Papers by Atilla Biyikoglu
Sabi̇t Yatakta Kömür Yanma Prosesi̇ni̇n Modellenmesi̇
DergiPark (Istanbul University), Apr 12, 2013
Bir sabit yataktaki komur yigininin pseudo-kararli durum yanmasi incelenmistir. Komurun kul, su, ... more Bir sabit yataktaki komur yigininin pseudo-kararli durum yanmasi incelenmistir. Komurun kul, su, sabit karbon ve ucucu maddeden olustugu kabul edilmistir. Bu model, karbonun oksijen ve karbon-dioksit ile heterojen reaksiyonlarini dikkate almaktadir. Sabit yatak icerisindeki isi ve kutle aktarimini yoneten denklemler, degisken sicaklik sartlarinda, karbon-gaz reaksiyonlarina dayanilarak elde edilmislerdir. Komur yaricap denklemi ile isi ve kutle aktarimi icin elde edilen nonlineer adi diferansiyel denklemler cifti, yari-acik Uclu Bant Matris Algoritmasi kullanilarak es-zamanli cozulmuslerdir. Bunun yani sira, komur tuketimi icin gecis suresi, “Simpson” sayisal integrasyon teknigi kullanilarak hesaplanmistir. Kati debisinin hem gecis suresine hem de donusum oranina olan etkileri incelenmistir.
Nucleation and Atmospheric Aerosols, 2022
The fact that the energy produced by renewable sources cannot be consumed instantaneously has bro... more The fact that the energy produced by renewable sources cannot be consumed instantaneously has brought energy storage systems to the fore. Due to its low cost and ease of use, the thermally integrated pumped thermal energy storage (TI-PTES) system is widely used. In this study, unlike the literature, the Kaline cycle with TI-PTES system was investigated thermodynamically. In the system analysis, heat pump, evaporator and hot tank temperatures were selected as variable parameters and their effects on system performance were examined. The results showed that the system efficiency increases with the increase in evaporator temperature but the increase in hot tank temperature significantly reduces the system efficiency.
Determination of Optimum Insulation Thickness Based on Heating Load by Life-Cycle Cost Analysis for Residential Buildings in Turkey
Politeknik dergisi, Dec 1, 2019
Binalarda yalıtım kalınlığı, bina kabuğunun tasarımında önemli bir parametredir. Binalarda yalıtı... more Binalarda yalıtım kalınlığı, bina kabuğunun tasarımında önemli bir parametredir. Binalarda yalıtım kalınlığının belirlenmesinde, ömür maliyet analizi sıklıkla kullanılan bir optimizasyon yöntemidir. Literatürde, yakıt maliyeti ve yalıtım maliyetinden oluşan toplam maliyetin minimum olduğu yalıtım kalınlığı, optimum yalıtım kalınlığı olarak tanımlanmaktadır. Bu çalışmanın amacı, Türkiye’deki konut tipi binalar için ısıtma etkisi altında optimum yalıtım kalınlıklarının ömür maliyet analizi yöntemi ile belirlenmesidir. Binaların yıllık ısıtma enerji ihtiyacı TS 825 “Binalarda Isı Yalıtım Kuralları” standardına göre hesaplanmıştır. Yalıtım malzemesi olarak; tavanda cam yünü, tabanda ekstrüde polistiren (XPS) ve dış duvarlarda genişletilmiş polistiren (EPS), yakıt olarak doğalgaz kullanılmıştır. Optimizasyon metodu olarak toplam maliyete dayalı optimizasyon yaklaşımını temel alan ömür maliyet analiz metodu kullanılmıştır. Optimum yalıtım kalınlıkları (U-değerleri), 30 yıllık kullanım ömrü için iklim bölgelerine göre; dış duvar için 8,1 cm ile 16,4 cm (0,38-0,20 W/m2K), tavan için 14,2 cm ile 26,8 cm (0,29-0,16 W/m2K), zemin için 5,0 ile 9,8 cm (0,57-0,32 W/m2K) arasında hesaplanmıştır. Sonuç olarak, TS 825 standardında belirtilen limit yalıtım kalınlıkları ile karşılaştırıldığında, optimum yalıtım kalınlıkları kullanılarak yalıtım yapılan bir binanın ülke genelinde sağlayacağı enerji tasarrufunun bölgelere göre %10,08 ile %18,88 arasında değiştiği belirlenmiştir. Geri ödeme sürelerindeki artışların en kötü durumda bile %10 değerini geçmediği düşünüldüğünde, TS 825 standardında belirtilen dört farklı iklim bölgesi için optimum yalıtım kalınlıklarının (U-değerlerinin) revize edilmesi gerektiği sonucuna ulaşılmıştır.
