Capillary-porous Bodies Research Articles

Thermally induced phase separation of UHMWPE mixture with dioctyl adipate: Competition of liquid–liquid phase separation and polymer crystallization

The thermal behavior of ultra-high molecular weight polyethylene (UHMWPE) with dioctyl adipate (DOA) was investigated by the differential scanning calorimetry (DSC) method. Capillary-porous bodies were obtained via thermally induced phase separation of DOA mixtures with polyethylenes of different molecular weight at different cooling rates. Analysis of the morphology of the prepared porous bodies together with DSC data and results of cloud point estimation revealed an unexpected effect of a cooling rate on the type of phase separation occurring in the mixture during its cooling from homogeneous state. Particularly it was shown that increase in the cooling rate reduces the probability of realization of liquid – liquid phase separation in the mixture. It was argued that such behavior, different from the standard semicrystalline polymers, is a result of kinetic hindrance of liquid – liquid phase separation in mixtures containing a polymer with such a high molecular weight.

Modeling mass transfer processes in multicomponent capillary-porous bodies under mixed boundary conditions

In this study, we present a physicomathematical model for convective drying of a multicomponent body of the capillary-porous structure, considering moisture transfer dynamics at both macro and micro levels. Recognizing the impact of the material's local structure on drying processes, particularly in phase transformations, the model integrates the continuum-thermodynamic approach pioneered by Ya. Burak, Ye. Chaplya, and B. Gayvas. This approach addresses the interrelated mechanical, thermal, and diffusion processes occurring in heterogeneous, nonequilibrium systems, where local thermodynamic equilibrium assumptions allow equilibrium state descriptions by conjugate physical parameters. The unique dual-level approach captures moisture exchange between an individual grain and the grain bed, enabling realistic simulations of the drying process by directly accounting for phase transformations and material structure influences. The presented methodology allows simultaneous solving of mass transfer equations for the grain bed and individual grains, supported by numerical experimentation. The results reveal distinct moisture distribution patterns across the grain bed and within individual grains, with variations influenced by drying agent velocity. The novelty of this approach lies in its simultaneous treatment of grain-scale and bed-scale moisture transfer, providing a detailed perspective on moisture dynamics. This model has potential applications in optimizing industrial drying processes for capillary-porous materials, enhancing efficiency and cost-effectiveness.

Массопроводность дисперсных и листовых материалов в условиях термодинамического равновесия

The intensification of drying of wet capillary-porous bodies and their structural and deformation transformations is determined by the internal mechanism of moisture transfer in the material being dried. The scientific papers of A.V. Lykova, S.P. Rudobashty, B.S. Sazhina, E.N. Ochneva, N.V. Churaeva are devoted to the study of mass conductivity of various bodies. They confirm the importance to determine the characteristics of internal moisture transfer in the form of liquid and vapor to calculate the intensity of moisture exchange between the surface of a wet material and the coolant and to establish the ratio of moisture and heat flows not only during the drying process, but also during storage of materials. For dispersed and sheet capillary-porous materials of different composition and porous structure, determining the intensity of internal moisture transfer during their interaction with the environment is a relevant area of the research. It determines the drying method, thermal treatment conditions and energy efficiency. Dispersed and sheet capillary-porous materials of various shapes, sizes, structures, and humidity have been used as the objects of the study. To determine the mass conductivity parameters of a wet body during its interaction with a coolant, a thermodynamic method is used. It is based on the use of experimental desorption isotherms and calculated parameters characterizing the porous structure of the material. The authors have applied the method to calculate the mass conductivity coefficients of dispersed and sheet materials based on experimental data obtained under conditions of thermodynamic equilibrium of a wet body and gas. Calculated curves of the dependence of effective mass conductivity coefficients and the moisture content of the dried material are obtained considering environmental parameters. The data obtained on the patterns and the changes in mass conductivity coefficients makes it possible to establish the types of relationships between moisture and the material with the mechanisms of its transfer for a number of dispersed and sheet bodies. The data obtained can be used for the kinetic calculation of the drying process and to determine the conditions of their storage, as well as to identify the conditions for increasing the energy efficiency of dryers with convective supply.

