The article presents the results of spraying tests of highly viscous coal-water slurries with a pneumatic nozzle and numerical studies of the structure of the gas-drop jet. An increase in the viscosity of coal-water slurries was ensured by introducing a third component into its composition - industrial waste (pyrogenetic liquid). The moderate effect of the slurry viscosity on the average droplet size of coal-water slurries in the jet is due to the high efficiency of the aerodynamic characteristics of the pneumatic nozzle. Introduction of pyrogenetic liquid in the amount of 20 % by weight into the composition of coal-water slurry significantly increases its viscosity. The value of the surface tension of such a slurry is more than doubled. The increase in the average droplet size was no more than 25 % when pyrogenetic liquid content in the composition of coal-water slurry was over 10 % by weight. The average droplet size of coal-water slurries varied in the range from 180 to 210 microns in the study area of gas droplet jet. The results of experimental and numerical studies have shown good convergence. High air velocities at short distances from the nozzle ensure high crushing efficiency of the jet of coal-water slurry. The breakdown of the boundary layer of the liquid from the periphery of the droplets of coal-water slurries and its subsequent destruction was observed at short distances from the nozzle. The values of the Weber number were 100<We<350. At considerable distances from the nozzle (more than 0.5 m), droplets of coal-water slurries were subjected to vibrational crushing (We<50).

Experimental studies were conducted to investigate the rheological properties and atomization characteristics of coal-water slurries sprayed by a pneumatic nozzle with addition of pyrogenetic liquid. The research object was coal-water slurries prepared on the basis of long-flame coal using a rotary hydrodynamic cavitation generator. The dynamic viscosity of samples was investigated using a Reotest-2 rotary viscometer. The droplet size of atomized slurries was determined by the interferometric particle imaging method. A pneumatic nozzle designed for spraying of coal-water slurry fuels was used. The calorific value of coal-water slurry compositions was estimated by a theoretical method using Mendeleev's equation for calculating the lower heating value of combustion of organic substances with a certain elemental composition. It was found that cavitation treatment of a two-component coal-water fuel for 90 s leads to a 48% decrease in its viscosity. It was shown that substitution of water with a similar amount of pyrogenic liquid (5 to 20%) leads to an increase in the viscosity of coal-water fuels. The cavitation treatment of such slurries reduces the viscosity of the respective three-component coal-water fuels by 27–45%. According to the results of static sedimentation studies, coal particles start to precipitate 24 h after the onset of cavitation treatment. The treatment of the slurries under consideration for 27 and 90 s in a rotary hydrodynamic cavitation generator was established to reduce the average droplet size in the jet after spraying with a pneumatic nozzle by 5.5% and 6.5%, respectively. The introduction of pyrogenetic liquid into the composition of coal-water fuels increases their calorific value by 6.9%. It can be concluded that the use of pyrogenetic liquid in the composition of coal-water slurry fuels followed by their treatment in a rotary hydrodynamic cavitation generator can solve the problem of low reactivity of coal-water slurries.

In the present paper, the process of co-combustion of coal-water slurry (CWS) and pulverized coal fuel (PCF) in the E500 pilot-industrial boiler employing a stepwise arrangement of afterburning is investigated based on numerical simulation. To describe the CWS and PCF co-combustion, the authors used a model of the motion of a multicomponent non-isothermal gas medium (carrier phase) based on the RANS approach, a model of droplet/particle motion based on the Lagrange approach, and a model of combustion in the gas phase based on a hybrid model. The proposed comprehensive mathematical model was tested based on data from a full-scale experiment. For the first time, a detailed comparative analysis of the impact of changes in the design of a pilot-industrial boiler, using a three-stage arrangement of combustion and the flare-drip combustion technology for CWS on the physicochemical processes in the combustion chamber and environmental indicators was carried out. The change of circulation zones depending on the coal fuel supply method during the implementation of three-stage combustion was investigated. It has been revealed that using CWS as a reducing agent allows reducing the amount of harmful NOx emissions relative to the basic version by more than 40%.

A model of a rivulet formed on the coils of a tubular heat exchanger has been developed. The cross-sectional shape of the rivulet is determined taking into account the forces of gravity of liquid, the forces of surface tension, and centrifugal forces. The equations for the coordinates of the free boundary points of the rivulet are presented in the integral form based on the analytical solution of the problem. The cross-sectional areas of rivulet and liquid bridge are compared, as well as the areas of their contacts with the working tubes.

