Energy Technology Data Exchange (ETDEWEB)
Bondar, A.; Buzulutskov, A. [Budker Institute of Nuclear Physics SB RAS, Lavrentiev avenue 11, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation); Dolgov, A. [Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation); Nosov, V.; Shekhtman, L.; Shemyakina, E.; Sokolov, A. [Budker Institute of Nuclear Physics SB RAS, Lavrentiev avenue 11, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogov street 2, 630090 Novosibirsk (Russian Federation)
2017-02-11
A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49±7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N{sub 2} content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.
Ahmad, Zahoor; Hanif, Muhammad
2013-01-01
The development of estimators of population parameters based on two-phase sampling schemes has seen a dramatic increase in the past decade. Various authors have developed estimators of population using either one or two auxiliary variables. The present volume is a comprehensive collection of estimators available in single and two phase sampling. The book covers estimators which utilize information on single, two and multiple auxiliary variables of both quantitative and qualitative nature. Th...
International Nuclear Information System (INIS)
Olive, J.
1990-01-01
The design, operation and safety of nuclear components requires increasingly accurate knowledge of two-phase flows. This knowledge is also necessary for some studies related to electricity applications. The author presents some concrete examples showing the range of problems and the complexity of the phenomena involved in these types of flows. Then, the basic principles of their numerical modelling are explained, as well as the new tendency to use increasingly local and refined models. The newest computer codes developed at EDF are briefly presented. Experimental studies dealing with twophase flow are also referred to, and their connections to numerical modelling are explained. Emphasis is placed on the major efforts devoted to the development of new test rigs and instrumentation [fr
International Nuclear Information System (INIS)
Hsu, Y.Y.
1974-01-01
The following papers related to two-phase flow are summarized: current assumptions made in two-phase flow modeling; two-phase unsteady blowdown from pipes, flow pattern in Laval nozzle and two-phase flow dynamics; dependence of radial heat and momentum diffusion; transient behavior of the liquid film around the expanding gas slug in a vertical tube; flooding phenomena in BWR fuel bundles; and transient effects in bubble two-phase flow. (U.S.)
International Nuclear Information System (INIS)
Delaje, Dzh.
1984-01-01
General hypothesis used to simplify the equations, describing two-phase flows, are considered. Two-component and one-component models of two-phase flow, as well as Zuber and Findlay model for actual volumetric steam content, and Wallis model, describing the given phase rates, are presented. The conclusion is made, that the two-component model, in which values averaged in time are included, is applicable for the solving of three-dimensional tasks for unsteady two-phase flow. At the same time, using the two-component model, including values, averaged in space only one-dimensional tasks for unsteady two-phase flow can be solved
Nanomechanics of slip avalanches in amorphous plasticity
Cao, Penghui; Dahmen, Karin A.; Kushima, Akihiro; Wright, Wendelin J.; Park, Harold S.; Short, Michael P.; Yip, Sidney
2018-05-01
Discrete stress relaxations (slip avalanches) in a model metallic glass under uniaxial compression are studied using a metadynamics algorithm for molecular simulation at experimental strain rates. The onset of yielding is observed at the first major stress drop, accompanied, upon analysis, by the formation of a single localized shear band region spanning the entire system. During the elastic response prior to yielding, low concentrations of shear transformation deformation events appear intermittently and spatially uncorrelated. During serrated flow following yielding, small stress drops occur interspersed between large drops. The simulation results point to a threshold value of stress dissipation as a characteristic feature separating major and minor avalanches consistent with mean-field modeling analysis and mechanical testing experiments. We further interpret this behavior to be a consequence of a nonlinear interplay of two prevailing mechanisms of amorphous plasticity, thermally activated atomic diffusion and stress-induced shear transformations, originally proposed by Spaepen and Argon, respectively. Probing the atomistic processes at widely separate strain rates gives insight to different modes of shear band formation: percolation of shear transformations versus crack-like propagation. Additionally a focus on crossover avalanche size has implications for nanomechanical modeling of spatially and temporally heterogeneous dynamics.
International Nuclear Information System (INIS)
Boure, J.A.
1974-12-01
Two-phase flow instabilities are classified according to three criteria: the static or dynamic nature of the phenomenon, the necessity or not of a triggering phenomenon, and the pure or compound character of the phenomenon. Tables give the elementary instability phenomena, and the practical types of instability. Flow oscillations (or dynamic instabilities) share a number of characteristics which are dealt with, they are caused by the dynamic interactions between the flow parameters (flow rate, density, pressure, enthalpy and their distributions). Oscillation types are discussed: pure oscillations are density wave oscillations, acoustic oscillations may also occur, various compound oscillations involve either the density wave or the acoustic wave mechanism, interacting with some of the boundary conditions in the device. The analysis of slow oscillations has been made either by means of a simplified model (prediction of the thresholds) or of computer codes. Numerous computer codes are available [fr
Two phase titanium aluminide alloy
Deevi, Seetharama C.; Liu, C. T.
2001-01-01
A two-phase titanic aluminide alloy having a lamellar microstructure with little intercolony structures. The alloy can include fine particles such as boride particles at colony boundaries and/or grain boundary equiaxed structures. The alloy can include alloying additions such as .ltoreq.10 at % W, Nb and/or Mo. The alloy can be free of Cr, V, Mn, Cu and/or Ni and can include, in atomic %, 45 to 55% Ti, 40 to 50% Al, 1 to 5% Nb, 0.3 to 2% W, up to 1% Mo and 0.1 to 0.3% B. In weight %, the alloy can include 57 to 60% Ti, 30 to 32% Al, 4 to 9% Nb, up to 2% Mo, 2 to 8% W and 0.02 to 0.08% B.
International Nuclear Information System (INIS)
Zhao Pingde; Xu Zhiqing; Tang Xiaowei
1986-01-01
The characteristics of multiwire proportional chamber and multistage avalanche chamber filled with argon and photoionization gas (C 2 H 5 ) 3 N were measured. The spatial resolution curves and output pulse height spectra were measured as well. Low concentration (C 2 H 5 ) 3 N can play an effective part in quenching. At very low concentration, the phenomena of avalanche transverse expansion was observed obviously
Zhu, Zhaoxuan; Wiese, Kay Jörg
2017-12-01
In disordered elastic systems, driven by displacing a parabolic confining potential adiabatically slowly, all advance of the system is in bursts, termed avalanches. Avalanches have a finite extension in time, which is much smaller than the waiting time between them. Avalanches also have a finite extension ℓ in space, i.e., only a part of the interface of size ℓ moves during an avalanche. Here we study their spatial shape 〈S(x ) 〉 ℓ given ℓ , as well as its fluctuations encoded in the second cumulant 〈S2(x ) 〉 ℓ c. We establish scaling relations governing the behavior close to the boundary. We then give analytic results for the Brownian force model, in which the microscopic disorder for each degree of freedom is a random walk. Finally, we confirm these results with numerical simulations. To do this properly we elucidate the influence of discretization effects, which also confirms the assumptions entering into the scaling ansatz. This allows us to reach the scaling limit already for avalanches of moderate size. We find excellent agreement for the universal shape and its fluctuations, including all amplitudes.
A microstrip gas avalanche chamber with two-dimensional readout
International Nuclear Information System (INIS)
Angelini, F.; Bellazzini, R.; Brez, A.; Massai, M.M.; Spandre, G.; Torquati, M.R.
1989-01-01
A microstrip gas avalanche chamber with a 200 μm anode pitch has been built and successfully tested in our laboratory. A gas gain of 10 4 and an energy resolution of 18% (FWHM) at 6 keV have been measured using a gas mixture of argon-CO 2 at atmospheric pressure. A preliminary measurement of the positional sensitivity indicates that a spatial resolution of 50 μm can be obtained. (orig.)
Avalanches in insulating gases
International Nuclear Information System (INIS)
Verhaart, H.F.A.
