Modeling and optimization of free overfall melt flow on a stone wool spinner

V delu je bila opravljena vizualizacija vpliva hitrosti kolesne površine in hitrosti curka na obliko in škropljenje kapljevine v okolici natočnega mesta z uporabo hitre kamere. Izvedena je bila vizualizacija prostega toka modelne kapljevine iz kanala s prerezom v obliki črke V pod kotom 90 °. Izdelan je bil numerični model prostega natoka modelne kapljevine iz V-kanala, U-kanala in pravokotnega kanala. Prosti natok kapljevine smo simulirali z laminarnim modelom in uporabo VOF modela za obravnavanje proste površine. Z rezultati numeričnih simulacij in vizualizacije s hitro kamere je bila predlagana optimalna oblika prostega kanala za natok taline na kolo centrifuge. Kriterij za izbiro optimalne oblike kanala je bilo razmerje med širino in debelino curka. Najboljše rezultate smo dobili za V-kanal, kjer je znašalo razmerje med širino in debelino curka 2,17. Na podlagi rezultatov numeričnih simulacij smo potrdili, da je širino in debelino curka pri natoku na kolesno centrifugo možno razložiti s teorijo mehanizma kapilarnih valov.In the thesis, a visualization of the influence of wheel surface speed and jet speed on the shape and spraying of liquid in the jet impact point was performed by means of high-speed imaging. Visualization of the free flow of model liquid from the channel with a V - shaped cross section at a 90 ° angle was performed. A numerical model of free flow of model liquid from V-channel, U-channel and rectangular channel was developed. Free flow of liquid was simulated with a laminar model and the use of VOF model to address the free surface. Based on the results of numerical simulations and visualization with a speed camera, the optimal shape of free channel for the flow of melt on a wheel spinner was proposed. The criteria for selecting the optimal channel shape was the ratio of jet width to thickness. The best results were obtained with the V-channel, where the ratio of jet width to thickness was 2,17. Based on analysis of numerical simulation results, we confirmed that the width and thickness of the jet on the wheel spinner can be explained by the theory of the capillary wave mechanism

Model of melt fiberization on a two wheel spinner

Razvlaknjenje taline mineralne volne je kompleksen proces, katerega poznavanje je ključnega pomena pri proizvodnji izolacijskih materialov. Postavili smo preizkuševališče, ki omogoča proučevanje procesa razvlaknjenja. Pomembni vhodni parametri, ki vplivajo na proces, so vrtilna frekvenca koles centrifuge, položaj natoka in volumski pretok taline. Izdelali smo regresijski model izkoristka razvlaknjenja taline v odvisnosti od vhodnih parametrov. Z opazovanjem procesa s hitro kamero je bila ugotovljena neenakomerna gostota porazdelitve vlaken na zbiralni mreži v odvisnosti od vhodnih parametrov.Melt fiberization is a complex process and its understanding is crucial for production of insulating materials. A measurement setup has been designed to allow the study of important input parameters that influence the fiberization process such as wheel rotational speed, angular position of the melt and the melt volume flow. A regression model of melt fiberization efficiency was made based on the input parameters. By visualization of the fiberization process with a high-speed camera, an uneven density of fiber distribution on the collecting grid was determined depending on the input parameters

Analogna eksperimentalna študija tvorbe vlaken na dvokolesni centrifugi

In this paper, the process of mineral fiber formation was investigated experimentally on a two-wheel spinner by means of high-speed imaging. Analogue isomalt melt was fiberized at different rotational speeds of spinner wheels, melt flow rates and impingement positions so that the fiberization process was dynamically similar to an industrial mineral wool production process. Images of fiber formation and transport reveal highly complex dynamics of these processes, as fibers mostly occur in form of 3D mutually intertwined structures such as clusters, strands and veils periodically shedding from the melt film. Despite the complexity of flow structures, there is a clear trend of increasing mean fiber length and expansion angle of the coaxial fiber-laden flow as the Weber number and the ratio of melt film velocity to blowing air velocity are increased. The fiberization efficiency (ratio of fiber mass deposited on the collecting mesh to the mass of melt poured) is affected by the impingement position and flow rate of melt as well as the Weber number of melt film. The optimum efficiency was attained at 30° (1 o\u27clock) impingement position and the ratio of melt film to blowing air flow velocity close to unity

Free surface lubrication of rotating cylinders by impacting Newtonian liquid jet

Free surface lubrication of rotating cylinders by Newtonian liquid jets was investigated at different impingement positions, jet- and circumferential velocities. The interaction between impinging round laminar jet and rotating surface was characterised by high-speed imaging. Compared to flat surface impingement, the liquid deposition mechanism is more complex and often accompanied by phenomena such as splashing, jet deflection and formation of radial surface stripes. Liquid splashing initially develops in direct deposition regime due to hydraulic jump-induced droplet shedding, transitioning to lamella instability splash at higher Reynolds numbers. The critical Reynolds number for splash onset is of same order of magnitude as for flat surface impingement and fairly constant at low relative jet impingement angles, but increases exponentially when angle approaches 90°. Liquid film width and thickness were both determined proportional to the square root of the jet/surface velocity ratio, with respective power law models in good agreement with measured values

A Review on Rotary Generators of Hydrodynamic Cavitation for Wastewater Treatment and Enhancement of Anaerobic Digestion Process

The issue of ever-increasing amounts of waste activated sludge (WAS) produced from biological wastewater treatment plants (WWTPs) is pointed out. WAS can be effectively reduced in the anaerobic digestion (AD) process, where methanogens break down organic matter and simultaneously produce biogas in the absence of oxygen, mainly methane and CO2. Biomethane can then be effectively used in gas turbines to produce electricity and power a part of WWTPs. Hydrodynamic cavitation (HC) has been identified as a potential technique that can improve the AD process and enhance biogas yield. Rotary generators of hydrodynamic cavitation (RGHCs) that have gained considerable popularity due to their promising results and scalability are presented. Operation, their underlying mechanisms, parameters for performance evaluation, and their division based on geometry of cavitation generation units (CGUs) are presented. Their current use in the field of wastewater treatment is presented, with the focus on WAS pre/treatment. In addition, comparison of achieved results with RGHCs relevant to the enhancement of AD process is presented