Human Performance

The article presents the synthesis of carbon nanotubes (CNT), which are intended to obtain functional properties in polymer composites. One of these functional properties of polymer composites is electrical and thermal conductivity. CNTs synthesized using the microwave method differ in both geometric and morphological characteristics, as well as the presence of deposited iron particles on the surface of the CNT graphene layer. Microwave synthesis of CNT is carried out in a 700 W setup using different ratios of the graphite–ferrocene mixture (4 : 1 (10 s), 5 : 1 (10 s), 6 : 1 (10 s), and 4 : 1 (20 s)). The obtained CNT samples are characterized by Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction analysis. It is shown that as a result of combinations of ferrocene and graphite in various ratio (4 : 1 (10 s), 5 : 1 (10 s), 6 : 1 (10 s), and 4 : 1 (20 s)), different CNT morphologies are formed. This circumstance allows effective filling of polymers, including silicones, thereby creating functional composites. Analysis of electron microscopy data allows us to conclude that all of the synthesized CNTs have different geometric characteristics. The diameter of the CNTs can range from 30 to 60 nm and iron particles are present on the surface of the CNTs. At the same time, an increase in the specific surface area of the studied CNTs is observed. When microwaves are applied to a mixture consisting of ferrocene and graphite, the microwaves form local electric dipoles in the material, which is caused by structural defects in individual graphite layers. It is established that microwave synthesis is a fast method for obtaining CNT (synthesis time is approximately 10 s at a microwave radiation power of 700 W) and can be used for the targeted synthesis of CNT with different structures and morphologies, which are intended for modifying polymers and creating functional composites with a wide range of thermal and electrophysical properties.

At the present stage of development in heat-supply systems, there is a trend toward shifting from shell-and-tube structures to a plate design of heat exchangers. The advantages of the plate design are its compactness and efficiency. The major operational problem is fouling in the interplane channels, which decreases the thermal efficiency and increases the operational expenditures. The objective of this study is to demonstrate the effect of scale deposits and individual hydraulic conditions in each channel on the temperature regime of a plate heat exchanger. Since this problem in the theory of heat exchangers is insufficiently studied and involves important assumptions, the diagnosis of fouling in the channels is incorrect. The hydrodynamic regime in a plate heat exchanger is established by using the theory of resistance characteristics in hydraulic systems. The temperatures of the heating and heated heat-transfer fluids at the outlet from each heat-exchange channel are set on the basis of the mass-conservation law. This method makes it possible to use the results of hydrodynamic calculation on resistance characteristics to determine the temperature regime in a plate heat exchanger along the length of a package of plates, including with consideration of the effect of scale deposits. The proposed methods are validated by comparing with computer-aided modeling results by the Pearson’s and Student’s tests. The dependence between the final temperatures of a heat-transfer fluid at the outlet from the channels on its nonuniform flow distribution in the channels with fouling is revealed. The theory of resistance characteristics as applied to calculate the hydrodynamic regime in a plate heat exchanger along with the proposed thermal regime calculation, including with consideration of the factor of scaling, will make it possible to improve the precision of fouling diagnosis and decrease the operational losses. The performed studies confirm the effect of scale deposits in heat exchangers and individual hydraulic conditions in interplate channels on their temperature regime. The results of this research are of scientifical and practical interest for the study and development of intensified heat-exchange surfaces with the purpose of increasing the energy characteristics of heat exchangers, as well as in the field of diagnosing the regime parameters of water heating equipment in the period of its operation.

The reliability and efficiency component of third-generation heat- and power-supply networks is characterized by the application of heat-exchange devices, particularly of the plate type, the major function of which consists in heating a heat-transfer fluid for the needs of hot-water supply and heating systems. Some specific features inherent in the chemical composition of the heat-transfer fluid, however, can lead to fouling in heat exchangers in the form of scale layers on their heating surfaces. The process of scaling on the plates of heat exchangers is one of the key factors influencing the failure of equipment and the growth of the power consumption parameters at heat-distribution stations, worsening the quality of the provided services and increasing the financial expenditures in the sphere of heat supply. In the work, generalizing the known data, the sequence of calculating the transport expenditures on the operation of plate heat exchangers under different scaling conditions is put forward. In this case, the effect produced by the scale thickness on the total cost of pumping of 1 m3 of heat-transfer fluid is taken into account, providing the possibility of comparing the transport expenditures with the cost of scale removal from the heating surfaces (by an accepted cleaning method) depending on the thickness of the salt-forming layer and the cleaning period. The results of the study confirm the need for regular monitoring of the thickness of scale-forming layers in plate heat exchangers to decrease the operational expenditures on the pumping of a heat-transfer fluid.