1982-01-01
Avalanches of charged particles in gases are often studied with the ''electrical method'', the measurement of the waveform of the current in the external circuit. In this thesis a substantial improvement of the time resolution of the measuring setup, to be used for the electrical method, is reported. The avalanche is started by an N 2 -laser with a pulse duration of only 0.6 ns. With this laser it is possible to release a high number of primary electrons (some 10 8 ) which makes it possible to obtain sizeable signals, even at low E/p values. With the setup it is possible to analyze current waveforms with a time resolution down to 1.4 ns, determined by both the laser and the measuring system. Furthermore it is possible to distinguish between the current caused by the electrons and the current caused by the ions in the avalanche and to monitor these currents simultaneously. Avalanche currents are measured in N 2 , CO 2 , O 2 , H 2 O, air of varying humidity, SF 6 and SF 6 /N 2 mixtures. Depending on the nature of the gas and the experimental conditions, processes as diffusion, ionization, attachment, detachment, conversion and secondary emission are observed. Values of parameters with which these processes can be described, are derived from an analysis of the current waveforms. For this analysis already published theories and new theories described in this thesis are used. The drift velocity of both the electrons and the ions could be easily determined from measured avalanche currents. Special attention is paid to avalanches in air becasue of the practical importance of air insulation. (Auth.)
Study of influence of gas mixture composition on the multistep avalanche chambers characteristics
International Nuclear Information System (INIS)
Abdushukurov, D.A.; Zanevskij, Yu.V.; Peshekhonov, V.D.
1987-01-01
The influence of the concentration of organic quenchers on the operation of multistep avalanche chambers /MSAC/ has been studied. An empirical dependence of the gas amplification factor of MSAC on the quencher concentration has been derived. Measures are considered to increase the stability of the MSAC operation. To improve the MSAC operation argon + n-heptane, neon + methane and neon + argon + methane mixtures are suggested
Avalanche photoconductive switching
Pocha, M. D.; Druce, R. L.; Wilson, M. J.; Hofer, W. W.
This paper describes work being done at Lawrence Livermore National Laboratory on the avalanche mode of operation of laser triggered photoconductive switches. We have been able to generate pulses with amplitudes of 2 kV to 35 kV and rise times of 300 to 500 ps, and with a switching gain (energy of output electrical pulse vs energy of trigger optical pulse) of 10(exp 3) to over 10(exp 5). Switches with two very different physical configurations and with two different illumination wavelengths (1.06 micrometer, 890 nm) exhibit very similar behavior. The avalanche switching behavior, therefore, appears to be related to the material parameters rather than the optical wavelength or switch geometry. Considerable further work needs to be done to fully characterize and understand this mode of operation.
Avalanche photoconductive switching
Energy Technology Data Exchange (ETDEWEB)
Pocha, M.D.; Druce, R.L.; Wilson, M.J.; Hofer, W.W.
1989-01-01
This paper describes work being done at Lawrence Livermore National Laboratory on the avalanche mode of operation of laser triggered photoconductive switches. We have been able to generate pulses with amplitudes of 2 kV--35 kV and rise times of 300--500 ps, and with a switching gain (energy of output electrical pulse vs energy of trigger optical pulse) of 10{sup 3} to over 10{sup 5}. Switches with two very different physical configurations and with two different illumination wavelengths (1.06 {mu}m, 890 nm) exhibit very similar behavior. The avalanche switching behavior, therefore, appears to be related to the material parameters rather than the optical wavelength or switch geometry. Considerable further work needs to be done to fully characterize and understand this mode of operation. 3 refs., 6 figs.
Sputtering of two-phase AgxCuγ alloys
International Nuclear Information System (INIS)
Bibic, N.; Milosavljevic, M.; Perusko, D.; Wilson, I.H.
1992-01-01
Elemental sputtering yields from two phase AgCu alloys were measured for 20, 40 and 50 at % Ag. Argon ion bombardment energies were in the range 35-55 keV and the ion dose was 1 x 10 19 ions cm -2 . The sputtering yield for silver was found to be considerably below what was expected by simple selective sputtering of a two component alloy. Analysis by electron probe X-ray microanalysis and scanning electron microscopy of the eroded surface indicated that surface diffusion of copper from copper rich grains and geometrical constraints in the dense cone forest on Cu/Ag eutectic regions combine to reduce the sputtering yield for silver. (author)
Ductile fracture of two-phase welds under 77K
International Nuclear Information System (INIS)
Yushchenko, K.A.; Voronin, S.A.; Pustovit, A.I.; Shavel', A.V.
1984-01-01
The effect of the type of welding and fillers on crack resistance of welded joints high-strength steel EhP810 and its various compounds with steels EhP666, 08Kh18N10T has been studied. For the welding of steel EhP810 with steels EhP810, EhP666, 08Kh18N10T electron-beam, automatic, argon tungsten arc with non-consumable electrode with various fillers, as well as argon metal-arc welding with consumable electrode, were used. It is shown, that for a joint, made by electron-beam welding, parameters σsub(u), Ksub(IcJ), KCV are higher than for a joint of a similar phase structure made using filler wire EhP659-VI. It is explained by the fact, that during electron-beam welding joint metal refining takes place, which removes gases. In welded joints of chP810 steel, having joints with austenitic structure, characteristic of crack resistance Ssub(c) increases by more than 0.2 mm in contrast to two-phase joints, which conventional yield strength at 77 K exceeds 1000 MPa. It is worth mentioning, that for other classes of steels formation of two-phase structure of joint increases welded joint resistance to brittle fracture. It is possible to obtain the required structure of joint with assigned level of resistance to brittle fracture by means of the use of different fillers, optimum and welding procedure, regulaing the part of the basic metal in joint content
Two-phase flow characteristics in BWRs
International Nuclear Information System (INIS)
Katono, Kenichi; Aoyama, Goro; Nagayoshi, Takuji; Yasuda, Kenichi; Nishida, Koji
2014-01-01
Reliable prediction of two-phase flow characteristics is important for safety and economy improvements of BWR plants. We have been developing two-phase flow measurement tools and techniques for BWR thermal hydraulic conditions, such as a 3D time-averaged X-ray CT system, an ultrasonic liquid film sensor and a wire-mesh sensor. We applied the developed items in experiments using the multi-purpose steam-water test facility known as HUSTLE, which can simulate two-phase thermal-hydraulic conditions in a BWR reactor pressure vessel, and we constructed a detailed instrumentation database. We validated a 3D two-phase flow simulator using the database and developed the reactor internal two-phase flow analysis system. (author)
Investigation of avalanche photodiodes
Energy Technology Data Exchange (ETDEWEB)
Si Mohand, D.; Benhammou, Y.; Depasse, P.; Goyot, M.; Ille, B.; Linard, E.; Martin, F.; Musienko, Y.
1996-06-01
Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO{sub 4} crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO{sub 4} crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm{sup 2}. We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab.
Investigation of avalanche photodiodes
International Nuclear Information System (INIS)
Si Mohand, D.; Benhammou, Y.; Depasse, P.; Goyot, M.; Ille, B.; Linard, E.; Martin, F.; Musienko, Y.
1996-06-01
Some characteristics and performances of a set of nine Hamamatsu avalanche photodiodes have been investigated. These APDs have equipped a small 3x3 PbWO 4 crystal matrix in X3 beam during the summer of 1995. This note summarizes the main results of this work. An electromagnetic calorimeter with a high resolution is necessary to search for the Higgs if it has a mass between 80 and 160 GeV. A PbWO 4 crystal option has been chosen by the CMS collaboration to achieve this task. The light is collected and converted into an electric charge by an Avalanche Photodiode (APD) followed by a fast preamplifier. The advantage of the APDs is that they are not sensitive to the strong magnetic field when compared to photomultipliers and they are a small nuclear counter effect when compared to PIN diodes. In this study, we have tested nine low capacitance Hamamatsu APDs (S5345) received in spring, 1995 with an area of 0.2 cm 2 . We have measured the capacitance and dark current for each APD. The gain measurements have also been done with gamma sources, continuous and pulsed light. The gain sensitivity versus bias and temperature have also been investigated succinctly. (author). 8 refs., 16 figs., 1 tab
Two-phase gas bubble-liquid boundary layer flow along vertical and inclined surfaces
International Nuclear Information System (INIS)
Cheung, F.B.; Epstein, M.
