International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Globalization in the modern world covers all areas of life, economy and modern technology, politics and culture. The rapid development of information and communication technologies makes it possible to provide competitive advantages to business organizations. In recent decades, information systems have led to a dramatic increase in the productivity of large and small businesses. This enables an accelerated transition to climate neutrality and digital transformation of the economy, society and industry and requires new technologies, investments and innovations to ensure the sustainable development and competitiveness of every business and a resource-efficient and competitive economy as a whole. The integration of digital technologies in production processes plays an increasingly important role in shaping the competitiveness of enterprises and their sustainable development in the modern world.

In a world of constant change, there is an increasing need for tools and methods that help organizations become more efficient and competitive. Overcoming traditional thinking in business management requires organizations to quickly adapt to market innovations and fully focus on “processes, results, and customers.” Otherwise, many traditionally operating organizations may struggle to survive in a dynamic business environment. The modern concept of production efficiency is no longer limited to individual production units but focuses on the entire value chain, i.e., the “delivery of value” to all stakeholders. Despite the existence of various practices, methods, approaches, or theories that identify and deliver value to different stakeholders, the implementation of improvements within enterprises remains a subjective process. Based on the achievements of existing methods, tools, and best practices for realizing rapid-response and low-cost production processes, this publication proposes a conceptual model for increasing production efficiency in industrial enterprises in Bulgaria. The model takes into account the new realities of the Fourth Industrial Revolution and its logical continuation into Industry 5.0 by identifying and delivering value to all stakeholders.

Solar energy is a cornerstone in the transition towards sustainable and renewable energy sources. Enhancing the efficiency of solar cells is critical to maximizing energy capture and utilization. One promising approach to improve solar cell performance is the application of self-cleaning coatings. This research work explores the enhancement of the energy efficiency of solar cells through the application of a SiO2/WO3-B5 self-cleaning coated film. These coatings not only help in maintaining the cleanliness of the solar cell surfaces but also contribute to better light absorption and reduced reflection losses, ultimately leading to higher energy output.

The set of methods and rules in the process of providing raw materials can be considered a strategy for stock management. Each strategy is associated with specific and expected costs. Still, optimally, we can call that strategy that, under the given conditions, leads to minimal expenses related to the material provision of the studied system. Part of the stock management process is establishing the timing of the deliveries, the necessary volumes and the distribution of the incoming lots to the various warehouses and units. The search for optimal strategies is subject to the theory of optimal stock management. This makes it possible to release significant funds frozen in the form of stocks, which leads to increased efficiency of the material resources used. The optimal inventory management strategy and flexibility also lead to improved production processes and reduced and excluded possible interruptions caused by lack or shortage of materials. The stock management process influences the planning, forecasting, and fulfilment of production needs and orders.
The elements of the business system described so far, in which raw materials, materials and their stocks have a significant impact, show the importance of the stock management strategy of each economic unit. That the chosen and functioning system is optimal is a substantial part of the overall success in any enterprise or other form of business process implementation.

The escalating global demand for sustainable and efficient energy solutions has spurred increased exploration into waste heat recovery technologies. Among these, the integration of Organic Rankine Cycle (ORC) systems with diverse industrial processes stands out as a promising avenue for effectively harnessing low-grade waste heat. This integration not only holds the potential to significantly improve overall energy efficiency but also plays a crucial role in mitigating the environmental impact associated with industrial operations.
Recognizing this potential, the primary focus of this research lies in the meticulous design, optimization, and performance evaluation of a modular Flue Gas Waste Heat Exchanger (FGWHE). This modular FGWHE is strategically crafted to seamlessly integrate with ORC systems across a spectrum of applications, offering versatility and adaptability to varying industrial settings. This paper further extends the exploration of this research through a comprehensive presentation of Computational Fluid Dynamics (CFD) simulations. These simulations delve into the intricacies of a specifically designed modular FGWHE tailored for Organic Rankine Cycle systems. Through detailed CFD analyses, the performance characteristics, heat transfer efficiencies, and fluid dynamics within the modular FGWHE are rigorously examined. The simulation outcomes provide valuable insights into the thermal behavior and overall effectiveness of the modular FGWHE under various operating conditions.

In this paper are presented results of a low-pressure steam turbine energy and exergy analysis during turbine extractions opening/closing. All possible combinations of extractions opening/closing are observed. The highest mechanical power which can be produced by this turbine (when all steam extractions are closed) is 28017.48 kW in real and 31988.20 kW in an ideal situation. For all observed steam extractions opening/closing combinations is obtained that energy efficiency and energy losses range is relatively small (from 87.56% to 87.94% for energy efficiency and from 3360.46 kW to 3970.72 kW for energy losses). Trends in energy and exergy losses (destructions) are identical for all observed extractions opening/closing combinations. Analyzed turbine efficiencies (both energy and exergy) will decrease for a maximum 1% during the steam extractions closing. Turbine steam extractions closing decrease turbine efficiencies and increases turbine losses (destructions), what is valid from both energy and exergy aspects.