В процессе обогащения углей образуются огромные объемы отходов, которые, как правило, выбрасываются в окружающее пространство, загрязняя его. При этом отходы могут содержать до 50% углерода. Малая промышленная энергетика, муниципальные котельные используют преимущественно слоевое сжигание углей. При этом коэффициент выгорания углерода составляет 50–60%, и коэффициент полезного действия котлов нередко не превышает 60%, а их экологические показатели не удовлетворяют современным требованиям. Эффективным способом решения проблемы утилизации углеотходов может оказаться перевод котлов на сжигание углей в виде водоугольной суспензии (ВУС). В статье представлены результаты авторов по технологии приготовления водоугольного топлива (ВУТ) и его сжиганию в вихревых топках котлов. Представлены данные по новому оборудованию, необходимому для реализации технологии. Показано, что и рядовые угли, и антрацит, и угольные шламы, а также отходы углеобогащения могут служить основой для производства ВУТ. Приведены примеры опытно-промышленного применения водоугольной технологии. При этом коэффициент выгорания топлива достигает значений порядка 95%, а коэффициент полезного действия котлов превышает 85%.

Characteristics of gas-droplet flow created by spraying a liquidusing an advanced pneumatic nozzle for suspension fuel were studiedexperimentally. The measurements were made using the shadow photographymethod. On the example of water, the disperse composition of thegas-droplet flow, jet expansion angle, and flow structure stability weredetermined for different regimes. It was shown that most droplets wereless than 10  $$\mu$$ min size. The disperse composition of the flow remained unchanged for awide range of operating parameters. The nozzle designed generatesdroplets of a size sufficient for efficient combustion of suspensionfuel under real conditions.

Operating characteristics of aeronautic and marine vehicles, as well as hydraulic machines designed for various purposes are largely affected by flow separation. Therefore, control of separated flows is an extremely important problem for modern aviation and marine engineering. Based on dynamometric measurements of forces and torque acting on model hydrofoils and the ship rudder, jet control of flow separation in cavitation-free and cavitation regimes at low and high angles of attack is studied. It is shown that generation of a near-wall jet can ensure a separationless flow around test models at angles of attack greater than 30 degrees. In this case, the lift coefficient of the hydrofoil can increase approximately by two or three times. Pressure fluctuations near the body and in its wake vanish due to flow stabilization; as a result, oscillations of hydrodynamic loads on the body decrease.

Abstract The paper studies a promising method of spraying, based on the interaction of cumulative and near-wall jets with the impinging liquid and the Coanda effect. The measurements are based on shadow photography (SP) and interferometric method (IPI). In a wide range of performance parameters data have been obtained on the disperse composition of a gas-droplet flow at water spray by a special pneumatic atomizer intended for coal-water fuel. The dependences of droplet sizes on the flow rate of liquid and spraying air have been found.

•Converging annular jet forms the straight and recurrent cumulative axial jets.•Toroidal vortex is formed in the diffuser.•Annular jet is characterized by the presence of shock-wave structures.•Mach discs are forming in the initial region of the axial jet.One of the topical problems of coal power engineering both from the standpoint of increasing efficiency and ecological safety of heat energy production and the need to utilize low-grade coals and coal wastes is the development and enhancement of combustion technology for coal in the form of a coal-water slurry (CWS). The technologies of CWS combustion place high demands on the spraying devices (nozzles): there should be no narrow fuel channels to avoid clogging; low fuel velocities relative to the solid walls, which will reduce abrasive wear. The authors of the paper propose and investigate a novel pneumatic nozzle based on the use of the properties of near-wall and cumulative jets of liquid and gas and Coanda effect, which meets the basic requirements for CWS injectors. Aerodynamics control plays the determining role in the efficiency of pneumatic nozzle operation. In this paper, the structure of a single-phase gas flow generated by the proposed pneumatic nozzle is studied under different regime parameters using the experimental and numerical methods. The studies were carried out using the particle image velocimetry (PIV) and mathematical modeling of the flows by means of the DES and RSM turbulence models. In the entire investigated range of excess air pressure, the converging annular jet is shown to turn into the concentrated one and forms the direct and return cumulative axial jets in the nozzle near the axis of symmetry. Due to interaction of the return and annular jets in the diffuser, a toroidal vortex is formed. At an excess air pressure of 1 bar in the nozzle, a converging annular sonic jet is formed at the nozzle exit. With a further increase in pressure, the outflowing jet becomes supersonic. At that the oblique shock waves are formed, and the axial jet acquires a barrel-like shape with formation of the Mach disks. Spatial arrangement of the flow (both in and outside of the toroidal vortex) contributes to efficient dispersion of liquid fuel in the proposed nozzle. The obtained results of the study of a single-phase gas flow structure justify the effectiveness of this nozzle for the formation of a fine multiphase flow during the CWS spraying.

