Hydrodynamic Modes Research Articles

Friction regulation of laser textured PVA hydrogels against a titanium alloy

Hydrogels have exhibited extremely complex tribological behaviors. Although various physical mechanisms have been proposed to explain their tribological behaviors, it is still a challenge to develop convenient and efficient regulation methods for tribological behaviors. We propose micro-grooves with different depths and spacings prepared on the PVA hydrogels surface by ultraviolet laser texturing to provide an effective method for understanding the tribology of hydrogels. At the sliding velocity range of 0.085 mm/s < v less than 2.3 mm/s, the effect of interlocking and ploughing force between the direct contact interfaces are the dominant origins of friction. Frictional stress increases when the spacing of the micro-groove getting smaller as the frequency of interlocking getting higher. Interestingly, frictional stress doesn’t increase with increasing micro-groove depth. Once the velocity exceeds to 6.9 mm/s, all the micro-grooves begin to wear and fracture, and the results of the frictional test become inaccurate. Smooth hydrogels without any micro-grooves enter elasto–hydrodynamic transition at the lowest velocity, which have minimum friction stress. These results take us a step closer to deriving a more effective, accurate, and dependable guideline for sliding friction control in hydrogel applications.

Hydrodynamic and acoustic pressure fluctuations in water pipes due to an orifice: Comparison of measurements with Large Eddy Simulations

The present article investigates the turbulent wall pressure fluctuations due to flow through single-hole sharp-square-edged orifices (opening area ratios of 11%, 20% and 31%) in a water-filled pipe by means of measurements and incompressible Large Eddy Simulations (LES) for opening area ratios of 20% and 31%. The orifice plate thickness was half the orifice diameter. The static pressure measurements and simulations show that the vena-contracta factors of the orifices are dependent on Reynolds numbers, which is due to the finite thickness of the orifices. These LES simulations provide a good prediction of the near-field hydrodynamic wall pressure fluctuations, which dominate up to the first three pipe diameters downstream of the orifice. Upstream and far downstream wall pressure fluctuations are dominated by acoustic pressure fluctuations. The source of the radiated sound field was estimated from the surface integral of the fluctuations across the orifice in the LES. The sound field was calculated by implementing the sound source in a one dimensional acoustic model of the test section. The power spectrum density (PSD) of the wall pressure fluctuations for pipe Reynolds numbers varying from 4000 to 10000 collapsed when presented in dimensionless form, which uses the dynamic pressure in the orifice as reference pressure and the ratio of cross-sectional averaged orifice velocity and orifice diameter as characteristic frequency. In the inertial range of the turbulence a global decay of the pressure PSD and of the sound source show a power of the Strouhal number between −113 and −2.8. For higher frequencies the pressure fluctuations were dominated by acoustic resonances. For wider orifices the magnitude of these acoustic pressure fluctuations is predicted within a factor two by the acoustic model. For the narrowest orifice (opening ratio of 11%) the measured PSD of pressure fluctuations displays sharp peaks due to self-sustained oscillations (whistling). A simple power law of the sound source is not accurate due to the unstable hydrodynamic modes related to orifice thickness. However, using the simple model for the sound source the acoustic model predicts the acoustic pressure fluctuations reasonably well for all orifices. At low frequency one observes a peak in the PSD hydrodynamic wall-pressure fluctuations at one pipe diameter downstream of the orifice. It is probably due to an acoustically silent “edge-tone-like” sinusoidal self-sustained motion of the jet.

Перемішування металевих розплавів як засіб підвищення ефективності функціонування агрегатів «ківш – піч». Повідомлення 1. Способи та системи перемішування рідких сплавів у металургійних агрегатах (огляд)