Abstract—One of the most pressing problems in piston engine engineering is the toxicity of the exhaust gases from internal combustion engines. Recently, the possibilities of using catalytic converters directly in the engine combustion chamber have been considered. Such converters can be created by applying special coatings to the surfaces of components of the combustion chamber. The most promising method is microarc oxidation, which allows the formation of ceramic coatings with high adhesive strength on aluminum alloy parts. Many experimental studies have demonstrated that such coatings can reduce the amounts of some components of exhaust gases in the combustion chamber. Since theoretical justifications for the use of such coatings to reduce the toxicity of exhaust gases have not been developed, the purpose of this work was the theoretical justification, development, and verification of a mathematical model of neutralizing exhaust gas components by coating combustion chamber parts by the microarc oxidation method. The developed mathematical model of reducing the amount of individual exhaust gas components in the engine combustion chamber takes into account many factors: geometric parameters and performance characteristics of the engine, as well as coating properties and exhaust gas composition. Based on previously obtained experimental data on an RMZ-551i engine, the developed mathematical model was verified over a wide range of speeds (2000–6000 min–1) and throttle opening values (25–100%). Verification by CO showed that the mathematical model allows calculations to be carried out with a sufficiently high convergence, at the level of an order of magnitude, and that it can be used for a preliminary assessment of the influence of various factors on the amounts of toxic components in engine exhaust gases.

An algorithm has been developed for temperature control in the gas mixture at the outlet of the desorption column. The mathematical description of the control system based on the heat balance equation is given. The coefficients of the PID controller were determined. The transient process on a real object is described.

The issue of repairing and subsequent operation of imported piston compressors that run without lubrication is examined. At present, foreign manufacturing companies have ceased to provide servicing, major repairs, and supply of spare parts, tools, and accessories. Since it is quite challenging, and often practically impossible, to find a domestic equivalent for foreign materials or their production technology, components produced by repair and mechanical plants operate ten times less effectively and reduce the quality indicators of technological equipment. The current study is conducted to determine a method for increasing the lifespan of foreign products used in piston compressors operating without lubrication, focusing on the sleeve–piston-ring friction pair. It is proposed to replace the steel sleeve with a sleeve made of antifriction self-lubricating material, the hardness of which is lower than that of the material from which the piston ring is made. To test this hypothesis, experimental samples are manufactured from the following materials: AFGM, F4, F4K15M5, polyamide 6, and steel 45. The results of the tests confirm the feasibility of increasing the lifespan of the friction pair using the proposed method.

When substantiating the measures and technical means of emergency protection for fire and explosion hazard in the petrochemical and oil-refining industries, it is necessary to determine the explosion hazard indicators of technological units. These indicators are determined by the amount of vapor released into the environment during accidental spills. For the technological facilities of the petrochemical and oil-refining industries, the handling of large volumes of flammable liquids in a heated state in technological processes is typical. In the case of emergency releases of non-boiling heated liquids, the main source of vapor entering into the environment is the process of evaporation from the free surfaces of pools. The complexity of calculating the mass of evaporated substance from emergency spills of heated liquids is related to the non-stationarity of the vapor supply due to liquid cooling. The dominant factor that determines the dynamics of the temperature change of the heated liquid in the pool is the heat removal in the zone of contact between the liquid phase and the underlying solid layer. The choice of the model of heat exchange between the pool and the underlying layer can significantly affect the reliability of estimates of the evaporated mass from spills of heated liquids. In this work, a comparative analysis of the results of calculating the mass of evaporated liquid, obtained using analytical and numerical models for calculating the heat flow in the contact zone of the liquid phase and the solid underlying layer, is carried out.

The design of vacuum systems for technological installations poses a formidable challenge, necessitating the use of mathematical modeling and computational tools. The application of modeling programs of chemical-technology systems allows the significant reduction in design time, facilitates the analysis of more variants of arrangement of the elements of the system, and also allows analysis of the influence of the elements of the system on each other. This study aims to develop a methodology for coupled modeling of intricate chemical-technology systems operating under vacuum conditions and to employ it in the design of practical industrial processes. The subject of this investigation is the vacuum-generation system in an amine mixture separation unit. The system consists of two series-connected Rust-type vacuum pumps and a forevacuum stage—a liquid ring vacuum pump. The coupling of the properties of the technological object and the vacuum-generation system implies coordination of their main characteristics, which are the main parameters describing the operating conditions of these units as a whole. To determine the intermediate pressures and equipment sizing, a computational model of the Rust-type vacuum pump is meticulously developed within the Aspen HYSYS V12 software suite, leveraging custom modules. The computed inlet pressures are subsequently incorporated via a purpose-built external-control program. Following calculations based on the chosen inlet pressures, the appropriate main and ancillary equipment are selected, while the overall system performance is meticulously assessed depending on the inlet pressures. The proposed configuration of the vacuum system promises to eliminate the formation of a chemically contaminated condensate, reduce circulating water consumption by a significant factor of 11, and concurrently reduce CO2 emissions by an impressive 66%.

