Stationary Mode Of Operation Research Articles

The characteristics of heat exchanger for local utilization of wastewater heat under different operating conditions

RELEVANCE. The authors research the local utilization of wastewater heat (in close proximity to the place of their formation) based on a heat exchanger. To select rational characteristics of the heat exchanger and correctly assess the potential energy effect, it is necessary to take into account the influence of the operating conditions of the device (duration of individual use of the shower, mass flow of heated and heating water, temperature of heated water at the inlet to the heat exchanger, temperature of the flow at the moment the device is turned on).THE PURPOSE. The purpose of the work is to research the dependence of the efficiency of wastewater heat utilization on the operating conditions of the heat exchanger and to identify the parameters that have the greatest impact on the effect of energy-saving measures.METHODS. Based on a verified mathematical model of the thermal operation of a recovery heat exchanger, the temperature distribution inside the flows of the heated and heating water in time is calculated (from the moment of switching on until reaching a stationary operating mode). Based on the data obtained (the temperature of the heated water at the outlet of the heat exchanger at each point in time), the absolute and relative heat savings are determined under various operating conditions.RESULTS. The influence of the non-stationary phase of the heat exchanger operation on its energy efficiency is considered. For a specific heat exchanger configuration, the time required for the device to reach a steady state of thermal operation is determined. It was revealed that the greatest influence on the relative and absolute savings of thermal energy is exerted by such operating conditions as mass flow and temperature of heated water at the entrance to the heat exchanger. The temperature of the flow at the initial moment of time has the least influence on the energy effect.CONCLUSION. The operating conditions that have the greatest impact on the effect of local wastewater heat recovery are determined. The need to take these conditions into account when designing a heat exchanger and choosing its optimal parameters has been confirmed.

An analysis of the “Fast” noise measurements of the dynamic VVER processes

Studies of maneuverable modes of VVER to confirm the possibility of participation of nuclear power plants in the mode of daily carrying capacity have been conducted for quite a long time. Tests at various nuclear power plants with VVER-1000 (Zaporizhzhia NPP in 1998, Khmelnitsky NPP in 2005, Tianwan NPP in 2007) have shown the practical possibility of NPP participation in the daily schedule of carrying capacity, however, the commissioning of nuclear power plants with VVER-1200 requires similar work on all new units with VVER-1200: NVAES-2, LNPP-2 Belarusian NPP. The article presents some aspects of the use of noise control methods for analyzing the condition of equipment and the core. Since the emergence of the technology of noise analysis of signals from VVER reactor installations, researchers have formulated several criteria for obtaining results of appropriate quality. The fundamental requirement for conducting noise experiments was the registration of data in stationary modes of operation of power units, since any non-stationarity made significant changes in spectral estimates, which ultimately complicated the work and “distorted” the results obtained. This requirement was included in the operating instructions of various diagnostic systems using noise signal analysis methods (the SUS system, manufactured by Siemens). For a long period of time, the current situation suited both developers of various diagnostic systems and NPP personnel operating them at power units. On the one hand, this was due to the imperfection of the technical means used (low speed of analog-to-digital converters, limited storage capacity, bulky equipment, etc.), on the other hand, the use of domestic NPP power units only in the base load mode without tracking daily power fluctuations in the power system. The standard archives of the upper block level system, the in-reactor control system and additionally produced multi-channel “fast” measurements with a frequency of 1 kHz for the analysis of maneuverable mode 95-55-95% of the VVER-1200 reactor plant were analyzed. Global disturbances of the core have been detected after one step of the regulatory body of the control and protection system, which attenuates within one second if the next step of the control and protection system has not occurred during this time. Such fast neutron processes can be controlled only by neutron-noise measurements with an upper frequency of at least 20 Hz.

