Search

Your search keyword '"Koşar, Ali"' showing total 572 results
Start Over Author "Koşar, Ali"
572 results on '"Koşar, Ali"'

25. Biphilic Functional Surfaces for Frost Prevention and Efficient Active Defrosting.

Author

Saeidiharzand, Shaghayegh, Sadaghiani, Abdolali Khalili, Orejon, Daniel, Sefiane, Khellil, and Koşar, Ali

Abstract

The present work addresses the systematic accurate fabrication and design of biphilic surfaces having superhydrophobic circular islands surrounded by a hydrophilic background by investigating their condensation frosting and defrosting behavior. A significant delay in frost formation is observed on samples with higher superhydrophobicity ratio A*, defined as superhydrophobic area to total area ratio. As the superhydrophobic island diameter D increases from D = 500 µm to D = 700 µm (A* from 19.62% to 38.46%), a 50% improvement/delay is observed in terms of frost formation or densification. Besides delaying icing/frosting, the presence of superhydrophobic areas empowers the formation of porous and nonuniform frost structure, which facilitates ice removal during the defrosting process. To this end, as the surface is recovered the ambient temperature, almost complete passive cleaning performance within only 23 s is observed on the biphilic design having superhydrophobic islands with the diameter of D = 500 µm, that is, a superhydrophobicity ratio A* of 19.62%. This work concludes on the optimum biphilic ratio, which is not only effective as a passive method by hindering frosting but also leads to a slush/water free surface after defrosting eased by the Laplace pressure gradient which is imposed by the different biphilic wettability patterns. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

26. New insights on cavitating flows over a microscale backward-facing step.

Author

Maleki, Mohammadamin, Rokhsar Talabazar, Farzad, Toyran, Erçil, Priyadarshi, Abhinav, Sheibani Aghdam, Araz, Villanueva, Luis Guillermo, Grishenkov, Dmitry, Tzanakis, Iakovos, Koşar, Ali, and Ghorbani, Morteza

Subjects
SURFACE forces, POROSITY, REYNOLDS number, MICROFLUIDIC devices, SHEAR strength, CAVITATION
Abstract

This study introduces the first experimental analysis of shear cavitation in a microscale backward-facing step (BFS) configuration. It explores shear layer cavitation under various flow conditions in a microfluidic device with a depth of 60 μm and a step height of 400 μm. The BFS configuration, with its unique characteristics of upstream turbulence and post-reattachment pressure recovery, provides a controlled environment for studying shear-induced cavitation without the complexities of other microfluidic geometries. Experiments were conducted across four flow patterns: inception, developing, shedding, and intense shedding, by varying upstream pressure and the Reynolds number. The study highlights key differences between microscale and macroscale shear cavitation, such as the dominant role of surface forces on nuclei distribution, vapor formation, and distinct timescales for phenomena like shedding and shockwave propagation. It is hypothesized that vortex strength in the shear layer plays a significant role in cavity shedding during upstream shockwave propagation. Results indicate that increased pressure notably elevates the mean thickness, length, and intensity within the shear layer. Instantaneous data analysis identified two vortex modes (shedding and wake modes) at the reattachment zone, which significantly affect cavitation shedding frequency and downstream penetration. The wake mode, characterized by stronger and lower-frequency vortices, transports cavities deeper into the channel compared to the shedding mode. Additionally, vortex strength, proportional to the Reynolds number, affects condensation caused by shockwaves. The study confirms that nuclei concentration peaks in the latter half of the shear layer during cavitation inception, aligning with the peak void fraction region. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

35. Removal of per- and polyfluoroalkyl substances (PFAS) from wastewater using the hydrodynamic cavitation on a chip concept

Author

Talabazar, Farzad Rokhsar, Baresel, Christian, Ghorbani, Reza, Tzanakis, Iakovos, Koşar, Ali, Grishenkov, Dmitry, Ghorbani, Morteza, Talabazar, Farzad Rokhsar, Baresel, Christian, Ghorbani, Reza, Tzanakis, Iakovos, Koşar, Ali, Grishenkov, Dmitry, and Ghorbani, Morteza

Abstract

The elimination of micropollutants such as highly fluorinated substances, including per- and polyfluoroalkyl substances (PFAS), in wastewater treatment plants has been receiving growing attention due to the urgent need to minimize their adverse effects on natural water and associated ecosystems. Conventional treatment methods often fall short in effectively removing PFAS. In this study, the Hydrodynamic Cavitation on a Chip concept (HCOC) was utilized to degrade 11 common PFAS variants (PFAS11) for the first time in three different hydrodynamic cavitation reactor set-ups, each enhanced with surface modifications involving roughness elements. Stockholm municipal wastewater treated by a Membrane BioReactor (MBR) process was subjected to fully developed cavitating flow treatment using the three distinct microscale hydrodynamic cavitation (HC) reactors. The obtained results indicate that the chemical-free HCOC technique employed in this study has a significant potential in the degradation of nearly all investigated PFAS11 compounds at a notable rate of 36.1 % while the combination with MBR process can prevent blockage within the fluidic channels, enabling continuous operation with high throughput processing rates. Our proposed methodology demonstrated promising results in eliminating PFAS and could contribute to advancements in the use of microscale HC to treat micropollutants in wastewater. These findings could be a major leap in water treatment technologies addressing the global burden of resource-efficient micropollutant water treatment.

Published
2024

Catalog

Books, media, physical & digital resources
See catalog results