Browsing by Subject "Heating"
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Item Open Access Coupling and power transfer efficiency enhancement of modular and array of planar coils using in-plane ring-shaped inner ferrites for inductive heating applications(American Institute of Physics Inc., 2017) Kilic V.T.; Unal, E.; Demir, Hilmi VolkanWe propose and demonstrate a highly effective method of enhancing coupling and power transfer efficiency in inductive heating systems composed of planar coils. The proposed method is based on locating ring-shaped ferrites in the inner side of the coils in the same plane. Measurement results of simple inductive heating systems constructed with either a single or a pair of conventional circular coils show that, with the in-plane inner ferrites, the total dissipated power of the system is increased by over 65%. Also, with three-dimensional full electromagnetic solutions, it is found that power transfer efficiency of the system is increased up to 92% with the inner ferrite placement. The proposed method is promising to be used for efficiency enhancement in inductive heating applications, especially in all-surface induction hobs.Item Restricted Eshot genel müdürlüğünün kuruluşundan itibaren İzmir’de belediye bünyesine bağlı toplu taşımanın tarihi(Bilkent University, 2022) Bilir, Ece; Tağı, Nergis; İdemen, Gökay Yusuf Tulga; Başaran, Süleyman Yağız; Koçkan, Selçuk Efeİzmir’de demografik unsurların genişlemesiyle ortaya çıkan altyapı sorunların giderilmesi amacıyla teşkilatlanan belediyeye, yıllar içerisinde çeşitlenen, bazı yükümlülükler verilmişti. Öncelikle su, havagazı ve elektrik gibi unsurların dağıtımı ve daha sonrasında toplu taşıma yönetiminin sorumluluğu verilen İzmir Belediyesi, büyükşehir olması sonucunda şehrin refah düzeyini arttırma ve koruma alanlarında yetki sahibi olmuştu. Böylece belediyenin alt kuruluşlarından olan ESHOT genel müdürlüğü toplu taşıma ve enerji dağıtımlarında rol oynamıştı. ESHOT bir müddet elektrik, su, havagazı, otobüs ve troleybüs işletmelerinin tek elde toplanmasını sağladıysa halkın talepleri, idare kolaylığı, teknolojik gelişme gibi faktörler sonucu ESHOT isim olarak kaldıysa da sadece otobüs işletmeciliğine yoğunlaşılmıştı. Günümüze kadar uzanan İzmir belediyesince sağlanan toplu taşıma hizmeti, talepler doğrultusunda değişmekte ve gelişmekte olan bir unsur olarak devam etmektedir.Item Open Access Heating of magnetic fluid systems driven by circularly polarized magnetic field(Elsevier BV * North-Holland, 2010) Ahsen, O. O.; Yilmaz, U.; Aksoy, M. Deniz; Ertas, G.; Atalar, ErginA theory is presented to calculate the heat dissipation of a magnetic suspension, a ferrofluid, driven by circularly polarized magnetic field. Theory is tested by in vitro experiments and it is shown that, regardless of the character of the relaxation process, linearly and circularly polarized magnetic field excitations, having the same root-mean-square magnitude, are equivalent in terms of heating efficiency.Item Restricted Kuruluşundan bugüne tarihi İzmir havagazı fabrikası(Bilkent University, 2021) Civan, Fazlı Eren; Bahçeci, Levent; Taşkın, Hüseyin Bora; Karadoğan, Yiğit Ali; Oran, Gülceİzmir Havagazı Fabrikası; kentin ulaşılabilirlik açısından kolay olan ve ticari açıdan hareketli olan Alsancak, o zamanki adıyla Darağacı, bölgesinde kurulmuştur. Kuruluş amaçlarının başında aydınlatma ve ısıtma gelmektedir. Fabrikanın kurulmasıyla İzmir halkının yaşam standartları yükselmiş, güvenlikleri artmış ve halkın istihdam oranı yükselmiştir. Fabrikanın uzun bir süre sorunsuz bir şekilde işletilmesinin ardından, yönetim açısından zor duruma düşmesi sebebiyle İzmir Belediyesi tarafından devralınmıştır. Fabrika yenilenmiş, makineler otomatikleşmiş, havagazının metreküp fiyatında indirime gidilmiş ve fabrikanın değeri 30 kat artmıştır. Abonelik taleplerinin artmasından bir süre sonra fabrika taleplere yetişememeye başlamış ve çalkantılı bir döneme girmiştir. Eş zamanlı olarak elektriğin yaygınlaşması, fabrikanın teknolojinin gelişme hızına ayak uyduramaması, çevre kirliliğine sebep olması ve daimi olarak zarar etmeye başlaması sebebiyle fabrika 1994 yılında kapatılmıştır. 14 yılın ardından tarihi dokusu korunarak restore edilip yeniden açılmış ve kültür sanat etkinliklerinde kullanılmaya başlanmıştır.Item Open Access Modeling of electrodes and implantable pulse generator cases for the analysis of implant tip heating under MR imaging(Wiley-Blackwell Publishing, Inc., 2015) Acikel, V.; Uslubas, A.; Atalar, ErginPurpose: The authors purpose is to model the case of an implantable pulse generator (IPG) and the electrode of an active implantable medical device using lumped circuit elements in order to analyze their effect on radio frequency induced tissue heating problem during a magnetic resonance imaging (MRI) examination. Methods: In this study, IPG case and electrode are modeled with a voltage source and impedance. Values of these parameters are found using the modified transmission line method (MoTLiM) and the method of moments (MoM) simulations. Once the parameter values of an electrode/IPG case model are determined, they can