Thermophysics and Thermal Power Engineering

SMALL-SIZED TURBOJET ENGINES AND THEIR COMBAT APPLICATION IN UNMANNED AVIATION

A.A. Khalatov — 2026-06-30

The relevance of the work is due to the urgent need to respond to the changing nature of the combat operations of unmanned aircraft of Ukraine by timely development of preliminary measures of both tactical and technical content. The purpose of the work is to draw attention to the expansion of the possibilities of using unmanned aircraft with a small turbojet engine (MTRE) as a propulsion system. The task of the work is to analyze the features of the MTRE workflow and design, determine its advantages and disadvantages, features of operational characteristics and scope of application on military drones. Research methods include the study and analysis of literature, statistical data, information and reports from the front on the Internet. The analysis of the combat operations in the war of the Russian Federation against Ukraine showed the unforeseen in terms of scale and consequences of the use of unmanned aircraft in them. This caused fundamental changes in the tactics of military operations, and subsequently in the organizational structure of the Armed Forces of Ukraine (AFU). The paper considers the possibilities of increasing the effectiveness of the use of Ukrainian unmanned aerial vehicles (UAVs) of the strike type. The features of the design, control and operation of existing drones and their engines are presented. It analyzes how the nature of the combat use of strike drones on the front and in the enemy's near rear changed during the four years of the war. Technical and tactical factors are identified that significantly weaken the combat capabilities of helicopter-type aircraft with a battery engine, which are operated by the AFU. To take these factors into account, it is proposed to massively introduce aircraft-type strike drones with MTRD as an engine into combat operations. The main advantage of such an engine is its ability to provide high maneuverability, speed and flight altitude of the UAV, while providing a significant load on board in the form of ammunition and fuel. According to the most general operational characteristics of the UAV, its take-off weight and engine type, MTRD is most suitable for light and medium-class drones. The use of a strike drone with MTRD is usually one-time or, at least, multiple. Therefore, the choice of parameters of the working process and engine design must ensure its technical resource that would correspond to the short life cycle of the attack UAV. In this case, the engine becomes structurally simple and cheap to manufacture, although less economical than a full-size turbojet.

ANALYTICAL MODELING OF COMPLEX HEAT EXCHANGE UNDER FREE CONVECTION ON A VERTICAL PLATE

A.A. Avramenko — 2026-06-30

The purpose of this article is to analytically model a complex heat transfer process that includes radiation heat transfer, natural convection, and slip conditions on a flat surface immersed in a stationary gas.

Research into the combined effect of natural convective heat transfer with thermal radiation is an integral part of solving heat transfer problems, providing an understanding of the fundamental concepts of changing the dynamics of a working fluid.

This article analytically describes the case of stationary natural convection near a heated vertical plate placed in a large volume of gas. The gas is stationary and has a constant temperature T∞. The temperature of the heated plate Tw is also constant. We consider the case Tw > T∞. The results obtained will also be valid for the case Sr >> 1.

As a result of mathematical transformations, equations for the velocity and temperature profiles, average velocity, flow rate, thickness of the boundary moving layer, and the Nusselt number are obtained. During the solution of the problem, it was found that the increase in the slip effect accelerates the boundary layer due to the presence of convection and a velocity jump on the surface. The radiation effect gives a slight acceleration of the boundary layer. The obtained Nusselt number distributions showed that the effect of radiation significantly intensifies the heat transfer process, in contrast to the slip effects, which almost do not affect the dynamics of heat transfer improvement.

STUDY OF THE KINETICS OF DRYING OF FOLATE-CONTAINING COMBINED RAW MATERIALS

Zh.O. Petrova — 2026-06-30

Every year, the preservation of nutrients and energy resources becomes increasingly important in the processing of plant raw materials worldwide.

Vegetables are a staple food because they are rich in fibre, minerals, vitamins and antioxidants.

Folate is a water-soluble B vitamin that plays a vital role in cell growth and development. The names folic acid and folate come from the Latin word folium, meaning ‘leaf,’ and it was first isolated from spinach leaves in 1941.

