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Thermal properties variations in unconsolidated material for very shallow geothermal application (ITER project)
Full text linkAbstract
In engineering, agricultural and meteorological project design, sediment thermal properties are highly important parameters, and thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially in very shallow geothermal systems. Herein, the first 2 m of depth from surface is of critical importance. However, the heat transfer determination in unconsolidated material is difficult to estimate, as it depends on several factors, including particle size, bulk density, water content, mineralogy composition and ground temperature. The performance of a very shallow geothermal system, as a horizontal collector or heat basket, is strongly correlated to the type of sediment at disposal and rapidly decreases in the case of dry-unsaturated conditions. The available experimental data are often scattered, incomplete and do not fully support thermo-active ground structure modeling. The ITER project, funded by the European Union, contributes to a better knowledge of the relationship between thermal conductivity and water content, required for understanding the very shallow geothermal systems behaviour in saturated and unsaturated conditions. So as to enhance the performance of horizontal geothermal heat exchangers, thermally enhanced backfilling material were tested in the laboratory, and an overview of physical-thermal properties variations under several moisture and load conditions for different mixtures of natural material was here presented.</jats:p
Soil thermal behavior in different moisture condition: an overview of ITER project from laboratory to field test monitoring
No full textThe thermal properties of soils can be considered one of the most important parameters for many engineering projects designing. In detail, the thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially very shallow geothermal (VGS) systems, interesting the first 2 m of depth from the ground level. However, the determination of heat transfer in soils is difficult to estimate, because depends on several factors, including, among others, particle size, density, water content, mineralogy composition, ground temperature, organic matter.
The performance of a VSG system, as horizontal collectors or special forms, is strongly correlated to the kind of sediment at disposal and suddenly decreases in case of dry-unsaturated conditions in the surrounding soil. Therefore, a better knowledge of the relationship between thermal conductivity and water content is required for understanding the VSG systems behavior in saturated and unsaturated conditions.
Key challenge of ITER Project, funded by European Union, is to understand how to enhance the heat transfer of the sediments surrounding the pipes, taking into account the interactions between the soil, the horizontal heat exchangers and the surrounding environment.
In order to obtain reliable data for modelling, an interdisciplinary approach is used. In laboratory the physical-thermal properties of more than 15 soil mixtures, consisting in (i) natural soil, (ii) pure sand and (iii) mixtures of pure sand and clay additives, have been tested under different water content percentages and different consolidation degree. Then the same parameters are monitored in the project case study, in Eltersdorf, (Germany), where five helix collectors are installed in horizontal trenches filled in with five different mixtures already tested in laboratory. In addition, a monitoring system allows to record every 15 minutes, by means of devoted sensors, values related to ground temperature (undisturbed, inside and outside each helix), fluid temperature and flow running in the collectors, volumetric water content at 20 and 60 cm depth. Moreover, a meteorological station provides climatic data acquisition as rainfall, wind speed, relative humidity and air temperature.
The main results achieved until now are useful for future modeling because shed new light (i) on the differences between data collected in laboratory and in the field and (ii) on the influence of the technical solution adopted in situ to fill in the trenches, able to create a non-homogeneous distribution of the soil bodies around the helix.Abstract
5th International Conference Novel Methods for Subsurface Characterization and Monitoring: From Theory to Practice, NovCare 2017, Dresden, Germany, 06-09.06.201
Factors Influencing the Thermal Efficiency of Horizontal Ground Heat Exchangers
Full text linkThe performance of very shallow geothermal systems (VSGs), interesting the first 2 m of depth from ground level, is strongly correlated to the kind of sediment locally available. These systems are attractive due to their low installation costs, less legal constraints, easy maintenance and possibility for technical improvements. The Improving Thermal Efficiency of horizontal ground heat exchangers Project (ITER) aims to understand how to enhance the heat transfer of the sediments surrounding the pipes and to depict the VSGs behavior in extreme thermal situations. In this regard, five helices were installed horizontally surrounded by five different backfilling materials under the same climatic conditions and tested under different operation modes. The field test monitoring concerned: (a) monthly measurement of thermal conductivity and moisture content on surface; (b) continuous recording of air and ground temperature (inside and outside each helix); (c) continuous climatological and ground volumetric water content (VWC) data acquisition. The interactions between soils, VSGs, environment and climate are presented here, focusing on the differences and similarities between the behavior of the helix and surrounding material, especially when the heat pump is running in heating mode for a very long time, forcing the ground temperature to drop below 0 °C
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Selection of backfill grout for shallow geothermal systems: Materials investigation and thermo-physical analysis
Full text linkA main aspect of the geothermal well design is the selection of grouts backfilling the space between a geothermal probe and the surrounding ground, taking into consideration the mineralogical, thermo–physical, mechanical and flowability properties. The EU GEO4CIVHIC project aimed at developing efficient and cost-effective geothermal systems suitable for the air-conditioning refurbishment of urban buildings. A selection of different grouts was performed to ensure the whole efficiency of shallow geothermal heat exchangers designed within the project. Experimental tests were executed to identify flowable grouts with the best possible combination of different material properties, while also fulfilling a competitive cost target set forth in the preliminary project cost analysis. Grout acceptance criteria were defined: a working time of at least 4 h, a water bleeding target of 2% and a volumetric shrinkage upper bound of 4%, a thermal conductivity in water saturated conditions of at least 1.4 to 1.5 Wm−1K−1, a compressive strength range of 1 to 2.1 MPa, a flow time range of 60 ± 15 s. Two out of six commercial grouts were selected for installations onsite
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