bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations on Slug Flow in a Horizontal Pipe Using Stereoscopic Particle Image Velocimetry and CFD Simulation With Volume of Fluid Method
Authors: Czapp Marek , Utschick Matthias , Rutzmoser Johannes , Sattelmayer Thomas 
Published: October 2013

Investigations on gas-liquid flows in horizontal pipes are of immanent importance for Reactor Safety Research. In case of a breakage of the main cooling circuit of a Pressurized Water Reactor (PWR), the pressure losses of the gas-liquid flow significantly govern the loss of coolant rate. The flow regime is largely determined by liquid and gas superficial velocities and contains slug flow that causes high-pressure pulsations to the infrastructure of the main cooling circuit.
Experimental and numerical investigations on adiabatic slug flow of a water-air system were carried out in a horizontal pipe of about 10 m length and 54 mm diameter at atmospheric pressure and room temperature. Stereoscopic high-speed Particle Image Velocimetry in combination with Laser Induced Fluorescence was successfully applied on round pipe geometry to determine instantaneous three-dimensional water velocity fields of slug flows.
After grid independence studies, numerical simulations were run with the open-source CFD program OpenFOAM. The solver uses the VOF method (Volume of Fluid) with phase-fraction interface capturing approach based on interface compression. It provides mesh refinement at the interfacial area to improve resolution of the interface between the two phases. Furthermore, standard k-ε turbulence model was applied in an unsteady Reynolds averaged Navier Stokes (URANS) model to resolve self-induced slug formation.
The aim of this work is to present the feasibility of both relatively novel possibilities of determining two-phase slug flows in pipes. Experimental and numerical results allow the comparison of the slug initiation and expansion process with respect to their axial velocities and cross-sectional void fractions.
Developing Heat-Transfer Correlations for Supercritical CO2 Flowing in Vertical Bare Tubes
Authors: Gupta Sahil , McGillivray Donald , Surendran Prabu , Trevani Liliana , Pioro Igor 
Published: October 2013

This paper presents an analysis of three new heat-transfer correlations developed for supercritical carbon dioxide (CO2) flowing in vertical bare tubes. A large set of experimental data was obtained at Chalk River Laboratories (CRL) AECL. Heat-transfer tests were performed in upward flow of CO2 inside 8-mm ID vertical Inconel-600 tube with a 2.208-m heated length. Data points were collected at outlet pressures ranging from 7.4 to 8.8 MPa, mass fluxes from 900 to 3000 kg/m2s, inlet fluid temperatures from 20 to 40°C, and heat fluxes from 15 to 615 kW/m2; and for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature.
The objective of the present experimental research is to obtain reference dataset on heat transfer in supercritical CO2 and improve our fundamental knowledge of the heat-transfer processes and handling of supercritical fluids. In general, heat-transfer process to a supercritical fluid is difficult to model, especially, when a fluid passes through the pseudocritical region, as there are very rapid variations in thermophysical properties of the fluid. Thus, it is important to investigate supercritical-fluid behaviour within these conditions.
In general, supercritical carbon dioxide was and is used as a modelling fluid instead of supercritical water due to its lower critical parameters compared to those of water. Also, supercritical carbon dioxide is proposed to be used as a working fluid in the Brayton gas-turbine cycle as a secondary power cycle for some of the Generation-IV nuclear-reactor concepts such as a Sodium-cooled Fast Reactor (SFR), Lead-cooled Fast Reactor (LFR) and Molten-Salt-cooled Reactor (MSR). In addition, supercritical carbon dioxide was proposed to be used in advanced air-conditioning and geothermal systems.
Previous studies have shown that existing correlations deviate significantly from experimental Heat Transfer Coefficient (HTC) values, especially, within the pseudocritical range. Moreover, the majority of correlations were mainly developed for supercritical water, and our latest results indicate that they cannot be directly applied to supercritical CO2 with the same accuracy as for water.
Therefore, new empirical correlations to predict HTC values were developed based on the supercritical CO2 dataset. These correlations calculate HTC values with an accuracy of ±30% (wall temperatures with accuracy of ±20%) for the analyzed dataset.
Improvement of the Fast Breeder Reactor Plant Dynamic Analysis Code ADYTUM
Authors: Tatewaki Isao , Endo Hiroshi , Ishizu Tomoko , Shindo Yoshihisa 
Published: October 2013

