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Use of optical methods for temperature evaluation of switching CuCr contacts in vacuum
Full text linkProperties of switching vacuum arcs are affected by melting and evaporation of the electrodes.The surface temperature dynamics during high-current operation was studied for the case of cylindrical contacts made of materials conventionally used for switching applications, namely CuCr40 and CuCr50. The measurements of the arc current and voltage have been accompanied by electrode temperature determination using a combination of near infrared radiation (NIR) spectroscopy and high-speed camera imaging enhanced by narrow-band filter. Special attention was put on the cooling dynamics of cathode and anode after current interruption. Lower thermal conductivity of CuCr alloy with higher Cr content leads to longer temperature decay. Faster cooling of the cathode surface comparing to the anode due to better current density distribution and moving of attachment points were found
Modelling studies of arcs of short length between copper electrodes
Full text linkIn this work, we focus on the electrical properties of arcs of length of a few millimeters at a current level of 2 A. The computation is based on a unified non-equilibrium model that resolves the entire inter-electrode region, applies a deformed mesh to simulate the contact opening, and couples the heat transfer to the electrodes. The arcs are burning in atmospheric pressure air at the presence of Cu metal vapour. Experimental findings are used to calibrate the model
Free burning arc black-box modeling in CO2/O2
Full text linkBlack-box arc parameters were fitted from free-burning arc experiments in a 3 bar abs. CO2/O2 (90%/10%) mixture for the first time. Best fits were achieved with a novel Cassie-based model for low-current arcs. Averaged arc time parameters were τ ≈ 170 µs at low currents (20–50 A) and τ ≈ 33 µs at high currents (1–3 kA), respectively. A decrease of τ could be observed for elongated arcs. Explanations based on thermodynamic arc properties are consistent with measured variations of τ
Optical emission spectroscopy evaluation of exhaust gas temperatures after high current interruption in CO2/O2
Full text linkIn high voltage gas circuit breakers, the pressure buildup necessary for arc extinguishing is partially generated by ablated PTFE nozzle material, which mixes with the insulating gas before being blown through the arcing zone during current interruption. When high short-circuit currents are interrupted, this mixture can retain elevated temperatures for milliseconds as it expands into the circuit breaker’s exhaust volume, and therefore needs to be effectively managed to ensure adequate insulation is maintained. From a circuit breaker design standpoint, this makes accurate knowledge of the exhaust temperature immediately after current zero essential. In this work, two optical emission spectroscopy based temperature determination methods were applied to study the temperature near the exhaust plane exit in a CO2/O2-filled model circuit breaker near current zero. The measured broadband spectra show strong continuum emission from soot particles, in addition to band emission from CuF molecules formed in the exhaust gas. Gray-body spectral fits were performed to estimate temperatures from the continuum emission, which is dominated by the high emissivity soot particles, while temperatures were also obtained via Boltzmann plot evaluation of the emission band intensity ratios. The two methods reveal a temperature mismatch that may suggest slower cooling of the larger soot particles in comparison to the rest of the exhaust gas mixture.
Modern Concrete and Composites 2024
No full textThe 3rd International conference Modern Concrete and Composites 2024 is a conference held by Faculty of Civil Engineering in Prague. The conference is focused on the sharing knowledge of modern technologies, materials, investigation techniques and approaches applicable in the concrete industry and composite design.
The conference key topics were following:
new binders,
advanced technologies,
non-cementitious composites,
measurement techniques,
admixtures and additives,
recycling,
concrete under severe condition,
unique structures.
