The mechanisms of rotation of dust particles in a magnetic field inside an insert that determines the position of the first standing stratum in a glow discharge are considered. It has been shown that in fields exceeding 0.5 T, the drag of dust particles by a neutral gas can acquire considerable significance in addition to ion drag. Taking this mechanism into account leads to a significant increase in the rotation rate and good agreement with experimental data.
The paper presents the results of laboratory studies of electromagnetic and resistive heating of oil source rock under unilateral irradiation to kerogen pyrolysis onset temperatures. Comparison of the two heating methods showed that microwave electromagnetic heating is more preferable than resistive heating. Electromagnetic heating studies were carried out at a radiation frequency of 2.45 GHz. The presented results show that the intensity of electromagnetic heating of the oil source rock is nonlinear and depends on the change in the dielectric properties of the rock during heating and the weakening of the microstructure of the sample due to nonuniform heating of the rock.
Thermodynamic modeling is used to optimize a hybrid power plant circuit with a solid oxide fuel cell with internal methane reforming and a gas turbine. Assuming complete one-way conversion, the possibility of fuel cell operation without generating heat for recycling is demonstrated. As a result of optimization of the hybrid power plant, an original scheme was obtained with a fuel cell with internal heat regeneration and methane reforming and an efficiency of over 90
As a result of studying degassing on an electrode as a current pulse flows through the electrolyte, modes were identified in which gaseous electrolysis products appear explosively. The degassing kinetics was studied by perturbing the electrical resistance between the electrodes. The experimental results are generalized using the theories of electrocapillarity and fluctuation nucleation of the gas phase.
A unified fundamental equation of state for methane has been developed, conveying experimental data on density, isochoric and isobaric heat capacity, and the speed of sound within the experimental uncertainty of these data in the range of parameters of state for pressure up to 500 MPa, density up to 450 kg/m3, at temperatures from 90.641 to 620 K. A unified fundamental equation of state has been developed using the large-scale theory of critical phenomena. In accordance with the power laws of scale theory, this equation conveys the behavior of isothermal compressibility, isochoric and isobaric heat capacity, and the speed of sound in the asymptotic vicinity of the critical point. The expression for the Helmholtz free energy, which underlies the unified fundamental equation of state, consists of three terms: the ideal gas component, the regular component, and the singular component. The structure of the singular component includes a crossover function in the form of an exponential dependence on density, which in the region of low densities and pressures ensures the transition of the unified fundamental equation of state to a virial equation of state. The singular component of the unified fundamental equation of state is calculated based on a new representation of the scaling hypothesis, which is based on the linear Scofield–Litster–Ho model and Benedek hypothesis. The similarity relation is also used to calculate the parameters of the singular component of the unified fundamental equation of state, based on which a relationship is established between the parameters of the singular component of the unified fundamental equation of state and parameters of the Pokrovsky model for a real liquid. It is shown that the use of the similarity relation made it possible to reduce the number of individual parameters of the unified fundamental equation of state and exclude data on the isochoric heat capacity C_v related to the asymptotic vicinity of the critical point from the calculation scheme when determining its coefficients. The agreement between results obtained and calculations performed, first, using crossover models for a wide vicinity of the critical region, and second, using Setzmann and Wagner’s fundamental equation of state (1991) and Bezverkhy and Dutova’s combined equation (2023) is discussed.
The article studies the displacement of liquid hydrocarbons from a model of a porous medium using the example of oils with different contents of asphaltene–resin–paraffin substances, as well as dielectric properties, when an electromagnetic field of a certain frequency is applied to an oil-saturated model. The results of experimental studies are presented, showing the correlation of an increase in the oil displacement coefficient with the content of asphaltene–resin–paraffin compounds in oils and the dielectric parameters of oils. It is demonstrated that a high content of polar components of oil (asphaltenes and resins) leads to the greatest increase in the oil displacement coefficient, and with an increase in the paraffin content, an increase in the oil displacement coefficient decreases. Also, with an increase in the value of the dielectric loss tangent, there is an increase in the growth rate of the oil displacement coefficient. It was found that for all studied oils, a positive increase in the oil displacement coefficient is observed in the presence of an electromagnetic field.
