Machines. Technologies. Materials.
Vol. 15 (2021), Issue 8

Table of Contents

  • MACHINES

    • EGR operated engines process water equipment operational safety procedure

      pg(s) 291-293

      In this publication the wash water subsystem features of an exhaust gas recirculation (EGR) system of marine diesel engine are considered. In regard with the safety of the operation, a procedure for handling the wash water system of the EGR is proposed. The chemical reactions between the flue gas and the process water are observed. The wash water system components and their specifics related to the chemical reactivity are presented. The problems with the water impurities, pH value and the operation of the EGR system are highlighted. The engineering crew special precautions on safety on using caustic soda on board is considered. Recommendations are proposed.

    • Analytical and numerical analysis of shafts’ stress and strain states of the hydro-power unit

      pg(s) 294-298

      The paper presents both the analytical and numerical procedure for the analysis of the stress and strain states of the hydropower unit of the hydropower plant. Numerical analysis allows a comprehensive view of the states of stress and strain of the observed shaft. The analytical procedure is very difficult to apply to structural elements with complex geometry such as the shaft of a hydropower unit. Analytical analysis of stress and strain states serves to test only some of the results obtained on the basis of numerical analysis. A comparative analysis of stress and deflection values was performed on some characteristic shaft cross sections. Analytical determination of deflection, due to the complexity of the shaft construction, was performed on the basis of Mohr’s graph – analytical procedure. The numerical procedure is based on the application of the finite element method. The obtained results confirm the extremely good match of the results obtained by analytical and numerical procedures. Within the numerical analysis based on the given load and boundary conditions, ie. on the basis of the formed computational model of the shaft, the analysis of stress and strain, and displacement, was performed. The analysis of both normal and tangential stresses, as well as equivalent stresses according to the Von-Misses criterion, was performed. The places of maximum stresses are located. Therefore, it is concluded that the numerical analysis of the stress and strain state will give quality results if the computational model is well formed. This means that it is necessary to take into account all the discontinuities in the geometry of the shaft, which is characterized by a variable cross section. Certainly, there is no need to apply a very, very demanding analytical procedure for integrating the differential equation of an elastic line or a procedure based on Mohr’s graph – analytical procedure when calculating the shaft.

  • TECHNOLOGIES

    • Kinetic and equilibrium study of the CO2 adsorption on activated carbon

      pg(s) 299-302

      The presented research are concerned with the modelling of isotherms and chemical kinetics of mass transport for the CO2 adsorption on activated carbon, taking place in the fluidized and fixed bed. To determine the nature of CO2 binding under low-pressure conditions, adsorption complex and thermodynamic effects occurring during the process, four isothermal models were used: Langmuir, Freundlich, Temkin and Halsey. The evaluation of the factors affecting the course and rate of CO2 binding was based on four kinetic models, i.e. pseudo-first-order (PFO), pseudo-second-order (PSO), intraparticle diffusion (IPD) and the Elovich model. The validation of mathematical models showed that the linearized Freundlich and Halsey isotherms models are best suited to empirical data. In the case of process kinetics, the analysis showed that the non-linearized pseudo-first-order model (PFO) proved to be unrivalled in fitting to experimental data. The comparison of two types of tested beds suggested faster kinetics for a fluidized bed, while a larger amount of CO2 at equilibrium was adsorbed by the fixed bed.