Japan Nuclear Energy Safety Organization, JNES has been studying the methodology to apply the risk informed regulation (RIR) to the safety regulation for Light Water Reactors (LWRs) and Fast Breeder Reactors (FBRs). A best estimate code of plant dynamic analysis is necessary for the RIR application and it must be validated very carefully.
To fulfill this requirement, JNES has been developing a FBR plant dynamic analysis code ADYTUM, which has flexible code structure and algorisms for applying to the safety evaluation. ADYTUM is composed of several inherent components of physical model named “module”, based on one-dimensional flow network model which calculates the sodium flow and the heat transfer between sodium and structures in primary and secondary loop systems. In addition, ADYTUM is designed so that variables of each module have no connection with other modules. Therefore, ADYTUM allows us to calculate and validate each module alone [1].
In order to reinforce the precision of the analysis model of ADYTUM, we are trying to quantify the uncertainty of the model parameters by use of the Code Scaling, Applicability, and Uncertainty (CSAU) methodology for the primary pump stick accident in FBRs. The approaches of the CSAU are (1) to define the physical value and the range of time scale which are focused on, (2) to select the input parameters which have a profound effect on the physical value of focus by use of the phenomena identification and ranking table, and finally (3) to provide the uncertainty quantification of the focusing value.
A Pre-Test CFD Analysis of HLM Fuel Pin Bundle
Authors: Di Piazza Ivan , Scarpa Marco , Tarantino Mariano 
Published: October 2013

A pre-test CFD analysis has been performed for the new Fuel bundle experiment to be carried out in the CIRCE facility. For a fixed pitch to diameter ratio of 1.8, fully developed and 3D analysis are presented for the elementary subchannel. The full 3D subchannel with non-active zones and spacer grids is simulated to study the entry effects and the local perturbation induced by the grid. The thermal peaking factor and the pressure loss induced by the central spacer grid is also evaluated.
In liquid metals, due to the low Prandtl number, the thermal boundary layer is much larger than the mechanical one, and therefore the bulk temperature does not coincide with the central channel temperature. On the basis of computational results, the ‘correct’ heat transfer coefficient based on wall temperature and bulk temperature is compared with the practical experimental measurement evaluation based on wall-thermocouples and central channel temperature. Moreover, The realistic non-uniform heat flux of the pins is taken into account in order to evaluate the local variation of heat transfer coefficient and temperature due to this effect.
Calculation of Curvature Using Linear Thermal Gradient
Authors: Bae Sungjin 
Published: October 2013

Reinforced concrete structures for nuclear power plants are designed for thermal effects. When a structure is subject to transient temperature rise, the temperature distribution in a member becomes nonlinear. Commentary of ACI 349 code provides a method of converting a nonlinear temperature distribution to an equivalent linear temperature distribution in order to facilitate calculating curvature due to temperature change. However, the accuracy of estimated thermal curvatures for concrete sections with a liner plate needs to be examined because the ACI 349 method is based on a pure concrete section.
The objective of this paper is to investigate the accuracy of thermal curvatures calculated using the equivalent linear temperature distribution for concrete sections with a liner. Temperature distributions across concrete sections are obtained from heat transfer analyses. Free thermal curvatures are calculated by converting temperature distribution to the equivalent linear temperatures and compared with those from a finite element analysis. Based on the study, the modified expression for linear thermal gradient is proposed which includes the effect of liner on curvatures.
The Analysis of Partial Flow Blockage Accidents for a Sodium Cooled Fast Reactor
Authors: Chang Won-Pyo , Ha Kwi-Seok , Lee Kwi-Lim , Jeong Hae-Yong 
Published: October 2013