Determination of Optimum Insulation Thickness Based on Heating Load by Life-Cycle Cost Analysis for Residential Buildings in Turkey
Politeknik Dergisi, 2018
Binalarda yalıtım kalınlığı, bina kabuğunun tasarımında önemli bir parametredir. Binalarda yalıtı... more Binalarda yalıtım kalınlığı, bina kabuğunun tasarımında önemli bir parametredir. Binalarda yalıtım kalınlığının belirlenmesinde, ömür maliyet analizi sıklıkla kullanılan bir optimizasyon yöntemidir. Literatürde, yakıt maliyeti ve yalıtım maliyetinden oluşan toplam maliyetin minimum olduğu yalıtım kalınlığı, optimum yalıtım kalınlığı olarak tanımlanmaktadır. Bu çalışmanın amacı, Türkiye’deki konut tipi binalar için ısıtma etkisi altında optimum yalıtım kalınlıklarının ömür maliyet analizi yöntemi ile belirlenmesidir. Binaların yıllık ısıtma enerji ihtiyacı TS 825 “Binalarda Isı Yalıtım Kuralları” standardına göre hesaplanmıştır. Yalıtım malzemesi olarak; tavanda cam yünü, tabanda ekstrüde polistiren (XPS) ve dış duvarlarda genişletilmiş polistiren (EPS), yakıt olarak doğalgaz kullanılmıştır. Optimizasyon metodu olarak toplam maliyete dayalı optimizasyon yaklaşımını temel alan ömür maliyet analiz metodu kullanılmıştır. Optimum yalıtım kalınlıkları (U-değerleri), 30 yıllık kullanım ömr...
New Analytical Model for Investigation of Temperature Distribution and Melt Geometry of Selective Laser Melting Process Under Different Operating Parameters
SSRN Electronic Journal
Parametric Study of A Single Cell Proton Exchange Membrane Fuel Cell For A Bundle of Straight Gas Channels
gazi university journal of science, 2011
Normal 0 21 false false false TR X-NONE X-NONE MicrosoftInternetExplorer4 In this analysis, a sin... more Normal 0 21 false false false TR X-NONE X-NONE MicrosoftInternetExplorer4 In this analysis, a single cell proton exchange membrane (PEM) fuel cell model was constructed in a three dimensional coordinate system. The effects of operating pressure and mass flow rate of the cathode and anode gases on the fuel cell characteristics were investigated parametrically. Besides, the mass fraction of water at the cathode side and the mass fraction of hydrogen at the anode side were selected as investigation parameters and their effects were presented on the polarization curves. The model was tested at the atmospheric pressure based on an experimental result existing in the literature. It was observed that the current density had not been sensitive to any changes in the mass flow rate of the anode gases unlike the cathode gases’. It was also observed that there were current limitations which were more dominant over the water rather than the hydrogen. Key Words : PEM fuel cell, straight gas chann...
Historical Development, Working Principles and State of the Art of Fuel Cells
Gazi University Journal of Science, 2010
International Journal of Pioneering Technology and Engineering
It is necessary to understand the efficiency of the filters, which are the most important part of... more It is necessary to understand the efficiency of the filters, which are the most important part of the ventilation systems, in order to hinder the spreading of the Covid-19 virus. In this article, a model was created using theoretical solutions developed for single fiber efficiency and with this created model, the previous theoretical data were confirmed. Then, the theoretical data in the model created with the experimental data were compared. Also, factors such as fiber diameter, particle diameter, or flow velocity affecting single fiber efficiency were changed and the effects of these parameters were investigated. As a result of this investigation, it was seen that, as the Peclet number increased, the single fiber efficiency decreased, and the efficiency of the single fiber increased when the particle diameter increased. Finally, when the solidity, which can be considered as the fiber density in the filter, increased, the single fiber efficiency increased along with it. When solidi...
