Mass Transfer Theory Research Articles

Analytical solutions for the diffusive mass transfer at cylindrical and hollow-cylindrical electrodes with reflective and transmissive boundary conditions

• Unified theory for the diffusive mass transfer at cylindrical electrodes. • Analytical solutions are infinite series involving Bessel functions. • Semi-Infinite diffusion results in improper integral representations. • Analytical solutions confirm numerical results obtained from Talbot’s NILT method. The theoretical treatment of cyclic voltammetry or chronoamperometry at cylindrical electrodes by means of convolutive modeling requires an a priori knowledge of the time-dependent mass transfer functions and of the diffusive flux of the electrochemically active species. In this paper, analytical solutions for both of these quantities are derived for cylindrical and hollow-cylindrical electrodes with reflective and transmissive boundaries by means of Laplace transformation techniques. Furthermore, explicit equations for the concentration profiles of a Cottrellian potential step experiment are provided. All of these expressions are given in terms of infinite series involving Bessel functions of the first and of the second kind. It is demonstrated that the summation of only a few terms of these infinite series is usually sufficient to accurately compute the desired time-dependent mass-transfer function or the current. This renders the numerical inversion of Laplace transformations, utilized so far, obsolete and represents a mathematical supplement to the recent theory.

Influence of Phosphatide Content in the Unrefined Sunflower Oil on Its Thermal and Rheological Properties

The results of a study of the effect of the content of phosphatides in sunflower oil on its heat capacity and viscosity are presented. These studies are needed for more accurate calculations of thermal and hydrodynamic conditions in the technology of production and processing of sunflower oil. New results can become the basis for further understanding of the nature of the structure of sunflower oil under various conditions in real processes. This complements the fundamental knowledge and theory of heat and mass transfer. The adaptation of general experimental and data processing techniques to the conditions of the task is presented. Recommendations for reducing the time of experiments are proposed. New data on heat capacity and viscosity values have been obtained for unrefined sunflower oil with different fatty acid composition, for a wide range of operating parameters from 20 to 140 °C, with a phosphatide content from 0.005 to 0.9683 g/100 g. An unambiguous correlation has been established between the thermal and rheological properties of unrefined sunflower oil. The results show that these properties can have a significant impact on equipment efficiency and oil quality. The developed and repeatedly tested research methodology can be successfully applied to other oils and other conditions.

Dynamic modelling based on surface renewal theory, model validation and process analysis of rotating packed bed absorber for carbon capture

Rotating packed beds can reduce the equipment size and costs in solvent-based carbon capture. However, difficulties are encountered when modelling rotating packed beds due to turbulent fluid flows inside rotating packed beds and the cross-sectional area of mass transfer unit that changes with radius. This study aims to develop a validated dynamic model of a rotating packed bed absorber and to carry out process analysis through steady state and dynamic simulations. Innovatively, the dynamic model was developed based on surface renewal theory for mass transfer. The model can calculate distributed mass transfer coefficients and other key variables related with absorption performance. Experiments were carried out and new experimental data for the rotating packed bed absorber under realistic operating conditions were obtained for model validation. Process analysis about the effects of key operational variables such as rotating speed, liquid-gas ratio and solvent concentration on absorption performance was performed with benchmark MEA solvent. It was found that the optimal MEA concentration is around 70 wt%. Dynamic simulation results reveal that the RPB absorber has fast responses for process changes. This new distributed dynamic model and the insights obtained through process simulation will promote rotating packed bed technology towards its industrial deployment in large scale carbon capture processes.

On a theory of mass transfer during the evaporation of a spherical droplet

An analytic model of evaporation of a spherical droplet into the surrounding gas without consideration of the Stefan flow and vapor buoyancy is presented. This model is based on the use of the diffusion equation and contains a kinetic description of the evaporation process. In addition, this model is based on the assumption that droplet temperature does not change over time. In the framework of the presented model, an equation for the rate of droplet evaporation that is an alternative to the Fuchs equation is obtained. Analysis of the model showed that, depending on droplet size, evaporation can take place in three regimes.