Analyses were performed for flow blockage accidents postulated in a conceptual design of a 600 MWe demonstration sodium cooled fast reactor with 3 types of core designs, i.e., Uranium, *L-TRU (TRansUrium) and **M-TRU cores, using the MATRA-LMR-FB code. The analysis was addressed for the 6 sub-channel blockage which is a design basis event (DBE). The accidents for 24 and 54 sub-channel blockages were also analyzed to estimate the extent of the blockage size which could lead to sodium boiling or fuel melting. Three radial blockage positions were also taken into account in the analysis.
In result, a higher maximum coolant temperature in the subassembly was obtained as the number of blocked subchannels increased. A recirculation region was usually developed right above the blockage for large blockage cases. The analysis results showed that a favorable safety margin was assured for the design basis event, i.e., the 6 sub-channel blockage accident. For the 24 and 54 sub-channel blockage cases, the peak cladding temperature limit was breached, and there was a case in which fuel melting could be threatened.
* TRU extracted from LWR fuel
** Mixture of L-TRU and TRU extracted from self-recycled SFR fuel
Distributed Energy Storage Control for Optimal Adoption of Solar Energy in Residential Networks
Authors: Arghandeh Reza , Broadwater Robert 
Published: October 2013

Environmental concerns, global warming and fossil fuel prices are creating a shift in the expectations of consumers and industries to move toward renewable energy resources. However, the inability to control the output of renewable resources, like wind and solar, results in operational challenges in power systems. The operational challenges of renewable resources can be met by energy storage systems. The energy storage systems scheduling can be used to control the effect of intermittent renewable energy resources. Furthermore, energy storage systems can be used for ancillary services, peak reduction, and mitigating contingencies in the distribution and transmission networks [1].
Distributed photovoltaic (DPV) rooftop panels are considered as renewable energy resources in this paper. Depending on the DPV size and solar irradiation, DPV adoption can create problems for the distribution network. In addition, utility companies have to pay different prices for electricity during different times of the day due to the dynamic electricity market. Therefore, the DPV adoption can be controlled with the help of real-time electricity price and the load profile.
Facing these challenges, this paper presents an operational optimization algorithm for a Distributed Energy Storage (DES) system. The DES system presents a fleet of batteries connected to distribution transformers. The DES can be used for withholding DPV power before it is bid into the market. Withholding DPV generation represents a gaming method to realize higher revenues due to the time varying cost of electricity. Energy storage systems may be used to control DPV power variation and thus help distribution network operations [2].
The objective of this paper is to present a DES optimal economic control system to improve the DPV adoption in power distribution networks. The control system decisions depend on the load profiles, and the real-time Locational Marginal Price (LMP).
Economic operation of the DES is a complex problem because of the time dependency of the battery capacity (where sufficient energy reserves must be maintained in case of power loss), the solar irradiation uncertainty, and the real-time electricity price variability. The mathematical approach used is the Discrete Ascent Optimal Programming (DAOP) algorithm. An advantage of DAOP is its assurance of convergence after a finite number of computational iterations.
Vibration Isolation System to Reduce High Frequency Vibrations due to Airplane Crash
Authors: Niwa Hiroshi , Watanabe Urara , Warashina Masahiko , Tanoue Tetsuharu 
Published: October 2013

Electrical panels in Nuclear power plants are usually designed to be rigid enough to reduce seismic response. However, design dynamic loadings for nuclear power plant are not only seismic loadings. The airplane crash (APC) load is also important dynamic load for nuclear power plant equipments. If the electrical panels are rigid enough for seismic loadings, the higher-mode vibrations of local floors due to the airplane crash will excite resonant vibration of electrical devices inside electrical panels, and so, the panels could lose its electrical functions.
In this study, a vibration isolation system is applied to the electrical panels in order to reduce high frequency vibrations. The system consists of vertical and horizontal isolation rubbers which support four corners of lower end of electrical panels. Using this system, acceleration responses of panels during high frequency excitation due to airplane crash and so on, are reduced less than floor response. However, the rocking mode vibration is excited during an earthquake, because of its predominant frequency. Therefore, in the vibration isolation design, it is important to consider coupled vibration of horizontal and vertical mode and set the natural frequencies in the range that avoids spectrum peaks of acceleration, peaks arising from both the impact vibration and the seismic wave. In this paper, the design method and the vibration test are presented.
SuhB Is a Regulator of Multiple Virulence Genes and Essential for Pathogenesis of Pseudomonas aeruginosa
Authors: Li Kewei , Xu Chang , Jin Yongxin , Sun Ziyu , Liu Chang , Shi Jing , Chen Gukui , Chen Ronghao , Jin Shouguang , Wu Weihui 
Published: October 2013

