Home – Home – Jornals – Thermophysics and Aeromechanics 2023 number 3

Results of an experimental study of the influence of argon addition on microwave plasma chemical vapor deposition of diamond from a hydrogen-methane mixture are reported. A specific feature of this method is the use of a high-velocity jet for transporting gases activated in a microwave plasma in the discharge chamber to the substrate located in the deposition chamber. Optical emission spectroscopy is used for systematic investigations of the microwave discharge plasma in the discharge chamber. Diamond coating samples obtained on the molybdenum substrate are studied by methods of scanning electron microscopy and Raman scattering spectrography.

The present numerical study is aimed at revealing the influence of the distance between the nozzle exit and the resonator edge on the gas-dynamic characteristics of the acoustic-convective flow in the flow path of a bichannel system. The aim of the work is the development of a computational technology for describing the physical processes in the flow path of multichannel systems that generate high-intensity acoustic fields. Five configurations of the bichannel system were considered, where the gap was 0.85, 1.10, 1.35, 1.60, and 1.85 of the resonator diameter. As a result of the study, a complete picture of the gas-dynamic flow formed in the flow path of the bichannel system was obtained, including the resonating cavity and the region in between the nozzle and the resonator. With the help of numerical simulation, the formation of a flow with high-frequency, low-amplitude oscillations at a small gap between the nozzle exit and the resonator edge, which was observed in experiments, has been demonstrated. Pure-tone oscillations with maximum intensity occur when the resonator is placed in the region of the beginning of the second barrel, this observation being in good agreement with the data by other authors. Subsequent increase in the distance between the nozzle and the resonator leads to the emergence of subharmonics and multiple harmonics. Verification of gained numerical results with known experimental data is carried out.

Modeling of processes with phase transition in confined spaces needs high-accuracy simulations with account for non-equilibrium. In the present paper, we use the direct simulation Monte Carlo method for describing evaporation into a vapor-filled half-space with a subsonic monoatomic gas flow. Two types of boundary conditions for open half-space are considered: the interaction approach with consecutive calculating of temperature and pressure, and the approach with a fixed velocity. We compared these approaches for obtaining the accurate solution of the problem. The fixed-velocity approach provides a higher accuracy for the flow with a low Mach number. The calculated results are compared with a known solution of a model kinetic equation.

The present work deals with the design optimization of different vehicle configurations for planetary entry. Choosing the aerothermodynamic characteristics of heat flux and drag as the objective function we have analyzed and simulated the effects of atmospheric resistance on planetary entry vehicles in the rarefied atmosphere. We have utilized the SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) DSMC simulator for our simulation. The optimization is carried out with the help of MATLAB optimization module. We have simulated the descent of the present work demonstrates two of the planetary atmospheric conditions, the first one is Earth, and the later one is Mars. The vehicle geometry is then optimized according to the planetary atmospheric conditions. This work ultimately provides insight into how the effects of geometrical parameters play a pivotal role in the aerothermal loads of planetary entry vehicles.

The problem of laminar mixed convection is considered in a flat vertical channel with lifting and lowering flow and liquid heating, i.e., for cases of coincidence of the directions of free and forced convection, as well as their opposite directions. The solution of the system of equations of motion, continuity and energy is performed by the finite difference method. Data on the profiles of the longitudinal velocity, temperature, and Nusselt numbers at the lifting and lowering flows have been obtained. An explanation is given for the peculiarities of these values under the influence of buoyancy force. All components of the hydraulic resistance coefficient for lifting and lowering flow have been analyzed. The influence of the Prandtl number and the velocity profile at the channel input on the hydrodynamic and thermal characteristics of the flow is considered.

Within the framework of the linear subsonic theory, the problem of influence of flow boundaries on the flow around airfoil according to the measured distribution of pressures on the airfoil and on the test-section walls is solved. For the test case (testing a BGK1 airfoil in the IAR1.5m wind tunnel), we compared the corrections to the oncoming-flow Mach number and to the airfoil angle of attack that were obtained using our method and in works by other authors. For a OSPB-77 airfoil model tested in the T-128 wind tunnel for two values of wall permeability, ƒ = 0 and 3 %, correction of distributed data and integral loads was applied in the range of Mach numbers from 0.2 to 0.78. The application of corrections has made it possible to bring the results for ƒ = 0 and ƒ = 3% in closer agreement up to the angles of attack at which flow separation occurs on the airfoil.

