An experimental study of the macroscopic laws of the ignition of coal-water slurry containing petrochemicals (CWSPs) based on coal and flammable liquids processing waste is presented. Investigations ...have been performed to determine the prospects for burning such fuel mixtures prepared from raw materials in power plants at temperatures ranging from minimal (700–800K) to high (not <1000K). Oxidizer flow velocities varied between 0.5 and 5m/s. The study specifies the main stages of the processes at different heating rates and heat flows through a fuel surface element (a droplet or a particle). Investigations have been conducted on a single droplet (radius from 0.25mm to 1.5mm) of a specified fuel composition (we have considered over 20 different compositions). With the use of cross-correlation and high-speed video cameras coupled with software applications Tema Automotive, Actual Flow, we have examined the interactions of oxidizer flow with a fuel droplet surface. The ignition delay time and durations up to complete combustion of CWSP droplets have been measured. The experimental results allowed us to elaborate the heat and mass transfer mathematical model including phase transitions and chemical reactions in the main stages of the processes under study, which are: the inert heating up of the sample, the evaporation of moisture from a superficial layer (water and flammable liquid), the thermal decomposition of coal in the superficial layer of a droplet, the mixing of volatiles with an oxidizer, the combustion initiation of the emerging gas mixture, the heating up of coke, and its heterogeneous ignition. From the mathematical model and experimental data, we have defined the necessary and sufficient conditions for the ignition of CWSP.
•Experimental method and mathematical model of droplet ignition are developed.•Typical ignition stages for coal-water slurry containing petrochemicals are specified.•Temperature change of droplet in the center and surface is determined.•Influence of heat source and droplet parameters on ignition conditions is analyzed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The research is focused on the ignition of solid fuels in a heated air flow. The experimental conditions correspond closely to solid fuel combustion in coal-fired boiler furnaces. Charcoal, wood, ...brown and bituminous coals were used as independent solid fuels and as fuel mixture components. The particle sizes of these fuels were less than 40 μm, 40–140 μm, 140–250 μm, 250–375 μm and 375–800 μm. They were ignited under the conditions of radiant-convective heating as they were moving in a heated air flow with a temperature of 500–800 °C and at a velocity of 5 m/s. The ignition delay time was the main investigated characteristic, recorded by a high-speed video camera. The induction period of bituminous coal shortens by 25–35% when 25–50% brown coal or wood in an air-dry state is added. The lowest ignition delay times were established for the fuel mixtures of bituminous coal with dry charcoal. The experimental curves of the ignition delay times of fuels and their mixtures versus the heated air temperature were presented as approximation equations. Based on the conducted research findings, a muffle burner design with a vortex structure of the fuel-air flow was proposed for the fuel oil-free start-up of coal-fired boilers.
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•Oil-free start-up of coal-fired boilers can be put into practice.•Adding 25–50% of highly reactive components to the main solid fuel reduces ignition time by 25–35%.•Particle size of fuel mixtures should not exceed 250 μm.•They are reliably ignited within 0.1–0.2 s at an oxidizer flow temperature of 500–800 °C.•Design of a burner unit for fuel oil-free start-up of a coal-fired boiler was proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Patterns and characteristics of gel fuel ignition by a hot particle were experimentally established.•Mathematical model of corresponding physical and chemical processes was ...developed.•Conditions and characteristics of the process necessary for ignition were established.•Induction period duration is conditioned by the initial fuel and hot particle temperatures, hot particle size and material.
The research investigates interdependent physical and chemical processes, occurring when a typical gel fuel is ignited by a hot particle. In the conducted experiments, high-speed video recording made it possible to establish the consistent patterns and characteristics of the ignition of gel fuel, based on an organic polymer thickener, by a disc-shaped steel particle 5 mm in radius and height. The fuel ignition delay times are 0.5–2.5 s when the initial temperature of the steel particle is varied from 1230 to 1500 K. A mathematical model of the investigated process was developed using experimental data obtained. It describes the interdependent processes of conductive heating and melting of gel fuel, melt evaporation, cooldown of the particle and its gradual immersion in the near-surface layer of the fuel, formation of a combustible gas–vapor mixture around the local heating source and its ignition under the conditions of diffusion-convective heat and mass transfer. The numerical simulation results are in good agreement with the experimental data. The developed mathematical model can be used in practice to predict the characteristics of gel fuel ignition by hot particles, when a group of factors in the particle – fuel – air system is varied in wide ranges.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We experimentally determined ignition and combustion of a sessile droplet of coal-water-oil slurry on modified steel samples at mixed heat transfer (radiation, conduction, and convection). The ...surfaces were modified by two different methods: using abradants and nanosecond laser irradiation. It was shown that a texture of steel samples formed by abradants allows changing the spreading diameter of a 50-mg coal-water-oil slurry droplet (0.44 mm in diameter) from 0.628 mm to 0.743 mm, and, thereby, changing the ignition delay time more than 2 times (from 0.108 s to 0.212 s). A multimodal hierarchical texture formed on steel samples after laser texturing allows increasing the effective contact area of a coal-water-oil slurry droplet with a conductive heat source by more than 18% at identical values of the droplet spreading diameter. This intensifies the droplet heating, increases the formation rate of a combustible vapor-gas mixture, and decreases the ignition delay time by 10–20% (to 0.093 s). A texture formed by laser irradiation increases the number of nucleation centers and intensifies puffing. Modification of steel by nanosecond laser irradiation makes it possible to diminish the intensity of ash deposition on the heating surface after the combustion of coal-water-oil slurry.
