The Experts below are selected from a list of 14253 Experts worldwide ranked by ideXlab platform
Noam Lior - One of the best experts on this subject based on the ideXlab platform.
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the cooling process in Gas Quenching
Journal of Materials Processing Technology, 2004Co-Authors: Noam LiorAbstract:Gas Quenching is a relatively new process with several important advantages, such as minimal environmental impact, clean products, and ability to control the cooling locally and temporally for best product properties. To meet the high cooling rates required for Quenching, the cooling Gas must flow at very high velocities, and such flows are highly turbulent and separated. Consequently, there is a need for good understanding of these flows and their consequences for the process. To that end, we researched the state of the art, and have conducted numerous numerical and experimental studies and developed CFD models on this subject, and show the results for flows inside quench chambers and their components, and for external flows, including multi-jet impingement, on cylindrical and prismatic single and multiple bodies (the quench charge). Velocity distributions and uniformity, pressure drop, and flow effects on heat transfer coefficients and product uniformity, as well as recommendation for improved processes, are shown.
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an evaluation of Gas Quenching of steel rings by multiple jet impingement
Journal of Materials Processing Technology, 2003Co-Authors: Jerome Ferrari, Noam Lior, Jan SlyckeAbstract:Abstract Multiple Gas jet impingement cooling for Quenching is a very promising approach for increasing the heat transfer coefficients ( h ) and thus the overall cooling rates in the Gas-Quenching process. Appropriate correlations for h were selected based on an extensive critical literature review, and used in a numerical heat conduction model and a numerical phase transformation model which were developed and solved for evaluating the Quenching capacity of such cooling methods for Quenching steel rings. The models allow prediction of the steel phase transformation extent as a function of h , for different ring sizes. An optimization of the jet nozzle dimensions and configuration was performed, and the effects of the jet spent flow and the cooling Gas temperature were discussed and estimated. It was also found that while the spent flow effect on h is not adequately known, it tends to lower h , while the cooling Gas temperature has minimal effect on h . Validation experiments were performed and show that the predicted trends are reasonable, within the errors of the Johnson–Mehl–Avrami phase transformation model and the experimental method used.
Anita Hobaillie - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of potassium and iodine from potassium triiodide complex additive on Gas quenched perovskite solar cells
Nano Energy, 2019Co-Authors: Meng Zhang, Jianghui Zheng, Cho Fai Jonathan Lau, Martin A Green, Shujuan Huang, Jueming Bing, Yongyoon Cho, Anita HobaillieAbstract:Abstract Gas-Quenching has been demonstrated to be a robust and reliable method for fabricating perovskite solar cell (PSCs) and is a technique for large area and large-scale production. Although additive engineering has been used to improve various perovskite fabrication methods, it is yet to be utilised by Gas-Quenching. Herein, we introduce potassium triiodide complex (KI3) as a novel additive to the perovskite precursor solution for Gas-quenched PSCs. The resultant perovskite film exhibits broader spectral response, enhanced photoluminescence and prolonged carrier lifetime, due to halide exchange and defect passivation brought about by the I2 supplied by the KI3 complex. The champion device fabricated from precursor with mixed KI and KI3 additives delivered a steady-state power conversion efficiency of 21.2% with negligible hysteresis due to the presence of potassium salt. This efficiency is the highest for PSCs fabricated by Gas-Quenching. Moreover, the KI3 additive has substantially improved the stability of the precursor solution, allowing high performance devices to be fabricated with aged solution, which widens the process window for perovskite film deposition and lengthens the lifetime of precursors which are important prerequisites for large scale production of PSC.
Shujuan Huang - One of the best experts on this subject based on the ideXlab platform.