Folic acid is naturally present in high concentrations in leafy vegetables such as spinach, lettuce, cabbage, broccoli, asparagus, tomatoes, leeks, wild garlic, green onions, fruits, legumes (green beans, beans, peas, lentils), nuts, yeast, mushrooms, and animal products.

Spinach (Spinacia oleracea L.) is an annual leafy green plant rich in beta-carotene (provitamin A), folic acid (vitamins A and C), minerals (phosphorus, sodium and potassium) and dietary fibre.

Green beans are young, immature fruits of various varieties of common beans (Phaseolus vulgaris). In 100 grams (3.5 ounces) of raw green beans, there are 31 calories and a moderate amount (10-19% of the daily value) of vitamin C, vitamin K, vitamin B6, and manganese, as well as a rich amount of folic acid (vitamin B9).

Vegetables spoil quickly after harvesting and are only consumed during the growing season. They are often sold canned or frozen.

Drying is one of the preservation methods that allows extending the shelf life of plant raw materials while preserving their vitamin content and preventing the growth and production of microorganisms that cause rotting.

Various methods can be used to dry these raw materials, namely convective, sublimation, microwave, spray drying and various combined methods.

Convective drying is one of the most common methods for processing dark green leafy vegetables.

To stabilise folates, plant raw materials must be combined with raw materials that are high in vitamin C.

The aim of the work is to study the kinetics of drying folate-containing combined raw materials, namely a mixture based on spinach, dill, parsley and a mixture based on green beans and green onions.

The work studies the drying kinetics of folate-containing combined raw materials, namely a mixture based on spinach, dill, parsley, and a mixture based on green beans and green onions.

It was determined that when drying a mixture based on spinach, dill and parsley, the duration and nature of the curves are close to the results obtained in the study of parsley.

It has been determined that increasing the temperature from 60 to 70ºC when drying a mixture based on green beans and green onions intensifies the process by 21%. The use of low heat transfer temperatures is confirmed by the fact that when drying at 60ºC, folate preservation is 3.9 times higher than at 100ºC.

THERMOPHYSICS OF RADIATION HEAT EXCHANGE FOR THERMAL MASKING

B.I. Basok — 2026-06-30

This paper analyzes modern thermal masking methods. These methods are used to prevent detection of heated objects using thermal imaging cameras and other similar devices. These methods are particularly important during combat operations to conceal personnel and military equipment. It is shown that the main areas of thermal masking technology development are related to methods for reducing the surface temperature of a heated object and decreasing its emissivity. These measures reduce the intensity of infrared radiation detected by a thermal imager. It is noted that the most effective solution to these problems is the creation of low emissivity surfaces in atmospheric windows and selective emission in other electromagnetic wave ranges for thermal monitoring and surface temperature reduction.

NFLUENCE OF HEAT FLOWS ON THE COOLING CAPACITY OF A CRYOGENIC MICRO-REFRIGERATOR WITH THE JOULE-THOMSON EFFECT

P.G. Krukovsky — 2026-06-30

This paper presents an investigation into the influence of heat inflows on the performance characteristics of a Hampson-type microrefrigerator (MCR). This device, which operates based on the thermodynamic Joule-Thomson effect, is a critical component of modern high-tech systems, as it provides efficient cooling for infrared sensors, laser emitters, and various microelectronics used in medical, space, and defense sectors. The technological process of cooling target objects in such systems is implemented by supplying nitrogen under ultra-high pressure, ranging from 10 to 40 MPa, through a thin capillary tube of the heat exchanger, followed by rapid expansion through a throttle device to a pressure of approximately 1.1 atm and cryogenic temperatures in the range of 60–80 K. Given that direct experimental study of heat flows in systems of such a small scale is an extremely difficult technical task, the authors applied a method of complex computer modeling. This method is based on the integration of a three-dimensional geometric model of the housing and the holder with a nodal model of the internal thermodynamic processes occurring directly within the microrefrigerator channels. During the modeling, the influence of heat inflows was analyzed in detail as the vacuum level changed from high vacuum (0,01 Pa) to full atmospheric pressure

