Theoretical Foundations of Chemical Engineering最新文献

The influence of direct atomic–molecular mechanisms (considering the structure of the Gibbs potential distribution) and hydrodynamic mechanisms (with flows and waves) of energy transfer is analyzed, and their effect on the structure and dynamics of the impact flows of a freely falling drop is evaluated. The analysis of the processes is carried out taking into account the properties of complete solutions of the system of fundamental equations describing waves, ligaments, vortices, and flows. The results of visualization of mass transfer and the evolution of thin fibrous structures during the formation and collapse of the primary cavity and the subsequent rearrangement of flow patterns in neutral and chemically reacting media are presented. Possible applications are discussed.

The operation of a vacuum-pulse drying unit is divided into two stages. The first stage is pumping air out of the receiver. The second stage begins after gas starts flowing into the receiver from the vacuum chamber through the pipeline. The mass flow rate of the gas mixture depends on the pressure at the inlet and outlet of the pipeline. In the work, the load characteristics of the vacuum pump used in the unit are approximated using the spline method. The dependences of productivity and power on the rotor speed are non-monotonic. The purpose of the study is to substantiate the mathematical model of gas-dynamic processes in vacuum-pulse drying of food products. The operation of the liquid-ring vacuum pump ELRS-6 is considered. High rotor speed provides higher vacuum pump performance, while the expended power increases. An increase in the volume of the vacuum chamber leads to an increase in the duration of the second stage at an unchanged volume of the receiver, and the final pressure and mass of air in the operating chamber increase due to the increase in the total volume of the hydraulic system. An increase in the initial pressure in the receiver leads to a decrease in the pressure drop. Therefore, the air flow in the pipeline decreases and the pressure and mass of gas in the vacuum chamber decrease more slowly. An increase in the pipeline diameter leads to a decrease in hydraulic losses and an increase in the mass flow of air in the second stage. With increasing length of the pipeline, hydraulic losses increase and the mass flow of air decreases.

The wave mass transfer associated with the propagation of periodic capillary–gravity flows along the interface between inviscid stratified ocean and atmosphere is analyzed. The problem is considered in a two-dimensional formulation. The contacting fluids are assumed to be uniformly stratified. Each of the media is characterized by its own stratification scale. The wave mass transfer rates in both contacting media are studied, and expressions to describe the trajectories of individual liquid particles in the upper and lower liquids are obtained.

In the paper, a method for improving the thermodynamic efficiency of a jet engine intended for space exploration is considered. In the proposed engine design, the nozzle is equipped with a second contour. The outer contour is located coaxially above the main nozzle. An additional coolant, hydrogen, is fed to the input of the second contour. The use of the heat removed from the operating fluid of the main contour to heat the external coolant increases the thermal efficiency of the engine from 75.6 to 85%. Due to heat transfer from the hot gases of the internal contour and the special shape of the channel, the flow is accelerated and an increase in the engine thrust to 3882 N is achieved. Numerical modeling of the flow and heat transfer process in the nozzles of engines of classical and modified designs is performed. The characteristic cross-sectional shape of the engine nozzle allows the use of an axisymmetric analytical model. Based on the calculation results, the values of thermal efficiency, jet thrust, specific impulse, and increase in nozzle mass are compared.

In chemical and related industries, mixing bulk materials is often accompanied by an undesirable effect, segregation of the mixture, meaning its separation during processing and discharge [1, 2]. Segregation reduces homogeneity, increases mixing time, and raises energy consumption. It is most pronounced when the particles of the mixed materials differ in density and size. Segregation can also occur during discharge of the finished mixture, further reducing its uniformity. In many chemical processes, separation of the mixture is driven primarily by particle density and size differences. Conventional mixers perform adequately when the particles are similar in size, density, shape, and other characteristics. When these properties differ, however, segregation frequently occurs, leading to separation of the mixture. Effective mixing of such materials requires specialized equipment designed to suppress segregation [1, 2].