    • Biosensor based on directly immobilized hemoglobin and myoglobin

      pg(s) 303-305

      Immobilization of proteins on a surface plasmon resonance (SPR) transducer is a delicate procedure since loss of protein bioactivity can occur upon contact with the untreated metal surface. Solution to the problem is the use of an immobilization matrix having a complex structure. In this paper we study the impact of direct immobilization of heme proteins (hemoglobin (Hb) and myoglobin (Mb)) on their bioactivity. We have used spin coating, for direct immobilization and matrix-assisted pulsed-laser evaporation (MAPLE) [1] for elaboration of the SPR biochip. The performance of both SPR chips – direct and MAPLE immobilized, was studied by SPR registration of the binding activity of Hb and Mb ligands with carbon monoxide (CO), carbon dioxide (CO2) and nitride oxide (NO). The experimental facts showed that direct immobilization of an intact molecule was achieved

    • Dynamic mesh adaption in shockwaves simulations

      pg(s) 306-308

      The goal of the article is to compare the accuracy and computational time of the shock wave simulations, using the stand ard, structured mesh and the dynamic mesh adaption. The coarse and fine mesh will be compared with the dynamically adapted mesh in terms of computational time and accuracy. Based on the results, histograms depicting computational time will be created. The simulation, on which those meshes will be examined will be a simple, two-dimensional oblique shock wave forming over a wedge inclined at 15°, with the Mach number at the domain inlet being equal to 2. The adaption will be based upon the pressure gradient criterion.

  • MATERIALS

    • Utrafine-grained structure and thermal stability of the two-phase titanium alloy VT8M-1

      pg(s) 309-310

      In this work, the method of backscattered electron diffraction (EBSD) and transmission electron microscopy (TEM) was used for microstructural analysis of the improved VT8M-1 alloy (Ti-5.7 Al-3.8 Mo-1.2 Zr-1.3 Sn) subjected to equal-channel angular pressing (ECAP) and rotary forging (RF). It was found that the process of globularization induced during deformation processing is regulated by the conventional boundary-splitting mechanism. It was shown that an orientation relation is established between the spheroidized a – and bphases. This result is achieved due to the high activity of dislocation sliding at the boundary of the a-and b-phases. The thermal stability of the VT8M-1 alloy with an ultrafine-grained (UFG) structure is s -term (up to 500 hours) annealing the UFG structure is thermally stable. The mechanical properties and the effect of annealing on the microstructure are discussed. It is shown that particles of the Ti-Zr-Si system are isolated at the interphase boundaries.

    • The methodology of functional modifiers choice for nanocomposites based on industrial thermoplastics

      pg(s) 311-315

      The methodological principles for the implementation of the concept of multilevel modification of polymer matrices by components with given energy parameters to obtain nanocomposites with a synergistic com-bination of performance characteristics have been developed.
      These principles based on:
      – established crystal-chemical prerequisites for the natural and synthetic carbon-, metal- and silicon-containing semi-finished products choice for the directed formation of active nanosized particles with given structural, morphological and energy parameters under optimal technological impact (mechanical and chemical, thermal, laser);
      – implementation of the conditions for the energetic compliance of nanomodifiers to the prevailing mechanism for the formation of the optimal structure of polymer, oligomer and blend matrices at various levels of organization – molecular, supramolecular and interphase;
      – creating the conditions for the reveal of the prevailing mechanisms of interphase physical and chemical interactions of components with the formation of boundary layers of the optimal structure, which deter-mine the mechanisms of destruction of products from nanocomposites under various operational factors impact;
      – achieving the conditions for the synergistic effect of structuring by using a complex of modifiers with a certain combination of parameters of dimensional, geometric and energy characteristics.

    • Investigation of the coalescence of twin coplanar semi-elliptical fatigue cracks in structural steel elements under cyclic loading

      pg(s) 316-318

      The solution to the scientific task of identifying the fundamental laws of surface cracks development during their coalescence in the elements of steel structures under cyclic loading is presented in this article. A simulation model of coalescence of identical coplanar surface cracks has been developed. The model considers the solution to two problems: substantiation of the crack geometry during coalescence, and obtaining calculation formulas for estimating the stress intensity factors along a series of saddle-shaped contours. Based on the definition of stress intensity factors for contours modeling the gradual propagation of cracks in the coalescence zone using the finite elements method, the proposed model was tested to compare the calculated durability with experimental data.