Based on the global trends in the metallurgy, the features of the further development of technologies for the cast metal productions are predicted. At the same time, there is considered the constant tightening of requirements for energy and resource saving, environmental and work safety, with the simultaneous need to improve the quality of casting, widening the range of obtained alloys and products from them. Also, ensuring reliable operation and expanding the functional capabilities of “ladle – furnace” units has particular importance, since they provide the complex out-of-furnace processing of melts, including averaging on temperature and chemical composition (at alloying and modifying too), removal gases and non-metallic inclusions, etc. It is noted that for the successful implementation of the listed technological operations, “ladle – furnace” units are equipped with additional devices and systems for heating the melt, vacuuming, blowing with inert gas (argon) and electromagnetic stirring. A comparative analysis of different methods of liquid metal stirring (by gas blowing and under the action of an external alternating electromagnetic field) showed that electromagnetic stirring is more effective and appropriate, especially at manufacturing relatively small batches of high-quality and special alloys on metallurgical mini- mills. At that, the most common at metallurgical enterprises and among research developments are electromagnetic stirrers of travelling magnetic field.There are indicated that applications of such stirrers have certain limitations due to physical characteristics. It relates to the need (in most cases) to supply them with a low frequency, making changes to the design of operating metallurgical aggregates for installation of the stirrer, as well as with not always rational hydrodynamic modes of melt stirring.The requirements concerning the development and application of electromagnetic stirrers for “ladle – furnace” units were formulated. Such devices should be simpler in design and operation, ensuring their long-term reliable working at obtaining a wide range of high-quality alloys. Keywords: “ladle – furnace” unit, metallic melt, gas blowing, electromagnetic stirring.

On turbulent flow and aerodynamic noise of generic side-view mirror with cell-centred finite difference method

This paper investigates the turbulent flow and aerodynamic noise of a half-cylinder body mounted on a flat plate at using high-order cell-centred finite difference method with delayed detached-eddy simulation (DDES) and large-eddy simulation (LES). Transient flow patterns from the two simulations are found to be very different in consideration of the small-scale structures. The profiles of mean velocity, resolved turbulent kinetic energy and resolved Reynolds shear stress are found to be similar among all the simulations, indicating mean quantities are relatively insensitive to turbulence modelling and grid resolution. The power spectra density of the pressure fluctuations show that LES is more capable of resolving energies in high-frequency range than DDES. After computing the normalised wavenumber-frequency spectra of fluctuating pressure on the window, we further carried out the wavenumber-frequency decomposition to separate the acoustic and the hydrodynamic components from the pressure fluctuations. The energy distribution shows that the acoustic energy has a much slower decaying rate in the high-frequency range than the hydrodynamic energy. In addition, the space-averaged sound pressure levels of pressure fluctuations on the window indicate that the present simulation with a high-order method is able to improve the accuracy in predicting pressure spectra. Finally, we carry out proper orthogonal decomposition to extract the dominating features of the decomposed acoustic and hydrodynamic components of pressure fluctuation. Patterns of multi-scale turbulence in hydrodynamic modes and propagating wavefronts of cylinder shape in acoustic modes are identified. The present research indicates that a relatively coarse grid is still capable of resolving fluctuating quantities of energy-containing structures, and LES is suggested against DDES when near-wall aerodynamic noise is the main concern.

A versatile user-friendly electrochemical cell with three 3D-pen-printed electrodes in a tiny micropipette tip

This work describes a practical, portable and versatile electrochemical cell containing three-electrode integrated in a small disposable micropipette tip. The electrodes were manufactured using 3D pen and a commercial carbon black-polylactic acid filament and the tip-based cell was fabricated using alternative materials. The cell requires low sample volumes (10 μL) and may be operated with several commercial micropipettes (manual and electronic) that performs the aspiration of solution before or simultaneously to the electrochemical measurement, resulting in electroanalysis under static or flowing conditions, respectively. As proof-of-concept, measurements of catechol were performed in stationary and hydrodynamic mode, in which the sensitivity of the hydrodynamic was around five-fold greater when compared to the stationary method (47 vs 9 nA μmol−1 L), due to the faster mass transport of the analyte. Moreover, the proposed cell exhibited analytical parameters for catechol comparable with a commercial screen-printed electrode. The versatility of the cell was also demonstrated for square wave anodic stripping voltammetry in the presence of lead ions, in which the deposition (pre-concentration) step was performed during the solution aspiration controlled by an electronic pipette. The obtained LOD was 6-fold better than a conventional system for ASV (0.010 vs 0.059 μmol L-1). The analytical feasibility of the cell was demonstrated through the determination of catechol and lead in tap and ground water, being obtained recoveries close to 100%. The proposed cell and is cheaper (< US$ 0.10), smaller and more versatile than other tip-based and 3D-printed cells, being promising for on-site analyses and education purposes.

