Yazar "Kayfeci, Muhammet" seçeneğine göre listele
Listeleniyor 1 - 20 / 28
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe COMPARATIVE ANALYSIS OF A SOLAR TRIGENERATION SYSTEM BASED ON PARABOLIC TROUGH COLLECTORS USING GRAPHENE AND FERROFLUID NANOPARTICLES(Vinca Inst Nuclear Sci, 2021) Ibrahim, Alla; Kayfeci, MuhammetIn this comparative study, the thermodynamic analysis of a trigeneration system driven by a parabolic through solar collector based on two different types of nanofluid is performed. A standard trigeneration system consists of two subsystems, including an absorption heat pump and the organic Rankine cycle. Two types of nanoparticles (graphene and ferrofluid) that possess excellent and diverse physical properties within a base fluid (Syltherm 800) were selected to be the absorption fluids in the solar cycle. Four organic fluids, namely R123, R401a, R601, and R601a, for the organic Rankine cycle are examined. The results clearly depicted improvement in the system performance. It was found that graphene nanoparticles performed better as compared to the ferrofluid nanoparticles. The largest temperature of the collector outlet was obtained at 257.4 degrees C with Syltherm 800/graphene. The highest net power produced by the system was 134.1 kW and the maximum overall energy and exergy efficiencies of the system were 160.5% and 21.84%, respectively. The highest net power produced by the system was 134.1 kW and the maximum overall energy and exergy efficiencies of the system were 160.5% and 21.84%, respectively. The solar collectors are the main source of the exergy destruction and the highest value was recorded about 683 kW.Öğe Computational analysis of hydrogen storage capacity using process parameters for three different metal hydride materials(Pergamon-Elsevier Science Ltd, 2018) Elmas, Umran; Bedir, Feuzi; Kayfeci, MuhammetIn this study, hydrogen storage capacity were analyzed by considering hydrogen absorption test rig depending on some reactor design parameters such as metal hydride particle size, having fins at the tank, hydrogen inlet pressure, inlet radius of the tank, coolant temperature, general convective heat transfer coefficient and wall thickness of the tank. In the specified design parameters of the hydrogen storage system we put these in COMSOL Multiphysics 5.1 software to obtain some approaches in the large scale. All parameters were analyzed using three different metal hydrides of the MmNi(4,6)Al(0,4), LaNi4.75Al0.25 and LaNis. Some parameters like temperature distribution inside the tank, amount of the hydrogen mass to be stored in the tank, the time durations of them and the variations of the equilibrium pressure of the system were optimized. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Determination of energy saving and optimum insulation thicknesses of the heating piping systems for different insulation materials(Elsevier Science Sa, 2014) Kayfeci, MuhammetLarge amounts of heat losses occur in pipelines of district heating system. If these lines become insulated, a significant energy savings would be obtained. In this study, by using life cycle cost analysis (LCCA) method, the optimum insulation thickness, energy savings, annual costs and payback period were estimated for various pipe diameters and insulation materials of the heating systems in Isparta/Turkey and in the regions with different degree-day values. As a fuel, natural gas was used in the study. In consequence of the calculations, the optimum insulation thickness was found vary between 0.048 and 0.134m, the energy-saving was found vary between 10.84 and 49.78 $/m; and the payback period was found vary between 0.74 and 1.29 years. According to these results, EPS insulation material with a nominal diameter (DN) of 250 mm provides the highest energy savings, while the lowest value was found to be in fiberglass insulation material with DN 50 mm. As a result, heating systems, selection of suitable pipe diameters and insulation materials with optimum thicknesses provide significant economic advantages and savings. (C) 2013 Elsevier B.V. All rights reserved.