Evaluation of hydrodynamic flows of cellular fluid in artificially formed continuums of plant material structure

Aim. The aim of the research is to evaluate hydrodynamic flows of cellular fluid in artificially formed channels of the structure of plant materials as a result of exposure to atmospheric spark discharge. The article presents some features of the flow of cellular fluid in artificially formed channels of plant materials after passing an atmospheric spark discharge. Expressions of hydrodynamics of idealized physical models are used to describe them. As a confirmation of the received data, the experimental part has been set.The Methods. The authors consider the case when the initial plant material is pre-treated with a spark discharge; its influence arises a new continuum in the structure of the material in the form of a throughinduced channel. Expressions of intracellular fluid outflow time and pressure power based on Poiseuille's law are given for electrically induced channels. The experimental part of the work includes spark discharge treatment of plant material – carrots cut into discs with a diameter of 24 mm and a thickness of 3 and 9 mm to determine the dependence of the amount of released cellular fluid on the duration of the experiment and the discharge current mode.The Results. It has been established that atmospheric spark discharge treatment contributes to the formation of new continuums in the structure of plant materials. With an increase in the intensity of treatment, the area of the moisture trace from the carrot disk increases and, as a result, the amount of released intracellular fluid. For the sake of clarity of the experiments, graphs of the dependence of the processing intensity on the amount of liquid released have been presented, corresponding expressions given.Conclusion. The obtained experimental data and dependencies will be useful when considering more complex mass transfer processes in capillary-porous bodies using preliminary electrophysical processing.

Heat exchange in wet capillary-porous bodies of various compositions during convective heating in vapor-air media

The results of the study of the heating process of wet capillary-porous bodies of various compositions (meat products) during heat treatment in dry air and steam-air mixture under conditions of forced circulation of the heating medium are presented. The studies were carried out on a moist fat-free sample (chicken fillet meat) and a low-moisture fat sample (pork shoulder blade) formed in the form of a cylinder and a plate. It is shown that the process of heating of meat products of various compositions obeys the laws of the theory of unsteady thermal conductivity of homogeneous bodies, despite the variety of accompanying phase and physico-chemical transformations. It is established that the regular mode of non-stationary thermal conductivity occurs at Fo ≥ 0.2 for all the studied variants. Based on the processing and analysis of experimental data, criterion equations of the form Θ = f(Fo,Bi) for the central layer of the studied products in the temperature range 160–240 °C were obtained. It has been established that the peculiarities of heating of meat products in a vapor-air mixture environment lead to lower values of the coefficients μ1 and N(Bi) at regular operation compared with heating in dry air. It was found that low-moisture fatty samples are characterized by lower values of μ1 and N(Bi) in comparison with moist fat-free ones. As a result of comparison with tabular data for solids, it is shown that the experimental coefficients μ1 and N(Bi) are characterized by lower values for all the studied variants. It is established that the nature of the change in N(Bi) and μ1 for solids and the studied products is opposite, i.e., with an increase in the number of Bi, an increase in N(Bi) and μ1 is characteristic for solids, while their decrease is characteristic for the studied products. The practical significance of the research consists in improving the quality characteristics of minced meat products and optimizing operational production planning through the use of the methodology of predictive calculation of the duration of thermal operations.

The fractal scale-invariant structure of a temporal hierarchy in the relaxation and energy dissipation processes in a visco-elastic/capillary-porous medium

The phenomena of elastic aftereffects during loading/unloading of viscoelastic and capillary-porous bodies, relaxation of their stresses is accompanied by the energy accumulation and dissipation to be taken into account in the theory of oscillations which also considers the behavior of materials when the force is applied to them. The elastic aftereffect and stress relaxation forms ostensibly opposite energy processes. In the first case, under constant load deformation, the work increases in course of time, and in the second case, under constant load deformation, the work (energy) decreases. While researching on the energy dissipation in the conditions of oscillations application, i.e. within the frame of internal friction theories, one can find that some theories are based on the dependence of friction on the oscillations’ velocity, other ones establish the dependence of friction on the amplitude. Research papers are based on the hypothesis of M.M. Davydenkov, according to which the energy when subjected to oscillations depends on the amplitude and does not depend on the velocity. According to E.S. Sorokin, the theory of internal friction is poorly consistent with the theories describing the inherited properties of materials (viscoelastic and capillary-porous ones). A tendency is observed: the better a theory reflects hereditary properties, the worse this theory is adapted to describe energy losses due to oscillations.In this paper, an attempt has been made to harmonize both these theories and numerous experiments on the destruction of materials described in the academic literature. It turns out that in order to remove contradictions, it is necessary to take into account the dependence of body deformation changing in the course of time.It is shown that the hierarchy of times determining shear and bulk relaxation in viscoelastic/capillary-porous medium has a fractal (scale-invariant) structure. It was observed that the presence of time fractality eases the modeling of viscoelastic/capillary-porous bodies resulting in the universal relaxation function of a rather simple kind. In particular, for the scale-invariant distribution of relaxation characteristics medium, the application of algebraic relaxation law for viscoelastic/capillary-porous materials is possible: this resulting in rheological models and state equations with the derivatives of fractional order.