КОМУТАЦІЙНИЙ СТРУМ ПЕРВИННОЇ ОБМОТКИ ТРАНСФОРМАТОРА ПРИ ВАРІАЦІЯХ СТРУМУ ЙОГО ХОЛОСТОГО ХОДУ

Transformers are an indispensable component of various types of electrical circuits. Various restrictions are imposed on the transformer switching operation, which are caused by the functional purpose of the systems, their configuration, parameters and characteristics of existing or available switching components or devices and associated transient processes. When the power transformer is switched on asynchronously, current surges in its primary winding, including in modes close to the min-imum load, may exceed its nominal current by several times. Such processes are undesirable from the point of view of energy efficiency, electromagnetic compatibility, transformer reliability and the functioning of protection systems. Proper analysis of electromagnetic processes was performed by numerical calculation methods followed by computer modeling using the MATLAB/Simulink software package. The purpose of the study is to highlight the extreme nature of switching current surges of the primary transformer and their dependence on the relative value of the no-load current of the winding. This current, in turn, depends on the slope of the main functional segment of the magnetization curve of the transformer core corresponding to its stationary mode of operation. The research shows that the increase in the idle speed of the transformer causes a directly proportional decrease in the switching current surges of the primary winding of the transformer. At the same time, the difference between the amplitude values of adjacent semi-periodic current surges decreases. It is noted that an increase in the value of the transformer's no-load current is often aimed at stabilizing the burning of the alternating currentarc in electric welding installations. They are characterized by a repeated short-term mode of switching, and therefore the determination of the mag-nitude of switching current surges is relevant here

Model of the turboprop engine reduction gear tooth harmonic spectral component

The width of spectral components in rotary machines is determined by the frequency modulation of the carrier from the rotor speed deviation in the stationary operation mode. It was shown that, for the tooth spectral component, it is not enough to take into account this factor only. The analysis of publications and the studies performed show that it is also determined by the effect of many other factors: process-related ones (errors in manufacturing and assembly of gear wheels), operation mode parameters (rpm, temperature, transmitted load); design-related factors (flexibility of drive parts; modification of the tooth face), as well as uneven wear of tooth flanks. Using the planetary gearbox of a turboprop engine as an example, the structure of the tooth spectral component width in function of the analyzed influencing factors was considered. Based on the vibration statistics for eighteen gearboxes in overhauled engines, the choice of a ratio for the spectral component width of a frequency modulated process was justified. This choice showed readings closest to the corresponding experimental data. For the vibration of ten gearboxes with different degrees of tooth flank wear, the corresponding dependence of the width on the wear is presented. A mathematical model for the tooth spectral component width in overhauled and newly manufactured gearboxes as the product of the constant coefficient with the deviation dispersion sum from the considered factors was proposed. The same dependence was also given for gearboxes with wear when adding the dispersion from wear to the dispersion sum. It was demonstrated that, for the presented case of the maximum wear, its fraction in the total width was about 50%, whereas the fraction of the frequency modulation from the operating system of adjusting relative rotor speed constancy in the stationary engine operation mode was equal to half of all the other factors.

Calculation of the parameters and characteristics of a rotating lunar jet penetrator

The purpose of the work is to determine the parameters of the internal ballistics of a solid fuel jet engine mounted on a jet penetrator entering the ground at a high rotation speed around its own axis. Research methods: to determine the pressure in the chamber of a rotating engine, the known equations for the balance of gas inflow and consumption are usually used, as in the case of a non-rotating solid fuel jet engine. The difference between the internal ballistics of a rotating solid fuel jet engine is that the effect of rotation on the operating process is taken into account by the coefficient of gas flow from the chamber of the rotating engine; a change in the rate of erosive combustion of solid fuel during rotation of a solid fuel jet engine; heat loss coefficient. Results: it was found that the parameters of the internal ballistics of rotating jet engines of solid fuel are mainly influenced by the coefficient of gas flow from the chamber of the rotating engine; effect of erosive combustion of solid fuel and change in heat loss coefficient. The main calculated dependencies for determining the pressure in the combustion chamber of a rotating solid fuel engine are presented for periods when the pressure reaches a stationary mode of operation of the engine, operation of the engine in a stationary mode and during the period of free flow of gases from the chamber of a solid fuel jet engine. A method for selecting the linear and angular dimensions of a rotating engine nozzle is presented. An estimate of the thrust force for a single nozzle rotating solid fuel jet engine is given. It has been established that the magnitude of the thrust force of rotating engines (under other identical conditions in the combustion chamber) is 1.1–1.36 times less than that of non-rotating solid fuel jet engines. The experiments carried out showed a decrease in the degree of swirl of the gas flow of rotating solid fuel engines with an increase in the number of fuel pellets in the engine charge. Conclusion: the results presented in the article can be useful for scientists, graduate students and engineers involved in the creation and operation of aviation and rocket and space technology, and can also be useful for students of technical universities studying in relevant specialties.