JUSTIFICATION OF A RATIONAL METHOD AND EQUIPMENT FOR DRYING HIGH-MOISTURE SEEDS OF MELONS

The main reason holding back the wide distribution of pumpkin, like some other crops, is the lack of quality seeds. The receipt and storage of seed is largely dependent on the methods and means of drying. When choosing a technology and means for drying pumpkin seeds, one must take into account their adhesion properties, that is, the tendency to form conglomerates under certain conditions, sticking to working bodies, etc. Drying equipment should ensure uniform drying throughout the entire volume of products with different moisture content, as well as a change in the main process parameters – temperature and drying agent feed rate, which will allow the use of differential drying modes. But in drying installations used for grain processing, it is practically impossible to organize a high-quality process due to the impossibility of using differentiated modes of drying seeds, as well as increased cohesive-adhesive properties of the pumpkin seed layer. A much greater effect is achieved by devices with active hydrodynamic modes, in particular, in a fluidized bed with its modifications: an aerial boiling, vibroboiling and aerovibroboiling bed. In order to improve the flowability of a layer of materials prone to sticking, sticking, the formation of channels in the material layer, agglomeration, at the initial stage of drying, along with vibration and aeration mixing, it is advisable to use additional mechanical mixing devices. The article proposes a fundamentally new concept of energy-saving drying of high-moisture seed materials, in particular pumpkin seeds, the drying process of which through specific morphological, thermophysical, increased cohesive-adhesive properties, the presence of residues of the surface film and fruit in the seed layer is the most energy-intensive. At the first stage in the process of filtration drying, in which the heated drying agent under the influence of pressure drops moves through the cellular structure of the gas-permeable material, the drying of the material also occurs due to a change in the state of aggregation of the available, mainly surface, moisture. At the second stage, when the seeds acquire discrete properties, drying occurs in the aerovibroboiling layer due to the developed phase contact and an increase in the convective diffusion rate, which contributes to an increase in the drying rate in general and allows the process to be carried out at the maximum permissible values of seed heating. To carry out research to determine the rational technological parameters of the process, a structural and technological scheme of a vibration unit has been developed and a prototype has been created, which sequentially implements the filtration and convective stages of drying pumpkin seeds.

Air entrained into viscous liquid by a disk: Confinement induced suppression of breakup

When a solid object falls into a bath of viscous liquid due to gravity with zero initial velocity, air can be entrained into the viscous liquid with the solid. We study such an air entrainment by a metal disk falling in the direction perpendicular to its axis in a confined space. We previously reported that the entrained air is extended and forms a thin sheet, which finally detaches from the disk with a topological change: The extended air breaks up into two parts, after which the lower part becomes a small bubble and the upper part starts retracting upwards [Phys. Rev. Fluids 3, 054004 (2018)]. In the present paper, we further confined the air sheet using thinner disks, to surprisingly find a complete suppression of a topological change: The entrained air detaches from the disk without breakup (i.e., without creating a small bubble) but with forming, instead of a sheet, an elliptic corn at the tip. The physical origin of the confinement induced suppression of breakup is discussed from the viewpoints of the inversion of curvature of an air-liquid interface and the movement of the contact line. Near the corn-forming detachment, three length scales characterizing the dynamics are all proportional to a single characteristic length as in the previous sheet-forming case, which leads to a fixed aspect ratio for the elliptic corn in the present case. The characteristic scale satisfies a simple scaling law, which is different from the previous sheet-forming case, and governs the self-similar dynamics near the detachment point. The present corn-forming case provides a remarkable scenario for the self-similar dynamics discussed in various fields such as statistical physics, applied mathematics, and hydrodynamic topology transitions.

