Browsing by Author "Saka, Kenan"
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Publication Analysis and modeling of a membrane electrode assembly in a proton exchange membrane fuel cell(Amer Inst Physics, 2020-07-01) Orhan, Mehmet F.; Kahraman, Huseyin; Saka, Kenan; SAKA, KENAN; Bursa Uludağ Üniversitesi/Yenişehir İbrahim Orhan Meslek Yüksekokulu.; 0000-0002-2296-894X; AAH-5303-2021In this study, a membrane electrode assembly of a proton exchange membrane fuel cell is modeled. Using the analytical model, a computational analysis has been conducted along with an extensive parametric study. Variation of ohmic losses, water content, and voltage drops from anode to cathode side of the membrane electrode assembly with many design/operation parameters such as thickness, temperature, pressure, and local/total humidity and conductivity, diffusivity, and resistivity have been evaluated at various current densities. Also, effect of molar concentration of hydrogen on hydrogen diffusive flux due to pressure change between the anode and cathode at different membrane thicknesses has been presented. Furthermore, variation of water uptake and concentration with the ratio of water and hydrogen fluxes, the current density, and membrane dry density have been studied along with their interrelation. It is observed that as the membrane thickness increases, its resistivity increases as well, causing higher ohmic losses. On the other hand, the water content increases with the thickness until a maximum point and then starts to decrease. Therefore, the membrane thickness should be optimized carefully to have desirable humidity levels with minimum crossover and losses.Publication Analysis of stack operating conditions for a polymer electrolyte membrane fuel cell(Pergamon-elsevier Science Ltd, 2022-08-07) Orhan, Mehmet Fatih; Saka, Kenan; SAKA, KENAN; Bursa Uludağ Üniversitesi/Yenişehir Meslek Yüksekokulu.; Bursa Uludağ Üniversitesi/Mühendislik-Mimarlık Fakültesi.; 0000-0002-2296-894X; AAH-5303-2021A polymer electrolyte membrane fuel cell is investigated in this study to assess its efficiency. In this regard, various operating conditions such as cell temperature, pressure, reactant/product flow rates and humidity affects are investigated analytically, and their interrelationships are discussed. The stack water management, mass transport phenomenon, ionic and electrical conductivity are also evaluated. The results are experimentally verified using a polymer electrolyte membrane fuel cell with an active surface area of 100 centimeters square. The membrane electrode assembly consists of Nafion (R) HP membrane. Also, AvCarb EP40 gas diffusion layers with 200 mu m thicknesses are used. Results confirm that the overall stack efficiency can increase remarkably with the optimization of its operating parameters. The highest efficiencies are achieved around 100% humidity ratio of reactants at both cathode and anode. While high operating pressures improves individual cell efficiency, there are contradictory concerns at the stack level such as parasitic loads, losses, leakages and manufacturing costs.Publication Design and analysis of gas diffusion layers in a proton exchange membrane fuel cell(Mdpi, 2023-01-01) Orhan, Mehmet Fatih; Hamada, Ahmed T.; Saka, Kenan; SAKA, KENAN; Bursa Uludağ Üniversitesi/Yenişehir Meslek Yüksekokulu.; 0000-0002-2296-894X; AAH-5303-2021; AAI-6045-2021A proton exchange membrane fuel cell is an energy convertor that produces environmentally friendly electrical energy by oxidation of hydrogen, with water and heat being byproducts. This study investigates the gas diffusion layer (GDL) of the membrane electrode assembly (MEA) in proton exchange membrane fuel cells (PEMFCs). In this regard, the key design concerns and restraints of the GDL have been assessed, accompanied by an inclusive evaluation of the presently existing models. In addition, the common materials used for the GDL have been explored, evaluating their properties. Moreover, a case study of step-by-step modeling for an optimal GDL has been presented. An experimental test has been carried out on a single cell under various compressions. Lastly, a parametric study has been performed considering many design parameters, such as porosity, permeability, geometrical sizes, and compression of the GDL to improve the overall efficiency of the fuel cell. The results are presented in this paper in order to help ongoing efforts to improve the efficiency of PEMFCs and facilitate their development further.Publication Design and optimization of fuel cells: A case study on polymer electrolyte membrane fuel cell power systems for portable applications(Wiley-Hindawi, 2022-07-21) Orhan, Mehmet Fatih; Saka, Kenan; Yousuf, Mohammad; SAKA, KENAN; Bursa Uludağ Üniversitesi/Yenişehir İbrahim Orhan Meslek Yüksekokulu.; AAH-5303-2021Fuel cells are energy conversion devices that directly convert chemical energy of fuels such as hydrogen to useful work with negligible environmental impact and high efficiency. This study deals with thermodynamic analysis and modeling of polymer electrolyte membrane fuel cell (PEMFC) power systems for portable applications. In this regard, a case study of powering a computer with a PEMFC is