Computer modelling is increasingly essential for advancing the practice of the most widespread and efficient basic oxygen furnace (BOF) steelmaking process. An urgent problem in the BOF process is the need for greater durability of the refractory lining in the top-blown converter. One of the most advanced methods of hot repair for the converter lining is the inter-melting slagging technology for refractories, with a durable skull coating. An essential task in implementing the progressive slag-splashing process is ensuring proper and stable durability of the slag-splashing lances used. A mathematical model of the thermal regime of the top water-cooled slag-splashing lance barrel during the hot repair operation of the converter lining by the slag-splashing method has been developed. The regularities of heat transfer and temperature changes in the outer pipe of the slag-splashing lance for two primary forms of blast devices, operated under technological conditions of lining slagging in top-blown converters with typical capacities of 160 tonnes and 250 tonnes, are numerically investigated. Regression dependencies for estimating the thermal regime of the slag-splashing lance barrel at different cooling water flow rates have been obtained. The results obtained are used to design a slag-splashing lance and to develop its operating technology during hot repair of the lining of a 250-tonne top-blown converter with the use of the slagging method. The results contribute to the development and improvement of automated design systems, the modernisation of slag-splashing lances, and the control of BOF steelmaking. They also contribute to the development and improvement of automated design and modernisation systems, as well as to the solution of optimisation and predictive analysis problems for the thermal regime of slag-splashing lances in the context of BOF steelmaking control.
Due to harmful emissions from vehicles on fossil fuels, rising prices for petroleum products and natural gas, the use of electric vehicles is on the rise. The rapid growth of electric vehicle production will ultimately satisfy these problems in cities. Outside the city, it is advisable to develop intercity electric transport, primarily rail, which can significantly reduce the cost of passenger and freight transportation. The paper considers the possibility of using switched reluctance motors in the traction drives of railway locomotives to replace less efficient, outdated direct current motors. It was designed in a direct current motor housing to study the static characteristics of the switched reluctance traction motor. A simulation model of a switched reluctance motor was developed, and its static characteristics were calculated at various supply voltages and load torque when operating in traction electric drives of railway transport. A comparison of the traction, mechanical and energy characteristics of a switched reluctance motor and a direct current traction motor at different supply voltages was carried out to assess the efficiency of its application. With this approach, as with direct current motors, the supply voltage of the switched reluctance motors was regulated by changing the wiring diagram. An algorithm for controlling the switched reluctance motor through pulse-width modulation of its phase voltage to form a family of traction characteristics is proposed. The study results showed that the proposed approach to regulating the rotation speed of the switched reluctance motor allows for the formation of the required number of traction characteristics and, if necessary, for performing stepwise or smooth transitions between them to regulate the vehicle speed. The results indicate the efficiency of switched reluctance motors in direct current traction electric locomotives.
One of the most essential characteristics of a complex technical system is that it performs ‘an important useful function only with the assistance of a human operator and standard infrastructures…’ [1]. At the earliest stages of the development of a system, deciding whether the human operator should be regarded as part of the complex system or an external entity is necessary. In most cases, the human operator should be treated as an external entity.Most complex technical systems cannot function without the active involvement of a human operator, who retains responsibility for decision-making, control, and management functions. From a functional standpoint, operators can be considered an integral part of the system. However, the system designer rarely possesses sufficient authority over the operator to incorporate them fully into the system’s design. From the perspective of the systems engineer, the human operator instead represents an element of the system’s environment.Under this paradigm, the systems engineer must devote particular attention to the design and development of the operator interface, which is a critically important aspect of any complex technical system [2]. Accordingly, the development of universal technical solutions that enhance the quality of the human–machine interface in complex technical systems represents both a significant and timely challenge, the resolution of which can be applied across a wide range of practical applications.The primary objective of the present work is to improve the performance of the human–machine interface by compensating for the inertial and nonlinear characteristics of the human operator as a control element within a complex technical system.
