130,382 research outputs found
Analysis of vibrations due to the steam condensation at sub-atmospheric condition
No full textThe condensation of steam in water may cause pressure oscillations, vibrations, and damages to piping and, in some extreme conditions to the internals of suppression tank. Significant R&D activity, especially focusing on the emergency cooling system in BWRs, has been conducted in the past decades to clarify the mechanism of the condensation oscillation evolving/related to the Direct Contact Condensation (DCC). The present paper deals with the pressure oscillations due to the condensation of steam jet in water, at sub-atmospheric condition; phenomena that have not been fully investigated yet. Vibrations, arisen as flow patterns transformed from stable to unstable, are investigated with particular attention to the dynamic behaviour of the whole suppression system, behavior of the interface, flow patterns etc. To the purpose, a numerical study is performed by means of suitable FEM in order to identify the dominant frequency associated to the steam jet condensation oscillation in water flow, and determine the resulting values of pressure and acceleration. The obtained results allowed to formulate a correlation between the dominant frequency and the condensation driving potential and steam mass flux
A new active method for continuous radon measurements based on a multiple cell proportional counter
No full textA new active method for continuous airborne radon activity concentration measurements is developed. It is based upon the use of a specially designed radon Multiple Cell Proportional Counter (MCPC). The constructed MCPC prototype is described and its operation principle presented. This gas-flow counter is a pile-up of 20 adjacent multiwire proportional counters. It uses argon–propane (1%) as the main counting gas mixture to which an appropriate fraction of ambient air is admixed. The airborne radon activity concentration is to be continuously measured through a periodic integral counting of the a particles emitted by 222Rn and its short-lived decay products within the sensitive volume. A Monte Carlo simulation program, taking into account the major physical processes that determine directly the detector performances, has been written and used for design optimization purposes. The simulation results show that the admixture of 10% of ambient air seems to be sufficient to continuously assess radon activity concentration levels ranging from about 15 Bqm3 up to 2.6105kBqm3 for an integral counting time period of 10 min. The expected radon sensitivity is about 1.16 cpm/10 Bqm3 with a radon counting efficiency of about 180%. The detector a-pulse height spectra obtained by simulation show a very good agreement with those delivered by the constructed MCPC prototype in its minimal configuration
Experimental analysis of steam condensation patterns within a pressure suppression system operating at sub-atmospheric pressure conditions
No full textFor some specific applications, the pressure suppression systems should be maintained at sub-atmospheric pressure, such as in fusion plants systems. This operation conditions differ considerably from those experienced in the suppression pools of BWR operating at atmospheric pressure. The steam condensation in water at sub-atmospheric conditions is not sufficiently known, if not at all; therefore its effectiveness has to be investigated experimentally. In fact the steam condensation at sub-atmospheric pressure requires a subcooling capacity 2.5 times higher than that at atmospheric pressure. In consideration of that, a low scale experimental facility was designed and built at the University of Pisa. More than 350 steam condensation tests were performed in broad influencing parameters range (e. g. pressure within the condensation tank, water temperature and steam mass flux) to study of effectiveness of the steam condensation. In doing that, different sparger configurations (with single or multiple holes) were considered to check possible interference of condensing steam jets and bubble coalescence. Results indicate a high efficiency of condensation for all the examined conditions. The 3D map of the condensation regimes demonstrate they are dependent only on the downstream exit pressure, the water temperature and the steam mass flux per hole
Experimental investigation of functional performance of a vacuum vessel pressure suppression system of ITER
No full textImportant challenges for fusion technology deal with the design of safety systems aimed to protect the Vacuum Vessel (VV) from pressurizing accidents like the Loss Of Coolant Accident (LOCA). To prevent or mitigate structural damages, the solution proposed is a safety system able to quickly condense released steam in cold water at sub-atmospheric conditions. This water suppression tank (VVPSS) is so aiming at limiting the maximum pressure in the VV to 0.2. MPa during in-vessel coolant leak events and at maintaining the VV long-term pressure below atmospheric pressure during air or incondensable gases ingress, through the Direct Contact Condensation (DCC).The novelty of this study resides especially in the working condition of VVPSS, which operates precisely to sub-atmospheric pressure: up to date no explicit experimental data or investigation of DCC are in fact available in literature. To overcome this lack an extensive experimental work has been done at DICI - University of Pisa, where numerous condensation tests (more than 300) were performed. The operation condition investigated took into account downstream pressure between 30 and 117. kPa and water pool temperature from 30 up to 85. °C.The experimental measurements allow to study the influence of steam mass flux, water temperature and pool pressure on the steam condensation phenomenon (and in turn, based on the stable condensation regime, correctly analyze the design parameter of VVPSS). The results obtained are presented and discussed. Innovative condensation regime maps are in addition provided
Experimental investigation of steam condensation in water tank at sub-atmospheric pressure