Wireless charging technologies for electric vehicles: Inductive, capacitive, and magnetic gear

AbstractWireless charging technologies have emerged as a promising solution for electric vehicle (EV) charging, offering convenience and automation. This paper provides a comprehensive review of the three key wireless charging technologies: inductive, capacitive, and magnetic gear. For inductive and capacitive technologies, the working principle, architectures, topologies, advantages, and challenges are discussed and analyzed considering both stationary and dynamic modes of operation. In addition, the paper introduces and analyzes the concept of mixed wireless power transfer, which combines inductive and capacitive charging systems. Additionally, the study explores the magnetic gear wireless power transfer technology, which leverages the interaction between synchronous permanent magnets to transmit power wirelessly. Various research and development efforts related to these technologies are reviewed considering academia, research labs and industry. A comparative analysis among different technologies is presented, considering key performance metrics such as power transfer, efficiency, cost, and operating frequency was presented. This review paper serves as a comprehensive resource for researchers, engineers, and industry professionals interested in wireless charging technologies for EV charging. It highlights the advancements, trade‐offs, and potential synergies among inductive, capacitive, and magnetic gear systems, paving the way for the widespread adoption of wireless charging and the development of self‐charging and self‐driving EVs.

Methodology for calculating hydrogenerators in strength problemsMethodology for Calculating Hydrogenerators in Strength Problems

In the presented scientific work, the basic design versions of the thrust bearings of Hydrogenerators are considered. The main causes of emergencies in the thrust bearing unit of a high-power Hydrogenerator are considered. The main requirements for the operation of thrust bearings are submitted. Cause-and-effect relationships of emerging and development of defects are established. Existing methods for calculating the stressed state of a thrust bearing in the classical formulation for a stationary mode of operation are considered. The main features of the operation of the thrust bearing unit are investigated in relation to the features of the sliding bearings. The calculation of the elastic chambers of the hydraulic thrust bearing in a three-dimensional formulation is carried out, taking into account the physical properties of the oil, the material of the chambers and distribution of the acting loads. It is shown that the applied designs of Join Stock Company “Ukrainian Energy Machines” can be used in high-power Hydrogenerators.

ENERGY- AND RESOURCE-SAVING PROCESSES INVOLVING THE POLYMER PHASE

The paper deals with the processes of application and production of various polymer materials. By coating the surface of mineral fertilizer granules with hydrophobic polymer films, fertilizers with controlled release of nutrient components were obtained. Such fertilizers can prevent the leaching of nutrients, prevent the negative impact on the environment and reduce fertilizer consumption. Methods for calculating the particle distribution function by the degree of coating characterizing the uniformity of coating on fluidized bed particles for stationary and non-stationary modes of operation of the apparatus are considered. The process of applying a thick composite coating to the surface of urea granules in a pan granulator was also investigated. A simple method for calculating the size distribution of the obtained granules with a composite shell is proposed. The actual problem of developing a method for predicting the kinetics of nutrient release from polymer-coated fertilizer granules based on a fairly simple mathematical model of the process has been solved. Studies of the combined polymerization and drying process in the synthesis of polyacrylamide and sodium methacrylate copolymer with methacrylic acid amide have shown that its use at the final stage of obtaining water-soluble acrylic polymers is very effective. This technique allows to reduce the total time of the technological cycle. The process of obtaining polyethylene powder by the method of elastic-deformation grinding of polymer gel and a two-stage process of solvent removal from polymer powder with the return of the solvent to the technological cycle has been developed. The rational technological parameters of the electrodialysis process of contaminated steam condensate of mineral fertilizers plant have been identified, which allows to obtain a more concentrated salt solution, which is used as a secondary raw material, as well as a desalinated solution used as process water. For citation: Lipin A.G., Lipin A.A. Energy- and resource-saving processes involving the polymer phase. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 203-213. DOI: 10.6060/ivkkt.20236607. 6836j.

