High-temperature Gas Flow Research Articles

Experimental study of the low-melting hydrocarbons regression rate in the air flow

Gasification of organic and inorganic materials in a high-temperature gas flow is a promising technology for various industrial applications like chemical industry, waste processing, rocket and air-breathing propulsion, etc. However, the characteristics of the gasification process of low-melting hydrocarbon materials remain insufficiently studied so far. In this work, experiments on the gasification of cylindrical polypropylene (PP) samples by the airflow passing through multiple longitudinal channels 3 to 4 mm in diameter and 200 mm long are performed. The temperature, pressure, and velocity of the airflow in the experiments range from 300 to 1500 K, 0.35 to 1.38 MPa, and 17 to 100 m/s. As expected, oxygen available in the airflow interacts with PP and creates an additional heat source for PP gasification, thus, enhancing the gasification process. At an airflow temperature of 1480 K, the maximum mass flow rate of gasification products is shown to attain 17.7 g/s. The minimum ratio of the mass flow rates of the airflow and gasification products reaches the value of 2. In tests with airflow temperature of 300 K, the maximum mass flow rate of gasification products is 8.5 g/s. The minimum ratio of the mass flow rates of airflow and gasification products is 5 in these experiments.

Numerical Simulation of the Stress-Strain State of the Rocket Retention Module

The paper considers the thermal stress state of the module for retaining the rocket during firing. The high-temperature gas flow leaves the cruise propulsion system and flows around the retention module. As a result, it heats up. The temperature field, which is nonstationary with large gradients, causes the elastoplastic deformation of the structure. A procedure is proposed to determine the stress-strain state, which consists of two stages. In the first stage, the temperature field of the retention module is calculated. To this end, the high-temperature supersonic flow leaving the cruise propulsion system is numerically investigated. The flow parameters are used in a semiempirical procedure, by which the temperature field in the retention module is determined. At the second stage, the stress-strain state caused by the temperature field is calculated. The elastoplastic deformation of the material is described by a bilinear deformation curve and is calculated by the finite element method, which is implemented in the ANSYS software. As a result of a numerical simulation, it has been found that the most dangerous stress state is observed in the lower part of longitudinal reinforcement, where plastic strains occur.

Gas-Vapor Mixture Temperature in the Near-Surface Layer of a Rapidly-Evaporating Water Droplet.

Mathematical modeling of the heat and mass transfer processes in the evaporating droplet–high-temperature gas medium system is difficult due to the need to describe the dynamics of the formation of the quasi-steady temperature field of evaporating droplets, as well as of a gas-vapor buffer layer around them and in their trace during evaporation in high-temperature gas flows. We used planar laser-induced fluorescence (PLIF) and laser-induced phosphorescence (LIP). The experiments were conducted with water droplets (initial radius 1–2 mm) heated in a hot air flow (temperature 20–500 °C, velocity 0.5–6 m/s). Unsteady temperature fields of water droplets and the gas-vapor mixture around them were recorded. High inhomogeneity of temperature fields under study has been validated. To determine the temperature in the so called dead zones, we solved the problem of heat transfer, in which the temperature in boundary conditions was set on the basis of experimental values.

Evolution of the structure and phase state of the heat-resistant intermetallic coating of operating turbine blades

The paper treats important problems of domestic engineering, namely, the urgent necessity to increase service life of large-sized turbine blades of the power gas-turbine stations operated on thermal power plants. The heat-resistant coating of the Ni–Co–Cr–Al–Y system with intermetallic phase structure β-(Ni, Me)Al + γ′-(Ni, Me)3Al has been developed. It was made by high-energy plasma powder spraying and intended for protection of blade surface against high-temperature and erosive gas flow. The article studies microstructure, phase structure and physicomechanical properties of a coating given in an initial state, and after laboratory research of heat resistance and a post-operational state at ~29 000 hours (time of real operation of the gas-turbine engine of the GTE-45-3 power station on thermal power plant). After long-term operation, a decrease in the content of the intermetallic phase of β-(Ni, Ме)Al in the phase composition, an increase in the pore size and a decrease in the hardness of the coating have been established. At the same time, erosion resistance and heat-resistant properties of the coating remain, and, consequently, there is a sufficient resource.