No full textThe International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System (VVPSS) limits the Vacuum Vessel (VV) internal pressure, in case of loss of coolant (LOCA) or other pressurizing accidents from the in-vessel components, to 150 kPa (abs). This is key safety function because a large internal pressure could lead to a breach of the primary confinement barrier. Safety is ensured by discharging the steam evolved during the accident event to the VVPSS suppression tanks where it is condensed. Steam condensation occurs at sub-atmospheric pressure condition. Moreover, being this latter not standard for traditional nuclear systems, this investigation is quite new (not studied in detail before) and deals with an experimental investigation of the direct contact condensation at VVPSS prototypical thermal-hydraulic conditions. To the purpose, a small-scale experimental rig was properly designed and built at Lab. B. Guerrini of DICI-University of Pisa as well as different temperature, pressure and steam mass (flow rate per hole) conditions and sparger patterns have been investigated. The experimental test matrix is also presented in this study. The obtained results show high efficiency of condensation for all examined conditions. The main condensation regimes at sub-atmospheric pressure conditions were identified. In addition, a comparison was done between the condensation regimes experimentally determined and those available in the literature, which were obtained at atmospheric pressure. Finally, results demonstrated to be representative of the real configuration at ITER reactor
Investigation of vibrations caused by the steam condensation at sub-atmospheric condition in VVPSS
No full textFusion technology deployment passes through the design of safety systems aimed to protect the Vacuum Vessel (VV) from pressurizing accidents event such as LOVA (Loss Of Vacuum Accident) or the failure of the Tokamak Water Cooling System (TWCS) causing the LOCA (Loss Of Coolant Accident). One of important safety systems of the ITER plant is the Vacuum Vessel Pressure Suppression System (VVPSS), which is designed to protect the VV by the steam condensation at sub-atmospheric pressure conditions in Suppression Tanks. The aim of this study is to investigate vibrations phenomenon, originated during the steam-water direct contact condensation (DCC) at sub-atmospheric conditions, and determine any correlations between the steam jet dynamic and water temperature (TW), steam mass flux (GS) and downstream pressure (PW). According to the thermal hydraulic conditions characterising the DCC, vibrations may evolve because of the latent heat of the phase change (large amount of heat transmitted quickly to the water). In the paper also presents the numerical investigations performed by means of proper FEM code, the set-up procedure and the experimental activity carried out at Lab. B. Guerrini of DICI- University of Pisa. This latter allowed correlating the different steam condensation regimes (chugging, condensation oscillation, etc.) to the acceleration and force, to be in turn used to determine the strength capacity of the VVPSS
Investigating social and labor sustainability performance of fashion production facilities: a case study from developing country
No full textTo achieve the sustainable development goal (SDG), it is necessary to reduce inequalities in facilities social and labor activities and decent workplaces to ensure economic growth. While the number of the published research works on measuring the eco-indices of fashion products and facilities are plenty, no significant work has been presented on measuring the sustainability of social and labor performance. Therefore, this article investigates the social and labor sustainability performance of two fashion factories: a knit factory (Factory A) and a denim factory (Factory B). The Higg Index Facility Social and Labor Module (FSLM) by the Sustainable Apparel Coalition (SAC) were applied to measure the scores. Three (3) sections in the Facility Module-Social and Labor were considered. Section 1 offers factory performance values out of 391 for (a) recruitment and hiring, (b) compensation, (c) working hours, (d) employee engagement and communication, (e) employee treatment and development, (f) health and pay, and (g) termination and retrenchment. Section 2 offers a performance values score 125 points in the Facility's Labor and Workplace Performance Management for the Value Chain. Section 3 indicates values out of 78 on (a) external participation and cooperation, (b) community effect, and (3) transparency and public disclosure. Based on qualitative short questionnaires, data were generated for each sub-section of FSLM. The result shows high-level to low-level performance scores for both factories covering a diverse aspect. Overall social performance score achieved for both factory cases was 384 (factory A) and 394 (factory B) out of a total of 594. Among these, section 1 provides scores of 264 (factory A) and 275 (factory B); section B provides value score 80 and 79, and section 3 give scores 40 and 40 in both facility cases, respectively. The study reveals technical, managerial, and contextual limitations on social and labor performance in both knit and denim factories. The findings have important theoretical and practical implications and could be extended to other fashion production facilities across the fashion supplier countries. Overall, findings will help fashion stakeholders, especially factory practitioners, brands, retailers, academics, and researchers, to reformulate their strategic approaches and current practices to improve social and labor performances. We suggest factory practitioners, including academics and researchers, focus on how to improve the factory working environment, social issues and other disparities in order to drive the fashion industry to be more sustainable across the multi-tier supply chain
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Effect of air on gas multiplication characteristics in argon-propane (1%) based proportional counters for airborne radon monitoring
No full textAiming for the development of a new technique of on-line airborne radon activity concentration measurement, the effect of air on some detection properties of argon–propane (1%)-based proportional counters is investigated when a fraction of 2%, 6% and 10% of it is successively and intentionally admixed to the counting gas in a single-wire proportional counter. The influence of the electron attachment, principally due to oxygen component, on the ionization saturation plateau and the gas amplification process is particularly examined. The previously developed semimicroscopic gas gain formula is found to describe well the gas gain data obtained in each of the gas mixtures analyzed, thus allowing a consistent examination of the air effect on the relevant gas constants. Finally, the possibility to use such air-mixed counting gases in specially designed gas-flow proportional counters intended for new on-line measurement methods of airborne radon (222Rn) activity concentration appeared quite viable
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
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