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    Carbon nanotube (CNT) modified carbon fiber/epoxy composite plates for the PEM fuel cell bipolar plate application
    (Pergamon-Elsevier Science Ltd, 2023) Daricik, Fatih; Topcu, Alparslan; Aydin, Kadir; Celik, Selahattin
    Light structures of the composite materials are prominent outcomes for reducing the total stack weight. However, the poor electrical properties of the composite structures pose an obstacle to wide employment as a bipolar plate for the PEMFC systems. In the current study, the carbon fiber/epoxy composite laminates were modified with the multi-walled carbon nanotube superconductor materials to overcome conductivity issues. The effects of CNTs additives in a range of 0.25-1.25% wt on the electrical, mechanical, and perfor-mance features of the carbon fiber/epoxy laminates were investigated. Electrical conduc-tivities of the nonconductive carbon fiber/epoxy plates increased with the rising additive ratio, as expected, and reached 120 S/cm for the 1.25% CNT reinforcement. Although the mechanical strength of the pristine composite BP is already satisfactory, CNTs can increase the flexural strength and flexural modulus of the BP up to 42% and 27%, respectively. Each composite plate was subjected to the single-cell performance test. 1.25% wt CNT modified plate was executed pretty close performance compared to the aluminum alloy (AA 3105) bipolar plate under the same conditions.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Effects of Short-Term Thermal Aging on the Fracture Behavior of 3D-Printed Polymers
    (Springer, 2021) Daricik, Fatih; Delibas, Hulusi; Canbolat, Gokhan; Topcu, Alparslan
    3D printing technologies offer numerous advantages and have attracted the attention of researchers recently. Yet, the most commonly preferred additive manufacturing system is the extrusion-based process that is called fused deposition modeling (FDM) as it is simple, low cost, and prone to customization. In this paper, the effects of the short-term aging of the additively manufactured PLA and ABS specimens were investigated experimentally. The test specimens were aged by keeping them at ambient temperatures of - 80, - 20, 60, 100 degrees C for 10, 20, and 30 days. Thermally aged specimens and the pristine specimens were forced to fracture with bending load at room temperature. Thus, the permanent effects of thermal aging of the specimens were investigated utilizing the load-deflection curve, plane-strain fracture toughness, and the morphologies of fracture surfaces. It was concluded that the printed PLA materials are more susceptible to the thermal aging than the ABS printed materials. The contraction and expansion of the fused polymer filaments affect directly the bonding strength between the adjacent layers. Therefore, plane-strain fracture characteristics of the FDM polymer materials exposed to thermal aging differ according to the filament orientation and the aging time.
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    Experimental study on the flow field geometry of the PEM fuel cell bipolar plates: The effects of various shaped blocks embedded in serpentine pattern on cell performance
    (Elsevier Sci Ltd, 2024) Celik, Selahattin; Yagiz, Mikail; Yildirim, Fuat; Topcu, Alparslan
    The flow field pattern is crucial in many aspects such as cost-efficiency (in terms of excessive fuel consumption), water management on the cathode side, and achieving a high cell performance. The studies on the reconnaissance of much more effective flow field design have been continuing for years. As a matter of fact, it may be succeeded with some manipulations on the flow area. The current research proposes to investigate the effects of blocks in various shapes and positions on the net power output by changing the shape of the channels in the flow field (FF). For this reason, semicircular and triangular blocks were machined on the serpentine channels and their short-term performances were compared with the conventional serpentine pattern. In addition to the related new FF designs, performance evaluation was made by using nickel foam placed to fill the inner part of the serpentine FF. First, ultimate operating conditions were optimized with the traditional serpentine FF. Then, the performance outputs of the proposed FF designs were compared under the same conditions assigned in the previous section. The single-cell performance tests yielded that the highest power density was ensured with nickel foam (NF)-serpentine FF with 0.267 W/cm2. This increment corresponds to a 38 % enhancement in the power output when compared to the classical serpentine-type FF. Triangular (T) and semicircular (S) obstacles increased the performance significantly. Each manipulation on the traditional serpentine FF affected the power output positively, essentially. The pattern structures of the diagonal semicircle (DS) and diagonal triangular (DT) FFs reduced both water evacuation ability and performance increase rate. NF-serpentine FF contact highly decreased the ohmic resistance level of the cell when compared to the other designs according to the impedance (EIS) measurements. In addition, a correlation was observed between the performance and pressure drop test results. The highest-pressure drop was recorded with NF-serpentine FF (4.225 kPa) whereas the lowest is conventional serpentine FF (0.55 kPa). Traditional serpentine pattern is famous for with high-pressure drop structure. Consecutively, the pressure drop tests proved that the manipulations increased the pressure level of the system directly.
