Volumetric Losses Research Articles

Effect of Electrical Current on Sliding Friction and Wear Mechanisms in a-C and ta-C Amorphous Carbon Coatings

This study investigates the sliding wear behaviour of amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) coatings, two forms of diamond-like carbon (DLC) coatings, against SAE 52100 steel using a modified ball-on-disk tribometer with applied electrical currents ranging from 100 mA to 1800 mA. It focuses on the variations in sliding friction and wear characteristics of these coatings as electrical currents increase under constant load and speed conditions. The a-C coatings exhibited lower coefficient of friction (COF) values and reduced volumetric wear losses up to 1500 mA, while ta-C coatings studied displayed higher wear, similar to uncoated M2 steel, at 300 mA with degradation occurring at low currents, resulting in failure due to severe oxidational wear. The a-C coatings showed no significant electrical damage at these currents. Raman spectroscopy revealed structural changes on the wear tracks of sp2-rich a-C coatings, specifically the formation of graphene layers. In comparison, the wear tracks of sp3-rich ta-C coatings did not display such transformation under the conditions studied. The graphene coverage on the surfaces of the a-C coatings increased with the increase in the current as revealed by the Raman intensity maps of 2D peaks and this increase was accompanied by a higher defect density in the graphene. The low COF of graphene-covered a-C surfaces was consistent with the proposed mechanisms of moisture adsorption. However, at currents exceeding 900 mA, surface temperatures of a-C coatings exceeded 100 °C, impairing graphene’s ability to maintain low friction, resulting in an increased COF.

A multi-directional redundant 3D-LPT system for ship–flight–deck wind interactions

In the past years, volumetric velocimetry measurements with helium-filled soap bubbles as tracer particles have been introduced in wind tunnel experiments and performed at large-scale, enabling the study of complex body aerodynamics. A limiting factor is identified in the field of wind engineering, where the flow around ships is frequently investigated. Considering multiple wind directions, the optical access for illumination and 3D imaging rapidly erodes the measurement regions due to shadows and incomplete triangulation. This work formalizes the concepts of volumetric losses and camera redundancy, and examines the performance of multi-directional illumination and imaging for monolithic and partitioned modes. The work is corroborated by experiments around a representative ship model. The study shows that a redundant system of cameras yields the largest measurement volume when partitioned into subsystems. The 3D measurements employing two illumination directions and seven cameras, yield the time-averaged velocity field around the ship. Regions of flow separation and recirculation are revealed, as well as sets of counter-rotating vortices in several stations from the ship bow to the flight–deck. The unsteady regime at the flight–deck is examined by proper orthogonal decomposition, indicating that the technique is suited for the analysis of large-scale unsteady flow features.

Analysis of the factors affecting erosion in the beach-dune system of Guardamar del Segura, Spain

Dune systems have recently become fundamental natural solutions for the protection of the coast. The study of its morphodynamic features in storm situations is well documented in the literature. However, the morphological behaviour of these ecosystems when they are artificially modified by humans is still not adequately known. In this study, the morphological parameters of the restored dunes of Viveros Beach in Guardamar del Segura, Spain, are analysed. For this, a profile study was carried out using digital elevation models (DEM). In addition, the waves and incident storms are studied and, finally, a statistical analysis of the different variables that define the three dune zones is conducted. Results show that during periods of increased wave intensity and duration (2016–2017 and 2017–2020), there is correspondingly greater erosion in the dune. Additionally, the slope and the height of the dune present a strong correlation with changes in its volume. Greater volumetric losses occur the greater the slope of the foredune and the dune height. This situation occurs especially in the northernmost area, located next to the breakwater at the mouth of Segura River (Zone 1), where they reach up to 53° and 10.24 m, respectively. A better understanding of these factors provides coastal managers with effective tools for designing new dune landforms or conserving existing ones.

Investigation of the effects of radial clearance on the screw conveyor performances for different inclinations

Screw conveyors are widely used for bulk material transportation. This study investigates the critical role of radial clearance, the gap between the screw and the conveyor body, on performance across various inclination angles. The Discrete Element Method (DEM) is employed to analyze the effects of different radial clearances on conveyor performance for concrete aggregate and sand as bulk materials. Volumetric efficiencies and capacity losses serve as key performance indicators, quantitatively assessed for each radial clearance and inclination combination. Experimental validation is conducted to corroborate the findings. In the study, the optimal radial clearance was identified as 1.5 to 3 times of the particle size. This optimal clearance minimizes the material jamming and increases the performance for screw conveyors with different inclinations and bulk material types as a result.