be connected to any lead, and tip heating can be analyzed. To validate these models, both MoM simulations and MR experiments were used. The induced currents on the leads with the IPG case or electrode connections were solved using the proposed models and the MoTLiM. These results were compared with the MoM simulations. In addition, an electrode was connected to a lead via an inductor. The dissipated power on the electrode was calculated using the MoTLiM by changing the inductance and the results were compared with the specific absorption rate results that were obtained using MoM. Then, MRI experiments were conducted to test the IPG case and the electrode models. To test the IPG case, a bare lead was connected to the case and placed inside a uniform phantom. During a MRI scan, the temperature rise at the lead was measured by changing the lead length. The power at the lead tip for the same scenario was also calculated using the IPG case model and MoTLiM. Then, an electrode was connected to a lead via an inductor and placed inside a uniform phantom. During a MRI scan, the temperature rise at the electrode was measured by changing the inductance and compared with the dissipated power on the electrode resistance. Results: The induced currents on leads with the IPG case or electrode connection were solved for using the combination of the MoTLiM and the proposed lumped circuit models. These results were compared with those from the MoM simulations. The mean square error was less than 9%. During the MRI experiments, when the IPG case was introduced, the resonance lengths were calculated to have an error less than 13%. Also the change in tip temperature rise at resonance lengths was predicted with less than 4% error. For the electrode experiments, the value of the matching impedance was predicted with an error less than 1%. Conclusions: Electrical models for the IPG case and electrode are suggested, and the method is proposed to determine the parameter values. The concept of matching of the electrode to the lead is clarified using the defined electrode impedance and the lead Thevenin impedance. The effect of the IPG case and electrode on tip heating can be predicted using the proposed theory. With these models, understanding the tissue heating due to the implants becomes easier. Also, these models are beneficial for implant safety testers and designers. Using these models, worst case conditions can be determined and the corresponding implant test experiments can be planned.Item Open Access Suppression of thermoelectric Thomson effect in silicon microwires under large electrical bias and implications for phase-change memory devices(American Institute of Physics Inc., 2014) Bakan G.; Gokirmak, A.; Silva H.We have observed how thermoelectric effects that result in asymmetric melting of silicon wires are suppressed for increasing electric current density (J). The experimental results are investigated using numerical modeling of the self-heating process, which elucidates the relative contributions of the asymmetric thermoelectric Thomson heat (∼J) and symmetric Joule heating (∼J2) that lead to symmetric heating for higher current levels. These results are applied in modeling of the self-heating process in phase-change memory devices. While, phase-change memory devices show a clearly preferred operation polarity due to thermoelectric effects, nearly symmetric operation can be achieved with higher amplitude and shorter current pulses, which can lead to design of improved polarity-invariant memory circuitry. © 2014 AIP Publishing LLC.Item Open Access Ultrafast burst-mode fiber lasers: source development and material processing(IEEE, 2015) İlday, F. ÖmerHigh-precision processing of materials with ultrafast laser pulses is drawing increasing attention as laser sources are finally catching up with industry requirements. In particular, very rapid progress has been achieved in ultrafast fiber lasers, which are popular as a result of their highly repeatable, environmentally robust performance, compact size and possibility to reach high average powers. Meanwhile, our understanding of the rich physics of ultrafast laser-material interaction remains incomplete, wherein lies new opportunities. A particularly exciting possibility concerns the use of groups of pulses, which are extremely closed in time. This changes the interaction physics drastically: A unqualified increase in laser repetition rate would result in severe heat accumulation and other undesirable effects. The average power can be kept at a desirable level by operating the laser in the so-called burst mode, whereby each burst contains a number of closely spaced pulses, benefiting from accumulative effects, while the bursts are repeated at much lower repetition rate. Under the right conditions, including keeping average power low enough to prevent excessive heat accumulation, relatively low peak powers for which plasma shielding and similar effects are reduced, ultrafast burst mode can lead to an order-of-magnitude increases in processing speed compared to uniform repetition rate operation of an otherwise identical laser source.