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1
Content available remote Research of environmental and technological problems of cavitation
EN
The comparative analysis of systems of conversion of electric energy into mechanical and mechanical into thermal with realization of effect of cavitation in a stream of the liquid transported in a closed circuit is carried out. The optimal dimensions and relief of working surfaces of swirlers in tubular and rotary cavitators are determined. The regularities of the change of the coolant temperature depending on its nature, the intensity of cavitation, which is determined by the rotational-translational and rotational motion in cavitators of two types - tubular and rotary.
EN
The generating station in which diesel engine is used as a prime mover for generating electrical energy is known as diesel power plant. The cylinders liner are cylindrical component that are fixed inside the engine block. The function of the cylinder liners is to retain the working fluid and to guide the piston. Most diesel power plant uses wet-cylinder liners that are exposed to intensive cavitation. The paper aimed at studying the behavior of the cylinder liners that can lead to cavitation. The analysis involves, modeling and simulation in using Solidworks software. The analysis shows that the cylinders are subjected to harmonic vibration resulting to momentary separation of the coolant from the cylinder wall, creating a pressure difference around the coolant surface which forms air bubbles. These bubbles explode at an extreme velocity. The explosion of these bubbles release surface energy known as cavitation. The energy hammers the cylinder liner surface thereby removing minute particles of metal from the surface of the vibrating cylinder leading to cavitational deterioration. The paper hereby calls on automotive designers to take critical measures in designing of; cylinder liner, water jacket and the entire cooling system, in order to control this phenomenon.
EN
Cavitation is an essential problem that occurs in all kinds of pumps. This cavitation contributes highly towards the deterioration in the performance of the pump. In industrial applications, it is very vital to detect and decrease the effect of the cavitation in pumps. Using different techniques to analysis and diagnose cavitation leads to increase in the reliability of cavitation detection. The use of various techniques such as vibration and acoustic analyses can provide a more robust detection of cavitation within the pump. In this work therefore, focus is put on detecting and diagnosing the cavitation phenomenon within a centrifugal pump using vibration and acoustic techniques. The results obtained from vibration and acoustic signals in time and frequency domains were analysed in order to achieve better understanding regarding detection of cavitation within a pump. The effect of different operating conditions related to the cavitation was investigated in this work using different statistical features in time domain analysis (TDA). Moreover, Fast Fourier Transform (FFT) technique for frequency domain analysis (FDA) was also applied. Furthermore, the comparison and evaluation system among different techniques to find an adequate technique incorporating for accuracy and to increase the reliability of detection and diagnosing different levels of cavitation within a centrifugal pump were also investigated.
EN
This article focuses on the cavitation mechanism from the perspective of utilizing the effect of gas desorption from the solution with nucleation of gas bubbles. This effect is an innovative approach to improving the operating parameters, including emissions parameters, in the compression-ignition engines. The article presents the concept of applying this process in practice and draws attention to the problems associated with its practical implementation. With regard to this issue, an original pump design with a hypocycloid power transmission, enabling application of the desorption effect, was presented. The second part of the article focuses on evaluating the possibility of cavitation occurring in the pump. This task was realized by simulating the cavitating flows in the pump’s return valve – the site at the greatest risk of formation of the first nuclei of this unfavorable phenomenon.
PL
W artykule zaprezentowano wyniki niestacjonarnych trójwymiarowych obliczeń numerycznych przepływu kawitacyjnego przez niewielkowymiarową zwężkę zbieżno-rozbieżną o współczynniku przewężenia mniejszym niż 0,1 oraz proces walidacji uzyskanych wyników z zastosowaniem komputerowej analizy obrazu. W obliczeniach numerycznych wykonanych w programie ANSYS Fluent w procesie modelowania zjawiska kawitacji wykorzystano podejście homogeniczne z uwzględnieniem dwóch modeli: modelu Schnerra i Sauera oraz modelu Zwarta i in. Celem pracy była walidacja wyników symulacji numerycznych i ocena przydatności komputerowej analizy obrazu w tym procesie. Motywacją do przeprowadzenia symulacji numerycznych zjawiska kawitacji były trudności w uzyskaniu wyników odzwierciedlających w stopniu zadowalającym przeprowadzone pomiary eksperymentalne w analizowanej klasie urządzeń.
