Matevz Dular

University of Ljubljana · Faculty of Mechanical Engineering

Recently van Rijsbergen et al. [1], by simultaneous observation of cavitation and acoustic emission measurements, and Petkovsek & Dular [2], by simultaneous observation of both cavitation structures and cavitation damage, have pointed to the fact that the small scale structures and the topology of the cavitation clouds play a significant role in ca...

The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed. In the first part of this paper a general overview of techniques that employ hyd...

One of the remaining open questions in cavitation erosion research is the one on the importance of the microjet and the shock wave on the formation of the pit. Up until now, no successful attempt has been made to study this in detail, mainly because the damage could only be detected and evaluated after several successive bubble collapses. A bubble...

A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for...

Cavitation used to be associated with negative outcomes in hydraulic turbomachinery but nowadays it is often used for water cleaning, microorganism’s destruction and degradation of organic compounds. This study investigated the amount of ●OH formed during hydrodynamic cavitation using salicylic acid dosimetry. The radical’s amount was evaluated by...

The collapse of microbubbles near a fiber is an example often encountered in water treatment situations and cavitation fibrillation processes. However, due to the broken symmetry conditions, this process has not been studied in detail experimentally or numerically, making it difficult to precisely measure or simulate the rapid bubble evolution duri...

The alarming increase in water pollution is driving research into novel, environmentally friendly treatment solutions such as hydrodynamic cavitation. This study is part of the research on the pin disc rotational generator of hydrodynamic cavitation, which utilises the low pressure wake behind the rotor pins to induce cavitation and the short gap b...

Contamination with toxic metals prevents the use of sewage sludge (SS) as a soil fertilizer. Hydrodynamic cavitation, thermal microwaving, microwave-assisted alkaline, and acid hydrolysis coupled with ethylenediaminetetraacetate (EDTA) washing were tested as a method to remove toxic metals from SS. Acid hydrolysis coupled with EDTA washing was most...

Aiming at modeling the cavitation bubble cluster, we propose a novel nonlinear dynamic cavitation model (NDCM) considering the second derivative term in Rayleigh-Plesset equation through strict mathematical derivation. There are two improvements of the new model: i) the empirical coefficients are eliminated by introduction of the nonuniform potenti...

Large quantities of wastewater sludge (WWS) that are produced during wastewater treatment need to be stabilized for safe use and disposal. The most common method used for sludge stabilization is anaerobic digestion (AD). Here, microorganisms break down organic matter in the absence of oxygen while also producing biogas, mainly CO2 and methane. Biog...

Graphene is a valuable and useful nanomaterial due to its exceptionally high tensile strength, electrical conductivity and transparency, as well as the ability to tune its materials properties via functionalization. One of the most important features needed to integrate functionalized graphene into products via scalable processing is the effectiven...

Acoustic cavitation, generated by a piezo-driven transducer, is a commonly used technique in a variety of processes, from homogenization, emulsification, and intensification of chemical reactions to surface cleaning and wastewater treatment. An ultrasonic horn, the most commonly used acoustic cavitation device, creates unique cavitation conditions...

The research on the potential of cavitation exploitation is currently an extremely interesting topic. To reduce the costs and time of the cavitation reactor optimization, nowadays, experimental optimization is supplemented and even replaced using computational fluid dynamics (CFD). One of the approaches towards sustainable water treatment is use of...

Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-...

Hydrodynamic cavitation was evaluated for its reactive oxygen species production in several convergent-divergent microchannel at the transition from micro to milli scale. Channel widths and heights were systematically varied to study the influence of geometrical parameters at the transitory scale. A photomultiplier tube was used for time-resolved p...

Presented study analyses different jet parameters that appear during and after bubble collapse, namely bubble center displacement, length of a jet-pierced bubble and size of the rebounded bubble and their relation to anisotropy parameter in a vicinity of a liquid-liquid interface. In experiments cavitation bubble was produced with a focused pulsed...

ABSTRACT: Cellulose fibrils are the structural backbone of plants and, if carefully liberated from biomass, a promising building block for a bio-based society. The mechanism of the mechanical releasefibrillationis not yet understood, which hinders efficient production with the required reliable quality. One promising process for fine fibrillation...

The applications of bacterial sonolysis in industrial settings are plagued by the lack of the knowledge of the exact mechanism of action of sonication on bacterial cells, variable effectiveness of cavitation on bacteria, and inconsistent data of its efficiency. In this study we have systematically changed material properties of E. coli cells to pro...

Waterborne plant viruses can destroy entire crops, leading not only to high financial losses but also to food shortages. Potato virus Y (PVY) is the most important potato viral pathogen that can also affect other valuable crops. Recently, it has been confirmed that this virus is capable of infecting host plants via water, emphasizing the relevance...

