Capillary-porous Materials Research Articles

Influence of selected factors on the energy consumption of frozen logs subjected to thermal treatment in veneer production

ABSTRACT This study puts forward an approach for calculating the specific energy consumption and its components required for heating of frozen logs for veneer production, depending on the logs’ initial temperature and moisture content. The approach is based on the use of two personal models: unsteady model of the temperature distribution along the radius of frozen logs during their thermal treatment and stationary model of the energy consumption of logs subjected to such treatment as a function of its four multifactorial components. The influence of all combinations between five values of the initial temperature of frozen logs from −1 oC to −40 oC and three values of their moisture content from 0.4 kg·kg−1 –0.8 kg·kg−1 on the specific energy required to heat and placticize beech logs with a diameter of 0.4 m at operating temperature of the steaming or boiling medium of 80 oC was investigated. The obtained results show that this energy changes in the range from 46 kWh·m−3 (at −1 oC and 0.4 kg·kg−1) to 114 kWh·m−3 (at −40 oC and 0.8 kg·kg−1) The approach could be applied to calculate the energy and its components required for carrying out of the thermal treatment of various frozen capillary-porous materials.

THEORETICAL AND EXPERIMENTAL ANALYSIS OF DRYING KINETICS OF COLLOID CAPILLARY-POROUS MATERIALS AS DRYING OBJECTS

Considering the current situation in the energy sector of Ukraine, the urgent need to improve and develop energy-efficient thermal technologies for dehydration of plant raw materials is urgent and timely, which would ensure minimal energy consumption and high quality of the final product. The processing of vegetable raw materials into dried products is important for the sustainable development of the food industry. Cultivated Pleurotus eryngii mushrooms, which are valued for their high content of protein, carbohydrates, unsaturated fatty acids, vitamins and other nutrients, etc., are increasingly relevant in the mushroom industry on the world food market. It is important, in order to optimize energy consumption during dehydration and to select rational equipment, in addition to experimental studies, to perform theoretical calculation analysis of heat and mass transfer based on mathematical models. The article provides a theoretical and experimental analysis of the drying kinetics of colloidal capillary-porous materials. To determine the characteristics of the convective drying process, in addition to experimental studies, numerical modeling of this process was performed, which is performed on the basis of the numerical solution of the system of heat and mass transfer equations in colloidal capillary-porous materials. The calculation model can be used for the approximate determination of the main characteristics of the drying process of colloidal capillary-porous materials.

An engineering approach for calculating the energy required for defrosting and subsequent heating of frozen wood during thermal treatment

ABSTRACT An approach for calculating the energy required for defrosting and subsequent heating of frozen wood during thermal treatment in the production of veneer has been presented. Using two own unsteady models the duration of regimes for steaming of prisms in an autoclave and for boiling of logs in a pit, and also the average mass temperature of the prisms and logs and the energy accumulated by them at the end of heat carrier introduction in these regimes was determined. The obtained values of average temperature were introduced in third own model for engineering calculation of the energy considered in the approach. Computer simulations were carried out for beech prisms with a cross section of 0.4 × 0.4 m and beech logs with a diameter of 0.4 m at an initial wood temperature of −10°C, −20°C, and −30°C and moisture content of 0.6 kg·kg−1. The operating temperature of the prism steaming regimes was equal to 130°C, and that of the log boiling regimes was 80°C. The approach can be applied using Excel for computing the energy and its components needed for defrosting and heating of different frozen capillary-porous materials subjected to multiple types of thermal treatment.

Experimental and computer study of the mechanism and identification of conditions for energy-efficient removal of moisture from materials under ultrasonic exposure.