In the article, based on the known experimental values of the contact angles and surface energy of liquid nickel alloys with iron, chromium, and niobium at the boundary with solid yttrium oxide and nickel alloys with chromium at the boundary with zirconium nitride, the surface and interfacial energies of the systems at certain concentrations of the components are calculated.
A method of mirror reflections of electrostatics is presented for a point charge located near a plane-layered medium consisting of three films on a dielectric half-space. The method is generalized to the case of an arbitrary system of charges and is applied to solving mathematically similar problems of electrostatics and stationary heat conduction of plane-layered media. As an example of application of the method, the problem of finding the distribution of electrostatic potential around a conducting charged sphere is considered. Solutions to similar problems of finding the temperature distribution of uniformly heated bodies located near a heat-conducting plane-layered structure of three heat-conducting films on a heat-conducting half-space are discussed.
The article presents the results of experimental testing of a system for igniting natural gas in an air flow using a microwave discharge. The data were obtained for a model high-enthalpy air flow generator. The pressure ranges for stable ignition of an air + natural gas mixture at a fuel component ratio close to stoichiometric are established. The data can be used in analyzing the characteristics of ignition systems for high-enthalpy air flow generators and power plants.
In this article, based on the concept of instantaneous normal modes, a simple semiempirical formula for calculating the heat capacity of liquids is proposed. The calculation results were compared with experimental data on the heat capacity of sodium, lead, and bismuth. It is shown that the formulas make it possible to assess properties in the high-temperature region with satisfactory accuracy.
An experimental setup has been developed for studying electric discharge along a steel needle in an electrolyte-bubble medium of an ammonium sulfate solution in tap water, which has practical significance for cleaning and polishing medical devices. The current–voltage characteristics of the electric discharge under such conditions were studied. A mechanism for developing processes for cleaning and polishing medical stainless steel needles via immersion in a solution of ammonium sulfate in tap water has been established. It was found that electrical discharges at high of concentrations can damage the sharp end of a needle.
An improved icing model is proposed, which makes it possible to enhance the accuracy of three-dimensional calculations of the icing process on various aviation equipment elements. The model was verified based on the results of calculations using the Ansys Fensap-Ice and Flow vision software packages. In the process of validating the model using available experimental data, the correctness of the calculation methods used in modeling heat and mass transfer processes occurring on the surface of ice buildup was demonstrated. Using model objects as an example, the advantages of the proposed model for calculating complex forms of ice buildups that arise in real icing conditions, including icing conditions with large supercooled drops (ice frost) are shown.
A study was carried out on the process of boiling water in a large volume of liquid at atmospheric pressure on surfaces with cavities obtained by laser ablation and hydrophobized by chemisorption of fluorinated methoxysilane from vapors at a temperature of 105°C. The results of the experiment are analyzed and compared with previously obtained and literary data. The influence of the size, shape, and location of hydrophobic cavities is studied on the intensity of heat transfer during boiling. It is shown that the main parameter determining the intensity of heat transfer is the specific density of hydrophobized cavities on the heating surface, or the step between them. The shape and size of the cavities do not have a significant effect on heat transfer. Removal of the water repellent from the cavities leads to a significant reduction in the intensity of heat transfer.
The article studies the characteristic equation arising in the problem of heating/cooling a hollow sphere under boundary conditions of the first kind using analytical methods. The obtained mathematical formulas make it possible to calculate the eigenvalues μ_n of this problem and determine the numerical values of the dimensionless temperature. Expressions for the eigenfunctions K_n( ψ) and coefficients A_n are also given. To improve calculation accuracy, the simple principle of subsequent approximation can be used by passing to the inverse function.
