Search

Thermoforming of thermoplastic composites attracts increasing attention in the community due to the mechanical performance of these materials and their recyclability. Yet there are still difficulties concerning the uniformity of the heating and overheating of parts prior to forming. The need for higher energy efficiencies opens new opportunities for research in this field. This is why this study presents a novel experimental method to classify the efficiency of infrared heaters in combination with different thermoplastic composite materials. In order to evaluate this, different organic sheets are heated in a laboratory scale heating station until a steady state condition is reached. This station mimics the heating stage of an industrial composite thermoforming device and allows sheets to slide on top of the pre-heated radiator at a known distance. By applying thermodynamic balances, the efficiency of chosen parameters and setups is tested. The tests show that long heating times are required and the efficiency of the heating is low. Furthermore, the efficiency is strongly dependent on the distance of the heater to the sheet, the heater temperature and also the number of heating elements. Yet, using a full reflector system proves to have a huge effect and the heating time can be decreased by almost 50%.

Solid oxide fuel cells represent a promising technology to increase the electrical efficiency of biomass-based combined-heat-power systems in comparison to state-of-the-art gas engines, additionally providing high temperature heat. To identify favorable fuel gas compositions for an efficient coupling with gasifiers at low degradation risk is of major importance to ensure stability, reliability, and durability of the systems used, thus increasing attractiveness of electricity production from biomass. Therefore, this study presents a comprehensive analysis on the influence of main gas components from biomass gasification on the performance and efficiency of a cell relevant for real application. An industrial-size electrolyte supported single cell with nickel/gadolinium-doped ceria anode was selected showing high potential for gasifier-solid oxide fuel cell systems. Beneficial gas component ratios enhancing the power output and electric efficiency are proposed based on the experimental study performed. Furthermore, the degradation stability of a SOFC fueled with a synthetic product gas representing steam gasification of woody biomass was investigated. After 500 h of operation under load at a steam-to-carbon ratio of 2.25 in the fuel gas, no performance or anode degradation could be detected.

Prediction of shrinkage and warpage of injection molded plastic parts is a key issue of injection molding simulation. In the present work a U-shaped part is investigated experimentally and by means of state of the art injection molding simulation software. The part has thick walls in the corner where inner defects such as voids and porous zones may appear. Experiments and simulations were performed with POM and glass fiber reinforced polyamide. Measurements of pressure in the cavities and temperature profiles around the cavities were used to validate the numerical model. In case of POM it was found that warpage predictions are way off when the void volume is high and in good agreement when the void volume is minimized. No such correlation was observed in case of fiber reinforced materials. Here, shrinkage and warpage are dominated by the fiber orientation state with minor influence of the processing conditions. Predicted warpage was found to be extremely dependent on the used closure approximation.

The paper shows the capability of state-of-the-art models and software to predict the fiber orientation distribution (FOD) on injection molded parts with a complex and thick-walled geometry. Predictions by the standard Folgar-Tucker model and the Reduced Strain Closure model were compared to measurements of the fiber orientation distribution obtained by X-ray Computed Tomography. Measurements and simulations were performed under different processing conditions to investigate the influence of injection velocity and packing pressure on the FOD. It was found that the predicted fiber orientation is in good qualitative agreement with the measurements. The measured orientation shows a distinct shell-core structure with high alignment of the fibers in flow direction in the shell layer and a orientation perpendicular to the flow direction in the core layer. While the orientation in the shell layer is predicted fairly well, a significant deviation is found in the prediction of the orientation in the core layer.

The aim of this paper is to determine the reason for the large warpage of an injection molded chunky part made of glass fiber reinforced polyamide 6. State of the art commercial 3D injection molding simulation software was used to predict the warpage of the part. While the simulation predicted a product virtually free of warpage the molded parts showed a large deformation. Several molding experiments and X-ray computed tomography (µCT) scans of the moldings have been performed to figure out the reason for this. The µCT scans revealed voids in the thick walls of the part. It was found that these defects were the main cause of the unreliable simulation results. Therefore it is concluded that voids can have a major influence on the reliability of numerical warpage predictions. This paper shows a simplified method to determine the zones were voids will appear and shows the comparison with µCT-data.

The authors want to acknowledge, that during the production of the final version of the publication the image for Figure 9 has been replaced with the image for Figure 12, however without changing the content of the paper. This issue is resolved in the current version of the publication.