Разработка метода исследования режимной надежности электроэнергетических систем

The article considers the urgent choice of a solution to the problem of reliable operation of power plants in the maneuvering modes. The performance reliability of power units is assessed. There are listed actual methods of studying the reliability of power plants, which are used in the practice of operation and design of power plants, in particular the electrical part in a statistical state. There is proposed a structural-functional method of studying the reliability of power plants, which allows to analyze the cause-and-effect relationships of the structural diagram elements in the stationary and transient modes of operation and obtain a synthesizing assessment of the final result of the power plant operation, taking into account the factors affecting the mode change. The scheme of directed graphs is illustrated: serial and parallel connection of elements, with direct and reverse stochastic connections. Formulas are given for calculating the availability factor (operability of an individual element or a functional circuit), as well as the inoperability factor due to the frequency of failures and remedial repairs. A case of practical application of the structural-functional method studying the reliability of power plants is considered. The elements of the block diagram of the power unit, turbine plant, electrical connections are listed. An algorithm for calculating the reliability of operation of a 250-300 MW power unit in the modes of start-up, shutdown, load control, stationary and emergency shutdown is considered. The logical sequence of operations of the technological process of the power unit is given. It is noted that the calculations were made on a personal computer in an interactive mode, labor costs amounted to about eight hours for an engineer of average qualification. According to the calculations performed, the conclusions were drawn for the power plant operating in the shunting mode as a whole: frequent starts/stops have a negative impact on the performance of power units, therefore, there is recommended a load mode within the allowable limits of power change.

Analysis of the thermal state of the electromagnetic mill inductor with oil cooling in stationary operation modes

Introduction. An electromagnetic mill (EMM) for the technological processing of various substances, which is based on the stator of a three-phase induction motor, is being studied. The stator winding has an increased current density, so the mill is provided with a system of forced cooling with transformer oil. Problem. Currently, there are no works on the thermal state calculation of the EMM with the given design and oil cooling. Therefore, the study of such EMMs thermal state is relevant, as it will contribute to increasing the reliability and efficiency of their work. Goal. Formation of a mathematical model of the thermal state of the electromagnetic mill inductor and the analysis of its heating in stationary modes of operation with cooling by transformer oil. Methodology. The problem of calculating the thermal state, namely the temperature distribution in the main parts of the electromagnetic mill, is solved by the equivalent thermal resistance circuit method. The design of the EMM is provided in a sufficiently complete volume, and on this basis, a corresponding equivalent thermal replacement circuit is formed, which is supplemented by an equivalent hydraulic circuit of oil passageways. An explanation is provided for the composition and solution of the equations algebraic system that describes the distribution of temperatures by the constituent elements of the EMM. Results. The thermal calculation results of the electromagnetic mill showed that the maximum heating temperature is much lower than the allowable one for the selected insulation class. According to the hydraulic scheme, the necessary oil consumption, its average speed and the corresponding pressure at the inlet of the intake pipe are determined, which are at an acceptable level. It is noted that the rather moderate temperature state of the inductor and the hydraulic parameters of the oil path are facilitated by such innovations in the design of the EMM as the loop double layer short chorded winding and axial ventilation channels in the stator core. Originality. Now EMM thermal equivalent circuits with air cooling only have been presented. Therefore, the developed thermal circuit of the oil-cooled inductor is new and makes it possible to evaluate the operating modes of the EMM. Practical value. The proposed technical solutions can be recommended for practical implementation in other EMMs. Taking into account the identified reserves of the EMM temperature state, a forecast was made regarding the transition from its oil cooling to air cooling. But the use of air cooling requires a change in the design of the EMM.

Experimental Investigation On Machining Performance of Ti6Al4V On Electro Discharge Machining Using Stationary and Rotary Electrode

Titanium alloys are commonly used in different industries due to its high strength and less in weight. Even though the machinability of titanium alloys is very less, due to its high strength, it becomes more useful in aerospace and medical industries. In this paper, the performance of stationary and rotary copper electrodes on machining of Titanium alloy Ti-6Al-4V with Electro Discharge Machining (EDM) have been studied. Material removal rate (MRR), tool ware rate (TWR) and surface roughness (SR) were analyzed with three controllable input parameters such as pulse on time (Ton), Peak Current (Ip) and Gap Voltage (V). The design of experiment is chosen for the experimentation as the Box-Behnken response surface design method. The results are analyzed using grey relational analysis (GRA) coupled with firefly algorithm. In both the case of stationary and rotary electrode, it was revealed that gap voltage is significant for overall grey relational grade. The machining performance of Titanium alloy Ti-6Al-4V in the case of rotary mode of electrode is quite better as compared to the stationary mode of operation.