Wastewater treatment plants, the last barrier between ever-increasing human activities and the environment, produce huge amounts, of unwanted semi-solid by-product - waste activated sludge. Anaerobic digestion can be used to reduce the amount of sludge. However, the process needs extensive modernisation and refinement to realize its full potential....

Hydrodynamic cavitation poses as a promising new method for wastewater treatment as it has been shown to be able to eradicate bacteria, inactivate viruses, and destroy other biological structures, such as liposomes. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental questio...

Single bubble dynamics are of fundamental importance for understanding the underlying mechanisms in liquid–vapor transition phenomenon known as cavitation. In the past years, numerous studies were published and results were extrapolated from one technique to another and further on to “real-world” cavitation. In the present paper, we highlight the i...

The research on the potential of cavitation exploitation is currently an extremely interesting topic. To reduce the costs and time of the cavitation reactor optimization, nowadays, experimental optimization is supplemented and even replaced using computational fluid dynamics (CFD). This is a very inviting opportunity for many developers, yet we fin...

In this study, the hydrodynamic cavitation and wastewater treatment performance of a rotary generator with pin disk for hydrodynamic cavitation are investigated. Various geometrical features and arrangements of rotor and stator pins were evaluated to improve the configuration of the cavitation device. The pilot device used to perform the experiment...

The paper shows visualization of cavitation inside a micro-Venturi channel. While the initial aim of the study was to establish supercavitating conditions inside a micro-Venturi, yet we found that this regime is suppressed due to the formation of a Kelvin-Helmholtz instability, which triggers a semi periodical attached cavity collapse. In depth obs...

Recently the development of Kelvin-Helmholtz instability in cavitating flow in Venturi microchannels was discovered. Its importance is not negligible, as it destabilizes the shear layer and promotes instabilities and turbulent eddies formation in the vapor region, having low density and momentum. In the present paper, we give a very brief summary o...

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed...

Understanding and controlling the interaction of cavitation bubbles and nearby material is becoming essential optimization of various processes. We examined the interaction of a single bubble with a membrane with different fluids on each side of it. Significant differences in bubble behavior depending on the fluid properties were observed, while th...

Upon cavitation cloud collapse an omnidirectional shock wave is emitted. It then travels through the flow field, causing a cascade of events resulting in erosion, noise, vibration and the cavitation shedding process. Despite that the accumulated data points evidently to the presence of the shock waves, the direct measurements hardly exist - and eve...

Cavitation bubble collapse close to a submerged sphere on a microscale is investigated numerically using a finite volume method in order to determine the likelihood of previously suspected mechanical effects to cause bacterial cell damage, such as impact of a high speed water jet, propagation of bubble emitted shock waves, shear loads, and thermal...

The initial motivation for the study was to gain deeper understanding into the background of emulsion preparation by ultrasound (cavitation). In our previous work [1] we observed rich phenomena occurring near the liquid-liquid interface which was exposed to ultrasonic cavitation. Although numerous studies of bubble dynamics in different environment...

Biofilm formation and removal from dead-ends is a particularly difficult and understudied area of water distribution system biology. In this work, we have built a model drinking water distribution system to probe the effect of different hydrodynamic flow regimes on biofilm formation and removal in the main pipe and in the dead-end. The test rig was...

This paper presents the results of an experimental study of the flow visualization of the refrigerant R600a through a capillary tube with an internal diameter of 0.8 mm made from an FEP (fluorinated ethylene propylene) polymer that was installed in a small-scale vapor-compression refrigeration system. The main purpose of the study was to determine...

Please cite this article as: J. Kosel, M. Šuštaršič, M. Petkovšek, M. Zupanc, M. Sežun, M. Dular, Application of (super)cavitation for the recycling of process waters in paper producing industry, Ultrasonics Sonochemistry (2020), Abstract In paper production industry, microbial contaminations of process waters are common and can cause damage to pap...

Laser ranging is a measurement method, applied in a wide range of applications. In this study, laser ranging is used to measure the height of turbulent water flows. Measurements were performed in three cross sections of a confluence where a tributary flow meets the main flow. Both flows exhibited high Reynolds and Froude numbers where the free-wate...

Tumbling Multi-Chamber (TMC) gear pump is a generally unknown type of hydraulic device, which features a unique three-dimensional shape of the gears. The main benefits of such design over the conventional gear pumps are self-adapting tightness of the pump parts, the possibility to mold the parts from a polymer material and high volumetric efficienc...

Wastewater recycling and sludge removal in the paper industry account for about 60 % of all process costs. New and environmentally friendly wastewater treatment techniques are, therefore, continually being developed. Cavitation exploitation is currently a well-investigated topic that is also interesting for the paper production industry. This study...

A short report is given on the 16th ERCOFTAC SIG 15 Workshop on Turbulence Modelling, which was organized at the Jožef Stefan Institute of Ljubljana on 15th and 16th of October 2019. The workshop was focused on turbulent natural convection. The test cases were differentially heated vertical channel flows and differentially heated square cavities.

