The concentration–temperature dependences of the moisture diffusion coefficient (mass conductivity coefficient) during drying of soya and bean kernels were experimentally obtained and analyzed. The values of the moisture diffusion coefficient were calculated from the experimental drying curves of the studied samples, recorded in the absence of external diffusion resistance using the zonal method, based on solving the linear mass conductivity problem at constant environmental parameters in a regular mass transfer mode. In parallel experiments, changes in the linear dimensions of the samples during drying were recorded. By comparing the drying and shrinkage curves, data on sample size changes during drying were obtained, which were taken into account when calculating the moisture diffusion coefficient. Since the soya and bean samples had a shape close to a bounded cylinder, the moisture diffusion coefficient was calculated using a formula derived from the solution of the mass conductivity problem for a bounded cylinder. The results of the study on moisture diffusion coefficients for soya and beans were compared with similar results for other grain crops, and the shrinkage data were compared with those for high-moisture plant materials: slices of apple, pear, carrot, and beet. The possibility of representing the moisture diffusion coefficient as a function of the drying agent temperature was discussed. The obtained data can be used for analysis and calculation of drying kinetics of soya and bean grains by the theoretical method, i.e., based on the use of thermophysical characteristics of materials without conducting experimental studies on physical modeling of the drying unit under laboratory conditions.
Theoretical ballistic design of a small-caliber laboratory pneumatic launcher for accelerating projectiles has been carried out. Prototypes of the pneumatic launcher components have been manufactured, and the structure has been assembled. A series of model experiments on projectile launch using compressed air as the working gas at different initial pressures has been performed. The main ballistic parameters of the launch were recorded using modern measuring and recording equipment. A detailed numerical gas-dynamic analysis of the fast processes accompanying the launch has been conducted. The discrepancy between the calculated and experimental muzzle velocity values did not exceed 2
This study focuses on the Cu (copper)–kerosene nanoparticles in a magnetohydrodynamic mixed convective flow at a stagnation point of a Sisko fluid in a stretched cylinder. The influence of heat source, Arrhenius energy, and heat radiation are considered. To convert dimensional nonlinear equations to a nondimensional form, perfect similarity variables are chosen. After that, dimensional-free equations are solved by applying the bvp4c numerical approach. Numerical outcomes of dimensionless fluid velocity, skin friction, concentration, temperature, rate of heat and mass transport, for some factors are presented graphically. Observation reveals that the curvature parameter raises the velocity profile and rate of mass transfer. Fluid concentration is enhanced by an energy activation parameter. The velocity ratio parameter and Prandtl number reduce fluid temperature. Furthermore, the heat transfer rate for kerosene-based oil is faster in the presence of Cu nanoparticles than in their absence. Also, a table is used to compare the current computed results with the previous ones.
Modern space technology typically requires structures operating under intense, often extreme, thermal conditions since the trend in technological development is toward an increasing number of critical, heat-loaded technical objects, with increasingly stringent thermal loading conditions, while simultaneously increasing reliability and service life and reducing material consumption. For spacecraft, thermal management is a critical design aspect, determining key design and engineering decisions. Highly porous thermal insulation materials with low thermal conductivity are widely used in thermal protection structures for modern space technology. These materials typically have an open-pore structure. This means that the thermophysical properties of these materials are significantly dependent on the gas pressure of the environment in which the thermal protection structures based on them operate. It can also be seen that as ambient pressure increases, the thermal conductivity coefficient increases more rapidly. The overall objective of this work is to develop a set of experimental and mathematical tools for a system of identifying the properties of highly porous materials operating under not only changing thermal loads but also variable pressure. This section of the work is devoted to processing experimental data to determine the dependence of the thermophysical properties of fibrous materials on temperature and pressure, as well as to analyzing the computational efficiency of the developed algorithms.
An analysis of the refrigeration unit operation using a water–LiBr mixture and an alternative methanol–LiBr mixture was carried out. The refrigerant transfer through the membrane wall was simulated in order to construct a mathematical model of the working substance separation. The advantages and disadvantages of using these mixtures in refrigeration units were revealed. The prospects of searching for new mixtures in order to increase the efficiency of refrigeration units and expand their operating temperature ranges are shown.