Overview of recent experimental results from the ADITYA-U tokamak

Since the 2018 IAEA-FEC conference, in addition to expanding the parameter horizons of the ADITYA-U machine, emphasis has been given to dedicated experiments on inductively driven particle injection (IPI) for disruption studies, runaway electron (RE) dynamics and mitigation, plasma rotation reversal, radiative-improved modes using Ne and Ar injection, modulation of magneto–hydrodynamic modes, edge turbulence using periodic gas puffs and electrode biasing (E-B). Plasma parameters close to the design parameters of circular plasmas with H2 and D2 as fuel have been realized, and the shaped plasma operation has also been initiated. Consistent plasma discharges having I P ∼ 100–210 kA, t ∼ 300–400 ms, n e ∼ 3–6 × 1019 m−3, core T e ∼ 300–500 eV were achieved with a maximum B T of ∼1.5 T. The enhanced plasma parameters are the outcome of repeated cycles of baking (135 °C), followed by extensive wall conditioning, which includes pulsed glow discharge cleaning in H, He and Ar–H mixture, and lithiumization. A higher confinement time has been observed in D2 compared to H2 plasmas. Furthermore, shaped plasmas are attempted for the first time in ADITYA-U. A first of its kind inductively driven particle injection for disruption mitigation studies has been developed and operated. The injection of solid particles into the plasma core leads to a fast current quench. Two pulses of electron cyclotron resonance wave at 42 GHz are launched in a single discharge: one pulse is used for pre-ionization and the second for heating. In a novel approach, a positively biased electrode is used to confine REs after discharge termination. E-B is also used for controlling the rotation of drift-tearing modes by changing the plasma rotation. Cold pulse propagation and signatures of detachment are observed during the injection of short gas puffs. A correlation between the plasma toroidal rotation and the total radiated power has been observed with neon gas injection-induced improved confinement modes.

Surface pressure spectrum variation with Mach number on a CD airfoil

The surface pressure spectrum characteristics are studied on a Controlled Diffusion airfoil at varying Mach numbers and a fixed Reynolds number. Compressible large eddy simulation datasets have been used for this analysis. The study focusses on the noise generation mechanism and the source locations responsible for it. A mid-high frequency hump is observed for the higher Mach number cases in the pressure spectrum and the amplitude of this observed hump increases with Mach number. To investigate the cause of this hump, different hydrodynamic and acoustic pressure modes traveling at specific speeds are obtained by a wavenumber–frequency decomposition. The acoustic component originating from the separation bubble region near the leading edge is found to be responsible for the hump in the pressure spectrum. The interaction of hydrodynamic and acoustic waves also plays a significant role in the appearance of the hump in the spectrum. There is also an increase in the amplitude of the high frequency region in the acoustic spectrum as we go towards the trailing edge for higher Mach number which can be attributed to an increase in turbulent fluctuation amplitude in the leading edge region. Furthermore, stability analysis has been performed on one-dimensional mean boundary-layer profiles. The higher reverse velocity in the separation bubble with increasing Mach number seems to be causing higher growth rates of instabilities, ultimately resulting in the significant surface spectrum variations. The directivity in the farfield also confirms a significant contribution of the hump in the spectrum in the overall sound pressure level.

On the compressible biglobal stability of the mean flow motion in porous channels

This work relies on a compressible biglobal stability approach to describe the wave dynamics in a planar rocket chamber modeled as a porous channel. At first, the effectiveness of the compressible formulation is demonstrated by reproducing, in the absence of a mean flow, the Helmholtz frequencies and mode shapes. Next, the unsteady vorticity fluctuations, which intensify near the walls, are shown to be consistent with those associated with parietal vortex shedding. In this context, the penetration depth of vorticoacoustic waves is found to be strongly dependent on the penetration number. The latter gauges the cubic power of the injection speed to the product of kinematic viscosity, chamber half-height, and frequency squared. As for the strictly hydrodynamic modes, they seem to develop at the porous walls and grow in the core region, where the mean flow velocity is most appreciable. The ensuing modal analysis enables us to predict both longitudinal and transverse modes for several test cases, thus illustrating the tendency of hydrodynamic modes to intensify at higher injection speeds and longer chambers. Furthermore, by repeating the analysis with an active mean flow, one finds that successive increases in the injection speed gradually reduce the predicted frequencies relative to the eigenmodes obtained in a quiescent medium. Finally, recognizing that the spectral analysis is capable of recovering both longitudinal and transverse modes induced by acoustic and hydrodynamic disturbances, their coupled interactions, which often lead to specifically amplified frequencies in static tests, are robustly captured, namely, without resorting to any particular wave decomposition.

