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Öğe A comparative analysis study of alternative energy sources for automobiles(Pergamon-Elsevier Science Ltd, 2015) Ugurlu, Adem; Oztuna, SemihaDepletion of oil resources and some environmental factors have been pushing automobile makers and the scientific communities to study on the use of alternative energy sources in automobiles. In this respect, some energy sources will come to the forefront with some advantages while some others not. To determine which alternative energy source is suitable for automobiles in terms of the existing conditions is a very important issue. It is necessary to know the characteristics of these energy types and evaluate their advantages and disadvantages to make this determination. In this study, a comparative analysis is performed for fuels such as LPG, CNG, hydrogen, biodiesel, ethanol and methanol, which could be used as an alternative to gasoline and diesel, and electric, hybrid and fuel cell vehicles. According to the comparison, LPG and CNG are best alternative fuels for economical reasons, while electric and fuel cell vehicles stand out as their emission advantages. Also, hydrogen can be considered as a key fuel due to its usage as an energy source for both internal combustion engines and fuel cell vehicles. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Design and thermodynamic analysis of a solar-assisted cini ceramic drying system(Pergamon-Elsevier Science Ltd, 2017) Buyukakin, Mustafa Kemalettin; Oztuna, Semiha; Demir, HakanNowadays, solar-assisted systems have been identified as one of the best solutions to use in order to save energy in industrial processes. Energy costs and environmental pollution emanating from these proposed systems are unequivocally lower than conventional systems. In this study, a traditional Turkish cini ceramic drying kiln, with a daily capacity of 600 kg, was designed and analysed from a thermodynamic perspective. A new solar energy system was introduced, which was integrated into a drying kiln, and the size of the solar energy system components were determined. The storage capacity and the initial temperature of the water tank, the airflow rate in the drying kiln and the heat exchanger size were analysed throughout the drying process. The number of solar collectors required for the system was calculated, based on the average summer insolation conditions in Iznik, which is located in north west Turkey. A comparative analysis was undertaken to determine the daily energy savings between this solar-assisted system and conventional systems. (C) 2017 Elsevier Ltd. All rights reserved.Öğe Effects of hydrogen enrichment of methane on diffusion flame structure and emissions in a back-pressure combustion chamber(Pergamon-Elsevier Science Ltd, 2020) Oztuna, Semiha; Buyukakin, Mustafa KemalettinIn the present study, the effects of hydrogen enrichment of methane are investigated numerically from the diffusion flame structure and emissions aspect. Fluent code is utilised as the simulation tool. In the first part of the study, four experiments were conducted using natural gas as fuel. A non-premixed burner and a back-pressure boiler were utilised as the experimental setup. The natural gas fuel consumption rate was changed between 22 Nm(3)/h and 51 Nm(3)/h. After the experimental studies, the numerical simulations were performed. The non-premixed combustion model with the steady laminar flamelet model (SFM) approach was used for the calculations. The methane-air extinction mechanism was utilised for the calculation of the chemical species. The numerical results were verified with the experimental results in terms of the flue gas emissions and flue gas temperature values. In the second part of the study, four different hydrogen-enriched methane combustion cases were simulated using the same methane-air extinction mechanism, which included the hydrogen oxidation mechanism as a sub mechanism. The same energy input (432 kW) was supplied into the boiler for all the studied cases. The obtained results show that the hydrogen addition to methane significantly change the diffusion flame structure in the combustion chamber. The hydrogen-enriched flames become broader and shorter with respect to the pure methane flame. This provides better mixing of the reactants and combustion products in the flame regions due to the use of a back-pressure boiler. In this way, the maximum flame temperature values and thermal NO emissions are reduced in the combustion chamber, when the hydrogen addition ratio is less than 15% by mass. The maximum temperature value is calculated as 2030 K for the case with 15% hydrogen addition ratio by mass, while it is 2050 K for the case without hydrogen enrichment. Therefore, it is determined that the hydrogen-enriched methane combustion in a back-pressure combustion chamber has the potential of reducing both the carbon and thermal NO emissions. