We investigated the conditions, characteristics, and outcomes of liquid droplet interaction in the gas medium using video frame processing. The frequency of different droplet collision outcomes and their characteristics were determined. Four interaction regimes were identified: bounce, separation, coalescence, and disruption. Collision regime maps were drawn up using the Weber, Reynolds, Ohnesorge, Laplace, and capillary numbers, as well as dimensionless linear and angular parameters of interaction. Significant differences were established between interaction maps under ideal conditions (two droplets colliding without a possible impact of the neighboring ones) and collision of droplets as aerosol elements. It was shown that the Weber number could not be the only criterion for changing the collision mode, and sizes and concentration of droplets in aerosols influence collision modes. It was established that collisions of droplets in a gaseous medium could lead to an increase in the liquid surface area by 1.5–5 times. Such a large-scale change in the surface area of the liquid significantly intensifies heat transfer and phase transformations in energy systems.
Differences in the rates of heating and evaporation of droplets with the component composition are important parameters of heat transfer processes and phase transformations. This paper presents the values of high-temperature (up to 600 °C) evaporation rates of droplets of promising fire-extinguishing compositions (water, bentonite suspension, bischofite solution, EA-5 solution, and foaming agent emulsion) at convective (in the air stream), conductive (on a heated surface), and radiation (in a muffle furnace) heating. A high-speed video recording system and tracking software algorithms are used. At identical initial sizes of droplets of fire-extinguishing suspensions, known as emulsions and solutions, the times of their complete evaporation are shown to differ 3.7 times when heating on the substrate, 1.25 times in the air flow, and 1.9 times in the muffle furnace. A general approximation expression is formulated, and the empirical constants are calculated to predict the evaporation rate of the droplets of extinguishing agents in a wide range of temperatures (up to 600 °C) and heat fluxes (up to 100 kW/m2), which are characteristic of forest fires. With the use of the experimental data obtained, it is possible to predict the completeness of evaporation of promising extinguishing liquids at different schemes of heat supply.
Abstract. This article presents findings of experimental research into suppressing the thermal decomposition of forest fuel (birch leaves, spruce needles, kindling wood and mixed forest fuel) under conditions of exposure water aerosol and single water droplets, as well as water with specialized additives. We used typical model of fire source with fixed height 0.04 m and varied diameter 0.02-0.1m. Water spraying process, as well as interaction between water and forest fuel was registered using highspeed video camera (recording frequency 6•10 5 fps) and panoramic optical methods ("Particle Image Velocimetry", "Shadow Photography"). We established principles of water additions' influence on termination of combustion and thermal decomposition of fire source model.
In this research, we present the results of experiments measuring the
interaction times of colliding liquid droplets in different modes (bounce,
coalescence, separation, and disruption). The experiments involve water and
typical water-based slurries, emulsions, and solutions. The main
experimental parameters are close to those of high-potential
gas-vapor-droplet technologies (heat and mass transfer power plants, thermal
and flame water treatment systems, and fuel technologies): droplet size
0.1-5 mm; velocities 0.1-10 m/s; liquid temperature 20-80 ?C; impact angle
0-90?; relative volume and mass fractions of liquid and solid additives in
water 0-10%. We explore how a set of parameters and effects influence the
characteristics of the processes under study. The most important of these
parameters are relative droplet velocity, impact angle, impact parameter,
and temperature. Using dimensionless linear and angular interaction
parameters as well as the Weber, Reynolds and Ohnesorge numbers, we produce
interaction mode maps to consider the correlation of the main forces:
inertia, surface tension, and viscosity. We determine the interaction times,
number, size, and total surface area of the newly formed post-collision
droplets and obtain approximations for the experimentally determined
functions.
Abstract. The danger of forest fires and their large-scale consequences is facing humanity more and more sharply from year to year. We carried out experimental studies to determine the thermal characteristics (thermal conductivity, heat capacity, thermal diffusivity) and thermokinetic characteristics (activation energy, pre-exponential factor) of typical forest combustible materials and their mixtures for a wide range of temperatures (298-423 K). A generalization of experiments for typical forest combustible materials of the Far Eastern Federal District of Russia was performed. The established experimental values can be used for mathematical modeling of occurrence, propagation and extinguishing of forest fires.
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