Data-driven and physical property-based hydro-acoustic mode decomposition

A data-driven and physical property-based hydrodynamic and acoustic mode decomposition method combining dynamic mode decomposition and Helmholtz decomposition is proposed. It allows decomposition and fast prediction of hydrodynamic and acoustic components of the flow field. The method is tested by a two-dimensional subsonic open cavity flow and a supersonic cold jet, and the hydrodynamic and acoustic features are revealed. For the cavity flow, it is found that the acoustic velocity inside the cavity is composed of several pairs of standing waves. The propagating trajectory of the acoustic waves in the cavity is well captured. The dynamic relation between the hydrodynamic and acoustic motion is investigated. For the supersonic jet, the method successfully identifies the screech in the far field and the “trapped wave” within the potential core.

The breakdown of magneto-hydrodynamics near AdS2 fixed point and energy diffusion bound

We investigate the breakdown of magneto-hydrodynamics at low temperature (T) with black holes whose extremal geometry is AdS2×R2. The breakdown is identified by the equilibration scales (ωeq, keq) defined as the collision point between the diffusive hydrodynamic mode and the longest-lived non-hydrodynamic mode. We show (ωeq, keq) at low T is determined by the diffusion constant D and the scaling dimension ∆(0) of an infra-red operator: ωeq = 2πT∆(0), {k}_{mathrm{eq}}^2 = ωeq/D, where ∆(0) = 1 in the presence of magnetic fields. For the purpose of comparison, we have analytically shown ∆(0) = 2 for the axion model independent of the translational symmetry breaking pattern (explicit or spontaneous), which is complementary to previous numerical results. Our results support the conjectured universal upper bound of the energy diffusion Dle {omega}_{mathrm{eq}}/{k}_{mathrm{eq}}^2:= {v}_{mathrm{eq}}^2{tau}_{mathrm{eq}} where veq := ωeq/keq and τeq := {omega}_{mathrm{eq}}^{-1} are the velocity and the timescale associated to equilibration, implying that the breakdown of hydrodynamics sets the upper bound of the diffusion constant D at low T.

Electrooptic, pyroelectric and dielectric spectroscopic studies of nematic and twist bend nematic phases of achiral hockey-shaped bent-core liquid crystal

Experimental and theoretical investigations of the twist-bend nematic (NTB) phase in liquid crystals have recently received significant attention for reasons of unusual and interesting characteristics of the NTB. Though NTB was predicted to exist for rigid bent-core LCs by Ivan Dozov in 2001, nevertheless it has unambiguously been proven to exist only in a few bent-core systems so far. Here the characteristics of both the nematic (N) and NTB phases are investigated for a hockey shaped achiral rigid bent-core LC, called BCI, in planar and homeotropic aligned cells, using polarizing optical microscopy, electro-optics, pyroelectricity and wide band dielectric spectroscopy. Spontaneous polarization measured for a bias field of 2.2 V/μm of a chiral domain using the pyroelectric effect is found to be only ∼5 nC/cm2. A measurement of the spontaneous polarization using pyroelectricity in general is unaffected by the sample’s dc conductivity except when its conductance dominates the admittance. As helix of NTB is partially unwound by the field, results lead to the identification of NTB as polar and chiral. The first and the second harmonics of the applied field are observed of higher amplitudes in NTB and N phases, respectively. The hockey-shaped bent-core system exhibits a large negative dielectric anisotropy over a wide range of temperatures than observed for any other compound so far. The large negative dielectric anisotropy is the highly desirable characteristic parameter of the NTB for exploring the field induced phases at relatively lower field strengths. The orientational order parameter characteristically jumps at the N-NTB transition temperature. The complex dielectric permittivity is measured as a function of frequency in the range 1 Hz to 10 MHz, the analysis of results reveales two collective modes in the dielectric spectra. Amplitude of the lower frequency mode is much higher than of higher frequency, former is assigned to the hydrodynamic mode q=qzz^ with z-dependent rotation of the heloconical director n^(r), this in turn involves compression and dilation of the pseudo-layers. The higher frequency mode corresponds to fluctuations of the tilt director and closer to the transition temperature, it exhibits a typical soft mode characteristic feature.

