Heat transfer for the boiling crisis in porous systems

In this paper we analized and investigated the heat exchange crisis of boiling in porous structures, applicable in thermal power plants. Then we describe the heat exchange processes mechanism and determined the ideal sizes and thicknesses of porous structures. The designed porous structures can be implemented in gas turbine’s nozzles and combustion chambers. From an environmental point of view, the consumption coolant liquid is reduced by ten times in comparison the standard flow system. It’s effectively to develop mesh structures to allow the extension of the critical loads and manage the surface border.

Optically Transparent and Highly Conductive Electrodes for Acousto-Optical Devices

The study was devoted to the creation of transparent electrodes based on highly conductive mesh structures. The analysis and reasonable choice of technological approaches to the production of such materials with a high Q factor (the ratio of transparency and electrical conductivity) were carried out. The developed manufacturing technology consists of the formation of grooves in a transparent substrate by photolithography methods, followed by reactive ion plasma etching and their metallization by chemical deposition using the silver mirror reaction. Experimental samples of a transparent electrode fabricated using this technology have a sheet resistance of about 0.1 Ω/sq with a light transmittance in the visible wavelength range of more than 60%.

The Electromagnetic Shielding of Optoelectronic Devices by Mesh Structures

In this work, the shielding properties of mesh structures with various cell sizes on a K108 glass substrate are studied. The transmission spectra of the samples were obtained in a frequency range from 1 GHz to 1620 THz. A comparison of the experimental transmission spectra with those obtained using several theoretical models, and a numerical calculation were carried out. The most optimal theoretical model used to describe the shielding properties of a mesh structure in the frequency range upper-bounded by a resonant frequency is the one-mode calculation model. Anti-reflection coatings were used to increase the transmission coefficient of the structures in the visible and near-IR spectral ranges. These mesh structures can be used to shield optoelectronic devices such as a video camera or a laser rangefinder from microwaves.

A novel approach of fabricating monodispersed spherical MoSiBTiC particles for additive manufacturing

It is very challenging to fabricate spherical refractory material powders for additive manufacturing (AM) because of their high melting points and complex compositions. In this study, a novel technique, freeze-dry pulsated orifice ejection method (FD-POEM), was developed to fabricate spherical MoSiBTiC particles without a melting process. Elemental nanopowders were dispersed in water to prepare a high-concentration slurry, which was subsequently extruded from an orifice by diaphragm vibration and frozen instantly in liquid nitrogen. After a freeze-drying process, spherical composite particles with arbitrary composition ratios were obtained. The FD-POEM particles had a narrow size range and uniform elemental distribution. Mesh structures were formed within the FD-POEM particles, which was attributed to the sublimation of ice crystals. Furthermore, owing to their spherical morphology, the FD-POEM particles had a low avalanche angle of 42.6°, exhibiting good flowability. Consequently, the combination of FD-POEM and additive manufacturing has great potential for developing complex refractory components used in industrial applications.

A Novel Approach of Fabricating Monodispersed Spherical MoSiBTiC Particles for Additive Manufacturing

It is very challenging to fabricate spherical refractory material powders for additive manufacturing (AM) because of their high melting points and complex compositions. In this study, a novel technique, freeze-dry pulsated orifice ejection method (FD-POEM), was developed to fabricate spherical MoSiBTiC particles without a melting process. Elemental nanopowders were dispersed in water to prepare a high-concentration slurry, which was subsequently extruded from an orifice by diaphragm vibration and frozen instantly in liquid nitrogen. After a freeze-drying process, spherical composite particles with arbitrary composition ratios were obtained. The FD-POEM particles had a narrow size range and uniform elemental distribution. Mesh structures were formed within the FD-POEM particles, which was attributed to the sublimation of ice crystals. Furthermore, owing to their spherical morphology, the FD-POEM particles had a low avalanche angle of 42.6°, exhibiting good flowability. Consequently, the combination of FD-POEM and additive manufacturing has great potential for developing complex refractory components used in industrial applications.

КОНСТРУКТИВНО-ТЕХНОЛОГІЧНІ ОСОБЛИВОСТІ ХВОСТО-ВИХ БАЛОК СІТЧАСТОГО ТИПУ З ПОЛІМЕРНИХ КОМПО-ЗИЦІЙНИХ МАТЕРІАЛІВ ВЕРТОЛЬОТІВ ТРАНСПОРТНОЇ КАТЕГОРІЇ

The analysis of the design and technological features of the tail boom (ТB) of a helicopter made of polymer composite materials (PCM) is carried out.Three structural and technological concepts are distinguished - semi-monocoque (reinforced metal structure), monocoque (three-layer structure) and mesh-type structure. The high weight and economic efficiency of mesh structures is shown, which allows them to be used in aerospace engineering. The physicomechanical characteristics of the network structures are estimated and their uniqueness is shown. The use of mesh structures can reduce the weight of the product by a factor of two or more.The stress-strain state (SSS) of the proposed tail boom design is determined. The analysis of methods for calculating the characteristics of the total SSS of conical mesh shells is carried out. The design of the tail boom is presented, the design diagram of the tail boom of the transport category rotorcraft is developed. A finite element model was created using the Siemens NX 7.5 system. The calculation of the stress-strain state (SSS) of the HC of the helicopter was carried out on the basis of the developed structural scheme using the Advanced Simulation module of the Siemens NX 7.5 system. The main zones of probable fatigue failure of tail booms are determined. Finite Element Analysis (FEA) provides a theoretical basis for design decisions.Shown is the effect of the type of technological process selected for the production of the tail boom on the strength of the HB structure. The stability of the characteristics of the PCM tail boom largely depends on the extent to which its design is suitable for the use of mechanized and automated production processes.A method for the manufacture of a helicopter tail boom from PCM by the automated winding method is proposed. A variant of computer modeling of the tail boom of a mesh structure made of PCM is shown.The automated winding technology can be recommended for implementation in the design of the composite tail boom of the Mi-2 and Mi-8 helicopters.

Determination of the possibility of manufacturing mesh structures using additive technologies

In comparison with conventional technologies, additive technologies are based on fundamentally different physical phenomena. One research direction is the determination of the marginal possibilities of complicating the shape of manufactured products. This article discusses the possibility of introducing mesh structures into the volume of a manufactured part, the possibility of manufacturing such structures without additional supporting elements and boundary conditions, i.e. the minimum thickness of the mesh and the largest length of the hanging surface. Another objective was to develop and test a methodology for designing and creating G-codes when developing mesh structures.