    • Decreasing pressure losses by applying drilling mud with nanoparticles

      pg(s) 319-322

      During mud circulation pressure losses occur in all sections of the wellbore: surface pipeline, inside drill string, drill bit and around drill string. The sum of the pressure losses calculated for each section is equal to the total pressure loss in the system, i.e. the pressure that is read on the manometer of the mud pump. The mud flow through annulus (between drill pipes/collars and open hole/casing) causes an increased pressure loss for the certain flow rate which increases the pressure exerted on the wellbore wall, so it is important to manage it. In this paper, the influence of SiO2 nanoparticles on the rheological properties of bentonite mud was examined. After tha t, for a typical wellbore construction and selected mud flow was calculated their influence on pressure losses in the area around drilling pipes and collars. The pressure losses were determined using the Bingham model which provides an easy way to obtain data of acceptable accuracy for the case of application in conventional vertical wells. The results indicate that the addition of SiO2 nanoparticles can reduce the pressure loss during mud circulation, in some cases by more than 50%.

    • Impact of chemical composition on tribological properties of AlxCoCrFeNi high-entropy alloys

      pg(s) 323-324

      High-entropy alloys were first extensively described in 2004 [1]. Despite the increasing scientific interest in these materials, there is still much to discover. The AlCoCrFeNi alloy is one of the most popular HEAs. Scientists often study the mechanical properties of this alloy and the effect of varying the different component contents on its properties [2,3]. There are also studies on the effects of alloying additives on structure and properties [4,5]. In this study, high-entropy alloys were obtained by induction melting. The influence of aluminium content and titanium addition on tribological properties of AlxCoCrFeNi alloy was tested. Furthermore, the alloys were characterised by X-ray diffraction (XRD), hardness, and microstructure examination. The occurring wear mechanisms and tribological properties of the tested high-entropy alloys were analysed and compared with the results obtained for C45 steel. The received results confirm the influence of Al content in AlxCoCrFeNi alloy and Ti addition on tribological properties

    • Operational characteristics of nanocomposite lubricants

      pg(s) 325-327

      The study of the structure and physicomechanical characteristics of carbon nanostructures, lubricants and cooling liquids was carried out by methods of scanning electron microscopy, atomic force microscopy, IR spectroscopy, physicomechanical and physicochemical analysis. Tribotechnical tests were carried out on a friction machine operating according to the “sphere – plane” scheme.The possibility of modifying various liquid media with nanosized carbon particles of various composition, structure, production technology, including those obtained by the method of self-propagating high-temperature synthesis, has been studied. The studies carried out made it possible to establish general trends in the implementation of the synergistic effect in liquid matrices differing in structure, polarity of macromolecules, and molecular weight.

    • Morphological study of rubber granules used in artificial turf systems with SEM and DSC methods

      pg(s) 328-330

      Rubber is different from other polymeric materials because it needs to be crosslinked or vulcanised and mixed with several additives like fillers to achieve its state. The recycled rubber materials presented as granules are rapidly used as infill material for different fields. One of the most important issues, especially in Albania is proving that these materials are recycled. One of the most important issues, especially in Albania is proving that these materials are recycled. Through the images provided by SEM we could study the microstructure of our samples. Also, after conducting an EDX spectrum analysis, we observed additives in the recyclable materials. The DSC methods analyses that will provide info regarding the composition in rubber granules. Thermal analysis is an essential technique to measure the temperature or time dependent response of physical and chemical changes that occur in materials.

    • Influence of the rate of cooling on the formation of non-equilibrium eutectics in preeutectic alloys of the AL-SI system

      pg(s) 331-333

      Computer experiments were carried out with a simulation model of alloy crystallization in this work. The model was preliminarily calibrated for alloys of the Al-Si system. The presence of a non-equilibrium eutectic in pre-eutectic alloys with a silicon content of 1.0% – 1.6% has been detected. The minimum cooling rates at which the formation of an eutectic in these alloys is possible have been determined.