Entrainment Phenomena Research Articles

Comparative study on effect of air–water and steam–water mediums on liquid entrainment through ADS-4 in AP1000

For the previous experiments of entrainment at T-junction, the air–cold water two-phase flow is always selected as working medium, and the theoretical models of liquid entrainment are established mainly based on the experimental data of air–water entrainment through a small break. The saturated steam–water entrainment experiments are gravely insufficient, especially the steam–water experiments of entrainment through a large size branch are even fewer. Hence, a scale-down experiment of steam–water entrainment at T-junction has been conducted referring to liquid entrainment through ADS-4 (Fourth Stage Automatic Depressurization System) in AP1000 nuclear plant. The steam–water experimental results are comprehensively compared with the results of the previous similar air–water experiment: The visualization research shows that the same entrainment phenomena can be observed including intermittent flow entrainment, stratified flow entrainment and annular flow entrainment; The transition conditions between the two entrainment phenomena have a little difference but can be negligible; The comparison of experimental data of entrainment onset and stable entrainment indicates that the experimental data of steam–water and air–water have the same change tendency, and the air–water correlation can agree well with the steam–water data. Hence, we can make a conclusion that effect of different working mediums on liquid entrainment is negligible. In addition, based on the analysis of model formation, we suppose that effect of the system pressure on entrainment can be neglected under 0.22MPa.

Synergy Between Intercellular Communication and Intracellular Ca(2+) Handling in Arrhythmogenesis.

Calcium is the primary signalling component of excitation-contraction coupling, the process linking electrical excitability of cardiac muscle cells to coordinated contraction of the heart. Understanding [Formula: see text]handling processes at the cellular level and the role of intercellular communication in the emergence of multicellular synchronization are key aspects in the study of arrhythmias. To probe these mechanisms, we have simulated cellular interactions on large scale arrays that mimic cardiac tissue, and where individual cells are represented by a mathematical model of intracellular [Formula: see text]dynamics. Theoretical predictions successfully reproduced experimental findings and provide novel insights on the action of two pharmacological agents (ionomycin and verapamil) that modulate [Formula: see text]signalling pathways via distinct mechanisms. Computational results have demonstrated how transitions between local synchronisation events and large scale wave formation are affected by these agents. Entrainment phenomena are shown to be linked to both intracellular [Formula: see text]and coupling-specific dynamics in a synergistic manner. The intrinsic variability of the cellular matrix is also shown to affect emergent patterns of rhythmicity, providing insights into the origins of arrhythmogenic [Formula: see text]perturbations in cardiac tissue in situ.

Experimental investigation of upper plenum entrainment in AP1000

Upper plenum liquid entrainment can reduce the coolant inventory in the reactor pressure vessel and poses great threats to core uncovering and melting in the accident conditions. To make up for the deficiency of upper plenum entrainment database, the Automatic Depressurization and Entrainment TEst Loop (ADETEL) was constructed and upper plenum entrainment experiments were conducted. The test matrix was designed with various variables to investigate the upper plenum entrainment comprehensively. Entrainment phenomena and test data were obtained and analyzed. The entrainment deposition effect of reactor internals was also investigated. The test results indicate that the steam flow rate has little on the entrainment rate under stable experimental conditions. The entrainment rate decreases dramatically with the mixture liquid level in the pressure vessel when the liquid level drops below the hot leg elevation. The entrainment rate is promoted after the installation of reactor internals due to the increase of steam velocity in the upper plenum. Huge discrepancy exists between the test data and Kataoka and Ishii's (1984) pool entrainment model in the near surface region suggesting that the upper plenum entrainment is mainly dominated by side branch entrainment mechanism which is different from the pool entrainment mechanism.

Exploring how musical rhythm entrains brain activity with electroencephalogram frequency-tagging.

The ability to perceive a regular beat in music and synchronize to this beat is a widespread human skill. Fundamental to musical behaviour, beat and meter refer to the perception of periodicities while listening to musical rhythms and often involve spontaneous entrainment to move on these periodicities. Here, we present a novel experimental approach inspired by the frequency-tagging approach to understand the perception and production of rhythmic inputs. This approach is illustrated here by recording the human electroencephalogram responses at beat and meter frequencies elicited in various contexts: mental imagery of meter, spontaneous induction of a beat from rhythmic patterns, multisensory integration and sensorimotor synchronization. Collectively, our observations support the view that entrainment and resonance phenomena subtend the processing of musical rhythms in the human brain. More generally, they highlight the potential of this approach to help us understand the link between the phenomenology of musical beat and meter and the bias towards periodicities arising under certain circumstances in the nervous system. Entrainment to music provides a highly valuable framework to explore general entrainment mechanisms as embodied in the human brain.