Self-induced hydrodynamic coil-stretch transition of active polymers.

We analyze the conformational dynamics and statistical properties of an active polymer model. The polymer is described as a freely jointed bead-rod chain subject to stochastic active force dipoles that act on the suspending solvent where they drive long-ranged fluid flows. Using Langevin simulations of isolated chains in unconfined domains, we show how the coupling of active flows with polymer conformations leads to emergent dynamics. Systems with contractile dipoles behave similarly to passive Brownian chains with enhanced fluctuations due to dipolar flows. In systems with extensile dipoles, however, our simulations uncover an active coil-stretch transition whereby the polymer spontaneously unfolds and stretches out in its own self-induced hydrodynamic flow, and we characterize this transition in terms of a dimensionless activity parameter comparing active dipolar forces to thermal fluctuations. We discuss our findings in the context of the classic coil-stretch transition of passive polymers in extensional flows and complement our simulations with a simple kinetic model for an active trimer.

Hydrodynamic effect of technological lubrication and friction modes formation at sheet rolling

One of the main engineering industries is the processing of metals by pressure. Its purpose is the formation of products from metal blanks of simple forms. An important role in this case belongs to the technology of sheet rolling. The solution of issues related to the choice of optimal modes of sheet rolling is relevant for specialists in the field under consideration. The process of rolling metal products is special, since the contact stresses can exceed the deformation resistance of rolled metal by several times. The tasks of predicting the quality of products, taking into account the prevention of sheet metal continuity defects, as well as the study of technological operations reliability of rolling process are associated with the solution of industrial and scientific problems in this area. Domestic and foreign researchers have noted a significant influence of external friction in the deformation center on the technological parameters of rolling process and quality of the resulting metal products. It is known that rolling is impossible without external friction between metal and roll. The reduction of friction provides an opportunity to increase the economic indicators of sheet rolling, and the rolling production technology itself has significant opportunities for further improvement. Technology of sheet rolling in the conditions of hydrodynamic friction mode allows modeling of friction conditions in the deformation zone. Taking into account the hydrodynamic effect of lubrication allows us to assess the influence of technological factors on the conditions of contact friction during metal pressure treatment and to control the rolling process. Regularities of the flow of liquid Newtonian lubricant are investigated, taking into account features of the deformation zone geometry during sheet rolling. Pumping capacity of the lubricating wedge during rolling is determined, which allows us to explain the regularities of lubrication influence on friction conditions. As an example, the results of calculation of the lubricant pressure depending on the rolling speed are presented. The rolling speeds that provide a liquid friction mode are given. The obtained relations allow us to estimate the influence of contact friction on technological parameters of sheet rolling and can be used in technological calculations of this process

Unconventional relaxation of hydrodynamic modes in anharmonic chains under strong pressure fluctuations

We develop an effective numerical scheme to capture hydrodynamic (HD) modes in general classical anharmonic chains. This scheme is based on the HD theory suggested by Ernst–Hauge–van Leeuwen, which takes full role of pressure fluctuations into account. With this scheme we show that the traditional pictures given by the current nonlinear fluctuating HD theory are valid only when the system’s pressure is zero and the pressure fluctuations are weak. For nonvanishing pressure, the HD modes can, however, respond to small and large pressure fluctuations and relax in some distinct manners. Our results shed new light on understanding thermal transport from the perspective of HD theory.