1985-01-01
The behavior of a two-phase gas bubble-liquid boundary layer along vertical and inclined porous surfaces with uniform gas injection is investigated experimentally and analytically. Using argon gas and water as the working fluids, a photographical study of the two-phase boundary layer flow has been performed for various angles of inclination ranging from 45 0 to 135 0 and gas injection rates ranging from 0.01 to 0.1 m/s. An integral method has been employed to solve the system of equations governing the two-phase motion. The effects of the gas injection rate and the angle of inclination on the growth of the boundary layer have been determined. The predicted boundary layer thickness is found to be in good agreement with the experimental results. The calculated axial liquid velocity and the void fraction in the two-phase region are also presented along with the observed flow behavior
Two-phase flow in refrigeration systems
Gu, Junjie; Gan, Zhongxue
2013-01-01
Two-Phase Flow in Refrigeration Systems presents recent developments from the authors' extensive research programs on two-phase flow in refrigeration systems. This book covers advanced mass and heat transfer and vapor compression refrigeration systems and shows how the performance of an automotive air-conditioning system is affected through results obtained experimentally and theoretically, specifically with consideration of two-phase flow and oil concentration. The book is ideal for university postgraduate students as a textbook, researchers and professors as an academic reference book, and b
A real two-phase submarine debris flow and tsunami
International Nuclear Information System (INIS)
Pudasaini, Shiva P.; Miller, Stephen A.
2012-01-01
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
A real two-phase submarine debris flow and tsunami
Energy Technology Data Exchange (ETDEWEB)
Pudasaini, Shiva P.; Miller, Stephen A. [Department of Geodynamics and Geophysics, Steinmann Institute, University of Bonn Nussallee 8, D-53115, Bonn (Germany)
2012-09-26
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
Two-phased flow component loss data
International Nuclear Information System (INIS)
Fairhurst, C.P.
1983-01-01
Pressure loss measurements were made for valves and orifice plates under horizontal and vertical two-phase, air/water flow. The results displayed similar trends and were successfully correlated using a semi-empirical approach. (author)
Neuronal avalanches and learning
Energy Technology Data Exchange (ETDEWEB)
Arcangelis, Lucilla de, E-mail: dearcangelis@na.infn.it [Department of Information Engineering and CNISM, Second University of Naples, 81031 Aversa (Italy)
2011-05-01
Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.
Neuronal avalanches and learning
International Nuclear Information System (INIS)
Arcangelis, Lucilla de
2011-01-01
Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.
Abnormal breakdown characteristic in a two-phase mixture
International Nuclear Information System (INIS)
Ye Qizheng; Li Jin; Lu Fei
2006-01-01
A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration. Based on Townsend's theory, a new cell-iterative model in analytical form for the breakdown mechanism in TPM is presented. Compared with the original cell-iterative model in our previous paper, the obstructive factor of the macroparticles that influences the electron avalanche propagation is considered, except for the macroparticles distorting the electrical field and capture of the electrons. The cell attractive parameter k is presented according to the classical continuum theory for field charging. The modified Paschen law for a TPM is presented to calculate the breakdown voltage. The breakdown voltage of the TPM, U TPM , increases gradually with an increase in the macroparticle number density (m). The voltage U TPM is lower than that of the pure gas at low m values and larger at high m values. With a decrease of the macroparticle volume fraction and the dielectric mismatch, the voltage U TPM increases gradually at low m values and decreases gradually at high m values. The voltage U TPM at pd 200 cm Torr is lower than that at pd = 760 cm Torr for low m values and larger for high m values. This kind of abnormal breakdown characteristic in the TPM occurs in the case of high macroparticle volume fraction. On the other hand, the minimum of the TPM's Paschen curve increases with increase in m. It provides the possibility and the conditions of greatly increasing the breakdown voltage in a nearly uniform field
Imaging findings of avalanche victims
Energy Technology Data Exchange (ETDEWEB)
Grosse, Alexandra B.; Grosse, Claudia A.; Anderson, Suzanne [University Hospital of Berne, Inselspital, Department of Diagnostic, Pediatric and Interventional Radiology, Berne (Switzerland); Steinbach, Lynne S. [University of California San Francisco, Department of Radiology, San Francisco, CA (United States); Zimmermann, Heinz [University Hospital of Berne, Inselspital, Department of Trauma and Emergency Medicine, Berne (Switzerland)
2007-06-15
Skiing and hiking outside the boundaries remains an attractive wilderness activity despite the danger of avalanches. Avalanches occur on a relatively frequent basis and may be devastating. Musculoskeletal radiologists should be acquainted with these injuries. Fourteen avalanche victims (11 men and 3 women; age range 17-59 years, mean age 37.4 years) were air transported to a high-grade trauma centre over a period of 2 years. Radiographs, CT and MR images were prospectively evaluated by two observers in consensus. Musculoskeletal findings (61%) were more frequent than extraskeletal findings (39%). Fractures were most commonly seen (36.6%), involving the spine (14.6%) more frequently than the extremities (9.8%). Blunt abdominal and thoracic trauma were the most frequent extraskeletal findings. A wide spectrum of injuries can be found in avalanche victims, ranging from extremity fractures to massive polytrauma. Asphyxia remains the main cause of death along with hypoxic brain injury and hypothermia. (orig.)
Two phase cooling for superconducting magnets
International Nuclear Information System (INIS)
Eberhard, P.H.; Gibson, G.A.; Green, M.A.; Ross, R.R.; Smits, R.G.
1986-01-01
Comments on the use of two phase helium in a closed circuit tubular cooling system and some results obtained with the TPC superconducting magnet are given. Theoretical arguments and experimental evidence are given against a previously suggested method to determine helium two phase flow regimes. Two methods to reduce pressure in the magnet cooling tubes during quenches are discussed; 1) lowering the density of helium in the magnet cooling tubes and 2) proper location of pressure relief valves. Some techniques used to protect the refrigerator from too much cold return gas are also mentioned
Two phase cooling for superconducting magnets
International Nuclear Information System (INIS)
Eberhard, P.H.; Gibson, G.A.; Green, M.A.; Ross, R.R.; Smits, R.G.; Taylor, J.D.; Watt, R.D.
1986-01-01
Comments on the use of two phase helium in a closed circuit tubular cooling system and some results obtained with the TPC superconducting magnet are given. Theoretical arguments and experimental evidence are given against a previously suggested method to determine helium two phase flow regimes. Two methods to reduce pressure in the magnet cooling tubes during quenches are discussed; (1) lowering the density of helium in the magnet cooling tubes and (2) proper location of pressure relief valves. Some techniques used to protect the refrigerator from too much cold return gas are also mentioned. 10 refs., 1 fig., 5 tabs
Nonlinear dynamics of two-phase flow
International Nuclear Information System (INIS)
Rizwan-uddin
1986-01-01
Unstable flow conditions can occur in a wide variety of laboratory and industry equipment that involve two-phase flow. Instabilities in industrial equipment, which include boiling water reactor (BWR) cores, steam generators, heated channels, cryogenic fluid heaters, heat exchangers, etc., are related to their nonlinear dynamics. These instabilities can be of static (Ledinegg instability) or dynamic (density wave oscillations) type. Determination of regions in parameters space where these instabilities can occur and knowledge of system dynamics in or near these regions is essential for the safe operation of such equipment. Many two-phase flow engineering components can be modeled as heated channels. The set of partial differential equations that describes the dynamics of single- and two-phase flow, for the special case of uniform heat flux along the length of the channel, can be reduced to a set of two coupled ordinary differential equations [in inlet velocity v/sub i/(t) and two-phase residence time tau(t)] involving history integrals: a nonlinear ordinary functional differential equation and an integral equation. Hence, to solve these equations, the dependent variables must be specified for -(nu + tau) ≤ t ≤ 0, where nu is the single-phase residence time. This system of nonlinear equations has been solved analytically using asymptotic expansion series for finite but small perturbations and numerically using finite difference techniques
Two phase transitions in Nuclear Physics
International Nuclear Information System (INIS)
Bes, D.R.