Modeling the mass transfer process in membranes for carbon capture and separation with concentration polarization effect

Membrane separation is regarded as the most promising carbon capture technology due to its low operating cost and requirements for installation. The main parameters in membrane separation are selectivity and permeability. This study presents a mathematical model to analyze factors influencing membrane separation. The separation process was investigated based on mass transfer theory by analyzing the influence of pressure, initial composition, permeability and doped gas on the separation result. An increase in pressure ratio, mole fraction of CO2 and permeability will improve the separation efficiency. The influence of doped gas on the separation efficiency is depended on the permeability and the content of the doped gas. Moreover, the study also presents the effect of concentration polarization on the separation. Results of studied cases provide a reference for the membrane separation for carbon capture. It is found that the concentration polarization significantly affects the membrane gas separation process. The two-dimensional distribution of concentration was obtained with concentration polarization. The concentration of CO2 on the retentate side becomes lower near the membrane due to permeation. Influences of pressure and permeability on the two-dimensional distribution of gas concentrations were also analyzed.

Efficiency Criteria for Thermal Insulation Structures of Glass Furnaces

The optimal operation of high temperature reactors such as glass furnaces requires many factors to be considered. These are, for example, the duration of the campaign, operating costs, heat losses, trouble-free operation of units and many others, presented in the article. The aim of this study is to synthesize an efficiency criterion for optimizing the heat-insulating construction of a glass-melting furnace (HICGF), as well as obtaining the optimal values of the efficiency criterion for HICGF, which for the furnace under study are about 3.8 billion rubles. In the course of the study, the phenomenological heuristic-evolutionary optimization method by G. E. Kanevets (PHEOM.GEK), which has a number of advantages over other evolutionary methods. As the main generalizing criterion, taking into account the most significant production (volume, cost of the produced glass mass) and financial (costs for the construction and operation of the HICGF, the monetary equivalent of heat losses) indicators, the maximum gross income for the furnace campaign was adopted, which differs from prototypes in that it allows to take into account most fully the peculiarities of the work of the insulated side fence of the glass furnace. Using the software complex created on the basis of PHEOM.GEK complex systems for the side fence of a glass-melting furnace, the optimal set (sequence of location and thickness) of thermal insulation materials HICGF was determined, which allow maximizing the furnace campaign with minimal heat losses. The reliability of the data obtained is achieved by the correct use of the theory of heat and mass transfer and PHEOM.GEK. An efficiency criterion is proposed, which, by solving an optimization problem, made it possible to determine the optimal HICGF. The solution of the optimization problem in conjunction with the calculation of the duration of the furnace campaign makes it possible to form recommendations for the development of optimal HICGFs in the construction of new and cold repair of existing glass furnaces by specialized institutes and industrial companies

Drying Stress and Strain of Wood: A Review

Wood drying stress causes various drying defects, which result from the wood microstructure and the transfer of heat and mass during the drying. It is the fundamental way to solve the problem of defects to clarify the law and mechanism of wood stress and strain development during drying. In this paper, based on the defects of wood drying, the theory and experimental testing methods of drying stress and strain were summarized. Meanwhile, artificial neural networks (ANN) and their application in the wood drying field were also investigated. The traditional prong and slicing methods were used practically in the research and industry of wood drying, but the stress changes in-process cannot be trapped. The technologies of image analysis and near-infrared spectroscopy provide a new opportunity for the detection of drying stress and strain. Hence, future interest should be attached to the combination of the theory of heat and mass transfer and their coupling during drying with the theory of microscopic cell wall mechanics and macroscopic drying. A more complete image acquisition and analysis system should be developed to realize the real-time monitoring of drying strain and cracking, practically. A more feasible and reasonable prediction model of wood drying stress and strain should be established to achieve the accuracy of the prediction.