EN
The article presents the results of non-stationary three-dimensional numerical calculations of cavitation flow through a small-sized with a throat ratio less than 0.1 and the process of validation of the obtained results using computer image analysis. In the numerical calculations performed using the ANSYS Fluent software, the modelling process of the cavitation phenomenon using the homogeneous approach includes two models: the Schnerr and Sauer model and the Zwart et al. model. The aim of the work was to validate the results of numerical simulations and to assess the usefulness of the computer image analysis in this process. The motivation to perform the numerical simulations of the cavitation phenomenon were difficulties in obtaining results reflecting satisfactorily the experimental measurements conducted for the analyzed class of devices.
6
Content available remote Electromagnetic vibratory cavitator
EN
It was found that the principles and regularities of the multiplicity frequency apply to hydraulic objects, and in particular to suspended in liquid medium its foreign objects - air and gas bubbles, solid particles, and similar formations. Vibrational resonant cavitators provide 25÷30% increase of the intensity of cavitation field, hence, proportional productivity increase of cavitation liquid treatment, соmparing with hydrodynamic cavitators.
PL
Wykryto, że zasady i reguły częstotliwości powielonych mają zastosowanie do obiektów hydraulicznych, a w szczególności do ciał obcych zawieszonych w ośrodku ciekłym, takich jak pęcherzyki powietrza i gazu, cząstki stałe, itp. Wibracyjne kawitatory rezonansowe zapewniają wzrost intensywności pola kawitacji o 25÷30%, a więc także proporcjonalny wzrost wydajności płynu kawitacyjnego, w porównaniu z kawitatorami hydrodynamicznymi.
EN
The paper concerns experimental and numerical investigations focused on the cloud cavitation phenomenon over a hydrofoil. The results of flow visualization by means of a high- -speed camera are presented. The cavitation cycles including vapour structures occurrence, development and collapse were recorded and described. Within the numerical investigation, transient calculations of cavitating flow were performed. OpenFOAM software was used. To model mass transfer between phases, the Kunz cavitation model was chosen. Turbulences were modelled by means of k-ω SST model. The vapour areas appearance, their shapes and changes in time were described and compared with experimental results. The characteristic features of cavitating flow were observed, however further adjustment of the cavitation model was advised.
8
Content available Cavitation defects in farm vehicle engines
EN
The article identifies and analyses selected examples of cavitation erosion occurring in farm tractor engines and their systems at different mileages. The analysis has been carried out on the basis of known theoretical rudiments of this phenomenon. The paper presents photographs from maintenance work selected by the authors, which illustrate the discussed matter graphically. There is a discussion on how to prevent cavitation phenomena occurring in coolant, which induce engine defects.
PL
W artykule poddano identyfikacji i przeanalizowano wybrane przykłady występowania erozji kawitacyjnej w silnikach ciągników rolniczych i ich układach, po różnych przebiegach. Analizę przeprowadzono na podstawie znanych podstaw teoretycznych tego zjawiska. Zamieszczono zdjęcia wybrane przez autorów z pracy serwisowej, które graficznie przedstawiają zagadnienie. Omówiono również jak zapobiegać zjawiskom kawitacji w cieczy chłodzącej powodującej uszkodzenia silników.
EN
The research goal was to develop an improved water purification technology for public reservoirs by adding the vibrocavitation purification before a reagent method with sodium hypochlorite, produced via electrolysis of salt. The main tasks of the research include the determination of vibrocavitation treatment efficiency and the development of a new low-frequency vibration resonance cavitation process for water purification, as well as equipment for this process. The vibroresonance method supporting the intensity of spatial displacements of cavitation exciters was developed on the basis of the theory of cavitation fields in liquids. While using this method, it was possible to establish the boundary conditions for stable support of the cavitation field created by low-frequency vibrations. The developed method is based on the formation of high intensive cavitation fields in liquids by vibratory decks. The advanced technological scheme of water purification for pools and public use reservoirs was proposed, which includes the addition of resonance vibrocavitators to a closed circulation cycle of water purification with the reagent method.