РЕАЛИЗАЦИЯ МЕХАНИЗМА ИЗБИРАТЕЛЬНОГО ПЕРЕНОСА В ПОДВИЖНЫХ СОПРЯЖЕНИЯХ СИЛОВЫХ ПЕРЕДАЧ ПРИ ЭКСПЛУАТАЦИИ СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН

Searching for new effective ways of increasing the wear resistance of power transmissions and improving their durability, the authors propose a device for enriching the lubrication system of power transmissions with copper-alloying elements. The tribochemical processes have been studied and the components of the lubricating composition have been selected to provide for the self-organized selective transfer in the “steel-steel” friction couples accompanied by the formation of a servovit film. The authors developed a utility model for enriching the lubricating system oil with copper-alloying elements for power transmission. For testing the effectiveness of the proposed additive and the method of forming the servovit film during operation, a roller test bench was used. It provided for synchronous measurement of the wear rate and the friction force moment during the whole experiment without disconnecting the friction zone. The friction zone (test contact) was formed by the cyclic surfaces of a roller with a diameter of 70.0 ± 0.1 mm made of steel 45 (HRs 50) and a homogenized pad with a radius of 35.0 ± 0.1 mm and dimensions (plan view) of 2.01 mm (along the sliding line) and 7.27 mm (across the sliding line). The friction area was 0.1461 cm2. A set of normal forces: 730; 925; and 1130 N – was experimentally determined to ensure that there was no seizure. The shaft speed of 100 min-1 (a linear velocity of 0.37 m) was experimentally chosen under the condition of guaranteed absence of the hydrodynamic lubrication mode. The presented method of cladding additive production is easily implemented in the transmission units and also prevents the sedimentary instability of the lubricating composition. The device for enriching the lubricating system oil with copper alloying elements in the process of operation provides for a stable and self-organized mode of selective transfer. The results of tribological studies have shown the high efficiency of the cladding additive – the wear rate in the range of the normal force of 720 to 1130 N has reduced in 2.8…7 times.

Technology for Porous Ammonium Nitrate Production: Analysis of Drying Machines’ Operating Modes

The article is devoted to the development of the technological principlesregarding thefinal drying process of the porous ammonium nitrate (PAN) granules in multistage gravitational shelf dryers. The data on the dryer’s optimal technological operatingmodes are obtained. PAN samples are studied; the regularity of the change in the porous structure of the granule depending on the hydrodynamic and thermodynamic conditions of the dryer is established. Experimental data obtained during the research will be used to create a methodology for the engineering calculation of gravitational shelf dryers.The data for calculating the residence time of particles in the dryer under various hydrodynamic operating modes are obtained. Moreover, the data about the optimal operating conditions of the drying machines at the final drying stage will be used to improve the technology to form porous granules from ordinary ammonium nitrate.

Исследование износостойкости радиального подшипника с полимерным покрытием, работающего на микрополярном смазочном материале

The article is devoted to one of the important problems of increasing the wear resistance of tribosystems by applying an antifriction polymer composite coating containing a groove that operates in a hydrodynamic mode to the tribocontact surface. Based on the equation of the flow of truly viscous liquid for a «thin layer» and the continuity equation, a self-similar solution is found taking into account the groove and without taking into account the groove, as a result, the velocity and pressure fields in the groove and on the surface of the polymer antifriction composite coating are determined, as well as the load capacity and friction force allowing to determine the increase in wear resistance; an increase in duration of the hydrodynamic regime. The results of numerical analysis of the obtained theoretical calculation models and experimental evaluation of the proposed design are also presented in order to verify and confirm the effectiveness of the obtained theoretical models.

Research and results of mathematical modeling of block ion-exchange water treatment plants operating modes and regeneration

The problem of water treatment at thermal power plants using ion-exchange technologies is a multi-parameter task. Mathematical modeling is essential for research and optimization of ion exchange technology. The analysis of hydrodynamic processes during the operation of ion-exchange filters was carried out according to the developed mathematical model. Also, a physicochemical analysis of the composition of the water treatment plant solutions under real conditions was carried out. It is shown that in the cationite and anionite filters, the flow movement occurs mainly in a mixed hydrodynamic mode. This mode of regeneration and the filter design do not allow achieving the minimum consumption of the reagent for regeneration, the minimum volume of wastewater and the maximum output of demineralized water. The mixed mode of the anion exchange filter operation allows division of the outgoing solution flow into fractions, which can be successfully used in the TPP water cycle.