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The article presents the results of experimental studies of the collisions characteristics for water droplets in an aerosol at its entry into the air counter flow. The temperature of the latter ranged from 20 °C to 500 °C. Experiments were also carried out with the flow of combustion products having a temperature of 800- 850 °C. The initial dimensions (radii) of the droplets in the aerosol were 50-1000 μm. Visualization of the droplet motion in the counter flow of air and combustion products required the use of a hollow cylinder made of quartz glass with a height of 1 m and an internal diameter of 0.15 m, a cross-correlation complex and optical methods (particle image velocimetry, particle tracking velocimetry, interferometric particle imaging). The characteristics of the droplet interaction (size, velocity, total surface area of the liquid before and after) were controlled using a high-speed video camera and tracking algorithms in the TEMA AUTOMOTIVE software package. The main modes of drops interaction have been identified: bounce, coagulation, scatter, and breakup. The statistical information database has been obtained to describe the interaction modes using diagrams, taking into account the ratio of the sizes of colliding drops, velocities of their motion, and an angle between trajectories of motion. The influence of gas temperature on the probabilistic criteria of droplet collisions, as well as the integral criterion characterizing the change in the liquid surface area due to the intensification of droplet collisions in the gas medium has been established. [ABSTRACT FROM AUTHOR]

The experimental results shown that the mode of droplet disintegration dominates in the laminar flow, and the intensive fragmentation is prevalent in the turbulent flow during almost the entire time of heating. Typical dependences of the time of droplet heatup before disintegration or fragmentation on the temperature, flow rate, structure and regime (laminar and turbulent) are established. The studies are conducted with heated air and flue gases to ensure the application of the research results in the technology of thermal and flame cleaning of liquids from irregular impurities. It is shown that in the flow of combustion products the droplet disintegration occurs 15-20% faster than in the air-flow. In this case, the explosive puffing is more often realized. At high-temperatures (more than 400 °C) the characteristics of the explosive droplet disintegration in the studied flows are almost identical (differences in disintegration times do not exceed 5% at different flow turbulization). At lower temperatures, the disintegration times differ 3-4 times for the range Re = 2200-3400. In this case, the more Reynolds number is, the more intense is the fragmentation of two-component droplets throughout the heating time. Due to explosive disintegration of intensely evaporating two-component droplets the growth of the relative area of evaporation was 10-25 times. [ABSTRACT FROM AUTHOR]

To expand the database of kinetic parameters used for modeling the ignition of coals and their processing waste, promising coal-water slurry and coal-water slurry containing petrochemicals, studies have been performed on an experimental set-up using thermal gravimetric analysis. The research into coals of various ranks (flame, gas, coking, low-caking, and non-baking) and their processing waste (filter cakes) has yielded the decomposition parameters of the organic matter of coal and the formation of volatile substances as well as the oxidation parameters of the coke residue of all the coals and filter cakes under study. The studies cover the temperature range of the burning processes: 450-1300 K (for low-, medium-, and high-temperature burning modes). We have ascertained the dependence of kinetic parameters (pre-exponential factor and activation energy) describing the thermal decomposition of the organic matter of coal on the rank of coals and filter cakes. The findings show that the kinetic parameters describing the thermal decomposition of the organic matter of coal and its processing waste are practically the same. The thermokinetic parameters of coke residue oxidation are close for all the coals under study but they differ significantly for coke residue of filter cakes. The values of thermokinetic parameters obtained in the research are necessary to devise adequate physical and mathematical models and perform numerical studies (for mathematical modeling) of fuel slurry combustion processes in the combustion chambers of power plants. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results about fire extinction in the model fire sites of forest combustible materials. We use the high-speed video recording tools during the experiments, as well as the system of multiphase media diagnostics based on panoramic optical flow visualization techniques. The presented experiments prove that it is possible to extinguish the forest combustible material (FCM) by small amount of water. The study considers several ways to stop FCM thermal decomposition: by individual large water droplets (1-3 mm), by an aerosol flow (the droplet size is from 0.05 mm to 0.12 mm), or through water film formation on the FCM surface. Typical durations of the FCM thermal decomposition and time of fire suppression are determined for various conditions of interaction with water. The experimental results identify which amount of water is enough to extinguish the FCM by different ways of water transfer to the reacting surface layer. Furthermore, it is estimated how the component composition and the properties of the tested FCM mixtures effects onto the characteristics of the investigated processes. The residual fraction of the FCM was evaluated by comparison of initial and final (after extinguishing) mass of the sample. [ABSTRACT FROM AUTHOR]

