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Simulation of an active cooling system for low-concentratinag photovoltaic solar cells
Full text linkOne of the key challenges of concentrating photovoltaic (CPV) systems is the need for effective thermal management, as the increased solar irradiance significantly raises the operating temperature of solar cells, thereby reducing their efficiency. This study proposes a passive cooling solution for a Π-shaped low-concentration photovoltaic (LCPV) system, designed without a mechanical pump and uses gravity-fed water circulation. The thermal performance of the system was analysed using COMSOL Multiphysics. The simulation results demonstrate that the developed cooling system achieves high temperature uniformity, with a maximum surface temperature difference of only 0.07 °C for a radiator comprising five tubes. The system is capable of reducing the solar cell temperature from 40 °C to 22 °C in 10 seconds. Various radiator configurations were investigated for a module consisting of nine solar cells, confirming that the proposed system enables rapid cooling and maintains the cell temperature within optimal operating conditions. The presented design offers a simple, energy-efficient, and cost-effective solution for thermal regulation in LCPV modules
Energy management for electric vehicles with battery and supercapacitor
Full text linkThis paper proposes an energy management strategy for battery and supercapacitor hybrid energy storage systems for electric vehicles. The main objective of the hybrid energy storage systems is to extend the durability of the battery pack by minimising peak currents of the battery during the charging and discharging of the battery in high power demand operations. During regenerative braking, energy is captured in the supercapacitor and is later used in high-power demand operations. In the proposed approach, energy consumption is reduced, the size of the battery pack is reduced, and the vehicle range is extended. The approach is based on a simple rule of power splitting in average, peak, and regenerative modes. The proposed hybrid energy management system is implemented and tested in MATLAB Simulink environment for different standard drive cycles
Carbonizable calcium silicates by CO2 atmosphere in a pressure chamber
Full text linkThe paper deals with the possibility of different calcium silicate minerals namely wollastonite (CS), belite (C2S), and rankinite (C3S2) on their curing in CO2 atmosphere. It describes the laboratory preparation of these individual minerals from p.a. pure chemical clean materials. For comparison a representative sample of natural mined wollastonite was chosen for carbonation as well. Following this, for setting basic parameters analyses determining the properties of the samples by XRD analysis and Rietveld evaluation, particle size characterization by laser granulometry and milling fineness by the Blaine method. It also addresses the issue of forming samples suitable for carbonation using a hydraulic press and the actual curing and conditions necessary for carbonation of the minerals in pressure chamber. It summarizes the measured results of compressive strengths, weight changes and mineralogical evaluation of the composition of the samples before and after carbonation. In the conclusion, together with a summary of the measured findings, it is pointed out what direction further research in this field should be aimed for
Solid-state synthesis of pure belite polymorphs
Full text linkThe solid-state synthesis of pure belite polymorphs is still not described in detail. The study of this issue is important for understanding modification transformations, especially between beta and gamma modifications. In this paper, the two-step firing procedure was used to study belite transformations. The first firing step was designed to produce samples with high content of γ-C2S. These samples were fired again and successfully transformed into β-C2S without any additional chemicals. In addition to firing parameters, the effect of particle size was also monitored. The experiment succeeded in creating a sample containing 64 % gamma belite in total and also a sample containing a total of 90 % of beta belite
Numerical study on the TBM mucking performance in EH project and optimization of the supporting ribs
Full text linkTo study the cutterhead’s muck transfer performance of the TBM applied in EH project, China, a discrete element method (DEM) based numerical model was built and the mucking process was simulated at different penetration rates and cutterhead rotational speed. It is found that the conventional straight-supporting-rib cutterhead performed well at different penetration rates and low RPMs, but the muck excessive-thrown problem was serious when the RPM was higher than 10 rev/min. To overcome this problem, a new arched-supporting-rib cutterhead was proposed. The curvature radius of the arched supporting ribs is suggested between 1.25 m and 1.75 m, and the offset angle is suggested between 40° and 45°. The newly proposed arched-supporting-rib cutterhead can performed well in muck transfer at a greater RPM range of 4~13 rev/min, which allow the TBM to excavated at low, medium and high RPMs considering ground conditions and requirement of construction progress