The article is devoted to investigation of energy-efficient moisture removal from capillary-porous materials. Moisture is removed by dispersion at collapse of cylindrical cavitation bubbles, formed by ultrasonic vibrations in the capillaries of the material. Mathematical model, which allowed to investigate the mechanism of moisture dispersion, has been developed. Necessity of realization of cavitation bubble full life cycle in capillary (slow growth, rapid expansion with deformation, collapse) was found. An optimal range of sound pressure levels from 150 dB ("critical level" at which dispersion of water from capillary starts) up to 170 dB (dispersion productivity growth stops due to cavitation bubbles reaching maximum size equal to diameter of capillary) was determined. It is shown that the size of the dewatered sample for maximum drying efficiency should correspond to the ultrasonic wavelength in air. Ultrasonic dispersion of liquid during drying was confirmed experimentally. It is found that for significant reduction of drying time (up to 50% and more) it is necessary to affect in the range of 165-170 dB. And the materials to be dried must be placed as particles or layers having dimensions or thicknesses corresponding to the length of the ultrasonic wave in air. The implementation of ultrasonic drying, on the example of food products (beets) provided a reduction in drying time of 1.9 times, while reducing energy costs by 1.7 times in comparison with convective drying.

Modeling heat and mass transfer in grain drying processes under the influence of electromagnetic field

Drying of grain materials by traditional convective methods typically involves significant energy consumption, primarily due to unproductive losses of thermal energy with the exhausted drying agent. Optimizing this process entails reducing the volume of drying agent used and compensating for reduced thermal energy through non-contact heat transfer methods such as microwave (MW) or infrared (IR) irradiation. However, mathematical modeling of these processes requires refinement as they differ from traditional convective heat drying processes. Grain drying is a complex thermophysical process, with heat and moisture transfer occurring within the capillary-porous material in a mutually dependent manner. To better understand these processes, it is necessary to establish mathematical models that account for the influence of the electromagnetic field. This article aims to theoretically investigate the drying process of plant raw materials under the influence of MW and IR electromagnetic fields based on analytical mathematical models. The conducted research indicates the potential of using electromagnetic fields to intensify the drying of plant raw materials, particularly through MW and IR irradiation, which allows for targeted heating of the moist zones of the material. The obtained analytical dependencies enable the calculation of temperature and moisture content fields in materials and determine the degree of influence of electromagnetic field parameters on heating and drying processes. These dependencies also help to more accurately identify heat and mass transfer model coefficients based on experiments. Such an analytical-empirical approach can be utilized to calculate rational processing regimes for grain raw materials under the influence of electromagnetic fields.

Solution of the Heat and Mass Transfer Problem for Soil Radiant Heating Conditions Using the Method of Finite Integral Fourier Transform

To achieve high agricultural yields, it is essential to predict the soil temperature and moisture regime, considering the heating technology employed. The research object is soil heated by a ceiling-mounted infrared emitter. The research subject encompasses one-dimensional unsteady fields of soil moisture content and temperature. The research goal is to forecast the soil temperature and moisture regime under radiant heating conditions. The research methods involve the analytical solution of heat and mass transfer differential equations using the method of finite integral Fourier transforms. Research results indicate that the top layer of milled peat, with an initial moisture content of 3.7 kg/kg, will reach a final moisture content of 1.0 kg/kg in approximately 6 hours during infrared drying. As a result of radiant heating, the soil temperature will rise from an initial 5 ℃ to a final 22.6 ℃ in approximately 3 hours. The analytical solution of the mass transfer differential equation can be utilized for theoretical studies of drying capillary-porous materials, such as determining the drying period or the thickness of the material layer that will dry to a specified final moisture content. The analytical solution of the heat transfer differential equation, accounting for both thermal conductivity and the Dufour effect, can be employed to manage the operation of the infrared radiation source, such as determining its operational and shutdown periods when the soil surface temperature reaches its maximum (critical) value. The mathematical solutions discussed in the article do not consider thermodiffusion processes in the soil layer (Soret effect), which presents a promising direction for further scientific research.

