MASS CONDUCTIVITY FOR DRYING NUCLEI AND SEED SUNFLOWER SHELLS

The mass-conduction (diffusion) properties of sunflower seeds of the "MAS 95 OL" variety were experimentally investigated. From the experimental drying curves obtained in the intradiffusion kinetic mode at two temperatures of the drying agent (air), the coefficients of mass conductivity (moisture diffusion) were calculated by the zonal method, which are presented as dependences on the moisture content of the core and shell, respectively. It is shown that the coefficients of mass conductivity of nuclei and shells depend on the moisture content of the material and differ significantly both in magnitude and in the nature of the concentration dependences. The coefficient of mass conductivity of nuclei in different areas of moisture content is 15-25 times higher than that of shells, this is explained by differences in the structure of these materials. In the area of moisture content less than 0.5 kg / (kg of dry materiall), both dependences have the same character of concave functions increasing with moisture content, this is a consequence of the same mechanism of mass transfer dominating in this area of moisture content, which is osmotic mass transfer. In seed kernels, the area of moisture content of more than 0.5 kg / (kg of dry material) is absent, but in seed shells it is present and vapor diffusion dominates in it. The data on the coefficient of mass conductivity for seed shells were compared with the coefficient of mass conductivity of another capillary-porous colloidal material with a similar structure - wood. The nature of the concentration dependences for both materials is the same, which is explained by the similarity of the morphological structure of wood and seed shells, which have a tree-like structure. The coefficient of mass conductivity of the seed kernel was compared with the coefficients of mass conductivity of other capillary-porous colloidal materials of plant and animal origin. Comparison showed that they have the same order of mass conductivity coefficient: 10-9 m2/s. This is explained by the identical structure of these materials, which have a cellular structure, and, probably, by the same mechanisms of mass transfer at the corresponding moisture content. The obtained data on the coefficients of mass conductivity of the kernel and shell of sunflower seed can be used for the kinetic calculation of the process of convective drying of this material based on the solution of the differential equations of internal heat and mass transfer A.V. Lykov with the representation of the seed as a two-layer body.

APPLICATION OF «MICRO-PROCESSES» METHOD FOR MODELING HEAT CONDUCTION AND DIFFUSION PROCESSES IN CANONICAL BODIES

This paper shows that, in many technological processes, raw materials are subjected to high-temperature heat treatment and, in most cases, they have a geometric shape of the canonical form: a plate, a cylinder and a sphere. The convection drying process is considered as a typical heat and mass transfer process. The processes occurring under heat treatment conditions are reduced to transfer problems for an unbounded plate, cylinder, and ball with boundary conditions of the first kind, when the transfer potential (temperature, moisture content) is set on the surface of a solid. A number of expressions for calculations in the context of arbitrary distribution of initial values of transfer potentials as well as for uniform distributions are presented. It is shown that, when modeling heat and mass transfer processes in which the thermophysical characteristics of a solid body change significantly in the course of thermal treatment thereof, the use of already known solutions that have been previously developed becomes problematic. The «zonal» method and the «micro-processes» method are considered herein. It is shown that, for both methods, on the basis of experimental data referring to the dynamics of temperature and mass (moisture) content of the material over the course of the process, their dependences on the average (for the «zone» or «micro - process») temperatures and mass contents are determined. The next stage for calculations using the «zonal» method is formalization of the results obtained in the form of histograms of the values of mass conductivity coefficients from the average values of mass contents. For the «micro-processes» method, the kinetic curve can be used in calculations simultaneously. The smaller the range of measured values of temperatures and mass contents is the greater is the adequacy of calculated experimental data. It is emphasized that, under uneven initial conditions, analytical solutions to the heat transfer problem are usually presented in the form of infinite Fourier series. The convergence of the Fourier series deteriorates with decreasing time intervals. The great relevance of the application of the considered methods can be traced when modeling heat and mass transfer with intensive processes of phase transitions.