Modelling heat and mass transfer processes is essential in designing and optimising technological processes in power engineering, mechanical engineering, metallurgy, chemical industry, and other engineering fields. For the mathematical description of such processes, differential equations of heat conduction and diffusion are used, the solution of which requires the application of efficient numerical methods, especially in the case of complex geometries and diverse boundary conditions. This study presents a unified methodology for the numerical solution of boundary value problems of heat conduction with internal heat sources, based on locally one-dimensional implicit finite difference schemes derived using the integral-interpolation method (balance method) in Cartesian and cylindrical coordinate systems. Special attention is given to discretising boundary conditions of the first, second, and third kinds, focusing on Robin conditions, the most commonly encountered in engineering practice. A quasi-linear approximation scheme and spatial splitting schemes are recommended to increase the efficiency of numerical solutions. This approach enables the application of the unconditionally stable Tridiagonal Matrix Algorithm (TDMA). The introduction of indica-tor coefficients provides flexibility in implementation, allowing the balance equation to be used variably by manipulating the terms responsible for heat fluxes and the location of com-putational nodes. This ensures ease of implementation and improves code readability, facili-tating software development for computational modelling. The results of the numerical simu-lation obtained using the proposed method are compared with known analytical and numerical solutions and demonstrate high accuracy. The proposed methodology opens broader opportu-nities for modelling thermal regimes in complex engineering systems.
Digital transformation (DT) in the energy sector is pivotal in meeting energy transformation challenges. DT is reshaping energy production, distribution, and consumption by integrating advanced technologies such as artificial intelligence (AI), the Internet of Things (IoT), blockchain, and digital twins. While existing research has extensively documented individual technological applications, there remains a significant gap in understanding how these technologies interact synergistically in real-world implementations [11]. Comprehensive analyses comparing digital transformation outcomes across different socioeconomic contexts are limited, particularly regarding the scalability of swarm electrification models. These technologies collectively address the ‘three Ds’ – decentralisation, decarbonisation, and digitalisation – essential for the evolution of modern energy systems. By leveraging these innovations, the sector can significantly enhance efficiency, optimise renewable energy integration, and expand access to underserved regions.One of the most impactful applications of DT is in the realm of decentralised energy systems, exemplified by swarm electrification. This concept, pioneered by Groh et al [3], utilises interconnected solar home systems (SHSs) to form scalable microgrids that evolve from standalone setups to full integration with national grids. These systems empower communities by facilitating energy sharing, reducing operational costs, and creating new income streams. Case studies from Kenya, Madagascar, Yemen, Germany, and Bolivia demonstrate the real-world success of swarm electrification in bridging the energy access gap while advancing sustainability goals.AI plays a pivotal role in digital energy systems by enabling predictive maintenance, optimising energy flows, and improving system reliability. Algorithms analyse vast datasets in real time to forecast energy demand, detect anomalies, and automate grid management. IoT further complements AI by providing the physical infrastructure to gather and transmit data, enabling real-time monitoring and control of energy assets. Together, AI and IoT support the development of smart grids and energy communities, fostering greater flexibility and resilience in energy networks.Blockchain technology is emerging as a transformative tool for energy trading and distribution. By enabling peer-to-peer (P2P) energy markets, blockchain enhances transparency and reduces transaction costs. This decentralisation of energy trading allows consumers to become prosumers, actively participating in energy production and exchange. Projects such as Esmat et al. decentralised platforms exemplify how blockchain empowers individuals and communities to take ownership of their energy futures while ensuring security and scalability.Despite these advancements, the implementation of digital technologies in energy systems is facing significant challenges. High initial costs, the complexity of integration, and cybersecurity risks pose barriers to widespread deployment. Furthermore, the digital divide in underserved regions limits equitable access to these transformative solutions. Environmental concerns related to the energy consumption of digital infrastructures, such as data centres and blockchain networks, also