A competitive design and material consideration for fabrication of polymer electrolyte membrane fuel cell bipolar plates

The bipolar plate is one of the most significant components of a polymer electrolyte membrane (PEM) fuel cell, and contributes substantially to the cost structure and the weight of the stacks. A number of graphite polymer composites with different fabrication techniques have been reported in the literature. Graphite composites show excellent electromechanical properties and chemical stability in acidic environments. Compression and injection molding are the most common manufacturing methods being used for mass production. In this study, a competitive bipolar plate design and fabrication technique is adopted in order to develop a low-cost and light-weight expanded graphite (EG) polymer composite bipolar plate for an air-breathing PEM fuel cell. Cutting molds are designed to cut fuel flow channels on thin expanded graphite (EG) sheets (0.6 mm thickness). Three separate sheets, with the flow channel textures removed, are glued to each otherbyacommercialconductiveepoxytobuildasinglebipolarplate. Thefinalproducthasadensity of 1.79 g/cm3. A bipolar plate with a 20 cm2 active area weighs only 11.38 g. The manufacturing cost is estimated to be 7.77 $/kWe, and a total manufacturing time of 2 minutes/plate is achieved with lab-scale fabrication. A flexural strength value of 29 MPa is obtained with the three-point bending method. A total resistance of 22.3 milliohms.cm2 is measured for the three-layer bipolar plate. We presume that the suggested design and fabrication process can be a competitive alternate for the small-scale, as well as mass production of bipolar plates

Arthroscopic reconstruction of chronic isolated posterior cruciate ligament instability in a professional dancer: A case report

Objectives: Chronic isolated injuries of the posterior cruciate ligament (PCL) are very rare in the literature. PCL injuries are often presented undiagnosed because of the weak signs of the injury compared to the anterior cruciate ligament (ACL) injuries. We report the surgical outcome of arthroscopic reconstruction of the chronic isolated PCL rupture with ipsilateral autologous hamstring tendon in a professional Caucasian dancer. Methods: A 21-year-old male professional Caucasian dancer presented severe instability without any pain in his right knee lasting for one year. The patient did not describe any specific traumatic event but his both knees received repeatitive direct pretibial trauma during hyperflexion of the knee while landing to the floor. At the physical examination, posterior sagging of the tibia was observed on the affected side at 90o of knee flexion and step off test and posterior drawer test were positive preoperatively under general anesthesia. The Tegner Lysholm score was evaluated as 59 (poor). A magnetic resonance image (MRI) revealed the isolated total rupture of PCL. The treatment of choice was arthroscopic single bundle reconstruction of PCL with ipsilateral autologous hamstring tendon. A standard arthroscopic exploration of the joint was performed preoperatively and we didn’t observe any meniscal, cartilage or ligamentous lesion. Anteromedial and anterolateral portals were made in order to visualize the posterior cortex of the tibia with a 70 degree scope. Intra-operative fluroscopy was used to confirm proper tunnel position. During postoperatively first week, the patient was allowed to mobilize nonweight bearing with the use of two crutches without functional knee brace. Quadriceps musculature and passive range of motion was trained. Results: At the 6 month- follow-up, the patient achieved full symmetric restoration of motion. He had returned to full daily activies. The Tegner Lysholm score was evaluated as 95 (excellent) postoperatively. Functional examination of the right knee reveled 140 of flexion, and full knee extension. No posterior sagging was observed and step off test and posterior drawer test was negative. The complaint of instability was disappeared. At 1-year follow-up, clinical findings were unremarkable, with no sign of re-rupture and he returned to his professional career. Conclusion: Surgical reconstruction technique of the PCL and associated rehabilitation protocols has not yet been fully standardized and much work still has be done optimizing correct treatment of PCL injuries. The arthroscopic reconstruction of chronic isolated PCL instability is a very difficult technique as well as its diagnosis. The reconstruction is very beneficial in the athletes and the patients who are not responding well to the conservative treatment. © The Author(s) 2014

Experimental and Numerical Analysis of Supercritical Open Channel Flow Downstream of a Sill

