Results of field experiments on determination of the macroscopic mechanisms of heat and mass transfer in the localization of a ground forest fire with the use of a barrier strip in the form of a ...wetted layer of forest combustible materials (needles, leaves, twigs, and their mix), positioned upstream of the front of combustion of such materials, are presented. Most attention has been concentrated on the complex analysis of the influence of the dispersity of a water aerosol (the concentration of the water droplets in it and their sizes), used for the formation of a barrier strip, on the parameters of this strip. It is shown that the conditions of effective localization and suppression of the flaming and thermal decomposition of forest combustible materials can be realized in the case where a group of barrier strips of different widths, wetted to different depths, is formed in front of a forest fi re. The parameters of barrier strips (the volume of water supplied to a strip, the width of the strip, the depth of its wetting, and the specific density of the water in it) necessary and sufficient for the localization of ground forest fires of different sizes were estimated.
Presented are results of experiments on high-speed video recording of collisions of water droplets in a gas medium as part of aerosol. Parameters of the gas (air) flow and aerosol cloud were ...monitored using cross-correlation complexes and optical methods of Particle Image Velocimetry, Particle Tracking Velocimetry, Interferometric Particle Imagine, and Shadow Photography. Conditions at different degrees of gas flow turbulence were considered. The characteristic Reynolds numbers ranged from 1100 to 2800. The relative probabilities of coagulation, scattering, and fragmentation of water droplets upon their collisions were calculated. Experimental dependences of probabilistic criteria on parameters of droplets and flow have been obtained for subsequent mathematical modeling. It has been shown that fragmentation and complete breakup of droplets can enable several-fold increase in the relative area of the liquid. The effect of the degree of gas flow turbulence on parameters of recorded processes of interaction of droplets has been established. The results of the experiments were subjected to criterion processing, theWeber and Reynolds numbers taken into account.
Experimental investigations have been performed in an effort to obtain a general approximate expression for the definition of the transition boundaries between the four collision regimes of droplets ...(their rebound, dispersion, coagulation, and fragmentation) depending on the key parameters of the interaction of the droplets (their Weber number, the dimensionless linear collision parameter of the droplets, and the ratio between their sizes). Water was used as a base liquid. An information background of values of the indicated parameters has been created for the purpose of their use in the prediction of the critical Weber number of droplets experiencing transitions between the four collision regimes.
Principal differences are shown as to the number and size of newly formed droplets after the collision of spheres, disks, and ellipsoids as well as critical Weber numbers sufficient for intense ...atomization. The typical breakup times differ for the sphere – sphere, sphere – disk, and sphere – ellipsoid systems within 5–7%, and the number and total surface areas of post-collision droplets in such systems vary several-fold (sometimes, by more than an order of magnitude). We compare three droplet disruption modes: disintegration of a bridge between variously shaped droplets, inflation of a target droplet (usually a disk or ellipsoid) by a projectile droplet (mostly sphere), and aerosol formation induced by the axisymmetric collision of liquid fragments with similar initial shapes. Conditions are determined for the many-fold and, on the contrary, insignificant increase in the number of droplets in an air flow due to their collisions in the breakup mode.
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•Shape of the colliding droplets affects the disruption mode and outcomes.•Three disruption modes are singled out.•Critical Weber numbers of stable disruption are much lower for disk-shaped droplets.•Breakup time of spherical drops is ~10% longer than this time of ellipsoids and disks.•Child-droplets number increase significantly for different-shaped primary drops.
A comparative analysis of the results of experimental investigations on determination of the conditions necessary and sufficient for the localization of ground, crown, and combined forest fires with ...the use of a barrier strip of moistened forest materials has been performed. The rational volumes of water used for the formation of such a strip in front of a forest fire and its sizes were determined. Different variants of localization of flame combustion and thermal decomposition of forest combustible materials depending on the action of an air flow (wind) on them were analyzed.
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•CO2 and vapor bubbles in colliding droplets enhance their secondary atomization.•Bounce and disruption are typical regimes for gas-saturated or boiling water droplets.•The number of ...child droplets of gas-saturated water is 70–90% higher than that of distilled water.•Micro-explosion delay times are 12–18% lower when water contains CO2 bubbles.