Liquid Films Instability Analysis of Liquefying Hybrid Rocket Fuels Under Supercritical Conditions

Numerical analysis on the instability of liquid/dense fluid films under supercritical operating conditions is performed on methane fuel. A numerical code for compressible fluid flows, accommodated for the van der Waals equation of state, is developed in order to deal with supercritical fluid and dense fluid layers and has shown good convergence, even at a very low-Reynolds-number flow typically seen in actual hybrid rocket engines. A linear instability analysis is conducted and shows that an amplification rate has a peak at a certain wave number of initial perturbations. The perturbation becomes unstable as the Reynolds number and chamber pressure increase, and the instability region of the wave number is enlarged when an acceleration body force in the streamwise direction is imposed. A limit cycle of the amplitude of perturbations is observed at low-Reynolds-number flows, and the instability of dense fluid layers leads to the entrainment phenomena at high-Reynolds-number flows. It is deduced that the perturbation with the peak value of the amplification rate dominates in an actual hybrid rocket engine.

Measurements of liquid film and droplets of annular two-phase flow on a rod-bundle geometry with spacer

Measurements have been conducted to simultaneously consider both liquid films and droplets of the annular flow on a 3×3 simulating BWR fuel rod-bundle test-section with spacers. The optical system of a high speed camera and a tele-microscope was used to record the backlight images at the gap between a corner rod and a side rod of the bundle at high time and space resolutions. The data obtained from the liquid film showed that the mean film thickness, wave height, power spectral density, and wave velocity at the corner rod are larger than those at the side rod, and that the influences of the spacer are different in the cases of low and high gas superficial velocities. Simultaneously, the data containing size and spatial distributions as well as the axial velocity distribution of liquid droplets were obtained. In the case of lower gas flow rates, the spacer generates not only a large number of small droplets but also big droplets whose size exceeds the maximum droplet diameter at upstream. At further downstream, the spatial distribution of the droplets indicates an asymmetry characteristic, which emphasizes the contribution of the droplet impingement mechanism to the entrainment phenomena. Moreover, a close-up observation at right up- and downstreams of the spacer was conducted to describe the interactions between the two-phase flow and this structure. By using these new experimental arrangements, the interaction mechanisms among the wavy liquid film, droplets and spacer were discussed.

Numerical evaluation of gas core length in free surface vortices

The formation and evolution of free surface vortices represent an important topic in many hydraulic intakes, since strong whirlpools introduce swirl flow at the intake, and could cause entrainment of floating matters and gas. In particular, gas entrainment phenomena are an important safety issue for Sodium cooled Fast Reactors, because the introduction of gas bubbles within the core causes dangerous reactivity fluctuation. In this paper, a numerical evaluation of the gas core length in free surface vortices is presented, according to two different approaches. In the first one, a prediction method, developed by the Japanese researcher Sakai and his team, has been applied. This method is based on the Burgers vortex model, and it is able to estimate the gas core length of a free surface vortex starting from two parameters calculated with single-phase CFD simulations. The two parameters are the circulation and the downward velocity gradient. The other approach consists in performing a two-phase CFD simulation of a free surface vortex, in order to numerically reproduce the gas- liquid interface deformation. Mapped convergent mesh is used to reduce numerical error and a VOF (Volume Of Fluid) method was selected to track the gas-liquid interface. Two different turbulence models have been tested and analyzed. Experimental measurements of free surface vortices gas core length have been executed, using optical methods, and numerical results have been compared with experimental measurements. The computational domain and the boundary conditions of the CFD simulations were set consistently with the experimental test conditions.

