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Abstract: Pollution of water by plastic contaminants has received increasing attention, owing to its negative effects on ecosystems. Small plastic particles propagate in water and can travel long distances from the source of pollution. In order to research the settling motion of particles in water flow, a small-scale experiment was conducted, whereby spherical plastic particles of varying diameters were released in an open-channel flow. Three approaches were investigated to numerically simulate the motion of particles. The numerical simulation results were compared and validated with experimental data. The presented methods allow for deeper insight into particle motion in fluid flow and could be extended to a larger scale to predict the propagation of mesoplastics in natural environments.
Keywords: dense discrete phase model, discrete element method, diameter, discrete phase model, mesoplastics, particles, settling
Published in DKUM: 20.03.2025; Views: 0; Downloads: 4
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Abstract: Hidravlični sistemi so lahko podvrženi eroziji zaradi pojava kavitacije ali zaradi prisotnosti delcev v toku tekočine. V hidravličnih sistemih je pogosto prisotna hidrodinamska kavitacija, ki je posledica spremenjene dinamike toka, kjer pride do lokalnega povečanja hitrosti in posledičnega padca tlaka do tlaka uparjanja. Na trdni površini, ki je izpostavljena toku s kavitacijo, se lahko pojavi erozija zaradi kavitacije. Ob tem so lahko v tekočini tudi suspendirani delci, ki se ob trku s trdno površino odbijejo in pri tem oddajo del gibalne količine steni zaradi česar lahko nastopi erozija trdne površine. Ob poznavanju mehanizmov in sposobnosti modeliranja erozije zaradi kavitacije in delcev ostaja odprto področje hkratna obravnava pri modeliranju erozije zaradi obeh pojavov. Zato je bil razvit numeričen model za napoved erozije hidravličnih sistemov zaradi kavitacije in delcev. Numerični model sestoji iz modela homogene zmesi za večfazni tok, kjer je kavitacija modelirana z izvornim členom v dodatni prenosni enačbo mase pare, ki ga podaja Schnerr-Sauer kavitacijski model. Gibanje delcev je modelirano po pristopu Lagrangevega sledenja z dvosmernim sklapljanjem gibalne količine med delcem in tekočino. V komercialni program za računalniško dinamiko tekočin je preko uporabniško definiranih funkcij vpeljan model kavitacijske erozije. Erozija delcev je modelirana z McLaury modelom. Turbulenca je modelirana s tremi različnimi modeli, dvema RANS (k-ε RNG in k-ω SST) in enim hibridnim (DDES-SST). Z namenom validacije so izvedeni tudi eksperimenti s kavitacijo v toku z delci in brez delcev pri treh pretokih na primeru Venturijevega kanala, kjer erozijo na površini posredno napovemo z metodo barvnega nanosa. Narejena je primerjava rezultatov numeričnih simulacij z različnimi turbulentimi modeli, kjer je ugotovljeno, da daje najboljšo napoved DDES-SST model. Pri treh pretokih toka brez delcev in z delci je ugotovljeno zadovoljivo ujemanje med simulacijo in eksperimentom, s čimer je potrjena ustreznost numeričnega modela za napoved erozije zaradi kavitacije in zaradi delcev.
Keywords: kavitacija, delci, erozija
Published in DKUM: 22.10.2024; Views: 0; Downloads: 39
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Abstract: Plastic is one of the most widely used materials worldwide. The problem with plastic arises when it becomes waste, which needs to be treated. One option is to transform plastic waste into synthetic fuels, which can be used as replacements or additives for conventional fossil fuels and can contribute to more sustainable plastic waste treatment compared with landfilling and other traditional waste management processes. Thermal and catalytic pyrolysis are common processes in which synthetic fuels can be produced from plastic waste. The properties of pyrolytic oil are similar to those of fossil fuels, but different additives and plastic stabilizers can affect the quality of these synthetic fuels. The quality of fuels and the permissible particle sizes and number density are regulated by fuel standards. Particle size in fuels is also regulated by fuel filters in vehicles, which are usually designed to capture particles larger than 4 µm. Problems can arise with the number density (quantity) of particles in synthetic fuels compared to that in fossil fuels. The present work is a numerical study of how particle size and number density (quantity) influence cavitation phenomena and cavitation erosion (abrasion) in common-rail diesel injectors. The results provide more information on whether pyrolysis oil (synthetic fuel) from plastic waste can be used as a substitute for fossil fuels and whether their use can contribute to more sustainable plastic waste treatments. The results indicate that the particle size and number density slightly influence cavitation phenomena in diesel injectors and significantly influence abrasion.
Keywords: plastic waste, synthetic fuels, pyrolytic oil, common rail, cavitation, erosion, particles
Published in DKUM: 05.07.2024; Views: 131; Downloads: 16
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Abstract: The presented paper addresses two significant issues of the present time. In general, the studies of the effect of synthetic fuels on cavitation formation and cavitation erosion prediction in the nozzle tip of common-rail diesel injectors were addressed. The first problem is plastic waste, which can have a significant negative environmental impact if not treated properly. Most plastic waste has high energy value, so it represents valuable material that can be used in resource recovery to produce various materials. One possible product is synthetic fuel, which can be produced using thermal and catalytic pyrolysis processes. The first issue addressed in the presented paper is the determination of fuel properties since they highly influence the fuel injection process, spray development, combustion, etc. The second is the prediction of cavitation development and cavitation erosion in a common-rail diesel injector when using pyrolytic oils from waste plastic. At first, pyrolytic oils from waste high- and low-density polyethylene were obtained using thermal and catalytic pyrolysis processes. Then, the obtained oils were further characterised. Finally, the properties of the obtained oils were implemented in the ANSYS FLUENT computational program and used in the study of the cavitation phenomena inside an injection nozzle hole. The cavitating flow in FLUENT was calculated using the Mixture Model and Zwart-Gerber-Belamri cavitation model. For the modelling of turbulence, a realisable k–ε model with Enhanced Wall Treatment was used, and an erosion risk indicator was chosen to compare predicted locations of cavitation erosion. The results indicate that the properties of the obtained pyrolytic oils have slightly lower density, surface tension and kinematic viscosity compared to conventional diesel fuel, but these minor differences influence the cavitation phenomenon inside the injection hole. The occurrence of cavitation is advanced when pyrolytic oils are used, and the length of cavitation structures is greater. This further influences the shift of the area of cavitation erosion prediction closer to the nozzle exit and increases its magnitude up to 26% compared to diesel fuel. All these differences have the potential to further influence the spray break-up process, combustion process and emission formation inside the combustion chamber.
Keywords: plastic waste, synthetic fuels, pyrolytic oils, common-rail, cavitation, erosion, transient simulation
Published in DKUM: 18.03.2024; Views: 299; Downloads: 36
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Abstract: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Keywords: cavitation, erosion potentional, driving pressure, numerical simulations
Published in DKUM: 21.02.2024; Views: 400; Downloads: 279
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