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe An Experimental Study on SiO2-ND Hybrid Nanofluid: Thermal Conductivity, Viscosity, and Stability with New Forecast Models(Bentham Science Publ Ltd, 2022) Yalcin, Gokberk; Oztuna, Semiha; Dalkilic, Ahmet Selim; Nakkaew, Santiphap; Wongwises, SomchaiObjective: In the present investigation, thermal conductivity and viscosity properties of water-based SiO2-ND hybrid nanofluid were measured, experimentally. Methods: Nanofluids were prepared by using a two-step method and with three different (0.5%, 0.75%, and 1%) concentrations. Every concentration had three different SiO2-ND mixtures (50% SiO2 - 50% ND, 33% SiO2 - 66% ND, 66% SiO2 - 33% ND). Results: The most stable sample was measured as -33.4 mV. Measurements of viscosity and thermal conductivity were done from 20oC to 60oC at every 10oC. Thermal conductivity data were measured by thermal conductivity analyzer and viscosity data were measured by tube viscometer. The highest thermal conductivity enhancement was measured for 1% SiO2 (0.33): ND (0.66) at 40oC and the highest relative dynamic viscosity was calculated as 4.19 for 1% SiO2 (0.33): ND (0.66) at 40oC. A comparison table is also given to show the zeta potential values-concentration relations. Conclusion: Finally, two different correlations for predicting thermal conductivity and viscosity were proposed for practical usage.Öğe Experimental study on the thermal conductivity of water-based CNT-SiO2 hybrid nanofluids(Pergamon-Elsevier Science Ltd., 2018) Dalkilic, Ahmet Selim; Yalcin, Gokberk; Kucukyildirim, Bedri Onur; Oztuna, Semiha; Eker, Aysegul Akdogan; Jumpholkul, Chaiwat; Nakkaew, Santiphap; Wongwises, SomchaiThis experimental study includes measurement of thermal conductivity of distilled water-based CNT-SiO2 hybrid nanofluids. Nanofluids were prepared by using two-step method, 3 different concentrations and 4 different mass range of CNT-SiO2. SiO2 has 2200 kg m(-)(3) density, 1.4 W m(-1) K (-1) thermal conductivity and 7 nm average particle size. CNT has 2620 kg m(-3) density, 25 W m (-1) K(-1 )thermal conductivity and 6-10 nm average particle size. Samples were placed in ultrasonic homogenizer maximum power capacity for 3 h. Throughout sonication process temperature of nanofluids have been kept under control in order not to chance volumetric fraction of nanofluids. All measurements of thermal conductivity were done by using thermal conductivity meter. Thermal conductivity meter was calibrated by di-water. Measurements of thermal conductivity was done range from 25 degrees C to 60 degrees C for every 5 degrees C. Validation of measurements had been performed by using di-water and shown in a thermal conductivity-temperature figure. Minimum and maximum thermal conductivity enhancements were revealed in detail. Alteration of the thermal conductivity with temperature according to various volumetric fractions were in literature rated and it is found that the thermal conductivity increases with temperature and vol. fraction clearly. Enhancement on the thermal conductivity to di-water were also depicted for various temperatures and vol. fraction in figures. Almost well-known correlations in the literature were given with their predictable rates. Moreover, comparisons with other studies were provided in this present study. A practical correlation was proposed for other researchers.Öğe How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?(Pergamon-Elsevier Science Ltd, 2020) Ugurlu, Adem; Oztuna, SemihaEmissions variations of liquid hydrogen (LH2) production methods in liquid hydrogen powered vehicles are investigated in this study. Volatile organic compounds (VOC), carbon monoxide (CO), nitrogen oxides (NOx), particulate matters (PM10 & PM2.5), sulfur oxides (SOx), and carbon dioxide (CO2) emissions, which are on well-to-wheel (WTW) basis, are evaluated for 2013 model year's cars in the target year of 2018. GREET software is utilized for the emissions. When the average values of all emissions are compared, hydrogen production by the solar power, nuclear, and electrolysis methods have the lowest emissions, respectively, and hydrogen production by coal and electricity methods have the highest emissions, respectively. On the other hand, it is found that in all emission types and hydrogen production methods, fuel cell vehicles (FCV) emit less emission than spark ignition hybrid electric vehicles (SI HEV) and SI HEVs emit less emission than spark ignition internal combustion engine vehicles (SI ICEV). Emissions decrease by 22.4% in SI HEVs compared to SI ICEVs, 35.1% in FCVs compared to SI HEVs, and 49.6% in FCVs compared to SI ICEVs for average of all emissions. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe The influence of particle size on the viscosity of water based ZnO nanofluid(Elsevier, 2023) Yalcin, Gokberk; Oztuna, Semiha; Dalkilic, Ahmet Selim; Wongwises, SomchaiThis experimental work investigated, the effect of ZnO particles' size on the water-based nanofluid viscosity. Nanofluid samples with 0.5, 0.75, and 1% volume concentrations were prepared using 20 and 50 similar to 150 nm ZnO nanoparticle sizes. Their viscosity was determined at 20, 30, 40, 50, and 60 similar to C. Scanning electron microscopy was employed to investigate the morphology of the nanoparticles. The maximum relative viscosity was measured for 1% ZnO (50 similar to 150 nm) as 1.35 times water. The stability of samples was evaluated for 1% ZnO (20 nm) and 1% ZnO (50 similar to 150 nm) by measuring their Zeta potential values which were similar to 21.4 mV and -23.1 mV, respectively. The correlation for the dynamic viscosity using measured data was compared with wellknown ones. The offered correlation has R-2 = 0.988, R-adj(2) = 0.987, and +/- 5.58% maximum deviation. The results showed that 12.8% reduction in viscosity is possible by varying nanoparticle sizes. The current study proposes additional new findings on the nanofluids' usability. (C) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.Öğe Measurement of thermal conductivity and viscosity of ZnO-SiO2 hybrid nanofluids(Springer, 2022) Yalcin, Gokberk; Oztuna, Semiha; Dalkilic, Ahmet Selim; Wongwises, SomchaiPreparing and defining of thermal properties of new type hybrid nanofluids are essential to understand the fluidity mechanism of hybrid nanofluids and select suitable nanofluids in terms of application. This research aims to provide an alternative fluid for different applications and complete the new type of nanofluid necessity in the literature that has been reported by different research groups. In this current investigation, water-based ZnO-SiO2 hybrid nanofluid is prepared by using the two-step method, and thermal conductivity and dynamic viscosity values are experimentally specified. ZnO-SiO2 hybrid nanofluid has 0.5%, 0.75%, and 1% with 50% ZnO-50% SiO2; 33.3% ZnO-66.6% SiO2, and 66.6% ZnO-33.3% SiO2 nanoparticle mixtures. Thermal conductivity and dynamic viscosity are experimentally measured from 20 to 60 degrees C. Maximum thermal conductivity rising is 2.26%, and it is obtained for 1% ZnO0.66-SiO2(0.33) at 50 degrees C. Maximum dynamic viscosity increment is measured as 1.36 times of base fluid for 1% ZnO0.33-SiO2(0.66) at 50 degrees C. Changes in thermal properties are reasonable to use ZnO-SiO2 hybrid nanofluid in different thermal applications to increase system heat transfer rate and efficiency and reduce pressure drop and power consumption. Finally, two different regression equations are developed to predict the thermal conductivity and dynamic viscosity, respectively.Öğe NATURAL CONVECTION BEAT TRANSFER OF NANOFLUIDS IN A PARTIALLY DIVIDED ENCLOSURE(Turkish Soc Thermal Sciences Technology, 2013) Oztuna, Semiha; Kahveci, KamilIn this study, natural convection heat transfer of water-based nanofluids in a partially divided enclosure is investigated. Governing equations are solved for partition locations of 0.2, 0.4, 0.6, and 0.8, partition lengths of 0.25, 0.50, 0.75 and 1, solid volume fractions ranging from 0-10%, and Rayleigh numbers varying from 10(4) to 10(6). Three different nanoparticles, Cu, CuO, and Al2O3, are taken into consideration, and the ratio of the nanolayer thickness to the original particle radius is taken at a fixed value of 0.1. The results show that heat transfer decreases considerably with increasing partition height. Furthermore, as the distance of the partition from the hot wall increases, an initial decrease and subsequent increase is observed in the average Nusselt number for low Rayleigh numbers, and an initial increase and subsequent decrease is observed for high Rayleigh numbers. The results also reveal that heat transfer increases considerably when nanoparticles are used and that the largest and smallest increase are obtained for Cu and Al2O3 nanoparticles, respectively. Nanoparticle usage results in an increase in the average Nusselt number up to 35% for Ra=10(4), up to 32% for Ra=10(5), and up to 25% for Ra=10(6). The results also indicate that the average Nusselt number increases almost linearly with solid volume fraction.Öğe Numerical investigation on hydrogen-enriched methane combustion in a domestic back-pressure boiler and non-premixed burner system from flame structure and pollutants aspect(Pergamon-Elsevier Science Ltd, 2020) Buyukakin, Mustafa Kemalettin; Oztuna, SemihaIn this paper, the non-premixed hydrogen-enriched methane-air combustion was investigated numerically with the use of a CFD code. In the first part of the study, the combustion experiments were performed in a back-pressure boiler using natural gas. The intake rate of fuel was kept constant as 45 Nm(3)/h while the coefficient for the air excess ratio was changed between 1.2 and 1.35. After the experiments, the numerical analyses were performed. The Fluent code was utilized as the simulation instrument. The eddy dissipation combustion model was selected to be used in the numerical analyses, since it is known that this combustion model can save computational time and fairly predict the combustion flame structure and emissions. Pure