Experimental investigation of liquid entrainment in ADS-4 depressurization line with steam–water

The fourth stage Automatic Depressurization System (ADS-4) is an important part in Westinghouse AP600/AP100 which enables controlled depressurization of reactor coolant system during small break LOCA. However, the coolant may be entrained into the containment through the ADS-4 branch line simultaneously, which poses great threats to reactor core uncovering and melting. To investigate the entrainment phenomenon of ADS-4 in AP1000, ADS-4 Depressurization and Entrainment TEst Loop (ADETEL) with a scaling ratio of 1:5.6 was constructed and visualization experiments were conducted with steam–water. The experiment were conducted at atmospheric pressure with the maximum steam flow rate of 700kg/h. The entrainment processes were recorded by a high speed camera and analyzed in detail. Onset of entrainment and entrainment rate data were obtained and compared with existing test data and correlations. Empirical correlation of ADS-4 branch entrainment onset has been developed. A clear difference exists between ADETEL entrainment onset data and available correlations, which may caused by the differences in fluids physical properties, horizontal pipe flow conditions, determination of entrainment onset and d/D ratios. The entrainment onset is more likely to be reached in small d/D ratios conditions due to the stronger Bernoulli effect. Besides, AP1000 has a higher branch quality than AP600 at the same liquid level in the hot leg.

Experimental investigation of liquid entrainment in vertical up tee branch with double-end gas inlets

Tee branches are widely used in nuclear power plants for varying purposes. The tee branch is adopted by the fourth stage Automatic Depressurization System (ADS-4) in Westinghouse AP600/AP1000 to depressurize the primary loop during the small break loss of coolant accident (SBLOCA). However, large amount of coolant will be entrained simultaneously through the ADS-4 branch which poses the threat of core uncovering and melting. Visualization experiments with double-end gas inlets were conducted to investigate the ADS-4 tee branch entrainment phenomena in AP1000. Entrainment process were recorded by high speed camera and analyzed in detail. The onset of liquid entrainment and entrainment rate data were obtained and compared with existing data and correlations, and discrepancies were found in the comparison due to the difference of test section geometric configuration. The gas flow rate has little effect on the branch quality at the same dimensionless gas chamber height in entrainment rate tests. The entrainment frequency was also studied. The test data reveal that the entrainment period decreases rapidly with the increase of entrainment rate in low range of the entrainment rate, and gradually stabilizes in high range of the entrainment rate.

Doing Duo - a case study of entrainment in William Forsythe's choreography "Duo".

Entrainment theory focuses on processes in which interacting (i.e., coupled) rhythmic systems stabilize, producing synchronization in the ideal sense, and forms of phase related rhythmic coordination in complex cases. In human action, entrainment involves spatiotemporal and social aspects, characterizing the meaningful activities of music, dance, and communication. How can the phenomenon of human entrainment be meaningfully studied in complex situations such as dance? We present an in-progress case study of entrainment in William Forsythe’s choreography Duo, a duet in which coordinated rhythmic activity is achieved without an external musical beat and without touch-based interaction. Using concepts of entrainment from different disciplines as well as insight from Duo performer Riley Watts, we question definitions of entrainment in the context of dance. The functions of chorusing, turn-taking, complementary action, cues, and alignments are discussed and linked to supporting annotated video material. While Duo challenges the definition of entrainment in dance as coordinated response to an external musical or rhythmic signal, it supports the definition of entrainment as coordinated interplay of motion and sound production by active agents (i.e., dancers) in the field. Agreeing that human entrainment should be studied on multiple levels, we suggest that entrainment between the dancers in Duo is elastic in time and propose how to test this hypothesis empirically. We do not claim that our proposed model of elasticity is applicable to all forms of human entrainment nor to all examples of entrainment in dance. Rather, we suggest studying higher order phase correction (the stabilizing tendency of entrainment) as a potential aspect to be incorporated into other models.

