Person: KARAGÖZ, İRFAN
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KARAGÖZ
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İRFAN
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Publication Numerical investigation of heat and flow characteristics in a laminar flow past two tandem cylinders(Vinca Inst Nuclear Sci, 2021-01-01) Aydın, Neslihan; Özalp, Alper; Karagöz, İrfan; AYDIN, NESLİHAN; ÖZALP, ABDURRAHMAN ALPER; KARAGÖZ, İRFAN; 0000-0002-7442-2746; AAB-9388-2020; AAB-9496-2022Heat and flow characteristics were investigated numerically for a laminar stream past two tandem circular cylinders placed in a channel. The blockage ratios (beta = D/H) were chosen to be 0.6, 0.7, and 0.8, respectively, and the gap between the cylinders was varied proportionally to the cylinder diameter as g = 0.2D, 0.7D, 1.5D, and 4D at a low Reynolds number (Re = 40). The effects of the blockage ratio, as well as the gap between two cylinders on heat and flow features were examined in detail. Shear stresses, dimensionless static pressure, heat transfer coefficient, and separation points from the cylinders were determined from the velocity and temperature fields in the flow domain. The results showed that the separation angle decreases with both the blockage ratio and the gap size on the downstream cylinder, whereas heat transfer increases with both the blockage ratio and the gap size on the upstream cylinder.Publication Response of a proton exchange membrane fuel cell to step changes in mass flow rates(Wiley-v C H, 2021-06-20) Küpeli, Seda; Çelik, Erman; Karagöz, Irfan; Karagöz, Irfan; KARAGÖZ, İRFAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-7442-2746; JCN-7685-2023; AAB-9388-2020Transient regime effects are particularly important in fuel cells designed for vehicles. Three-dimensional modeling of a proton exchange membrane fuel cell with a serpentine channel is presented, and the response of the fuel cell to a step-change in the mass flow rates is analyzed by using the computational fluid dynamics techniques. After a validation study of the mathematical and numerical model, step increases of 20% in mass flow rates are applied to the inlet boundary conditions, and time dependent power and current density responses of the fuel cell are analyzed. Polarization curves are generated for the assessment of the fuel cell performance, and their variations in time are presented. The results show that current and power densities increase with time at low cell voltage values due to concentration losses; however, increases in power and current are negligible at high voltages.Publication Investigation of the effects of intermediate reservoirs and intermediate feedings applications on the performance of proton exchange membrane fuel cells(Elsevier, 2023-02-09) Çelik, Erman; Karagöz, İrfan; KARAGÖZ, İRFAN; Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0002-7442-2746; AAB-9388-2020This study presents the design principles and details of a new flow field based on the shape and reflex similarity of the circulatory systems of living things. This design has intermediate reservoirs that collect and distribute the flow channels and also allow for intermediate feedings. This design is applied to a proton exchange membrane fuel cell, and its performance is tested and compared with a conventional serpentine type of flow channel. The novel fuel cell with intermediate reservoirs reaches a current density of 0.171 A/cm2 at 0.406 V and displays a power density 10 % higher than the serpentine flow field. Moreover, eleven cases involving symmetrical and asymmetrical feeding arrangements are also examined. The case of 70 %, 20 % and 10 % symmetrical feeding at the main and intermediate inlets shows the highest performance by providing a 38 % higher power density compared to the serpentine flow field.Publication Performance assessment of a four-pass serpentine proton exchange membrane fuel cell with non-humidified cathode and cell state estimation without special measurement(Pergamon-Elsevier Science Ltd, 2022-01-01) Çelik, Erman; Karagöz, İrfan; KARAGÖZ, İRFAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-7442-2746; AAB-9388-2020Proton exchange membrane fuel cells are promising electrochemical energy conversion devices especially important for mobile technologies, including the automotive industry thanks to their quick start-up, low operation temperature, and relatively higher energy density characteristics. However, cell performance depends on many parameters like reactant temperature and humidification ratio, cell operating temperature, reactant feeding pressure, and flow field. In this study, the performance of a 50 cm(2) active area four-pass serpentine flow field hydrogen-air proton exchange membrane (PEM) fuel cell experimentally investigated for various cell operating temperatures and reactant back pressures without humidification on the cathode side. Dehydration or flooding condition of the cell is showed to be determined with tafel slope, limiting current density and types of voltage losses without using a special measurement. The results show that flooding, which is called mild flooding, is possible to be seen even at high cell temperature in a non-humidified cathode fuel cell, in case of exceeding operating pressures. Behavior of cell parameters under mild flooding and ongoing severe flooding are different from each other. Pressure increase at above 45 degrees C operating temperature is seen to served higher power output. However, at low back pressure with escalated operating temperature doesn't result with a substantial increase on performance since less amount of water is produced as a product of reaction causing membrane dehydration at relatively low current density levels thus increasing ohmic loss. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Publication Design of a biomimetic wing from maple samara and investigation of the aerodynamic performance(Aip Publishing, 2023-09-01) Çalışkan, Mehmet E.; Kaya, Fuat; Sabırlı, Muhammet U.; Karagöz, İrfan; ÇALIŞKAN, MEHMET; Sabırlı, Muhammet U.; KARAGÖZ, İRFAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-7442-2746; AAB-9388-2020; ISD-7974-2023; JIW-9877-2023The morphological structure and airborne behavior of maple samaras have attracted increasing attention due to their potential use in wind turbines and air vehicles. This study introduces a new methodology based on mathematical modeling to transfer the geometric structure of maple samaras to a virtual environment and presents an experimental and numerical investigation of the performance of a model wing designed with this method. Certain sections were taken along the structure of maple samaras, measurements were made, curves were obtained mathematically for each section, and these curves were transferred to a design program. A biomimetic three-dimensional model was generated by combining these curves. The mathematical modeling of these curves was obtained with certain degrees of expansion of the Fourier series. Experimental and numerical studies of the designed biomimetic model were performed at different free stream velocities and angles of attack. The trend of the lift coefficient curves indicated that the samara wing model has a larger range of angle of attack, up to 40(circle)-45(circle) without a stall, and the maximum lift to drag ratio (CL/CD) was obtained at 8(circle) angle of attack. In addition, the present model showed more stable performance, and the lift and drag forces did not change as much as in conventional blades at varying free flow velocities. In the analysis results, the air flowing over the wing caused the formation of these vortices inside the ordered trough top structures of the model. These vortices, seen from the leading edge, are thought to play an effective role in the lift coefficient of the biomimetic samara model.Publication Investigation of water motion in a fuel cell channel with a reservoir(Elsevier Sci Ltd, 2022-02-16) Çelik, Erman; Altıntaş, Arin Göksel; Karagöz, İrfan; KARAGÖZ, İRFAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi.; 0000-0002-7442-2746; AAB-9388-2020This study presents a novel gas distribution channel configured with a reservoir and an extra outlet to prevent channels from being clogged by long slugs in the vicinity of the outlet port in fuel cells. The motion of water droplets in this channel was investigated using the volume of fluid method. The behavior of the water droplets in the channel is examined under varying outlet pressures, droplet size, the initial position of the droplets, and the direction of the gravitational acceleration. The results showed that the proposed design yields the water droplets to break up while preventing channel clogging and facilitating water removal. It has also been observed that water discharge accelerates as the reservoir outlet relative pressure decreases, and discharge occurs to a large extent when the gauge pressure is lower than-1000 Pa. The proposed intermediary water evacuation approach and design have been determined to have the capability of active water discharge from multiple points via an appropriate pressure differential. It is seen that liquid water propagation to larger areas, especially in long flow lengths, can be prevented via the proposed new design and approach.Publication An experimental study of the aerodynamic performance of a maple wing model at low reynolds numbers(Elsevier, 2023-04-17) Aydın, Neslihan; Çalışkan, Mehmet Erman; Sabırlı, Muhammed U.; Karagöz, İrfan; AYDIN, NESLİHAN; ÇALIŞKAN, MEHMET; Sabırlı, Muhammed U.; KARAGÖZ, İRFAN; Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği; 0000-0002-6123-9627; 0000-0002-7442-2746; 0000-0003-3650-0886; AAB-9388-2020; AAB-9496-2022; DUS-9551-2022; ISD-7974-2023Maple seeds are widely known for their autorotation and may achieve remarkably long-distance flights owing to their unique wing morphology. These features suggest the adaptability of the blades to wind turbines and air vehicles. However, the effects of these morphological features on aerodynamic force generation are still poorly understood. An enlarged replica of a sample 3D maple wing was produced using additive manufacturing. Direct force experiments were conducted in a low-speed wind tunnel using a two-component force balance to obtain the lift and drag coefficients of the model wing. The polar curves of the wing were obtained for three different Re numbers by repeating the experiments over a wide angle of attack range of-50 to 50 degrees. The best aerodynamic performance is obtained at 18 degrees and-12 degrees attack angles for positive and negative angles, respectively, regardless of the Re number. This preliminary study shows that maple seed can be mimicked in the design of propellers and wind-turbine blades.Publication Effects of separation space diameter on the performance of a novel reverse flow cyclone(Taylor, 2019-10-13) Sakin, Ali; Karagöz, İrfan; Avcı, Atakan; KARAGÖZ, İRFAN; AVCI, ATAKAN; Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0002-7442-2746; AAB-9388-2020A numerical study was carried out to investigate the effect of separation space diameter on the performance of a novel reverse flow tangential inlet cyclone design by using the Eulerian-Lagrangian approach. The design of this cyclone is based on the idea of increasing vortex length and decreasing pressure drop compared with traditional cyclones. This novel cyclone differs from the traditional cyclones with separation space and vortex limiter instead of the conical part. A qualitative numerical study was performed to analyze the effect of separation space diameter on the cyclone performance at different flow rates by evaluating velocity profile, pressure drop, fractional and overall efficiencies. The results show that the collection efficiency of smaller particles increases while pressure drop decreases significantly with the increase in separation space diameter for D-1/D < 0.5.