Traditional methods of treating open wounds are not always effective, as they require frequent and traumatic dressing changes, as well as the use of various medications, which can negatively affect the body. Current research is focused on developing new wound coverings that promote faster and more effective recovery of damaged tissues. The development of new fibrous materials based on polylactic acid and the diterpene alkaloid songorine, isolated from the above-ground part of the Aconitum barbatum plant, is proposed in this work. These materials are designed to serve as targeted delivery systems for effective healing of damaged skin surfaces. Scaffolds based on the aliphatic polymer were prepared by electrospinning. Two-stage (combined) surface treatment of the samples was carried out by low-temperature plasma treatment in a nitrogen flow for 5 min, followed by surface adsorption of songorine in the amount of 5 wt % onto the plasma-modified surface of the materials. The method of combined modification leads to the formation of nitrogen- and oxygen-containing bonds on the surface of polymer materials, as determined by X-ray photoelectron spectroscopy, which results in improved physicochemical and biological properties. Macrophage viability studies showed that all scaffolds were biocompatible: the number of living cells corresponded to the control level. Scanning electron microscopy revealed that surface treatment does not affect the morphology of the scaffold surface. It was found that songorine accelerates the degradation of the materials. Using UV detection, it was shown that the release of songorine from the surface of the samples follows a “burst release” type of release characteristic of antibacterial coated systems.

In a two-dimensional formulation, complete solutions of dispersion relations describing large-scale wave and fine-structure ligament components of periodic flows are analyzed. For an incompressible viscous uniformly stratified fluid, the method of calculating the Stokes drift with allowance for both wave and ligament components of periodic flows is considered.

The article provides a justification for the gel-forming composition for well water insulation based on sodium silicate, polyacrylamide (PAA), and chromium acetate, with increased strength characteristics due to the introduction of a dispersed additive, rice husk, which simultaneously exhibits viscoplastic and viscoelastic properties. Oscillation testing is used to determine the elastic modulus (G') and loss modulus (G"), the linear measurement range, and the quantitative determination of the viscoelastic and viscoplastic properties of the hydrogel, based on the interpretation of creep and recovery study results using the mechanical models of Maxwell, Kelvin–Voigt, and Burgers, which are successfully applied to the behavior of polymer systems. It is established that when approximating experimental measurements, one link of the Kelvin–Voigt model is not sufficient; therefore, the Burgers computational model is recommended, which corresponds to two relaxation times of a viscoelastic medium due to two types of crosslinking: ionic (from the bonding of the chromium ion with the polymer) and flocculation (from the flocculation of dispersed rice husk particles by polymer macromolecules). Filtration studies performed on a model of an ideal crack with different openings (from 0.01 to 0.1 cm) establish that the introduction of rice husk into the hydrogel composition increases its strength characteristics and resistance to mechanical destruction. In the case of filtration through a 0.1 cm slit, there is no noticeable difference in the rheological behavior of the hydrogel with and without rice husk, except for some strengthening of the gel during filtration at low shear rates. A mechanism responsible for the behavior of the hydrogel with this dispersed additive in cracks of various openings is proposed. The application of the developed hydrogel composition is promising in real fractured reservoirs through which water flows to the well and, as a consequence, causes flooding.

With the development of alternative energy sources, an important task is the design and improvement of hydrogen generators for fuel cells. A promising approach is the reaction of nanodispersed aluminum with water, which produces a large amount of hydrogen within a short time. The interaction of highly dispersed aluminum with water must be controlled to prevent sharp increases in pressure and temperature. For this purpose, we propose metered powder injection into water using a pulsed disperser powered by explosive magnetic energy. The advantage of pulsed powder injection is the fragmentation of particle agglomerates and the disruption of the oxide shell, which is also an important technological challenge. To ensure the reaction proceeds in an optimal mode, it is necessary to study the propagation of particles in water during pulsed injection. To estimate the time required for particle distribution in the reaction volume, we propose a mathematical model of dispersion of highly dispersed powder in a liquid using a pulsed (explosive) disperser. The model takes into account the specific features of this method of dispersion, including rapid expansion of explosive magnetic reaction products, collapse of the gas bubble containing particles, and diffusion-driven particle propagation in the volume. A parametric study of the model was performed. Experimental results are presented on pulsed dispersion of a nanodispersed model powder (aluminum oxide) into water. The calculated dependences and order of magnitude of the studied parameters agree with experimental observations. The identified regularities of particle propagation in liquid during pulsed injection can be further applied to calculating the technical parameters of hydrogen generation systems based on the reaction of nanodispersed aluminum with water.

The article discusses methodological approaches to the practical application of a vibrodynamic classifier for screening various abrasive materials, and sets and solves the problem of ensuring optimal tuning parameters of the electromechanical part of the vibroclassifier to obtain high-grade abrasive grains with an increased content of the main fraction and a specified shape of abrasive particles. The distribution of particles of the size-classified material along the perimeter of the vibrating deck was studied as a function of its parameters. It was shown that the yield of products depends on the ratio of fractions in the feed material.