In this work the effects on numerical calculations of in-flight particle motion and heating within a semi-industrial scale shaft furnace are presented. Therefore, experiments and numerical calculations with a type of boiler slag powder were conducted. It consists of particles with various size and shape. The obtained results were used for validation purposes of the proposed numerical model. This model differs in two main modifications compared to the current state-of-the-art CFD models. First, the application of a numerically inexpensive combustion model with a detailed chemical reaction mechanism enabled a significant reduction of the computational demand. Furthermore, the used burner type in the furnace with its characteristics can be modeled with sufficient accuracy. Second, various particle sizes and shapes were considered within the numerical model by application of corresponding drag formulations and empirically determined drag model parameters. Latter were obtained using a particle classification method proposed in a previous study. With this approach influences due to particle drag, rotation, oscillation and surface friction of different particle sizes and shapes were considered. Nevertheless, particle trajectories and heat transfer between particles and the fluid can be modeled with a low computational effort. The obtained results were compared to a commonly used approach, considering only one particle shape factor and one particle injection. Resulting particle trajectories and temperatures reveal significant differences between the latter and the proposed approach. Finally, influences on the heating characteristics due to preheated combustion air were investigated. It was shown that particle trajectory and temperature calculations in the shaft furnace are mainly affected by considering various particle shapes. Furthermore, the numerical results were improved by applying empiric model parameters. Using preheated combustion air as oxidizer results in a higher amount of spheroidized particles.

Internal reforming of light hydrocarbons is one of the major advantages of solid oxide fuel cells (SOFCs). This reforming process includes the risk of carbon formation and/or nickel re-oxidation on the active nickel sites of the porous fuel electrode. Knowledge of the absolute and relative amounts and positions of surface adsorbed species helps to achieve an understanding of the processes that occur and can be used to identify prevalent cell degradation mechanisms induced by internal reforming. This heterogeneous process was numerically investigated at an operating temperature of 800°C by means of a detailed computational fluid dynamics (CFD) model. The surface composition of adsorbed species within the porous structure of a Ni/YSZSOFC anode caused by different carbon-containing feeds will be discussed. Six fuel mixtures that represent diesel reformates or other carbon containing fuels with varying S/C ratio and methane to carbon monoxide ratio were analyzed in the context of their propensity to coking and oxidation. It was shown that highest carbon surface coverages occur when using feeds with a high methane to carbon monoxide ratio. Fuels that contain only carbon monoxide as carbon precursor lead to considerably lower coverages. Furthermore, surface specific coverage ratios were introduced that were used as effective methods to analyze coking or oxidation of the porous substrate.

Solid oxide fuel cells (SOFCs) can be operated on a wide range of fuels, including hydrocarbons. Such a fuel supply includes the risk of carbon formation on the catalytically active nickel centers within the porous anodic substrate. Coking is very critical for the reliability and durability of the SOFCs. Thus, within this study, coking propensity of the most prominent carbon containing fuels was analyzed by thermodynamic equilibrium calculations for two fundamentally different types of carbon and detailed transient numerical simulations based on heterogeneous reforming kinetics. This approach is new to the literature and reveals the strengths and weaknesses of both fundamentally different approaches. It was shown that in thermodynamic equilibrium calculations, carbon formation is most likely due to pure methane. Carbon monoxide will form the least amounts of carbon in typical SOFC temperature ranges. Furthermore, based on a validated computational fluid dynamics (CFD) simulation model, detailed heterogeneous reaction kinetics were used to directly simulate elementary carbon adsorbed to the reactive substrate surface. The amounts, spatial and temporal distribution, of carbon atoms within the porous structure were identified between 600?°C and 1000?°C for a broad steam-to-carbon ratio range of 0.5–2. It was shown that most carbon is formed at the beginning of the substrate. A key finding was that steady-state results differ greatly from results within the first few seconds of fuel supply. An increment in temperature causes a significant increase in the amount of carbon formed, making the highest temperatures the most critical for the SOFC operation. Moreover, it was shown that mixtures of pure methane deliver the highest amounts of adsorbed elementary carbon. Equimolar mixtures of CH4/CO cause second highest surface coverages. Pure carbon monoxide blends led to least significant carbon formations. This work has shown the important contribution that thermodynamic equilibrium calculation results, as well as the outcomes of the detailed CFD simulations, allow to identify suitable operating conditions for the SOFC systems and to minimize the risk of coking on porous anodes.

Solid oxide fuel cells (SOFCs) can be operated on a wide range of fuels, including hydrocarbons. Such a fuel supply includes the risk of carbon formation on the catalytically active nickel centers within the porous anodic substrate. Coking is very critical for the reliability and durability of the SOFCs. Thus, within this study, coking propensity of the most prominent carbon containing fuels was analyzed by thermodynamic equilibrium calculations for two fundamentally different types of carbon and detailed transient numerical simulations based on heterogeneous reforming kinetics. This approach is new to the literature and reveals the strengths and weaknesses of both fundamentally different approaches. It was shown that in thermodynamic equilibrium calculations, carbon formation is most likely due to pure methane. Carbon monoxide will form the least amounts of carbon in typical SOFC temperature ranges. Furthermore, based on a validated computational fluid dynamics (CFD) simulation model, detailed heterogeneous reaction kinetics were used to directly simulate elementary carbon adsorbed to the reactive substrate surface. The amounts, spatial and temporal distribution, of carbon atoms within the porous structure were identified between 600 °C and 1000 °C for a broad steam-to-carbon ratio range of 0.5–2. It was shown that most carbon is formed at the beginning of the substrate. A key finding was that steady-state results differ greatly from results within the first few seconds of fuel supply. An increment in temperature causes a significant increase in the amount of carbon formed, making the highest temperatures the most critical for the SOFC operation. Moreover, it was shown that mixtures of pure methane deliver the highest amounts of adsorbed elementary carbon. Equimolar mixtures of CH4/CO cause second highest surface coverages. Pure carbon monoxide blends led to least significant carbon formations. This work has shown the important contribution that thermodynamic equilibrium calculation results, as well as the outcomes of the detailed CFD simulations, allow to identify suitable operating conditions for the SOFC systems and to minimize the risk of coking on porous anodes.

