A.V. Luikov Heat and Mass Transfer Institute

The paper presents the results of the thermomechanical analysis of the heat exchanger of the helium preparation system for pressurizing the oxidizer and fuel tanks of a liquid rocket engine. Based on the results of numerical simulation of the thermally stressed state in the heat exchanger, which is based on the results of modeling the flow and heat transfer, critical locations of potential structural failure of the heat exchanger are shown.

The article presents the results of substantiation and approbation of the model of electromagnetic radiation interaction with rough surfaces. This model differs from analogues in the following: 1) surface roughness profiles are described using fractal geometry; 2) it is taken into account that the distribution of the electric field over the surfaces is characterized by the presence of strong discontinuities. The second of the indicated differences led to the use of Maxwell’s equations reduced to wave equations in the framework of the developed model. The developed model is recommended for use in the design of thin-film electromagnetic shields for microelectronics products protection from external and internal interference impact, as well as in the design of such products, in the design of radiophotonics products and theoretical evaluation of the optical and thermal properties of materials.

Rubia tinctorum L. roots are a valuable source of anthraquinones and other bioactive phytochemicals. In this study, nine hydrophilic deep eutectic solvents (DESs), based on choline chloride or tetrabutylammonium bromide, were evaluated as green extractants for the selective recovery of bioactive compounds. Their performance was compared with four conventional solvents (acetonitrile, methanol, ethanol-water, and water). Among DESs, choline chloride-lactic acid and choline chloride-malonic acid showed the highest extraction efficiency for gallic acid, caffeine, quercetin, alizarin, and purpurin. Extraction conditions were optimized using response surface methodology. The antioxidant, antimicrobial, and phytochemical profiles of the resulting extracts were comprehensively evaluated. GC-MS analysis revealed the presence of key metabolites including alizarin, rubiadin, purpurin, scillarenin, and fucosterol. The results demonstrate the potential of hydrophilic DESs as sustainable, efficient, and selective media for the extraction of biologically active compounds from plant materials.

The heat-transmitting capability, i.e., the ability to transfer heat flux with minimal losses, of thermosyphons and the prospects for using passive systems based on them for heat exchangers of various purposes, such as those for the utilization of heat from renewable energy sources and secondary energy resources (water basins, soil, groundwater, waste water and steam from industrial production, etc.) are considered. In small-scale power engineering, thermosyphons can be used to increase the potential of heat pumps that use heat from alternative sources. Passive heating/cooling systems ensure savings in the electricity required to power electric motors. Thermosyphons are easy to operate, do not require constant maintenance and can be effective intermediate links between heat sources and consumers, and are capable of maintaining a constant temperature of cooled objects. They can be used to organize the removal and transfer of heat outside a high-temperature environment. The design of a loop thermosyphon with a porous evaporator (LTSPE) and a condenser installed horizontally is presented. The article presents the results of experimental studies of a thermosyphon with two working fluids (freon R245fa and water). The temperature distribution and thermal resistances of the evaporator, condenser and thermosyphon as a whole are determined under different thermal loads. The effect of the cooling medium temperature on the heat-transmitting capability of the thermosyphon heated by a constant heat flux is analyzed. With an increase in the cooling medium temperature, the thermal resistance of the thermosyphon monotonically decreases. The studied device has a high heat-transmitting capability (up to 1.5 kW), a short start-up time, and a dynamic attainment of a steady-state mode when the load changes. The developed loop thermosyphons can be recommended for use in energy-saving systems, in particular in solar power engineering (thermal control of PV and PVT panels1); in combination with heat pumps – in trigeneration plants generating electricity, heat and cold; in thermostatic equipment for electric transport, electronic equipment and in other areas

The analysis of the operating features of closed-type electric heaters of the radiant tube type is performed. Based on the operating experience of the radiant tubes manufactured by “PromTermoSistema” LLC (Belarus), the key aspects affecting the durability of the heaters are shown. One of the main technical problems is the dense arrangement of heating elements (metal rods) in a small volume and the associated electrical breakdowns of electrically insulating ceramic inserts. Based on graph theory, a method is proposed for analyzing the commutation of heating elements with dense packing, which made it possible to find new rational commutation schemes. The method is based on constructing numbered graphs on the holes for heating rods in the ceramic element and finding the graph with the minimum weight. According to the meaning of constructing a graph, its weight is proportional to the maximum potential difference between the rods. The found commutation schemes reduce the maximum potential difference on ceramic insulators by 35–50 %, from 70 V to 35÷45 V, and the electric field strength from 10 kV/m to 5.0÷6.5 kV/m. This allows proportionally increasing the reliability and durability of heaters, reducing the probability of electrical breakdowns of ceramics.

Investigation of compression plasma flows impact on structure, phase, and elemental composition, as well as mechanical properties of Ti-6Al-4V titanium alloy with ZrN coating was carried out in this work. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, samples weight measurements, microhardness and tribological tests were used as investigation techniques. The findings showed that plasma impact led to the formation of a composite surface layer based on titanium alloy containing inclusions of undissolved ZrN coating. Growth of the absorbed energy density resulted in a decrease of zirconium and nitrogen concentration in the surface layer due to erosion. Formation of solid solutions on the basis of α-Ti and β-Ti was found in the layer analyzed by X-ray diffraction. Presence of nitrogen in a vacuum chamber as plasma generating gas led to the formation of TiN on the surface. Plasma impact resulted in decrease of ZrN/Ti-6Al-4V system microhardness and decrease of friction coefficient (at specific treatment regimes).