bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ Visualization of Evaporation Induced Self-Assembly Phenomena of Nanofluids Detecting the Interfacial Surface Plasmon Reflectance
Authors: Kim Iltai (Isaac) , Kihm Kenneth David 
Published: November 2015

Innovative optical techniques based on nano-biophotonics such as surface plasmon resonance (SPR) imaging and R-G-B natural fringe mapping techniques are developed to characterize the transport and optical properties of nanofluids in situ, real-time, and full field manner. Recent results regarding the characterization of nanofluids are summarized and future research directions are presented.
47 nm Al2O3 nanoparticles are dispersed in water with various concentrations. Al2O3 nanofluids droplets are placed on substrates and evaporated in room temperature. In-situ visualization of evaporation-induced self-assembly is conducted to detect concentration, effective refractive index, and different self-assembled pattern including cavity with various nanofluids concentrations and surface hydrophobbicities with SPR and fringe mapping.
During the evaporation, time-dependent and near-field nanoparticle concentrations are determined by correlating the SPR reflectance intensities with the effective refractive index (ERI) of the nanofluids.
With increasing the concentrations of nanofluids, the existence of hidden complex cavities inside a self-assembled nanocrystalline structure or final dryout pattern is discovered in real-time. R-G-B natural fringe mapping allowed the reconstruction of the 3D cavity formation and crystallization processes quantitatively. The formation of the complex inner structure was found to be attributable to multiple cavity inceptions and their competing growth during the aquatic evaporation.
Furthermore, the effect of surface hydrophobicity is examined in the formation of hidden complex cavities, taking place on three different substrates bearing different levels of hydrophobicity; namely, cover glass (CG), gold thin film (Au), and polystyrene dish (PS).
These surface plamson resonance imaging and natural fringe mapping techniques are expected to provide a breakthrough in micro-nanoscale thermal fluids phenomena and nano-biochemical sensing when coupled with localized surface Plasmon and metamaterials techniques.
Experimental and Measurement Uncertainty Associated With Characterizing Slurry Mixing Performance of Pulsating Jets at Multiple Scales
Authors: Bamberger Judith Ann , Piepel Greg F. , Enderlin Carl W. , Amidan Brett G. , Heredia-Langner Alejandro 
Published: November 2015

Understanding how uncertainty manifests itself in complex experiments is important for developing the testing protocol and interpreting the experimental results. This paper describes experimental and measurement uncertainties, and how they can depend on the order of performing experimental tests.
Experiments with pulse-jet mixers in tanks at three scales were conducted to characterize the performance of transient-developing periodic flows in Newtonian slurries. Other test parameters included the simulant, solids concentration, and nozzle exit velocity. Critical suspension velocity and cloud height were the metrics used to characterize Newtonian slurry flow associated with mobilization and mixing. During testing, near-replicate and near-repeat tests were conducted. The experimental results were used to quantify the combined experimental and measurement uncertainties using standard deviations and percent relative standard deviations (%RSD) The uncertainties in critical suspension velocity and cloud height tend to increase with the values of these responses. Hence, the %RSD values are the more appropriate summary measure of near-replicate testing and measurement uncertainty.
1-D Modeling of the Denebulization of Fogs by Hygroscopic Seeding
Authors: Reuge Nicolas , Fede Pascal , Berthoumieu Jean-François , Foucoin Florian , Simonin Olivier 
Published: November 2015

The purpose of the study is the modeling of the denebulization of fogs by micronic hygroscopic particles from the initial seeding to the fall of the rain droplets on the ground. The microparticles generated by flares are made of hygroscopic salts. Three stages occur: first, the condensation of water vapor on solid particles, this is the deliquescent stage which is very fast and can be ignored by the model, then the stage of condensation of water vapor on liquid salted particles / evaporation of fog droplets and finally the coalescence stage when the liquid salted particles diameter become large enough. Three different salts have been tested: NaCl, CaCl2 and KCl. The 1-D modeling approach studied considers the conservation equations (salt mass, water mass, salted droplets number density, fog droplets number density), the hygroscopicity of the salts through the water activity in the aqueous solution and the coalescence induced by gravity.
The model reveals that NaCl is the most efficient salt because of its stronger hygroscopicity at high dilution rates although CaCl2 is the more hygroscopic at low dilution rates. A cloud of NaCl particles of 9 μm diameter initially generated over a height of about 7 m with a number density of 12 cm−3 allows to completely dissipates a typical fog layer of 40 m within less than 13 mn. This means that 10 kg of NaCl particles could be able to clear such a fog over 13.25 ha. The model shows that a layer of 100 m can be cleared within 29 mn. From the calculations, the contribution of the coalescence to the denebulization process is less than 1%, phenomena of condensation / evaporation are preponderant for these operating conditions.
Physical and Mathematical Modeling of Solid-Liquid Flow at High Bed Shear in Steep Flume
Authors: Matoušek Václav , Zrostlík Štěpán , Krupička Jan , Picek Tomáš , Bareš Vojtěch 
Published: November 2015

