741 research outputs found

    Shear-induced pressure changes and seepage phenomena in a deforming porous layer-I

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    We present a model for flow and seepage in a deforming, shear-dilatant sensitive porous layer that enables estimates of the excess pore fluid pressures and flow rates in both the melt and solid phase to be captured simultaneously as a function of stress rate. Calculations are relevant to crystallizing magma in the solidosity range 0.5–0.8 (50–20 per cent melt), corresponding to a dense region within the solidification front of a crystallizing magma chamber. Composition is expressed only through the viscosity of the fluid phase, making the model generally applicable to a wide range of magma types. A natural scaling emerges that allows results to be presented in non-dimensional form. We show that all length-scales can be expressed as fractions of the layer height H, timescales as fractions of H2(nβ'θ+ 1)/(θk) and pressures as fractions of . Taking as an example the permeability k in the mush of the order of magnitude 1015 m2 Pa1 s1, a layer thickness of tens of metres and a mush strength (θ) in the range 108–1012 Pa, an estimate of the consolidation time for near-incompressible fluids is of the order of 105–109 s. Using mush permeability as a proxy, we show that the greatest maximum excess pore pressures develop consistently in rhyolitic (high-viscosity) magmas at high rates of shear ( , implying that during deformation, the mechanical behaviour of basaltic and rhyolitic magmas will differ. Transport parameters of the granular framework including tortuosity and the ratio of grain size to layer thickness (a/H) will also exert a strong effect on the mechanical behaviour of the layer at a given rate of strain. For dilatant materials under shear, flow of melt into the granular layer is implied. Reduction in excess pore pressure sucks melt into the solidification front at a velocity proportional to the strain rate. For tectonic rates (generally 1014 s1), melt upwelling (or downwelling, if the layer is on the floor of the chamber) is of the order of cm yr1. At higher rates of loading comparable with emplacement of some magmatic intrusions (1010 s1), melt velocities may exceed effects due to instabilities resulting from local changes in density and composition. Such a flow carries particulates with it, and we speculate that these may become trapped in the granular layer depending on their sizes. If on further solidification the segregated grain size distribution of the particulates is frozen in the granular layer, structure formation including layering and grading may result. Finally, as the process settles down to a steady state, the pressure does not continue to decrease. We find no evidence for critical rheological thresholds, and the process is stable until so much shear has been applied that the granular medium fails, but there is no hydraulic failure

    Multiobjective Optimization of Cement-Based Panels Enhanced with Microencapsulated Phase Change Materials for Building Energy Applications

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    Thermal energy storage using phase change materials (PCMs) is a promising technology for improving the thermal performance of buildings and reducing their energy consumption. However, the effectiveness of passive PCMs in buildings depends on their optimal design regarding the building typology and typical climate conditions. Within this context, the present contribution introduces a novel multiobjective computational method to optimize the thermophysical properties of cementitious building panels enhanced with a microencapsulated PCM (MPCM). To achieve this, a parametric model for PCM-based cementitious composites is developed in EnergyPlus, considering as design variables the melting temperature of PCMs and the thickness and thermal conductivity of the panel. A multiobjective genetic algorithm is dynamically coupled with the building energy model to find the best trade-off between annual heating and cooling loads. The optimization results obtained for a case study building in Sofia (Bulgaria-EU) reveal that the annual heating and cooling loads have contradictory performances regarding the thermophysical properties studied. A thick MPCM-enhanced panel with a melting temperature of 22 (Formula presented.) C is needed to reduce the heating loads, while a thin panel with a melting temperature of 27 (Formula presented.) C is required to mitigate the cooling loads. Using these designs, the annual heating and cooling loads decrease by 23% and 3%, respectively. Moreover, up to 12.4% cooling load reduction is reached if the thermal conductivity of the panels is increased. Therefore, it is also concluded that the thermal conductivity of the cement-based panels can significantly influence the effectiveness of MPCMs in buildings

    Multiobjective Optimization of Cement-Based Panels Enhanced with Microencapsulated Phase Change Materials for Building Energy Applications