1985-01-01
The status of the art of the problem associated with two phase transitions in the nuclear matter, viz.: the disappearance of the nuclear superfluiditiy with the raising of the rotation velocity and the appearance of an octupolar deformation in the actinide zone, is presented. (L.C.) [pt
Two-phase flow in fractured rock
International Nuclear Information System (INIS)
Davies, P.; Long, J.; Zuidema, P.
1993-11-01
This report gives the results of a three-day workshop on two-phase flow in fractured rock. The workshop focused on two-phase flow processes that are important in geologic disposal of nuclear waste as experienced in a variety of repository settings. The goals and objectives of the workshop were threefold: exchange information; describe the current state of understanding; and identify research needs. The participants were divided into four subgroups. Each group was asked to address a series of two-phase flow processes. The following groups were defined to address these processes: basic flow processes; fracture/matrix interactions; complex flow processes; and coupled processes. For each process, the groups were asked to address these four issues: (1) describe the two-phase flow processes that are important with respect to repository performance; (2) describe how this process relates to the specific driving programmatic issues given above for nuclear waste storage; (3) evaluate the state of understanding for these processes; and (4) suggest additional research to address poorly understood processes relevant to repository performance. The reports from each of the four working groups are given here
Two-phase gas bubble-liquid boundary layer flow along vertical and inclined surfaces
International Nuclear Information System (INIS)
Cheung, F.B.; Epstein, M.
1985-01-01
The behavior of a two-phase gas bubble liquid boundary layer along vertical and inclined porous surfaces with uniform gas injection is investigated experimentally and analytically. Using argon gas and water as the working fluids, a photographical study of the two-phase boundary layer flow has been performed for various angles of inclination ranging from 45 0 to 135 0 and gas injection rates ranging from 0.01 to 0.1 m/s. An integral method has been employed to solve the system of equations governing the two-phase motion. The effects of the gas injection rate and the angle of inclination on the growth of the boundary layer have been determined
Argon analytical procedures for potassium-argon dating
International Nuclear Information System (INIS)
Gabites, J.E.; Adams, C.J.
1981-01-01
A manual for the argon analytical methods involved in potassium-argon geochronology, including: i) operating procedures for the ultra-high vacuum argon extraction/purification equipment for the analysis of nanolitre quantities of radiogenic argon in rocks, minerals and gases; ii) operating procedures for the AEI-MS10 gas source mass spectrometer
Avalanche risk assessment in Russia
Komarov, Anton; Seliverstov, Yury; Sokratov, Sergey; Glazovskaya, Tatiana; Turchaniniva, Alla
2017-04-01
The avalanche prone area covers about 3 million square kilometers or 18% of total area of Russia and pose a significant problem in most mountain regions of the country. The constant growth of economic activity, especially in the North Caucasus region and therefore the increased avalanche hazard lead to the demand of the large-scale avalanche risk assessment methods development. Such methods are needed for the determination of appropriate avalanche protection measures as well as for economic assessments during all stages of spatial planning of the territory. The requirement of natural hazard risk assessments is determined by the Federal Law of Russian Federation. However, Russian Guidelines (SP 11-103-97; SP 47.13330.2012) are not clearly presented concerning avalanche risk assessment calculations. A great size of Russia territory, vast diversity of natural conditions and large variations in type and level of economic development of different regions cause significant variations in avalanche risk values. At the first stage of research the small scale avalanche risk assessment was performed in order to identify the most common patterns of risk situations and to calculate full social risk and individual risk. The full social avalanche risk for the territory of country was estimated at 91 victims. The area of territory with individual risk values lesser then 1×10(-6) covers more than 92 % of mountain areas of the country. Within these territories the safety of population can be achieved mainly by organizational activities. Approximately 7% of mountain areas have 1×10(-6) - 1×10(-4) individual risk values and require specific mitigation measures to protect people and infrastructure. Territories with individual risk values 1×10(-4) and above covers about 0,1 % of the territory and include the most severe and hazardous mountain areas. The whole specter of mitigation measures is required in order to minimize risk. The future development of such areas is not recommended
An introduction to two-phase flows
International Nuclear Information System (INIS)
Lemonnier, Herve
2006-01-01
This course aims at proposing the necessary background for a rational approach to two-phase flows which are notably present in numerous industrial devices and equipment designed to perform energy transfer or mass transfer. The first part proposes a phenomenological approach to main two-phase flow structures and presents their governing variables. The second part presents some proven measurement techniques. The third part focuses on modelling. It recalls the equation elaboration techniques which are based on basic principles of mechanics and thermodynamics and on the application of different averaging operators to these principles. Some useful models are then presented such as models of pressure loss in a duct. The last chapter addresses some fundamental elements of heat transfers in ebullition and condensation
Apparatus for monitoring two-phase flow
Sheppard, John D.; Tong, Long S.
1977-03-01
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Geometrical automata for two phase flow simulation
International Nuclear Information System (INIS)
Herrero, V.; Guido-Lavalle, G.; Clausse, A.
1996-01-01
An automaton is an entity defined by a mathematical state which changes following iterative rules representing the interaction with the neighborhood. A model of automata for two-phase flow simulation consisting in a field of disks which are allowed to change their radii and move in a plane is presented. The model is more general than the classical cellular automata in two respects: (1) the grid of cellular automata is dismissed in favor of a trajectory generator; and (2) the rules of interaction involve parameters intended to represent some of the most relevant variables governing the actual physical interactions between phases. Computational experiments show that the algorithm captures the essential physics underlying two-phase flow problems such as bubbly-slug pattern transition and void fraction development along tubes. A comparison with experimental data of void fraction profiles is presented, showing excellent agreement. (orig.)
Review of two-phase water hammer
International Nuclear Information System (INIS)
Beuthe, T.G.
1997-01-01
In a thermalhydraulic system like a nuclear power plant, where steam and water mix and are used to transport large amounts of energy, there is a potential to create two-phase water hammer. Large water hammer pressure transients are a threat to piping integrity and represent an important safety concern. Such events may cause unscheduled plant down time. The objective of this review is to provide a summary of the information on two-phase water hammer available in the open literature with particular emphasis on water hammer occurrences in nuclear power plants. Past reviews concentrated on studies concerned with preventing water hammer. The present review focuses on the fundamental experimental, analytical, and modelling studies. The papers discussed here were chosen from searches covering up to July 1993. (author)
Modelling aspects of two phase flow
International Nuclear Information System (INIS)
Mayinger, F.
1977-01-01
In two phase flow scaling is much more limited to very narrowly defined physical phenomena than in single phase fluids. For complex and combined phenomena it can be achieved not by using dimensionless numbers alone but in addition a detailed mathematical description of the physical problem - usually in the form of a computer program - must be available. An important role plays the scaling of the thermodynamic data of the modelling fluid. From a literature survey and from own scaling experiments the conclusion can be drawn that Freon is a quite suitable modelling fluid for scaling steam-water mixtures. However, whithout a theoretical description of the phenomena nondimensional numbers for scaling two phase flow must be handled very carefully. (orig.) [de
Apparatus for monitoring two-phase flow
International Nuclear Information System (INIS)
Sheppard, J.D.; Tong, L.S.
1977-01-01
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods. 3 claims, 9 figures
Pumped two-phase heat transfer loop
Edelstein, Fred
1988-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Study of nonequilibrium dispersed two phase flow
International Nuclear Information System (INIS)
Reyes, J.N. Jr.