(101325 Pa). The generated results convincingly demonstrate that complete depressurization and loss of vacuum lead to an increase in total heat inflows and, consequently, to an almost twofold increase in nitrogen consumption to maintain the operating temperature. At the same time, it was established that under such conditions, the cooling time for sensors and microcircuits is reduced by 1,8 times, which creates a risk of unstable operation or thermal damage to the equipment. A significant conclusion of the work is the distribution of heat inflows: under high vacuum conditions, 58% of the heat enters through the end part of the Dewar vessel where the sensor is located, while the cylindrical wall allows only 6% to pass through. However, during depressurization, the share of heat inflow through the side wall increases sharply to 42%, which completely changes the thermal profile of the product. The scientific novelty of this study lies in the theoretical and practical substantiation of implementing additional thermal insulation for the holder, made of fluoroplastic 1 mm thick with a thermal conductivity coefficient of 0,25 W/(m·K). It was established that the use of such an insert allows for a local reduction in heat inflow through the holder assembly by 3 times, ensuring significant savings in working gas (a 30% reduction in consumption from 0,033 g/s to 0,025 g/s). The overall rate of reduction in heat inflows due to the use of insulating components reaches 16%. This opens up new opportunities for increasing operational reliability, extending autonomous operation time, and enhancing the overall efficiency of cryogenic systems in complex real-world operating conditions, allowing for the provision of scientifically based recommendations for MCR design. The results obtained can also be used to develop real-time vacuum state monitoring systems based on indirect gas consumption indicators. The paper emphasizes that it is precisely the comprehensive approach to modeling that allows for accounting for the mutual influence of design parameters and external conditions, which is critically important for miniature systems where even minor heat losses can lead to a disruption of cryogenic regime stability.

FEATURES OF SELECTING TECHNICAL AND ECONOMIC INDICATORS OF COGENERATION AND COGENERATION-HEAT PUMP PLANTS

B.D. Bileka — 2026-06-30

Cogeneration or combined production of electrical and thermal energy has gained significant popularity and development in both large and small energy sectors around the world. Such installations are of particular importance and significance in the case of energy autonomy in the absence of centralized energy systems or in the event of their disruption, in the event of force majeure circumstances. Such autonomy of the energy sector leads to the need to consider a large number of options for cogeneration plants (CGU), the choice of their optimal thermal schemes, as well as the main energy equipment. To solve these problems, it is necessary to have a simple, but sufficiently reliable and universal calculation methodology.

One of the most important parameters characterizing the energy efficiency of a CHP is the amount of fuel consumed for energy generation. Therefore, the purpose of this work is to conduct an initial comparative analysis of thermal schemes of cogeneration plants and assess the prospects for their implementation to increase the energy efficiency of using the energy potential of fuel, while producing the same amount of electrical and thermal energy by the plants.

The article considers the methodology for comparative calculation of consumption characteristics of various thermal schemes of CHP using the main energy parameters of installations – electrical and thermal efficiency coefficients (EFC) of engines and installations, thermal efficiency of boilers and boilers – waste heat exchangers, heat transformation coefficient of heat pumps. When selecting these parameters, traditionally, the engine data is used, which are usually design data. However, when forming a CHP, the characteristics of the power equipment may differ from the design ones, or may be unknown altogether.

For such cases, as well as to accelerate and simplify the comparative analysis, it is proposed to use statistical data on the values of electrical and thermal efficiency of piston engines and gas turbine plants of more than 50 foreign and domestic companies. Based on these data, a graphical dependence of thermal efficiency on electrical efficiency is constructed, which is approximated by an analytical dependence used for comparative analysis. For example, two thermal schemes are considered - a cogeneration plant with a boiler and a power plant and a cogeneration plant with a heat pump and a boiler, in the heat-only mode.