Review of entrainment correlations in gas–solid fluidization

• Review of applicability of entrainment correlations to Geldart Groups A and B. • Monodisperse, binary, and continuous particle size distributions (PSDs) considered. • Discrepancies among correlations span several orders of magnitude. • Unphysical phenomena predicted include preferential elutriation of larger particles. • Poor predictive capability underscores need for more physically-based models. Despite the abundance of entrainment correlations in gas–solid fluidization made available in the past few decades, the discrepancy between empirical prediction and experimental data has been noted to be up to a hundredfold in some cases. Hence, a comprehensive review of the available correlations is warranted, with the goal of extracting the underlying physics giving rise to the disparities, and thereby providing insights towards an enhanced understanding of entrainment. This review addresses a comprehensive spectrum of particle systems, ranging from monodisperse to binary to continuous particle size distribution (PSD) systems for the more predominant Geldart Groups A and B classifications. Three key observations are highlighted. First, comparisons of the predicted entrainment values among available correlations reveal discrepancies spanning several orders of magnitude, with the maximum being 20 orders of magnitude, evidencing that available empirical correlations do not extrapolate well beyond the scope of tested parameters. Second, unphysical phenomena predicted include qualitative discordance on the shapes of the elutriated PSDs, the most notable of which is the anomaly whereby larger particles are preferentially elutriated. Third, whether a particular correlation was developed for a specific Geldart Group or for monodisperse and/or polydisperse systems seems inconsequential to giving better predictions even when appropriately applied to the particular subset. These observations underscore the need for more physically-based models to enable a more accurate prediction of entrainment and elutriation phenomena.

Vibration Control by Time Delayed Linear and Non-Linear Acceleration Feedback

The forced Duffing oscillator is investigated by time-delayed linear and nonlinear acceleration feedbacks. The method of Slowly Varying Parameter (SVP) can efficiently develop frequency response curves with stability of solutions. Appreciable reduction in peak value of response and gradual reduction in the skew-ness in frequency response curve is observed with the introduction of gain and delay. For some values of control parameters the entrainment phenomena are also observed. Appropriate choice of gain and delay parameters are made from the primary stability zone of linear stability analysis graph. The results obtained by this method are compared with numerical integration (NI) method and they are in good agreement.

Ejecta evolution during cone impact

AbstractWe present findings from an experimental investigation into the impact of solid cone-shaped bodies onto liquid pools. Using a variety of cone angles and liquid physical properties, we show that the ejecta formed during the impact exhibits self-similarity for all impact speeds for very low surface tension liquids, whilst for high-surface tension liquids similarity is only achieved at high impact speeds. We find that the ejecta tip can detach from the cone and that this phenomenon can be attributed to the air entrainment phenomenon. We analyse of a range of cone angles, including some ogive cones, and impact speeds in terms of the spatiotemporal evolution of the ejecta tip. Using superhydrophobic cones, we also examine the entry of cones which entrain an air layer.

Experimental research of liquid entrainment through ADS-4 in AP1000

In this study, based on a T-junction that consists of Automatic Depressurization System Stage Four (ADS-4) and hot leg in an AP1000 plant, a small-scale experimental research on entrainment at a T-junction was performed. This study mainly focused on the effect of various factors on entrainment, such as the effect of branch size, branch shape and liquid crossflow. The flow pattern map was plotted from the experimental data, and the visualization research indicated that the entrainment phenomena through a large size branch were apparently different from that through a small branch. Three entrainment phenomena were observed in the studies, two entrainment mechanisms could be found in the stratified flow regime entrainment area, the existence of branch contributed to generating intermittent flow in the horizontal main pipe, and the backflow region was observable in the vicinity of a large size branch inlet. Also, experimental research showed that downstream of the branch of T-junction had an important effect on the onset entrainment, and liquid crossflow did not seem to affect the onset entrainment.

Experimental investigation of liquid entrainment in AP1000 ADS-4 branch line with air–water

ADS-4 branch line provides a controlled depressurization of the Westinghouse AP600/AP1000 primary loop during a small break LOCA. However, the coolant will be entrained to the containment simultaneously which leads to the loss of liquid inventory. ADS-4 Depressurization and Entrainment TEst Loop (ADETEL) scaled after AP1000 was constructed and visualization experiments were conducted to investigate the entrainment phenomenon at the ADS-4 tee branch line. Entrainment phenomena were recorded by high speed camera and analyzed in detail. The entrainment onset and stabilized entrainment rate data were collected and compared with available data. Discrepancies were found between ADETEL experimental data and available data due to the difference of experimental conditions and test section geometric configuration. The test data reveals that the tee branch liquid entrainment model used in RELAP5 cannot estimate the ADS-4 entrainment for AP1000 accurately and therefore more practicable model should be developed. The ADETEL data also manifest that AP1000 has a higher degree of safety performance during ADS-4 branch depressurization process than AP600 design.