require attention. Addressing these issues necessitates a multi-stakeholder approach involving policymakers, industry leaders, and researchers to create enabling environments for innovation.This review provides a comprehensive analysis of the role of DT in advancing energy systems, focusing on AI, IoT, blockchain, and swarm electrification. It synthesises insights from over 100 scholarly sources, including real-world case studies, and evaluates the social, economic and technological impact of digitalisation on energy systems. The study adopts a mixed-method approach, integrating literature analysis, quantitative modelling, and case study evaluations to provide actionable insights for policymakers and industry practitioners.The findings of this review highlight the transformative potential of DT in addressing energy challenges, particularly in achieving the United Nations Sustainable Development Goal 7 [2]: universal access to affordable, reliable, and modern energy. By adopting digital innovations, energy providers can enhance operational efficiency, integrate renewable energy sources, and support community-based energy initiatives. The concept of swarm electrification exemplifies how decentralised approaches can complement centralised grids, ensuring scalability and adaptability to local needs.Policy recommendations emphasise the need for financial incentives, capacity-building programmes, and regulatory frameworks to facilitate digital adoption. Investment in human capital is particularly critical, as skilled personnel are required to implement and manage complex digital systems. International cooperation and knowledge sharing are essential to ensure digital transformation efforts align with global sustainability goals.In conclusion, DT represents a paradigm shift in energy systems, offering solutions to some of the sector’s most pressing challenges. Realising its full potential requires overcoming technical, financial, and institutional barriers. This review underscores the importance of a collaborative, multidisciplinary approach to harnessing the power of digital technologies for sustainable energy transitions.
The study presented in the paper investigates rigorously the methods for enhancing the performance of interconnected electric drives within the finishing group of a hot rolling mill. In particular, it examines the impact of supply voltage fluctuations on drive precision and the interactions mediated by the rolled metal strip. A detailed analysis of the existing power supply system identifies the primary causes of dynamic deviations in drive operation.A combined angular velocity control system is proposed to regulate the excitation of DC electric motors. The adaptive control strategy modulates magnetic flux during grid voltage drops, thereby reducing speed fluctuations and minimising tension inconsistencies in the inter-stand gaps. Unlike conventional systems that disregard supply voltage variations, the adaptive approach significantly improves the stability of the rolling process.A mathematical model of the system, incorporating second- and third-order elastic couplings arising from both mechanical and electromagnetic interactions among the drives, is developed. Numerical simulations conducted in MATLAB/Simulink validate the efficiency of the proposed method. Optimal values for the relative reduction in the magnetic flux are determined to minimise discrepancies in drive currents and strip elongation. The results confirm that implementing adaptive control enhances system stability, improves rolling quality, and reduces the load on the power supply, thereby supporting its adoption in rolling mills operating under unstable grid voltage conditions.
In the company SEDA Huánuco, high consumption of reactive energy, attributed to the intensive use of motors, was identified, negatively affecting the power factor, which ranged between 0.73 and 0.77, and posing a significant challenge. The main objective of this study was to evaluate the relationship between reactive energy compensation and the electricity billing of SEDA Huánuco S. A. in Tingo María, 2024. The hypothetical-deductive method was applied with a quantitative approach and classified as applied research with a non-experimental design and a correlational-causal level of longitudinal scope. To obtain the data, the electric energy meter code No.74677479 of the company SEDA Huánuco was selected as a sample due to its high consumption of inductive reactive energy. Its behaviour during months of high and low demand was observed to determine the optimal amount of energy to compensate. After designing and simulating tariffs, it was identified that the MT3 tariff, with two energy charges and one power charge, was the most suitable for optimising billing costs in relation to the new power factor of 0.965. In conclusion, reactive energy compensation is significantly related to electricity billing, supported by the acceptance of the alternative hypothesis (H1), leading to the installation of a 73.5 kVAr capacitor bank in parallel at 440 V, distributed in three stages: one of 10.5 kVAr, two of 21 kVAr, and two of 10.5 kVAr.
