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ÖZDEMİR, MEHMED RAFET

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ÖZDEMİR

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MEHMED RAFET

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2018 - 20202
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Has files: false × Subject: Boiling heat transfer ×

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    Experimental studies on ferrofluid pool boiling in the presence of external magnetic force
    (PERGAMON-ELSEVIER SCIENCE LTD, 2018) ÖZDEMİR, MEHMED RAFET; Ozdemir, Mehmed Rafet; Sadaghiani, Abdolali K.; Motezakker, Ahmad Reza; Parapari, Sorour Semsari; Park, Hyun Sun; Acar, Havva Yagci; Kosar, Ali
    The past decade has witnessed rapid advances in thermal-fluid applications involving nanoparticles due to existing heat transfer enhancements. The main challenges in working with nanoparticles are clustering, sedimentation and instability encountered in many studies. In this study, magnetically actuated Fe3O4 nanoparticles were coated with a fatty acid and dispersed inside a base fluid (water) in order to avoid clustering, sedimentation and instability as well as to improve the thermal performance. Boiling heat transfer characteristics of the ferrofluids were experimentally investigated with magnetic actuation and compared to the results without magnetic actuation. Nanoparticle mass fraction was the major parameter. Boiling heat transfer coefficient of the magnetically actuated system was found to be significantly higher compared to the case without magnetic actuation. The results showed that boiling heat transfer coefficient was not sensitive to the nanoparticle mass fraction.
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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) ÖZDEMİR, MEHMED RAFET; Sadaghiani, A. K.; Rajabnia, H.; Celik, S.; Noh, H.; Kwak, H. J.; Nejatpour, M.; Park, H. S.; Acar, H. Y.; Misirlioglu, I. B.; Ozdemir, M. R.; Kosar, A.
    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.