Liposomes are widely applied in research, diagnostics, medicine and in industry. In this study we show for the first time the effect of hydrodynamic cavitation on liposome stability and compare it to the effect of well described chemical, physical and mechanical treatments. Fluorescein loaded giant 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) li...

Numerical prediction of cavitation erosion is a great scientific and technological challenge. In the past many attempts were made - many successful. One of the issues when a comparison between a simulation and erosion experiments is made, is the great difference in time scale. In the present work we do not attempt to obtain quantitatively accurate...

Refining of cellulose pulp is a critical step in obtaining high quality paper characteristics, however, this process is slow and costly especially for refining longer conifer fibers which are the preferred source for high quality paper production and give the paper its strength. In this study, we have applied a novel rotation generator of hydrodyna...

Understanding and predicting thermodynamic effects is crucial when the critical point temperature is close to the operating temperature of the fluid, like in cryogenics. Due to the extreme difficulties of experimental investigation, predicting of thermodynamic effects in cavitation often bases on data in liquids other than cryogenics. Most often us...

Spraying a coating on the surface of wet parts of a solid-liquid two-phase flow centrifugal pump could effectively increase its service life. To research the effect of coating thickness on the performance of the pump, a solid-liquid two-phase flow pump with a speed of n s = 81.5 was chosen, and polyurethane coatings with different thicknesses were...

To study the working mechanism of a high-efficiency hydrodynamic cavitation generator, the irregular cavitation patterns of a rotor-stator centrifugal hydrodynamic cavitation generator were investigated by experimental test and numerical simulation. The simulation result agrees well with the test result. It was found that three different cavitation...

In this study, a comparison of two different Kaplan turbine runners with differently shaped turbine blades was performed. The two turbines differed in the selection of the hydrofoil, the main hydrofoil parameters of which had been modified including, the position of maximum thickness and curvature and the inlet edge radius. Both turbines (unmodifie...

Cavitation has bothered the hydraulic machinery for centuries, especially in pumps. It is essential to establish a solid way to predict the unsteady cavitation evolution with considerable accuracy. A novel cavitation model was proposed, considering the rotating motion characteristic of centrifugal pump. Comparisons were made with three other cavita...

The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed. In the first part of this paper a general overview of techniques that employ hy...

Today emulsion preparation is receiving a lot of scientific attention, since emulsions are playing an essential role in many of the big industries, such as food, pharmaceutical or cosmetic industry. One of the most promising techniques for emulsion preparation is ultrasound emulsification. The purpose of this study is to expand the knowledge on the...

Cavitation has bothered the hydraulic machinery for centuries, especially in pumps. It is essential to establish a solid way to predict the unsteady cavitation evolution with considerable accuracy. A novel cavitation model was proposed, considering the rotating motion characteristic of centrifugal pump. Comparisons were made with three other cavita...

the microjet and shock wave on the formation of the pit. Up until now no successful attempt was made to study this in detail, mainly because the damage could only be detected and evaluated after several successive bubble collapses. Based on our previous work on laser induced shock waves [1] and on simultaneous observation of the dynamics of cavitat...

Thermodynamic effects in cavitation become significant only when the critical-point temperature is close to the operating temperature of the fluid, as in the case of cryogenic fluids. Therefore, the understanding and the prediction of the cavitation effects in such cases is crucial in many applications - for example the turbopumps for liquid hydrog...

In sufficient concentrations, the pathogenic bacteria L. pneumophila can cause a respiratory illness that is known as the "Legionnaires" disease. Moreover, toxic Shiga strains of bacteria E. coli can cause life-threatening hemolytic-uremic syndrome. Because of the recent restrictions imposed on the usage of chlorine, outbreaks of these two bacteria...

Surfactants play an important role in numerous chemical applications. Their effects on dispersion systems, as emulsions and colloids, are vastly studied. Yet, the dissolution (kinetics) of surfactants themselves has not received much scientific attention, despite the high implications for industrial applications. Nevertheless one can acknowledge th...

The performance of a rotor-stator centrifugal cavitation generator was experimentally studied, aiming at investigating the correlation between its cavitation mechanism and damage distribution. The generator was modified from a centrifugal pump, including a cut impeller, a volute, a rotor and a stator. The rotor and stator consist of 12 teeth each,...

When dealing with liquid flows, where operating temperature gets close to the liquid critical temperature, cavitation cannot be assumed as an isothermal phenomenon. Due to the relatively high density of vapor, the thermodynamic effect (decrease of temperature in the bulk liquid due to latent heat flow) becomes considerable and should not be neglect...

A comprehensive investigation on cavitating flow and cavitation-induced erosion was performed experimentally in an orifice plate system. Three image post-processed approaches were applied to analyze the test data, in order to obtain the cavitation characteristics. The cavitating flow pattern was studied by high speed images. In one cavitation devel...