Micro-tubular solid oxide fuel cells (MT-SOFCs) are a much smaller version of larger tubular SOFCs. They are operational within seconds and allow a higher power density per volume than the larger version. Hence they are a potential technology for automotive, auxiliary and small scale power supply devices. In this study a commercially available computational fluid dynamic (CFD) software program was used to predict a MT-SOFCs performance when located inside a high temperature wind tunnel experimental apparatus. In Part I, experimentally measured temperature profiles were recorded via thermo-graphic analyses and I/V curves. These measurements were used in this study to establish the predictability and validity of the CFD code and furthermore understand the MT-SOFC attributes measured in Part I. A maximum 4% I/V curve deviation and 6 K temperature deviation between the experimentally measured and model predicted results was observed. Thus, the model predicted the MT-SOFCs performance in the experimental environment very accurately. A very critical observation was the current density and temperature profile across the MT-SOFC that was strongly dependent on the distance from the hydrogen/fuel inlet. Not only was the model validated but also a grid and quantitative solution analysis is explicitly shown and discussed. This resulted in the optimum grid density and the indication that a normally undesirable high grid aspect ratio is acceptable for similar MT-SOFC modeling. These initial simulations and grid/solution analysis are the prerequisite before performing a further study including multiple MT-SOFCs within a stack using different fuels is also envisaged.

Micro-tubular solid oxide fuel cells (MT-SOFCs) are a much smaller version of larger tubular SOFCs. They are operational within seconds and allow a higher power density per volume than the larger version. Hence they are a potential technology for automotive, auxiliary and small scale power supply devices. In this study a commercially available computational fluid dynamic (CFD) software program was used to predict a MT-SOFCs performance when located inside a high temperature wind tunnel experimental apparatus. In Part I, experimentally measured temperature profiles were recorded via thermo-graphic analyses and I/V curves. These measurements were used in this study to establish the predictability and validity of the CFD code and furthermore understand the MT-SOFC attributes measured in Part I. A maximum 4% I/V curve deviation and 6 K temperature deviation between the experimentally measured and model predicted results was observed. Thus, the model predicted the MT-SOFCs performance in the experimental environment very accurately. A very critical observation was the current density and temperature profile across the MT-SOFC that was strongly dependent on the distance from the hydrogen/fuel inlet. Not only was the model validated but also a grid and quantitative solution analysis is explicitly shown and discussed. This resulted in the optimum grid density and the indication that a normally undesirable high grid aspect ratio is acceptable for similar MT-SOFC modeling. These initial simulations and grid/solution analysis are the prerequisite before performing a further study including multiple MT-SOFCs within a stack using different fuels is also envisaged.

The purpose of the first part of this study was to compare four different temperature measuring methods. The application of these tools for possible temperature monitoring or calibration of monitors of microtubular solid oxide fuel cells (MT-SOFCs) is explored. It was found that a thermographic camera is very useful to visualize the temperature gradient on the outside of a cell, while an electrochemical impedance spectroscopy method was useful for estimating the core temperature of a test cell. A standard thermocouple was also used in combination with the previous two methods. Furthermore, an inexpensive laser guided thermometer was also tested for MT-SOFC temperature measurement. This initial study has opened up a range of questions not only about the effect of the experimental apparatus on the measurement results but also about the radial temperature distribution through a MT-SOFC in a working mode. Both these topics will be further investigated in part II of this study through a computational fluid dynamics study. This should provide additional interesting information about any differences between testing single cells and those within a bundle of cells. The discussed results are expected to be mainly temperature related, which should have direct consequences on power output and optimized gas inlet temperatures.

The purpose of the first part of this study was to compare four different temperature measuring methods. The application of these tools for possible temperature monitoring or calibration of monitors of microtubular solid oxide fuel cells (MT-SOFCs) is explored. It was found that a thermographic camera is very useful to visualize the temperature gradient on the outside of a cell, while an electrochemical impedance spectroscopy method was useful for estimating the core temperature of a test cell. A standard thermocouple was also used in combination with the previous two methods. Furthermore, an inexpensive laser guided thermometer was also tested for MT-SOFC temperature measurement. This initial study has opened up a range of questions not only about the effect of the experimental apparatus on the measurement results but also about the radial temperature distribution through a MT-SOFC in a working mode. Both these topics will be further investigated in part II of this study through a computational fluid dynamics study. This should provide additional interesting information about any differences between testing single cells and those within a bundle of cells. The discussed results are expected to be mainly temperature related, which should have direct consequences on power output and optimized gas inlet temperatures.