Citizen science monitoring of beach and dune erosion during Hurricane Fiona

ABSTRACT Hurricane Fiona made landfall as an extra-tropical storm along the north shore of Prince Edward Island (PEI), Canada, in October 2022. The state of the beach and dune immediately before and after the storm was captured through the Coastie citizen science beach and dune photo monitoring initiative, as part of the global CoastSnap Community Beach Monitoring program. Coastie monitoring sites within Prince Edward Island National Park (PEINP) revealed extensive dune scarping, capturing a 12–17 m retreat of the foredune at Brackley and Cavendish Beaches. Using foredune scarp and post-storm shoreline positions, volumetric losses between 28 and 76 m3 m−1 are estimated from profiles located within the first 150 m of the stations. The average horizontal position of the projected foredune scarp position was within 2.8 m of the position identified from high accuracy unoccupied aerial system (UAS) surveys, corresponding to a mean absolute difference of 15.3 m3 m−1 or 45.3% for dune volume changes estimated from the images. Continued monitoring will yield further improvements to the volume loss estimation methodology, and insight on the timing and mechanisms of beach and dune recovery.

Modeling and experimental validation of twin lip balanced vane pump considering micromotions, contact mechanics, and lubricating interfaces

This paper presents a model formulation for balanced twin lip vane pumps and an experimental activity to validate the model. The simulation model begins with a geometrical module that preprocesses the CAD drawings of a given unit. The model then performs a fluid dynamic analysis using a lumped-parameter formulation to solve for the pressures inside properly defined control volumes within the unit. The fluid dynamic model is solved simultaneously with a motion module that evaluates the planar motions of the vanes using Newton’s law of motion and with a lubricating interface solver based on the Reynolds equation. Contact dynamics formulations and elastohydrodynamic relations are applied at the vane locations in contact with the cam ring. The comparison with experimental results highlights a good match in volumetric and hydromechanical efficiencies. The measured outlet pressure ripple matches the simulated one for all tested speeds and pressures. The paper also shows a breakdown of the distribution of volumetric and power losses arising from various components of the machine. The proposed methodology is computationally inexpensive, so it can be used in future design and optimization studies aimed at improving the performance of such units.

Influence of Friction Stir Additive Manufacturing Parameters on Dry Friction and Wear Properties of Al-Mg-Si Alloy's Built Surfaces Fabricated by Sheet Lamination

Abstract In this article, friction-stir additive manufacturing, a solid-state process for rapid fabrication of large components, is employed to investigate laminated Al-Mg-Si alloy blocks. The study delves into microstructural changes, hardness distribution, and wear behavior on two distinct surfaces using various parameters such as rotational speed (800 and 1200 rpm), traverse speed (41 and 82 mm/min), and a 50% pin overlap for block fabrication. Macrographs demonstrate the influence of adjacent toolpath overlap on layer integrity through interfacial mixing and consolidation of plastically deformed material. Within the overall stirred zone, re-stirring effects lead to refined grain formation and the dissolution of Mg2Si precipitates, resulting in an uneven micro-hardness distribution due to varying thermal cycles. Notably, specimens with a traverse speed of 41 mm/min exhibit reduced wear loss, attributed to microstructural changes that enhance resistance to plastic deformation during sliding, thereby improving tribolayer stability. This enhancement is attributed to increased hardness arising from refined grains and the strain hardening effect. Interestingly, the study finds that the horizontal surface of the fabricated blocks displays superior wear resistance compared to the vertical surface, due to the more homogeneous microstructure in individual layers. Further analysis using FESEM and EDS unveils the presence of glaze layers, oxide films, galling surfaces, grooving, trimming impacts, ploughing marks, and the accumulation of wear debris within wide pits and on worn-out pin surfaces. Scar morphology reveals that both abrasive and adhesive wear mechanisms contribute to volumetric losses in the specimens.