This work addresses the topical problem of improvement of the mathematical model for calculating the evaporation rate from the free surfaces of accidental spill pools to determine the explosibility indicators of technological units. A comparative analysis of the results of calculating the mass of evaporated liquid from the pool surface of heated benzene is carried out using a semi-empirical model and a computational fluid dynamics (CFD) model. The effect of wind velocity and pool length and depth on the mass of the evaporated liquid is analyzed. It is shown that for pools of liquids with high molecular weight and at low wind velocity (1 m/s), the semi-empirical model can result in significant overestimation (severalfold) of the values of the evaporated mass, since, unlike the CFD model, it does not take into account the buoyancy effects. The buoyancy effects are expressed in the fact that the vertical density gradient that occurs above the pool surface contributes to the suppression of turbulence (stable density stratification), which, in turn, prevents the removal of vapors from the interface, leading, as a result, to a decrease in the intensity of evaporation. It is shown that the role of buoyancy effects is higher when the wind velocity is lower, the initial thickness of the pool is larger, and the horizontal pool size is larger. It is shown that the semi-empirical model demonstrates a weaker dependence of the mass of the evaporated liquid on the horizontal dimensions of the pool compared to the CFD model, since it does not take into account the effects of buoyancy, which increase with an increase in the dimensions of the pool.

At present, automatic control systems are mainly developed by linear methods. This is due to the existence of a consistent theory of linear analytical methods, which has been developed over many decades and has its own mathematical apparatus and software. The analysis of accuracy, stability, and controllability and the further synthesis of linear systems are performed surprisingly simply and clearly. At the same time, linearization involves cumbersome mathematical transformations, which may lead to difficult-to-interpret results. Moreover, linearization is inapplicable to the cases of strong impacts, nonstationary systems, and significant nonlinearities. The development of the general theory of numerical experiment and, simultaneously, the hardware and software of computers allows one to analyze systems without linearization because the same information, also in a more reliable form, can be obtained directly by the numerical study of systems. And some parameters, e.g., accuracy, can be obtained analytically from the same differential equations. In this article, by the example of a typical problem, it was shown how accuracy, stability, and controllability can be analyzed using the initial differential equations without resorting to analytical methods.

The article considers the kinetics of the process of monomolecular isothermal adsorption of drilling reagents: of the raw material base (sulfite lignosulfonate (LST) and neutral-sulfite lignosulfonate (N‑LST)); and of a form based on neutral lignosulfonate modified by polyvalent cations (ferrochromolignosulfonate (FCLC)) and by polyvalent cations and phosphonic groups of ethidronic acid (Ferrochromolignosulfonate (FCLC-2M)). The study is based on the kinetic concepts of the adsorption process, which determine the rates of adsorption and desorption in equilibrium conditions. Their main adsorption characteristics are calculated. The values of the average residence time of the adatoms (adsorbed atom) of the studied reagents at the liquid–solid boundary are determined. According to the main Langmuir equation, the dependences of the number of adatoms in the saturated layer of each regent are obtained. The empirical dependences and values of adsorption rates for the “working” concentration zone (5.1 × 10—5–76 × 10–5 mol/L) of these reagents at a constant temperature of 298 K are obtained. It is revealed that the adsorption equilibrium constant in the Langmuir equation Kl carries information about the rate of the adsorption process and knowing its value and its relationship with the filling density of the saturated layer at a certain concentration, it is possible to obtain the value of the rate of adsorption of the reagent. As a result, it is revealed that the rate of adsorption of sulfite lignosulfonate LST is almost 125 times, and the rate of adsorption of the modified form based on neutral lignosulfonate by polyvalent cations and phosphonic groups of ethidronic acid (ferrochromolignosulfonate FCLC-2M), more than 20 times higher than the rate of adsorption of N-LST at the maximum “working concentration.” The analytical dependences of the adsorption/desorption rates on the adsorption/desorption coefficients are graphically constructed. The corresponding coefficients are numerically obtained. It is noteworthy that the adsorption coefficient exceeds the desorption coefficient at equal speeds. It is revealed that the adsorption on a solid surface (clay) of the studied lignosulfonate systems in the “liquid–solid” system is physical.