The article considers the problem of heat and mass transfer during natural convection of gas in a heated closed volume with an isothermal lower boundary in a mass force field. A simplified equation is proposed to describe heat transfer under temperature stratification conditions. For the problem of a free-convective boundary layer of a compressible gas on a plate under external temperature stratification conditions, analytical dependences for the velocity and temperature in the boundary layer are obtained. Good agreement is demonstrated between the analytical solutions for the boundary layer, the results of calculations using the stratification equation, and the simulation data of the full convection equations for the problem of heating of a vertical cylinder.
Based on a series of experimental data, a one-parameter description of the temperature–pressure dependence of the effective thermal conductivity of granites is proposed as a function of its value at one fixed temperature and atmospheric pressure. The proposed description agrees quite well with experimental data in a fairly wide temperature-baric range with no irreversible changes in the samples as a result of thermobaric exposure.
The article considers problems and specific features of accounting for collisions of solid particles with each other. The fundamentals of the theory of interparticle collisions are briefly described. The analytical methods developed to date for calculating the nuclei of collisions of monodisperse and bidisperse particles in homogeneous isotropic turbulence, a gradient turbulent flow, as well as under the combined action of turbulence and gravity are described and analyzed. The brunt of the focus is on describing the methods for numerical simulation of two-phase flows, which represent the interphase boundary, interphase interactions, and turbulence of the carrier medium at different hierarchical levels.
The study numerically simulated the mixing of hydrogen with air and its subsequent combustion with a direct jet injection of hydrogen and its ignition from an external source. The pulsed jet flow is simulated using a high-pressure chamber where hydrogen is initially stored at a pressure of up to 700 atm. The hydrogen flow is achieved through a system of valves, the number of which varies from one to six. The hydrogen supply time is calculated based on an estimate of the hydrogen content in the combustion chamber, corresponding to the stoichiometric ratio of the components of the hydrogen–air mixture. The dimensions of the combustion chamber are selected to correspond to the dimensions of the combustion chamber of a small-sized gas piston engine. In this way, the process of direct injection of hydrogen to the combustion chamber is simulated. In a series of calculations, ignition occurs at different stages of mixing, which allows us to evaluate the efficiency of the direct hydrogen injection system, including the completeness of combustion of the fuel supplied to the combustion chamber. It is shown that the fastest mixing occurs when hydrogen is supplied through a system of six slits, with the mixing time being about 25 ms. Subsequent ignition leads to combustion of the hydrogen–air mixture in about 1 ms, and the degree of hydrogen incomplete combustion is 9.5
The article considers the physical processes occurring under the influence of the plasma flow of the arc of a two-jet plasma torch on the intermediate electrode—a metal workpiece with a diameter of 5 cm rotating around its axis at a velocity of 10 000 rpm. The heated surface of the metal workpiece is melted, due to centrifugal forces the material is torn off from the workpiece in the form of droplets, and after their cooling in an inert gas environment a powder of spherical metal particles is obtained (PREP process). This powder is used in additive technologies. The authors present a three-dimensional stationary model of a two-jet plasma torch with an arc closing through an intermediate electrode—a rotating metal workpiece (near-electrode processes are not taken into account). The influence of the arc current value and plasma gas flow rate on the efficiency of workpiece heating is considered. Both distributed (temperature, plasma velocity, etc.) and integral (power into the workpiece, power loss due to radiation, etc.) calculation results are presented. It is shown that the dependence of the power into the workpiece on the plasma-forming gas flow rate has a “saturation”; i.e., when a certain gas flow rate is exceeded, the power into the workpiece stops increasing. In this case, increasing the arc current is the most effective way to increase the power delivered to the workpiece.
In this study, the temperature dependences of the contact wetting angles θ(T) were measured using the large sessile drop method on high-purity samples with an automated experimental setup. The surface of stainless steel 12Cr18Ni9Ti with a lithium alloy was based on tin with the composition Sn + 15 at