Predicting performance of a thermal shield of a spacecraft in a high-temperature gas flow

A fundamental understanding of the mechanism of material interaction with a medium is based on correspondence between experimental studies and actual operating conditions of a given model or a structure. We estimated performance of thermal shield structures based on computations brought about considering physical properties of materials obtained under conditions simulating re-entry of a spacecraft into the atmosphere.A thermal shield is considered of a layered type shell, made of fiber glass with phenol-phormaldehide matrix. Both elastic and thermo-physical characteristics are varied depending on the temperature change.A thermal-stressed state of a cylindrical shield subjected to action of a high-temperature gas flow, is defined based on solving a 3D problem simultaneously using equations of theory of elasticity, thermal conductivity, and numerical analysis. Results are given as dependencies of stress distributions through the thermal coating, taking into account such parameters of atmosphere in re-entry as temperature, heating rate, pressure of a gaseous medium.

Effect of the Conditions of Formation of W–C Nanopowders in a Plasma Jet on the Synthesis of Hexagonal Tungsten Carbide

The effects of the conditions of a raw material introduction as well as mixing of it with a high-temperature gas flow under the plasma chemical synthesis of superdispersed powder of W–C have been studied. In the case of incomplete raw material evaporation and its fast quenching, preferred cubic tungsten carbide β-WC formation is found to occur, as well as nano- and microparticles with a complicated phase composition. In the case of complete raw material evaporation, the products of reducing synthesis are nanopowder of tungsten or semicarbide W2C depending on the amount of hydrocarbon introduced. There is a second stage of the process of low-temperature synthesis which leads to a single-phase of tungsten carbide α-WC formation. Complete evaporation of raw material must be ensured in the plasma chemical process for obtaining of α-WC powder with a maximum specific surface area.

Model of continuous production of fine silicon carbide

A detailed analysis of heat and mass transfer processes and chemical transformations in a high-temperature gas flow with solid particles is a very difficult task. Using the phenomenological approach, the authors succeeded in obtaining a closed system of equations, the solution of which allows us to determine the main parameters of the stationary process for the production of silicon carbide. It is assumed that the implementation of two technological conditions: maintaining the required temperature level of the system “fluidizing gas - solid particles” in the production process and the continuous removal of both the final product - silicon carbide, and small unreacted particles. Variant calculations were carried out with the determination of the parameters of the continuous process for the production of fine silicon carbide, in particular, the optimal ratio of the initial sizes of carbon-containing particles and SiO2 particles and the maximum possible yield of the final product. The qualitative agreement of the calculation results with the data obtained in experiments with periodic loading of reacting components is shown.

Effect of high-temperature gas flow on ignition of the water-coal fuel particles

The mathematical model of the ignition process of a drop of water-coal fuel (WCF) developed by the authors in the flow of a high-temperature oxidizer (air) has been presented. According to the results of the mathematical modeling, it has been established that the zone of ignition of the WCF particle with an increase in the flow velocity shifts to the area of the aerodynamic trace of the drop. A prognostic modeling of the ignition processes of the water-coal fuel drops under conditions corresponding to the furnace spaces (intensive radiation-convective heating, change in the dynamics of the aerodynamic spectrum of a fuel particle) of typical boiler units has been carried out. A comparative analysis of the ignition delay times (tign), obtained theoretically, and published earlier experimental values of (tign) has showed their good conformance.The results of the mathematical modeling have shown that the best option for stable ignition and burning of the WCF drop can be a combustion space consisting of two successive combustion chambers: in the first one, the thermal preparation and ignition of the WCF particle is carried out, and the second one is direct combustion.

