1,720,989 research outputs found
Thermal Energy Losses During Night, Warm-up and Full-Operation Periods of a CSP Solar Field Using Thermal Oil
Full text linkAbstractIn Concentrating Solar Power (CSP) systems, solar radiation allows to keep the Heat Transfer Fluid (HTF) at the design temperature (250-400°C using thermal oil) during daylight. During night, the thermal losses of the receiver tubes lead to a fast reduction of this temperature. The very first hours of daily solar irradiance are used to warm-up the Solar Field to the nominal temperature. This work focuses on a detailed analysis of the thermal losses of a 8,400 m2 Solar Field based on Linear Fresnel Collectors (LFC) using thermal oil as Heat Transfer Fluid. The proposed simulation model evaluates the performance of the Solar Field as a function of solar radiation, solar position, ambient temperature and wind speed for given values of the main geometrical and technical characteristics of the SF components (insulated piping and solar receivers), as well as for assigned thermodynamic properties of the Heat Transfer Fluid. The time-step considered (1 second) and the dense spatial discretization chosen allow the energy-balance-equation-based model to be suited to simulate night, warm-up and full-operation phases
Development and implementation of a 3D numerical code for designing and predicting performances of PCM thermal energy storage systems
No full textThe present work is focused on the development of thermal energy storage systems (TES) based on phase changing materials (PCM), to be used as back-up devices during transient operations of small and medium scale concentrated solar plants (CSP). The development of the storage device will be performed recurring to numerical simulation and experimental testing in the laboratory.
At the current stage the laboratory is being built, while the implementation of a numerical tool to simulate the behaviour of tanks with different geometries and different working materials has started.
The preliminary development of the storage device is carried out by means of a 3D numerical simulation code specifically implemented in the COMSOL Multiphysics environment. The code is used to solve direct (design) and indirect (analysis) problems considering heat storage tanks with different geometries and different working materials. The geometry chosen for this preliminary analysis is the shell and tube heat exchanger, whose shell is filled with PCM and the working fluid flows on the tube side (up to 200-220°C to simulate the heat transfer fluid from the solar field). The system is designed for a heat storage capacity of 36 MJ
L’impianto solare termodinamico di Ottana. Valutazione delle perdite termiche del campo solare durante le diverse fasi operative
No full textCFD Simulation of Melting and Solidification of PCM in Thermal Energy Storage Systems of Different Geometry
No full textAt the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari an experimental and numerical research project has begun with the aim of developing highly efficient thermal energy storage (TES) systems using phase change materials (PCM) of particular interest in concentrating solar power (CSP) applications. The present work aims to simulate the melting and solidification processes in containing boxes and heat transfer devices of different geometrical features which may constitute the elementary cell of a more complex TES system.
Two-dimensional axisymmetric numerical models, developed with COMSOL Multiphysics are considered and used to simulate TES, heat conduction and natural convection. The models are used to determine the temperature profile inside the PCM to identify which configurations are capable of enhancing thermal response between a solid wall and a PCM. The results obtained will be used for comparison with experimental data acquired from a pilot plant under construction in the DIMCM laboratories. At the current stage the laboratory is being brought to completion
Integrating Modelling of Maintenance Policies within a Stochastic Hybrid Automaton Framework of Dynamic Reliability
Full text linkThe dependability assessment is a crucial activity for determining the availability, safety and maintainability of a system and establishing the best mitigation measures to prevent serious flaws and process interruptions. One of the most promising methodologies for the analysis of complex systems is Dynamic Reliability (also known as DPRA) with models that define explicitly the interactions between components and variables. Among the mathematical techniques of DPRA, Stochastic Hybrid Automaton (SHA) has been used to model systems characterized by continuous and discrete variables. Recently, a DPRA-oriented SHA modelling formalism, known as Stochastic Hybrid Fault Tree Automaton (SHyFTA), has been formalized together with a software library (SHyFTOO) that simplifies the resolution of complex models. At the state of the art, SHyFTOO allows analyzing the dependability of multistate repairable systems characterized by a reactive maintenance policy. Exploiting the flexibility of SHyFTA, this paper aims to extend the tools’ functionalities to other well-known maintenance policies. To achieve this goal, the main features of the preventive, risk-based and condition-based maintenance policies will be analyzed and used to design a software model to integrate into the SHyFTOO. Finally, a case study to test and compare the results of the different maintenance policies will be illustrated
A review on three decades of manufacturing maintenance research: past, present and future directions
Full text linkMaintenance engineering has taken up more and more a strategic function in recent decades due to technological advancements and its role in asset productivity. Over time, a plethora of methods have been proposed, shifting from reactive approaches to complex, data-driven strategies focused on failure prediction (e.g. through Machine learning) and knowledge management (e.g. based on ontologies and large language models). The advancements achieved by maintenance have also beneficially impacted production quality, sustainability, and safety. This work presents the results of a systematic literature review of papers published on the topic of maintenance in the past 30 years. In particular, natural language processing has been used to analyze abstract, extract topics and, through further analysis delineate past, current, and future trends in the field of maintenance engineering in manufacturing. This work contributes to define a vision on how maintenance in manufacturing will evolve in the next future
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermo-fluid Dynamic Analysis of a CSP Solar Field Line during Transient Operation
Full text linkConcentrating Solar Power (CSP) technology allows to produce high temperature thermal energy from solar radiation. The thermal energy can be converted into electricity or it can be directly used for industrial processes. Most of the available simulation models of CSP plants evaluate the behavior of the solar field in stationary conditions, neglecting transient thermo-fluid-dynamic effects. Nevertheless, the study of the dynamic behavior of the solar field is a very challenging and interesting task and allows obtaining useful information for the design and the effective management strategies of CSP plants. This paper presents a thermo-fluid-dynamic analysis of a solar field line of the CSP plant currently under construction in Ottana, Sardinia (Italy), which uses thermal oil as heat transfer fluid. Dynamics of the system due to solar irradiance variations have been evaluated by using an axisymmetric unsteady 2D numerical model developed in Comsol to evaluate the oil temperature distribution along the receiver tube for different operating conditions. The results have been compared with those obtained with a simpler, non-stationary one-dimensional model, developed in Matlab environment. The comparative analysis show very similar results for the two models and demonstrate that the dynamic effects on the temperature distribution along the solar field line are not negligible
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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