Numerical modeling of heat and mass transfer processes in a capillary-porous body during contact drying

The problem of conductive (contact) drying of a capillary-porous body in a steam-air (gas) environment by heat transfer to the material during its contact with the heated surfaces of the material is considered. A system of significantly nonlinear differential equations of heat and mass transfer to describe such a process is obtained. To solve the formulated problem of heat and mass transfer (without taking into account deformability), the method of solving nonlinear boundary value problems is applied in the form of an iterative process, at each step of which a linear boundary value problem is solved. The results of the application of the method are verified based on the popular numerical scheme used. They agree well. A numerical experiment is conducted for materials of three types of porosity. The results are presented graphically and tabularly. The regularities of contact drying of capillary-porous materials in a steam-air environment are deduced.

Исследование гигроскопических параметров желатина из отходов переработки рыбы

We studied the hygroscopic properties of gelatin from waste-products after processing of common fresh-water fish species form the Astrakhan region (skin, scales, bones, fins, and cartilage) as an object of drying. The analysis of the thermodynamics of internal mass transfer was carried out during the interaction of the substance of the specified product with water. The objects of study were concentrates obtained by convective-radiation drying of gelatin granules, previously foamed to a constant expansion ratio and cooled to the gelatinization temperature. The studies were carried out experimentally and analytically using the tensometric method by Van Bamelen. For the thermodynamic analysis of hygroscopic characteristics, classical Gibbs–Helmholtz equation was used. On the basis of empirical data, sorption isotherms were obtained – functional dependences of the level of water activity Aw on the equilibrium moisture content and temperature of the product. The isotherms of the concentrates of the studied gelatin are S-shaped, typical for colloidal capillary-porous bodies, which is due to the foam structure of the product. The curves can be conventionally subdivided into three zones, corresponding to the moisture of monomolecular and polymolecular adsorption, structural, microcapillary, and microcapillary moisture. Based on the analysis of sorption isotherms for the product under study, the hygroscopic moisture content of gelatin was determined for its various temperatures: Wg1 = 0.280 kg/kg for T = 283 K and Wg2 = 0.301 kg/kg for T = 303 K. The specified moisture content is a threshold for the range of hygroscopic states and is important from the point of view of rationalization and modeling heat and mass transfer during material dehydration. As a result of calculations using sorption isotherms and the Gibbs–Helmholtz equation, the dependences of free, bound, and internal energy as well as the total specific thermal energy of water evaporation on moisture content and temperature of the product under study were derived. It has been established that the nature of these dependences for the studied samples of gelatin concentrates is generally consistent with the published data for a number of materials of a biopolymer nature. These dependencies can be used in the development of dehydration processes and in the design of drying equipment for the production of gelatin concentrates from fish waste.

Решение краевой задачи тепломассопереноса методом источников для условий лучистого обогрева почвы