Dependence of the temperature of the beginning of the heating season on the energy efficiency class of the building

The heat supply of most Russian cities is provided by centralized sources of thermal energy. During the operation of buildings, the transition period of the year is not given due attention. The transition periods of the year (before and after the heating season) complicate the task of providing thermal comfort in the rooms of residential and community buildings. The paper deals with the problem of microclimate troubles in multistorey residential buildings during transition periods. The purpose of this work is to test the hypothesis that there is a dependency of the temperature of the beginning of the heating season, depending on its energy efficiency class. For the thermal conditions of the rooms, the classical dependences of the thermal balance, technical thermodynamics and the theory of heat and mass transfer are used. On the example of a nine-storey apartment block, a calculation was carried out, as a result of which the rational temperature of the beginning of the heating season for various energy efficiency classes was determined, as well as the internal air temperature at the outdoor air temperature equal to 8°C (the existing value of the temperature of the beginning and end of the heating season). The results obtained confirm the hypothesis of the study that there is a dependency of the rational temperature of the beginning of the heating season for a particular building, depending on its energy efficiency class. At the temperature of the beginning of the heating season, the internal air temperature of 20°C will be achievable with a deviation of -41.182%, which corresponds to energy efficiency class A (excluding heat gain from solar radiation). It is established that at the current temperature of the beginning of the heating season, the internal air temperature of 20°C will be achievable with a deviation of -41.182%, which corresponds to energy efficiency class A, for buildings of a lower class, the temperature of the beginning of the heating season is not optimal.

CFD-based structure optimization of plate bundle in plate-fin heat exchanger considering flow and heat transfer performance

Abstract The plate-fin heat exchanger has been widely applied in the field of air separation and aerospace due to its high specific surface area of heat transfer. However, the low heat transfer efficiency of its plate bundles has also attracted more attention. It is of great significance to optimize the structure of plate-fin heat exchanger to improve its heat transfer efficiency. The plate bundle was studied by combining numerical simulation with experiment. Firstly, according to the heat and mass transfer theory, the plate bundle calculation model of plate-fin heat exchanger was established, and the accuracy of the UDF (User-Defined Functions) for describing the mass and heat transfer was verified. Then, the influences of fin structure parameters on the heat and mass transfer characteristics of channel were discussed, including the height, spacing, thickness and length of fins. Finally the influence of various factors on the flow field performance under different flow states was integrated to complete the optimal design of the plate bundle.

Calibration of silicone for passive sampling of semivolatile organic contaminants in indoor air

Semivolatile organic compounds (SVOCs) are mostly man-made chemicals that distribute between the gas and solid phase in the environment. Many of them could pose harm to people and therefore it is important to know their concentrations in the indoor environment to evaluate the related risks. Inhalation exposure can be assessed using passive sampling. In this study, we employed silicone elastomer as a passive sampler for monitoring gaseous polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) in indoor air. We performed a sampler calibration study in which samplers consisting of 0.5 mm thick silicone sheets with a total surface area of 300 cm2 were exposed to indoor air in a university lecture theatre for up to 56 days. Uptake kinetics of SVOCs was studied by collecting 2 samplers every week. The results were used to develop a model based on mass transfer theory that can be used to estimate the air sampling rate RS as a function of compound’s molecular volume. We examined release kinetics of performance reference compounds that covered a broad range of silicone-air partition coefficient (log KSA 5.95–9.49) and investigated a hypothesis of isotropic exchange kinetics, i.e. equality of rate constants for uptake and release, of SVOCs. PCBs and OCPs concentration in air calculated from contaminant amounts accumulated in passive samplers were in good agreement with those determined by active sampling running simultaneously during the entire study. The use of performance reference compounds is suitable for in situ passive sampler calibration.