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    Morphological, mechanical, magnetic, and thermal properties of 3D printed functional polymeric structures modified with Fe2O3 nanoparticles
    (Wiley, 2021) Aktitiz, Ismail; Delibas, Hulusi; Topcu, Alparslan; Aydin, Kadir
    The Fe2O3 nanoparticle structures, which have many application areas such as electronics, marine, and aviation, have been studying extensively due to the compliance between organic polymer and inorganic Fe2O3 nanoparticles. Nanocomposite structures are successfully produced in the desired complexity with the additive manufacturing method. In the current study, Fe2O3 nanoparticles were doped into the photocurable resin at different concentrations (pristine, 0.25%, 0.5%, and 1% in wt), and the prepared 3D polymer nanocomposite mixtures were printed via stereolithography method. To investigate the morphological, mechanical, magnetic, and thermal properties of the printed nanocomposite structures, scanning electron microscopy, hardness, vibrating sample magnetometer, thermogravimetric analysis, and differential scanning calorimeter analysis were performed, respectively. It was revealed that the Fe2O3 nanoparticles improved the thermal stability of the structures. Moreover, an increase in magnetic properties has been observed up to 459%.
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    Performance comparison of bio-inspired flow field designs for direct methanol fuel cell and proton exchange membrane fuel cell
    (Pergamon-Elsevier Science Ltd, 2024) Yagiz, Mikail; Celik, Selahattin; Topcu, Alparslan
    Bipolar flow channel plate design, which is a key component and performance qualifier of fuel cells, is an extensively investigated area. Recently, bio-inspired flow fields (FFs) have been designed to increase the overall performance as an alternative to traditional FFs. In the present study, performance evaluation of the various bioinspired FFs was carried out in PEM fuel cell and direct methanol fuel cell modes. The effects of the main performance characteristics including the clamping force of the short stack assembly, air flow rate, and operating temperature on the cell power were investigated for both PEMFC and DMFC modes. The highest performance output was ensured with the Morus leaf-inspired FF (MLFF) at PEMFC mode at 55 degrees C with a peak power density of 313 mW/cm2. Besides, the highest performance for DMFC mode was achieved at 35.8 mW/cm2 with the Ficus Carica leaf-inspired FF (FCLFF).