presented. Also, an inclusive evaluation of various parameters such as voltage polarization, overall system efficiency, power output, and heat generation is reported. In addition, a parametric study is conducted to study the effect of many design and operation parameters on the overall efficiency. Results show the direct influence of current density and temperature values on optimization of the design parameters in PEMFCs.Item Energy and exergy analysis of a double effect absorption refrigeration system based on different heat sources(Pergamon-Elsevier, 2015-12) Kaynaklı, Ömer; Saka, Kenan; Kaynaklı, Faruk; Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; Uludağ Üniversitesi/Yenişehir Meslek Yüksekokulu/İklimlendirme ve Soğutma Bölümü.; Uludağ Üniversitesi/Gemlik Meslek Yüksekokulu/Makine Bölümü.; AAH-5303-2021; AAG-6158-2021; 8387145900; 56865845300; 56866411500Absorption refrigeration systems are environmental friendly since they can utilize industrial waste heat and/or solar energy. In terms of heat source of the systems, researchers prefer one type heat source usually such as hot water or steam. Some studies can be free from environment. In this study, energy and exergy analysis is performed on a double effect series flow absorption refrigeration system with water/lithium bromide as working fluid pair. The refrigeration system runs on various heat sources such as hot water, hot air and steam via High Pressure Generator (HPG) because of hot water/steam and hot air are the most common available heat source for absorption applications but the first law of thermodynamics may not be sufficient analyze the absorption refrigeration system and to show the difference of utilize for different type heat source. On the other hand operation temperatures of the overall system and its components have a major effect on their performance and functionality. In this regard, a parametric study conducted here to investigate this effect on heat capacity and exergy destruction of the HPG, coefficient of performance (COP) of the system, and mass flow rate of heat sources. Also, a comparative analysis is carried out on several heat sources (e.g. hot water, hot air and steam) in terms of exergy destruction and mass flow rate of heat source. From the analyses it is observed that exergy destruction of the HPG increases at higher temperature of the heat sources, condenser and absorber, and lower temperature of the HPG, LPG and evaporator. This destruction is maximized when hot air heat source is used and minimized with utilizing hot water heat source.Item Exploitable biomass status and potential of the Southeastern Anatolia Region, Turkey(Taylor & Francis Inc, 2018) Yılmaz, İbrahim Halil; Saka, Kenan; Uludağ Üniversitesi/Yenişehir İbrahim Orhan Meslek Yüksekokulu.; 0000-0002-2296-894X; AAH-5303-2021; 56865845300In this study, the exploitable biomass potential of nine provinces located in the Southeastern Anatolia region of Turkey was investigated. Animal- and vegetal-derived biomasses were taken into consideration in the analyses. The animal-derived biomass was handled as poultry, small ruminants, and cattle. The vegetal-derived biomass was accounted as field, garden, and vegetable crops. The contribution of each species on the biomass energy potential was studied. The available animal and vegetal residues in the region were estimated to be, respectively, equal to 6.2% and 9.4% of the corresponding residual amount in Turkey. The annual total biomass potential of the region was found to be approximately 83.4 PJ which could meet 15.7% energy demand of the region.Item İki kademeli soğurmalı soğutma sistemlerinin I. ve II. kanun analizleri(Uludağ Üniversitesi, 2016-10-04) Saka, Kenan; Kaynaklı, Ömer; Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Makine Mühendisliği Anabilim Dalı.Bu çalışmada iki kademeli soğurmalı soğutma sistemlerine ait termodinamiğin birinci ve ikinci kanun analizlerine yer verilmiştir. Soğurmalı soğutma sistemleri güneş enerjisi kaynaklı ya da endüstriyel atık ısı ile çalışabilen ve ozona zararlı olabilecek akışkanlara bünyelerinde yer olmayan çevre dostu sistemlerdir. Çalışmada DELPHI programı yardımıyla su – Lityum Bromür çözeltisi ile çalışan seri akışlı bir sisteme ait oluşturulan simülasyon üzerinde analizler yapılmıştır. Bu çalışmada özgün olarak incelenen yönlerden biri sistemin enerji ihtiyacının sıcak su, kızgın su buharı ve sıcak hava ile karşılanarak enerji ve ekserji analiz sonuçlarının gösterilmesidir. Sistem elemanlarının farklı çalışma şartlarına bağlı olarak sistem performans katsayısındaki değişim, yüksek basınçlı kaynatıcıya ait kapasite değeri, ekserji kayıpları ve ısı kaynağına ait debi miktarı her bir kaynak türü için şekiller üzerinde gösterilmiştir. Sistem içerisinde yer alan eşanjörlerin de sistem üzerindeki etkilerinin incelendiği çalışmada eşanjörler aktif ya da devre dışı olduğu durumlarda sistem performans katsayısındaki değişim gösterilmiştir. Sistem içerisindeki ısı dengesinin dikkate alındığı analizlerde yüksek basınçlı yoğuşturucu sıcaklığına bağlı olarak sistem performans katsayısının değişimi hesaplanmıştır. Tezde incelenen diğer bir yön ise sistemin mevsimsel performansıdır. Buna bağlı yapılan analizde absorber ve yoğuşturucu