation of the dispersed phase. The processes of dispersed-phase motion, the modes of particle deformation and fragmentation, and the instability mechanisms are some of the classic problems of hydrodynamics, which attracted the attention of researchers from different generations for a long time. To date, a number of fundamental theoretical solutions has been obtained and many results of experimental and numerical studies of these processes have been accumulated. Fairly detailed reviews of both classic and contemporary results of studies of deformation and fragmentation of dispersed inclusions are given in [1][2][3][4][5][6][7][8][9][10].Two instability mechanisms in droplet motion in a flow, namely, the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, are known. In accordance with these mechanisms, the deformation and fragmentation of the dispersed phase occur at certain critical values of the Weber and Bond numbers [11]. In most of wellknown studies, the main criterion responsible for the deformation and fragmentation of a droplet in a flow is the Weber number (the development of the Kelvin-Helmholtz instability). From the Hadamard solution [12] for a spherical dispersed inclusion moving in a viscous fluid at low Reynolds numbers, it follows that the difference of the normal stresses on the particle surface is constant and does not tend to deform it. Based on this, G.K. Batchelor [13] come to the following conclusion. If the viscosities and densities of the dispersed phase and the carrier medium are such that at low Reynolds numbers the inertial forces can be neglected, then there are no limitations on the size of a spherical inclusion of the dispersed phase.The results of theoretical studies [9,11,14] showed that at a critical value of the Bond number Bo cr...

This paper reports results from experimental studies of the formation of secondary drops during impact interaction of a drop with a liquid surface. The experimental data are compared with analytical estimates of the parameters of the cavern formed and the Rayleigh column.The interaction of a falling drop with a liquid surface is a classical problem of hydrodynamics which has attracted the attention of researchers for many years [1][2][3][4][5][6][7][8][9]. Reviews on the problem in question are given in [5,8]. The literature deals primarily with experimental studies of the qualitative picture of the interaction process [1][2][3][4][5][6][7]. A numerical solution of the problem of cavern collapse using the ideal fluid model is presented in [8,9].The physics of impact interaction of a drop with a liquid surface is of interest for the solution of a number of applied problems, such as the estimation of the depth of the crater produced by the cumulative effect of micrometeorite impact on the spacecraft body [6, 10], the determination of the parameters of underwater acoustic noise due to raindrop fall on a marine surface [7,9], etc. In particular, an important ecological problem is predicting the propagation topology and dynamics of drops of toxic agents which are formed during precipitation on the surface of catch basins located on the territory of chemical plants, near nuclear facilities, etc. [11]. To solve this problem, it is necessary to know the quantitative mass-transfer characteristics and the parameters of the secondary drops produced by impact of precipitating drops on the liquid surface.The present paper gives experimental results and analytical estimates for the quantitative characteristics of mass transfer during formation of secondary drops of various sizes produced by the impact interaction of a drop with a liquid surface.Experimental Setup and Technique. The study was performed on a setup consisting of a generator of monodisperse drops, a system for visualizing the interaction of falling drops with a liquid surface, and a system for measuring the parameters of the falling drops before impact [12]. A diagram of the experimental setup is shown in Fig. 1. The liquid from the overhead tank 1 was supplied to a capillary 2 through a flow microregulator 3, which controlled the rate of drop formation. The overhead tank, flow regulator, and capillary were fixed on a support which adjusted the height of drop fall in the range h = 0.07-2.5 m. The drop formed at the polished end of the capillary fell in a tank 4 with dimensions 0.1 × 0.1 × 0.07 m made of optical plane-parallel plates glued together. The optical transparency of the tank walls allowed the visualization and recording of the interaction of the falling drops with the surface and volume of the liquid in the tank 4. The interaction was recorded by an NV-DA1EG digital video camera or a Zenit-TTL mirror camera 5 provided with an electrical trigger 6. The electrical trigger was actuated by the signal of an amplifier 7. The signal actuating the electrical tri...