Due to the progressing complexity of modern energy systems, the need to forecast energy consumption and generation, optimise processes and develop new technologies in the energy sector, analyse scenarios for the development of energy systems and elaborate a strategy for their development, modelling and simulation is of particular relevance in this industry. The growing need to improve the productivity of computer simulation in the energy industry is effectively addressed by utilising modern computer architectures and advanced software tools that provide acceleration for computationally intensive tasks. Research presented in this paper focuses on enhancing the performance of computationally intensive algorithms using the Thomas algorithm by employing modern asynchronous programming techniques. The work implements classical and develops and implements asynchronous computational algorithms of the sweep method with subsequent assessment of the time and efficiency of their execution for the order of systems of linear equations (SLAEs) up to 5 × 107. The program code was developed using Microsoft Visual Studio C++ and the standard template for asynchronous programming. The numerical experiments showed the possibility of increasing of the implementation speed of the asynchronous algorithm by 1.87–2.91 times. Research results correspond with the literature data and the results previously obtained by the authors in similar studies using alternative parallel programming software. In general, the results of this study determine the potential for further improvement and development of methods and technologies for parallel implementation of computational tasks using the Tridiagonal Matrix Algorithm. These approaches can be extended to developing various computer models of energy processes and systems based on the solution of SLAEs with tridiagonal matrices on computers with multiprocessor or multi-core architectures.
The paper is aimed at analysing policies and energy consumption related trends motivating the development of the value chain for wind energy component (WEC) manufacturing in Lithuania. A comparative literature review and statistical data (2000–2022) analysis were employed for the purpose. The policy overview revealed that investment, climate and energy policy, and related measures establish the preconditions for the entry of manufacturing enterprises into the value chain for WEC as they are creating the demand for domestic and foreign WEC. The results of statistical data analysis showed that from 2009 through 2019, the annual rate of primary energy consumption (PEC) decreased by an average of 0.5% per year, and in 2020 as much as 8.5% due to the COVID-19 lockdown in the European Union (EU). Though the EU countries are still dominated by fossil fuels and related carbon dioxide (CO2) emissions are high (2.8 Gt in 2022), over the last decade, the use of renewable energy sources (RES) was growing rapidly, with a tenfold increase in solar energy and a threefold increase in wind energy consumption. As a clean energy technology, wind power plants (PPs) have the highest CO2 emission reduction potential per MW; also, wind energy is among the cheapest sources of electricity production. Since the EU is a worldwide leader in installations of wind energy capacity and technology deployment, it provides a solid basis for further development. Currently, most of the off-shore plants are operating in the North Sea, but with the new wind parks in the Baltic, Black and Mediterranean seas as well as in the Atlantic Ocean, wind energy could meet more than 80% of electricity demand in Europe. The implementation of wind energy projects requires development of WEC manufacturing activities in EU countries.
The article examines the integration of the circular economy business model into the packaging industry and analyses the integration of circular economy principles into the model of a functioning EU packaging company. The main objective is to offer adaptable solutions for the integration of the principles of the circular economy into the EU packaging company and the business models of other companies in the sector. The first part of this article provides an analysis of the scientific literature on circular economy principles, the models used, the identification and review of the basic principles of the circular economy, and the assessment of the main driving and limiting factors. When analysing the models applied, the one most suitable for enterprises in the field of packaging production is selected, thus creating a solid theoretical basis for the further integration of the principles of the circular economy into the company’s operating model. The second part analyses the innovations that integrate the principles of the circular economy into the EU packaging company’s business model. The goal is to find out what is important for customers in this sector and what is valued by the company’s employees and management. The third part of the article describes the results of the empirical study.
