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Öğe Comparison of bi-directional multi-wave alternating magnetic field effect on ferromagnetic nanofluid flow in a circular pipe under laminar flow conditions(Pergamon-Elsevier Science Ltd, 2020) Tekir, Mutlu; Taskesen, Edip; Aksu, Bahri; Gedik, Engin; Arslan, KamilNanofluids have been attracting huge attention because of their heat transfer enhancement capabilities. Furthermore, magnetic field effect has been being researched recently. By reason of further heat transfer enhancement potential, constant and alternating magnetic fields have been utilized in the present work. Forced convection heat transfer of Fe3O4/water nanofluid flow in a straight pipe under constant and alternating magnetic field effect has been investigated experimentally. Experiments were performed under laminar flow regime (1122 < Re < 2124) and constant heat flux was applied externally on the pipe surface. It is aimed to study effect of different parameters such as Reynolds number, volume concentration of nanoparticle (0 <= phi <= 0.05), constant magnetic field (B = 0.3 T), alternating magnetic field with different wave types (sinus, square and triangle) and different frequencies (2, 5 and 15 Hz) of alternating magnetic field on the convective heat transfer. Experimental results showed that the constant magnetic field offers 13% convective heat transfer enhancement compared to the absence of a magnetic field. On the other hand, the alternating magnetic field increases the convective heat transfer in the pipe up to 35%. Furthermore, lower frequencies of the alternating magnetic field have been more effective in convective heat transfer enhancement. Square wave type alternating magnetic field steps forward in the aspect of convective heat transfer enhancement rate among the other wave types. The alternating magnetic field applications look promising in the future for increasing energy efficiency, and it can also be implemented in heat exchangers, solar collectors, emergency heat removal systems in nuclear power plants.Öğe Cooling of a photovoltaic module with temperature controlled solar collector(Elsevier Science Sa, 2014) Ceylan, Ilhan; Gurel, Ali Etem; Demircan, Husamettin; Aksu, BahriThe efficiency of photovoltaic modules decreases with heating, so there has been an increase with regard to the solution of the problem. Photovoltaic module converts the incoming solar radiation into heat and electric energy. Due to this heating feature of photovoltaic modules, it is likely to produce heat energy from PV modules as well. Such systems are called as both a photovoltaic and thermal systems in the literature. A lot of experimental studies were done by special processing on the PV module. Since the studies require special processing on the module, they remain as laboratory work only. In this study, different PV/T systems were experimentally analyzed for the cooling photovoltaic modules. A simple pipe was placed on PV module as a spiral heat exchanger in order to provide active cooling. Also, the system can easily be applied to large-scale systems. As a result of experimental research, the module efficiencies with cooling were calculated as 13%, and the module efficiencies without cooling were about 10%. As the set temperature increased, module temperature can be increased or decreased. The module temperature was changed according to solar radiation and set temperature. As the solar radiation increased the module temperature decreased in this experimental system. The solar radiation has nothing to do with set temperature for this system. (C) 2014 Elsevier B.V. All rights reserved.Öğe Effect of constant magnetic field on Fe3O4-Cu/water hybrid nanofluid flow in a circular pipe(Springer, 2022) Tekir, Mutlu; Taskesen, Edip; Gedik, Engin; Arslan, Kamil; Aksu, BahriThe purpose of this study is to investigate experimentally the convective heat transfer of Fe3O4-Cu/water hybrid nanofluid flow and to obtain the optimum mixing ratio of the hybrid nanofluid in a straight pipe under the influence of a constant magnetic field, applied perpendicularly to the flow direction. An experimental test rig has been designed and built for this purpose followed by rigorous tests that were performed on it for various parameters such as flow rate (corresponding 994 < Re < 2337) and nanoparticle volume concentration (0 < phi < 0.02). The experimental data are consistent with the existing literature. Increasing flow rate has led to an increased Nu number. Furthermore, the addition of both Fe3O4 and Cu nanoparticles into the distilled water increases the convective heat transfer inside the pipe. A significant finding of the study is that the constant magnetic field enables up to 14% convective heat transfer enhancement as opposed to the absence of a magnetic field. Furthermore, 1.0 vol.% Fe3O4-1.0 vol.% Cu/Water hybrid nanofluid performs the best under the effect of the constant magnetic field. Accordingly, the constant magnetic field applied externally to the flow is a key factor to enhance the convective heat transfer.Öğe FARKLI ÇALIŞMA ŞARTLARINDA CO2 SOĞUTUCU AKIŞKANLI ISI POMPASI PERFORMANSININ DENEYSEL VE TEORİK OLARAK İNCELENMESİ(2020-02-21) Aksu, BahriBu çalışmada, farklı çalışma şartlarında CO2 (R744) soğutucu akışkanlı buhar sıkıştırmalı sudan suya bir ısı pompasının performansı subkritik bölgede deneysel ve teorik olarak incelenmiştir. Sudan suya bir ısı pompası sistemi tasarlanarak, kurulan deney düzeneğinde farklı kondenser ve evaporatör su giriş sıcaklıkları ile farklı kondenser ve evaporatör su debilerinde iki farklı durum için deneyler gerçekleştirilmiştir. Birinci grup deneylerde; evaporatör su debisi 500 lt/h değerinde sabit tutularak, kondenser ve evaporatör giriş suyu sıcaklıkları 11 °C, 13 °C ve 15 °C değerinde değiştirilerek, 600 lt/h, 700 lt/h ve 800 lt/h değerlerindeki farklı kondenser su debilerinin ısı pompası performansı üzerindeki etkileri gözlemlenmiştir. İkinci grup deneylerde ise; kondenser su debisi 500 l/h değerinde sabit tutularak, kondenser ve evaporatör giriş suyu sıcaklıkları 11 °C, 13 °C ve 15 °C değerlerinde değiştirilerek 600 lt/h, 700 lt/h ve 800 lt/h değerlerindeki farklı evaporatör su debilerinin ısı pompası performansına etkisi gözlemlenmiştir. Deneylerde; sistem üzerinde basınç, sıcaklık, debi ve güç gibi parametreler ölçülmüştür. Deneysel ölçümlerden elde edilen veriler kullanılarak ısı pompasının enerji, ekserji ve termoekonomik analizleri yapılmıştır. Enerji analizi sonuçlarına göre birinci grup deneylerde ısı pompasının ısıtma tesir katsayısı (COPHP) değerinin 3,75 ile 4,049 aralığında, ikinci grup deneylerde ise 3,192 ile 3,75 aralığında değiştiği görülmüştür. Ekserji analizinden elde edilen sonuçlardan, ısı pompası ekserji veriminin birinci grup deneylerde 0,403 ile 0,428 aralığında, ikinci grup deneylerde ise 0,394 ile 0,416 aralığında değiştiği belirlenmiştir. Isı pompasının termoekonomik analizi MOPSA metoduna göre yapılmış, kondenserden suya aktarılan birim kW ısı enerjisi başına harcanan mali değerin; birinci grup deneylerde 0,153 $/kW ile 0,163 $/kW aralığında, ikinci grup deneylerde ise 0,160 $/kW ile 0,165 $/kW aralığında değiştiği tespit edilmiştir.