The purpose of the research is to find, predict and regulate the temperature and humidity regime of the soil for the conditions of radiant heating of cultivation facilities using dark-type ceiling infrared emitters. A system of differential equations (in dimensional and dimensionless forms) is presented, reflecting the relationship of thermal and mass transfer processes in colloidal capillary-porous bodies in the case of surface radiant heating. A partial analytical solution of this system of differential equations for a semi-bounded body is considered with the exclusion of the phenomenon of thermal and thermal conductivity and period diffusion processes. On the example of milling peat, taking into account the initial data, the solution of the boundary value problem of heat and mass transfer by the method of sources is obtained, which is one-dimensional non-stationary fields of moisture content and temperature. It is established that under the given initial and boundary conditions, as well as taking into account the thermophysical properties of milling peat, the required moisture content will be achieved in six hours, the temperature in three hours. By adjusting the thermal power of the infrared radiation source, and, therefore, the intensity of moisture evaporation from the soil surface into the environment, it is possible to control the rate of heating and drying of the layer (for example, to determine the time or frequency of watering the soil). To clarify the values of moisture content and soil temperature by coordinate and over time, it seems expedient to consider analytical solutions that took into account not only basic, but also conjugate processes of heat and mass diffusion

A New Look at the Structure and Thermal Behavior of Polyvinylidene Fluoride–Camphor Mixtures

An experimental quasi-equilibrium phase diagram of the polyvinylidene fluoride (PVDF)-camphor mixture is constructed using an original optical method. For the first time, it contains a boundary curve that describes the dependence of camphor solubility in the amorphous regions of PVDF on temperature. It is argued that this diagram cannot be considered a full analogue of the eutectic phase diagrams of two low-molar-mass crystalline substances. The phase diagram is used to interpret the polarized light hot-stage microscopy data on cooling the above mixtures from a homogeneous state to room temperature and scanning electron microscopy data on the morphology of capillary-porous bodies formed upon camphor removal. Based on our calorimetry and X-ray studies, we put in doubt the possibility of incongruent crystalline complex formation between PVDF and camphor previously suggested by Dasgupta et al. (Macromolecules 2005, 38, 5602-5608). We also describe and discuss the high-temperature crystalline structure of racemic camphor, which is not available in the modern literature.

Influence of vacuum on diffusion of moisture inside seeds of cereals

The article solves the problem of thermal injury of seeds of grain crops during drying, which are capillaryporous bodies. It is hypothesized that the use of a vacuum in the drying chamber reduces the risk of thermal stress. In this regard, the article studies the effect of a vacuum inside the drying chamber on the diffusion of moisture inside the seeds. Seeds are complex materials in which moisture has different bonds with dry matter. During the working process, the drying speed in the surface layers and inside the seeds occurs at different speeds. As a result, drying stresses occur, which cause cracks on the surface of the seeds. Based on the solution to the differential diffusion equation with an absorbing screen as a boundary condition, the condition for drying without thermal stresses is found. Experimental verification of theoretical studies is carried out on a specially made experimental setup on the example of corn seeds. The effect of thermal stress on seed viability is determined by laboratory germination. Experimental studies confirm the adequacy of theoretical statements. Thus, when drying the seeds of grain crops, which are capillary-porous bodies, there is a limit value of rarefaction, above which cracks appear on the surface of the seeds due to different drying rates on the surface and inside. For drying seeds of grain crops without thermal stresses, it is necessary to consider not only the heating temperature but also the rarefaction in the drying chamber, which should be close to the limit value.

Modeling an Elastic Stress in a Colloid Capillary-Porous Body in Its Dehydration by Depressurization

Modeling an Elastic Stress in a Colloid Capillary-Porous Body in Its Dehydration by Depressurization

Generalization of the Fourier Problem on Fluctuations in the Temperature of the Earth’s Crust

The problem of asymptotic fluctuations of temperature and moisture content in a half-space is solved by the method of complex amplitudes. The material filling the half-space consists of a solid base (capillary-porous body) and water. The well-known Fourier solution for temperature fluctuations in half-space in the absence of moisture and under the boundary conditions of heat exchange of the first kind is generalized to the case of a wet material under the boundary conditions of Newton for temperature and Dalton for moisture content. The results of the work can be used in geocryology to model seasonal fluctuations in the thermophysical characteristics of frozen rocks and soils.

Generalization of the Fourier problem of temperature waves in half-space

The problem of asymptotic fluctuations of temperature and moisture content in a half-space whose boundary is blown by an air flow with a temperature varying according to the harmonic law is solved by the method of complex amplitudes. The material filling the half-space consists of a solid base (capillary-porous body) and water. The well-known Fourier solution for temperature fluctuations in half-space in the absence of moisture and under the boundary conditions of heat exchange ofthefirst kind is generalized to the case of a wet material under the boundary conditions of Newton for temperature and Dalton for moisture content. The results of the work can be used in geocryology to model seasonal changes in the thermophysical state offrozen rocks and soils, in the theory of building structures to study the thermal regime of indoor premises with fluctuations in ambient temperature, in the theory of drying by electromagnetic radiation to study the processes of heat and mass transfer inoscillating modes.

