Flow Of Combustion Products Research Articles

Numerical simulation of submicron particles formation during the combustion of coals, taking into account coagulation and dust content of combustion products

Homogeneous-heterogeneous bulk condensation of potassium sulfate vapor has been numerically simulated in a dusty vapor-gas flow of coal combustion products upon their cooling along a technological path. A closed model that we have proposed for the formation of submicron particles in coal combustion products has been employed. Data on the concentration of particles formed at varied parameters of heterogeneous condensation sites have been obtained. Variations in the relative contributions of the homogeneous and heterogeneous mechanisms with variations in flow dustiness have been considered. Data on the influence of coagulation processes on the parameters of submicron particles resulting from coal combustion have been presented.

Thermal calculation of the radiation chamber of an ethane pyrolysis furnace

Using our own application package that implements the differential method of thermal calculation of furnaces, we calculated the temperature fields in the radiation chamber and the distribution of heat fluxes along the tubular reactors in a ethane pyrolysis furnace. The interconnected combustion processes of fuel gas, the turbulent flow of combustion products, radiant-convective heat transfer are described by two-dimensional equations of transport and motion. Wall burners are installed in eight horizontal rows on both walls of the radiation chamber. The combustion products of fuel gas in the air leaving the nozzles 128 of the burner create complex fields of flow velocities and temperatures in the radiation chamber of the furnace. Heat fluxes to the reaction pipes are formed due to the radiations of flue gases, soot particles and hot lined surfaces of the walls of the combustion chamber.

Temperature Fields of the Droplets and Gases Mixture

In this research, we obtain gas–vapor mixture temperature fields generated by blending droplets and high-temperature combustion products. Similar experiments are conducted for droplet injection into heated air flow. This kind of measurement is essential for high-temperature and high-speed processes in contact heat exchangers or in liquid treatment chambers, as well as in firefighting systems. Experiments are conducted using an optical system based on Laser-Induced Phosphorescence as well as two types of thermocouples with a similar measurement range but different response times (0.1–3 s) and accuracy (1–5 °C). In our experiments, we inject droplets into the heated air flow (first scheme) and into the flow of high-temperature combustion products (second scheme). We concentrate on the unsteady inhomogeneous temperature fields of the gas–vapor mixture produced by blending the above-mentioned flows and monitoring the lifetime of the relatively low gas temperature after droplets passes through the observation area. The scientific novelty of this research comes from the first ever comparison of the temperature measurements of a gas–vapor–droplet mixture obtained by contact and non-contact systems. The advantages and limitations of the contact and non-contact techniques are defined for the measurement of gas–vapor mixture temperature.

Arc Steel Furnace Operation at Changing Working Space Aerodynamic Flows

Results of the design analysis carried out using computer software are presented for boundary data complying with the currently operating state-of-the-art arc steel furnace. Flow of natural gas combustion products and oxygen are reviewed for the radial and tangential burner arrangement in the working space between the wall and the electrodes. Location of high temperature fields is determined and the expected heat transfer to the charge materials through the active surface participating in heat exchange is evaluated. Precipitation degree is determined for the dust participating in scull generation on a wall water-cooled surface and significant reduction of dust effect on electrodes.

Simulation of combustion and combustion of fl ow products in K-2 thermal spraying torch for thermal spraying of protective coatings

The finite volume method to solve of the Reynolds-averaged Navier—Stokes equations in the SST model together with the equation for the total energy with the viscosity terms is used to analyze of combustion and combustion products flow in kerosene-oxygen torch used for protective coatings high-velocity spraying (HVOF technology). The distributions of the flame temperature and the flow velocity of the gas mixture are calculated. The most heat-stressed section of the device is found. Two calculation methods are compared. These are the modeling of chemical reaction in combustion chamber and the flow of mixture of oxidation reaction products of fixed (frozen) composition determined by thermodynamic calculation of isobaric combustion chamber. The thermodynamic calculation is carried out by means of specially created computer code. It is based on the thermodynamic potential minimization. Comparative analysis is carried out for lean, enriched, and stoichiometric mixture of fuel and oxidizer. Methodically important conclusion is made on the possibility of replacing of complex calculation with chemical reaction by simpler calculation with predetermined thermodynamically equilibrium gases composition. The error is about 3 %.

Адаптация математической модели обобщенного теплообмена в топках

Consideration of the scheme of flows of combustion products in furnaces and flow chambers of combus-tion within the framework of the heat transfer paradigm made it possible to determine the ratio of the genera-lized mechanisms of heat transfer – convection and radiation. The transition from uniform distribution of gas flow velocity to uneven distribution in furnaces with a geometrically peculiar fence has been implemented. This made it possible to take into account the use of recirculation gases, dual-light shades, changes in the shape and size of the cross-section of the furnace, and installation of shade surfaces in a furnace. The condi-tions for the correctness of the mathematical model are considered, and the eigenvalues of the boundary value problem under conditions of an asymmetric temperature field and the function of the gas temperature changing along the height of the furnace are obtained. A comparative analysis of the nature of the change in gas temperature with height according to the proposed model with the calculation for a steam boiler with a capacity of 950 t/h according to the standard method showed a satisfactory agreement of the calculated data with an accuracy of +4.87 %.

