Machines. Technologies. Materials.
Vol. 15 (2021), Issue 2

Table of Contents

  • MACHINES

    • Energy and exergy losses analysis of back-pressure steam turbine from CHP plant

      pg(s) 42-45

      In this paper is analyzed back-pressure steam turbine which operates in CHP (Combined Heat and Power) plant from the aspect of energy and exergy losses. Produced turbine power, used for electricity generator drive equals 62548.77 kW, while the turbine mechanical loss is 1934.50 kW. Exergy analysis of the turbine shows that cumulative exergy loss is composed of two losses – mechanical loss and steam exergy loss. Steam exergy loss is additional loss which takes into account the state of the ambient in which turbine operates (unlike energy analysis which is independent of the ambient state). Change in the ambient temperature resulted with a change in turbine exergy efficiency and exergy loss. Ambient temperature change for 10 °C resulted with change in turbine exergy efficiency for less than 0.5 % on average, while the change in the turbine exergy loss (for the same temperature change) equals 266.21 kW on average.

  • TECHNOLOGIES

    • Development and analysis of normative teqchnique for designing the small sea port facilities

      pg(s) 46-48

      At present, with rapid growth in maritime transport, the issue of improving the quality and reducing the time of design of marine terminals, ports and related facilities comes to the forefront. To this end, it is necessary to perform design works which are of integrated nature and are distinguished by high level of automation. The problem can be solved by creating a highly efficient automated system of design based on modern methods of engineering analysis and modeling

    • Thermodynamic analysis of a 17.5 MW geothermal power plant operating with binary Organic Rankine Cycle

      pg(s) 49-52

      This article presents the thermodynamic analysis of a 17.5 MW gross electric geothermal power plant based on binary cycle technology with isobutane. The geothermal power plant comprises two separate closed loops: the geothermal fluid flows in one loop and the Organic Rankine Cycle (ORC) fluid flows in the second loop. The geothermal fluid is extracted from a depth of 2500-3000 m with a temperature of 170 °C and a pressure of 25 bar. Two production wells supply geothermal fluid (brine and steam) with a high fraction of noncondensable gases (NCG). A separator extracts NCG from the geothermal fluid. Isobutane is preheated and evaporated before entering the ORC turbine with a temperature of 133 °C and a pressure of 28 bar, where expands to the condenser pressure of 4 bar. Electricity is generated by a 17.5 MW axial ORC turbine and additionally by a 1.5 MW NCG turbine. The analysis revealed that the configuration without NCG turbine achieves a net efficiency of 12.73% and a net electric power of 13.68 MW while the configuration with NCG turbine achieves a net efficiency of 14.04% and a net electric power of 15.16 MW but with much higher CO2 emissions into the atmosphere.

    • The use of encapsulated sodium ferrate in wastewater treatment in the production of animal feed

      pg(s) 53-55

      The article presents the results of studies devoted to the use of ferrate in wastewater treatment in the production of animal feed. A method of wastewater treatment from various substances is proposed using the example of phenol. The possibility of obtaining of encapsulated sodium ferrate based on hexane, ethylcellulose and paraffin was revealed; its stability in air and in an alkaline solution was established. It has been proven that the reuse of industrial wastewater is a determining direction in preserving the health of animals and birds and the ecological cleanliness of the environment in general.

  • MATERIALS

    • Polypropylene-Polycarbonate composites with graphene oxide nanosheets: synthesis and characterization

      pg(s) 56-61

      Herein the effect of graphene oxide nanosheets (GOSs) on the thermo-mechanical stabilities of polypropylene (PP)/polycarbonate (PC), polymer blend nanocomposites (PNCs) fabricated via melt compounding has been explored. The comparison of properties of pure blend with PNCs, pointed out whether the mixing sequences have any effect on thermo-mechanical stabilities of PNCs. The PP/PC/GO nanocomposite exhibited an excellent increment in tensile strength and melting temperature as compared to the neat blend. In contrast, the PC/GO/PP nanocomposite, prepared by mixing the GOSs with PC first and then PC/GO with PP, has lower thermo-mechanical stability than PP/PC/GO. Interestingly, PP/GO/PC nanocomposite prepared by mixing the GOSs with PP first and then PP/GO with PC, showed the highest improvement in thermo-mechanical stability as compared to pure blend, PP/PC/GO, and PC/GO/PP. We attribute this trend of stabilities for PNCs due to the different extent of GOSs distributions within the polymer matrix. For PP/PC/GO, the GOSs were effectively dispersed in the PP phase due to low viscosity. In the case of PC/GO/PP, only small amount of GOSs was localized in PP and most of GOSs remain in PC phase. However, in case of PP/GO/PC, almost all GOSs were dispersed homogeneously in both phases resulting in a distinct increment of thermo-mechanical stabilities.