Performance evaluation of modified turbulent models in simulating arc quenching process in circuit breakers
Full text linkGas circuit breakers rely on rapid gas expansion and turbulent mixing within a converging–diverging nozzle to effectively cool and extinguish arcs during current interruption. The transientarc interruption process involves coupled physical phenomena, including turbulent flow, electric current, convection and radiation. Selection of a suitable flow model is vital in obtaining simulation results matching the experimental data. In this study, the transient behaviour of the SF6 flow during the current ramp-down phase is investigated. Performance of the standard k-ϵ turbulence model is compared with modified k-ϵ models, in which the turbulence dissipation constant C1ϵ is systematically varied to identify the effect on the cooling process. Simulation results demonstrate that the adjustment of C1ϵ can improve the arc cooling process by enhancing turbulent kinetic energy, resulting in maximum rate-of-rise of recovery voltage (RRRV) estimation values similar to the experimental conditions.
Towards plasma-enhanced gasification: Investigating free-burning carbon arcs in molecular gas mixtures
Full text linkA pre-study of free burning arcs between carbon electrodes for potential use in gasification processes is presented. Free-burning arcs offer the potential to be used without additional gas feed or significant changes to gas flows in established gasification systems as well as with minimal cooling requirements for improved energy efficiency. Direct current (DC) arcs with currents up to 200 A and power levels up to 40 kW have been operated in molecular gas mixtures of H2, CO and CO2. The electrical characteristics and dynamic behaviour of the arcs under various electrode configurations have been analysed, along with an assessment of electrode erosion. Finally, concepts for the power sources have been deduced and tested
Characterization of the switching arc in hydrogen under different pressure conditions
Full text linkThe characteristics of filling gas and its resulting arcing behavior is a major factor influencing the current-limiting and switching performance of gas-filled direct current (DC) switches. The use of hydrogen (H2) or mixtures containing H2 as dielectric gas has shown increased breaking performance in compact DC switches. However, arcs in such gases, especially in pure H2 show a complex fluctuating dynamics, especially at higher filling pressures and by simultaneous use of magnetic blown-off. This paper conducts an electrical and optical study of the rapid and unstable arc behavior in H2 at pressures of 1 and 6 bar using a model switch with arc runners. The results remark the significant impact of filling pressure on the arc voltage and the coupled current limiting performance. Moreover, the arc dynamics become more unstable and faster, and the arc shape becomes strongly distorted. Compared to atmospheric pressure, the rate of increase in arc voltage and arc length are noticeably higher
Deep learning-based modeling and simulation of heat conduction
Full text linkThe present study focuses on applying deep neural networks (DNNs) to surrogate modeling of heat conduction problems. Deep learning algorithms, valued for their ability to learn hierarchical data representations through multi-layered networks, excel at identifying complex patterns. In this work, the U-Net architecture – widely recognized for its effectiveness in image segmentation – is adapted to model stationary heat transfer, providing a novel approach to a critical challenge in engineering and physics. Specifically, we propose a deep learning-based surrogate model to predict stationary temperature fields in 2D rectangular domains representing two-phase heterogeneous materials
Post-CHF nuclear fuel operation with Time-at-Temperature criteria
Full text linkThe dryout and departure from nucleate boiling criteria are used to set safety limits on nuclear heat transfer and temperature values in nuclear reactors. This review argues for the use of a Time-at-Temperature criterion to improve efficiency and utilization of nuclear fuels and reduce costs. To illustrate the importance of such criteria, the review presents the different phenomena of cladding and fuel rods that could impact the continued operation of nuclear reactors, as well as the experiments and operating events that occurred in light-water reactors