Öğe Determination of optimum insulation thickness of external walls with two different methods in cooling applications(Pergamon-Elsevier Science Ltd, 2013) Kayfeci, Muhammet; Kecebas, Ali; Gedik, EnginThermal insulation is one of the most effective energy conservation for the cooling applications. For this reason, determination of the optimum thickness of insulation and its selection is the main subject of many engineering investigations. In this study, the optimum insulation thickness on the external walls in the cooling applications is analyzed based on two different methods used to determine annual energy consumption. One of the methods is the degree-hours method (Method 1) that is the simplest and most intuitive way of estimating the annual energy consumption of a building. The other is the method (Method 2) which using the annual equivalent full load cooling hours operation of system. In this paper, a Life Cycle Cost (LCC) analysis is used to evaluate accuracy of these methods, and the results are compared. The results show that the life cycle savings are overestimated by up to 44% in Method 2, while the optimum insulation thickness and payback period are respectively overestimated by up to 74% and 69% in Method 1. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.Öğe Effect of Optimum Insulation Thickness on Refrigeration Costs for Different Climate Zones(Asce-Amer Soc Civil Engineers, 2013) Kayfeci, Muhammet; Kecebas, AliA large part of energy cost on cooling applications is attributable to heat income through external walls. The best way to save energy is to use the optimum insulation thickness. In this study, the optimum insulation thicknesses, insulation-energy costs, and savings resulting from the use of these insulations is calculated in cities selected from four different climate zones in Turkey for four various insulation materials such as foamboard, extruded polystyrene (XPS), rock wool, and expanded polystyrene (EPS) in cold storage applications. Calculations show that rock wool insulation material yields the highest savings. Optimum insulation thicknesses vary between 0.074 and 0.159 m, energy savings vary between 30.59 and 80.61 $/m(2), and payback periods for investment cost vary between 3.15 and 3.73 years for the cooling. DOI: 10.1061/(ASCE)EY.1943-7897.0000085. (C) 2013 American Society of Civil Engineers.Öğe Electrochemical hydrogen generation(Academic Press Ltd-Elsevier Science Ltd, 2019) Kecebas, Ali; Kayfeci, Muhammet; Bayat, Mutlucan[No abstract available]Öğe Enhancement of hydrogen charging in metal hydride-based storage systems using heat pipe(Pergamon-Elsevier Science Ltd, 2019) Elhamshri, Fawzi A. M.; Kayfeci, MuhammetHeat transfer in metal hydride bed significantly affects the performance of metal hydride reactors (MHRs). Enhancing heat transfer within the reaction bed improves the hydriding rate. This study presents performance analysis in terms of storage capacity and time of three different cylindrical MHR configurations using storage media LaNi5: a) reactor cooled with natural convection, b) reactor with a heat pipe on the central axis, c) reactor with finned heat pipe. This study shows the impact of using heat pipes and fins for enhancing heat transfer in MHRs at varying hydrogen supply pressures (2-15 bar). At any absorption temperature, hydrogen absorption rate and hydrogen storage capacity increase with the supply pressure. Results show that using a heat pipe improves hydrogen absorption rate. It was found that finned heat pipe has a significant effect on the hydrogen charge time, which reduced by approximately 75% at 10 bar hydrogen supply pressure. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Experimental investigation of the effects of vessel design and hydrogen charge pressure on metal hydride based hydrogen(2014) Kayfeci, Muhammet; Bedır, Fevzi; Kurt, HüseyinThe hydrogen charge time in metal hydride vessel (MHV) is strongly influenced by the heat transfer from hydride vessel. In this study, the effect of parameters such as reactor geometry and alloy characteristics on hydrogen charge procedure is studied experimentally. In the experimental setup two different types of hydride vessel are designed and manufactured. Both vessels have the same interior volume; the un-finned type vessel cooled with natural convection and the second one was manufactured with fins around the vessel. The temperature variations of the vessel at four locations were measured charging with a range of pressure from 2 to 8 bar. The finned vessel show the lowest temperature increase with the fastest charging time under all charging pressures investigated. The stored hydrogen mass was measured as 0.82, 0.94, 1.15 wt% on un-finned vessel and 0.91, 1.01, 1.24 wt% on finned vessel at 2, 6 and 10 bar respectively. The experimental results show that the charge time of the vessel is considerably reduced, when the