This study investigates the electro-spark initiation of a chemical reaction in a porous mechanochemically activated mixture of aluminum powder and copper oxide. The conditions for the formation and parameters of the electrical discharge are described. Based on the measurement results and a number of assumptions, an estimate is given for the volume of plasma penetration into the pores of the mixture. Experiments are conducted to initiate combustion in semi-enclosed volumes with a mass of up to 1 g to provide indirect evidence of the completeness of the chemical reaction. Combustion occurs with the formation of a flame in open space, and its dynamics over time are presented as a result of the parameters of the electrical discharge. The experimental results are approximated by appropriate functions, representing the dependences of the ignition delay time on the energy density of the electrical discharge and the flame formation rate of the mixture on the discharge energy. From the obtained dependences, the critical values of the energy parameters of the electro-spark discharge for stable ignition of the thermite mixture are determined.

Experimental studies of the dynamic sorption of model mixtures containing petroleum products are carried out. Dried and calcined ash-and-slag waste accumulated by the method of hydraulic ash removal at the ash dump of Novocherkassk State District Power Plant (Novocherkassk, Rostov Region, Russia) are studied as a sorbent. The weight of the calcined sorbent for each model solution is fixed and amounts to 5.0 g. The model solutions are passed through a column filled with calcined sorbent. At the first stage, experimental studies are conducted to optimize the filtrate flow rate in the range from 0.05 to 2.5 L/min with a step of 0.05 L/min. Model aqueous solutions with a hydrogen index of pH 7.5, containing 100 mg/L of petroleum products, are passed through a column containing 5 g of calcined sorbent. The optimal filtrate flow rate is 0.1 L/min with a maximum efficiency of extraction of petroleum products from the solution of 84%. At the second stage, the kinetic dependences of the sorption capacity and concentration of petroleum products in the filtrate are constructed. For this purpose, experimental studies are conducted on the saturation of the sorbent with petroleum products by means of passing a model aqueous solution containing 10 000 mg/L in portions of 0.05 L through a column filled with calcined sorbent in the amount of 5 g, with the filtrate collection rate of 0.1 L/min. The maximum value of sorption capacity was 560 mg/g with an extraction efficiency of petroleum products from the solution of 85%. Based on the analysis of the results of experimental studies, an approach to the mathematical description of the kinetics of the sorption of petroleum products is proposed. The calculation of the concentration of petroleum products in the filtrate is divided into two stages. At the first stage, the increase in the concentration of petroleum products in the filtrate occurs when the sorbent is saturated with petroleum products at less than the maximum value of the sorption capacity; the second stage occurs after the maximum value of the sorption capacity is reached. Kinetic equations are given for calculating the sorption capacity and concentration of petroleum products in the filtrate. Good qualitative agreement between the experimental and calculated data is obtained.

The problem of blocking technogenic fractures with a suspension mixture is relevant in order to prevent additional water inflow to producing wells. The aim of the work is to evaluate the effect of colmatation of a fracture by polymer-dispersed compositions using a mathematical model of transport of a suspension through a fracture. It is assumed that the suspension particles are larger than the size of the pore channels and do not penetrate into the reservoir. To solve the problem, a system of continuum mechanics equations is used. The leading edge of the suspension slug is a contact discontinuity. It is determined that at the moment of the approach of this discontinuity to the end of the fracture, a reflected wave of the volume fraction of particles is formed, which moves towards the flow and characterizes the blocking of the fracture. At the same time, due to the need to maintain the same flow rate and reduction of the size of the fracture, there is a sharp increase in the downhole pressure, which does not allow the fracture to be completely blocked. The maximum blocked fracture size is determined. The obtained estimates are compared with field data.

The problem statement for optimizing the design parameters and operating mode of mechanical mixing devices of vertical capacitive devices is presented, the optimality criterion for the solution of which is the total length of the velocity vector of the mixed medium. A mathematical model is developed of the mechanical mixing process using the Reynolds-averaged Navier–Stokes equations closed by the turbulence equations. The adequacy of the model is confirmed by experimental studies. A method for optimizing the design parameters and operating mode of mechanical mixing devices is proposed, which provides for the justification of the selection of the selected values of the design parameters and operating mode. The methodology is implemented in a problem-oriented system for optimizing the design parameters and operating mode of mechanical mixing devices, implemented in the design and engineering department of PAO Pigment (Tambov).