methane and natural gas were taken as fuels in the numerical analyses. The obtained results from the numerical analyses were validated with the experimental flue gas temperature and emission measurements. Then, the hydrogen-enrichment of pure methane fuel was investigated numerically in such a way that the boiler capacity (432 kW) was kept constant. The coefficient for the air excess ratio was 1.2 for all the considered combustion simulation cases. The hydrogen addition ratio was 25%, 50% and 75% by mass, respectively. The thermal NO emissions and temperature distributions in the combustion chamber were obtained according to the different hydrogen-enriched methane fuel combustion cases. In addition, the emissions contained in the flue gas together with the temperature values were calculated. The obtained results from the numerical studies indicate that the hydrogen-enrichment of methane reduces the carbon emissions, while it substantially augments the formation of the thermal NO emissions. The calculated thermal NO emission value in the flue gas is 147 ppm for the pure methane combustion case, and it is 566 ppm for the combustion case with 75% by mass of hydrogen addition ratio. Therefore, it is determined that hydrogen fuel is a pollutant from the thermal NO emission aspect for the considered enrichment ratios in the studied domestic boiler-burner system. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Preface to the special issue on the Fourth International Hydrogen Technologies Congress (IHTEC 2019), June 20-23 2019, Edirne, Turkey(Pergamon-Elsevier Science Ltd, 2020) Eroglu, Inci; Oztuna, Semiha[Abstract Not Available]Öğe A review of hydrogen usage in internal combustion engines (gasoline-Lpg-diesel) from combustion performance aspect(Pergamon-Elsevier Science Ltd, 2020) Akal, Dincer; Oztuna, Semiha; Buyukakin, Mustafa KemalettinDemand for fossil fuels is increasing day by day with the increase in industrialization and energy demand in the world. For this reason, many countries are looking for alternative energy sources against this increasing energy demand. Hydrogen is an alternative fuel with high efficiency and superior properties. The development of hydrogen-powered vehicles in the transport sector is expected to reduce fuel consumption and air pollution from exhaust emissions. In this study, the use of hydrogen as a fuel in vehicles and the current experimental studies in the literature are examined and the results of using hydrogen as an additional fuel are investigated. The effects of hydrogen usage on engine performance and exhaust emissions as an additional fuel to internal combustion gasoline, diesel and LPG engines are explained. Depending on the amount of hydrogen added to the fuel system, the engine power and torque are increased at most on petrol engines, while they are decreased on LPG and diesel engines. In terms of chemical products, the emissions of harmful exhaust gases in gasoline and LPG engines are reduced, while some diesel engines increase nitrogen oxide levels. In addition, it is understood that there will be a positive effect on the environment, due to hydrogen usage in all engine types. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Study on nonpremixed methane/air combustion from flame structure and NOX emission aspect for different burner head structures(Wiley, 2019) Buyukakin, Mustafa Kemalettin; Oztuna, SemihaIn the present study, the air turbulator, which is a part of a nonpremixed burner, is investigated numerically in terms of its effects on the diffusion methane flame structure and NOX emissions. A computational fluid dynamics (CFD) code was used for the numerical analysis. At first, four experiments were conducted using natural gas fuel. In the experimental studies, the excess air ratio was taken constant as 1.2, while the fuel consumption rate was changed between 22 and 51 Nm(3)/h. After the experimental studies, the CFD studies were carried out. Pure methane was taken as fuel for the simulations. The nonpremixed combustion model with the steady laminar flamelet model (SFM) approach was used in the combustion analyses. Methane-air extinction mechanism with 17 species and 58 reactions was used for the simulations. The results obtained from the CFD studies were confronted with the measurements of the flue gas emissions in the experimental studies. Then, a modified burner head was analysed numerically for the different air turbulator blade numbers and angles. The CFD results show that increasing the air turbulator blade number and angle causes the thermal NO emissions to be reduced in the flue gas by making the flame in the combustion chamber more uniform than the original case. This new flame structure provides better mixing of the fuel and combustion air. Thus, the diffusion flame structure in the combustion chamber takes the form of the partially premixed flame structure. The maximum reduction in the thermal NO emissions in the flue gas is achieved at 38% according to the original case.