Specific Features of Calculating the Radiant Component of the Heat Flow of Horizontal Bunch from Finned Tubes with Exhaust Shaft

The article discusses the heat exchange of radiation of bunches of round finned tubes with the environment and the exhaust shaft. The system of equations describing the entire set of primary processes that make up the radiation heat exchange of finned bundles is very complex mathematically; therefore, the calculations of radiant heat transfer are usually based on a number of simplifying assumptions with a involuntarily distortion of the real physical picture. The main methods for calculating radiation used in engineering practice, viz. calculation by the average angular coefficient and the zonal method are briefly considered. A refined zonal method for calculating the radiant component of the heat flow of a horizontal bunch of finned tubes with an exhaust shaft is proposed. An experimental study of single-row bunches of finned tubes with different annular steps S1 (64 and 70 mm) was carried out for small Reynolds numbers Re = 130–720 in a wide range of the determining temperature at the beam inlet (16–83 °C). The aluminum finning of the bunch tube had the following parameters: screw finning diameter d = 0.0568 m; diameter of the tube at the base d0 = 0.0264 m; height, step and average fin thickness, respectively, h = 0.0152 m, s = 0.00243 m and Δ = 0.00055 m. Air movement in the bunch was carried out by gravitational traction created by a rectangular exhaust shaft. The experimental bunch was installed above the shaft, and the air was preheated before entering the shaft, which allowed expanding the temperature range of the air at the entrance to the bunch. It was found that incorrect accounting for a bunch reemission with an exhaust shaft when calculating single-row finned bunches causes a decrease in convective heat transfer by 7–25 %.

Utilization of Zonal Method for Five-Hole Probe Measurements of Complex Axial Compressor Flows

Five-hole probe is widely used in the measurement of turbomachinery flows, but in the traditional way the measurable angle range is not big enough for some interested flows. In this paper, the zonal method is introduced to an L-shaped five-hole probe to measure axial compressor flows. First, the calibration theory of the zonal method in five-hole probe is presented, and the effects of some factors on the measurement accuracy of the five-hole probe are discussed. The results reveal that the two-step correlation method can yield a highest calibration accuracy, and the calibration angular grid spacing should not exceed 5 deg. While the overlap region seems to have no effect on the measurement accuracy of the five-hole probe using the two-step correlation method. Reynolds number (Re) has obvious influence on the measurement accuracy of the investigated five-hole probe, and this effect could be ignored only when Re is bigger than 6000. Then, the investigated five-hole probe using the zonal method is used to measure the inter-row flows of a low-speed large-scale axial compressor, and the measurement results are compared with the results using the traditional method. Besides, the Re corrected results using the zonal method are also compared. The measured results have shown that the zonal method has prominent advantages relative to the traditional method in measuring the corner stall flows. While there is no need to correct the Re effect if the probe is calibrated in the velocity nearly equivalent to the measured flow.

Оценка спектральной оптической толщины пламени в камере сгорания судового дизеля

Использование математических моделей, в основу которых положен зональный метод расчета теплообмена излучением, применительно к камере сгорания судового дизеля, требует предварительного определения ряда энергетических характеристик. Важнейшей из них является спектральная оптическая толщина племени. Целью данной статьи является разработка расчетного метода для оценки спектральной оптической толщины пламени в камере сгорания судового дизеля 6 ЧН 24/36. Показано, что величина спектральной оптической толщины пламени зависит от трех основных параметров: коэффициента ослабления излучения, концентрации частиц сажи и их оптических характеристик (среднего диаметра и параметра дифракции). Представлены распределение частиц сажи по размерам и значения спектральной оптической толщины пламени в функции угла поворота коленчатого вала для судового дизеля 6 ЧН 24/36 при испытании его по нагрузочной характеристике. Приведены основные подходы, позволяющие определить интегральную степень черноты пламени в камере сгорания с использованием полученных расчетных данных по его спектральной оптической толщине.Application of mathematical models in the base of them a zonal method of calculation of radiative transfer is included in additional to marine diesel combustion chamber, it is required first determination the number of power data. Spectral optical thickness of flame is very important. Development of method calculation for the estimation of spectral optical thickness of flame in marine diesel 6 ChN 24/36 combustion chamber is the purpose of this paper. A value of spectral optical thickness of flame depends from three basic data: coefficient of attenuation radiation, concentration of soot particles and its optical data (mean diameter and parameter of diffraction) is given. Distribution of soot particles according to sizes and values of spectral optical thickness of flame in function of crank angle degree for marine diesel 6 ChN 24/36 in its power data is shown. Basic methods per missing to determine integral degree of flame blackness in combustion chamber with application of calculation data on its spectral optical thickness is determined.

Numerical Calculation of Radiative Heat Transfer in Two-dimensional Rectangular Zone

The accuracy of the P1-approximation of the spherical harmonic’s method and the S2-approximation of the discrete ordinate method for calculating heat transfer by radiation are analyzed. The cases of an isotropically scattering homogeneous medium and a homogeneous absorbing medium are considered. The calculation results are compared with the exact solution, the P3-approximation and the zonal method. It is shown that the accuracy of the S2-approximation is higher compared to the P1-approximation at small and intermediate values of the optical thickness of the medium.