The paper discusses new results of our experimental- and mathematical modeling of sediment-laden open-channel flows in the upper plane bed regime associated with intense transport of sediment. Our recent studies showed that bed-load transport and bed friction are interrelated and classical formulae for bed friction (Nikuradse formula) and bed-load transport (Meyer-Peter and Muller formula) need to be modified to account for the intense transport of sediment.
The new results of our laboratory experiments in a tilting flume are presented and analyzed for different sediment fractions. The analysis is focused on the effect of solids density and size on the solid-liquid flow characteristics as the solids flow rate, flow depth, and bed slope for certain flow rate of water in a channel of given geometry. The experimental results are compared with outputs of our mathematical model simulating the observed phenomena. The simple 1-D model combines hydrodynamic- and sediment-transport equations and enables to use different transport- and friction formulae to predict the solids transport, flow depth and bed slope under the condition of (pseudo-) uniform flow of solid-water mixture in the open channel.
Efficiency Upgrade of a Double-Case Pump Using CFD-Based Design Optimization and Scaled Model Tests
Authors: van der Schoot Martijn , Visser Frank 
Published: November 2015

This paper presents a design optimization study of a low specific-speed, multistage, double-case, volute pump. The goal of this study was to accomplish an increase in overall pump efficiency by at least 3.5 percentage points. To that end, each hydraulic internal component of the pump was analyzed to find opportunities for improvement. This was done by performing a combined classical hydraulic evaluation and in-depth Computational Fluid Dynamics (CFD) analysis. The hydraulic assessment gives a good overview if the component is suitable for the desired operating conditions in a relatively quick manner. It is, however, not suitable for detailed understanding of why a certain component is underperforming.
Pump internals typically have a complex three-dimensional shape, which is not taken into consideration when performing a classical analysis. Therefore, a three-dimensional CFD simulation was performed to identify in detail the potential areas for improvement of each component.
Two different strategies were used for optimizing the internal components. The series impeller geometry was optimized automatically by an objective algorithm to obtain optimum performance; other components, including first-stage impeller, series volutes and short crossovers were redesigned by manual design iterations, which were evaluated using CFD. The results show that the distribution of the cross-sectional area in the crossovers had the greatest influence on the efficiency, and due effort was undertaken to optimize this. To validate the efficiency improvement that was predicted by CFD simulations, scaled model tests were conducted on the series stages. The entire design optimization resulted in better performance in terms of efficiency, power and head for the complete flow range.
Numerical Study of Pump-Turbine Instabilities Under Pumping Mode Off-Design Conditions
Authors: Ješe Uroš , Fortes-Patella Regiane , Dular Matevž 
Published: November 2015

Pumped storage power plants, using reversible pump-turbines, are a great solution to maintain the stability of an electrical network. The continuous operating area of reversible pump-turbines machines is usually delimited by cavitation or a hydraulic instability called hump phenomena at part load. If the machine operates under these off-design conditions, it might be exposed to vibrations and performance losses.
The paper focuses on the numerical analysis of the pumping mode regime and pays special attention to the prediction of the hump shaped characteristic curve and associated rotating stall. The investigations were made on a high head pump-turbine design (nq=27) at model scale for four different guide vane opening angles and a wide range of flow rates. Numerical simulations were performed and analyzed in LEGI and were compared to the global experimental data, provided by Alstom Hydro.
Numerical Simulation and Performance Prediction of Reversible Submersible Tubular Pumping System
Authors: Jin Yan , Liu Chao , Zhou Jiren , Yang Hua , Cheng Li 
Published: November 2015

Submersible tubular pump is a kind of horizontal pump with low head and large discharge, which uses the structure of postpositive tubular type with motor and pump coaxial. Nowadays, more and more urban pumping stations need to have the function of irrigation and drainage. In the plain areas, the head of many pumping stations are very low, even only about one meter. Considering the efficiency and practicability, the reversible submersible tubular pump is chosen to realize the function of irrigation and drainage.
Research on three-dimensional flow field in a submersible tubular pumping system using numerical simulation based on the Reynolds time-averaged Navier-Stokes equations and the RNG k-ε turbulent model. By using this method, the performance of pumping system such as head, shaft power and efficiency are predicted based on the calculation of different operating conditions. For verifying the accuracy and reliability of the calculation results, a model test was conducted. The comparison of simulation results and the experiment data shown that the calculation performances close agreement with the experiment results in the high efficiency area, but in the condition of large discharge and small discharge, deviations were existed between the two results. Combining with the numerical simulation and experimental, which can provide more evidences for the hydraulic performance prediction and optimization design of pumping system.
Shut-Off Head Prediction in Single Stage Centrifugal Pumps
Authors: Berten Stefan , Tomasini Filippo , Maurer Wolfgang , Dupont Philippe 
Published: November 2015