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    Thermal energy storage using phase change materials (PCMs) is a promising technology for improving the thermal performance of buildings and reducing their energy consumption. However, the effectiveness of passive PCMs in buildings depends on their optimal design regarding the building typology and typical climate conditions. Within this context, the present contribution introduces a novel multiobjective computational method to optimize the thermophysical properties of cementitious building panels enhanced with a microencapsulated PCM (MPCM). To achieve this, a parametric model for PCM-based cementitious composites is developed in EnergyPlus, considering as design variables the melting temperature of PCMs and the thickness and thermal conductivity of the panel. A multiobjective genetic algorithm is dynamically coupled with the building energy model to find the best trade-off between annual heating and cooling loads. The optimization results obtained for a case study building in Sofia (Bulgaria-EU) reveal that the annual heating and cooling loads have contradictory performances regarding the thermophysical properties studied. A thick MPCM-enhanced panel with a melting temperature of 22 (Formula presented.) C is needed to reduce the heating loads, while a thin panel with a melting temperature of 27 (Formula presented.) C is required to mitigate the cooling loads. Using these designs, the annual heating and cooling loads decrease by 23% and 3%, respectively. Moreover, up to 12.4% cooling load reduction is reached if the thermal conductivity of the panels is increased. Therefore, it is also concluded that the thermal conductivity of the cement-based panels can significantly influence the effectiveness of MPCMs in buildings.Fil: Bre, Facundo. Universitat Technische Darmstadt; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Caggiano, Antonio. Università degli Studi di Genova; ItaliaFil: Koenders, Eduardus A. B.. Universitat Technische Darmstadt; Alemani

    EVALUATION OF THERMAL AND MECHANICAL PROPERTIES OF DEMONSTRATION WALL UTILIZING PHASE CHANGE CEMENTITIOUS MATERIALS

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    International project PoroPCM involves partners from Germany, Czech Republic, Spain and Japan with the objective to develop new multifunctional Phase Change Materials modified porous cementitious nanocomposite (PoroPCM). Such material can be utilized for storing heat energy in the insulation layer of buildings compared to commonly used insulation materials since the phase change increases heat capacity. This enhanced feature reduces the amount of energy necessary for running the heating/cooling system. For the testing of the newly developed phase change cementitious composite a demonstration wall will be developed and tested for its thermal as well as mechanical performance. The topic of the paper is the description of the properties of the new phase change cementitious nanocomposite. The main emphasis of the paper is the description of the demonstration wall behaviour under typical environmental conditions. The wall design is supported by numerical simulation of the wall physical parameters. The numerical modelling involves the definition of suitable numerical models for the simulation of the thermal properties of the new phase change nanocomposite. The numerical model is then used to demonstrate the performance of the wall layer design. The presented pilot results show efficiency increase of the insulation material in the range 15–70%. Also modelling of wind resistance of the layered structure is included. The developed wall design and PoroPCM material will be tested and verified by a large scale test in the final year of the project

    Micro-scale thermal analysis of energy storage in cement-based composites containing phase change materials (PCMS)

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    In the last decades, the use of smart components embedded inside cementitious materials, like Phase Change Material (PCM), has become a more and more attractive solution for saving energy and for providing a more efficient thermal comfortability to modern buildings. Present research running at the Institute of Construction and Building Materials (WiB) of TU-Darmstadt deals with the investigation of advanced coupling of two physical mechanisms represented by a heat problem and microstructural heterogeneities. The thermal response of such a composite system, along with occurring phase change phenomena, will be simulated at the microscale level. A virtual 3D porous microstructure with embedded PCMs, created with the available hydration model Hymostruc, provides a fundamental basis for the analysis of the morphological influence of PCMs on the effective thermal diffusion parameters. The work is aimed at investigating the influence of the morphological effect on the thermal effective properties of hydrating cement combined with Micro-encapsulated (M)-PCMs. Laboratory characterization of the PCMs was performed using a designated test set-up. The thermal performance of cement-based pastes with and without MPCMs were experimentally evaluated and used as benchmark for calibration purposes. Particularly, the obtained results combined with specific heat capacity of PCM-cement pastes and thermal conductivity measurements were taken as reference for validating the proposed numerical technique.Publicado en: Mecánica Computacional vol. XXXV, no. 41Facultad de Ingenierí