1986-01-01
Understanding the behavior of liquid droplets in a superheated steam environment is essential to the accurate prediction of nuclear fuel rod surface temperatures during the blowdown and reflood phase of a loss-of-coolant-accident (LOCA). In response to this need, this treatise presents several original and significant contributions to the field of thermofluid physics. The research contained herein presents a statistical derivation of the two-phase mass, momentum, and energy-conservation equations using a droplet continuity equation analogous to that used in the Kinetic Theory of Gases. Unlike the Eulerian volume and time-averaged conservation equations generally used to describe dispersed two-phase flow behavior, this statistical averaging approach results in an additional mass momentum or energy term in each of the respective conservation equations. Further, this study demonstrates that current definitions of the volumetric vapor generation rate used in the mass conservation equation are inappropriate results under certain circumstances. The mass conservation equation derived herein is used to obtain a new definition for the volumetric vapor-generation rate. Last, a simple two phase phenomenological model, based on the statistically averaged conservation equations, is presented and solved analytically. It is shown that the actual quality and vapor temperature, under these circumstances, depend on a single dimensionless group
Review of two-phase instabilities
Energy Technology Data Exchange (ETDEWEB)
Kang, Han Ok; Seo, Han Ok; Kang, Hyung Suk; Cho, Bong Hyun; Lee, Doo Jeong
1997-06-01
KAERI is carrying out a development of the design for a new type of integral reactors. The once-through helical steam generator is important design features. The study on designs and operating conditions which prevent flow instability should precede the introduction of one-through steam generator. Experiments are currently scheduled to understand two-phase instability, evaluate the effect of each design parameter on the critical point, and determine proper inlet throttling for the prevention of instability. This report covers general two-phase instability with review of existing studies on this topics. The general classification of two phase flow instability and the characteristics of each type of instability are first described. Special attention is paid to BWR core flow instability and once-through steam generator instability. The reactivity feedback and the effect of system parameters are treated mainly for BWR. With relation to once-through steam generators, the characteristics of convective heating and dryout point oscillation are first investigated and then the existing experimental studies are summarized. Finally chapter summarized the proposed correlations for instability boundary conditions. (author). 231 refs., 5 tabs., 47 figs
Abnormal breakdown characteristic in a two-phase mixture
Energy Technology Data Exchange (ETDEWEB)
Ye Qizheng; Li Jin; Lu Fei [College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074 (China)
2006-05-21
A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration. Based on Townsend's theory, a new cell-iterative model in analytical form for the breakdown mechanism in TPM is presented. Compared with the original cell-iterative model in our previous paper, the obstructive factor of the macroparticles that influences the electron avalanche propagation is considered, except for the macroparticles distorting the electrical field and capture of the electrons. The cell attractive parameter k is presented according to the classical continuum theory for field charging. The modified Paschen law for a TPM is presented to calculate the breakdown voltage. The breakdown voltage of the TPM, U{sub TPM}, increases gradually with an increase in the macroparticle number density (m). The voltage U{sub TPM} is lower than that of the pure gas at low m values and larger at high m values. With a decrease of the macroparticle volume fraction and the dielectric mismatch, the voltage U{sub TPM} increases gradually at low m values and decreases gradually at high m values. The voltage U{sub TPM} at pd 200 cm Torr is lower than that at pd = 760 cm Torr for low m values and larger for high m values. This kind of abnormal breakdown characteristic in the TPM occurs in the case of high macroparticle volume fraction. On the other hand, the minimum of the TPM's Paschen curve increases with increase in m. It provides the possibility and the conditions of greatly increasing the breakdown voltage in a nearly uniform field.
International Nuclear Information System (INIS)
Cassignol, Charles; Cornette, Yves; David, Benjamin; Gillot, P.-Y.
1978-04-01
The main features of the method of processing rocks and minerals and measuring the extracted argon, for the purpose of potassium-argon dating are described. It differs in several respects from the conventional one, as described, f.i., in Dalrymple and Lanphere's monography. Principally it was established that the continual purification of the gases in the mass spectrometer cell during the measurement, stops the peaks of current drift, and renders them representative of the introduced argon. This allows on the one hand to improve the reliability and accuracy of measurements, on the other hand to get rid of the isotopic dilution method, with 38 A as a spike. Moreover the reliability of the radiogenic argon is improved by taking into account the mislinearness of the M.S. response. All this results in a higher performance of the K/Ar dating method, especially in the recent ages range. The technological side of the problem was only dealt with [fr
Coupling two-phase fluid flow with two-phase darcy flow in anisotropic porous media
Chen, J.
2014-06-03
This paper reports a numerical study of coupling two-phase fluid flow in a free fluid region with two-phase Darcy flow in a homogeneous and anisotropic porous medium region. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition on the interface between the free flow and the porous media regions. Obtained results have shown the anisotropic properties effect on the velocity and pressure of the two-phase flow. 2014 Jie Chen et al.
Coupling Two-Phase Fluid Flow with Two-Phase Darcy Flow in Anisotropic Porous Media
Directory of Open Access Journals (Sweden)
Jie Chen
2014-06-01
Full Text Available This paper reports a numerical study of coupling two-phase fluid flow in a free fluid region with two-phase Darcy flow in a homogeneous and anisotropic porous medium region. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition on the interface between the free flow and the porous media regions. Obtained results have shown the anisotropic properties effect on the velocity and pressure of the two-phase flow.
Two-phase flow dynamics in ECC
International Nuclear Information System (INIS)
Albraaten, P.J.
1981-07-01
The present report summarizes the achievements within the project ''Two-phase Systems and ECC''. The results during 1978 - 1980 are accounted for in brief as they have been documented in earlier reports. The results during the first half of 1981 are accounted for in greater detail. They contain a new model for the Basset force and test runs with this model using the test code RISQUE. Furthermore, test runs have been performed with TRAC-PD2 MOD 1. This code was implemented on Edwards Pipe Blowdown experiment (a standard test case) and UC-Berkeley Reflooding experiment (a non-standard test case.) (Auth.)
Two phase cooling for superconducting magnets
International Nuclear Information System (INIS)
Eberhard, P.H.; Gibson, G.A.; Green, M.A.; Ross, R.R.; Smits, R.G.; Taylor, J.D.; Watt, R.D.
1985-08-01
A closed circuit tubular cooling system for superconducting magnets offers advantages of limiting boiloff and containing high pressures during quenches. Proper location of automatic valves to lower pressures and protect the refrigerator in the event of quenches is described. Theoretical arguments and exprimental evidence are given against a previously suggested method to determine He two phase flow regimes. If loss of flow occurs due to some types of refrigeration failure and transfer lines have enough heat leak to warm up, quenches are induced when the flow is restored. Examples are taken from experience with the TPC magnet
Microgravity Two-Phase Flow Transition
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
International Nuclear Information System (INIS)
Sullivan, J.P.; Houze, R.N.; Buenger, D.E.; Theofanous, T.G.