Applicability of Dy-doped yttrium aluminum garnet (YAG:Dy) in phosphor thermometry at different oxygen concentrations

Phosphor thermometry is a method used to measure temperature based on the temperature-dependent phosphorescence of phosphors and elucidate heat transfer phenomena, such as high-temperature gas flow. Although various rare earth-doped thermographic phosphors are in use, the effect of oxygen concentration on their phosphorescence has not been sufficiently explored. We explore herein the applicability of Dy-doped yttrium aluminum garnet (YAG:Dy), a well-known rare earth-doped phosphor with temperature sensitivity above 1000 K, in phosphor thermometry at different oxygen concentrations. A third-harmonic Nd: YAG laser excited the sample. Phosphorescence was measured using a photomultiplier tube for lifetime detection. A spectrometer was used to detect the intensity ratio between two emission lines. The chamber was filled with a nitrogen–oxygen mixture with a controlled concentration. The phosphorescence intensity ratio depended on temperature over a wide temperature range and varied with the oxygen concentration, especially above 1000 K. The YAG:Dy lifetimes could be detected over the entire temperature range and remained constant up to 1000 K. In addition, the lifetimes decreased with the increasing oxygen concentration, especially above 1000 K, confirming the oxygen quenching effect. Consequently, YAG:Dy is confirmed to be sensitive to oxygen concentration for determining the intensity ratio and lifetime, especially above 1000 K.

Study of solid hydrocarbon gasification in spherical bedding under high-temperature gas flow

The paper presents a mathematical model and calculation results for the process of gasification of solid hydro-carbons (SHC) placed in form of spherical bedding inside channels with variable cross section and washed with high-temperature gas. Parametric study was performed for analysis of generator performance (mass flow rate and gasifica-tion products) as function of different parameters: temperature and composition of gas phase, thermophysical proper-ties of SHC, sphere diameter in the bedding, and channels configuration. The method for estimating the SHC gasifica-tion process in a flow duct of low temperature gas generator (LTGG) without loss of spheres shape (due to melting) was developed. The method offers recommendations for obtaining the required level of mass flow rate and gas temper-ature at the generator exit. These data can be used for analysis of experimental results on SHC sublimation at the stage of preliminary designing of the LTGG.

A high temperature gas flow environment for neutron total scattering studies of complex materials.

We present the design and capabilities of a high temperature gas flow environment for neutron diffraction and pair distribution function studies available at the Nanoscale Ordered Materials Diffractometer instrument at the Spallation Neutron Source. Design considerations for successful total scattering studies are discussed, and guidance for planning experiments, preparing samples, and correcting and reducing data is defined. The new capabilities are demonstrated with an in situ decomposition study of a battery electrode material under inert gas flow and an in operando carbonation/decarbonation experiment under reactive gas flow. This capability will aid in identifying and quantifying the atomistic configurations of chemically reactive species and their influence on underlying crystal structures. Furthermore, studies of reaction kinetics and growth pathways in a wide variety of functional materials can be performed across a range of length scales spanning the atomic to the nanoscale.

Simulation of motion, deformation, break-up and deposition of copper droplets transported in internal compressible flow including phase change effects

In this work, the motion, deformation, break-up, and deposition of molten copper droplets transported by high speed, high pressure, and high temperature gas flow along a steel internal flow path are examined numerically using a volume of fluid based approach. The study of the related phenomena is motivated by the erosion and fouling patterns along flow paths caused by such droplets. Good correlation to literature was achieved for a single drop impact. Methods were applied to multiple drops moving with gas flow in a main flow channel with a by-pass with the strength of the flow varied by changing the initial pressure in the main channel gas by up to a factor of four. The amount of copper removed from the main flow path grows from 58% to 87% when the driving pressure is quadrupled. A greater portion of the copper in the by-pass section is solidified as well with 90% solidified for the higher pressure, compared to 60% at the lower pressure. Solidification of the copper and melting of the steel require the proper combination of the molten copper location, the temperatures in the copper, steel, and gas, and the velocity of the transporting gas flow. The knowledge gained from the study can be applied to mitigate the fouling and erosion that may develop along internal surfaces. Because of the need for a small element size to prevent copper mass loss, the use of this method with complex three dimensional geometries may be limited.