Photon correlation spectroscopy in the fish salting process

The current study experimentally investigates the innovative photon correlation spectroscopy method application in fish salting process. The method is based on the Rayleigh scattering of light by a substance. The experiment aims to study the mass transfer laws, as well as technological and practical aspects of the fish salting process in brine without circulation. The paper focused on spatio-temporal dependence of the salt diffusion coefficients in the fish-brine system and their correlation with temperature, indicating that at a temperature close to 8°C a diffusion-osmosis equilibrium occurs between the brine and the muscle tissue of fish. The salt diffusion rate was estimated, confirming the validity of the Crean’s frontal theory of salt mass transfer in muscle tissue of fish. Based on the Stokes-Einstein equation, it was shown that the dynamic viscosity of fish tissue fluid could be determined by changing the diffusion coefficient and the diffusing particles size. Practical applications Fish salting is an important preservation method in many countries. The present work seeks to investigate the salting of herring, as it is prone to ripening during this process. Excessive sodium chloride consumption is known to have a negative effect on humans. At the same time, the salt content in the product is interrelated with its preservation effect. In this regard, it is necessary to accurately calculate the specified salt concentration in the finished product for the optimal shelf life. Improvement of this process requires a better understanding of the mass-transfer mechanisms using modern investigation methods. Research focuses on spatio-temporal salt distribution in fish muscle tissue to arrive at clear conclusions, which can facilitate the improved production of salted fish and can be widely used in the food industry for processing and preserving fish or fish products.

Conservation laws and invariant solutions of the wave equation on Bianchi I space–time: A comprehensive analysis

In accordance with Einstein’s theory of general relativity, gravity is a phenomenon attributed to the curvature of spacetime. This notion has allowed physicists to investigate behaviour of physical processes, with respect to different curved spacetime, occurring in the presence of gravitation. One of the most basic of these processes is wave propagation whose various behaviours due to curvature effects have been investigated in the literature. This present study exhaustively explores the invariant solutions of the wave equation on Bianchi I space–time using Lie symmetry method. Under the isotropic Bianchi I universe, we showed how the aforementioned wave equation is connected to one of the most important equations encountered in the heat and mass transfer theory. Furthermore, we completely classify its conservation laws when the potentials are O(tω) for any parameter ω.

Oxygen transport analysis in lead-bismuth eutectic coolant for solid-phase oxygen control

Oxygen concentration control is the most promising technique to solve the corrosion problem in LFRs. A numerical study on the oxygen transport characteristics in the solid-phase oxygen control is carried out in this paper. The geometry is created using the Discrete Elements Method (DEM). The mass transfer and boundary layer theory is adopted to model the PbO dissolution process. The dissolution rate, mass transfer coefficient, and Sherwood number are then calculated for different flow conditions. The simulation models are validated by the experimental data obtained in the CRAFT experiment by SCK·CEN with a deviation of 15%. Based on the validated models, the parameter sensitivity analysis is carried out. The results show that the mass transfer coefficient does not change with inlet concentration, increases with the increase in mass flow rate and temperature. Finally, an oxygen mass transfer relation for a packed bed of PbO spheres in flowing Lead-bismuth eutectic (LBE) considering the temperature dependence and velocity dependence separately is obtained based on the numerical results. The relation could be used in a one-dimensional analysis code for the design of an LBE-cooled system with an oxygen control system.

Characterization and modeling of thermal protective fabrics under Molotov cocktail exposure

This study aims to characterize and model the thermal protective fabrics usually used in workwear under Molotov cocktail exposure. Physical properties of the fabrics were measured; and, thermal protective performances of the fabrics were evaluated under a fire exposure generated from the laboratory-simulated Molotov cocktail. The performance was calculated in terms of the amount of thermal energy transmitted through the fabrics; additionally, the time required to generate a second-degree burn on wearers’ bodies was predicted from the calculated transmitted thermal energy. For the characterization, the parameters that affected the protective performance were identified and discussed with regards to the theory of heat and mass transfer. The relationships between the properties of the fabric systems and the protective performances were statistically analyzed. The significant fabric properties affecting the performance were further employed in the empirical modeling techniques − Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) for predicting the protective performance. The Coefficient of Determination (R2) and Root Mean Square Error (RMSE) of the developed MLR and ANN models were also compared to identify the best-fit model for predicting the protective performance. This study found that thermal resistance and evaporative resistance are two significant properties (P-Values < 0.05) that negatively affect the transmitted thermal energy through the fabric systems. Also, R2 and RMSE values of ANN model were much higher (R2 = 0.94) and lower (RMSE = 37.42), respectively, than MLR model (R2 = 0.73; RMSE = 191.38); therefore, ANN is the best-fit model to predict the protective performance. In summary, this study could build an in-depth understanding of the parameters that can affect the protective performance of fabrics used in the workwear of high-risk sectors employees and would provide them better occupational health and safety.

