Influence of the Temperature of Gases on the Deformation Characteristics of Moving Water Droplets

Abstract

An experimental analysis of the infl uence of the temperature of gases on the deformation characteristics of water droplets moving through them is carried out. High-speed (up to 10 5 frames per second) photography with video cameras and cross-correlation complexes, as well as panoramic optical methods of recording the motion parameters of gaseous and liquid fl ows, were used. The laws governing the movement of water droplets through gases with a temperature of about 1100 K and in air at relatively low (to 280 K) and moderate (about 300 K) temperatures have been studied. The principal characteristics of the deformation of water droplets (duration, extension, and amplitudes of "deformation cycles") have been established. The differences in the characteristic shapes of droplets during their motion in gaseous media (at different temperatures of the latter) have been determined. The times during which droplets retain a certain shape in the deformation process have been calculated.Introduction. The temperature of gases (T g ) through which water droplets pass in quenching typical forest fi res can vary within a rather wide range [1][2][3]. In particular, depending on the climatic conditions and the height from which the quenching water is dropped by aviation into the zone of fi re, a wide range of T g can be singled out (up to 1200 K) [2, 3]. Numerical investigations [4][5][6] showed that the introduction of large masses of water (several tons) into the zone of fi re is ineffi cient. It is expedient [4-6] to intensify endothermal phase transformations in the zone of fi re. The most common is the technology [7-12] of fragmentation of water droplets (or of any other quenching liquids) prior to the delivery to the fl ame zone to intensify steam generation. Experiments [13][14][15][16][17][18] showed that apart from the changing of the characteristic dimensions of droplets and of their dispersity, it is worthwhile to carry out a number of other operations, for example, preliminary heating of water, introduction of foreign solid inclusions and admixtures into water, and alternation of the velocities and trajectories of injection of a sputtered liquid.It has been established in numerical simulation [4-6] that the surface area of droplets (and, as a consequence, the steam generation surfaces) plays a decisive role in the processes of heat and mass transfer. The experiments in [13][14][15][16][17][18] have shown that this parameter depends substantially not only on the intensity of phase transformations, but also on the process of droplet deformation. It is of interest to carry out experimental investigations of the principal characteristics of the deformation of water droplets in their motion in a gaseous medium with variation of the latter′s temperature in a wide range (from 280 to 1100 K) typical of the conditions of quenching forest fi res [1-3].Experimental investigation of the infl uence of the temperature of gases on the deformation characteristics of moving water droplets constitutes the purpose of the present work.Exp...