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Department: search.filters.department.Department of ChemistrySubject: search.filters.subject.Thermodynamics

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Now showing 1 - 4 of 4
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    A novel magnetomechanical pump to actuate ferrofluids in minichannels
    (Begell House, Inc, 2011) Bilgin, Alp; Kurtoglu, Evrim; Erk, Hadi Cagdas; Sesen, Muhsincan; Kosar, Ali; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902
    An improvement in the current methods of ferrofluid actuation was presented in this paper. A novel magnetomechanical microfluidic pump design was implemented with a ferrofluid as the active working fluid. Obtained flow rates were comparable to previous results in this research line. It was also seen that the basic pump architecture, which the subject pump is based on, enables much more room for further development.
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    Experimental studies on ferrofluid pool boiling in the presence of external magnetic force
    (Pergamon-Elsevier Science Ltd, 2018) Ozdemir, Mehmed Rafet; Sadaghiani, Abdolali K.; Motezakker, Ahmad Reza; Parapari, Sorour Semsari; Park, Hyun Sun; Kosar, Ali; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902
    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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    Experimental study on convective heat transfer performance of iron oxide based ferrofluids in microtubes
    (ASME, 2014) Kurtoğlu, Evrim; Kaya, Alihan; Gözüaçık, Devrim; Koşar, Ali; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902
    Ferrofluids are colloidal suspensions, in which the solid phase material is composed of magnetic nanoparticles, while the base fluid can potentially be any fluid. The solid particles are held in suspension by weak intermolecular forces and may be made of materials with different magnetic properties. Magnetite is one of the materials used for its natural ferromagnetic properties. Heat transfer performance of ferrofluids should be carefully analyzed and considered for their potential of their use in wide range of applications. In this study, convective heat transfer experiments were conducted in order to characterize convective heat transfer enhancements with lauric acid coated ironoxide (Fe3O4) nanoparticle based ferrofluids, which have volumetric fractions varying from 0% to similar to 5% and average particle diameter of 25 nm, in a hypodermic stainless steel microtube with an inner diameter of 514 mu m, an outer diameter of 819 lm, and a heated length of 2.5 cm. Heat fluxes up to 184 W/cm(2) were applied to the system at three different flow rates (1 ml/s, 0.62 ml/s, and 0.36 ml/s). A decrease of around 100% in the maximum surface temperature (measured at the exit of the microtube) with the ferrofluid compared to the pure base fluid at significant heat fluxes (>100 W/cm(2)) was observed. Moreover, the enhancement in heat transfer increased with nanoparticle concentration, and there was no clue for saturation in heat transfer coefficient profiles with increasing volume fraction over the volume fraction range in this study (0-5%). The promising results obtained from the experiments suggest that the use of ferrofluids for heat transfer, drug delivery, and biological applications can be advantageous and a viable alternative as new generation coolants and futuristic drug carriers.
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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.