Due to their numerous technical and economic advantages, induction machines (IM) with squirrel-cage rotors are important components of many industrial processes. Their reliability, durability, and ease of operation make them indispensable in various industries, ensuring stable and efficient equipment performance. However, to minimise the risk of costly production failures caused by sudden stoppages, it is important to implement effective diagnostic and monitoring methods. The most common type of fault in squirrel-cage induction motors is the breakage of cage bars and end ring segments, particularly in motors with high inertia loads and frequent stops and starts. Regular maintenance and the implementation of modern control systems in the industry will help ensure the reliable and uninterrupted operation of these machines. In the technical literature, various diagnostic methods have been proposed. Some are based on analysing data collected from the induction motor (IM), detecting characteristic perturbations that indicate faults in the machine. Other methods involve comparing the data obtained from the actual induction motor with its digital model. It is clear that accurate and adequate IM models are necessary for the development and optimisation of fault diagnosis methods. This paper focuses on developing a mathematical model of an induction motor (IM) in a stator-fixed coordinate system, where the squirrel-cage rotor of the IM is represented as a multiphase, symmetrically distributed winding system in space. The adequacy of the obtained model is demonstrated. The developed model allows for the analysis of various types of asymmetries in both stator and rotor of squirrel-cage induction motors
Preservation of natural resources and the environment is an urgent task in human development. In Ukraine, there is a problem of overcrowded sludge sites, which negatively affect the environment by polluting groundwater and soils with toxic substances. Most sludge sites contain sludge that is over 30 years old and is called obsolete. The aim of the article was to study the process of incineration of obsolete sludge. Fuel characteristics of sludge deposits were determined. The obtained indicator of the specific heat of combustion of sludge deposits is close to peat, which will further create a composite fuel. The combustion process of a separate particle of sludge, which determined the duration and speed of combustion, was studied. Taking the results of the obtained experiments on the combustion of a particle of sludge into account, a study of flare combustion was conducted. The research showed that the process of combustion of sludge particles in the flare corresponds to the generally accepted process of combustion of solid fuel in the flare.
The task of determining the efficiency of operation of an absorption heat pump (AHP) with steam heating (COP conversion factor = 1.71) integrated into the thermal circuit of a PT-60/70-130/13 steam turbine that releases production steam and hot water during the partial heat load period (spring and autumn; also referred to as the inteheating period) is being solved in this paper. Variants of operation of the PT-60/70-130/13 with an integrated AHP with a capacity of ~17.25 MW in the partial heat load period were studied when steam with parameters of 1.296 MPa, 280°C was realised in the production selection of the adjustable turbine at flow rates of 20, 30, and 50 t/h with a variable heat load on hot water supply, which was determined by the return network water consumption task 1000–1400 t/h, while the ‘useful’ electrical power of the power complex was provided at ~30 MW. At electricity prices of 0.13 USD/(kWh) and standard fuel of 309 USD/t for Ukraine, the simple payback period of 17.25 MW AHP as part of the PT-60/70-130/13 steam turbine for the partial heat load period at a production load of 20–50 t/h of steam at the consumption of return network water of heat supply 1000–1200 t/h can decrease to two years. At the same time, during the partial heat load period, which lasts ~4404 hours in Ukraine, up to ~1.2% of fuel, up to 44% of technical water for feeding the circulation cooling system, and 0.4% of softened water for feeding are saved. A tangible environmental effect is achieved due to the reduction of harmful emissions – actual heat and hazardous gases – to the atmosphere: CO2 by 1118.7 tons, NOx by 5.87 t, thus saving ~41,000 of technical water.
The current energy security crisis is primarily a heating crisis. Space and water heating accounts for almost one-third of the EU’s final energy consumption, and unfortunately, around 62% of this demand is still met by fossil fuels. In this context, heat pumps, geothermal energy, and other renewable energy sources emerge as crucial technologies offering effective solutions to enhance energy efficiency and decrease dependence on fossil fuels as well as to achieve the EU energy and climate goals. This article focuses on the analysis of the potential and opportunities of using heat pumps and geothermal energy in conventional heating systems and district heating networks. This topic requires an in-depth analysis of the current state, challenges, benefits, and prospects of these technologies in the EU market. By examining the possibilities for wider adoption and discussing the associated factors, the article aims to provide valuable insights into and recommendations for the advancement of heat pumps and geothermal energy in the EU, along with the presentation of some case studies in this field.