The prediction of the performance characteristic in centrifugal pumps at flow rates other than the design flow is of high relevance but relatively uncertain.
In the present study, an evaluation of the existing shut-off head prediction methods and an assessment of both, the empirical approach and the numerical simulation are performed. For this purpose, after a review of existing methodologies, the empirical predictions are compared against available statistical data for single stage volute pumps. The CFD study, performed for 3 different single stage volute pumps with specific speeds between nq = 12 and nq = 54 is quantitatively compared against available model test data, which were obtained using precision manufactured hydraulic components.
Several empirical methods from open literature have been reviewed for the shut-off head prediction. An overview of different prediction methods has been presented by Dyson [1], these and an empirical correlation proposed by Guelich have been compared against available data.
The numerical study at shut-off condition requires a full-pump geometry, which also includes long suction and pressure pipes. Unlike several analyses present in the literature (Dyson & Texeira [2], Benigni et al. [3], Liu et al. [4]), which consider the internal leakage flow in the outlet boundary, the shut-off condition is obtained by imposing walls at inlet and outlet boundaries, but leakage flow through the gap between casing and impeller which is essential for the recirculation of the flow is numerically modeled. Because of the unsteady nature of the pressure in the pump volute, a transient simulation is performed and the predicted shut-off head is the average of the whole range of results for a minimum of 10 impeller revolutions.
Direct Numerical Simulation of the Flow Through a Structured Pebble Bed Near a Wall Boundary
Authors: Fick Lambert , Merzari Elia , Hassan Yassin 
Published: November 2015

Packed pebble beds occur in many industrial applications, including the very high temperature and molten salt nuclear reactor design concepts. These designs are currently being researched as possible fourth-generation nuclear power system designs. In order to ensure proper cooling of the reactor cores in these systems during normal operation, as well as under accident conditions, a detailed understanding of the coolant flow behavior is required. Direct numerical simulation (DNS) can be used to simulate specific pebble bed flow and geometry conditions in order to develop high-fidelity fluid flow data and hence improve scientists’ understanding and enhance lower-fidelity modeling.
We have used Nek5000, a spectral-element computational fluid dynamics code, to develop DNS fluid flow data for pebble bed flow, including budgets for the Reynolds stresses. The geometry is a structured pebble bed with a face-centered cubic packing arrangement. The flow domain features periodic boundaries in both streamwise and spanwise directions except for a single bounding wall parallel to the flow direction. In a fully periodic domain, the flow was found to be asymmetric. In this work we focus on turbulence properties in the near-wall region and their effect on the overall flow behavior. A set of preliminary Reynolds-averaged Navier-Stokes calculations was also performed to investigate the effect of geometric parameters such as the distance of the wall from the first row of pebbles.
Cavitation in Submerged Water Jet at High Jet Pressure
Authors: Kang Can , Liu Haixia , Li Xiuge , Cheng Xiaonong 
Published: November 2015

Recent industrial applications have unfolded a promising prospect for submerged water jet. Apart from widely acknowledged water jet properties, submerged water jet is characterized by the formation and complex evolution of cavitation bubbles. These bubbles not just alter the flow behavior of submerged water jet but also pose a profound effect upon impinged solid surface. At low jet pressures, some conclusions associated with submerged water jet have been acquired, while studies at high jet pressures have rarely been reported. From today’s view, both numerical and experimental approaches manifest apparent limitations in the presence of high-pressure submerged water jet. Consequently, validation of numerical results cannot be implemented conveniently due to lack of relevant experimental results.
The major purpose of the present study is to explore cavitation features in submerged water jets with jet pressures of 120 and 150 MPa. Numerical techniques are utilized to locate cavitation zone in submerged water jet stream and to delineate cavities as well. Meanwhile, velocity distribution in the jet stream is obtained to calculate jet kinetic energy. Under submerged conditions, bubbles disperse rapidly in ambient water and therefore impede the penetration of incident light. Thus submerged water jet stream cannot be distinguished accurately. Such a difficulty encountered in optical flow measurement and flow visualization for submerged water jet seems insurmountable. Thus experimental efforts are devoted to an interpretation of cavitation effect through examining surface morphology features of the solid sample impinged by submerged water jet. And these features are obtained quantitatively using an optical profiling system.
The results show that the occurrence of cavitation depends largely on the shear effect between fluid layers with different velocity magnitudes. Annular cavity shape is typical for submerged water jets. The existence of cavitation can be maintained within a limited streamwise distance from the nozzle. Furthermore, different jet pressures result in considerably different cavitation severity and effective streamwise lengths of cavity. According to the footprints on the impinged sample surface, it can be concluded that the impingement effect is ascribed to both cavitation effect and jet kinetic energy. The footprint produced on the target surface is in accordance with that predicted with numerical techniques in terms of size and shape. Several important aspects associated with the cavitation phenomenon in the submerged water jet are clarified in the present study.
An Investigation of the Flow Structure in the Radial Inflow Transonic Turbine
Authors: Zhu Cheng , Zhuge Weilin , Zhang Yangjun 
Published: November 2015