The structure of a slug gas-liquid flow and interfacial mass transfer during the flow of ethanol-N₂ and ethanol-CO₂ mixtures in a horizontal rectangular microchannel have been experimentally studied. The experiments were carried out in a straight microchannel with a cross-section of 380×190 µm. To determine a change in the volume of a gas slug along the microchannel length, the method of high-speed visualization with digital processing was applied. In a wide range of gas flow rates, the repetition rate and the volume of gas slugs and their velocity were measured, and he volumetric coefficient of mass transfer from liquid was determined for the ethanol-CO₂ mixture. A physically substantiated model of interfacial mass transfer for a slug flow in a channel of rectangular cross-section, which takes into account the circulation flow in a liquid bridge, is proposed.

One of the promising methods of geophysical research in operating wells is active thermometry. The method consists in creating an artificial temperature field in a well due to local heating of the metal casing. Observation of heat tags movement enables determining the fluid flow rate in the well and identifying the intervals of the behind casing flow. The article is devoted to the study of non-stationary thermal processes in a well during induction heating. The calculations were performed in the commercial simulator Ansys Fluent*. It was established that with an increase in the volumetric flow rate through the column from 5 to 50 m³/day for the modeling conditions, the maximum heating of the liquid (a change in the average mass cross-section temperature) is reduced by 85%, and the maximum heating of the column is reduced by 7%. The influence of natural convection on the formation of a temperature field in a liquid and a column has been studied. For the model with natural convection accounted, the column heats up significantly less than for the model without convection: the error in calculating the temperature changes due to neglect of natural convection can reach several hundred percent. During the process of induction heating for the casing, the effect of natural convection remains significant throughout the entire flow range of 5-50 m³/day.

The flow of liquid over the corrugated sheets of regular packings largely determines the processes of heat and mass transfer in distillation columns. An important role in the distribution of liquid over the structured packing sheets is played not only by the characteristics of packing surface microtexture, but also by the drip point location in the liquid distributor relative to the sheets in the structured packing plugs. It has been established that even a slight displacement of the drip point relative to the channels of a regular packing can lead to noticeable redistribution of liquid over the packing sheets. Knowledge of the detailed structure of the flow in the distillation column allows better understanding of the physical nature of the mechanisms that control the flow. It is shown experimentally that the negative impact of the uncertainty associated with the drip point position on the liquid distribution under a layer of structured packing can be reduced using liquid redistributors in the form of inclined plates with horizontal microtexture.

Three-dimensional numerical simulation of a transverse hydrogen jet blowing into a duct with a supersonic flow of air (warmed by a fire heater) has been carried out. The study is based on experimental data obtained at the ONERA-LAERTE facility. The RANS equations for the reacting gas were solved, closed by the SST model and various kinetic mechanisms of hydrogen combustion in air. The channel walls roughness was taken into account. The dependence of the flow characteristics on such physical factors as the shape of the fuel injector channel, the effective roughness height, and various methods of describing molecular diffusion has been studied. It has been established that the equivalent diameter of a grain of sand has a significant influence on the longitudinal pressure distribution in the duct. The influence of chemical kinetics on the flow structure in separation zones within the duct is demonstrated.

The study presents the results of simulation and experiment for motion of a supersonic two-phase jet passing through a round aperture in a mask. The mask is placed at different distances from the deposition substrate with performing the cold gas spraying. The calculations were performed using the fluid dynamics code ANSYS Fluent; flow visualization is achieved using the Schlieren method. Solution analysis and comparison of results were performed for example of aluminum powder spraying.