In this paper, we conducted an experimental investigation on water droplets gravitating in a layer of typical forest fuel (as illustrated by pine needle litter) in the course of its thermal decomposition. We used a high-speed (200 fps) video recording system, Tema Automotive software with continuous tracking of a moving object as well as a set of low-inertia (no more than 0.1 second) thermocouples. Similar experiments were performed at moderate temperatures (below the onset temperature of forest fuel pyrolysis, i. e. about 300 K). Two approaches were used: continuous tracking of a moving water droplet using high-speed video recording and registration of a droplet path using the readings of thermocouples placed at different levels in a forest fuel layer. We determined the typical depths of an forest fuel layer that water droplets reach with the initial volume of these droplets ranging from 90 to 900 µL. The typical velocities of water droplets were calculated at different depths of the forest fuel layer. We also determined the share of the mass of water spent in an forest fuel layer on evaporation and cooling of the material down to the temperatures below those of thermal decomposition. Finally, we identified the physical processes influencing water droplets moving through the layers of forest fuel heated up to the high temperatures similar to those of thermal decomposition. [ABSTRACT FROM AUTHOR]

The paper experimentally investigates the integral characteristics of the processes involved in the reduction of gas temperature by injecting the aerosol flow of water droplets into a counter flow of combustion products (period of steady low gas temperature, Tg', compared to the initial, Tg, range of temperature decrease (ΔTg = Tg - Tg'), rate of temperature recovery, the geometric dimensions of the temperature traces and their lifetime). We use the following recording devices: fast-response thermocouples (heat inertia less than 0.1 second), a multi-channel recorder, a high speed video camera (up to 105 frames per second), as well as a cross-correlation hardware and software package (with optical methods for recording the front and trace of the aerosol). The temperature trace of an aerosol is defined as the area with the temperature Tg' lower than the initial Tg by at least 10 K. We determine how the following group of factors affects the characteristics of temperature traces of water droplets: size (0.04-0.4 mm) and concentrations (3·10-5-11·10-5 m³ of droplet per m³ of gas) of droplets in a pulse, the initial temperature of water (280-340 K), the duration of a pulse (1-5 seconds), the temperature (350-950 K) and velocities (0.5-5 m/s) of combustion products. The temperature in a trace of water droplets during their motion in a flame can be reduced due to rapid vaporization or heat exchange between the gases and water. The conditions are identified, under which the low temperature of gases in a trace of droplet aerosol can be preserved for a long time (20-30 seconds). Finally, we forecast the parameters of temperature traces under the conditions of actual fires with combustion product temperatures over 1000 K. [ABSTRACT FROM AUTHOR]

Five models describing heat transfer during evaporation of the water sprayed over the forest to stop fires and to cool down the pyrolysis of the bio- top layer are established and investigated by a parametric approach. It aims to improve the understanding of the behaviour and the properties of the forest combustible material. A mathematical description of forest combustible material surfaces (needles of pine and fir-tree, leaves of birch) is established. The characteristic time, td, to cool down the forest combustible material layer below the temperature of the onset of the pyrolysis is the important parameter investigated in the present work. The effective conditions were determined allowing to reach the shortest td and the lowest consumption of e. g. water to be dropped [ABSTRACT FROM AUTHOR]

This paper examines the laws of stable ignition of organic coal-water slurry containing petrochemicals (CWSP). The CWSP is based on the filter cake of coal and scavenge oil. The experiments are performed for individual CWSP particles soaring in a special set-up. The temperature and velocity of an oxidizer flow are varied between 500-1200 K, and 0.5-3 m/s. The dimensions (longitudinal and transverse) of particles range are from 0.5 mm to 5 mm. The study indicates how the shape of a fuel particle (sphere, ellipsoid, and polyhedron) influences its ignition characteristics (delay time, minimum temperature, modes, stages). Based on the experimental results, the paper explains why the surface configuration of particles influences the conditions of heat transfer with an oxidizer. The results obtained for soaring particles are compared with the results for fixed CWSP particles having different surface configurations (sphere, ellipsoid, and polyhedron). In general, the study may contribute to the expansion of the fuel resource base. The experimental data may be used for the development of the technologies of burning CWSP prepared by recycling traditional fuels. As a result of this study, several recommendations for the practical application of research results are made. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results on heating and evaporation features of heterogeneous (with opaque solid particles - the size of 0.05-0.5 mm, relative mass concentration 0-1%) water droplets (the initial size - radius 1-3 mm) during their motion through high-temperature (500-1800 K) gases. A significant increase in the integral characteristics of evaporation by introducing opaque inclusions into droplets was observed. The influence of energy accumulation on the conditions of droplet evaporation at the internal solid/liquid interfaces was established. For proportioned inclusions, the conditions of intensive vaporization (leading to the explosive disintegration of droplets) at internal inclusion/liquid interfaces was set. To summarize research results, experiments were conducted with the combustion products of kerosene, gasoline, industrial alcohol, acetone, and oil. The particles of graphite, carbon, and aluminum as solid inclusions were used. The investigation compared integral characteristics of heterogeneous droplet evaporation under the conditions of non-stationary (gas temperature varied from 1800 K to 500 K over the length of channel) and nearly stationary (gas temperature was maintained at about 1100 K) heating. [ABSTRACT FROM AUTHOR]