Açık kanalda eşik sonrası oluşan kritik üstü açık kanal akımının hız alanı, laboratuvar ortamında Lazer Doppler Anemometresi (LDA) ile ölçülmüş ve deney ile aynı koşullardaki akım için temel denklemler, sonlu hacimler yöntemine dayalı ANSYS-Fluent paket programı ile üç boyutlu olarak çözülmüştür. Sayısal hesaplamalarda, Reynolds Ortalamalı Navier Stokes (RANS) denklemlerine dayalı Realizable k-? türbülans kapatma modeli ve Large Eddy Simülasyon (LES) modeli kullanılmış, su yüzü profili Akışkan Hacimleri Yöntemi ile hesaplanmıştır. Sayısal modellerden elde edilen akım hızları ve su yüzü profilleri deneysel ölçümlerle karşılaştırılmıştır. Farklı iki modelin deneysel olarak doğrulanması amacıyla yapılan karşılaştırmalarda, Realizable k-? türbülans kapatma modelinin, hız alanının hesaplanmasında ve su yüzünün belirlenmesinde LES modeline göre daha başarılı olduğu görülmüştür.The velocity field of supercritical open channel flow downstream of a sill is measured using Laser Doppler Anemometry (LDA). Basic equations of the problem are solved by ANSYS-Fluent program package based on finite volume method for the flow case having the same experimental conditions. In the numerical simulations, Realizable k-? turbulence closure model based on the Reynolds Average Navier Stokes Equations and Large Eddy Simulation model are used for the simulation of turbulence, and the flow profile is computed using Volume of Fluid Method. Computational results for velocities and free surface profiles are compared with measured data. Experimental validations of the turbulence models show that the Realizable k-? turbulence model is more successful than LES in predicting the velocity field and free surface profiles under the present flow conditions

Treatment of type 3 arthrofibrosis following arthroscopic reconstruction of ACL and posterolateral corner injury with tibia plateau fracture in a professional dancer: A case report

Objectives: Arthrofibrosis is a serious complication following the reconstruction of anterior cruciate ligament (ACL) and posterolateral corner (PLC) injury. Loss of motion caused by arthrofibrosis can be disabling in young and active patients. We report the clinical results of the treatment of arthrofibrosis following arthroscopic reconstruction of ACL with ipsilateral hamstring tendon graft and surgically repairing PLC with 2 suture anchors in a 30 year-old professional dancer, treated with surgical lysis and manipulation under general anesthesia followed by aggressive physical therapy. Methods: A 30 year-old male professional dancer presented with pain, effusion and severe instability in his left knee after falling in a dance event. The pain was evaluated on Visual analog scale (VAS) as 6 to 8. At the physical examination, anterior drawer test was evaluated as grade 3, pivot shift test, varus test, dial test and posterolateral drawer test were found positive. The Tegner Lysholm score was evaluated as 22 (poor). Under general anesthesia, left knee had tendency to external rotation and recurvatum when leg was suspended by toes. A magnetic resonance image (MRI) revealed the presence of a total ACL rupture, PLC injury and a fracture of lateral tibia plateau. The patient was treated with arthroscopic reconstruction of ACL with ipsilateral hamstring tendon graft fixed with endobutton through femoral tunnel and bio interference screw through tibial tunnel and PLC injury was treated with 2 suture anchors. Postoperatively first day, quadriceps musculature and active and passive ROM exercises was trained. During postoperatively third week, the patient was allowed to mobilize nonweight bearing with the use of two crutches without functional knee brace. At the sixth week, arthroscopic lysis was performed due to type 3 arthrofibrosis. At the tenth week, manipulation was performed to the left knee under general anesthesia. Results: At the 3 month- follow-up, the patient achieved full symmetric restoration of motion and he had returned to full daily activities. The Tegner Lysholm score was evaluated as 94 (excellent) postoperatively. Functional examination of the left knee reveled 155 of flexion, and full knee extension. The complaint of instability was disappeared. At 9 month-follow-up, clinical findings were unremarkable, with no sign of re-rupture and arthrofibrosis and he returned to his professional dance career. Conclusion: In the literature there is not any consensus regarding the management and rehabilitation intervention for arthrofibrosis in young athletes or professional dancers. The best treatment method is preventing the arthrofibrosis once it has occurred with surgical lysis and aggressive physical therapy. The combined surgical treatment and physiotherapy described in this case report may assist clinicians in the treatment of arthrofibrosis after arthroscopic reconstruction of ACL and PLC injury. © The Author(s) 2014