Radial inflow turbines which are an important component of a turbocharger consist essentially of a volute, a rotor and a diffuser. Vaneless volute turbines, which have reasonable performance and low cost, are the most widely used in turbochargers for automotive engines. In recent years the growing necessity of increasing specific output power of turbochargers has encouraged the design of high pressure ratio turbine stage. Two stage turbines, which can achieve the high pressure ratio require, are not suitable to for these applications due to volume and weight increases. The common design trend is thus to use single stage high pressure ratio radial transonic turbine.
This paper describes numerical investigations of the flow fields in a radial inflow transonic turbine whose design pressure ratio is 4. The S-A turbulence model and Jameson’s center scheme have been applied in order to get good viscous resolution, accuracy and computing efficiency. Limiting streamlines on the wall surface as well as different flow characteristics, such as entropy generation of the cross sections, were evaluated, and detailed endwall flow and secondary flow structure were analyzed. The development of different vortex, especially the tip leakage vortex, vortex caused by the shock wave, passage vortex and horseshoe vortex were discussed. The results have shown that there is a great secondary flow feature and complicated vortex system in the high pressure ratio radial inflow transonic turbine.
Single charge exchange in collision of fast protons with hydrogen molecules
Authors: Ghanbari-Adivi Ebrahim , Sattarpour Seyedeh Hedyeh 
Published: November 2015

Single charge transfer process in collision of energetic protons with molecular hydrogens is theoretically studied using a first-order two-effective-center Born approximation. The correct boundary conditions are incorporated in the formalism and the Hartree–Fock molecular wave function for molecular targets and the residual ions are used to calculate the transition amplitude. The interference patterns in the capture differential cross-sections (DCSs) for a given fixed orientation of the molecule, due to the scattering from the two-atomic centers in the molecular targets, are examined. The dependence of the DCSs upon the angle between the molecular axis and the direction of the incident velocity is theoretically investigated. Both average differential and integral cross-sections are calculated. The obtained results are compared with the available experimental data.
A Million Metaorder Analysis of Market Impact on the Bitcoin
Authors: Donier J. , Bonart J. 
Published: November 2015

We present a thorough empirical analysis of market impact on the Bitcoin/USD exchange market using a complete dataset that allows us to reconstruct more than one million metaorders. We empirically confirm the “square-root law” for market impact, which holds on four decades in spite of the quasi-absence of statistical arbitrage and market marking strategies. We show that the square-root impact holds during the whole trajectory of a metaorder and not only for the final execution price. We also attempt to decompose the order flow into an “informed” and “uninformed” component, the latter leading to an almost complete long-term decay of impact. This study sheds light on the hypotheses and predictions of several market impact models recently proposed in the literature and promotes heterogeneous agent models as promising candidates to explain price impact on the Bitcoin market — and, we believe, on other markets as well.
How many planet-wide leaders should there be?
Authors: Liu Shengyun , Vukolić Marko 
Published: November 2015

Geo-replication becomes increasingly important for modern planetary scale distributed systems, yet it comes with a specific challenge: latency, bounded by the speed of light. In particular, clients of a geo-replicated system must communicate with a leader which must in turn communicate with other replicas: wrong selection of a leader may result in unnecessary round-trips across the globe. Classical protocols such as celebrated Paxos, have a single leader making them unsuitable for serving widely dispersed clients. To address this issue, several all-leader geo-replication protocols have been proposed recently, in which every replica acts as a leader. However, because these protocols require coordination among all replicas, commiting a client's request at some replica may incure the so-called "delayed commit" problem, which can introduce even a higher latency than a classical single-leader majority-based protocol such as Paxos.
In this paper, we argue that the "right" choice of the number of leaders in a geo-replication protocol depends on a given replica configuration and propose Droopy, an optimization for state machine replication protocols that explores the space between single-leader and all-leader by dynamically reconfiguring the leader set. We implement Droopy on top of Clock-RSM, a state-of-the-art all-leader protocol. Our evaluation on Amazon EC2 shows that, under typical imbalanced workloads, Droopy-enabled Clock-RSM efficiently reduces latency compared to native Clock-RSM, whereas in other cases the latency is the same as that of the native Clock-RSM.