Effective Lewis number and burning speed for flames propagating in small-scale spatio-temporal periodic flows

Propagation of premixed flames having thick reaction zones in rapidly-varying, small-scale, zero-mean, spatio-temporal periodic flows is considered. Techniques of large activation energy asymptotics and homogenization theory are used to determine the effective Lewis number Leeff and the effective burning speed ratio ST/SL, which are influenced by the flow through flow-enhanced diffusion. The resultant effective diffusivity matrix is, in general, neither a scalar nor a diagonal matrix and therefore induces anisotropic effects on the propagation of multi-dimensional flames. As the flow Peclet number Pe becomes large, the flow-enhanced fuel diffusion coefficient and the thermal diffusivity behave respectively like (PeLe)σ and Peσ, where Le is the Lewis number and σ≤2 is a constant which depends on the flow and the direction of flame propagation. The maximal value σ=2 is achieved for steady, unidirectional, spatially periodic shear flows, while for steady two-dimensional square vortices, we have σ=1/2. In general, the constant σ is determined by solving a linear partial differential equation. The scaling laws for the diffusion coefficients lead to corresponding scaling laws for the effective Lewis number and the effective burning speed ratio of the form Leeff≃Le1−σ and ST/SL∼(Pe/Le)σ/2. Effects of thermal expansion and volumetric heat loss on the flame are also briefly discussed. In particular, it is shown that the quenching limit is enlarged by a factor 1/Leσ for Le<1 and diminished by the same factor for Le>1, due to the flow-enhanced diffusion. The potential implications of the results to better understand turbulent combustion are discussed. A special emphasis is placed on the dependence of the flame on Le in the presence of high-intensity, small-scale flows. In particular, it is shown that this dependence is intimately linked to the flow through Taylor-dispersion like enhanced diffusion, rather than through the traditional molecular diffusion coupled with curvature effects. The flow-dependent effective Lewis number identified may also provide an explanation to the peculiar experimental observation that turbulence appears to facilitate ignition in Le>1 mixtures and to inhibit it in Le<1 mixtures. Novelty and significance statementAn original study, combining asymptotic analysis and homogenization theory, is applied to describe flame propagation in small-scale, spatio-temporal periodic flow fields. Scaling laws are derived for the effective burning speed and the effective Lewis number for high-intensity small-scale flows, which are useful to better understand the behaviour of turbulent premixed flames in the distributed reaction zone regime. The formula for the flow-dependent effective Lewis number identified herein may explain the peculiar experimental observation that turbulence appears to facilitate ignition in Le>1 mixtures and to inhibit it in Le<1 mixtures. The high-intensity small-scale flows are shown to increase the quenching limit due to volumetric heat losses in Le<1 mixtures and decrease it in Le>1 mixtures

Modeling of 2D self-drifting flame-balls in Hele-Shaw cells

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front are interpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists. Novelty and significance statementThe existence and limits of self-propagating 2D flame-balls have been substantiated theoretically for the first time. They have been investigated analytically, displaying the crucial role of heat losses. The regime arises in praxis in thin enclosures such as Hele-Shaw cells. The design of flame arresters may well be influenced by these findings.

Characteristics and Potential Neural Substrates of Encoding and Retrieval During Memory Binding in Amnestic Mild Cognitive Impairment.

Whether encoding or retrieval failure contributes to memory binding deficit in amnestic mild cognitive impairment (aMCI) has not been elucidated. Also, the potential brain structural substrates of memory binding remained undiscovered. To investigate the characteristics and brain atrophy pattern of encoding and retrieval performance during memory binding in aMCI. Forty-three individuals with aMCI and 37 cognitively normal controls were recruited. The Memory Binding Test (MBT) was used to measure memory binding performance. The immediate and delayed memory binding indices were computed by using the free and cued paired recall scores. Partial correlation analysis was performed to map the relationship between regional gray matter volume and memory binding performance. The memory binding performance in the learning and retrieval phases was worse in the aMCI group than in the control group (F = 22.33 to 52.16, all p < 0.001). The immediate and delayed memory binding index in the aMCI group was lower than that in the control group (p < 0.05). The gray matter volume of the left inferior temporal gyrus was positively correlated with memory binding test scores (r = 0.49 to 0.61, p < 0.05) as well as the immediate (r = 0.39, p < 0.05) and delayed memory binding index (r = 0.42, p < 0.05) in the aMCI group. aMCI may be primarily characterized by a deficit in encoding phase during the controlled learning process. Volumetric losses in the left inferior temporal gyrus may contribute to encoding failure.

