scholarly journals MASS CONDUCTIVITY FOR DRYING NUCLEI AND SEED SUNFLOWER SHELLS

2021 ◽  
Vol 64 (5) ◽  
pp. 80-87
Author(s):  
Stanislav P. Rudobashta ◽  
Vadim N. Kochetkov ◽  
Galina A. Zueva ◽  
Vyacheslav M. Dmitriev
Keyword(s):  
Mass Transfer ◽  
Moisture Content ◽  
Internal Heat ◽  
Morphological Structure ◽  
Convective Drying ◽  
Animal Origin ◽  
Seed Kernel ◽  
Zonal Method ◽  
Concentration Dependences ◽  
Mass Conductivity

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.

Thermodynamic Theory of Convective Drying Process of Porous Media

2002 ◽  
Author(s):  
You-Rong Li ◽  
Dan-Ling Zeng
Keyword(s):  
Mass Transfer ◽  
Heat Source ◽  
Heat And Mass Transfer ◽  
Internal Heat ◽  
Internal Heat Source ◽  
Thermodynamic Theory ◽  
Convective Drying ◽  
Internal Mass ◽  
Drying Process ◽  
Mass Source

Based on non-equilibrium thermodynamic theory and combined with the conservation laws, a comprehensive theoretical model was established to describe heat and mass transfer during convective drying process, and numerical calculation was performed. The results show that: (a) the external convective heat and mass transfer may be treated as the conductive heat transfer with internal heat source and the molecular mass diffusion with internal mass source, respectively, and the ability of heat and mass transfer mainly depends on the strength of the heat source and mass source; the higher the temperature of the drying media, the lower the strength of the internal heat source, but the higher that of the internal mass sources; (b) the evaporation of internal water takes place inside the whole material, and the molecular mass diffusion of the internal vapor is in the direction of decreasing mass transfer potential, not along the decreasing partial pressure of vapor.

Forced Convective Drying of a Porous Cube: Non-Intrusive Temperature and Mass Transfer Measurements

2014 ◽  
Author(s):  
Eoin Fanning ◽  
Tim Persoons ◽  
Darina B. Murray
Keyword(s):  
Mass Transfer ◽  
Temperature Distribution ◽  
Moisture Content ◽  
Surface Temperature ◽  
Convective Drying ◽  
Drying Rate ◽  
Local Surface ◽  
Number Range ◽  
Rate Period ◽  
Local Surface Temperature

The evolution of the mass transfer rate and temperature of a porous body in a convective drying process shows two main stages: A constant-drying rate period and a falling-drying rate period. This study investigates the simultaneous time evolution of moisture content and local surface temperature of a porous cube inside a rectangular flow channel for a range of air flow temperatures and Reynolds numbers. The moisture content is measured using a precision mass balance. Local surface temperature distribution is measured using a thermal imaging camera. In the constant-drying rate period, an average Nusselt number in the range 7.1 ≤ Nu ≤ 13.3 and an average Sherwood number of 4.7 ≤ Sh ≤ 6.0 are calculated for a Reynolds number range of 180 ≤ Re ≤ 595. Infrared thermography shows that the falling-drying rate period begins, the temperature distribution becomes non-uniform and approaches the temperature of the surroundings. This transition occurs first near the edges of the cube and, in particular, near the leading edge of the cube, as witnessed in previous studies.

OPTIMIZATION OF DRYING BY ELECTROMAGNETIC RADIATION: ANALYTICAL STUDY OF THE PROBLEM

1970 ◽  
Author(s):  
A.M. Afanasiev ◽  
B.N. Siplivy
Keyword(s):  
Mass Transfer ◽  
Temperature Field ◽  
Moisture Content ◽  
Electromagnetic Radiation ◽  
Initial Boundary ◽  
Sample Surface ◽  
Convective Drying ◽  
Material Surface ◽  
Plate Boundaries ◽  
Optimization Parameters