Phenol oxidation in a water-oxygen fluid in a tubular batch reactor with its uniform heating (1°C/min) to 600°C was studied. An increase in the amount of O₂ over the stoichiometric ratio by 25% leads to an increase in the degree of carbon burnout by the factor of 1.09. Replacing 10% of the stoichiometric amount of oxygen with nitrous oxide leads to the same increase in the degree of carbon burnout, primarily due to its afterburning at a temperature of ≥ 400°C. Replacement of some part of phenol with isopropanol leads to an increase in the degree of carbon burnout by 1.02 times. It was established for the first time that the heterogeneous mechanism of phenol oxidation in a water-oxygen fluid is the main one. However, the overstoichiometric amount of O₂, as well as the addition of N₂O and isopropanol, intensifies gas-phase combustion of carbon. A catalytic effect of a Pt-Rh/Pt thermocouple on the degree of phenol conversion in the presence of O₂ at temperatures above 135°C was found.

The enthalpy and heat capacity of solid and liquid Mg₂Ca intermetallic alloy were measured with the help of mixing by massive high-temperature isothermal drop calorimeter over the temperature range of 298.15-1177 K. The estimated errors in the data on enthalpy and heat capacity were 0.2% and 2%, respectively. The fusion enthalpy of the Mg₂Ca intermetallic alloy was determined to be 483 ± 3 J/g. The heat capacity of the Mg²Ca melt was shown to be constant in the range of 993.2-1177 K. A comparison of the obtained results with literature data has been carried out.

The presented paper considers a number of problems. The first of them concerns the analysis of experimental (ρ_l, ρ_g, T)-data for SF₆ at relative temperatures (1,5∙10^-8< τ < 0,3). The second task is related to the development of combined models (ρ_l(D, C, τ), ρ_g( D, C, τ), … ), that agree with a number of boundary conditions, including the requirements of the scale theory of critical phenomena. The third task is to calculate (D, C)-parameters included in the combined models; at this stage, a basic array of (ρ_l, ρ_g, T)-data is formed, including experimental results obtained in the laboratory of Prof. Funke (Germany), and (ρ_l, ρ_g, T)-data obtained by recalculating the results in the laboratory of Prof. Garrabos (France). The models for (ρ_l(D, C, τ) and ρ_g(D, C, τ) served as the basis for calculating some thermodynamic properties of SF₆ in the critical region.

Using the method of differential scanning calorimetry, the heat capacity of Mg-Ca alloys containing 10.50, 33.34, and 73.00 at. % Ca, being promising for various practical applications (biocompatible and biodegradable alloys, ultralight construction materials, anode materials, hydrogen absorbent materials, etc.) has been studied experimentally. New reliable experimental results on the specific heat capacity in the temperature range of 190-576.692 K of the solid state have been obtained. The estimated errors of the received data were 2-3 %. The reference tables for temperature dependences of specific heat capacity of Mg-Ca alloys have been compiled. It has been established that over a wide temperature range the heat capacity of solid magnesium-calcium alloys can be estimated with high accuracy using the Neumann-Kopp rule.

The paper describes an algorithm that using numerical methods allows calculating the relationship between the temperature of the spectral ratio and the actual temperature of a "non-gray" object, which takes into account not only the dependence of the spectral emissivity of the object on the wavelength, but also its temperature dependence, inherent in almost all real objects (materials). This algorithm is applicable to any pyrometers of spectral ratio: narrowband and broadband ones. Previously, both in domestic and foreign literature, there has been no solution to the specified problem which would simultaneously consider both dependences. The proposed solution is based on a well-known algorithm that allows calculating the relationship between the temperature of the spectral ratio and the actual temperature of a "non-gray" object, taking account only the dependence of the spectral emissivity of the object on the wavelength. The presented algorithm has been modified to consider its temperature dependence as well. An example of the implementation of the described algorithm is given.

The results of an experimental study of the thermal expansion of gallium garnets Gd₃Ga₅O₁₂, Gd_3.04Sc_1.8Ga_3.16O₁₂ and Ca₃Nb_1.5Ga_3.5O₁₂ in a wide temperature range (293.15 - 1473 K) are presented. A noticeable effect of niobium in the structure of gallium garnets on the coefficient of thermal expansion has been found. The temperature dependences of the volumetric properties have been obtained.

Here we present the results of thermodynamic and kinetic calculations as well as experimental studies of plasma processing of rubber powder of recycled tires, demonstrating the promise of using the plasma-chemical technology for gasification of this powder with the production of energy gas. The results of experiment and calculations were compared and showed good agreement.