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•Abrasive processing of steel changes the ignition delay time more than 2 times;•Laser surface processing intensifies ignition and combustion of CWOS droplet;•Laser processing increases the number of nucleation centers and intensifies puffing;•A texture formed by laser irradiation reduces ash deposition during CWOS combustion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Micro-explosive dispersion of gel fuel particles occurs when they are ignited in high-temperature air.•Gel fuels with fine particles and without them feature different ignition ...mechanisms.•Average velocities of child droplets and size of the burnout area are 2 m/s and 8.0 cm3, respectively.•The heat generation rate of 10 mg gel fuel is about 190 W (vs. about 25 W for liquid fuel in original state)•Flame temperature during gel fuel combustion was for the first time established with two-color pyrometry.
The characteristics of processes developing during the ignition and combustion of single gel fuel particles with a mass of 10 mg in a high-temperature motionless air medium were investigated by means of a hardware and software system. The system featured a high-speed video camera, LED spotlights and a laptop with commercial and custom software. A group of fuel compositions was derived from oil-filled cryogels alone and with the addition of fine solid combustible components. Polyvinyl alcohol with 10 wt% in an aqueous solution was used as an organic polymer thickener. When exposed to rapid heating, fuel compositions (oil + aqueous solution of PVA + emulsifier; oil + coal dust + aqueous solution of PVA + emulsifier) were characterized by the micro-explosive dispersion of particles. The velocities of fine fragments after the micro-explosive dispersion of a fuel melt droplet were established when the air temperature was varied in the range of 700–1000 °C. The gas–vapor mixture temperature in the region of the fuel gas-phase combustion was determined using the original two-color pyrometry technique.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An approach to non-destructive evaluation of laminate composite plate elastic properties based on piezoelectrically induced elastic guided waves and laser Doppler vibrometry is presented and ...discussed. The reconstruction procedure is based on the genetic algorithm minimization of an objective function defined by the set of elastic moduli of the composite prepregs. The objective function defines discrepancy between theoretically calculated and experimentally measured dispersion characteristics of guided waves generated in the laminate anisotropic plate by piezoelectric wafer active sensors. The input data used for the identification are group velocities or wavelengths of the fundamental Lamb waves measured at varying excitation frequencies and propagation directions. The proposed approach has been experimentally tested on unidirectional and cross-ply carbon-fiber reinforced plastic plates and validated by conventional tensile tests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Comparative analysis of Hall effect in substitutional solid solutions Ho
0.5
Lu
0.5
B
12
, Mn
1 –
x
Fe
x
Si (0 ≤
x
≤ 1) and Eu
1 –
x
Gd
x
B
6
(
x
< 0.04) is carried out at temperatures 2–300 K in ...magnetic fields up to 8 T. Anomalous contribution to the Hall effect
~
has been identified for systems with various types of magnetic frustration. The linear scaling
~ ρ
xx
is detected in the resistivity range ρ
xx
~ 0.01–1 mΩ cm lying outside the range of applicability of the classical model of asymmetric scattering. It is associated with the increase in the amplitude of spin fluctuations in the paramagnetic phase of the investigated compounds with noncollinear magnetic structure. The topological contribution to the Hall effect is extracted for Ho
0.5
Lu
0.5
B
12
and Eu
1 –
x
Gd
x
B
6
. Its amplitude is found to vary from 80 nΩ cm (Ho
0.5
Lu
0.5
B
12
) to 7.5 μΩ cm (Eu
0.97
Gd
0.03
B
6
).
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The data in the literature on porous matrices and specific features of water in nanoporous structures are reviewed. This line of research is of great interest both for developing fundamental concepts ...about the behavior of liquids (in particular, water) under nanoconfinement conditions and in the context of possible practical applications of porous structures. Zeolite and silica matrices, carbon nanotubes, metalorganic materials, and various structures for medical and technical use are considered. It is shown that the structural and dynamic characteristics of nanoconfined water (density, viscosity, permittivity, structure and dynamics of hydrogen bonds, thermodynamic and relaxation processes, flows through pores, etc.) may differ from those typical of bulk water.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The possibilities of distributive bases from Gaussian sp-functions for calculating the correlation energy of molecules in the second order (Е(2)) of the Møller–Plesset perturbation theory (MPPT) have ...been investigated. The effectiveness of such bases has been demonstrated by comparing the Е(2) values obtained in distributive and standard atom-centered bases. Calculations have been performed for both the ground and excited states with ground symmetry. For this purpose, an analog of Møller–Plesset perturbation theory for excited states that preserves its advantages for the ground state has been developed. It has been shown that distributive
sp
-functions provide the accuracy of calculating Е(2) that is comparable to that of atom-centered bases including
s
-,
p
-, and
d
-functions.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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