The process of drying a flat sample with electromagnetic radiation is considered. As initial relations, the equations of the theory of heat and mass transfer are used. Lykov. To take into account the nonlinear nature of the process of mass transfer of the sample surface with the air medium, the boundary conditions for the moisture fluxes were adopted in the form of Dalton's evaporation law. A time-asymptotic analytic solution of the initial-boundary value problem is constructed, the characteristic feature of which is the stationarity of the temperature field T, the quasistationary nature of the moisture content field U, and the constancy of the drying intensity J. The presence of such features allows us to say that here we have, by analogy with convective drying, or a period of constant speed. The central notion in the relations obtained is the steady-state temperature of the material surface T∞, which is a generalization of the concept of the temperature of a wet thermometer to the case of electromagnetic drying. The problem of drying optimization has been solved and solved. The aim of optimization is to organize regimes in which the temperature field and/and the moisture content field are close to homogeneous. This corresponds to the minimization of the objective functions, which are the absolute values of the temperature and moisture content differences between the plate boundaries ç∆Т½ and ç∆U½. As optimization parameters, by varying the target functions, the intensity of radiation S and its penetration depth Δ are chosen. It is shown that the optimum regime should be chosen in the soft range, in which the ΔT and ΔU differences have the same signs, and the hard range in which these differences have opposite signs should be excluded from consideration. One of the limits of the soft range corresponds to the regime with ΔT=0, the other boundary to the regime with ΔU=0. An algorithm for calculating the optimization parameters S and Δ, corresponding to these modes, is developed, which makes it possible to organize drying within a soft range. As an example of using the developed algorithm, optimization of electromagnetic drying of a material with characteristics of quartz sand has been carried out.

scholarly journals Calculation of the kinetics of heat transfer using the experimental data of moisture exchange in the process of convective drying of thin flat materiаls

2018 ◽  
Vol 63 (3) ◽  
pp. 333-341
Author(s):  
A. I. Ol’shanskii ◽  
S. V. Zhernosek ◽  
A. M. Gusarov
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Moisture Content ◽  
Heat And Mass Transfer ◽  
High Reliability ◽  
Surrounding Medium ◽  
Convective Drying ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Values

In the paper, the authors analyzed the solution of the differential equation of non-stationary heat conduction for an unbounded plate during the heat exchange of plate surfaces with the surrounding medium according to Newton’s law at a constant temperature of the medium. To use the results of solving the equations in the drying of thin flat materials, the dependence of the heat transfer coefficients on temperature and moisture content was studied. As a result of studying and analyzing a number of literature sources, the regularities of the change in the heat transfer coefficients during drying are established with high reliability. Studies of drying of thin wet plates of white and red clays with known heat transfer coefficients have shown that for small values of the heat transfer criterion of the Bio and small temperature gradients over the section of a thin material, application of the results of solutions of the heat transfer equations gives completely satisfactory agreement between the calculated and experimental values of the temperatures and the duration of drying. It is established that for small Bio numbers, the main factor is the external heat and mass transfer of the surface of the material with the surrounding medium and the rate of drying depends little on internal mass transfer. It is shown that the use of numerical methods for solving differential equations is possible with varying degrees of approximation only for accurate and reliable dependences of heat and mass transfer coefficients on moisture content and temperature. For a number of materials with known heat transfer coefficients, the use of analytical methods in calculations is of considerable interest and brings the theory closer to the practice of drying.

scholarly journals STUDY OF HEAT- AND MASS TRANSFER DURING DRYING OF GRANULES OF ORGANO-MINERAL FERTILIZER IN DENSE LAYER

2019 ◽  
Vol 62 (6) ◽  
pp. 91-97
Author(s):  
Lev N. Ovchinnikov ◽  
Sergey I. Medvedev
Keyword(s):  
Mass Transfer ◽  
Moisture Content ◽  
Heat And Mass Transfer ◽  
Experimental Studies ◽  
Mineral Fertilizer ◽  
Quantitative Relationship ◽  
Convective Drying ◽  
Dense Layer ◽  
Cylindrical Shape ◽  
Power Functions

The paper presents a calculation method that enables the use of specially performed experiments to establish the quantitative relationship defined by a criterion(variable), for example, Sherwood (mass transfer), Nusselt (heat transfer) or the moisture content of the particles from the defining criterion of the Reynolds, Schmidt, and temperature. These relations are represented by power functions in the form of criterial equations of heat and mass transfer for the selected range of values of the Reynolds criterion Reg = 250-500 calculated for the gas phase. In the calculation-experimental study, the convective drying of wet granules of nitrogen - phosphorus - potassium (NPK) organic mineral fertilizer in a dense layer of the laboratory cylindrical-conical dryer by heated air is considered. The granules have a cylindrical shape with a particle size of five by five mm. The experimental technique involves conducting periodic studies to determine the time change in the moisture content of fertilizer granules, the temperature of the gas under the grid, layer, above the layer and the particle at different flow rates of the gas coolant. Processing of the results of experimental studies, carried out using the method of least squares, allowed to calculate the experimental coefficients included in the criterion equations. Illustratively it is shown that the mass transfer coefficient increases with the Reynolds criterion until they reach values of 0.8 Reкр1. (the beginning of fluidization), corresponding to the rational conditions of drying of the granules. Comparison of the calculated and experimental values of the Sherwood criterion, Nusselt criterion and moisture content of the dried material particles showed their satisfactory convergence in the considered hydrodynamic conditions of drying wet particles, which makes it possible to recommend the obtained experimental dependences for practical application.