Equations of thermodynamic balances for the substance, energy, and entropy have been written for the process of separation of a binary mixture of gases using the rectification column. To write the equation of the system’s entropy balance, expressions have been obtained for the entropy production at each node of the system. The form of the dependence of the maximum separation-process throughput, as far as the flow of the mixture to be separated is concerned, on the energy consumption (set of process feasibility) has been found. This dependence is bounded above and is close to a quadratic parabola. It has been shown that by the coefficients of this parabola, there may be expressed conditions with which the throughput is maximum and there is a relationship between the reversible efficiency and the efficiency corresponding to the throughput maximum.
The thermal behavior of brick walls with thermal insulation materials of different types, optimizing the indoor–outdoor air temperature conditions, was investigated. A simulation has been caried out using the Elmer software to evaluate the effects of position of an insulation and of the variation in its thickness and material. Different methods of using insulation layers to provide comfort in the indoor environments and to minimize the reemission of heat to the environment were discussed.
The density of liquid n-hexane was measured at temperatures of 298.15–433.15 K and pressures of 0.1–100.1 MPa. Based on diverse data on the thermodynamic properties, the parameters of the equation of state of n-hexane were obtained. This equation is applicable in the temperature range from the triple point to 573 K at pressures up to 1000 MPa. A good description of the experimental data with a deviation equal to the uncertainty level of these data is demonstrated. The equation of state allows one to calculate the values of density, sound velocity, isobaric and isochoric heat capacities, isobaric expansion coefficient, isentropic and isothermal compressibility coefficients, enthalpy, entropy, and saturation pressure.
A comparative analysis of the criteria of similarity of the oil flows in tubes of different geometries has been performed. It was established that, in the case where the viscosity of the oil depends on its temperature, the laminar regime of flow of the oil in a tube can change to the turbulent one. The CFD calculations of the flow of oil in a plane tube and in a tube having a helical shape have been conducted. The results obtained are of interest for the designing of helicoidal heat exchangers used for the pumping of oil.
An approach to describing the thermal radiation of liquid metals is proposed based on dimensional analysis using Buckingham’s π-theorem. The method allows one to construct the dependence of the radiation flux on the dimensionless entropy S/R, which ensures the transition to a universal description of the behavior of various elements. The entropy S/R = 12.5, characteristic of the liquid phase of most metals, is adopted as the reference value. A scale flow αq_1^* has been introduced, allowing one to normalize the experimental data and construct an exponential dependence. It was found that the logarithm of the normalized flux depends linearly on S/R with a determination coefficient of at least 0.97. The scale fluxes of metals exhibit periodicity along the 4th period of the Periodic Table similar to the behavior of the surface tension of these metals. The proposed dependence is applicable to estimating the emissivity of liquid d-metals and can be used for interpolation and approximation of experimental data.
A mathematical model of crack initiation in an isotropic heat-releasing massif weakened by a system of cooling cylindrical channels of circular cross section placed at intervals is constructed under the assumption that cracks are initiated with an increase in the intensity of heat release in the massif. The equilibrium of an isotropic perforated heat-releasing massif with nucleating cracks was determined based on the solution of a nonlinear singular integral equation with a Cauchy-type kernel. The forces acting in the crack nucleation band were found from the solution of this equation. The conditions for crack initiation were determined using the criterion of the maximum elongation of bonds in the massif material. The governing equations were obtained in the form of infinite algebraic systems and were solved in each approximation by the Gauss method with the choice of the principal element for different order values depending on the radius of the holes. Calculations were performed to determine the stresses in the connections of the end zones and the maximum loads causing crack growth.
The results of calculations of the self-sustaining Chapman–Jouguet detonation of a carbon dust–oxygen gas suspension are presented under the assumption of chemical equilibrium in the detonation combustion products. The influence of the mass fraction of carbon in such a gas suspension on the parameters realized at the detonation front is investigated. A self-similar solution is constructed numerically, allowing one to simulate the structure of a plane wave behind the detonation front. The influence of the presence of carbon particles in the detonation products on this structure is analyzed when the mass of carbon in the gas suspension exceeds the mass of oxygen.
A new multiparameter scheme of decomposition of nonlinear differential equations for, first of all, the boundary value problems on heat and mass transfer, is proposed. This scheme involves a simple computational algorithm of solving boundary-value problems using the well-developed mathematical technique based on Adomian polynomials. With the use of the new multiparameter decomposition method, approximate solutions of the equations for the radiative heat exchange and reaction diffusion in porous catalysts have been obtained. The proposed method gives compact analytical solutions simple in form. Several variants of determining the decomposition parameters are considered, and an advantage of integral approaches over the procedure of minimizing the squared residual error is demonstrated.