Solution of the Heat and Mass Transfer Problem for Soil Radiant Heating Conditions Using the Error Function

Achieving high yields of agricultural crops requires the ability to predict soil temperature and moisture regimes, taking into account soil heating technology. The object of study is soil heated by a ceiling infrared emitter. The subject of study is one-dimensional non-stationary fields of soil moisture content and temperature. The objective of the study is to predict soil temperature and moisture regimes under radiant heating conditions. Research methods: analytical methods for solving differential equations of heat and mass transfer using the error function. Research results: the top 5 mm layer of milled peat with an initial moisture content of 3.7 kg/kg will reach a final moisture content of 1.0 kg/kg in about 6 hours during infrared drying. As a result of radiant heating, the soil will heat up from an initial temperature of 5 ℃ to a final temperature of 20 ℃ in approximately 3 hours. The analytical solution of the mass transfer differential equation can be used for theoretical studies of drying of capillary-porous materials, for example, to determine the drying period or the thickness of the material layer that will dry to a given final moisture content. The analytical solution of the heat transfer differential equation can be used to control the operating mode of the infrared radiation source, for example, to determine the periods of its operation and switching off in case the soil surface temperature reaches the maximum (critical) value. The mathematical solutions considered in the article do not take into account the cross processes of heat and mass transfer, which is a promising direction for further scientific research.

PHASE CONCENTRATION EQUILIBRIUM DURING DRYING COLLOID CAPILLARY-POROUS MATERIAL - PEA

In this work, we studied experimentally the phase concentration equilibrium during drying of a colloidal capillary-porous material - peas. The studies were carried out by a static (exsicator) method using saturated aqueous solutions of mineral salts, with the help of which certain relative air humidity was created in the desiccators. To establish equilibrium, the samples were kept in desiccators for one month. The values of relative air humidity over salt solutions at the corresponding temperatures were found from the well-known Schneider diagram. Moisture desorption isotherms were determined, for which high-moisture pea samples were placed in exsicators. The experiments were carried out at three temperatures: 30, 40 and 50 °C. According to the measurement data, moisture desorption isotherms were constructed in the coordinates "relative air humidity - equilibrium moisture content of the material." The resulting desorption isotherms were described by the Henderson equation, for which the values of the coefficients of this equation were found and their statistical evaluation was given. The data on the balance of peas were compared with similar data for other plant colloidal capillary-porous materials: vegetables (carrot and beet cuts), grain crops (rye, wheat and corn grains), and vegetable seeds. A significant influence of the type of culture on the equilibrium moisture content of the material during drying is shown, while the intraspecific influence on the equilibrium moisture content is less important. The obtained data on moisture desorption isotherms during drying can be used for engineering calculations of the kinetics of drying pea grain and for choosing the temperature and humidity conditions for its storage after drying.

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.

ENERGY-EFFICIENT CHAMBER DRYER WITH THICK ALLOY HEATING ELEMENTS

Drying is one of the main technological processes of plant raw materials processing in the production of dry food products and powders from them. Convective drying is the most widespread method of drying vegetable raw materials, which is accompanied by high energy costs for the process. Increasing the energy efficiency of drying colloidal capillary-porous materials in a 2-zone chamber dryer occurs due to the use of coolant recirculation between drying zones and the installation of thick-film heating electric elements. The proposed design of the thick-film heating element and its technical characteristics are presented. Studies of the drying kinetics of colloidal capillary-porous plant materials were carried out on the created energy-efficient 2-zone chamber dryer with installed thick-film heating elements. Reducing energy costs for the drying process is possible through the design and manufacture of a 2-zone chamber dryer with the installation of 2 sections of thick-film heating elements (21 pieces in each). Installing this heater in a chamber dryer allows you to save electricity consumption by up to 30 %. The study of the kinetics and energy efficiency of the drying process in a chamber dryer is carried out on colloidal capillary-porous materials, in particular potatoes and pumpkins. The intensity of drying is limited by the quality characteristics of the material, so drying is carried out at low temperatures. Material quality control is assessed by recoverability and organoleptic indicators after drying. The results of experimental studies in a chamber drying unit showed that energy costs for the drying process increase significantly at the end of the process when the intensity of moisture evaporation decreases. The energy consumption of heat per kilogram of evaporated moisture and the efficiency of the installation were analyzed in order to determine the optimal drying time. Energy consumption per kilogram of evaporated moisture in the created chamber dryer corresponds to the effective indicators of this type of convective dryers. Bibl. 20, Fig. 8.