PL
W ciągu ostatnich kilku dziesięcioleci ultradźwięki znalazły szerokie zastosowanie w diagnostyce obrazowej. Ten artykuł przeglądowy omawia potencjalne efekty biologiczne związane z propagacją ultradźwięków w tkankach i podaje fizyczne podstawy wprowadzonych indeksów mechanicznego MI i termicznego TI zgodnych z Output Display Standard (ODS). W praktyce klinicznej otrzymywane wyniki są kompromisem pomiędzy jakością obrazu a możliwością systemu uzyskiwania zadowalających obrazów głęboko leżących struktur tkankowych – wyboru dokonuje się, biorąc pod uwagę minimalizację bioefektów. Moce wyjściowe ultrasonografów są regulowane i ograniczane do określonych poziomów. Bezpieczne dawki ultradźwiękowe wyznacza się według określonych zasad, a na ekranie wyświetlane są związane z nimi wielkości. Wielkości te określają możliwości wystąpienia zmian mechanicznych i termicznych w tkankach i dlatego mają znaczenia kliniczne. Wprowadzone wskaźniki – mechaniczny MI i termiczny TI uwzględniają fizyczny mechanizm oddziaływania między ultradźwiękami i biologiczną tkanką, który zależy od czasowych i przestrzennych parametrów pola akustycznego generowanego przez głowice ultradźwiękowe. Przewidywany wzrost temperatury określa się, stosując trzy różne modele tkankowe: homogeniczny, warstwowy i układ kość/tkanka.
EN
Ultrasounds have found widespread use in imaging diagnostics over the past few decades. This review article combines the reports on the biophysical effects and provides the rationale behind the mechanical index (MI) and thermal index TI complying with Output Display Standard (ODS). In clinical practice, the obtained diagnostic results are a compromise between the quality of the image and the possibility of a system of obtaining satisfactory images of deep-lying tissue structures – the choice is made taking into account the minimization of bioeffects. The output powers of ultrasonographs are regulated and limited to specific levels. Safe ultrasonic doses are determined according to specific rules, and the screen displays the associated quantities. These quantities determine the possibility of mechanical and thermal changes in the tissues and therefore have clinical significance. The introduced indexes MI and TI take into account the physical mechanism of interaction between ultrasounds and biological tissue, which depends on the temporal and spatial parameters of the acoustic field generated by ultrasound transducers. The predicted temperature increase is determined using three different tissue models: homogeneous, layered and bone/tissue interface.
EN
The pump performance and occurrence of cavitation directly depends on different operating conditions. To cover a wide range of operation conditions for detecting cavitation in this work, investigations on the effect of various suction valve openings on cavitation in the pump were carried out. In order to analyse various levels of cavitation in different operation conditions, the effect of the decrease in the inlet suction pressure of the centrifugal pump by controlling the inlet suction valve opening was investigated using this experimental setup. Hence, the acoustic and pressure signals under different inlet valve openings and different flow rates, namely, 103, 200, 302 l/min were collected for this purpose. A detailed analysis of the results obtained from the acoustic signal was carried out to predict cavitation in the pump under different operating conditions. Also, the acoustic signal was investigated in time domain through the use of the same statistical features. The FFT technique was used to analyse the acoustic signal in the frequency domain. In addition, in this work an attempt was made to find a relationship between the cavitation and noise characteristics using the acoustic technique for identifying cavitation within a pump.
EN
Ultrasonic processing in the cavitation mode is used to produce the composite materials based on the metal matrix and reinforcing particles of micro- and nano-sizes. In such a case, the deagglomeration of aggregates and the uniform distribution of particles are the expected effects. Although the particles can not only fragment in the acoustic field, they also can coagulate, coarsen and precipitate. In this paper, a theoretical study of processes of deagglomeration and coagulation of particles in the liquid metal under ultrasonic treatment is made. The influence of various parameters of ultrasound and dispersion medium on the dynamics of particles in the acoustic field is considered on the basis of the proposed mathematical model. The criterion of leading process (coagulation or deagglomeration) has been proposed. The calculated results are compared with the experimental ones known from the scientific literature.