Synchronization of map-based neurons with memory and synaptic delay

Abstract Synchronization of two synaptically coupled neurons with memory and synaptic delay is studied using the Rulkov map, one of the simplest neuron models which displays specific features inherent to bursting dynamics. We demonstrate a transition from lag to anticipated synchronization as the relationship between the memory duration and the synaptic delay time changes. The neuron maps synchronize either with anticipation, if the memory is longer than the synaptic delay time, or with lag otherwise. The mean anticipation time is equal to the difference between the memory and synaptic delay independently of the coupling strength. Frequency entrainment and phase-locking phenomena as well as a transition from regular spikes to chaos are demonstrated with respect to the coupling strength.

Simulation of dynamic characteristics of droplet impact on liquid film

A physical and mathematical model is established to simulate a single droplet impact onto a thin horizontal liquid film by using coupled Level Set and volume of fluid method, which has advantages in acquisition of interface geometrical parameters and keeping mass conservation. The evolution after the droplet impact is obtained together with isopiestic and velocity field at different parameters including impact velocity, droplet diameter and liquid film thickness. Influences of Weber number (We number), droplet size and film thickness on the crown diameter and crown height are acquired, and the results indicate that the crown diameter and height could be increased by increasing We number or by reducing film thickness. Furthermore, bubble entrainment phenomenon when the droplet impinges the liquid film are captured successfully and discussed. It is found that increment of both impact We number and droplet diameter could help the emerging of bubble rings.

Experimental and theoretical investigation of liquid entrainment through small-scaled ADS-4 in AP1000

An experimental and theoretical research has been performed for liquid entrainment at T-junction consisting of hot leg and ADS-4 pipe in view of the insufficiency of existing studies. Based on visualization research, three kinds of entrainment phenomena including intermittent entrainment, stratified entrainment and annular entrainment are clearly observed, and the feature of each flow regime is summarized and recorded by high-speed camera. Also, the flow pattern map is plotted from the experimental data to indicate the transition conditions of different flow regimes. For the purpose of modeling and expanding previous research, the influence of entrance length on entrainment is discussed on the basis of two different test sections. The effect of liquid flow on onset entrainment and stable entrainment is analyzed, and experiment results show that the effect of liquid flow on entrainment through ADS-4 pipe can be neglected. Also, onset entrainment model and branch quality model are established and accord with experimental data well.

Flow-improving elements in circular drop manholes

ABSTRACTDrop manholes are widely employed in urban drainage systems. They experience operating conditions in which insufficient energy dissipation leads to hydraulic problems that are enhanced by particular configurations of the manhole bottom. Therefore, specific jet-breaker devices were considered to improve the flow conditions. Two different types of jet-breakers have been tested in the present work: plane jet-breaker (PJB) and wedge jet-breaker (WJB). Both have proved to be effective in inducing adequate energy loss, if properly sized, and to improve the overall drop manhole performance. The selection of a jet-breaker element should account for additional features of the drop manhole hydraulics, including the pool depth, the air entrainment phenomena, as well as further practical aspects including cost-effectiveness, simplicity of realization and clogging risk. This study provides the hydraulic basis for the design of the jet-breakers, particularly of the PJB, which has an overall optimum performance, as laboratory experiments have shown.

Experimental investigation of free surface vortices and definition of gas entrainment occurrence maps

For the future development of Generation IV nuclear reactors, both safety and economic targets have to be achieved. In order to increase, at the same time, the power density generation and the safety features, a huge R&D effort is still required. Referring especially to Liquid Metal Cooled Fast Reactors, much attention is placed on Gas Entrainment (GE) phenomena, which could cause unlikely positive reactivity insertion accident. The GETS experimental facility (Gas Entrainment Test Section), especially aimed at studying the free surface vortices occurrence, has been built in the thermal-hydraulics laboratory of the DIAEE. The main purpose of this facility is to identify the most important parameters affecting the whirlpools formation and evolution. Experimental tests and preliminary observations have been performed. Different vortex behaviours related to different experimental conditions have been identified and presented in the present paper. 2D occurrence maps as function of different dimensionless groups (Reynolds, Froude and Weber numbers and H* = H/d ratio) have been defined. In the present paper, the results of a first experimental campaign, carried out with tap water, are discussed.