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

2020 ◽  
Vol 63 (10) ◽  
pp. 90-95
Author(s):  
Sergey V. Fedosov ◽  
Maxim O. Bakanov
Keyword(s):  
Experimental Data ◽  
Heat Treatment ◽  
Mass Transfer ◽  
Fourier Series ◽  
Moisture Content ◽  
Heat And Mass Transfer ◽  
Potential Temperature ◽  
Kinetic Curve ◽  
Arbitrary Distribution ◽  
Zonal Method

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.

scholarly journals Modeling of kinetics of drying process of polycaproamide granules considering its sorption properties

2018 ◽  
Author(s):  
Marina Sergeevna Maklusova ◽  
Maria Konstantinovna Kosheleva ◽  
Olga Roaldovna Dornyak
Keyword(s):  
Mathematical Modeling ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Moisture Content ◽  
Gas Phase ◽  
Heat And Mass Transfer ◽  
Sorption Properties ◽  
Convective Drying ◽  
Drying Process ◽  
Kinetics Of

The object of research is a fiber-forming polymer - polycaproamide. The process of drying of polycaproamide granules, after aqueous extraction of low-molecular compounds from them, is an important stage of producing of polyamide fiber nylon and largely determines the quality of the target product. To obtain a high-quality fiber, the drying of the granules should provide a sufficiently high degree of its dehydration. The average final moisture content of the material should be no more than 0.1%. With a low moisture content, the drying process slows down, so the calculation of the kinetics of dewatering of granules can not be carried out using a constant effective mass-transfer coefficient (moisture diffusion). In this paper we present a calculation technique for determining two local parameters of mass transfer: the water diffusion coefficient in polycaproamide (as a liquid) and the so-called criterion for phase transitions, which depend on the moisture content of the material and are determined by its sorption properties. The report presents the results of numerical calculations illustrating the development of two-dimensional fields of moisture content, temperature, pressure and vapor concentration in the vapor-gas phase for cylindrical granules in convective drying. To describe the processes of heat and mass transfer during the drying of granules, a nonstationary nonlinear 2D model is used that includes transport equations averaged over the microvolume of the material: the liquid phase transfer equation; heat equation; equation for vapor-gas phase pressure; equation for the concentration of the vapor component. The nonstationary nonlinear conjugate mathematical model is studied numerically. A feature of the presented model is the possibility of an analytical calculation of the local mass transfer coefficients of a liquid, taking into account the sorption properties of the material, the permeability coefficient and the local values ​​of humidity and temperature. Determination of the local coefficients of moisture transfer is carried out on the basis of the formulas obtained in the analysis of a more general mathematical model of heat and mass transfer carried out based on the mechanics of multiphase systems developed in the works of R.I. Nigmatulin, and S. Whitaker. The structure of the samples was investigated by three independent methods in order to obtain the most complete idea of ​​it and to compare the obtained characteristics. The isotherms of the sorption of polycaproamide were obtained experimentally on a vacuum sorption plant with Mac-Ben-Bakr weights. Comparison of the results of mathematical modeling of heat and mass transfer in the granule and data of the laboratory experiment on the kinetics of polycaproamide granule drying showed good agreement between the calculated and experimental data. The constructed mathematical model allows to form energy-efficient resource-saving regimes for drying granules of polycaproamide.Keywords: convective drying, mathematical modeling, polycaproamide.

scholarly journals STUDY OF MASS CONDUCTIVITY PROPERTIES OF SEEDS LAYER

2017 ◽  
Vol 60 (7) ◽  
pp. 72 ◽  
Author(s):  
Stanislav P. Rudobashta ◽  
Galina A. Zueva ◽  
Vyacheslav M. Dmitriev
Keyword(s):  
Moisture Content ◽  
Thick Layer ◽  
Dense Layer ◽  
Zonal Method ◽  
Influence Of Temperature ◽  
First Case ◽  
Mass Conductivity ◽  
Single Seeds ◽  
Kinetics Of ◽  
Material Temperature