used fins manufacture on vessel. Furthermore, the addition of Al to the LaNi5 alloys has caused to reduce the hydrogen charge time and decreased of the stored hydrogen massÖğe EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF VESSEL DESIGN AND HYDROGEN CHARGE PRESSURE ON METAL HYDRIDE BASED HYDROGEN STORAGE PARAMETERS(Turkish Soc Thermal Sciences Technology, 2014) Kayfeci, Muhammet; Bedir, Fevzi; Kurt, HuseyinThe hydrogen charge time in metal hydride vessel (MHV) is strongly influenced by the heat transfer from hydride vessel. In this study, the effect of parameters such as reactor geometry and alloy characteristics on hydrogen charge procedure is studied experimentally. In the experimental setup two different types of hydride vessel are designed and manufactured. Both vessels have the same interior volume; the un-finned type vessel cooled with natural convection and the second one was manufactured with fins around the vessel. The temperature variations of the vessel at four locations were measured charging with a range of pressure from 2 to 8 bar. The finned vessel show the lowest temperature increase with the fastest charging time under all charging pressures investigated. The stored hydrogen mass was measured as 0.82, 0.94, 1.15 wt% on un-finned vessel and 0.91, 1.01, 1.24 wt% on finned vessel at 2, 6 and 10 bar respectively. The experimental results show that the charge time of the vessel is considerably reduced, when the used fins manufacture on vessel. Furthermore, the addition of Al to the LaNi5 alloys has caused to reduce the hydrogen charge time and decreased of the stored hydrogen mass.Öğe EXPERIMENTAL INVESTIGATION OF USING GRAPHENE NANOPLATELETS AND HYBRID NANOFLUID AS COOLANT IN PHOTOVOLTAIC THERMAL SYSTEMS(Vinca Inst Nuclear Sci, 2022) Alshikhi, Omran; Kayfeci, MuhammetIt is a common observation that the photovoltaic (PV) panel shows a compromised performance when its temperature rises. To handle the performance reduction, most PV panels are equipped with a thermal absorber, for removing the solar cells' excessive heal with the help of a heat transfer fluid. The mentioned thermal absorber system is termed as PV thermal or simply PV/T. This study aims to experimentally investigate the effects of agraphene nanoplatelets nanofluid, distilled water, and hybrid nanofluid as transfer fluids in PV/T collectors. A hybrid nanofluid comprises Al2O3 and graphene nanoplatelets. An outdoor experimental setup was installed and tested under the climatic conditions in Karabuk, Turkey, to measure the inlet as well as outlet PV/T fluid temperatures, ambient temperature with solar radiation, and surface temperatures of both PV/T collector and the PV panel. The mass percentage of the coolant fluids was 0.5% (by weight) and their flow rate was 0.5 Lpm. Results show that the graphene nanoplatelets nanofluid is the most effective fluid because it showed superior thermal efficiency among all the tested fluids. Adding a thermal unit to the PV/T unit increased the overall energy efficiency by 48.4%, 52%, and 56.1% using distilled water, hybrid nanofluid, and graphene nanofluid, respectively.Öğe Experimental investigations of using MWCNTs and graphene nanoplatelets water-based nanofluids as coolants in PVT systems(Pergamon-Elsevier Science Ltd, 2019) Alous, Salaheldin; Kayfeci, Muhammet; Uysal, AliIn this study, a photovoltaic thermal collector)PVT(has been constructed in Karabuk University, Turkey to investigate the effects of utilizing multiwalled carbon nanotubes (MWCNT) and graphene nanoplatelets dispersed in water as a base fluid with a concentration of 0.5 wt% on the performance of PVT systems. Outdoor experiments were run with volume flow rate of 0.5 L/min for the aforementioned nanofluids and distilled water as a reference fluid. The study results, which were analyzed from energetic and exergetic viewpoints, have shown and revealed that the MWCNT-water nanofluid presented a better performance in terms of photovoltaic energetic conversion compared to graphene nanoplatelets-water nanofluid and distilled water, while graphene nanoplatelets-water nanofluid revealed the highest thermal energetic efficiency. Moreover adding thermal unit to photovoltaic module (PV) enhanced the total energetic efficiency by 53.4% for distilled water, 57.2% for MWCNT-water, and 63.1% for graphene-water. From the exergetic viewpoint, the increase in total exergetic efficiency was 11.2%, 12.1%, and 20.6% for PVT collector cooled by distilled water, MWCNT-water nanofluid, and graphene nanoplatelets-water nanofluid respectively.