The paper presents an experimental and computational study of various regimes of firing coal-water fuel in a low-power hot-water boiler that enable both dry and liquid slag removal. The experimental studies were carried out on a pilot industrial boiler adapted for firing coal-water fuel. The fuel was prepared using flotation products of beneficiation of K grade hard coal. The experiments were accompanied by numerical modeling of combustion processes. The mathematical model includes description of the carrier phase motion (based on the RANS approach with the two-parameter Menter SST k-ω turbulence model), radiation transfer (based on the P1 approximation of the spherical harmonics method for a two-phase two-temperature gray medium), particle motion (based on the Lagrange approach), and gas phase combustion (based on a combination of the kinetic model of combustion of gas components with the vortex break model). The physico-mathematical model was tested on the problem of combustion of coal-water fuel (CWF). One of the goals of the work was verification of a complex mathematical model. A comparative analysis of the results of the numerical modeling and experimental data showed that the model reliably described the process of burning in a combustion chamber. An advanced design of hot-water boiler enabling regimes of both dry and liquid slag removal was investigated. The chamber was shown to provide the necessary conditions for firing CWF in terms of reliability and economy.

The article presents results of an experimental study of the effect of gravitational orientation of the flow along its lower/upper solid boundaries on reduction of turbulent drag and void fraction profiles with injection of gas through a porous channel wall. The shear stress on the wall was measured in the Reynolds number range Re x = (0.23–1.1) × 10 7 by floating element transducers; the void fraction profile was determined using a fiber-optic sensor. The void fraction in the inner (near-wall) region of the boundary layer was shown to be a key parameter for turbulent drag reduction. The size of the inner region depends on the gas flow rate, the fluid velocity, the distance downstream of the gas generator, and the gravitational orientation of the wall.

A criterion was elaborated for the phenomenon of dry spot evolution in isothermal liquid films on a horizontal substrate. The formulas are presented for gravity force and surface tension acting upon an element of the rim around the dry spot. The forces balance gives the evolution of initial dry spot: to expand or to contract.

Thin liquid films formed near dry spots make a big contribution to heat and mass transfer processes due to intensive evaporation. Based on the solution to the problem of determining the shape of the film free boundary in a vicinity of a stationary dry spot formed by gravitational and capillary forces at a given contact angle, a criterion for the development (or shrinkage) of a dry spot in an isothermal liquid film on a horizontal flat substrate was derived without using additional assumptions and postulating the film shape near the spot.

Currently, in the world’s large-scale coal-fired power industry, the combustion of pulverized coal is the most widely spread technology of combusting the coals. In recent years, the micropulverization technology for preparation and combustion of the coal has been developed in this field. As applied to the small-scale power industry, the method of combusting the coal in the form of a coal–water slurry has been explored for years. Fine coal powders are produced and used in the pulverized-coal gasification. Therefore, the coal preparation methods that involve high-dispersion disintegration of coals attract the greatest interest. The article deals with the problems of high-energy impact on the coal during the preparation of pulverized-coal fuels and coal–water slurries, in particular, during the milling of the coal in ball drum mills and the subsequent regrinding in disintegrators or the cavitation treatment of the coal–water slurries. The investigations were conducted using samples of anthracite and lignite from Belovskii open-pit mine (Kuznetsk Basin). It is shown that both the disintegration and the cavitation treatment are efficient methods for controlling the fuel characteristics. Both methods allow increasing the degree of dispersion of the coal. The content of the small-sized particles reground by cavitation considerably exceeds the similar figure obtained using the disintegrator. The specific surface area of the coal is increased by both cavitation and disintegration with the cavitation treatment producing a considerably greater effect. Being subjected to the cavitation treatment, most coal particles assume the form of a split characterized by the thermodynamically nonequilibrium state. Under external action, in particular, of temperature, the morphological structure of such pulverized materials changes faster and, consequently, the combustion of the treated coal should occur more efficiently. The obtained results are explained from the physical point of view.

The present study is devoted to ultrasonication of exfoliated graphite in different organic solvents (dimethyl sulfoxide, propanol-2, and chloroform). Graphite nanoplatelets are obtained as a result of strong acoustic treatment (10 W/cm(3)). The obtained samples are investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, FTIR and Raman spectroscopies. It is found that the structural and texture characteristics of the obtained materials significantly depend on the type of a solvent.

The present paper describes the examples of experimental and industrial implementation of technologies of flame-droplet combustion of the coal-water mixture in furnaces above a bed consisting of burning coal and in a swirling-type furnace chamber. For preparing coal-water fuel (CWF), Kuznetsk coals of G and D ranks, as well as tailings of coking coals, were used. The future prospect of both technologies of coal combustion has been shown from both economic and environmental standpoints.

Mathematical simulation of isothermal film flow for a viscous ponderous capillary liquid with dry spots on a solid substrate was performed. The algorithm was developed for calculation of the shape of a ridge (around the dry spot): this algorithm takes into account gravity forces, surface tension, friction, and inertia effects. Simulation results performed by original method were compared with experiment and previous method that takes into account only gravity and capillary forces. It was demonstrated that both methods produce similar results at low Reynolds numbers. However, at Reynolds higher than one these two methods give different results.