Researcher:
Nejatpour, Mona

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PhD Student

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Mona

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Nejatpour

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Nejatpour, Mona

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2020 - 20213

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Researcher Of Publications: search.filters.isAuthorOfPublication.31190d15-8c79-472f-af4e-9670205c7f2a

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    Pool boiling heat transfer of ferrofluids on structured hydrophilic and hydrophobic surfaces: the effect of magnetic field
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2020) Sadaghiani, A. K.; Rajabnia, H.; Celik, S.; Noh, H.; Kwak, H. J.; Park, H. S.; Misirlioglu, I. B.; Ozdemir, M. R.; Kosar, A.; N/A; Department of Chemistry; Nejatpour, Mona; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902
    The combined effect of external magnetic field and surface modification on boiling heat transfer of ferrofluids was investigated in this study. Experiments were performed on suspensions of Fe3O4 nanoparticles (volume fraction of 0.025% vf%) with and without presence of magnetic field on structured (surfaces with artificial cavities) hydrophilic and hydrophobic surfaces. Surface related effects such as the hole diameter, pitch size and surface wettability on boiling heat transfer were revealed using the high speed camera system. According to the obtained results, application of magnetic field enhanced boiling heat transfer. The effect of magnetic field was more pronounced on surfaces with larger pitch sizes. Magnetic field promoted bubble nucleation on the superheated surfaces by generating an additional force via Fe3O4 nanoparticles, resulting in enhanced bubblebubble interactions and coalescence. Furthermore, the surfaces with the larger cavity diameter performed better in terms of heat transfer. Scanning Electron Microscopy (SEM) images showed that as the cavity diameter decreased, deposited nanoparticles tended to completely fill the cavities on hydrophilic surfaces and thus deteriorate boiling heat transfer. On hydrophobic surfaces, deposition of nanoparticles led to a biphilic surface, thereby enhancing boiling heat transfer. As the cavity size increased, smaller portion of the cavities was filled with nanoparticles, and nucleation could still occur from the nucleation sites.
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    A new magnetorheological damper for chatter stability of boring tools
    (Elsevier Science Sa, 2021) N/A; N/A; Department of Chemistry; Department of Mechanical Engineering; Saleh, Mostafa Khalil Abdou; Nejatpour, Mona; Acar, Havva Funda Yağcı; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; 178902; 179391
    Chatter is a limiting factor during boring of deep holes with long slender boring bars. In this article, a new magnetorheological (MR) damper is introduced to increase the stability of the boring process. The sponge-type configuration of the damper utilizes a minimal amount of MR fluid in the annulus around the boring bar. The MR fluid layer and the electromagnetic circuit are externally applied to the boring bar, which allows easy installation and adjustability in bar length. A custom made, bidisperse MR fluid is used to eliminate particle sedimentation and enhance the lifetime of the damper. The modal analysis of the boring bar with the new MR damper shows improvements in both the damping and the dynamic stiffness of the system. This enhancement significantly increases the chatter-free depth of cut on the stability lobe diagrams. This article presents the experimental validations on the boring of AL 7075 and Inconel 718 workpieces which are materials widely used in many aerospace applications. The damper is installed on a conventional boring bar for a CNC machining center setup, and its performance is tested under various machining conditions.
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    Bidisperse magneto-rheological fluids consisting of functional SPIONs added to commercial MRF
    (Elsevier Science inc, 2020) N/A; N/A; Department of Chemistry; Department of Chemistry; Nejatpour, Mona; Ünal, Uğur; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 42079; 178902
    Magnetorheological fluids (MRFs) are smart materials with a reversible and fast transition from a liquid to a semi-solid state when an external magnetic field is applied (magnetorheological effect). the sedimentation of micron-sized magnetic particles in commercial MRFs is a crucial problem limiting the long-term use in industrial applications. Here, we develop a new MRF based on commercial 140-CG LORD (R) with the addition of surface functional superparamagnetic iron oxide nanoparticles (SPIons). these new bidisperse MRFs are comprised of either poly(acrylic acid) (Paa) coated SPIons or lauric acid (La) coated SPIons and micron-sized fatty acid-coated magnetic particles of the commercial MRF. SPIons have specific coatings to interact with the fatty acid coating of the micron-sized Fe-particles. Sedimentation behaviour and the magnetorheological properties of these bidisperse MRFs with 6-12 wt % SPIon were examined. Bidisperse MRFs improved the stability and redispersibility of MRFs. Bidisperse MRFs with 12 wt% SPIon-Paa showed similar or better magnetorheological behaviour than the commercial MRF despite lower content of the micron size Fe-particles. Hence, A combination of magnetizable nano and micron-sized particles and utilization of correct surface chemistry that allows their favourable interaction improves the stability of MRFs without sacrificing magnetic response but even by improving it.