Studying and designing improved coatings for labyrinth seals of gas­turbine engine turbines

An analysis of improving efficiency of aircraft engine turbines by means of improvement of composition of sealing coatings used in labyrinth seals was made. It was established that a number of contradictory requirements to properties of such coatings are imposed at the initial stage of engine running-in and during further operation. Main types of damage of above coatings used in the design of labyrinth seals during operation of gas turbine engines were shown. In connection with the necessity of raising temperature of gases in turbines of aircraft engines, it was proposed to additionally dope the serial nickel-based coatings with yttrium-containing master alloys. The results of study of influence of doping of the wearing-in sealing coatings on operating properties in conditions of action of a high-temperature gas flow were presented. It was found that doping of the KNA-82 serial coating with a multicomponent Co-Ni-Cr-Al-Y master alloy is the most rational solution.It was established that the use of the developed coating in a temperature range of 1,100...1,200 °C makes it possible to reduce specific consumption of fuel by aircraft engines by improving turbine efficiency and prevent wear of the end faces of ridges of the rotor labyrinth seal. Based on simulation of flow in the labyrinth seal clearance by numerical method, it was shown that the use of the developed coating materials in seals of the compressor turbine and the free turbine makes it possible to reduce amount of cooling air leakage into the turbine air-gas channel by reducing wear of tops of the labyrinth rotor seal ridge

UNSTEADY FRICTION AND HEAT TRANSFER IN THE INITIAL PIPELINE SECTION AT THE RESET OF THERMAL LOAD

The results of numerical and experimental study of wall friction and heat transfer in a short cylindrical channel are presented. Hydrodynamic and thermal characteristics of nonstationary high-temperature gas flow are determined. The results are summarized in the framework of boundary layer theory.

Adaptation of Radiative Properties of the End Products of Fuels Combustion within the Temperature Range of 1,000…2,000 K

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Ablation behavior of C/C-ZrC-SiC composites prepared by reactive melt infiltration under oxyacetylene torch at two heat fluxes

C/C-ZrC-SiC composites were prepared by reactive melt infiltration and tested using an oxyacetylene torch with the heat fluxes of 4.18 and 2.38 MW/m2. The results showed that compared to C/C and C/C-SiC at the heat flux of 4.18 MW/m2, the mass ablation rates of C/C-ZrC-SiC were decreased by 60.8% and 44.8%, respectively. Its linear ablation rate was 7.3% higher than that of C/C, but was 13.5% lower than that of C/C-SiC. The C-SiC matrix and fibers of C/C-SiC in the center region were severely depleted by the high ablation temperature. C/C-ZrC-SiC composites experienced the temperature exceeding 2400 °C associated with intense mechanical scouring of gas flow. The severe depletion of SiC and carbon fibers on the surface led to the formation of the porous ZrO2 layer. The spallation of ZrO2 occurred in the center of the ablated surface as a result of mechanical denudation of high temperature gas flow. At the heat flux of 2.38 MW/m2, the mass and linear ablation rates of C/C-ZrC-SiC were decreased by 76.8% and 88.4% (C/C), 66.9% and 58.3% (C/C-SiC), respectively. The oxide was slightly peeled off in the center region of C/C-SiC. The surface temperatures of C/C-SiC and C/C-ZrC-SiC were lower than that of C/C composites. The island-like ZrO2 and SiO2 layer were formed on the ablated surface of C/C-ZrC-SiC and acted as effective barriers to shield the ablation heat and slow inward transport of oxygen to the underlying material.

Thermal to optical energy conversion: A multi megawatt carbon dioxide laser driven by an extremely high temperature gas cooled reactor