Kinetic dependences for the extraction of apricot pits kernels with ethanol-water solvent

During the extraction of a capillary-porous body, such as the nuclei of fruit seeds, the movement of the distributed substance in the solid phase is carried out by means of molecular diffusion. The amount of material flow in a solid per unit surface is determined by Fick’s law using the diffusion coefficient. The molecular diffusion coefficient depends on the structure of the solid, temperature and soluble substances, and does not depend on the hydrodynamic conditions on the surface of solid particles and the design of the apparatus. The article studies the kinetics of extraction of petals of apricot kernels with ethanol-water solvent. When calculating the value of the residual mass content of plant raw materials during the extraction process, an interval calculation method was used. Based on the experimental data of the extraction kinetics, the molecular diffusion coefficient was determined, which significantly increases during 600-700 s of extraction, and then decreases by 2 times after 1800 s. After 3000 s from the beginning of the process, the diffusion coefficient decreases less sharply. A significant increase in the diffusion coefficient at the beginning of the extraction process, including the impregnation stage, is associated with the uneven distribution of the extracted components in the initial sections of the capillaries. In the studies carried out, the nature of the change in the diffusion coefficient over time does not contradict modern concepts of the mechanism of extraction of a porous structure from plant raw materials.

SUBSTANTIATION OF ENERGY EFFICIENT REGIMES OF DRYING PRODUCTS FRACTIONAL PROCESSING OF ALFALFA

Shortage of quality feed significantly slows down the production of livestock products in Ukraine. One of the ways to overcome the crisis in the production of feed is the use of new high-energy feed, including the products of fractional processing of alfalfa. For the successful implementation of the skin type of feed, including the products of fractional processing of alfalfa, there should be an opportunity to create their reserves, feed should be canned for successful storage. The best way to preserve food is to dry it. Energy efficiency of the drying process, ie loss of nutrients, energy costs for the implementation of the process, etc. It depends on the method and its mode parameters. In this case, it is proposed to carry out the drying process in a thick layer of alfalfa pulp by active ventilation with heated air. To determine the rational parameters of the process, such as layer thickness, air flow, drying time and patents to conduct theoretical and experimental studies. Alfalfa pulp, like most wet plant materials, belongs to the capillary-porous bodies. The drying blood of these bodies has two distinct periods: constant and decreasing speeds (or the first and second drying periods). The moisture content of the material at which the transition from the first to the second period is called critical. As a result of theoretical research has obtained a dependence that determines the total duration of the drying process on a number of parameters, including initial, critical, equilibrium and final moisture content. To determine these coefficients, as well as to check the adequacy of the obtained dependence, experimental studies were conducted on a special installation. The main elements of the experimental setup are a fan, electric heater, containers with mass, shut-off, control and measuring equipment. According to the results of experimental research, graphical dependences of drying speed and process duration on regime parameters are obtained.

Thermally induced phase separation in semicrystalline polymer solutions: How does the porous structure actually arise?

Thermally-induced phase separation in semicrystalline polymer – solvent systems is revisited to analyze the formation of membrane precursors beyond the existing concepts. It is argued that the phase diagrams of such systems should include a commonly overlooked curve describing the solubility of a low-molar-mass liquid in the amorphous regions of a semicrystalline polymer. To illustrate our approach, the binary mixtures of isotactic polypropylene with dioctyl phthalate (good solvent), dibutyl phthalate (poor solvent), and their ternary mixtures are considered. Quasi-equilibrium phase diagrams are constructed using an original optical method and analyzed in terms of phenomenological thermodynamics, including the previously poorly studied region below the polymer crystallization temperature. The proposed scenario of morphology development during the cooling of pre-homogenized mixtures is illustrated with the data of optical and scanning electron microscopy, small-angle X-ray scattering, differential scanning calorimetry, and cloud point methods. It is found that cooling down and subsequent solvent extraction generally lead to the formation of capillary-porous bodies with large (micron-sized) pores formed via the liquid-liquid phase separation and small (submicron-sized) pores appeared due to the microphase separation of amorphous polymer regions under strain imposed by the presence of crystallites. The composition range most suitable for the formation of filtration membrane precursors extends between the polymer mass fraction values corresponding to the upper critical solution point and “monotectic” point, in which the solubility curve meets the curve of complete polymer amorphization.