Drag and heat transfer of metal and oxide agglomerates in flow of combustion products of solid propellant

Drag and heat transfer of metal and oxide agglomerates in flow of combustion products of solid propellant

Effect of Condensed Phase Particles on the Electromagnetic Field Characteristics of Combustion Products in a Flow Path of a Liquid-Propellant Engine. The Results of Experimental Studies

This paper describes the experimental study of amplitude (with a frequency of up to 50 kHz) and integral characteristics of the self-magnetic field of high-temperature combustion products of hydrocarbon fuel, which flow out of the nozzle of a standard liquid-propellant engine (LPE) with simulation of the heat of a combustion chamber with injection of aluminum-magnesium alloy particles (c-phase) into the combustion chamber. It is determined that the amplitude of the magnetic field intensity generated by high-temperature (up to 3500 K) combustion products depends on the LPE operation modes and the presence of k phase particles in the particle flow. The magnetic field amplitude increases by 20% during the LPE burnout ≈0.2 s earlier than the pressure drop in the combustion chamber. The total volumetric electric charge generated by the combustion product flow with the c-phase is estimated.

Mathematical Modeling of Electrization of Particles of Acondensing Phase in High-Temperature Flow of Combustion Products of Rocket Engine

Mathematical Modeling of Electrization of Particles of Acondensing Phase in High-Temperature Flow of Combustion Products of Rocket Engine

Selection of temperature and power parameters for multi-modular lunar jet penetrator

The questions and the particularity of the choice of design parameters of multi-module lunar jet penetrators are considered. A constructive layout of the penetrator is proposed and the advantages of a multi-modular design are presented. In particular, the limitation on the depth of penetration of the reactive penetrator of the standard scheme, associated with the characteristics of the flow of combustion products from the nozzle into a variable length channel left after the passage of the apparatus, is described. An algorithm is suggested for solving the problem of design parameters of multi-module lunar jet penetrators, which is based on the same methods for finding design parameters of single-module penetrators. Nonetheless, in this case, among the main design parameters that uniquely determine the appearance of both individual modules and the apparatus as a whole, in addition to pressure in the combustion chamber, elongation, pressure relationships at the nozzle and in the chamber, engine running time in air, structural mass and angle, contents of the head including, multiple modules (or sections of the remote control) of the device. By the above method, the calculation of the gas-dynamic parameters for the operation process in solid propellant rocket engines was carried out. Critical temperatures of solid fuel and pressure in the combustion chamber are limited by the ones leading to destruction of the engine and the penetrator.

NOVEL TRENDS OF DEVELOPMENT AND PERFECTION THE MODERN HEAT EXCHANGERS

Some actual aspects of advancement the problem of improvement the heat exchange equipment are considered in the paper. First of all the actual items related to middle and high temperature recuperators are discussed with proper up-to — date approaches.
 The classification of flue gases heat recovery appliances has been proposed along with the statement and analysis of the main characteristics of the recovery plants and option the ways of optimization the mentioned characteristics.
 The problem of Reynolds analogy (similarity of relative change the heat transfer phenomenon and variation the hydraulic resistance) within the channels of different purpose and of various cross-section supplied with and without the obstacles has been analyzed in application to separate cases of flow along the surfaces equipped with the cavities (dimples) or the convex elements.
 Thermal Performance Factor (TPF) of the heat exchange process is qualitatively like to Reynolds analogy factor and is highly depended upon rate of heat transfer and of friction factor in conditions of the scheme under consideration for flow over the surface or flow within the channel. The various media has been compared used as a working body in the heat exchanger’s channels: gaseous, liquid and the nanofluids, the last appeared in practice since 2000.
 Analysis has been carried out on effect of using the secondary energy emitters (SEE) arranged inside the tube channels, on resulting heat flux by heat exchange between outward flow of combustion products and the inner air flow. Bibl. 23, Fig. 6.

Characteristics of “Bounce” of Interacting Water Droplets

We report on the results of experiments devoted to analysis of conditions and characteristics of “bounce” (approach and interaction through a gaseous buffer envelope) of water droplets moving in a gaseous media with different parameters: velocity and direction of motion, temperature, and composition. Experiments were performed in flows of air, water vapor, and combustion products. Peculiarities of bounce of droplets with different initial temperatures are considered, and the results obtained at 18–20 and 60–80°C are compared. More than 1000 collisions of droplets recorded by high-speed photography are divided into groups of bounce, coalescence, separation, and disruption. The results of criterion processing using the Weber numbers are obtained.