Approach to solution of tank with hydrogen peroxide pressurization by its decomposition products

Aim. To find and confirm the possibility of hydrogen peroxide tank pressurization using high-temperature pressurization gas (~1100К) with a high percentage of steam (up to 70%) without its losses. Research methods. Mathematical modeling of pressurization system parameters with the theory of mass transfer and thermodynamic of variable mass bodies have been used. Results. The conducted research allowed us to find and confirm the possibility of using a new pressurization method with additional sources of heat and elaborate recommendations for its appliance during pressurization time. Scientific novelty. The main processes have been determined, which prevent implementation of the efficient high-temperature pressurization system of the tank with the hydrogen peroxide using peroxide decomposition products. The main obstacle is the volume condensation of vapor in the free volume of the tank when heat exchange processes with boundary surfaces take place. For the first time, by means of theoretical calculations, the expediency and rationality of using the additional sources of heat such as high-temperature combustion product of solid-fuel gas generator based on sodium azide have been proved. Using of this additional source for the first 30 seconds of engine operation has been proved. Practical value. Methodology of pressurization system parameters’ calculation was supplemented with discovered thermodynamic relation, which allowed us to calculate the amount of vapor and take some measures to eliminate the condensation. Results of the research allowed the designation of the pressurization system for the highly concentrated hydrogen peroxide tank with a high value of length to diameter relation with its high-temperature decomposition products.

Predicting Mass Transfer Extraction with Steam Flow, Applying Boundary-Layer Concepts

Theory and concepts of boundary layer mass transfer is applied to correlate experimental data on extraction of essential oils from vegetable leaves and stems, using steam. From these theory, concepts and experimental data with seven systems, two correlations are developed to predict the Sherwood number and mass transfer coefficient as function of Reynolds and Schmidt numbers. From these equations, the molar flux, the amount of solute extracted, and the yield of extraction is predicted. A steam of higher temperature normally improves the mass transfer and the yield. A method to estimate the enhancement for temperature increase is proposed. The correlations developed are applied to a case with industrial size that was no part of the data for correlation generation. Theory may be applied for industrial applications.

Принцип построения энергосберегающей сушильной установки с применением термоэлектричества

Most drying plants of small capacity for vegetables and fruits are convective without recirculation of the drying agent. Such dryers have a high energy consumption and cannot be attributed to energy-saving installations. (Research purpose) The research purpose is in developing a functional and technological scheme of an energy-efficient thermoelectric dryer that provides a reduction in energy costs during the drying process while maintaining high quality indicators of the finished product and increasing the drying efficiency. (Materials and methods) The methods of system analysis and synthesis of existing knowledge in the field of research on the development of energy-saving dryers, based on the provisions of the theory of drying, heat and mass transfer and thermoelectricity were used. (Results and discussion) The article presents the structural and functional-technological schemes of a convective condensation dryer with recirculation of the drying agent based on Peltier thermoelectric elements. The technological process and the principle of operation of a convective dryer of the condensation type with the use of a thermoelectric assembly operating in the heat pump mode were described. The article proposes a general method for calculating the heat and energy parameters of the dryer based on the heat balance equation. The thermal energy withdrawn by the hot circuit of the thermoelectric assembly, and directed to heating the cooled and drained air, exceeds the energy consumed from the electrical network. The uniform transverse blowing of the drying box with an air ensures uniform drying of the product. (Conclusions) When the drying box is cross-blown and the air flow is relatively fast, the moisture evaporation process is accelerated, the drying time is reduced and the drying quality is improved. It was revealed using preliminary technical and economic calculations that the proposed design provides a reduction in energy consumption compared to traditional dryers by up to 25 percent.