EN
Cavitation is a one of many wear mechanisms which are related to the flow of liquid. It is one of the most destructive wear methods for stainless materials. The local changes in the pressure of the liquid stream related to the flow across the metal component cause straightening of the surface area, as well as its erosion and the formation of pits on the surface layer. The erosion value of cavitation is related to the material’s microstructure, the geometry of the element, the phase composition of the material and the surface roughness. In this paper the investigation of the cavitation process for duplex stainless steel has been performed. Samples examined in the first stages of the experiments were not significantly changed, but after a long time the hardness increase was very visible. The result of the cavitation was also cracking along the interphase boundaries, which resulted in the chipping of the material. One of the most important results was a description of the change in the wear mechanisms and its intensity during the cavitation exposure time. At first plastic micro deformation of the material’s surface occurred, then the plastic deformation increased significantly and after some time this resulted in erosion of the material and interfacial boundary decohesion; these two effects increased simultaneously. The last of the mechanisms was mechanical destabilization of the austenite, but the clear result of the mechanical destabilization of the austenite was only observed in the last sample. Martensitic transformation of the material changed the material’s mechanical properties, but for the stainless steels this resulted in electrochemical corrosion of the material, especially through the formation of an electrochemical potential between austenite and martensite.
EN
The elimination of hazards caused by cavitation phenomena is an important issue to be considered in the design of process equipment including flow machinery. These hazards are: cavitation erosion, efficiency decrease as well as vibration and noise. One of the most intensive and dangerous forms of cavitation is vortex cavitation that accompanies the operation of hydraulic machines in which components comprised of rotating blades are applied. Velocity fields around cavitation vortices generated by the model of a propeller blade were experimentally studied in a cavitation tunnel. Flow images were recorded using a high-speed camera and processed using particle image velocimetry (PIV) complemented with computer-aided techniques that had been developed for the purpose of this research. These techniques included the removal of image distortions on the basis of a calibration mask, determination of instantaneous velocity distributions and removal of air-bubble traces from flow images. Experimental studies result examples were presented in the form of velocity fields determined in the longitudinal plane as well as in three transverse planes remote from the blade. Instabilities of the cavitating vortex stream and of the local liquid-flow velocity in its surrounding were detected. The effect of the angle of attack of propeller blade on the instability of the vortex stream and the effect of the presence of the cavitating vortex kernel on the local velocities of the surrounding liquid, were determined.
EN
The paper covers basics of the vortex model used for propeller-stator systems. The outline of the design algorithm is given and the results of its application are shown. The designed propeller-stator system was the subject of model tests run at the CTO model basin and cavitation tunnel. Stator’s influence on the delivered power required by the propeller and its revolution rate has been examined by conducting self-propulsion tests with and without stator. The tests performed in the cavitation tunnel revealed only weak tip vortex cavitation on the propeller. No cavitation was observed on the stator at the design point. A wide range of the performed tests allowed the authors to identify details of the developed theory which will require further improvement.
PL
Artykuł prezentuje wyniki symulacji numerycznych zjawiska kawitacji w zwężce zbieżno-rozbieżnej, z zastosowaniem podejścia homogenicznego. Analizowane są trzy modele: model Schnerra i Sauera, model Singhala i in. oraz model Zwarta i in. Symulacje są niestacjonarne. Geometria jest planarna. W symulacjach numerycznych wykorzystano oprogramowanie Fluent. Celem pracy jest ocena możliwości zastosowania planarnych symulacji numerycznych przepływu kawitacyjnego dla niewielkowymiarowych zwężek zbieżno-rozbieżnych. Motywacją do przeprowadzenia symulacji numerycznych zjawiska kawitacji dla planarnej geometrii są trudności w uzyskaniu wyników odzwierciedlających przeprowadzone pomiary eksperymentalne, zarówno dla geometrii dwu-, jak i trójwymiarowej. Otrzymane wyniki symulacji numerycznych wykazują duże podobieństwo do pomiarów eksperymentalnych dla wszystkich analizowanych modeli.