INFLUENCE OF COMBINED DRYING OF COLLOID CAPILLARY-POROUS MATERIALS ON ENERGY EXPENDITURES

One of the berry crops that has recently gained popularity among consumers is blueberry (Vaccinium corymbosum L.). The berry is a powerful antioxidant, and besides, it contains fructose in its composition, which automatically refers it to the products of the diabetic diet. Therefore, blueberries become an interesting colloidal capillary-porous drying object. Wax on the skin of berries performs a protective function in the process of ripening, harvesting and transportation, but is a negative factor for the implementation of technological processing by artificial dehydration. The latter causes significant energy costs for the processing process. Therefore, the aim of the work is to determine the effect of combined drying of blueberry on energy consumption.
 Experimental studies of the drying kinetics of blueberry were carried out on an experimental convective stand with forced recirculation of the coolant and infrared emitters, which was developed in ІEТ of NAS of Ukraine. The effect of pre-developed hygrothermal and infrared treatment of fresh blueberries on the kinetics and change in the drying speed of berries was investigated. The use of infrared radiation made it possible to reduce the total duration of the dehydration process by 1.2 times.
 The heat of evaporation of moisture from the samples and their heat capacity were investigated using the method created in ІEТ of NAS of Ukraine installations of synchronous thermal analysis DMKI-01, which is intended for the study of colloidal capillary-porous materials. Determination of specific heat capacity was carried out according to the standardized method of step-by-step scanning DSTU ISO 11357–4:2010 in the temperature range from 30 to 95℃.
 Experimental determination of heat capacity and heat of evaporation of moisture from pre-processed blueberry showed excess energy consumption for a possible phase transition of the waxy shell of the berry during drying and a decrease in the drying efficiency of the material at moisture values Wc ≤ 20%.

The Improvement of the Rheological Model of Leather

Fibrous capillary-porous materials, such as woven materials and leather, used in the light industry for clothing and footwear, differ sharply from metallic materials. These differences manifest themselves in a complex relationship between stress and strain, which depends on the strain rate and loading time. A method for determining the identified new rheological parameter of the inert resistance of a capillary-porous material (for example, leather) of accelerated deformation is presented in the article; it consists in determining the indentation force of a conical indenter at a constant speed and the coefficient that considers shear zones, and the angle formed by the boundaries of the material deformation zone and application of force value. An equation for an improved rheological model of leather is derived; it consists of the Kelvin model, the Bingham-Shvedov model, and the Khusanov model, expressed in terms of the rheological parameter in the form of a deformation inertness coefficient. The inclusion of the model of deformation inertness in the form of a coefficient into the rheological model of leather will allow the mathematical description of the rheological parameters of leather and the development of engineering methods for their calculation. The implementation of the developed method will allow obtaining numerical values of the rheological parameter of the inert resistance of the capillary-porous material under its accelerated deformation, namely, a new property of the capillary-porous material, which must be taken into account in various technological processing operations, for example, when treating moisture-saturated leather.

DEVELOPMENT OF A CELL AUTOMATA MODEL FOR SIMULATION OF THE DRYING PROCESS OF CAPILLARY-POROUS MATERIALS IN PERIODIC ACTION CHAMBERS

In this work, the main emphasis is placed on the creation of a cellular automaton model for simulating the drying process of capillary-porous materials. The possibility of creating a cell-automatic field for the studied 3D model of a periodic drying chamber is considered. Appropriate algorithms are developed and their software implementation is carried out, since the cellular automata field is one of the key requirements for using the cellular automata method. Another key requirement is the availability of adequate transition rules. For their development, the analysis of mathematical models of heat and moisture transfer processes in periodic drying chambers is carried out. Transition rules are being developed, which make it possible to determine changes in temperature and moisture content of the material, as well as changes in the main parameters of the drying agent, which include temperature and relative humidity. The paper also simulates the drying process of capillary-porous materials based on the developed cellular automaton model, which includes the cellular automaton field and transition rules. The input data for modeling are taken from the parameters of technological conditions that are used in real drying chambers. Pine with a thickness of 45 mm was chosen as the studied capillary-porous material. with an initial moisture content of 65%. As a result of the simulation, graphical dependences of the desired parameters of the material and the drying agent with respect to time were obtained. Verification of the obtained results is carried out by comparing them with data collected by sensors in a real drying chamber. For comparison, a relative error is determined, the average values of which do not exceed 10%. This result confirms the adequacy of the developed model of cellular automata.