Вплив конструктивних параметрів термоплати на гістерезис за тепловим навантаженням

The contact heat exchangers designed to remove heat from the cooled devices are used in mechanically pumped two-phase loops of thermal management systems for ground and space applications, a thermoplate (heat sink). After the device is turned on, it may overheat abnormally during the process of reaching a stationary operating mode. Overheating is associated with the phenomenon of thermal load hysteresis during the onset of boiling, the transition from single-phase convection to developed boiling in the evaporator of a heat sink material. This work studied the influence of the construction parameters of thermoplate on the hysteresis phenomenon at the integral level. For this purpose, a thermoplate testing methodology was implemented, which includes experiments with slow (quasi-stationary) and quick heating after turning on the device immediately at full power. Overheating of the device is possible during both "slow" and "quick" heating. The maximum overheating in the experiments performed was ~18 K. Such overheating can pose a danger to the reliability of the device. The study was performed with ammonia as a coolant on 5 models of thermoplate that differ in evaporator channel roughness, length, material, longitudinal thermal conductivity, the heat capacity of the structure, etc. The danger of overheating the device is also determined by the maximum thermal load at which the device is operated. The following conclusions were made: the greatest influence on the hysteresis parameters is the value of the evaporator channel surface roughness. Increasing the roughness reduces the risk of overheating the device, and changes the nature of the "boiling curves" in the thermoplate; an increase in the length and longitudinal thermal conductivity has a favorable effect on reducing the risk of overheating; the evaporator surface is made of aluminum alloy instead of stainless steel, which makes hysteresis impossible; in the case of rapid heating of the thermoplate, the maximum heat flux at steady-state has an ambiguous effect: with its increase, overheating due to hysteresis first increases, and in the case of further increase, it decreases and may disappear altogether. A significant increase in the maximum heat flux compared to the heat flux at the beginning of boiling reduces the danger of hysteresis affecting the overheating of the device. The results of this work provide recommendations on how to avoid the dangerous overheating of the device due to the hysteresis phenomenon.

Mathematical modeling of the rotor dynamics of a turbomachine on gas foil bearings subjected to vibration

BACKGROUND: The use of gas foil bearings is a promising development in the field of turbomachinery due to their economy, autonomous operation capability, and durability. However, gas foil bearings have lower load capacities than other types of bearings. However, turbomachines are complicated, dynamic systems that must meet high standards of safety, sustainability, and durability against external mechanical factors like vibration, shock, etc.
 AIM: Development of a mathematical model of rotor dynamics to predict the displacement of the rotor in foil bearings for maintaining separation between the rotor and the housing while being subjected to vibration.
 METHODS: A mathematical model of the dynamics of a stiff rotor on gas foil bearings was built and analyzed, taking into account the flexibility of the bearing bushing supports and the housing of the turbomachine. Stationary and transient modes of operation, including the transient modes combined with random vibration, are simulated. The system of ordinary derivatives equations describing the mathematical model was solved by the Rado IIA method. Random vibration was modeled using digital Fourier transformation. The modeling results were analyzed by discrete Fourier transformation and short-time Fourier transformation.
 RESULTS AND CONCLUSIONS: Rotor movement trajectories were obtained and the results were compared with authors previous experimental data. Upper bound of maximal displacements was obtained. The maximum values of rotor displacement can be used to set the optimal values of blade tip gaps.

Application of methods for modeling hydraulic and non-isothermal steady states of gas transmission systems

In the article, for the first time, an attempt was made to justify the effectiveness of the application of new generalized methods of the theory of hydraulic circuits for modeling stationary modes of operation of gas transmission systems of complex structure and configuration. A classification of the main models of a steady gas flow is given for individual elements of the system, including traditional ones, those implicitly specified in terms of flow rate and dependent on the pressure of the working medium. Generalized flow distribution models are proposed that take into account all these cases. Conditions for the applicability of generalized methods that ensure the existence and uniqueness of the solution to the flow distribution problem are considered. The characteristics of these methods and final algorithms are given, which provide confident convergence and require less computational costs compared to existing methods. Numerical examples illustrating such possibilities are given.