Enhancing ion extraction with an inverse sheath in negative hydrogen ion sources for NBI heating

Negative hydrogen ion (H−) sources employed in neutral beam injection (NBI) systems are subject to extraction efficiency issues due to the considerable volumetric losses of negative hydrogen ions. Here, we propose to improve the H− extraction by activating an alternative sheath mode, the electronegative inverse sheath, in front of the H− production surface, which features zero sheath acceleration for H− with a negative sheath potential opposite to the classic sheath. With the inverse sheath activated, the produced H− exhibits smaller gyration, a shorter transport path, less destructive collisions, and therefore higher extraction probability than the commonly believed space-charge-limited (SCL) sheath. Formation of the proposed electronegative inverse sheath and the SCL sheath near the H–-emitting surface is investigated by the continuum kinetic simulation. Dedicated theoretical analyses are also performed to characterize the electronegative inverse sheath properties, which qualitatively agree with the simulation results. We further propose that the transition between the two sheath modes can be realized by tuning the cold ion generation near the emissive boundary. The electronegative inverse sheath is always coupled with a plasma consisting of only hydrogen ions with approximately zero electron concentration, which is reminiscent of the ion–ion plasma reported in previous NBI experiments.

METHODS AND MEANS OF DIAGNOSING PUMPS AND HYDRAULIC MOTORS BY EFFICIENCY

To determine the technical condition of the elements of hydraulic drives during exploitation, it is proposed to choose a control method that provides an effective assessment at the lowest cost and allows you to determine those parameters, the change of which during exploitation leads to maximum losses. In addition, the selected parameters should allow to control the technical condition of the hydraulic drive elements without removing them from the machine and without disassembly. These requirements, first of all, corresponds to the control of the technical condition of the hydraulic drive by the coefficient of efficiency. The definition of total losses, hydromechanical losses and volumetric losses is considered. It is shown that it is possible to determine both the total energy efficiency and the hydromechanical efficiency, to estimate the losses by the specified equations, taking into account the effect of compressibility of the working fluid. To determine the real parameters of hydraulic systems and to assess the actual performance of the efficiency, a set of diagnostic tools for hydraulic systems developed by the Department of Hydraulic Machines named after academician G. F. Proskura was used, with which the measured parameters can be recorded on an internal memory card or transmitted via wireless Bluetooth to a personal computer PC or Android device (smartphone, tablet) for further processing. A scheme for testing pumps with open and closed circuits, as well as a scheme for testing hydraulic motors is given. These schemes indicate on which positions this set can be used. The given theoretical dependences, together with the processed data, and obtained with the help of the developed set of diagnostic tools, allow to determine and build the real characteristics of the units, taking into account the power loss, which can vary depending on the pressure level, fluid temperature and the amount of air dissolved in the liquid.

Microstructural, mechanical and tribological performance of a magnesium alloy AZ31B/Si3N4/eggshell surface composite produced by solid-state multi-pass friction stir processing

This study focused on the development of an AZ31B/Si3N4/Eggshell surface composite via solid-state multi-pass friction stir processing. The study aimed to characterize the developed surface composite based on its structural, microstructural, mechanical, and tribological performance at one, two and three successive tool-passes. The structural and compound analysis was conducted using an XRD pattern. Microstructural characterization and grain refinement studies were conducted using FESEM images and EBSD analysis. Furthermore, the mechanical properties were investigated through tensile tests equipped with digital image correlation (DIC) images and fractography analysis via FESEM images. In addition, tribological characteristics, such as COF, friction forces, and volumetric wear losses, were examined using a universal tribometer, and the 3D profile of the wear track was analyzed through surface profilometry. The results revealed the formation of structural compounds such as Mg2Al4, Mg2SiO4, Mg2Ca, and Ca2Mg4Zn13 in the stir zone. The morphological study revealed plenty of white-grey (ESP) and dark grey (Si3N4) sub-micron precipitates uniformly dispersed into the AZ31B matrix alloy. The EBSD map exhibited an average grain size of 2.95 ± 1.83 μm. The ultimate tensile stress at one, two and three successive tool-passes were found to be 357 MPa, 366.5 MPa and 375.4 MPa, respectively, which was comparatively 20–25% higher than the base alloy. The FESEM images of the fractured surface exhibited ductile striations and tear ridges with flat shear bands mixed with brittle fracture. The lowest COF obtained in this study was 0.29 for three too-passes at an average frictional force (Fx) of 2.17 N with a volumetric wear loss of 0.0769 mm3.