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.

Modeling of the drying process of a capillary-porous cylindrical body

In the process of drying capillary-porous materials, the movable surface of the phase transition, which separates the dried and wet zones in the body, depends on the properties of the material and the temperature due to external influence of the drying agent, is a function of coordinates and time. We assume that the above properties of the material are functions of porosity, density and heat capacity of body components.

Influence of plasma activation nanostructure collagen on process structurization without chrome a fur sheepskin

The influence of water-soluble non-isocyanate urethanglicol and plasma treatment on changes in the nanostructure of collagen in the process of organic tanning is investigated. Plasma modification leads to conformational changes in collagen fibers which contributes to increase in the diffusion of structuring agents into the sense of capillary-porous material. Input parameters of plasma processing determined. Pilot tests of the proposed technology led to the production of a semi-finished product of fur sheepskin with increased values of physical, mechanical and operational indicators in comparison with the control.

DEPENDENCIES FOR CALCULATION OF THERMAL CONDUCTIVITY OF WET CAPILLARY-POROUS WALL MATERIALS

Using the theory of generalized conductivity and geometric modeling of the structure of wet capillary-porous materials, dependencies were obtained for calculating their effective thermal conductivity. Depending on the values ​​of the moisture content of the pores, the limits of application of the obtained formulas are established. On examples for clay bricks, the features of the calculation of wet capillary-porous materials are demonstrated. It has been established that the results of calculations quite accurately predict the experimental data.

Equations for Calculating the Thermal Conductivity of Capillary-Porous Materials with over Sorption Moisture Content

This article is the result of the authors’ work on the method of calculating the effective thermal conductivity of moist capillary-porous materials used in wall partitions. The proposed methodology was developed based on the theory of generalized conductivity and geometric modeling of the structure. Materials are considered as heterogeneous ternary systems consisting of a solid skeleton, gas and liquid, and all components are simultaneously taken into account in the calculation. In this work, additional equations are constructed that allow calculation of the effective thermal conductivity of capillary-porous materials with over sorption moisture, thus extending the scope of application of the method to the entire possible range of changes in moisture content. The details of calculating the thermal conductivity of moist capillary-porous materials are demonstrated using experimental data for wall ceramics samples. It is shown that the proposed equations are capable of predicting the thermal conductivity of moist capillary-porous materials with sufficient accuracy. Knowledge of the thermal conductivity of materials in conditions of their actual moisture is fundamental in the sustainable design of new buildings as well as thermo-renovation and dump protection of historic ones.

Heat and Mass Transfer in a Dense Layer during Dehydration of Colloidal and Sorption Capillary-Porous Materials under Conditions of Unsteady Radiation-Convective Energy Supply

Heat and Mass Transfer in a Dense Layer during Dehydration of Colloidal and Sorption Capillary-Porous Materials under Conditions of Unsteady Radiation-Convective Energy Supply

Drying characteristics of two capillary porous building materials: Calcium silicate and ceramic brick

The wetting and drying ability of porous building materials plays a significant role in moisture transfer in the building envelope and thus influences the durability and energy efficiency of buildings. The drying characteristics of the material provide insight into the moisture transport feature over a wide moisture content range, and hence, the drying process can assist in improving the accuracy of moisture transport modelling for the heat, air and moisture (HAM) simulation and in comprehending the hygric behavior of buildings responding to environmental change.In this paper, the drying behaviors of calcium silicate and ceramic brick were experimentally and numerically investigated. The approaches to determine the drying rates of the first and second drying durations were first evaluated and proposed. The influence of the surface air flow velocity and sample dimension on the drying process was analyzed. The descriptive parameters to assess the drying rate were further discussed. The drying coefficient was shown to be able to describe the drying ability of porous building materials. Numerical simulation was conducted and compared with the measurement for a better understanding of the coupled heat and moisture transfer phenomena during the drying process.