MODELING AND ANALYSIS OF THE DEFORMED MEDIA (METAL CONSTRUCTION ELEMENTS) NON STATIONARY THERMAL FIELDS DURING THEIR LASER SHORT WAVES PULSES TREATMENT

Substantiated mathematical model for non-stationary thermoelastic deformed media during their laser processing by short waves pulses fields analysis is proposed . Precise analytical solutions of the thermal conductivity equations which simulate the short laser pulses interaction and allow to further determine their components thermally stress-strain state of the processed materials, in particular, thin porous films, capillary-porous bodies are obtained. Two analysis methods were used: 1) traditional separating variables method (Fourier method), 2) non-Fourier analysis of the non-stationary thermal fields that described by the telegraphic equation known in the literature. The results obtained in this work can be used further to establish the thermo stress-strain state of materials interacting with short waves laser radiation pulses parameters. Such approach is used at the modern building process for the rising of the reliability, durability and strength of the metal construction elements.

ФРАКТАЛЬНАЯ МАСШТАБНО-ИНВАРИАНТНАЯ СТРУКТУРА ВРЕМЕННОЙ ИЕРАРХИИ В ПРОЦЕССАХ РЕЛАКСАЦИИ

The phenomena of elastic aftereffects during loading/unloading of viscoelastic and capillary-porous bodies, relaxation of their stresses is accompanied by the energy accumulation and dissipation to be taken into account in the theory of oscillations which also considers the behavior of materials when the force is applied to them, the elastic aftereffect and stress relaxation forms ostensibly opposite energy processes that’s why the main problem to one is to understand and discovery laws for such aftereffects. The goal of the research to show that the distribution of relaxation time in viscoelastic and capillary-porous media may have a scale-invariant structure and that the indirect confirmation of the scale invariance of relaxation time hierarchy can be the principle of temperature-time superposition according to which the experimental relaxation functions obtained for different temperatures can be combined with each other using the appropriate coordinate axes stretching. We used methods of viscoelastic theory, fractal analysis and methods of mathematical physics. So, in this paper, an attempt has been made to harmonize both these theories and numerous experiments on the destruction of materials described in the academic literature. It is shown that the hierarchy of times determining shear and bulk relaxation in viscoelastic/capillary-porous medium has a fractal structure and it was observed that the presence of time fractality eases the modeling of viscoelastic/capillary-porous bodies resulting in the universal relaxation function of a rather simple kind.

Moisture sorption and thermodynamic properties of Camellia oleifera seeds as influenced by oil content

Moisture sorption isotherms and thermodynamic properties of Camellia oleifera seeds as influenced by oil content were investigated. Moisture desorption and adsorption isotherms of Camellia oleifera seeds, kernels and shells from three varieties were determined using constant temperature and humidity chamber method at different temperatures (10°C, 25°C, and 40°C) with water activity ranging from 0.20 to 0.90. Six selected mathematic models were employed to fit the experimental data. The Peleg model gave the best results for both seeds and kernels and Langmuir model was the best for shells. The difference of equilibrium moisture contents at the same water activities during desorption and adsorption indicated the occurrence of hysteresis of adsorption processes and the equilibrium moisture contents tended to decrease with the increasing oil content and temperature. The binding energy and average capacity per unit mass decreased with increasing temperature and oil content. The relationships between water activity and the logarithm of sorption activity showed the capillary porous body characteristics of the seeds. Keywords: Camellia oleifera seeds, moisture desorption and adsorption isotherms, equilibrium moisture content, oil content, thermodynamic property DOI: 10.25165/j.ijabe.20211401.5457 Citation: Zhu G F, Jin Q, Liu Y H, Lin Y W, Wang J, Li X Y. Moisture sorption and thermodynamic properties of Camellia oleifera seeds as influenced by oil content. Int J Agric & Biol Eng, 2021; 14(1): 251–258.