Irrigation is the most important step in agriculture. In order to obtain a good agricultural crop, water must be used wisely and appropriately without waste. This article presents an automatic solar irrigation system developed and designed by the authors. The system consists of two parts: a photovoltaic water pumping system and a unit of control based on programmable logic controller. The programmable logic controller (PLC) uses two sensors: one is placed in the field to measure the moisture in the soil, while the second is used to control the amount of water in the storage unit. The photovoltaic pumping system was designed to be able to irrigate one-hectare area of henna Lawsonia inermis L. with daily water need of 33 m3/day and total dynamic head (TDH) of 14 m. The region opted for this study and analysis is 34°41.1’ N latitudes and 6°29.6’ E longitudes in Zribet el Oued-biskra, Algeria.
Solar chimneys are popular systems for their simple structures and clean energy generation. Thanks to its semi-permeable structure, the collector, one of the system’s basic elements, transfers solar radiation to the system. As a result of the heating of the system air under the collector by the solar radiation passing through the collector, it is directed to the high chimney in the collector centre. During the upward movement of the system air, it converts its energy into electricity via a turbine. Due to its large structure, estimating the amount of energy entering the collector system creates a great cost. The ideal size for the collector is therefore important. This study offers a recommendation for the ideal collector size for the pilot plant in Manzanares in terms of collector size and power output. While 59 kW power output is obtained with the system with a collector radius of 122 m in the reference case, it is observed that the power output increases by 78% when the collector radius is increased to 170 m and the collector area is doubled. The ratio of the ideal collector radius to the reference size for the pilot plant should be in the range of 1–1.5.
The PSAT software was used in this study to analyse and compare the performance of hybrid compensators such as SSSC-STATCOM (controllers), TCSC-SVC (compensators), and UPFC in an electric grid coupled to a wind farm. The flexible AC transmission system (FACTS) technology is used to provide a continual power flow and to provide new ways to control the electric system network. In the FACTS devices, the UPFC (Unified Power Flow Controller) is one of the most adaptable, flexible, and complicated power electric devices. The active and reactive power flows and the local voltage on the bus can be regulated by UPFC; it can also resolve the problem of harmonics. The TCSC (Thyristor-Controlled Series Capacitor) consists as a series-compensating capacitor shunted by a thyristor-controlled reactor. The SVC (Static Var Compensator) is the first shunt generation FACTS controller. We can observe that the UPFC controller has an effective power flow control, shorter setting time and a shorter overshoot. The UPFC obtained a well-known reputation for high controllability in power systems. The multilevel Unified Power Flow Controller can be operated in Static Synchronous Compensator (STATCOM), in Static Synchronous Series Compensator SSSC and exactly in the UPFC compensator. The results of this research compare the hybrid controllers and investigate the effects of TCSC-SVC, SSSC-STATCOM, and UPFC on voltage, phase angle stability, and the active and reactive power in the tested system. The purpose of this comparison is to improve dynamic voltage regulation, especially when the utilisation of nonlinear loads and the presence of fault and breaker rise. These hybrid controllers have been shown to outperform series or shunt compensators; however, when compared to hybrid compensators SSSC-STATCOM, TCSC-SVC, and UPFC, the results employing the numerical method in the UPFC are more significant. The UPFC is the best hybrid controller in this study, and the compensators SSSC-STATCOM outperform the controllers TCSC-SVC.