Öğe EXPERIMENTAL STUDY ABOUT UTILIZATION OF MWCNT AND GRAPHENE NANOPLATELETS WATER-BASED NANOFLUIDS IN FLAT NON-CONCENTRATING PVT SYSTEMS(Vinca Inst Nuclear Sci, 2021) Alous, Salaheldin; Kayfeci, Muhammet; Uysal, AliAlthough the increment the performance of photovoltaic thermal (PVT) systems by using the nanofluids as working fluids have gained the attention of researchers during the last two decades, there is still, a lack in the literature study associated to this application. This study contributes to the investigations and researches of applying the nanofluids to increase the performance of PVT collectors. A flat non-concentrating PVT collector has been designed, constructed and, outdoor tested in Karabuk University, Turkey. The considered working fluids in this study are multiwall carbon nanotubes (MWCNT), and graphene nanoplatelets dispersed in water as a base fluid with a concentration of 0.5 wt. %. The experiments were run with a volume flow rate of 0.5 L per minute for the aforementioned nanofluids and distilled water (as a reference fluid). The study results have shown and revealed that the MWCNT-water nanofluid presented a better performance in terms of electrical energetic efficiency compared to graphene nanoplatelets-water nanofluid and distilled water, while graphene nanoplatelets-water nanofluid revealed the highest thermal energetic efficiency. Moreover adding thermal unit to photovoltaic module enhanced the total energetic efficiency by 53.4% for distilled water, 57.2% for MWCNT-water, and 63.1% for graphene-water.Öğe Fosil yakıtların kullanımından kaynaklanan hava kirliliği üzerine jeotermal enerji ve doğalgaz kullanımının etkisi: afyon örneği(2010) Keçebaş, Alı; Gedik, Engin; Kayfeci, MuhammetDünya nüfusunun sürekli arttığı, teknolojinin hızla gelistiği ve bu gelismelere paralel olarak enerji tüketiminde de büyük bir artıs olduğu görülmektedir. Günümüzde fosil kökenli enerji kaynaklarının sınırlı olması, tüketimin sürekli artması ve bu enerji kaynakların gittikçe azalması enerji fiyatlarının sürekli artmasına neden olmaktadır. Ayrıca bu enerji kaynakları bilinçsizce kullanıldığında çevre problemlerinin özellikle de hava kirliliğine neden olmaktadır. Hava kirliliğinin bilhassa kıs aylarında ölümcül boyutlara ulasması, bu konuda yakıt kaynaklı kirlenmenin önemini vurgulamaktadır. Bu çalısmada Afyon merkezde bulunan meskenlerde kullanılan yakıtlara göre atmosfere salınan emisyonlar belirlenir. Jeotermal enerji ve doğalgazın ısıtma amaçlı kullanımına dikkat çekilir. Ayrıca Afyon’da kullanılan kaynaklara sahip diğer sehirlerimize örnek olusturması için jeotermal enerji ve doğalgaz kullanımının hava kirliliğini önlemedeki katkısını güncel rakamlarla ortaya koymaktadır. Sonuçlar; yakıtların yakılması durumunda açığa çıkan $SO _2$ ve PM yerel emisyonları jeotermal için 1,7 bin ton $SO _2$/yıl ve 421 ton PM/yıl ve doğalgaz için ise 0,2 ton $SO _2$/yıl ve 3,8 ton PM/yıl azaldığını gösterir. Afyon örneğinden jeotermal ve doğalgaz ısıtma ile büyük miktarlarda $SO _2$ ve PM emisyonlarını önlemektedirler.Öğe Hydrogen production(Academic Press Ltd-Elsevier Science Ltd, 2019) Kayfeci, Muhammet; Kecebas, Ali; Bayat, Mutlucan[No abstract available]Öğe Hydrogen properties(Academic Press Ltd-Elsevier Science Ltd, 2019) Kecebas, Ali; Kayfeci, Muhammet[No abstract available]Öğe Hydrogen storage(Academic Press Ltd-Elsevier Science Ltd, 2019) Kayfeci, Muhammet; Kecebas, Ali[No abstract available]Öğe Improved hydrogen adsorption of ZnO doped multi-walled carbon nanotubes(Pergamon-Elsevier Science Ltd, 2020) Kaskun, Songul; Akinay, Yuksel; Kayfeci, MuhammetHydrogen storage is still one of the most important problems to improve hydrogen energy usage widespread. New materials capable of storing hydrogen with high efficiency must be introduced to overcome this problem. In recent years, addition of metals or inorganic compounds to multiwalled carbon nanotubes (MWCNTs) has been generally used for hydrogen uptake studies to enhance adsorption property of the nanotubes. In this study, Zinc oxide (ZnO) nanoparticles doped MWCNTs (ZnO-MWCNTs) have been produced as new reversible hydrogen storage materials, and we have investigated characterization of ZnO-MWCNTs by XRD, SEM, TGA, TEM and BET analyses. The functionalized MWCNTs and ZnO doped MWCNTs were subjected to hydrogenation step by dynamic gas sorption analyser under pressure of 5-50 bar. The hydrogen uptake capacities of the materials under different pressures were measured gravimetrically. It was indicated that by controlling the pressures for hydrogenation of ZnO-MWCNTs induces the spillover of ZnO nanoparticles in the layer of MWCNTs which in return with high hydrogen adsorption capacity. Consequently, the hydrogen adsorption of the functionalized MWCNTs (fMWCNTs) and the ZnO-MWCNTs were achieved to be 1.05 wt% and 2.7091 wt% under pressure of 50 bar as maximum. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Induction heated metal hydride tube for hydrogen storage system(Pamukkale Univ, 2022) Nacar, Salih; Oncu, Selim; Kayfeci, MuhammetIn this study, the metal tube is heated up to a certain temperature by induction heating method so that the hydrogen stored by metal hydride method in it can be discharged. The voltage fed series resonant inverter (SRI) is used in the power stage of the system and the power switches are turned on under soft-switching conditions. The closed loop controlled 300 W SRI is designed to set the temperature of the tube to the reference temperature of 250 degrees C. The power control of SRI is realized by frequency control. The temperature of the tube is controlled by hysteresis on-off control due to its simple structure and easy applicability. 16-bit DSPIC33FJ16GS502 is used in the control of the system.Öğe Life Cycle Assessment and Cumulative Energy Demand Analyses of a Photovoltaic/Thermal System with MWCNT/Water and GNP/Water Nanofluids(Mdpi, 2023) Dolgun, Gulsah Karaca; Kosan, Meltem; Kayfeci, Muhammet; Georgiev, Aleksandar G.; Kecebas, AliThe global climate crisis has led society toward cleaner energy sources. Another reason is the limited reserves of fossil energy resources. Efforts to increase the efficiency of photovoltaic modules (PVs) have gained momentum. The high temperature is the biggest factor causing a decrease in the efficiency of PVs. In this study, a commercial PV was cooled with distilled water, a multiwalled carbon nanotubes (MWCNT)/water mixture, and a graphene nanoplatelets (GNP)/water mixture. The environmental impact of electricity, total energetic efficiency, energy payback time, energy return on investment, and embodied energy of the PV/thermal (PV/T) system were compared using life cycle assessment and cumulative energy demand. The electrical efficiency of the PV/T changed between 13.5% and 14.4%. The total efficiency of PV/T changed between 39.5% and 45.7%. The energy returns on investment were 1.76, 1.80, and 1.85 for PV/T-distilled water, the PV/T-MWCNT/water mixture, and the PV/T-GNP/water mixture, respectively. Moreover, the embodied energy evaluation values were 3975.88 MJ for PV/T-distilled water, 4081.06 MJ for the PV/T-MWCNT/water mixture, and 4077.86 MJ for the PV/T-GNP/water mixture. The main objective of this research was to study the energy and environmental performances of PVs cooled with different nanofluids and draw general conclusions about the applicability of these systems.Öğe Numerical investigation on turbulent convective heat transfer of nanofluid flow in a square cross-sectioned duct(Emerald Group Publishing Ltd, 2019) Senay, Guelbanu; Kaya, Metin; Gedik, Engin; Kayfeci, MuhammetPurpose The purpose of this study is to numerically investigate the heat transfer enhancement by using two different nanofluids flow throughout the square duct under a constant heat flux (500x10(3) W/m(2)). Design/methodology/approach In numerical computations, ANSYS Fluent code based on the finite volume method was used to solve governing equations by iteratively. Water, Al2O3-water and TiO2-water nanofluids were used for different flow velocities changing 1 m/s to 8 m/s (i.e. Reynolds number varying from 3,000 to 100,000). Findings The results were compared with results published previously in the literature and close agreement was observed especially considering Dittus and Boelter correlation for water. It was found that from the obtained results, increasing flow velocity and volume fractions of nanoparticles has caused to increase Nu number for all cases. Besides, variations of pressure drop, Darcy friction factor are presented graphically and discussed in detail. The results are consistent with a deviation of 1.3 to 15 per cent with the results of other researchers. Originality/value The effects of the Re numbers and volume fractions of nanoparticles (0.01 <= Phi <= 0.04) on the heat transfer and fluid flow characteristics such as average Nu number, pressure drop (Delta P) and Darcy friction factor (f) were investigated.