РОЗРАХУНОК ХАРАКТЕРИСТИК СИСТЕМ МАСОВОГО ОБСЛУГОВУВАННЯ ІЗ ЗАСТОСУВАННЯМ МЕТОДУ ЕРЛАНГА І ЗАКОНІВ ЗБЕРЕЖЕННЯ

Any human activity (economic, entrepreneurial, commercial) is associated with the performance of many operations at the stages of movement of raw materials, goods, products from the supply sector to the sphere of production and consumption. Such operations are transportation, storage, processing, sales, etc. These types of activities are characterized by the massive receipt of products, goods, money, and clients at random times; their sequential servicing is carried out by corresponding operations, the execution time of which, as a rule, is also random. All this leads to inequalities in work, creates idle time, underload and overload in operations. Therefore, the tasks arise of analyzing existing options for performing a certain set of operations, identifying bottlenecks and reserves for developing and making management decisions to improve the operating efficiency of any organization. Such problems are successfully solved using queuing theory. The basis for making management decisions are parameters that characterize different aspects of the operation of both the system as a whole and its individual elements. To describe individual parts of the system, the distribution of random variables and their numerical properties are traditionally used. The main characteristics of the action and state of the QS are the average number of requests in the queue or system, the average waiting time for service and others, as well as the value of some probabilities (the probability of service denial, the probability that there are at least a certain number of requirements in the system, the probability that the system is free from maintenance, etc.).The article describes some methods and techniques for studying Markov systems (the processes of which have no history), which turn out to be applicable to more general systems. A Markov queuing system with a restriction on the largest number of requirements in the system is considered. The probabilities of state transitions for closed and open-loop systems are described and calculated using Erlang methods and using the laws of conservation of system probabilities and the Laplace transform. Calculations of queue safety under stationary operating modes of queuing systems are demonstrated.

Thermal and Stress State of the Intermediate Pressure Rotor of the Power Unit № 11 of Burshtyn TPP

Thermal power plants produce about a third of the total electricity generation in the United Energy System of Ukraine and provide maneuvering capacity. The work presents the results of research aimed at analyzing the reliability of thermal power equipment. The thermal and stress state of the medium-pressure rotor of power unit No. 11 of the Burshtyn TPP was investigated. When conducting calculation experiments, both the design geometry and samples of the rotor metal in the places where cracks appeared were taken into account. The temperature distribution and their gradients were calculated to solve the problem of the stress-strain state. The highest values ​​of stress intensity amplitudes are observed in the zone of end seals, which is explained by the more significant influence of the accumulation of low-cycle fatigue as a mechanism of destruction, compared to the exhaustion of the long-term strength of the metal in the stationary mode of operation.

PRINCIPLES OF OPTIMIZING CONTROL OF GAS TRANSPORTATION SYSTEMS UNDER CONDITIONS OF THEIR UNDERLOAD

The work is devoted to establishing the regularities of the flow of technological processes in gas transportation systems to optimize the operational management of operating modes under the condition of their incomplete loading. On the basis of the study of the stationary modes of operation of the gas transportation system with changes in the volume of gas pumping, the principle of building a mathematical model based on the superposition of the characteristics of linear sections and compressor stations is proposed, which makes it possible to estimate the throughput of the system, parameters of the operating mode, and energy consumption for gas transportation. The methods of building a system of integral influence coefficients for gas transportation systems in order to evaluate the parameters of its operation in stationary modes of operation are presented. Each change in the technological parameters of the operating mode at the entrance of the gas transport system will necessarily cause a reaction of the system, which will manifest itself in a change of the corresponding parameters at its exit. It is obvious that the input and output parameters of the system are interconnected by a complex system of equations, the implementation of which requires certain time costs and the collection of additional information about the technical and hydro-gas-dynamic conditions of the system at each moment of time. In the conditions of incomplete loading of the gas transportation system, which involves frequent changes in its operation modes, the implementation of the task is not always possible. It is proposed to create a system of integral influence coefficients that characterize the ratio of input and output information in various stationary modes and to formally present it in a matrix form. On the basis of the research results, the principle of optimizing the operation modes of the gas transportation system under conditions of partial loading according to the criterion of minimum energy consumption for gas transportation at the maximum level of gas supply reliability is proposed.