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synergistic effect of potassium and iodine from potassium triiodide complex additive on Gas quenched perovskite solar cells
Nano Energy, 2019Co-Authors: Meng Zhang, Jianghui Zheng, Cho Fai Jonathan Lau, Martin A Green, Shujuan Huang, Jueming Bing, Yongyoon Cho, Anita HobaillieAbstract:Abstract Gas-Quenching has been demonstrated to be a robust and reliable method for fabricating perovskite solar cell (PSCs) and is a technique for large area and large-scale production. Although additive engineering has been used to improve various perovskite fabrication methods, it is yet to be utilised by Gas-Quenching. Herein, we introduce potassium triiodide complex (KI3) as a novel additive to the perovskite precursor solution for Gas-quenched PSCs. The resultant perovskite film exhibits broader spectral response, enhanced photoluminescence and prolonged carrier lifetime, due to halide exchange and defect passivation brought about by the I2 supplied by the KI3 complex. The champion device fabricated from precursor with mixed KI and KI3 additives delivered a steady-state power conversion efficiency of 21.2% with negligible hysteresis due to the presence of potassium salt. This efficiency is the highest for PSCs fabricated by Gas-Quenching. Moreover, the KI3 additive has substantially improved the stability of the precursor solution, allowing high performance devices to be fabricated with aged solution, which widens the process window for perovskite film deposition and lengthens the lifetime of precursors which are important prerequisites for large scale production of PSC.
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high efficiency rubidium incorporated perovskite solar cells by Gas Quenching
ACS energy letters, 2017Co-Authors: Meng Zhang, Jae Sung Yun, Jianghui Zheng, Cho Fai Jonathan Lau, Xiaofan Deng, Jincheol Kim, Dohyung Kim, Jan Seidel, Martin A Green, Shujuan HuangAbstract:We apply Gas Quenching to fabricate rubidium (Rb) incorporated perovskite films for high-efficiency perovskite solar cells achieving 20% power conversion efficiency on a 65 mm2 device. Both double-cation and triple-cation perovskites containing a combination of methylammonium, formamidinium, cesium, and Rb have been investigated. It is found that Rb is not fully embedded in the perovskite lattice. However, a small incorporation of Rb leads to an improvement in the photovoltaic performance of the corresponding devices for both double-cation and triple-cation perovskite systems.
F Frerichs - One of the best experts on this subject based on the ideXlab platform.
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a mesoscopic approach of the quench cracking phenomenon influenced by chemical inhomogeneities
Engineering Failure Analysis, 2017Co-Authors: Diego Said Schicchi, F Hoffmann, F FrerichsAbstract:Abstract Heat treatment simulation can be an effective tool aimed at solving failure problems economically. However, the quality of numerical predictions depend on the quality of the applied models. It is well know that during Quenching cracks may form due to high localized stresses and strains fields generated within the component, but also residual states can cause in-service failures after treatment. In spite of the models improvements made in the field, a current limitation is the common assumption of homogeneous microstructures. Chemical (and consequently, structural) inhomogeneities are normally neglected. In this work, Gas Quenching tests on cylindrical specimens of 100Cr6 (SAE 52100) steel are proposed to experimentally investigate the microcrack generation. Metallographic, spectrometry and microprobe measurements are performed aimed at characterizing both inclusions (carbides) and segregation bands (carbon, chromium and manganese distribution). A finite element based model is proposed to numerically evaluate the criticality of the Quenching process in a two stage approach. Firstly, the Gas Quenching problem is solved, in direct correspondence with the experimental tests performed. Afterward, the mesoscale response is studied in a representative volume element based approach. The mesoscopic geometries are generated based on experimental determinations of the carbides and segregations' distributions. The extended finite element method is used to account for the fracture initiation. The influence of carbides (size and content) and chemical segregations on the mesoscale failure/criticality response is numerically analyzed. The numerical approach here presented is proposed as a failure prediction methodology specifically focused on quench cracking taking into account real steel meso-geometries.
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Influence of Rewetting Behavior on the Distortion of Bearing Races
Journal of Materials Engineering and Performance, 2013Co-Authors: Thomas Lübben, F FrerichsAbstract:Immersion Quenching in evaporable fluids like oil, polymer solutions, or water is a widely used technique in heat treatment shops because this technique provides higher heat transfer coefficients than the most alternative Gas Quenching techniques. The disadvantages of immersion Quenching in evaporating fluids are the complex heat transfer mechanisms which consist of the three phases, film boiling, nucleate boiling, and convection. Especially the transition from film to nucleate boiling—the rewetting of the sample surface—is a complex process which leads to a strong position dependence of the heat transfer coefficient of the cooled work pieces. In particular, immersion Quenching of thin-walled rings can result in large changes of ovality with comparable high scattering. To understand these results, two series of experiments were performed. Rings were quenched in oil in a special Quenching tank and the rewetting behavior was documented. Furthermore, bearing races were quenched in a standard tank. Before and after heat treatment, these rings were measured by a coordinate measuring system and the distortion was determined. The investigations have clearly shown that the vapor film can have an important influence on distortion generation during oil Quenching. The resulting distortion can principally be explained by the observed rewetting behavior.