The procedure of selecting the design parameters for a system of ensuring a thermal regime for a high-enthalpy vacuum furnace capable of heating up to 2500 K is proposed. The furnace consists of a cylindrical outer casing made of 12Kh18N10T alloy and an internal heated volume made of tungsten alloy. Due to the relatively low melting point of the steel chamber shell, it must be continuously cooled to prevent localized thermal deformations and deterioration of reflectivity and emissivity. In this study, when designing the thermal regime of the furnace, minimum flow rate of the coolant was selected for each of the heated elements of the chamber. The problem under consideration is solved using an extreme multiparameter formulation based on minimizing the root-mean-square deviation between the theoretical temperature field at each node of the tetrahedral finite element primitives and the melting temperatures of the materials from which the heat-controlled chamber is fabricated. The gradient method of conjugate directions is used as an optimization and most accurate method of the first order of convergence, which allows achieving the required accuracy of stopping the iterative process in a minimum number of iterative approximations.
Experimental and numerical investigations of the nonstationary gasdynamic and thermal processes realized in a discharge chamber in the case of simultaneous interaction of a shock wave and a cocurrent gas flow in it with the walls of its channel and with the plasma of a combined pulsed volume discharge initiated in this channel have been performed. Data of the high-speed shadow photography of the processes proceeding rapidly in a discharge chamber and data of the infrared thermography of these processes were compared with the corresponding numerical simulation data. The phenomena associated with the plasma and gasdynamic interactions in the discharge chamber of a shock tube at Mach numbers of 2–4 were investigated. Images of the nonstationary thermal fields of two types, realized in this discharge chamber at a time 1) as a result of the heating of the chamber due to the heat conduction of the inner surface of its quartz walls by the boundary layer of the gas flow during 200–300 μs and 2) as a result of the emission of thermal radiation by the plasma of the pulsed volume discharge formed upstream of the front of a shock wave in the chamber, have been obtained.
Coal is one of the most widespread and accessible carbonaceous resources, possessing a number of advantages compared to other starting materials, such as highly purified carbon or synthetic graphite. Its low cost and high energy density make it an attractive object for synthesizing carbon nanostructures. The focus of the present study is obtaining carbon nanomaterials through the laser impact on coal specimens. A Fiber Laser Marking and Cutting Machine fiber laser device with a wavelength of 1064 nm was used as the radiation source. Specimens obtained after the treatment were characterized by the methods of scanning electron microscopy, Raman spectroscopy, and x-ray diffraction. The results demonstrate the efficiency of laser ablation for forming nanostructures on the basis of natural coal.
Coal is one of the most widespread and accessible carbonaceous resources, possessing a number of advantages compared to other starting materials, such as highly purified carbon or synthetic graphite. Its low cost and high energy density make it an attractive object for synthesizing carbon nanostructures. The focus of the present study is obtaining carbon nanomaterials through the laser impact on coal specimens. A Fiber Laser Marking and Cutting Machine fiber laser device with a wavelength of 1064 nm was used as the radiation source. Specimens obtained after the treatment were characterized by the methods of scanning electron microscopy, Raman spectroscopy, and x-ray diffraction. The results demonstrate the efficiency of laser ablation for forming nanostructures on the basis of natural coal.
The results of numerical simulation of heat transfer of an electrically conductive fluid in a cylindrical layer are presented. The influence of the velocity field, internal heat sources/sinks, Joule heat dissipation, and of the thickness of the cylindrical layer on the temperature and magnetic induction fields of the fluid is investigated. The effects of the magnetic Reynolds number and the Hartmann number on Joule heat dissipation and of the magnetic Prandtl number on the width of the magnetic induction component intervals are studied; conditions for preserving the magnetic induction field are determined.
A method has been developed for calculating a square cascade with working substance losses and a specified concentration of the target component in the exit flows. A computational experiment on the separation of cadmium isotopes and the concentration of 116Cd in the presence of losses has been carried out. The features of calculating cascade parameters under isotopic overlap for cadmium dimethyl are shown.
The paper presents the results of a study of the temperature dependence of the heat capacity, heat transfer coefficient and thermodynamic functions of Zn–Ga system alloys. The investigations were carried out in the "cooling" mode. It is shown that with increasing temperature, the heat capacity, heat transfer coefficient, enthalpy and entropy of the alloys increase, while the Gibbs energy decreases. It was found that the addition of gallium up to 1 wt.