Thermodynamic analysis and optimization of a tehermal energy stroge system
Determination of optimum PV/T configuration on horizontal plane for maximum exergy output
International Journal of Exergy
Scientific Reports, May 25, 2022
This study was built on the basis of experimental results from a simple refrigeration system usin... more This study was built on the basis of experimental results from a simple refrigeration system using R134a as a refrigerant. Based on the real dimensions of the system and the experimental results, Ansys fluent software was used to simulate the system to prepare the system to introduce the nanoparticles theoretically. Since the nanoparticle preparation process is expensive, this research presents a simple, easy, and inexpensive method for the preparation process based on, distilled water, ammonia, copper nitrate, and cerium nitrate to synthesize seven types of nanoparticles as a single oxide and as a mixture from two different oxides The results of preparing using X-ray diffraction and scanning electron microscopy confirmed that the particles were spherical in shape, with suitable average diameters ranging between 78.95 nm, 79.9 nm, 44.15 nm and 63.3 nm for copper oxide, cerium oxide, the first mixture, and the second mixture respectively. The theoretical study confirmed that both copper oxide, cerium oxide, and the mixture consisting of both improved the performance of the refrigeration system and reduced energy consumption. Moreover using the numerical equations available in the literature to calculate the thermophysical properties proved an improvement in these properties with an increase in the nanoparticle concentration when mixed with R134a. Most of the current studies focus on improving the performance of refrigeration systems and air conditioners, as they are among the most energy consuming sectors. To improve the thermal properties of the working fluid, very small particles, ranging in size from millimeters to micrometers, are dispersed inside the base fluid, which was made by Maxwell in 1873, but this attempt faced many problems, including stability, clogging, and erosion. In the late twentieth century. Choi presented the working fluid in a new concept, where the nanoparticles are dispersed inside the primary fluid to improve its thermal properties 1,2. The nanofluid is classified as follows (i) mono-nanofluids which consist of similar nanoparticles, (ii) hybrid nanofluids which consist of dissimilar nanoparticles; and (iii) hybrid nanofluids which consist of composite nanoparticles 1. To achieve the best heat transfer properties between the fluids and the nanoparticles, the following must be provided (i) dispersibility of nanoparticles (ii) stability of nanoparticles (iii) chemical compatibility of nanoparticles and (iv) thermal stability of nanofluids 3. Recently, the concept of nanofluids has been developed to include refrigerants as nanorefrigerants and lubricant oils as nanolubricants, where the method of preparation is limited to using a one-step method and a two-step method. In the two-step the nanoparticles are manufactured as a powder, and then put into the base fluid, followed by several types of dispersion methods such as agitation either by ultrasonic or magnetic force, homogenizing, and high shear mixing to disperse nanoparticles inside a mixture. A one-step method is based on condensing vapor nanophase powders into liquid by reducing the pressure and then dissolving them inside the liquid immediately 4,5. Literature review. In this section, the latest studies, and results will be presented that include the addition of nanoparticles to refrigeration systems, as well as the effect of nanoparticles on improving the thermophysical properties of the working fluid.
Strojniški vestnik - Journal of Mechanical Engineering
Most studies report that dispersing nanoparticles into refrigerants and lubricating oils leads to... more Most studies report that dispersing nanoparticles into refrigerants and lubricating oils leads to performance improvements in refrigeration systems, due to improvements in the thermal physics properties of a pure refrigerant, which leads to reduced energy consumption. Using nanoparticles in a refrigeration system is associated with many difficulties, such as the cost of preparing and obtaining a stable and homogeneous mixture with less agglomeration and sedimentation. Most current studies focus on the use of metals, metal oxides, and a hybrid of oxides as nanoparticles in refrigeration systems. In this research, nanoparticles were prepared in an inexpensive and easy way as a single oxide and as a mixture consisting of copper and cerium oxides. The results of nanoparticle preparation using X-ray diffraction and scanning electron microscopy prove that the particles of the samples were spherical in shape, with suitable average diameters ranging from 78.95 nm, 79.9 nm, 44.15 nm and 63.3...
Development of thermal model for the determination of SLM process parameters
Optics & Laser Technology, 2021
Abstract In this study, a mathematical model is developed for determining the process parameters ... more Abstract In this study, a mathematical model is developed for determining the process parameters used in the manufacturing process of powder materials with selective laser melting method. Although the studies carried out to date cover detailed modeling studies including three-dimensional and time-dependent situations, obtaining quite different approaches from experimental results has led to the idea that a change should be made in the construction of the mathematical problem. Therefore, different from other studies and for the first time, the Eigen-function expansion method was used in the analytical solution of the selective laser melting thermal model. The developed mathematical model includes the steady-state solution with the appropriate boundary conditions of the 2-D non-homogeneous heat equation. The mathematical model was first solved analytically with the Eigen-function expansion method, and the function obtained as a result of the solution was introduced into the MATLAB software. The parametric study was performed numerically over laser power, laser spot size and powder bed thickness. With the developed model, the solution was converged in 30 s and 11.5% more accurate with respect to experimental results were obtained in width, 29% in depth and 3% in temperature as compared to other analytical models exist in the literature.
Bu calismada sentez gazi rafinesi icin seri bir model onerilmektedir. Birinci asamada, olusturula... more Bu calismada sentez gazi rafinesi icin seri bir model onerilmektedir. Birinci asamada, olusturulan sentez gazinin bir kismini cikis gazina transfer eden bir yangecit vardir. Bunun yani sira, iki asamada da her iki reaktore buhar takviyesi sunabilecek ayarli buhar girisleri bulunmaktadir; bunun sonucunda cikistaki sentez gazi karakteristikleri istenilen sekile getirilebilir. Reaktor cikisindaki H2/CO oraninin kisit olarak saglanmasi uzerine odaklanilmistir. Birinci asama girisine beslenen sentez gazinin kompozisyonu tum reaktor davranisini sekillendirmektedir. Sonucta, yapilandirilan model, arzu edilen sentez gazi karakteristiklerini saglayabilmek icin herhangi bir komur turune bagli olarak uygun proses parametre degerlerini olusturabilme yetenegine sahiptir. Model uc degisik komur ile test edilmis, ve her defasinda en uygun yangecit degeri ve buhar oranlari elde edilmistir.