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process technology for distortion compensation by means of Gas Quenching in flexible jet fields
International Journal of Materials & Product Technology, 2005Co-Authors: S Schuettenberg, M. Hunkel, F Frerichs, Udo FritschingAbstract:Controlled inhomogeneous Quenching (hardening) of a work-piece within the heat treatment process opens up the possibility of compensation of distortion potential. Suitable heat transfer conditions of the workpiece within the Quenching process are realised by impressing and regulation of adjusted (spatially and/or time-wise varying) flexible flow fields on the basis of Gas jet arrays. For analysis of work-piece distortion in heat treatment, the local asymmetric Quenching process in Gaseous media is analysed and described, modelwise, within the framework of the Collaborative Research Centre (SFB570) 'Distortion Engineering' at the University of Bremen. Here, the potential of measures for avoidance as well as reduction of distortion within the manufacturing process is appraised on the basis of simulation and experimental models. The aim of the examinations in the present project is the appliance of in-line control of asymmetric Quenching conditions as compensative measures in the flexible Gas Quenching process. In this contribution, the process technology for distortion compensation in asymmetric flow fields is introduced.
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simulation of Gas Quenching
Journal De Physique Iv, 2004Co-Authors: F Frerichs, F Hoffmann, Udo Fritsching, Th Lubben, H Lohner, A Rocha, G Lowisch, P MayrAbstract:The prediction of mechanical behaviour of specimen during heat treatment by means of numerical simulation requires numerous modules e.g. for heat transfer and mechanical behaviour. The quality of predictions depend on the quality of the applied models within the modules. In this paper the strain hardening model used in the mechanical module will be investigated. For simulation of mechanical behaviour during Gas Quenching it is first of all necessary to calculate the interaction between Gas and specimen. Using simulated flow field and temperature distribution within the Gas, the heat transfer coefficient is calculated from computational fluid dynamics. The cooling and further the mechanical behaviour e.g. residual stresses and distortion of the specimen are simulated by a commercial Finite Element program. To investigate strain hardening it is helpful to choose in a first step a material that will not show phase transformations due to heat treatment. Therefore simulation of mechanical behaviour of austenitic cylinders (SAE30300) is investigated. The required thermophysical properties such as thermal conductivity, density, and specific heat are taken from literature. With the exception of Poisson's ratio the mechanical properties are measured and calculated by own investigations. For description of the temperature dependent stress strain curves the Ramberg-Osgood model is used. The simulated results are compared with experimental data in order to decide which model better describes the mechanical response, whether the kinematic or isotropic strain hardening.
Jan Slycke - One of the best experts on this subject based on the ideXlab platform.
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an evaluation of Gas Quenching of steel rings by multiple jet impingement
Journal of Materials Processing Technology, 2003Co-Authors: Jerome Ferrari, Noam Lior, Jan SlyckeAbstract:Abstract Multiple Gas jet impingement cooling for Quenching is a very promising approach for increasing the heat transfer coefficients ( h ) and thus the overall cooling rates in the Gas-Quenching process. Appropriate correlations for h were selected based on an extensive critical literature review, and used in a numerical heat conduction model and a numerical phase transformation model which were developed and solved for evaluating the Quenching capacity of such cooling methods for Quenching steel rings. The models allow prediction of the steel phase transformation extent as a function of h , for different ring sizes. An optimization of the jet nozzle dimensions and configuration was performed, and the effects of the jet spent flow and the cooling Gas temperature were discussed and estimated. It was also found that while the spent flow effect on h is not adequately known, it tends to lower h , while the cooling Gas temperature has minimal effect on h . Validation experiments were performed and show that the predicted trends are reasonable, within the errors of the Johnson–Mehl–Avrami phase transformation model and the experimental method used.