    • High-temperature layered composite with a metal matrix, reinforced with single-crystal sapphire fibers

      pg(s) 62-66

      Heat-resistant composites with a layered niobium-based matrix reinforced with single-crystal sapphire fibers have been obtained. The fibers were grown from the melt by the modified Stepanov method. The composites were prepared by solid-phase technology by diffusion welding of multilayer packages of foils of the Nb–0.1% C and aluminum alloy, interlaid with sapphire fibers in layers of a suspension mixture of Nb powder. The production of fibers, their structure and strength testing procedure are described. The formation of multilayer packets, the structure and results of bending strength tests of composites are presented

    • Preparation and characterization of BaTi0.89 Sn0.11O3 and Ba0.89Sn0.11TiO3

      pg(s) 67-68

      In recent years, interest in the application and use of materials for supercapacitors for electric vehicles has grown significantly. The advantage of capacitor ceramics over other dielectric materials for producing supercapacitors is its environmental friendliness and high economic efficiency. This paper presents the results of a study of capacitor ceramics doped with Sn at different locations of the modifier (tin) in BaSnTiO3 and BaTiSnO3 crystal lattice. The influence of modifiers in low-temperature sol-gel synthesis was studied. The samples were annealed at 1000°C. The resulting phases were identified by X-ray phase analysis. Microscopic analysis was also performed.

    • Investigation of solders surface tension in temperature range from melting point up to 673К

      pg(s) 69-72

      Solders are fusible metal alloys, used in industry to create permanent bond between metal surfaces. In order to achieve this, solders need to be heated above their melting point and used in liquid phase. Low melting temperature is essential from technological point of view, as well as for soldered components safety. Typical solders have Lead (Pb) аs а base component, having melting temperature of 600.6 K. Adding up to 60% of Tin (Sn) to the alloy, reduces melting temperature down to 456-461 K in average. Since 2006, RoHS regulation enforce industrial use of Lead-Free solders, typically having much higher melting temperature. However, Pb:Sn solders with up to 40% Sn still have their industrial applications, usually used for soldering Cu and Zn coated pipes while the 60% Sn containing solders are used for soldering of
      electrical cables.
      The achieving of these goals requires knowledge of liquid phase surface tension. Because of the difficulties, related to such measurement, the available data in literature are limited. The current report presents an equipment for measurement of the surface tension, based on the Wilhelmy plate method as well as the applied measurement procedure. The Wilhelmy method has relatively good stability. The contact angle also can be considered zero for the examined samples therefore correction coefficients are not required for the measurement. The results from measurement of Pb:Sn in ratio 40:60 and also in ratio 60:40 show that the oxidation in excess of Pb lowers the surface tension while for the case with excess of Sn, the oxidation lead to increase of the surface tension if compare with the surface tension obtained for the same solders but under non-oxidizing conditions. This could be attributed to formation in excess of PbO and SnO on the liquid surface of the corresponding solder

    • Post welding residual stress in P91 alloy steel

      pg(s) 73-78

      The chromium-molybdenum steel pipe P91 is widely used in the power plants construction, because they can withstand higher temperatures and operating pressures, in order to increase operating efficiency and output. This material has a complex microstructure which is extremely vulnerable to convert into Austenite form near the temperature for heat treatment. During the welding procedure should be very carefully, because otherwise the residual stress installed post welding will reach high values. A series of experimental studies was carried out, which has shown the development in the magnitude of transverse and longitudinal residual stresses and the values in both directions were determined. For but welded joints the residual stresses in the three direction were measured and the results are reported here. For measuring was used the hole drilling method through “measuring balls” or electrical strain gauge. Except the experiments the finite element method was used to determinate the value and the distribution of the residual stresses. The experimental and FEM results were compared between them and no discrepancy was found.

    • Assessment of toxic gas emissions from flammable building thermal insulation materials upon fire conditions

      pg(s) 79-83

      Smoke generated during a fire is a serious danger to people as a result of reduced air visibility, high temperature, toxicity and reduced oxygen content. In regard to victims, the inhalation of a mixture of toxic gases, which are formed as products of combustion, plays a key role. In the conditions of modern construction, and in order to improve energy efficiency in the buildings’ construction, various insulating materials are used. Along with the advantages of good insulation, there are also dangers from the behavior of insulating materials in an event of fire. The purpose of the present study is to assess the hazards and to study the composition of the gas mixture released during the combustion of various thermal insulating materials: glass wool, stone wool; expanded polystyrene; extruded polystyrene.

    • Magnetism in 2D van der Waals halide VI3

      pg(s) 84-85

      Magnetic van der Waals (vdW) materials composed of two-dimensional (2D) layers bonded to one another through weak interactions exhibit promising potentials for high-tech magnetic, magneto-electric, and magneto-optic applications in nanostructures. Due to their intrinsic magnetocrystalline anisotropy, several vdW magnets could be thinned down to nanoscale thickness, while still maintaining magnetism. Prominent examples of such materials are transition metal trihalides, in particular CrI3, a first atomically thin ferromagnet, realized in 2017.
      Recently, VI3 has been found to belong among 2D ferromagnets at temperatures below 50K. It is a semiconductor undergoing a subtle structural phase transition at 78K. Furthermore, its magnetic anisotropy exhibits rather unusual features. We have studied its properties by first principles calculations and reproduced the unusual magnetic anisotropy. Its properties have been linked to lattice distortions present at some of its low temperature phases.