BIOETHANOL AS A STRATEGICALLY IMPORTANT FACTOR IN ENERGY AND ENVIRONMENTAL SECURITY OF UKRAINE

O.M. Obodovych — 2026-06-30

The article provides a review of literature on the problem of improving motor fuels by adding bioethanol to gasoline with subsequent cavitation treatment of this mixture. A review and analysis of literature data on the processing of lignocellulosic raw materials and its waste into fuel bioethanol and the possibility of its use in a mixture with gasoline for internal combustion engines in the conditions of the Ukrainian economy are conducted. The use of rotary-pulsation devices developed at the Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine for mixing and homogenizing gasoline-alcohol solutions in order to increase their stability and prevent stratification is proposed.

The most common is the addition of bioethanol to gasoline in concentrations of 5, 10 and 15 %, which does not affect the operation of the internal combustion engine and allows significantly reducing exhaust emissions.

The main difficulty in the production of second-generation bioethanol lies in the conversion of lignocellulosic raw materials, which involves the separation of cellulose, lignin and hemicellulose. The Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine has proposed innovative heat and mass exchange equipment to intensify this process.

The other problem of the full use of bioethanol in the preparation of fuel mixtures (gasoline-bioethanol) is their stratification during long-term storage. The literature suggests the use of various types of cavitation devices to solve this problem. The Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine has developed a special design of a rotary-pulsation apparatus (RPA) designed for mixing and homogenizing gasoline-alcohol solutions in order to increase their stability and prevent stratification.

Given the important role of bioethanol, it is advisable to adopt legislative initiatives that will have a simultaneous positive effect on several sectors of the economy. This will reduce the state's dependence on energy imports, increase the potential of the agricultural sector, provide additional impetus to the processing industry, and strengthen Ukraine's position in achieving environmental aims.

ANALYSIS OF BIOFUEL ROLE IN DECARBONIZATION OF TRANSPORT AND ACHIEVING CLIMATE NEUTRALITY

T.A. Zheliezna — 2026-06-30

The aim of the work is to develop recommendations for decarbonizing the transport sector of Ukraine by increasing the use of liquid and gaseous biofuels. The research methods include calculations, study and analysis of literature, statistical and other data. Ukraine is making significant efforts to implement the main principles of the European Green Deal. From the experience of the "green" energy transition in the EU, it is known that transport is difficult to decarbonize compared to the sectors of heat and power production. European practice also shows that the use of biofuels is the most effective measure to reduce greenhouse gas emissions in transport. In this case, the emphasis should be on second-generation biofuels, since they provide a reduction in greenhouse gas emissions by 80...90% compared to the use of petroleum fuels. The EU's successes in increasing the consumption of renewable energy and strengthening the decarbonisation process are largely due to the implementation of a long-term consistent climate policy. The goals of one specific period are reasonably updated by the next ones, the mechanisms for achieving the goals being constantly analysed and improved. Europe's climate policy is consistent with the energy policy, in particular with the goals of the EU Renewable Energy Directive. This approach is a positive example for Ukraine. In Ukraine, climate policy is aimed at achieving climate neutrality by 2050, which is in line with the goals of the European Green Deal. The intermediate goal is to reduce greenhouse gas emissions by at least 65% by 2030 compared to 1990 levels. Meeting these ambitious national goals requires decarbonisation of all sectors of the economy, including transport. For Ukrainian conditions, the consumption of compressed biomethane in transport seems to be promising, since Ukraine itself produces biomethane and has already had experience in using compressed natural gas as a motor fuel for buses and trucks. The use of compressed biomethane in transport instead of natural gas will make a significant contribution to decarbonisation, as Ukraine has a sufficient feedstocks for the production of biomethane with a very low carbon footprint. Such biomethane can be obtained from lignocellulosic agricultural residues, livestock manure, intermediate and cover crops. In terms of liquid biofuels, currently, Ukraine produces almost only first-generation bioethanol. In the future, it is recommended to launch the production of biofuels for aviation and maritime transport. The prerequisites for this are the availability of the potential of the necessary types of biomass, as well as the existing results of scientific and practical work. Initially, these biofuels can be exported to Europe, which will contribute to achieving the EU's goals for the decarbonisation of the relevant transport sectors. When the post-war development of Ukraine begins, these biofuels will also be consumed in domestic aviation and maritime transport. Production can be started from such types as hydrotreated ethers and fatty acids (HEFA) and hydrotreated vegetable oil, for example, from camelina as feedstock, and later move on to producing advanced liquid biofuels from lignocellulosic biomass. During the period of post-war development of Ukraine, it seems appropriate to additionally analyse Ukraine's climate policy and energy strategy for their consistency across various sectors, including the transport sector.