Data on the mass conductivity coefficient have been obtained during drying the onion seeds in a thick layer of 5 mm thick ventilated on the surface, which were calculated by the zonal method on the basis of experimental curves of drying and heating. These data are described by the dependence of the mass conductivity coefficient on temperature and moisture content of the material.  The comparison of the mass conductivity coefficient values for a layer and for single seeds is given,  which shows that: 1) the mass conductivity coefficient in the layer changes significantly during drying, therefore, this change must be taken into account; 2) the change in the mass conductivity coefficient is due to its dependence on both moisture content and temperature, but the influence of temperature prevails over the influence of moisture content, therefore, themass conductivity coefficient increases during drying, 3) the mass conductivity coefficient in the layer is two orders of magnitude higher than for single seeds. The curve of seeds drying in a layer of 5 mm thick have been calculated using the obtained data on the mass conductivity coefficient for the process of oscillating infrared seeds drying carried out at a material temperature fluctuation in the range from tmin = 34 °C to tmax = 40 °C, which showed satisfactory agreement of the results of calculation and experiment. Experimental and calculated curves of oscillating infrared seeds drying in a layer of 5 mm thick are compared with analogous curves of drying the seeds in a monolayer, which showed that, despite the fact that the mass conductivity coefficient of seeds in a layer of 5 mm thick is two orders of magnitude greater than in a monolayer, the drying of seeds in the first case is slower because of the greater thickness of the layer. To calculate the kinetics of the process of oscillating infrared seeds drying in a dense layer, when its surface temperature oscillates in the range from tmin = 34 °C to tmax = 40 °C, the zonal method is recommended using the obtained data on the mass conductivity coefficient, taking into account the change in the mass conductivity during the process.Forcitation:Rudobashta S.P., Zueva G.A., Dmitriev V.M. Study of mass conductivity properties of seedslayer. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 7. P. 72-77.

scholarly journals TRANSIENTS PROCESSES UNDER DRYING WITH CONVECTION AND INFRARED RADIATION

2017 ◽  
Vol 60 (10) ◽  
pp. 94
Author(s):  
Anatoly M. Afanas’ev ◽  
Arina V. Nikishova ◽  
Boris N. Siplivy
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Steady State ◽  
Moisture Content ◽  
Infrared Radiation ◽  
Transition Process ◽  
Convective Drying ◽  
Infrared Drying

Based on the theory of the A.V. Lykov for heat and mass transfer the mathematical model of propagation of heat and moisture in a flat sample, which is blown by the air flow and is exposed to infrared radiation. The model is based on the following views: the density of heat loss is determined by the heat transfer by convection and heat exchange by radiation, and the intensity of the mass exchange surface with the environment depends on the difference in partial pressure of water vapor through the thickness of the boundary layer (the boundary condition of mass transfer in the form of Dalton); temperature field inside the material is determined by the heat transfer due to the phenomenon of thermal conductivity, and the presence of internal heat sources caused by the absorption of penetrating electromagnetic radiation and the processes of evaporation (condensation); the transfer of moisture inside the material is partly liquid and partly in vapor form, and is caused by moisture content gradients (diffusion) and temperature (thermal diffusion). The results of analytical calculation of steady-state fields of temperature and moisture content for cases of convective drying and infrared drying, and the results of numerical calculation of the same field in transient conditions are presented. Numerical experiment allows us to estimate the duration of the transition process, as well as the behavior of the differential moisture content between the borders of the plate, with the increase which increases the probability of failure of the sample from mechanical deformation. It is shown that for convective drying of such a danger occurs in the transitional regime, and for infrared drying – mode steady-state. To reduce internal mechanical stresses when drying by convection, avoid sudden temperature changes of the air flow; the time during which there is an increase in air temperature, should be around the time of the transition process. When drying with infrared rays, if the differences of moisture content in the steady state are invalid for their reduction can be used or drying in the oscillating radiation, or drying under the combined effect of the sample electromagnetic waves with large and small penetration depth. The distinction in the nature of transients, infrared drying and drying with hot air can be explained using the formula of Dalton, which is part of the used mathematical model and determining the intensity of the problem through the boundary layer. Due to the great inertia of thermal processes, even in the case where the intensity of the infrared radiation changes rapidly in time (for example at the initial time gap of the first kind), the surface temperature of the material, and with it the intensity of drying, continue to be continuous functions; on the contrary, an abrupt change in air temperature in convective drier automatically leads to a gap function of the flux density of moisture on the surface.Forcitation:Afanas'ev A.M., Nikishova A.V., Siplivy B.N. Transients processes under drying with convection and infrared radiation. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 94-101 

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