Variation in the volumetric power and momentum losses in the JET-ILW scrape-off layer

In attaining the cold plasma condition at the divertor target via gas puffing and/or nitrogen seeding, a large variation in the pressure-momentum and cooling losses has, for the first time, been demonstrated on JET with the ITER-like wall, leveraging novel target electron temperature measurements and JET’s unique capability for disentangling the main-ion-driven net dissipation effects from impurity radiation. These observations provide key insights into the dependence of volumetric losses on the dominant dissipation mechanisms, whether due to neutral-plasma interaction processes, impurity radiation induced detachment, and their interplay.While numerical code studies indicate that both volumetric cooling and pressure-momentum losses in the scrape-off layer (SOL) are essential for detachment to occur, experimental confirmation has been largely lacking, in large part due to diagnostic limitations. In the present assessment of L-mode discharges in the diagnostically optimized outer horizontal target configuration, the onset of pressure-momentum losses in nitrogen seeding scans in low recycling conditions is shown to occur at relatively high target electron temperature of 10 eV compared to pure deuterium pressure scans, leading to a more pronounced reduction in the target heat flux, and demonstrating for the first time the importance of momentum losses in impurity radiation dominated dissipative divertors in the absence of strong neutral-plasma interactions. Conversely, a relatively constant target heat flux response is observed above Te,t = 5 eV in pure deuterium density ramps, where the decrease in Te,t is balanced by a rise in target pressure prior to the ion flux rollover, coinciding with the pressure-momentum loss onset. While in practice the relative strength of each dissipation channel will be driven by integrated scenario requirements and core plasma performance constraints, this work demonstrates that there is no universal form of the fmom-loss and fcooling volumetric loss factors and their correlation. Moreover, the results confirm the theoretical and code predictions that both volumetric loss processes are required for detachment, while also resolving an apparent, but counter-intuitive, finding of the code results that volumetric power loss is insensitive to the presence of impurities, demonstrating that this is not the case experimentally. Further interpretive modelling is required to elucidate the dominant momentum and cooling loss channels in the observed trends.

Classification of Wear State for a Positive Displacement Pump Using Deep Machine Learning

Hydraulic power systems are commonly used in heavy industry (usually highly energy-intensive) and are often associated with high power losses. Designing a suitable system to allow an early assessment of the wear conditions of components in a hydraulic system (e.g., an axial piston pump) can effectively contribute to reducing energy losses during use. This paper presents the application of a deep machine learning system to determine the efficiency state of a multi-piston positive displacement pump. Such pumps are significant in high-power hydraulic systems. The correct operation of the entire hydraulic system often depends on its proper functioning. The wear and tear of individual pump components usually leads to a decrease in the pump’s operating pressure and volumetric losses, subsequently resulting in a decrease in overall pump efficiency and increases in vibration and pump noise. This in turn leads to an increase in energy losses throughout the hydraulic system, which releases excess heat. Typical failures of the discussed pumps and their causes are described after reviewing current research work using deep machine learning. Next, the test bench on which the diagnostic experiment was conducted and the selected operating signals that were recorded are described. The measured signals were subjected to a time–frequency analysis, and their features, calculated in terms of the time and frequency domains, underwent a significance ranking using the minimum redundancy maximum relevance (MRMR) algorithm. The next step was to design a neural network structure to classify the wear state of the pump and to test and evaluate the effectiveness of the network’s recognition of the pump’s condition. The whole study was summarized with conclusions.

Evaluation of tribological property and coating reliability of alumina and aluminum silicate-coated A356 aluminum alloy

Material loss due to relative motion between the contact surfaces causes surface degradation leading to premature failure of engineering systems. Of the several techniques to improve the wear resistance of rubbing components, the process of providing a hard protective surface coating has gained tremendous significance. Aluminum alloys used in engineering applications are exposed to rubbing, resulting in progressive wear. Sol-gel coating is a widely accepted surface coating technique for aluminum alloys, and this paper focuses on alumina and aluminum silicate coating applied to aluminum alloys. The tribological characteristics such as coefficient of friction (COF) and volumetric wear losses (VWL) are evaluated using a pin on disc (POD) tribometer. Finite-element analysis (FEA) plays a vital role in bringing an approximate solution to various engineering and non-engineering problems. The POD tribometer is modelled in the design modeller of the Ansys workbench based on the Archard wear model. The coating reliability is experimentally estimated based on its tribological properties. Surface hardness is measured by microhardness indentation test, and materials characterization is done using atomic force microscopy (AFM) and Fourier transform infrared radiation (FTIR) spectroscopy. It is observed that alumina coating exhibits better tribological properties than aluminum silicate-coated A356 aluminum alloy.