On the Theory of Unsteady-State Operation of Bulk Continuous Crystallization

Motivated by an important application in the chemical and pharmaceutical industries, we consider the non-stationary growth of a polydisperse ensemble of crystals in a continuous crystallizer. The mathematical model includes the effects of crystal nucleation and growth, fines dissolution, mass influx and withdrawal of product crystals. The steady- and unsteady-state solutions of kinetic and balance equations are analytically derived. The steady-state solution is found in an explicit form and describes the stationary operation mode maintained by the aforementioned effects. An approximate unsteady-state solution is found in a parametric form and describes a time-dependent crystallization scenario, which tends toward the steady-state mode when time increases. It is shown that the particle-size distribution contains kinks at the points of fines dissolution and product crystal withdrawal. Additionally, our calculations demonstrate that the unsteady-state crystal-size distribution has a bell-shaped profile that blurs with time due to the crystal growth and removal mechanisms. The analytical solutions found are the basis for investigating the dynamic stability of a continuous crystallizer.

Оцінка технічного стану та визначення енергетичних характеристик насосних агрегатів головної насосної станції Нижньо-Дніпровської зрошувальної системи

Goal. To substantiate the organizational and technical measures to ensure the reliable operation of the pumping power equipment of the main pumping station (MPS) of the Lower Dniester Irrigation System (LDIS), and to increase the energy efficiency of machine water supply by modernizing the LDIS. Methods. Information-analytical — for the analysis of scientific results highlighted in domestic and foreign literary sources on the issues of ensuring the reliable operation of pumping equipment of pumping stations (PS), and energy efficiency of machine water supply. Field research — to determine the energy characteristics and technical condition of pumping units (PU) based on vibration levels using modern measuring equipment (ME), and vibration monitoring. Statistical — to analyze the gained experimental data. Results. The vibration levels are determined of PU with centrifugal horizontal pumps D4000-95 and drive asynchronous electric motors AN3-2-15-57-2 with a capacity of 1600 kW, 1000 rpm, as well as vibration levels of PU with centrifugal vertical pumps 1200V-6.3/100 and drive synchronous electric motors VDS-2-325/69-2 with a capacity of 8000 kW in stationary and transitional processes. Recommendations are provided for increasing the reliability of the pumping power equipment of the MPS and reducing operating costs for electricity. Conclusions. According to the vibration levels in the stationary mode of operation, the 1200V-6.3/100 pump is in good technical condition after major repairs. In the start-up mode and during the transient mode during the filling of the pressure pipeline of the MPS, increased vibration levels occur, which are 2–4 times higher than the vibration levels in the stationary mode of its operation. Over time, this mode of operation of the PU can lead to a deterioration in its technical condition, an increase in electricity consumption, a failure of the pump bearing, as well as failures in the operation of the pump power equipment.

Real-time temperature field recovery of a heterogeneous reactor based on the results of calculations in a homogeneous core

Advanced pressurized water reactors are the main part of a new generation of nuclear power plant projects under development that provide cost-effective power production for various needs (Yemelyanov et al. 1982, Klimov 2002, Boyko et al. 2005, Baklushin 2011, Bays et al. 2019, Nuclear Technology Review 2019). The innovative technologies are aimed at improving the safety and reliability as well as at reducing the cost of NPPs. At the same time, improvements in design, technological and layout solutions are focused primarily on the reactor core. Assessments of the efficiency of these improvements are preceded by numerical simulations of the processes in the core, in particular heat generation and sink, with account for the difference between the study object and the standard version tested in operational practice. The authors of the article propose a method for calculating the temperature field in the core of a heterogeneous reactor (using the example of a pressurized water reactor), which makes it possible to quickly assess the level of temperature safety of various changes in the core and has the necessary speed for analyzing transients in real time. This method is based on the energy equation for an equivalent homogeneous core in the form of a heat equation that takes into account the main features of the simulated heterogeneous structure. The procedure for recovering the temperature field of a heterogeneous reactor uses the analytical relation obtained in this work for the heat sink function, taking into account inter-fuel element heat leakage losses. Calculations of temperature fields in the model of the PWR type reactor (The Westinghouse Pressurized Water Reactor Nuclear Plant 1984) were carried out in stationary and transient operating modes. The calculation results were compared with the results of CFD simulation. The area of competing use of the temperature field recovery method was indicated.