atmosfere açık olarak Bursa ili şartlarında yıl boyu incelenmiştir. Mevsimsel analiz sonucunda sistemdeki ekserji kayıpları değişimi ve ısı atımı için gerekli hava debisi değişimi şekiller üzerinde gösterilmiştir. Ayrıca son olarak enerji analizine bağlı ekonomik analizde çalışma kapsamına dâhil edilmiştir. Geliştirilen ekonomik yaklaşımda birim maliyet değeri bilinen sistem elemanlarının kapasiteye bağlı yatırım ve işletme maliyetleri hesaplanarak sistem elemanlarının farklı çalışma şartları altında maliyet değişimi gösterilmiştir.Publication Performance assessment and solution procedure for series flow double-effect absorption refrigeration systems under critical operating constraints(Springer Heidelberg, 2019-06-01) Yılmaz, İbrahim Halil; Kaska, Önder; Saka, Kenan; SAKA, KENAN; Kaynaklı, Ömer; KAYNAKLI, ÖMER; 0000-0001-7840-9162; 0000-0002-2296-894X; AAH-5303-2021; AAX-2458-2020In this study, the effects of critical operational constraints on the operational domain of a double-effect lithium bromide/water absorption refrigeration system and its performance were investigated. These constraints were determined as the equivalence state of concentrations, the thermal unbalance between the system components of high-pressure condenser and low-pressure generator, freezing and crystallization risk of lithium bromide/water solution. For the system analysis, a simulation program was developed, and its detailed solution procedure was presented. The program outputs were initially validated with the literature. Subsequently, parametric studies were conducted for broad ranges of the component temperatures. The results demonstrate that the considered constraints were essential for acceptable design and the operational control of double-effect absorption refrigeration systems. The simulations will help to figure out under which operating conditions a double-effect absorption refrigeration system functions effectively and what kind of control strategies are essentially required to increase the coefficient of performance. Based on the operation scenario of fixed high-pressure generator temperature, the proposed system can enhance the coefficient of performance up to 31% and 84% as compared to its counterparts which function under the variable high-pressure generator temperature and the pinch point temperature difference (5K between the high-pressure condenser and the low-pressure generator), respectively.Item Tek kademeli absobrsiyonlu soğutma sisteminin termodinamik analizi(Uludağ Üniversitesi, 2010) Saka, Kenan; Kaynaklı, Ömer; Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Makine Mühendisliği Anabilim Dalı.Dünya genelindeki enerji ihtiyacının hızlı bir şekilde arttığı günümüzde, yeni enerji kaynakları arayışlarının yanı sıra var olan enerji kaynaklarının da en verimli şekilde kullanılması için araştırmalar devam etmektedir. Bu yüzden endüstriyel tesislerdeki atık ısı, güneş enerjisi ve jeotermal enerji kaynakları ile çalışabilen ve ozon tabakasına zarar vermeyen akışkanlar ile çalışan absorbsiyonlu sistemler cazip hale gelmişlerdir.Bu çalışmada Su- LiBr eriyiği kullanan tek kademeli absorbsiyonlu soğutma sisteminin, termodinamiğin birinci ve ikinci kanun analizleri ve bu analizler doğrultusunda çıkan sonuçların karşılaştırmaları yapılmıştır. Sistemin belirli noktalarındaki sıcaklık, basınç, entropi vb. değerleri gösterilmiştir. Sistem elemanlarının termodinamik analizleri yapılarak farklı çalışma şartlarında sistemin verimi grafik ve tablolar yardımıyla gösterilmiştir. Ayrıca sistemin verimini etkileyen eşanjör etkenlikleri hesaplara dâhil edilerek sonuçlar kıyaslanmıştır. Bütün analiz modellemelerinde Delphi bilgisayar programı kullanılmıştır.Item A thermodynamic evaluation on high pressure condenser of double effect absorption refrigeration system(Elsevier, 2016-07-25) Yılmaz, İbrahim Halil; Saka, Kenan; Kaynaklı, Ömer; Uludağ Üniversitesi/Yenişehir Meslek Yüksekokulu/İklimlendirme ve Soğutma Bölümü.; Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-2296-894X; AAH-5303-2021; 56865845300; 8387145900One of the parameters affecting the COP of the absorption system can be considered as the thermal balance between the high pressure condenser (HPC) and the low pressure generator (LPG) since heat rejected from the HPC is utilized as an energy source by the LPG. Condensation of the water vapor in the HPC depends on the heat removal via the LPG. This circumstance is significant for making an appropriate design and a controllable system with high performance in practical applications. For this reason, a thermodynamic analysis for the HPC of a double effect series flow water/lithium bromide absorption refrigeration system was emphasized in this study. A simulation was developed to investigate the energy transfer between the HPC and LPG. The results show that the proper designation of the HPC temperature improves the COP and ECOP due its significant impact, and its value necessarily has to be higher than the outlet temperature of the LPG based on the operating scheme. Furthermore, the COP and ECOP of the absorption system can be raised in the range of 9.72-35.09% in case of 2 degrees C-temperature increment in the HPC under the described conditions to be applied.