EN
The article presents results of numerical simulations of cavitation phenomenon in a converging-diverging nozzle using the homogeneous approach. Three cavitation models are considered: the Schnerr and Sauer model, the Singhal et al. model and the Zwart et al. model. The simulations are performed for transient. The geometry is two-dimensional and planar. In the numerical calculations Fluent software was used. The aim of the work is to estimate the possibility of applying of two-dimensional planar numerical simulations of cavitating flows for small-sized converging-diverging nozzles. The motivation to conduct numerical simulations for two-dimensional and planar geometry are difficulties in obtaining results, which reflect experimental measurements, both for two- and three-dimensional geometry. The achieved results show a big similarity between the results of performed numerical simulations and the material from the experimental measurements for all the analyzed models.
EN
The paper presents applicability of the computer system to model and simulate fluid and gas flow to assess surface cavitation wear. Abstract tube models with a decreasing inside diameter were developed and fluid flow with varying flow velocities was simulated. This facilitated identification of areas particularly at risk of cavitation wear. Results of simulation analyses were verified by comparing them with actual empirical results concerning cavitation erosion of tubing materials.
PL
W pracy przedstawiono możliwości wykorzystania systemów komputerowego modelowania oraz symulowania przepływu cieczy i gazów do oceny stopnia zużycia kawitacyjnego powierzchni. Opracowano abstrakcyjne modele przewodów o zmniejszającej się średnicy wewnętrznej oraz symulowano przepływ cieczy z różnymi prędkościami. Pozwoliło to wyznaczenie obszarów szczególnie narażonych na erozję kawitacyjną. Dokonano weryfikacji wyników analizy symulacyjnej porównując je z rzeczywistymi wynikami badań erozji kawitacyjnej materiałów do budowy przewodów.
EN
Analysis of a crystallographic texture (a preferred orientation) effect on cavitation wear resistance of the as-cast CuZn10 alloy, has been conducted in the present paper. The experiment was conducted on the CuZn10 alloy samples with <101>//ND or <111>//ND preferred orientations (where the ND denotes direction that is perpendicular to the exposed surface). The cavitation resistance examinations have been carried out on three different laboratory stands (namely, vibration, jet-impact and flow stands) that are characterized by a various intensity and a way of cavitation’s excitement. Obtained results point towards a higher cavitation resistance of the CuZn10 alloy with the <111>//ND preferred orientation.
19
Content available remote Visualization study of the flow processes and phenomena in the external gear pump
EN
External gear pumps make some of the most frequently used hydraulic energy generators. In spite of the fact that those well known machines feature good operational parameters, the research and development work on the pumps is still going on. There is a number of various research methods applied. One of them, an experimental method, is a visualization study, on which this paper is focused. In this article, the visualization research method has been presented, which has been used for the study of the flow processes and phenomena in the external gear pump. Findings of the research enabled a detailed description of the flow process, namely of the transporting of the working fluid through the pump, in each of the typical zones of the pump. It turns out that a characteristic feature of the process is the occurrence of various cavitation phenomena. All characteristic cavitation forms, as well as the degrees of their intensity, observed during the research, have been catalogued and specifically described. The research also made it possible to identify the critical areas of the pump, which, consequently, allowed the development of specific design, construction and operational recommendations. A result of applying those recommendations was a considerable reduction of the intensity of the cavitation phenomena, evidence of which is the experimental study presented in this paper.
EN
This article indicated at erosion as one of the causes of degradation of surfaces washed by fluids and conditions of its occurrence. Corrosive – erosive theory of metal surface degradation has been discussed linking it with an instance of destructive processes taking place in cylinder liner blocks of combustion engines. Physics and conditions influencing processes on liquid – washed operational surface phase boundary have been justified. Out of the contemporary hypotheses explaining the physics of cavitation erosion, the bubble theory has been considered. A mathematical model of erosion has been presented in the context of cavitation implosion energy determining crash interactions of liquid cumulative fluxes on the washed surface. Occurring plastic deformations have been graphically explained linking them with the occurrence of fatigue micro-cracks and later with erosive pits. Influence of initial steel hardness on intensity of cavitation erosion has been checked. Discussion of ways to increase metal surface resistance to cavitation erosion has been carried out.
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