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    Performance evaluation of machined and powder metallurgically fabricated Crofer®22 APU interconnects for SOFC applications
    (Pergamon-Elsevier Science Ltd, 2022) Topcu, Alparslan; Ozturk, Bulent; Cora, Omer Necati
    This study aimed to evaluate the performances of solid oxide fuel cell (SOFC) interconnects made of commercially available bulk Crofer (R) 22 APU alloy through machining, and powder metallurgy approach (P/M) from Crofer (R) 22 APU powders. To this goal, interconnects with 40 x 40 mm(2) active area were fabricated via both methods. Porosity, coefficient of thermal expansion (CTE) measurements, thermal shock, and single-cell performance tests were carried out. While no porosity was available for the machined interconnect, P/M inter-connect was found to have 9% porosity so the increased surface area. CTE values of interconnects, one of the critical parameters in fuel cell stack design, were found to be in close agreement. The maximum power values of 3.12 and 2.97 W were obtained for machined, and P/M interconnects, respectively, at operating temperature condition of 800 degrees C. Even though P/M interconnect exhibited slightly lower performance in terms of power density, it was concluded that P/M interconnect can be considered a reliable alter-native to the conventionally produced machined one due to ease of production, lower scrap rate, and potential to have a better cell performance as it has an increased surface scrap rate, and potential to have a better cell performance as it has an increased surface area. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    The effect of the heater and the pump operation durations on the cold start performance of the coolant heating assisted PEM fuel cell application
    (Wiley, 2022) Topcu, Alparslan; Aydin, Kadir; Celik, Selahattin
    The self-cold start ability of the proton exchange membrane (PEM) fuel cell system is limited due to the inadequate heat generation by the cell and the restricted effect of operating conditions. Fresh and useful heat may be provided by an external assisted technique that is adopted in the current study. The operation duration effect of the pump and the heater which are the most energy-consuming components of the coolant heating assisted method on the cold start performance of a PEM fuel cell stack was investigated, experimentally. Firstly, the inadequacy of the single-cell operation was proved by self-operation tests. The test was conducted at -10 degrees C and the temperature was raised to -7.5 degrees C levels during the test thanks to exothermic reactions that occurred in the cell. It manifests the cell may not be survived without any assistance and an external heat source is required. This fresh heat was supplied to the cell by the closed coolant cycle. Ethanol which can be operated at sub-zero temperatures was circulated throughout the machined external channels to the backside of the bipolar plates. The case studies were established considering various operation durations of the pump and the heater and the cold start tests were performed at -10 degrees C, -15 degrees C, -20 degrees C, -25 degrees C, and -30 degrees C temperatures. The effect of the pump and the heater operation durations on the temperature, voltage, and current profiles of the single-cell were investigated under the same energy consumption levels. The cell was operated throughout the whole case study and generated electricity successfully. It put forward the accomplishment of the proposed heating mechanism even at -30 degrees C. The time required for the cell temperature to rise above zero is increase with the decrease of the cold start test temperature. The cell temperature increased to zero at approximately 18, 39, and 53 seconds at -10 degrees C, -20 degrees C, and -30 degrees C operations, respectively. The PEM fuel cell stack, which does have not the capacity to operate itself at sub-zero temperatures, was successfully operated with the help of the established mechanism. No higher starter energy is needed for a -10 degrees C operation and the cell may be survived with a low operation of the auxiliary equipment. Failed starts were experienced with long heater and low pump cases at -20 degrees C and -25 degrees C temperatures. It is thought that a sharp drop in temperature after a pump shutdown prompts the cell into an unstable situation and fluctuations in voltage and current profiles. Although failed starts were recorded with implemented case studies at -30 degrees C at the initial stage, successful cold starts were achieved by the extended durations of the pump and heater, proportionally 2.6 and 5.5 A stable current, and 23.7 degrees C and 20 degrees C maximum temperature values were obtained with long heater operation and long pump operation cases, respectively. Although long heater operation provided a higher temperature increase, the long pump operation enabled a more homogeneous temperature distribution and stable current profile. This study revealed the strong sides of energy-consuming components and benefits at maximum to achieve a more stable cold start operation.
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    Theoretical Analysis on the Thermal and Electrical Properties of Fiber Reinforced Laminates Modified with CNTs
    (2020) Darıcık, Fatih; Topcu, Alparslan
    In the present study, the effect of the multi-walled carbon nanotubes (MWCNTs) fillers weight fraction on the mechanical, electrical, and thermal properties of the epoxy was calculated analytically. The results were then compared and it was found out that the MWCNTS has a significant effect on the electrical conductivity of the epoxy. The MWCNT modified epoxy composites were considered as the matrix material to design quasi-isotropic carbon fibre/epoxy composite. The change of the weight fraction of the MWCNTs on the mechanical, electrical, and thermal properties of the carbon fibre/epoxy laminates was also calculated. Finally, the hygrothermal load and the bending load response of the laminated composites were researched. MWCNTs fix the mismatch between the hygrothermal properties of the epoxy matrix and the carbon fiber.