Numerical Modeling of Supercritical Open Channel Flow with Detached Eddy and Large Eddy Simulation

Kritik üstü açık kanal akımının üç boyutlu sayısal analizi, sonlu hacimler yöntemine dayalı ANSYS-Fluent ile yapılmıştır. Sayısal hesaplamalarda türbülanslı akımın karakteristiklerinin belirlenmesinde Large Eddy ve Realizable k-? tabanlı Detached Eddy Simülasyonu kullanılmıştır. Sayısal hesaplamalarda su yüzü profili, Akışkan Hacimleri Yöntemi ile elde edilmiştir. Kritik üstü akımın hız alanı Lazer Doppler Anemometresi kullanılarak ölçülmüştür. Sayısal modellerden elde edilen akım hızları ve su yüzü profilleri deneysel ölçümlerle karşılaştırılmış, Detached Eddy Simülasyon modelinin hız alanının hesaplanmasında ve su yüzü profilinin belirlenmesinde Large Eddy Simülasyon modeline göre daha başarılı olduğu görülmüştürThree-dimensional numerical analysis of supercritical open channel flow is performed by ANSYS FLUENT-based on the finite volume method. In the numerical analysis of supercritical turbulent flow, Large Eddy Simulation and Detached Eddy Simulation based on the Realizable k-? turbulence models are used in order to determine turbulence characteristics. The free surface profile is computed using Volume of Fluid method. The velocity field of supercritical open channel flow is measured using Laser Doppler Anemometry (LDA). Computational results for velocities and free surface profiles are compared with measured data. Comparisons show that the Detached Eddy Simulation model is more successful than Large Eddy Simulation in predicting the velocity field and free surface profile

Numerical Modeling of Interaction of Turbulent Flow with a Buried Circular Cylinder on a Plane Surface

WOS: 000494262000005Turbulent flow characteristics around a partially buried horizontal circular cylinder are investigated numerically for the burial ratio of B/D=0.50 (B is burial depth, D is the diameter of the cylinder). The governing equations are numerically solved using ANSYS-Fluent for the flows having the same conditions with the experiments related to measurements of velocity field by Particle Image Velocimetry for Reynolds numbers based on the cylinder diameter, in the ranges of 1000 <= Re-D <= 7000. Standard k-epsilon, Renormalization-group k-epsilon, Realizable k-epsilon, Modified k-omega, Shear Stress Transport k-omega and Reynolds Stress turbulence models are employed. Experimental validations of the numerical results show that Shear Stress Transport k-omega model provides better predictions for the kinematic properties of the turbulent flow than the other turbulence models used herein. Force coefficients also predicted numerically at Reynolds numbers in the ranges of 1000 <= Re-D <= 7000 for the burial ratio, B/D=0, 0.25 and 0.5

Experimental and Numerical Analysis of Flow around a Circular Bridge Pier

WOS: 000444153900017The turbulent flow field around a circular pier is complex due to separation and generation of multiple vortices in different structures. This topic has a great interest in engineering applications for the design of the bridges over water. In this study, the velocity field of flow around a circular pier is measured using Laser Doppler Anemometry (LDA). The Basic equations of the problem are solved by ANSYS-Fluent program package based on finite volume method for the flow case having the same experimental conditions. In the numerical simulations, Standard k-epsilon, Renormalization Group k-epsilon and Realizable k-epsilon turbulence closure model are used for the simulation of turbulence, and the flow profile is computed using Volume of Fluid method. Grid Convergence Index (GCI) is performed to examine the effect of the selected grid structure on the numerical results. The computed results for velocities and free surface profiles are compared with measured data. The comparisons of the experimental and numerical results show that Realizable k-epsilon is more successful turbulence model among the other models in predicting the velocity field and free surface profiles