In countries with limited wood fuel resources, the use of straw for energy should be increased to comply with environmental commitments. Boiler houses burning whole straw bales have limited application because of unfavourable straw logistics and obstacles to their construction in most densely built-up settlements. Straw pellets are more convenient for transportation and safer for storage. Boilers with pellet burning can be operated in fully automatic mode. However, burning straw pellets instead of wood pellets is complicated with increased ash content and lower ash melting temperature. Approaches for low-temperature burning of straw pellets at temperatures below the initial deformation temperature of their ash are of practical interest. At low temperatures, burning is slowing and incomplete burnout with energy loss is possible. The rate of burnout also depends on the form and dimensions of the particle. It was common to accept the rate of carbon burnout as uniform on the reacting surface of the particle. This work aimed to study the low-temperature carbon burnout from the char of the cylindrical pellets of various lengths and to estimate the energy loss with unburned carbon. The aim was achieved by the mathematical description of pellet char burning, in which the actual cylindrical char was regarded as the infinite cylinder intersecting with the endless plate. The burnout of fixed carbon was accepted as layered, the carbon burning fronts as infinitely thin, and different rates of carbon burning in radial and axial directions were accepted. An experimental study of the low-temperature burning of fixed carbon from the char of wood and straw pellets was conducted at free air access at 700°C in the furnace, i.e., the temperature around a single pellet was certainly lower than the possible initial deformation temperature of the pellet ash. The duration of carbon burnout from the char of single cylindrical pellets depending on their lengths was studied. The research findings are as follows. Equations in a dimensionless form, describing changes in the remaining share of unburned fixed carbon in pellet char in time, were deduced analytically. At the experimental burning of single straw pellets, loose particles of ash with no signs of melting formed, but they contained unburned carbon. The share of unburned fixed carbon in ash was 0.016–0.020. The coefficient of determination of calculated and experimental duration of complete burnout of fixed carbon from wood pellet char was R2 = 0.96, and R2 = 0.87–0.91 at incomplete burnout from straw pellet char. The most significant scientific result is that for long pellets, the fixed carbon burnout is controlled mainly by its slower burnout rate in the radial direction, and for the shortest pellets by more intensive burnout rate in the axial direction. The practical value of the results obtained is that the use of shorter pellets, which are characterised by faster burnout, may become purposeful for intensive combustion. Conversely, for slow combustion, and especially with the aim of arranging low-temperature burning of straw pellets, it may be feasible to use longer pellets with extended burnout. In the given conditions of straw pellet burning, the unburned carbon presents in ash, but losses of the pellet energy with unburned carbon were estimated at 0.61–0.72%, which is acceptable for boiler burners.
In modern condensers of air conditioning systems, heat pumps, evaporators of seawater desalination systems, and heaters of power plants, the process of vapour condensation is carried out mainly inside the horizontal tubes and channels. Heat transfer processes occurring in condensers have a significant effect on the overall energy efficiency of the mentioned systems. In this paper, the experimental investigation of heat transfer during condensation of freons R22, R406a, and R407c in the plain smooth tube with d = 17 mm were carried out with the following parameters: ts = 35–40°C, G = 10–100 kg/(m2s), x = 0.8–0.1, q = 5–50 kW/m2, ΔT = 4–14 K. The unique measurements of circumferential heat fluxes and heat transfer coefficients were carried out with the thick wall method during different condensation modes. It can be inferred that with the increase of the heat flux, at the top part of the tube the thickness of the condensate film increases, which leads to the decrease in heat transfer. At the bottom of the tube, the increase in the heat flux enhances heat transfer coefficient, that is characteristic of the turbulent liquid flow in the tube. The obtained results allowed improving the prediction of effective heat transfer coefficients for vapour condensation, which takes into account the influence of condensate flow in the lower part of the tube on the heat transfer. This method generalises with sufficient accuracy (error ± 30%) the experimental data on condensation of freons R22, R134a, R123, R125, R32, R410a, propane, isobutene, propylene, dimethyl ether, carbon dioxide, and methane under stratified flow conditions. Using this method for designing heat exchangers, which utilise such types of fluids, will increase the efficiency of thermal energy systems.
Wind energy is a source of renewable energy derived from the kinetic force of the wind. It has experienced the greatest expansion due, above all, to its low impact on the environment and the gradual reduction of costs, which produce clean, competitive and economically viable energy. In order to ensure the stability of the energy produced, many studies are working to develop a reliable maintenance process based on new online diagnostic techniques, fast and accurate, optimised for wind turbine systems. For this, an experimental study was carried out on a wind system based on electric generators with the aim of contributing to the diagnosis and predictive detection of combined mechanical faults, where the configuration is complex because one fault can hide another. For this, it is imperative to associate each symptom with the appropriate method or methods in order to highlight it unambiguously to detect each defect at the appropriate time. Hence the interest in using more elaborate techniques in order to improve the procedures for detecting and analysing combined faults.