ABSTRACTDuring initial colonization and chronic infection, pathogenic bacteria encounter distinct host environments. Adjusting gene expression accordingly is essential for the pathogenesis.Pseudomonas aeruginosahas evolved complicated regulatory networks to regulate different sets of virulence factors to facilitate colonization and persistence. The type III secretion system (T3SS) and motility are associated with acute infections, while biofilm formation and the type VI secretion system (T6SS) are associated with chronic persistence. To identify novel regulatory genes required for pathogenesis, we screened aP. aeruginosatransposon (Tn) insertion library and foundsuhBto be an essential gene for the T3SS gene expression. The expression ofsuhBwas upregulated in a mouse acute lung infection model, and loss ofsuhBresulted in avirulence. Suppression of T3SS gene expression in thesuhBmutant is linked to a defective translation of the T3SS master regulator, ExsA. Further studies demonstrated thatsuhBmutation led to the upregulation of GacA and its downstream small RNAs, RsmY and RsmZ, triggering T6SS expression and biofilm formation while inhibiting the T3SS. Our results demonstrate that anin vivo-inducible gene,suhB, reciprocally regulates genes associated with acute and chronic infections and plays an essential role in the pathogenesis ofP. aeruginosa.IMPORTANCEA variety of bacterial pathogens, such asPseudomonas aeruginosa, cause acute and chronic infections in humans. During infections, pathogens produce different sets of virulence genes for colonization, tissue damage, and dissemination and for countering host immune responses. Complex regulatory networks control the delicate tuning of gene expression in response to host environments to enable the survival and growth of invading pathogens. Here we identifiedsuhBas a critical gene for the regulation of virulence factors inP. aeruginosa. The expression ofsuhBwas upregulated during acute infection in an animal model, and mutation ofsuhBrenderedP. aeruginosaavirulent. Moreover, we demonstrate that SuhB is required for the activation of virulence factors associated with acute infections while suppressing virulence factors associated with chronic infections. Our report provides new insights into the multilayered regulatory network of virulence genes inP. aeruginosa.
A retrospective study on the effects of colistin therapy in children with multidrug-resistant Gram-negative bacterial pathogens: impact of HIV status on outcome
Authors: Dimitriades Konstantinos , Morrow Brenda May , Jeena Prakash 
Published: October 2013

BackgroundNosocomially acquired multidrug-resistant (MDR) Gram-negative bacteria are important contributors to paediatric intensive care unit (PICU) mortality and morbidity, with limited treatment options.AimTo investigate the outcomes of all children treated with colistin for infection with MDR Gram-negative bacteria while admitted to PICU.MethodsRetrospective observational study of 19 months. Primary endpoints were all-cause intensive care unit mortality and safety. Secondary endpoints evaluated clinical and microbiological outcomes. Cases were stratified according to HIV status.ResultsTwenty-seven children received 30 colistin courses during the study period. Eight patients (29.6%) were HIV infected, six (22.2%) were HIV uninfected but exposed, and 11 (40.7%) were HIV uninfected and unexposed. Common MDR Gram-negative bacteria cultured were: Acinetobacter species (n=22, 81.5%), Pseudomonas aeruginosa (n=11, 40.7%) and Klebsiella pneumoniae (n=7, 25.9%). Mortality was 37%, with no significant difference between HIV strata. No adverse drug reactions were noted. A composite clinical improvement was noted in 16 courses (53.3%) of colistin. Only 30% of colistin courses used in HIV-infected children resulted in an improved clinical assessment as compared with 83.3% of courses in HIV-uninfected/unexposed children (p=0.04). In HIV-infected children, five of 10 (50%) courses of colistin showed bacteriological clearance compared to the HIV uninfected/unexposed group where all cases showed bacterial eradication (p=0.02).ConclusionsHIV-infected children had poorer clinical and bacteriological responses to colistin treatment than HIV uninfected/unexposed. These results require confirmation with prospective studies to determine whether findings are due to poor microbial response, immunodeficiency or repeated reinfections.
Mind the gap: difference between Framingham heart age and real age increases with age in HIV-positive individuals–a clinical cohort study
Authors: Davies Teri-Louise , Gompels Mark , Johnston Sarah , Bovill Begoña , May Margaret T 
Published: October 2013