ANALYSIS OF THE IMPACT OF CEREAL STRAW PRETREATMENT ON BIOGAS YIELD POTENTIAL

O.H. Dombrovskiy — 2026-06-30

The study investigates the effect of different pretreatment methods of cereal straw on the biogas yield potential under mesophilic anaerobic digestion conditions. The aim of the research was to evaluate how mechanical, hydration-based, biochemical, and extrusion pretreatments influence the biodegradability of cereal straw and its cumulative biogas production.

The objectives included comparative assessment of untreated chopped straw, pelleted and briquetted straw, hydration-mechanical pretreatment, biochemical treatment using an enzymatic-microbial additive, and extrusion pretreatment, with particular attention to changes in biogas yield per unit of volatile solids.

The methods involved biochemical methane potential (BMP) tests conducted in batch reactors under mesophilic conditions (37.5 ± 0.5 °C) in accordance with standardized procedures. Biogas production was monitored over a 40-day digestion period, and results were normalized to volatile solids content.

The results demonstrate that untreated cereal straw exhibits the lowest biogas yield (460 m³ t⁻¹ VS) due to the resistance of its lignocellulosic structure. Simple pretreatment methods significantly enhanced biogas potential: hydration combined with mechanical size reduction increased the yield to 507 m³ t⁻¹ VS, while biochemical treatment provided a moderate improvement (490 m³ t⁻¹ VS). Among physical forms, pelleted straw showed the highest increase (+19.3%), whereas hydrated briquettes achieved the maximum yield (561 m³ t⁻¹ VS). Extrusion pretreatment also improved substrate accessibility, resulting in stable biogas production (500 m³ t⁻¹ VS).

Overall, the findings confirm that pretreatment is a critical factor for intensifying hydrolysis and improving biogas production from cereal straw, with practical implications for optimizing substrate selection and processing strategies at existing biogas plants.

ESTIMATION OF THE LEVELIZED COST OF HEAT FOR THE LIFE CYCLE OF HOUSEHOLD SOLID WASTE DISPOSAL

H.O. Kuts — 2026-06-30

The article considers the problem of solid household waste disposal in Ukraine and promising ways to solve it. A five-stage hierarchical structure of household waste management has been introduced to solve the problem of solid household waste disposal in European countries. This technology has been adopted in Ukraine and included in the National Waste Management Strategy. All waste management technologies require their preliminary sorting. The best proven technology for the final disposal of household waste is the incineration of solid household waste in boiler plants with the production of thermal and electrical energy and the purification of waste gaseous combustion products from harmful substances. In Ukraine, sorting of household waste, reuse of waste in the production of products, extraction of biogas at landfills with subsequent use and burning of solid household waste at a single incineration plant in boiler units for the production of thermal energy are now increasingly used. This process solves two problems at the same time: the production of thermal energy for the population using alternative fuels of local origin and the disposal of solid household waste, which significantly reduces the volume of waste for subsequent disposal in landfills. In 2023, almost 10 million tons of household waste were collected in Ukraine. The use of the energy potential of residual solid household waste (MSW), which cannot be recycled, is the most accessible urban alternative energy source in Ukraine, for example, artificial fuel from MSW, located near thermal energy producers - enterprises for the production and supply of thermal energy for heating and hot water supply. The thermal energy of residual MSW can be a significant addition to other sources of natural gas substitution (biofuels, biogas extracted from landfills, etc.). The Government of Ukraine is developing a Concept of the State Targeted Economic Program for the construction of 207 new waste processing plants with the production of fuel from waste after sorting, which is intended to replace natural gas consumption at enterprises producing thermal energy. This will allow replacing about 10% of natural gas used for heating and hot water supply of the population of Ukrainian cities with a population of over 300 thousand inhabitants. The article notes the complexity of determining the calorific value of solid household waste, which may have a variable morphological composition and different moisture content of the components. The article provides a calculation of the levelized cost of thermal energy over the life cycle with the existing technology of combustion in a boiler unit for the production of thermal energy and estimates a possible reduction in the cost of thermal energy. The calculations were carried out for a waste incineration plant in the city of Kyiv. The calculated LCOH significantly exceeds similar indicators for boiler units using natural gas, coal, biofuels and even fuel oil. However, taking into account environmental and social factors, this technology for the disposal of solid household waste becomes acceptable. The introduction of solid household waste combustion technologies will allow replacing part of the fossil fuel burned in boiler plants for the production of thermal energy and revitalizing landfills.