The paper presents a theoretical analysis in the field of the application of planetary gear trains in vehicles. The following main areas have been considered: design features of planetary gear trains, specific aspects of the application use of planetary gears in vehicles and possibilities of increasing the efficiency coefficient of these drives. An analysis of the option for investigating these gear sets has been implemented as well. Special attention is dedicated to the options of minimizing energy consumption, taking into account the relevant limitations and operating conditions of planetary gear trains. Conclusions have been deduces. Ideas for future scientific work are presented

Recently, Albania as a developing country is focusing on the energy efficiency in residential and industry sector. Residential sector has very high contribution energy consumption in Albania due to many construction buildings without energy efficiency standards implementation. Most of the contribute city is Tirana where energy consumption in residential sector is very high in comparison to the other cities in Albania. Our research work will be focused on analysis of the energy audit on a private residence apartment which is located in the area of Tirana. The purpose of this paper is based on the relevant standards and norms to give appropriate recommendations for the implementation of energy efficiency which would increase the energy performance of this building.

In this paper is performed energy evaluation of steam turbine from the solar-based combined cycle power plant which includes analysis of each cylinder and the whole turbine. Steam turbine has three cylinders – high, intermediate and low pressure cylinders (HPC, IPC and LPC). Observed turbine is interesting because it possesses steam cooling before its expansion through the last cylinder (LPC). Due to unknown steam mass flow rates through each cylinder, for the evaluation are used specific variables. The highest specific work is obtained in LPC, while the lowest specific work is obtained in IPC. The highest loss of a specific work is obtained in LPC (29.8 kJ/kg), followed by HPC (24.5 kJ/kg), while the lowest loss of a specific work is obtained for the IPC (19.5 kJ/kg). Regardless of higher loss in specific work, HPC has higher energy efficiency in comparison to IPC (95.08% in comparison to 95.02%), while the lowest energy efficiency of all cylinders has LPC (94.92%). For the whole observed steam turbine loss of a specific work is equal to 73.8 kJ/kg, while the energy efficiency of the whole turbine is 95.00%.

This paper presents an exergy analysis of a complex four-cylinder steam turbine, which operate in a coal-fired power plant. Analyzed steam turbine consists of high pressure single flow cylinder (HPC), intermediate pressure dual flow cylinder (IPC) and two low pressure dual flow cylinders (LPC1 and LPC2). The highest part of cumulative mechanical power (787.87 MW) is developed in IPC (389.85 MW) and HPC (254.67 MW), while both low pressure cylinders develop a small part of cumulative mechanical power (70.29 MW in LPC1 and 73.06 MW in LPC2). Cylinder exergy destruction (cylinder exergy power loss) continuously increases as the steam expands through the turbine. The lowest exergy destruction has HPC (13.07 MW), followed by the IPC (20.95 MW), while the highest exergy destructions are noted in low pressure cylinders (24.37 MW in LPC1 and 27.17 MW in LPC2). Cylinder exergy efficiency continuously decreases as the steam expands through the turbine. The highest exergy efficiency has HPC (95.12%), followed by the IPC (94.90%) and LPC1 (74.25%), while the lowest exergy efficiency of all cylinders is obtained in LPC2 (72.89%). Exergy efficiencies of LPC1 and LPC2 are much lower in comparison to other low pressure dual flow cylinders from comparable steam power plants. The whole observed steam turbine has exergy
efficiency equal to 90.20%.

The following paper reviews all the possible cases of coupled two-carrier planetary gears with four external shafts. An emphasis is made on the work of these gears with one degree of freedom, one input and one output shaft and brakes on the other two shafts . When switching over the gears, the speed ratio of the gear is changed, thus allowing the use in two-speed mechanical transmissions of technological lifting and other machines. Some relations are deduced for determining the speed ratios and the efficiency of all structural schemes.
Recommendations for the selection of the most appropriate structural scheme according to the current necessities can be made. A 3D model of the S13V3 two-speed, two-carrier gearbox was created to demonstrate the process of determining the viability of a particular gearbox layout.

The hybrid electric vehicles (HEV) are promising vehicles with low exhaust emissions and increased autonomy of movement including internal combustion engine (ICE) and electric motor (EM) which is powered by the battery (B) . The main advantage of HEV over classic cars is the reduced fuel consumption, especially in urban traffic [1]. This is a prerequisite for good energy efficiency of HEV, which is determined by the fuel consumption and consumption, respectively the regeneration of electricity of HEV. These values depend on many factors such as speed, mileage, acceleration, mass, drag, climatic conditions and more. The modelling of the energy efficiency of HEV is related to the study and structuring of the factors that determine the fuel consumption and electricity consumption and the dependencies between them and their connection and construction in a model. The model of energy efficiency of HEV gives a quantitative assessment of the fuel consumption and the consumption (regeneration) of electricity of HEV, according to the main influencing parameters. In addition, the HEV energy efficiency model indicates the influencing parameters and their analytical or experimental determination. The correct modelling of energy efficiency is related to the correct determination of energy parameters and their logical connection in a selected model. The optimal model of energy efficiency of HEV is built from these factors that can be directly measured or calculated, which increases the accuracy and reliability of the results. This article discusses building an energy efficiency model of a hybrid electric vehicle.