Isı Bilimi ve Tekniği Dergisi, 2020
Systematic assessment of scientific events has become increasingly important for research communi... more Systematic assessment of scientific events has become increasingly important for research communities. A range of metrics (e.g., citations, h-index) have been developed by different research communities to make such assessments effectual. However, most of the metrics for assessing the quality of less formal publication venues and events have not yet deeply investigated. It is also rather challenging to develop respective metrics because each research community has its own formal and informal rules of communication and quality standards. In this article, we develop a comprehensive framework of assessment metrics for evaluating scientific events and involved stakeholders. The resulting quality metrics are determined with respect to three general categories-events, persons, and bibliometrics. Our assessment methodology is empirically applied to several series of computer science events, such as conferences and workshops, using publicly available data for determining quality metrics. We show that the metrics' values coincide with the intuitive agreement of the community on its "top conferences". Our results demonstrate that highly-ranked events share similar profiles, including the provision of outstanding reviews, visiting diverse locations, having reputed people involved, and renowned sponsors.
Performance analysis of R134a vapor compression refrigeration system based on CuO/CeO2 mixture nanorefrigerant
Journal of the Brazilian Society of Mechanical Sciences and Engineering
Simulation of Combustion in a Coal-Fired Boiler with a Fixed Bed
Energy Sources, 2004
ABSTRACT In this study, steady-state combustion in boilers with a fixed bed has been investigated... more ABSTRACT In this study, steady-state combustion in boilers with a fixed bed has been investigated. The solution method and the discretization of the governing equations of two-dimensional turbulent reactive flow in the combustion chamber and one-dimensional coal combustion in the fixed bed are explained. Control volume and finite difference methods are used in the discretization of the equations in the combustion chamber and in the fixed bed, respectively. Kinetic calculations are employed in the solution of turbulent reactive flow equations in the combustion chamber. The combustion of coal particles in the fixed bed is ruled by the reaction-controlled mechanism. The distributions of temperature and some of the chemical species through the combustion chamber and the fixed bed are presented. Also, the variation of coal particle size with the fixed bed height is given.
Energy Conversion and Management, 2013
In this study, a geothermal power cycle was analyzed for the generation of electricity at differe... more In this study, a geothermal power cycle was analyzed for the generation of electricity at different reservoir conditions by using carbon-dioxide at super-critical condition. The second law analysis was performed and it was found that the buoyancy effect was sufficient to cycle the working fluid of carbondioxide. A parametric study was performed to test the proposed system under different reservoir conditions, i.e., reservoir depth, temperature, permeability, distance between the injection and production wells, and also the environmental conditions. Finally, the proposed system was operated for the data that belongs to a geothermal district of Ömerbeyli near the city of Aydın in Turkey.
Applied Thermal Engineering, 2009
The flow experiencing the abrupt contraction suffers from the viscous dissipation due to vast cha... more The flow experiencing the abrupt contraction suffers from the viscous dissipation due to vast change in flow field across the plane of contraction. In the present study, simulation of flow field and entropy generation rate due to viscous dissipation are carried out for different upstream Reynolds numbers. The flow situation is considered to be isothermal to avoid the influence of heat transfer on the entropy generation rate. A control volume approach is introduced when discretizing the governing equations of flow. In order to secure the grid independent solution the grid independent tests are conducted. It is found that overshooting of axial velocity occurs along the symmetry axis across the plane of contraction. Entropy generation rate enhances with increasing Reynolds numbers. The location of maximum entropy generation rate becomes almost identical for all Reynolds numbers considered in the present study.
Sadhana, Apr 1, 2012
In this study, the effects of baffle blocks located in the flow channel on fuel cell characterist... more In this study, the effects of baffle blocks located in the flow channel on fuel cell characteristics were investigated. The higher current densities were obtained from the cells with blockage than without blockage. It was observed that the gap between the tip of the baffle block and the channel wall had a significant effect on the current density produced and on the convergence of solutions. The number and the size of blocks that are providing the highest current density from the cell were determined. No significant effects were observed in the polarization curves for cells with more than four blocks and gap ratio of 0.3. A parametric study was conducted to investigate the effect of the relative humidity and velocity of inlet gases on cells with four blocks and gap ratio of 0.3. It was concluded that the current density is strongly dependent on the relative humidity for low inlet velocities and on the other hand, on the inlet velocity for low relative humidities.
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Papers by Atilla Biyikoglu