1981-01-01
Hot film Anemometry and Laser Doppler Velocimetry have been employed in this work to study the turbulence characteristics of Bubbly and Stratified two-phase flows, respectively. Extensive consistency checks were made to establish the reliability and hence the utility of these experimental techniques for the measurement of turbulence in two-phase flows. Buoyancy-driven turbulence in vertical bubbly flows has been identified experimentally and correlated in terms of a shear velocity superposition approach. This approach provides a criterion for the demarcation of the buoyancy-driven turbulence region from the wall shear-generated turbulence region. Our data confirm the roughly isotropic behavior expected for buoyancy-driven turbulence. Upgrading of our experimental system will permit investigations of the wall-shear dominated regime (i.e., isotropy, superposition approach, etc.). The stratified flow data demonstrate clearly that the maximum in the mean velocity profile does not coincide with the zero shear plane, indicating the existence of a negative eddy viscosity region. Previous studies do not take into account this difference and thus they yield incorrect friction factor data in addition to certain puzzling behavior in the upper wall region. The conditioned turbulence data in the wavy region indicate interesting trends and that an appropriate normalization of intensities must take into account the shear velocity at the interfacial (wavy) region
Meshfree simulation of avalanches with the Finite Pointset Method (FPM)
Michel, Isabel; Kuhnert, Jörg; Kolymbas, Dimitrios
2017-04-01
Meshfree methods are the numerical method of choice in case of applications which are characterized by strong deformations in conjunction with free surfaces or phase boundaries. In the past the meshfree Finite Pointset Method (FPM) developed by Fraunhofer ITWM (Kaiserslautern, Germany) has been successfully applied to problems in computational fluid dynamics such as water crossing of cars, water turbines, and hydraulic valves. Most recently the simulation of granular flows, e.g. soil interaction with cars (rollover), has also been tackled. This advancement is the basis for the simulation of avalanches. Due to the generalized finite difference formulation in FPM, the implementation of different material models is quite simple. We will demonstrate 3D simulations of avalanches based on the Drucker-Prager yield criterion as well as the nonlinear barodesy model. The barodesy model (Division of Geotechnical and Tunnel Engineering, University of Innsbruck, Austria) describes the mechanical behavior of soil by an evolution equation for the stress tensor. The key feature of successful and realistic simulations of avalanches - apart from the numerical approximation of the occurring differential operators - is the choice of the boundary conditions (slip, no-slip, friction) between the different phases of the flow as well as the geometry. We will discuss their influences for simplified one- and two-phase flow examples. This research is funded by the German Research Foundation (DFG) and the FWF Austrian Science Fund.
Lumped transmission line avalanche pulser
Booth, Rex
1995-01-01
A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse.
Two Phase Flow Simulation Using Cellular Automata
International Nuclear Information System (INIS)
Marcel, C.P.
2002-01-01
The classical mathematical treatment of two-phase flows is based on the average of the conservation equations for each phase.In this work, a complementary approach to the modeling of these systems based on statistical population balances of aut omata sets is presented.Automata are entities defined by mathematical states that change following iterative rules representing interactions with the neighborhood.A model of automata for two-phase flow simulation is presented.This model consists of fie lds of virtual spheres that change their volumes and move around a certain environment.The model is more general than the classical cellular automata in two respects: the grid of cellular automata is dismissed in favor of a trajectory generator, and the rules of interaction involve parameters representing the actual physical interactions between phases.Automata simulation was used to study unsolved two-phase flow problems involving high heat flux rates. One system described in this work consists of a vertical channel with saturated water at normal pressure heated from the lower surface.The heater causes water to boil and starts the bubble production.We used cellular automata to describe two-phase flows and the interaction with the heater.General rule s for such cellular automata representing bubbles moving in stagnant liquid were used, with special attention to correct modeling of different mechanisms of heat transfer.The results of the model were compared to previous experiments and correlations finding good agreement.One of the most important findings is the confirmation of Kutateladze's idea about a close relation between the start of critical heat flux and a change in the flow's topology.This was analyzed using a control volume located in the upper surface of the heater.A strong decrease in the interfacial surface just before the CHF start was encountered.The automata describe quite well some characteristic parameters such as the shape of the local void fraction in the
Modeling of two-phase slug flow
International Nuclear Information System (INIS)
Fabre, J.; Line, A.
1992-01-01
When gas and liquid flow in a pipe, over a range of flow rates, a flow pattern results in which sequences of long bubbles, almost filling the pipe cross section, are successively followed by liquid slugs that may contain small bubbles. This flow pattern, usually called slug flow, is encountered in numerous practical situations, such as in the production of hydrocarbons in wells and their transportation in pipelines; the production of steam and water in geothermal power plants; the boiling and condensation in liquid-vapor systems of thermal power plants; emergency core cooling of nuclear reactors; heat and mass transfer between gas and liquid in chemical reactors. This paper provides a review of two phase slug flow modeling
Measurements of void fraction in transparent two-phase flows by light extinction
International Nuclear Information System (INIS)
Shamoun, B.; El Beshbeeshy, M.; Bonazza, R.
1998-01-01
We report a technique for the measurement of the 2-D distribution of the line average void fraction in a two-phase flow with transparent gas and liquid components based on the Mie scattering induced by the gas bubbles on a collimated laser beam. The 2-D distribution of the line average of the interfacial area density is measured directly; the void fraction is deduced from it through an image processing algorithm. The technique is demonstrated with experiments in a pool of water injected with air and illuminated with a CW argon ion laser. (author)
Two-phase ozonation of chlorinated organics
International Nuclear Information System (INIS)
Bhattacharyya, D.; Freshour, A.; West, D.
1995-01-01
In the last few years the amount of research being conducted in the field of single-phase ozonation has grown extensively. However, traditional aqueous-phase ozonation systems are limited by a lack of selective oxidation potential, low ozone solubility in water, and slow intermediate decomposition rates. Furthermore, ozone may decompose before it can be utilized for pollutant destruction since ozone can be highly unstable in aqueous solutions. Naturally occurring compounds such as NaHCO 3 also affect ozone reactions by inhibiting the formation of OH-free radicals. To compensate for these factors, excess ozone is typically supplied to a reactor. Since ozone generation requires considerable electric power consumption (16 - 24 kWh/kg of O 3 ), attempts to enhance the ozone utilization rate and stability should lead to more efficient application of this process to hazardous waste treatment. To improve the process, ozonation may be more efficiently carried out in a two-phase system consisting of an inert solvent (saturated with O 3 ) contacted with an aqueous phase containing pollutants. The non-aqueous phase must meet the following criteria: (1) non-toxic, (2) very low vapor pressure, (3) high density (for ease of separation), (4) complete insolubility in water, (5) reusability, (6) selective pollutant extractability, (7) high oxidant solubility, and (8) extended O 3 stability. Previously published studies (1) have indicated that a number of fluorinated hydrocarbon compounds fit these criteria. For this project, FC40 (a product of 3M Co.) was chosen due to its low vapor pressure (3 mm Hg) and high specific gravity (1.9). The primary advantages of the FC40 solvent are that it is non-toxic, reusable, has an ozone solubility 10 times that of water, and that 85 % of the ozone remains in the solvent even after 2 hours. This novel two-phase process has been utilized to study the rapid destruction of organic chlorine compounds and organic mixtures
Etching of anode wire deposits with CF4/isobutane (80:20) avalanches
International Nuclear Information System (INIS)
Openshaw, R.; Henderson, R.S.; Faszer, W.; Salomon, M.
1990-11-01
An ionization exposure of 0.5 coulombs per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chambers. Several chambers aged in argon/ethane (50:50) and argon/ethane/ethanol (50:50:0.2) and having pulse height reductions of 25-30% have recovered pulse heights and currents to greater than 98% of their initial values. Inspection of the anode wires indicates that the thick deposits caused by the exposure in argon/ethane have been removed. Auger electron spectroscopy reveals only a thin residual layer containing primarily carbon and oxygen. This etching ability of CF 4 /isobutane (80:20) avalanches may explain the extremely good ageing characteristics previously reported for this mixture. (Author) (13 refs., 3 tabs., 11 figs.)
Etching of anode wire deposits with CF4/isobutane (80:20) avalanches
International Nuclear Information System (INIS)
Openshaw, R.; Henderson, R.S.; Faszer, W.; Salomon, M.
1991-01-01
An ionization exposure of 0.5 C per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chambers. Several chambers aged in argon/ethane (50:50) and argon/ethane/ethanol (50:50:0.2) and having pulse height reduction of 25-30% have recovered pulse heights and currents to greater than 98% of their initial values. Inspection of the anode wires indicates that the thick deposits caused by the exposure in argon/ethane have been removed. Auger electron spectroscopy reveals only a thin residual layer containing primarily carbon and oxygen. This etching ability of CF 4 /isobutane (80:20) avalanches may explain the extremely good ageing characteristics previously reported for this mixture. (orig.)