Recycling of municipal solid waste using solar energy

The article proposes a solar installation for thermal processing of municipal solid waste and presents a method of technical and economic analysis of systems for processing municipal solid waste based on solar energy. The object of the research is a solar installation for thermal processing of municipal solid waste. The analysis of the heat balance of the developed solar installation was compiled and carried out, and the energy requirement for thermal processing of municipal solid waste was determined. The work uses the methods of the theory of heat and mass transfer and body balances of heat power and solar installations. The created solar installation for anaerobic fermentation of solid waste to obtain landfill gas and bio fertilizers has been investigated. Balance methods of numerical and experimental studies of anaerobic fermentation of solid waste were used to analyze the results. A calculation has been made showing the energy efficiency of a solar installation for the processing of municipal solid waste using solar energy. Based on the research carried out, it was found that at an average heating temperature of 50-55 °C, 200-250 m3 of landfill gas was obtained from one ton of household waste.

A full-scale field experiment to study the hydrothermal behavior of the multilayer asphalt concrete pavement in cold regions

As one of the widely used pavement materials and structures, the multilayer asphalt concrete pavement (MACP) presents evident heat absorption and hydrothermal accumulation behaviors, which is prone to severe frost and thaw damages in cold regions. A full-scale field experiment was performed to reveal the hydrothermal process within the MACP in Inner Mongolia of China. Based on the continuous three years’ monitoring data, the freezing-thawing process, moisture features, and hydrothermal interactions of the MACP were analyzed. The results indicate that: (1) the MACP generates an important heat absorption and storage effect. A high heat flux accumulation zone forms at the central part of the MACP. Compared to the natural surface, the thawing freezing ratio at the bottom of the embankment enlarges 1.65 times armed with the MACP, meaning a dominant thawing process over a year cycle. (2) Under the influence of the thermal effect, moisture migration is considerably active within the MACP. The liquid water content of the MACP varies sharply with the decrease of the temperature. Then the cement stabilized base (CSB) and asphalt treated base (ATB) undergo the maximum and minimum liquid water contents, respectively. Furthermore, a core-shaped moisture accumulation area develops, coinciding with the features of the yearly distribution of the temperature. (3) The heat and mass transfer theory in the unsaturated porous medium was used to separate liquid water flux drove by the temperature gradient within the MACP. The temperature gradient driving effect mainly occurs in cold seasons. Under the impact of the temperature gradient, the ATB layer presents only downwards liquid water movement, while the CSB layer presents upwards and downwards liquid water movements.

Non-abrasive Finishing of Mating Surfaces of Machine Parts Using Mixed Techniques with Electromagnetic Fields Application

In various branches of mechanical engineering, faucets, valves, gate valves and other shut-off devices are manufactured and used. Their main purpose is to regulate the flow rate and direction of flows of liquid and gas media. Features of such products in the aerospace and petrochemical engineering are special strict requirements due to the specificity of their operation. These include, for example, high pressure, resistance to aggressive, fire-and explosive environments, leaks of which are unacceptable according to safety rules and environmental legislation. The design of such products, as a rule, assumes high requirements for accuracy and roughness, especially at the interface of parts, high strength in case of impact pulse effects of the fluids in them. To ensure the above characteristics, finishing abrasive treatment is most commonly used, which can result in the effect of impregnation of the surfaces of products, which will negatively affect the useful life and performance indicators of the mating surfaces. At the same time, it is obvious that mechanical finishing without any use of abrasives is extremely difficult and time-consuming. The authors of the article suggest elimination of the negative effect of impregnation by means of mixed machining techniques with the application of electromagnetic fields. Purpose. The purpose of the work is to develop a technology for non-abrasive finishing of machine parts by developing a model that allows selection or calculation of the production modes of gapless mating parts of locking devices applied in various industries. Methods. The method of the research is the use of the scientific basis of mixed machining techniques, the theory of mass transfer in electrical machining, the fundamental foundations of mechanical engineering technology, modern methods for studying characteristics at the final stages of machining, modern measuring tools, special technological equipment, as well as computer technologies. Results. As a result of the research, new technique and devices were developed. This made it possible to implement a non-abrasive finishing operation of the mating surfaces of parts made of metal materials, the processing of which by mechanical methods is difficult. Conclusion. As a result of the conducted research, it became possible to obtain high-quality high-resource gapless locking products and to reduce labor intensity of the finishing operation up to 5 times and preparation for the production up to 2 times.