The Effect of Dustiness of Combustion Products and Coagulation Processes on the Parameters of Submicron Particles Resulting from Coal Burning

Homogeneous–heterogeneous bulk condensation of potassium sulfate vapor has been numerically simulated in a dusty vapor–gas flow of coal combustion products upon their cooling along a technological path. A closed model that we have proposed for the formation of submicron particles in coal combustion products has been employed. Data have been obtained on the concentration and size distribution of particles formed at varied parameters of heterogeneous condensation sites and rates of variations in the temperature of the flow. Variations in the relative contributions of the homogeneous and heterogeneous mechanisms with variations in flow dustiness have been considered. A criterion enabling one to judge the effect of flow dustiness on the bulk condensation process has been proposed. This criterion takes into account both dust parameters and rate of temperature variations in a condensation zone. Data have been presented on the influence of coagulation processes on the parameters of submicron particles resulting from coal combustion.

Experimentally determining the effects of water droplets collision when mixing aerosol with gas flow at different heating temperatures

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 ?m. 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.

Heat and mass transfer in low power condensation heat generators

A physical and mathematical model of heat exchange on the condensation surfaces of boilers is considered and analyzed. The profiles of the temperature and partial pressure of the components contained in the flow of combustion products on the condensation surface were studied., Generalized and partial dependencies (for specific designs of heat exchangers) are obtained for physical and mathematical model criteria. Qualitative standards of the influence of criteria on the overall performance of condensing heating surfaces of low-power boilers have been obtained.

Formation of solid residues in combustion of boron-containing solid propellants

Boron-containing solid propellants are promising propellants for ducted rockets. The experimental data show that combustion of boron-containing propellants is accompanied by an intense conglomeration of the boron particles near the burning surface. As a result, the boron particles conglomerates which are the branched coral structures composed of sintered boron particles are formed in combustion of boron-containing solid propellants. This results in decrease in combustion efficiency of ducted rockets. To calculate the ignition and combustion of a conglomerate in the secondary combustor of a ducted rocket, it is necessary to know the size, structure and shape of the boron particle conglomerates that can significantly affect these processes. In this paper, we consider a model and a method for calculating the boron particles conglomeration in combustion of the boron-containing solid propellants. The process of the boron particles conglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between the contacting boron particles and rupture of these bonds under the action of the aerodynamic detached force from the side the flow of gaseous combustion products of solid propellant. The criterion of formation of residues (slag) on the burning surface of boron-containing propellants is considered. It is shown that depending on the propellant burning rate law, two different types of propellants with different conglomeration behavior can exist. The results of calculations of the boron particles conglomeration which demonstrate the slag formation are shown.

Numerical Investigations of the Processes of Burning a Gaseous Fuel in the Furnace of the DE-10/14 Steam Water-Tube Boiler with a Secondary Tubular Radiator

The processes of burning a gaseous fuel in the furnace of the DE-10/14 steam water-tube boiler have been investigated numerically. The temperature and velocity distributions of the gases in the furnace space of the boiler, as well as the concentrations of combustion components have been determined. It has been shown that placing a secondary radiator along the horizontal axis of the burner in the furnace space of the boiler promotes the formation of a uniform temperature field along the length of the furnace and a decrease in the temperature in its space, and the reverse flow of combustion products to the combustion front provides a decrease in the concentration of nitrogen oxides to 123–125 mg/m3 at the furnace outlet.

The Fields of Flow and Temperatures in the Chambers of Radiation of Tube Furnaces with Multi-tier Wall Burners of Two Types

In the article, the differential method of thermal calculation of a furnace is used to determine the aerodynamic and thermal characteristics in the chambers of radiation of tube furnaces with wall burners of two types located on several tiers. In the methane steam reforming furnace, the acoustic burners of the near-wall flame gas fuel are arranged in three tiers on the side walls of the radiation chamber. In the primary reforming furnace for the production of ammonium nitrate, wall-mounted burners are located on six tiers. The method implies joint numerical solution of 2D radiation transfer equations using the S2-approximation of the discrete ordinate method, of energy equations, flow equations, k-e turbulence model, and two stage modeling of gas fuel combustion. Is it given a brief description of the boundary conditions for differential equations and the method of their numerical solution. The results of the calculation of the temperature fields and the flow of combustion products in the radiation chamber of the furnace obtained with the help of a computer program that implements the described method are given.

Характеристики "отскока" взаимодействующих капель воды

AbstractWe report on the results of experiments devoted to analysis of conditions and characteristics of “bounce” (approach and interaction through a gaseous buffer envelope) of water droplets moving in a gaseous media with different parameters: velocity and direction of motion, temperature, and composition. Experiments were performed in flows of air, water vapor, and combustion products. Peculiarities of bounce of droplets with different initial temperatures are considered, and the results obtained at 18–20 and 60–80°C are compared. More than 1000 collisions of droplets recorded by high-speed photography are divided into groups of bounce, coalescence, separation, and disruption. The results of criterion processing using the Weber numbers are obtained.

Explosive disintegration of two-component droplets in a gas flow at its turbulization

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.