Date: October 16 - 18, 2024Venue: Hotel SKI, Nové Město na Moravě, Czech Republic
Organised by: Faculty of Civil Engineering, Czech Technical University in Prague
Guest editors:Pavel ReitermanTomáš DavidVendula Davidová
Scientific committee:Jiří MácaLenka BodnárováPetr HuňkaTomáš KlečkaKarel KolářJiří LitošPavel Reiterman
Local organizing committee:Pavel ReitermanPetr HuňkaBohuslav SlánskýMiroslav BroučekVendula DavidováTomáš DavidDalibor KocábMartin LuňáčekMartin VyšvařilTomáš Vlach
Guarantor of the peer review process:Pavel Reiterman
Guarantor of language editing:Miroslav Brouče
Parametric study of a reinforced concrete footbridge strengthened by a layer of UHPFRC
Full text linkThis paper deals with the presentation of a parametric study of the strengthening of a reinforced concrete footbridge with a layer of reinforced UHPFRC on its upper surface. In order to increase its load carrying capacity, stiffness and durability, the design of strengthening with 50 mm thick UHPFRC layer was carried out. The geometry of the analyzed structure is based on the real structure. The parametric study solves its strengthening by considering different support options of the structure and its degradation. The design and assessment was carried out in the form of nonlinear numerical analysis using the FEM in Atena 3D
Advanced silicate composites – a contribution to sustainable construction
Full text linkIn view of the increasing number of natural and man-made disasters and the increasing economic and social problems, it is necessary to adapt the existing principles and methods of structural design, the corresponding construction techniques, and the operation of buildings to make them more sustainable, resilient, and adaptable to new situations in changing natural and socio-economic conditions in the world. Recent research and development of concrete composition, production technology, and development of concrete constructions, intensified over the last 20 years, have led to the improvement of technical parameters while reducing environmental impacts. Due to the optimization of the mixture, new types of concrete have significantly better characteristics from the perspective of strength, mechanical resistance, durability, and resistance to extreme loads.The paper presents examples and results of research focused on the use of new types of silicate composites and their effective combinations in the case study. It is generally necessary to apply new silicate composites in such a way that their potential is used to the maximum. The aim is to present the possibility of new practical and effective application of modern materials with an emphasis on reducing environmental impacts and at the same time increasing the resilience of structures. It covers the utilization of high-performance concrete as a protective and load-bearing thin skin with textile reinforcement using carbon textiles tube in combination with recycled concrete aggregate core.Developed technical solutions could contribute to addressing the Sustainable Development Goals (SDGs), which the United Nations set out in 2015 as a 2030 action plan
Bonding of timber and high-performance concrete
Full text linkTimber-concrete composite systems have emerged as a promising building technique, leveraging the strengths of both materials to improve load capacity, stiffness, and overall performance. In the presented study, high-performance concrete with perfect mechanical performance and durability is used in timber-concrete composite systems to further reduce the environmental footprint and optimize structural efficiency. The weakest point in general of these constructions is the interface between the concrete material and the wood. The focus in this study is on shear strength, specifically examining the combination of adhesive bonding with notch shear connections. Experimental results, by a push-off test, reveal that the inclusion of shear connectors is essential for effective and secure bonding, with adhesive application methods significantly influencing shear strength. The findings highlight the potential of timber-concrete composite systems high-performance concrete to achieve high shear strength and structural integrity through optimized adhesive and rib configurations. The goal is to make maximum use of the material’s mechanical potential and significantly reduce the primary sources of raw materials. The presented article is based on the diploma thesis of Nick Vanheeswijck
Rehabilitation of cement concrete pavement structures at Bratislava airport
Full text linkThe pavements on the movement areas of the airport are a specific group of pavements, due to their characteristics, different traffic loads and the time constraints for their repairs and maintenance. Increased requirements are on the proposed repairs already from the mentioned time point of view, as well as on the lifetime, which makes these repairs more economically demanding. Maintaining the optimal and efficient operation of the airport is primarily achieved by appropriate rehabilitation and innovation of the necessary parts of the airport. This was also subject to the replacement of the axial strips of the runway, part of the apron and the junction of the runways. The paper deals with the preparation, technical solution and implementation of these repairs with a description of individualtechnical parameters
STDweb: simple transient detection pipeline for the web
Full text linkWe present a simple web-based tool, STDWeb, for a quick-look photometry and transient detection in astronomical images. It tries to implement a self-consistent and mostly automatic data analysis workflow that would work on any image uploaded to it, allowing to perform basic interactive masking, object detection, astrometric calibration of the image, and building the photometric solution based on a selection of catalogues and supported filters, optionally including the colour term and positionally varying zero point. It also allows you to do image subtraction using either user-provided or automatically downloaded template images, and do a forced photometry for a specified target in either original or difference images, as well as transient detection with basic rejection of artefacts. The tool may be easily deployed allowing its integration into the infrastructure of robotic telescopes or data archives for an effortless analysis of their images