Browsing by Author "Orhan, Mehmet Fatih"
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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.Publication Thrombolysis with systemic recombinant tissue plasminogen activator in children: A multicenter retrospective study(Galenos Yayıncılık, 2021-08-18) Zengin, Emine; Sarper, Nazan; Erdem, Arzu Yazal; Al, Işık Odaman; Evim, Melike Sezgin; Yaralı, Neşe; Belen, Burcu; Akçay, Arzu; Yıldırım, Aysen Türedi; Karapınar, Tuba Hilkay; Güneş, Adalet Meral; Gelen, Sema Aylan; Oren, Hale; Olcay, Lale; Baytan, Birol; Gülen, Hüseyin; Öztürk, Gülyüz; Orhan, Mehmet Fatih; Oymak, Yeşim; Akpınar, Sibel; Tüfekci, Özlem; Albayrak, Meryem; Günen, Burçak Tatlı; Canpolat, Aylin; Özbek, Namık; SEZGİN EVİM, MELİKE; MERAL GÜNEŞ, ADALET; Baytan, Birol; Bursa Uludağ Üniversitesi/Tıp Fakültesi/Çocuk Sağlığı ve Hastalıkları Anabilim Dalı/Çocuk Hematoloji Bilim Dalı.; 0000-0002-4792-269X; 0000-0002-0686-7129; 0000-0002-9375-2855; JGX-6145-2023 ; AAH-1452-2021 ; DVW-8108-2022Objective: This study aimed to evaluate systemic thrombolysis experiences with recombinant tissue plasminogen activator (rtPA). Materials and Methods: Retrospective data were collected from 13 Turkish pediatric hematology centers. The dose and duration of rtPA treatment, concomitant anticoagulant treatment, complete clot resolution (CCR), partial clot resolution (PCR), and bleeding complications were evaluated. Low-dose (LD) rtPA treatment was defined as 0.01-0.06 mg/kg/h and high-dose (HD) rtPA as 0.1-0.5 mg/kg/h. Results: Between 2005 and 2019, 55 thrombotic episodes of 54 pediatric patients with a median age of 5 years (range: 1 day to 17.75 years) were evaluated. These patients had intracardiac thrombosis (n=16), deep vein thrombosis (DVT) (n=15), non-stroke arterial thrombosis (n=14), pulmonary thromboembolism (PE) (n=6), and stroke (n=4). The duration from thrombus detection to rtPA initiation was a median of 12 h (range: 2-504 h) and it was significantly longer in cases of DVT and PE compared to stroke, non-stroke arterial thrombosis, and intracardiac thrombosis (p=0.024). In 63.6% of the episodes, heparin was initiated before rtPA treatment. LD and HD rtPA were administered in 22 and 33 of the episodes, respectively. Concomitant anticoagulation was used in 90% and 36% of the episodes with LD and HD rtPA, respectively (p=0.0001). Median total duration of LD and HD rtPA infusions was 30 h (range: 2-120 h) and 18 h (2-120 h), respectively (p=0.044). Non-fatal major and minor bleeding rates were 12.5% and 16.7% for LD and 3.2% and 25.8% for HD rtPA, respectively. At the end of the rtPA infusions, CCR and PCR were achieved in 32.7% and 49.0% of the episodes, respectively. The most successful site for thrombolysis was intracardiac thrombosis. HD versus LD rtPA administration was not correlated with CCR/PCR or bleeding (p>0.05). Conclusion: Systemic thrombolytic therapy may save lives and organs effectively if it is used at the right indications and the right times in children with high-risk thrombosis by experienced hematologists with close monitoring of recanalization and bleeding.Item Undiagnosed cardiac abnormalities among school-aged children(Uludağ Üniversitesi, 2010-05-21) Karacan, Mehmet; Olgun, Haşim; Orhan, Mehmet Fatih; Altay, Nilgün Demet; Öztürk, Candan Ferai; Karakelleoğlu, Cahit; Ceviz, NaciIntroduction: The aim of this study was to assess the frequency of undiagnosed congenital and acquired heart diseases among school-aged children. Materials and Method: The study population consisted of 4.370 children (2081 boys and 2289 girls) who were chosen from a total school-aged children population of 51,891 students (aged 7-15 years) (10.7±2.4) (8.4%). Results: In this population, a total of 11 (0.25%) children had been diagnosed and treated for structural cardiac abnormalities before the study. In the study period (after an assessment by a questionmaire), cardiac evaluation was needed in 405 (9.3%) children who were invited to the pediatric cardiology unit. Among them, a total of 153 (37.8%) children were admitted for further evaluation, and 21 (13.7%) were diagnosed as having undiagnosed congenital (12.4%) or acquired (1.3%) heart diseases. Five children with congenital heart diseases were treated by surgical or invasive techniques, and penicillin prophylaxis was begun in two patients with rheumatic heart disease. The most frequent congenital heart diseases were atrial septal defect and mitral valve prolapse among the admitted children. Conclusions: Some children still reach school age with undiagnosed congenital or acquired heart diseases. All children should be examined carefully at the time of school registration in order to diagnose and treat congenital and acquired heart diseases in an effort to prevent the occurrence of undesirable events during sports or social activities.