The paper examines the integral characteristics (minimum temperature, ignition delay times) of stable combustion initiation of organic coal-water fuel droplets (initial radius is 0.3-1.5 mm) in the oxidizer flow (the temperature and velocity varied in ranges 500-900 K, 0.5-3 m/s). The main components of organic coal- -water fuel were: brown coal particles, filter-cakes obtained in coal processing, waste engine, and turbine oils. The different modes of soaring and ignition of organic coal-water fuel have been established. The conditions have been set under which it is possible to implement the sustainable soaring and ignition of organic coal-water fuel droplets. We have compared the ignition characteristics with those defined in the traditional approach (based on placing the droplets on a low-inertia thermocouple junction into the combustion chamber). The paper shows the scale of the influence of heat sink over the thermocouple junction on ignition inertia. An original technique for releasing organic coal-water fuel droplets to the combustion chamber was proposed and tested. The limitations of this technique and the prospects of experimental results for the optimization of energy equipment operation were also formulated. [ABSTRACT FROM AUTHOR]

The using of the high-speed (not less than 105 frames per second) video recording tools (Phantom) and the software package (TEMA Automotive) allowed carrying out an experimental research of laws of intensive vaporization with an explosive disintegration of heterogeneous (with a single solid non-transparent inclusion) liquid droplet (by the example of water) in high-temperature (500-800 K) gases (combustion products). Times of the processes under consideration and stages (liquid heat-up, evaporation from an external surface, bubble boiling at internal interfaces, growth of bubble sizes, explosive droplet breakup) were established. Necessary conditions of an explosive vaporization of a heterogeneous droplet were found out. Mechanisms of this process and an influence of properties of liquid and inclusion material on them were determined. [ABSTRACT FROM AUTHOR]

The experimental study of integral characteristics of extinguishing liquid (water) droplet evaporation in flaming combustion area has been held. Optical methods of two-phase and heterogeneous mixtures diagnostics (Particle Image Velocimetry and Interferometric Particle Imaging) have been used for heat and mass transfer process investigation. It was established that small-size solid particles, for example carbon particles in droplet structure can enhance water evaporation in flame area. It was shown that the rate of evaporation process depends on concentration and sizes of solid particles in a water droplet. The correlations have been determined between the sizes of solid particles and water droplets for maximum efficiency of fire extinguishing. The physical aspects of the problem have been discussed. [ABSTRACT FROM AUTHOR]

Physical and mathematical (system of differential equations in private derivatives) models of heat and mass transfer were developed to investigate the evaporation processes of water droplets and emulsions on its base moving in high-temperature (more than 1000 K) gas flow. The model takes into account a conductive and radiative heat transfer in water droplet and also a convective, conductive, and radiative heat exchange with high-temperature gas area. Water vapors characteristic temperature and concentration in small wall-adjacent area and trace of the droplet, numerical values of evaporation velocities at different surface temperature, the characteristic time of complete droplet evaporation were determined. Experiments for confidence estimation of calculated integral characteristics of processes under investigation - mass liquid evaporation velocities were conducted with use of cross-correlation recording video equipment. Their satisfactory fit (deviations of experimental and theoretical velocities were less than 15%) was obtained. The influence of radiative heat and mass transfer mechanism on characteristics of endothermal phase transformations in a wide temperature variation range was established by comparison of obtained results of numerical simulation with known theoretical data for "diffusion" mechanisms of water droplets and other liquids evaporation in gas. [ABSTRACT FROM AUTHOR]

Numerical researches have been carried out to study the influence of air flow temperature and a fossil fuel particle rate on sufficient conditions of ignition in a "coal particle - air" system. Developed mathematical model takes into account interconnected processes of heat transfer in a coal particle and gas area, thermal decomposition of organic material, diffusion and gas-phase oxidation of volatiles, heating of a coke (carbon) and its heterogeneous ignition. The effect of low-temperature (about 600 K) ignition for a single coal particle is impossible even at variation of its rate (radius) from 0.05 mm to 0.5 mm. Nevertheless this process is possible for group of particles (two, three, et al.) situated at close-range from each other. The physical aspects of the problem are discussed. [ABSTRACT FROM AUTHOR]