POSSIBILITIES OF STEAM-COMPRESSION HEAT AND COOLING SUPPLY BASED ON ENERGY FROM A BINARY LOW-TEMPERATURE -SOURCE IN CONDITIONS OF REGULATED HEAT STORAG

V.D. Petrash — 2026-06-30

The article is devoted to the development of opportunities and conceptual foundations for improving heat pump-based heating systems, including the development of new technical solutions for the rational combined use of binary low-temperature heat sources to provide energy-efficient heating and cooling for residential buildings during the relevant seasons.

The aim of this work is to improve the structural and functional design of the proposed heating and cooling supply system, providing a theoretical justification for the efficient utilisation of the energy potential of the binary heat exchange system utilising ground heat and ventilation air flows.

The paper establishes the relationship between the output parameters in the process of vapour-compression heat extraction from a low-temperature source in the evaporator, in accordance with the established relationship, as well as the conditions of its consumption by user subsystems downstream of the condenser under operational control conditions, forms the basis for a multi-factor assessment of the energy potential of a binary low-temperature source and the subsequent determination of the energy efficiency of the vapour compression heating and cooling system under consideration.

It has been established that in buildings with sufficient thermal energy resources in the ventilation air, the use of an improved heat pump system allows for a further extension of the period during which recovered heat is accumulated in the soil mass – at the beginning and end of the heating season. It has been demonstrated that the start of heat accumulation in the ground mass in buildings with a heat pump heating system can be achieved in regions of Ukraine where the outdoor air temperature equals its average value for the heating season.

The graphical relationships obtained show that an increase in the flow rate of the heat transfer medium through the ground heat exchanger, resulting from a reduction in the cross-sectional area of the heat exchanger used to cool the ventilation air, significantly reduces the system’s energy efficiency across the range of characteristic changes in circulating flow rates - through the evaporator 1 and condenser 3 GВ/GК over the entire considered range of outdoor air temperature variation (0...-18)°C. It has also been established that high energy efficiency in the conversion of energy flows in the analysed system can be achieved even under design conditions for the heating period (tзовн. = -18°C) with a ratio of circulating energy flow rates through the evaporator and the GВ/GК condenser > 1.8, provided that heat consumption is predominantly for heating and ventilation processes.

The performance characteristics of the improved system utilising integrated heat demonstrate enhanced efficiency in the conversion of energy flows for the heating and cooling of buildings, which indirectly justifies the feasibility of maximising the storage of excess heat from air flows in the ground, combined with the simultaneous cooling of buildings during the non-heating season. It follows that the use of integrated heat not only allows for the implementation of a combined or sequential process of general energy extraction, rationally coordinated with the optimal operational control regime of heat consumption systems, but also to ensure highly efficient accumulation of excess heat from a low-temperature source in the soil mass for its subsequent use during the heating season.

Conclusions. For the proposed vapour-compression heating and cooling system for buildings, a multifactorial relationship has been established for the actual conversion coefficient used to assess the efficiency of transforming low-grade heat from the ground and ventilation air. This allows for the analysis of the individual influence of parameters and operating modes of structural subsystems in the search for optimal conditions for utilising the energy of integrated flows for heating and cooling buildings during the relevant periods of the year. It has been established that high energy efficiency of the system is ensured under design and operating conditions during the heating season with a specific ratio of circulating energy carriers through the evaporator and condenser of the heat pump equipment.