In the conversion of ionizing radiation into energy, the production of heat is the most common first step in energy conversion systems, but it is also possible to use ions and excited states as the first step. The difference being that nearly all of the energy content of ionizing radiation is converted to heat but only 40–50% of the energy content of ionizing radiation is converted into ions and excited states. Conversion of the energy contained in ionizing radiation into ions and excited states starts out at a considerable disadvantage. Nuclear-pumped lasers have typically depended on the conversion of ionizing radiation into ions and excited states as a first step. Among the reasons that nuclear-pumped lasers have had low system efficiencies (1–2.5%) is the considerable inefficiencies in producing ions and excited states from ionizing radiation. A nuclear-pumped laser system which uses heat produced from the energy content of ionizing radiation as the driver for the laser system is described in this paper. The conversion of heat into vibrational states in molecular nitrogen allows energy to be stored in a long lived molecular state which can then be transported spatially where its energy is collisionally conveyed to carbon dioxide molecules in a resonance transfer process to produce the carbon dioxide upper laser level. The carbon dioxide laser emits a laser beam with a wavelength centered at 10.4 μm. The nitrogen vibrational state and its resonance conversion into the carbon dioxide upper laser level is one of nature's most efficient processes in laser physics (with laser efficiencies approaching ∼20% primarily being driven by the resonance process-extremely high for a laser). The laser system described here takes advantage of this highly efficient mechanism for conversion of thermal energy to optical energy. The feasibility of using nuclear rocket core technology for the generation of high temperature gas flows to power this thermal to optical conversion process is described. This study indicates that the thermal to optical conversion process can lead to a carbon dioxide laser with efficiencies on the order of 7% or perhaps better. Such a system would have potential applications in power beaming, space propulsion, asteroid mining, asteroid deflection and potential military applications.

Analogue Simulation Research on Heating Characteristics of Inner Channel of High-temperature Gas Flow

The thermal test of structure generally uses the quartz lamp radiation heating method, but this method is not suitable for heating of the internal surface of a long and narrow irregular channel. This paper puts forward a heating method of inletting the high-temperature gas flow to the channel, and uses CFD numerical simulation method to explore the internal surface temperature rise and temperature distribution conditions of the channel at different temperature and under the impact of Mach number of gas flow and verify the heating capacity of high-temperature gas flow, and also gives out Mach number of the best incoming flow when the total temperature ability of the high-temperature gas tunnel can obtain the highest wall temperature under certain conditions, thus providing a theoretical basis for reasonable determination of the best operating conditions for test.

Process simulation and thermodynamic evaluation for chemical looping air separation using fluidized bed reactors

Chemical looping air separation (CLAS) is considered as a promising method for providing an efficient and economic oxygen supply for integration into oxy-fuel combustion power plants. This study is the first to develop a process model, identify the process characteristics, and optimize the thermodynamic behavior for CLAS processes using fluidized bed reactors. In the process developed model, a fast fluidized bed model and a bubbling fluidized bed model are used to respectively represent the oxidation reactor and the reduction reactor, while fluidized bed hydrodynamics and oxygen carrier redox reaction kinetics are considered to grasp the unique characteristics of CLAS process. The effects of operating parameters on CLAS operation are identified and observed that high reduction temperature and high fluidizing gas flow rate can enhance oxygen carrier conversion and reduce energy penalty in the reduction reactor. Multi-variable optimization to minimize specified energy consumption illustrates that, 38.1% energy savings can be achieved and the optimal oxidation operating temperature, reduction operating temperature, air flow rate, and fluidizing gas flow rate are determined as 830 °C, 950 °C, 1133.7 L/h, and 58.4 L/h, respectively. These results are valuable for use by engineers to optimize the process design and achieve energy-efficient operation for CLAS processes.

Evaporation of water droplets with metallic inclusions

The dynamics of non-axisymmetric evaporating droplet with metallic inclusions heated in a high-temperature gas flow are experimentally studied. The type of metallic inclusion is found to play a critical role in the transient flow dynamics and associated heat transfer. Experiments were conducted with eight metals and alloys currently used in industrial applications. High-speed recording (up to 102–104 frames per second) allowed measuring lifetimes of water droplets with different metallic inclusions (1 mm or 2 mm in size) when increasing the gas temperature from ∼300 K up to about 900 K. We propose a candidate mechanism of evaporation that explains the differences between measured droplet lifetimes in the performed tests. Furthermore, the conditions to provide the most effective cooling are determined. They are based on the balance equations taking into account warm-up times of inclusions and the ratio between the latent heat of vaporization of water, the energy used to heat up water and the metallic particles.