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m3/d m−1. Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10-2 to 1.2 × 10-2 km3, respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Theoretical essentials for designing viscous liquid pumping systems in the conditions of the Arctic region

The purpose is the creation of a scientifically based solution for the design of hermetic electromechanical converters adapted to existing pipelines, as well as those under construction and development. These pipelines meet the energy efficiency requirements and operate in the conditions of the Arctic region. Methods: methods of mathematical analysis, numerical methods, and methods of mathematical programming were used as the main mathematical means. The CFD design package of Ansys Maxwell was used. Research results: we showed that an increase of the efficiency of the system of technological transportation of petroleum products at low temperatures is possible through the use of electromechanical devices that combine the functions of heating and pumping the working liquid. We solved the field problem based on the analytical calculations carried out by a computer. This allowed us to determine the distribution of eddy current density in the structural elements of these devices responsible for creating pressure and heating the pumped petroleum products. The importance of the electrical parameters of the secondary windings has been confirmed numerically and experimentally. The hydraulic characteristics, mechanical losses, volumetric losses and efficiency are determined. Taking into account the outcomes of theoretical studies the experimental sample of the sealed electromechanical converter with the specified physical and chemical characteristics was created at Emperor Alexander I St. Petersburg State Transport University. Practical relevance: the obtained analytical formulas can be used at the development of the systems for pumping viscous liquids at low temperatures using the sealed electromechanical converters which helps to reduce the installed power of energy equipment without degrading the values of technological indicators.

Оценка степени влияния фактора подвижности стенок щели при расчёте величины протечек в рабочей части спирального компрессора. Часть 2

Leakage of the working substance in the compressor's flow gaps accounts for a large share of its volumetric losses. The optimality of calculated and approximated characteristics depends on the accuracy of quantitative component determination. Accordingly, an adequate and qualitative mathematical model should include the factor of non-stationarity of the leakage process, taking into account the mobility of scroll elements. At the same time, the real properties of the working medium, characterized by the compressibility coefficient, play an important role in the nature of leakage. Thus, in this article the task of creating a mathematical model adequate to the actual process of compression and allowing to estimate the degree of influence of the slit walls mobility on the leakage through them is set. The result of numerical calculations has a smaller error in relation to experimental data, and it also showed a significant influence on the leakage rate of both the pressure difference at the edges of the slot and the viscosity properties of the vapour-oil mixture, a significant percentage of which is oil.

Оценка степени влияния фактора подвижности стенок щели при расчёте величины протечек в рабочей части спирального компрессора. Часть 1

The scroll type compressor is widely used in the medium capacity segment of refrigeration and air conditioning technology including heat pumps. Today there is an active process of changing from hydrofluorocarbons to natural refrigerants with low global warming potential. CO2, with its low critical point and correspondingly high operating pressures, is gaining in importance. For operation with new refrigerants, the scroll compressor has to be adapted to take account of all its design features, the most important of which are the clearances in the machine's flow area. It has to be considered that the thermodynamic properties of carbon dioxide, different from hydrofluorocarbons, have a significant influence on the volume and energy values of the compressor. In this case relevance consists in increase of accuracy of compressor losses calculation and prediction of refrigeration machine characteristics. As the basic volumetric losses in the scroll compressor are leakages of working substance in its working part, and the process of flow of medium is unsteady, their quantitative component causes interest. The purpose of this work is to clarify the physical basis of the leakage process in the radial clearance and the degree of influence of various factors on it. Such analysis gives further opportunity to refine the methodology of calculation of leakages of compressed medium, taking into account the mobility factor of gap walls. It will raise accuracy of the received results which can serve as a base to prognosis of optimum characteristics of the compressor, due to their approximation and will allow to optimize designing of refrigerating machines at the chosen modes of work.