Two-phase flow models in unbounded two-phase critical flows
International Nuclear Information System (INIS)
Celata, G.P.; Cumo, M.; Farello, G.E.
1985-01-01
With reference to a Loss-of-Coolant Accident in Light Water Reactors, an analysis of the unbounded two-phase critical flow (i.e. the issuing two-phase jet) has been accomplished. Considering jets external shape, obtained by means of photographic pictures; pressure profiles inside the jet, obtained by means of a movable ''Pitot;'' and jet phases distribution information, obtained by means of X-rays pictures; a characterization of the flow pattern in the unbounded region of a two-phase critical flow is given. Jets X-ray pictures show the existence of a central high density ''core'' gradually evaporating all around, which gives place to a characteristic ''dartflow'' the length of which depends on stagnation thermodynamic conditions
International Nuclear Information System (INIS)
Vella, E.
1992-10-01
The liquid argon calorimeter (LAC) of the SLD detector is a parallel plate -- liquid argon sampling calorimeter, used to measure particle energies in Z 0 decays at the Stanford Linear Collider. The LAC module design is based on a unique projective tower structure, in which lead plates and segmented lead tiles serve both as absorbers and electrodes. The LAC front end electronics incorporates several novel features, including extensive multiplexing and optical fiber readout, which take advantage of the low SLC beam crossing frequency. The operational performance of the LAC during the recently completed SLD physics run (which recorded over 10,000 Z 0 events) is discussed
STUDY ON SIMULATION METHOD OF AVALANCHE : FLOW ANALYSIS OF AVALANCHE USING PARTICLE METHOD
塩澤, 孝哉
2015-01-01
In this paper, modeling for the simulation of the avalanche by a particle method is discussed. There are two kinds of the snow avalanches, one is the surface avalanche which shows a smoke-like flow, and another is the total-layer avalanche which shows a flow like Bingham fluid. In the simulation of the surface avalanche, the particle method in consideration of a rotation resistance model is used. The particle method by Bingham fluid is used in the simulation of the total-layer avalanche. At t...
Avalanche hazard and control in Kazakhstan
Directory of Open Access Journals (Sweden)
V. P. Blagoveshchensky
2014-01-01
Full Text Available In Kazakhstan, area of 124 thousand km2 is prone to the avalanche hazard. Avalanches are released down in mountain regions situated along the eastern boundary of Kazakhstan. Systematic studies of avalanches here were started in 1958 by explorer I.S. Sosedov; later on, I.V. Seversky continued these investigations in Institute of Geography of the Kazakh Soviet Republic. Actually, he founded the Kazakh school of the avalanche studies. In 1970–1980s, five snow-avalanche stations operated in Kazakhstan: two in Il’ Alatau, two in Zhetysu Alatau, and one in the Altai. At the present time, only two stations and two snow-avalanche posts operate, and all of them are located in Il’ Alatau.Since 1951 to 2013, 75 avalanches took place in Kazakhstan, releases of them caused significant damages. For this period 172 people happened to be under avalanches, among them 86 perished. Large avalanche catastrophes causing human victims and destructions took place in Altai in 1977 and in Karatau in 1990. In spring of 1966, only in Il’ Alatau avalanches destroyed more 600 ha of mature fir (coniferous forest, and the total area of forest destroyed here by avalanches amounts to 2677 ha or 7% of the total forest area.For 48 years of the avalanche observations, there were 15 winters with increased avalanche activity in the river Almatinka basin when total volume of released snow exceeded annual mean value of 147 thousand m3. During this period, number of days with winter avalanches changed from three (in season of 1973/1974 to 28 (1986/1987, the average for a year is 16 days for a season. Winter with the total volume of snow 1300 thousand m3 occur once in 150 years. Individual avalanches with maximal volume of 350 thousand m3 happen once in 80 years.Preventive avalanche releases aimed at protection of roads and settlements are used in Kazakhstan since 1974. These precautions are taken in Il’ Alatau, Altai, and on Kalbinsky Range. Avalanches are released with the
Coupling two-phase fluid flow with two-phase darcy flow in anisotropic porous media
Chen, J.; Sun, S.; Chen, Z.
2014-01-01
in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition
Corinne Pralavorio
2015-01-01
Over the past few days, the SPS has been accelerating argon ions, which have started to be sent to the NA61/SHINE experiment. This operating mode, using a new type of ion, required a number of modifications to the accelerator. Picture 1: a “super-cycle” of the SPS, featuring a proton cycle for the LHC, followed by an argon ion cycle for the North Area. Today, the accelerators are once again juggling particles and even performing completely new tricks. The SPS is supplying beams of argon ions for the first time, at energies never before achieved for this type of beam. They are destined for the NA61/SHINE experiment (see box) located in the North Area, which began receiving the beams on 11 February. Argon ions have a relatively large mass, as they consist of 40 nucleons, so they can be used in a similar way to lead ions. The main difficulty in accelerating them lies in the SPS, where the variation in acceleration frequency is limited. “The SPS was designed for a...
Advances in gas avalanche photomultipliers
Breskin, Amos; Buzulutskov, A F; Chechik, R; Garty, E; Shefer, G; Singh, B K
2000-01-01
Gas avalanche detectors, combining solid photocathodes with fast electron multipliers, provide an attractive solution for photon localization over very large sensitive areas and under high illumination flux. They offer single-photon sensitivity and the possibility of operation under very intense magnetic fields. We discuss the principal factors governing the operation of gas avalanche photomultipliers. We summarize the recent progress made in alkali-halide and CVD-diamond UV-photocathodes, capable of operation under gas multiplication, and novel thin-film protected alkali-antimonide photocathodes, providing, for the first time, the possibility of operating gas photomultipliers in the visible range. Electron multipliers, adequate for these photon detectors, are proposed and some applications are briefly discussed.
Moerk, J. Steven (Inventor); Youngquist, Robert C. (Inventor); Werlink, Rudy J. (Inventor)
1999-01-01
A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.
Two-phase flux simulations by robots
International Nuclear Information System (INIS)
Barrera, F.D.
1997-01-01
Two-Phase flow systems are studied following the statistical formulation, which takes into account the bubble population balances. This is done by means of automata simulation. Geometrical automata are associated to the dispersed phase, and are represented by discs on the plane, resembling bubbles moving in a fluid environment. Following pre-determined rules, the automata evolve, and useful statistical information about their interaction is obtained. This information is applied in the present work to study the mechanisms that induce bubble coalescence. Models for one and two sized automata are presented. It was found that in the case of the model for one size, the probability of interaction among bubbles and the pair correlation function depends not only on the void fraction, but also on the number of elements of the dispersed phase. A correlation for the collision probability between two bubbles is obtained, and this result was extended to the pair correlation function. For the case of systems with two characteristic sizes, a model was formulated for analyzing the interaction among bubbles of the two groups. The interaction of bubbles for one and two sized systems were related by a symmetry factor, which shows the dependence of the interaction among bubbles with the size distribution. By means of the automata simulation, the phenomena of bubble confinement and screening were characterized. It was found that the first phenomenon is stronger in systems with greater distance among bubbles, and that the second effect increases with void fraction and bubble number. (author)
Constitutive equations for two-phase flows
International Nuclear Information System (INIS)
Boure, J.A.