ObjectivesTo measure the excess risk of cardiovascular disease (CVD) in HIV-positive individuals by comparing ‘heart age’ with real age and to estimate associations of patients’ characteristics with heart age deviation (heart age–real age).DesignClinical Cohort Study.SettingBristol HIV clinic, Brecon Unit at Southmead Hospital, Bristol, UK.Participants749 HIV-positive adults who attended for care between 2008 and 2011. Median age was 42 years (IQR 35–49), 67% were male and 82% were treated with antiretroviral therapy.Main outcome measuresWe calculated the Framingham 10-year risk of CVD and traced back to ‘heart age’, the age of an individual with the same score but ideal risk factor values. We estimated the relationship between heart age deviation and real age using fractional polynomial regression. We estimated crude and mutually adjusted associations of sex, age, CD4 count, viral load/treatment status and period of starting antiretroviral therapy with heart age deviation.ResultsThe average heart age for a male aged 45 years was 48 years for a non-smoker and 60 years for a smoker. Heart age deviation increased with real age and at younger ages was smaller for females than males, although this reversed after 48 years. Compared to patients with CD4 count <500 cells/mm3, heart age deviation was 2.4 (95% CI 0.7 to 4.0) and 4.3 (2.3 to 6.3) years higher for those with CD4 500–749 cells/mm3and ≥750 cells/mm3, respectively.ConclusionsIn HIV-positive individuals, the difference between heart age and real age increased with age and CD4 count and was very dependent on smoking status. Heart age could be a useful tool to communicate CVD risk to patients and the benefits of stopping smoking.
Treadmill walking speed and survival prediction in men with cardiovascular disease: a 10-year follow-up study
Authors: Chiaranda Giorgio , Bernardi Eva , Codecà Luciano , Conconi Francesco , Myers Jonathan , Terranova Francesco , Volpato Stefano , Mazzoni Gianni , Grazzi Giovanni 
Published: October 2013

ObjectiveTo determine whether the walking speed maintained during a 1 km treadmill test at moderate intensity predicts survival in patients with cardiovascular disease.DesignPopulation-based prospective study.SettingOutpatient secondary prevention programme in Ferrara, Italy.Participants1255 male stable cardiac patients, aged 25–85 years at baseline.Main outcome measuresWalking speed maintained during a 1 km treadmill test, measured at baseline and mortality over a median follow-up of 8.2 years.ResultsAmong 1255 patients, 141 died, for an average annual mortality of 1.4%. Of the variables considered, the strongest predictor of all-cause mortality was walking speed (95% CI 0.45 to 0.75, p<0.0001). Based on the average speed maintained during the test, participants were subdivided into quartiles and mortality risk adjusted for confounders was calculated. Compared to the slowest quartile (average walking speed 3.4 km/h), the relative mortality risk decreased for the second, third and fourth quartiles (average walking speed 5.5 km/h), with HRs of 0.73 (95% CI 0.46 to 1.18); 0.54 (95% CI 0.31 to 0.95) and 0.20 (95% CI 0.07 to 0.56), respectively (p for trend <0.0001). Receiver operating curve analysis showed an area under the curve of 0.71 (p<0.0001) and the highest Youden index (0.35) for a walking speed of 4.0 km/h.ConclusionsThe average speed maintained during a 1 km treadmill walking test is inversely related to survival in patients with cardiovascular disease and is a simple and useful tool for stratifying risk in patients undergoing secondary prevention and cardiac rehabilitation programmes.