The paper presents the experimental research findings for secondary atomization of gas-saturated (filled with CO2 bubbles) water droplets. Experiments were also conducted with water droplets, filled with vapor bubbles as a result of heating them to a near-boiling condition. Two schemes of droplet atomization have been considered: collisions and micro-explosive breakup due to rapid heating. The second scheme was implemented using two-component droplets, formed by adding a liquid combustible component (rapeseed oil – a promising biofuel) to water. A well-tested technique was used to generate a two-component droplet: water at the core with an envelope of rapeseed oil. Using the experimental data, the ratios of liquid surface areas were calculated before and after implementing each of the secondary atomization schemes. Additionally, interaction regime maps of droplets were produced, specifying the conditions of their rapid disruption. It has been shown that the micro-explosive atomization of droplets with CO2 bubbles occurs with a shorter delay, and the ratios of child droplet surface areas are higher than those of parent droplets without CO2 bubbles. Optimal conditions, defined for using two of the investigated methods of secondary atomization of droplets, make it possible to increase the liquid surface area more than tenfold.
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•Single-component and multi-component drops collide within the four regimes.•By changing from target to projectile and back, one can control interaction regimes.•Water drops may be ...several times smaller due to collision with slurry or diesel drops.•Diesel drops can be atomized more significantly if they collide with each other.•Heating of all liquid drops intensifies their disruption and bouncing.
This paper presents the results of experiments recording the collision characteristics of droplets of various liquids with each other in a gas medium. We use water-based compositions typical of fuel, petrochemical, and heat and mass transfer technologies: solutions, emulsions, slurries, immiscible two- and multi-component liquids. The study discusses how droplet dimensions, velocities, impact angles, component concentrations and properties affect interaction regime as well as the number and size of child droplets. Threshold conditions are analyzed for the occurrence of bouncing, separation, coalescence, and disruption of droplets. Basic hypotheses are formulated as to why the collision characteristics of single-component droplets in a gas differ from those of highly heterogeneous multi-component ones. We use the interaction regime maps based on the dimensionless processing of experimental results through angular and linear impact parameters, Weber, Reynolds, Ohnesorge, and capillary numbers. Collisions can provide major atomization, in which the relative surface area of the liquid increases 2–6 times. The values of these parameters are influenced by droplet velocity and size, component type (solid or liquid), concentration and properties (density, viscosity, surface tension), as well as temperature and role (projectile or target) of homogeneous and multi-component droplets.
The scintillation crystal bismuth germanate (BGO) is widely used in many applications. The unique technique developed in the Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia, allows ...routine production of top quality large-sized BGO crystals. One of the important properties of a scintillation crystal is its radiation hardness. The intensive study of the radiation hardness of BGO crystals has been carried out by the collaboration of the Institutes of Siberian Branch of the Russian Academy of Science, Novosibirsk. The influence of the raw material purity and growth procedure on radiation hardness has been studied. The final tests of the crystal radiation hardness were performed by irradiating it with gamma rays from the radioactive source. The degradation of a light output of the best crystals is less than 10% after irradiation with doses of 10-100 krad expected in astrophysics experiments at a satellite. Based on the results of this study, the radiation hard BGO crystals for the "INTEGRAL" and "ASTRO-H" satellite missions have been made. A selfrecovery of the crystal light output is clearly seen. The time scale of the self recovery strongly depends on a dose of irradiation. It is days for 1 krad irradiation, weeks - for a 10 krad dose and a much longer period is required for 100 krad irradiation. All the crystals irradiated with a dose of 100 krad completely recover after annealing. The study reveals that there will be no essential degradation if this dose will be integrated over years of operation.
Alpha backgrounds in the AMoRE-Pilot experiment Alenkov, V.; Bae, H. W.; Beyer, J. ...
The European physical journal. C, Particles and fields,
12/2022, Letnik:
82, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The Advanced Mo-based Rare process Experiment (AMoRE)-Pilot experiment is an initial phase of the AMoRE search for neutrinoless double beta decay of
100
Mo, with the purpose of investigating the ...level and sources of backgrounds. Searches for neutrinoless double beta decay generally require ultimately low backgrounds. Surface
α
decays on the crystals themselves or nearby materials can deposit a continuum of energies that can be as high as the
Q
-value of the decay itself and may fall in the region of interest (ROI). To understand these background events, we studied backgrounds from radioactive contaminations internal to and on the surface of the crystals or nearby materials with Geant4-based Monte Carlo simulations. In this study, we report on the measured
α
energy spectra fitted with the corresponding simulated spectra for six crystal detectors, where sources of background contributions could be identified through high energy
α
peaks and continuum parts in the energy spectrum for both internal and surface contaminations. We determine the low-energy contributions from internal and surface
α
contaminations by extrapolating from the
α
background fitting model.
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