    Understanding subterranean variability: the first genus of Bathynellidae (Bathynellacea, Crustacea) from Western Australia described through a morphological and multigene approach

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    The number of subterranean taxa discovered in the north of Western Australia has substantially increased due to the requirements for environmental surveys related to mining development. Challenges in estimating subterranean biodiversity and distributions are related to lack of knowledge of taxa with convergent morphological characters in a largely unobservable ecosystem setting. An integrated approach is warranted to understand such complexity. Bathynellidae occur in most Australian aquifers, but only one species has been described so far, and the group lacks a reliable taxonomic framework. A new genus and one new species from the Pilbara region of Western Australia, Pilbaranella ethelensis, gen. et sp. nov., is described using both morphological and molecular data. Three additional species of Pilbaranella are defined through mitochondrial and nuclear genes, using Automatic Barcode Gap Discovery and Poisson Tree Processes species delimitation methods. A comparison of morphology and 18S rRNA sequences between Pilbaranella, gen. nov. and known lineages provides the evidentiary basis for the decision to establish a new genus. This study provides a morphological and molecular framework to work with Bathynellidae, especially in Australia where a highly diverse fauna remains still undescribed

    Capturing Patient Value in an Economic Evaluation

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    OBJECTIVE: Economic evaluations predominantly use generic outcomes, such as EuroQol-5 Dimension (EQ-5D), to assess the health status. However, because of the generic nature, they are less suitable to capture the quality of life of patients with specific conditions. Given the transition to patient-centered (remote) care delivery, this study aims to evaluate the possibility to use disease-specific measures in a cost-effectiveness analysis (CEA).METHODS: A real-life cohort from Maasstad Hospital (2020-2021) in the Netherlands, with 772 Rheumatoid Arthritis (RA) patients, was used to assess the cost-effectiveness of electronic consultations (e-consultations) compared with face-to-face consultations. The Incremental Cost-Effectiveness Ratio (ICER) based on the generic EQ-5D was compared with ICER's based on RA specific measures; Rheumatoid Arthritis Impact of Disease (RAID) and Health Assessment Questionnaire-Disability Index (HAQ-DI). To compare the cost-effectiveness of these different measures, HAQ-DI and RAID were expressed in QALYs via estimated conversion equations.CONCLUSIONS: The conventional ICER (e.g. EQ-5D) indicates that e-consultations are cost-effective with cost savings of - €161k per QALY gained for a prevalent RA cohort treated in a secondary trainee hospital. RA specific measures show similar results, with ICER's of - €163k per HAQ-DI(QALY) and - €223k per RAID(QALY) gained. RA specific measures capture patient-relevant domains and offer the opportunity to improve the assessment and treatment of the disease impact.DISCUSSION: Disease-specific patient-reported outcome measures (PROMs) offer a promising alternative for traditional measures in economic evaluations, capturing patient-relevant domains more comprehensively. As PROMs are increasingly applied in clinical practice, the next step entails modelling of a RA patient-wide conversion equation to implement PROMs in economic evaluations. This article is protected by copyright. All rights reserved.</p

    Il Progetto EnCoRe : una iniziativa sovranazionale per promuovere il concetto di sostenibilità del calcestruzzo e dei materiali cementizi

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    Environmental issues are getting more and more relevant in several fields of human activities and the building industry is fully concerned by these concerns. Recycled concrete aggregates (RCA) can be produced by existing concrete members resulting by either industrial processes (i.e., precast structures) or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building industry (i.e., production of steel, management of glass, powders resulting from other depuration processes) could be efficiently disposed as concrete aggregates or employed as reinforcement for Fiber-Reinforced Concretes (FRC). The use of natural fibres can also result into an environmentally-friendly and cost-effective solution, especially in developing countries, because of the local availability of raw materials. In order to promote the use of concretes with recycled and/or natural constituents as construction materials, the compatibility between the non conventional constituents and the concrete matrix have to be deeply investigated and correlated to the resulting mechanical and durability properties of the composite. This is the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings will be summarized in this paper
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