1974-12-01
The mathematical model of a system of fluids consists of several kinds of equations complemented by boundary and initial conditions. The first kind equations result from the application to the system, of the fundamental conservation laws (mass, momentum, energy). The second kind equations characterize the fluid itself, i.e. its intrinsic properties and in particular its mechanical and thermodynamical behavior. They are the mathematical model of the particular fluid under consideration, the laws they expressed are so called the constitutive equations of the fluid. In practice the constitutive equations cannot be fully stated without reference to the conservation laws. Two classes of model have been distinguished: mixture model and two-fluid models. In mixture models, the mixture is considered as a single fluid. Besides the usual friction factor and heat transfer correlations, a single constitutive law is necessary. In diffusion models, the mixture equation of state is replaced by the phasic equations of state and by three consitutive laws, for phase change mass transfer, drift velocity and thermal non-equilibrium respectively. In the two-fluid models, the two phases are considered separately; two phasic equations of state, two friction factor correlations, two heat transfer correlations and four constitutive laws are included [fr
Numerical calculation of two-phase flows
International Nuclear Information System (INIS)
Travis, J.R.; Harlow, F.H.; Amsden, A.A.
1975-06-01
The theoretical study of time-varying two-phase flow problems in several space dimensions introduces such a complicated set of coupled nonlinear partial differential equations that numerical solution procedures for high-speed computers are required in almost all but the simplest examples. Efficient attainment of realistic solutions for practical problems requires a finite- difference formulation that is simultaneously implicit in the treatment of mass convection, equations of state, and the momentum coupling between phases. Such a method is described, the equations on which it is based are discussed, and its properties are illustrated by means of examples. In particular, the capability for calculating physical instabilities and other time-varying dynamics, at the same time avoiding numerical instability is emphasized. The computer code is applicable to problems in reactor safety analysis, the dynamics of fluidized dust beds, raindrops or aerosol transport, and a variety of similar circumstances, including the effects of phase transitions and the release of latent heat or chemical energy. (U.S.)
Condensation in a two-phase pool
International Nuclear Information System (INIS)
Duffey, R.B.; Hughes, E.D.
1991-01-01
We consider the case of vapor condensation in a liquid pool, when the heat transfer is controlled by heat losses through the walls. The analysis is based on drift flux theory for phase separation in the pool, and determines the two-phase mixture height for the pool. To our knowledge this is the first analytical treatment of this classic problem that gives an explicit result, previous work having established the result for the evaporative case. From conservation of mass and energy in a one-dimensional steady flow, together with a void relation between the liquid and vapor fluxes, we determine the increase in the mixture level from the base level of the pool. It can be seen that the thermal and hydrodynamic influences are separable. Thus, the thermal influence of the wall heat transfer appears through its effect on the condensing length L*, so that at high condensation rates the pool is all liquid, and at low rates overflows (the level swell or foaming effect). Similarly, the phase separation effect hydrodynamically determines the height via the relative velocity of the mixture to the entering flux. We examine some practical applications of this result to level swell in condensing flows, and also examine some limits in ideal cases
Velocity distribution in snow avalanches
Nishimura, K.; Ito, Y.
1997-12-01
In order to investigate the detailed structure of snow avalanches, we have made snow flow experiments at the Miyanomori ski jump in Sapporo and systematic observations in the Shiai-dani, Kurobe Canyon. In the winter of 1995-1996, a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches. Measurements during a large avalanche in the Shiai-dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m/s soon after the front. Velocities decreased gradually in the following 10 s. Velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure. Both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers. In addition, the velocity showed a periodic change. Power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 Hz, which might imply the existence of either ordered structure or a series of surges in the flow.
Avalanches and Criticality in Driven Magnetic Skyrmions
Díaz, S. A.; Reichhardt, C.; Arovas, D. P.; Saxena, A.; Reichhardt, C. J. O.
2018-03-01
We show using numerical simulations that slowly driven Skyrmions interacting with random pinning move via correlated jumps or avalanches. The avalanches exhibit power-law distributions in their duration and size, and the average avalanche shape for different avalanche durations can be scaled to a universal function, in agreement with theoretical predictions for systems in a nonequilibrium critical state. A distinctive feature of Skyrmions is the influence of the nondissipative Magnus term. When we increase the ratio of the Magnus term to the damping term, a change in the universality class of the behavior occurs, the average avalanche shape becomes increasingly asymmetric, and individual avalanches exhibit motion in the direction perpendicular to their own density gradient.
Two-phase Heating in Flaring Loops
Zhu, Chunming; Qiu, Jiong; Longcope, Dana W.
2018-03-01
We analyze and model a C5.7 two-ribbon solar flare observed by the Solar Dynamics Observatory, Hinode, and GOES on 2011 December 26. The flare is made of many loops formed and heated successively over one and half hours, and their footpoints are brightened in the UV 1600 Å before enhanced soft X-ray and EUV missions are observed in flare loops. Assuming that anchored at each brightened UV pixel is a half flaring loop, we identify more than 6700 half flaring loops, and infer the heating rate of each loop from the UV light curve at the footpoint. In each half loop, the heating rate consists of two phases: intense impulsive heating followed by a low-rate heating that is persistent for more than 20 minutes. Using these heating rates, we simulate the evolution of their coronal temperatures and densities with the model of the “enthalpy-based thermal evolution of loops.” In the model, suppression of thermal conduction is also considered. This model successfully reproduces total soft X-ray and EUV light curves observed in 15 passbands by four instruments GOES, AIA, XRT, and EVE. In this flare, a total energy of 4.9 × 1030 erg is required to heat the corona, around 40% of this energy is in the slow-heating phase. About two-fifths of the total energy used to heat the corona is radiated by the coronal plasmas, and the other three fifth transported to the lower atmosphere by thermal conduction.
Ostwald ripening in two-phase mixtures
International Nuclear Information System (INIS)
Voorhees, P.W.
1982-01-01
Experimental measurements of the temperature of a rapidly solidified solid-liquid mixture have been made over a range of volume fractions solid 0.23 to 0.95. These experiments demonstrate the viability of measuring the change in interfacial curvature with time via precision thermometry. The experimental measurements also indicate that there is no radical change in interface morphology over a wide range of volume fractions solid. A solution to the multi-particle diffusion problem (MDP) has been constructed through the use of potential theory. The solution to the MDP was used to describe the diffusion field within a coarsening two-phase mixture consisting of dispersed spherical second-phase particles. Since this theory is based upon the MDP, interparticle diffusional interactions are specifically included in the treatment. As a result, the theory yields, for the first time, insights into the influence of the local distribution of curvature on a particle's coarsening rate. The effect of interparticle interactions on the collective behavior of an ensemble of coarsening particles was also investigated. It was found that any arbitrary distribution of particle radii will tend to a specific time independent distribution when the particle radii are scaled by the average particle radius. Furthermore, it was determined that with increasing volume fraction of coarsening phase, these time independent distributions become broader and more symmetric. It was also found that the ripening kinetics, as measured by the growth rate of the average particle size, increases by a factor of five upon increasing the volume fraction of coarsening phase from zero to 0.5
Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Shingo; Namekata, Naoto, E-mail: nnao@phys.cst.nihon-u.ac.jp; Inoue, Shuichiro [Institute of Quantum Science, Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308 (Japan); Tsujino, Kenji [Tokyo Women' s Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666 (Japan)
2014-01-27
We report on visible light single photon detection using a sinusoidally-gated silicon avalanche photodiode. Detection efficiency of 70.6% was achieved at a wavelength of 520 nm when an electrically cooled silicon avalanche photodiode with a quantum efficiency of 72.4% was used, which implies that a photo-excited single charge carrier in a silicon avalanche photodiode can trigger a detectable avalanche (charge) signal with a probability of 97.6%.
A probabilistic model for snow avalanche occurrence
Perona, P.; Miescher, A.; Porporato, A.
2009-04-01
Avalanche hazard forecasting is an important issue in relation to the protection of urbanized environments, ski resorts and of ski-touring alpinists. A critical point is to predict the conditions that trigger the snow mass instability determining the onset and the size of avalanches. On steep terrains the risk of avalanches is known to be related to preceding consistent snowfall events and to subsequent changes in the local climatic conditions. Regression analysis has shown that avalanche occurrence indeed correlates to the amount of snow fallen in consecutive three snowing days and to the state of the settled snow at the ground. Moreover, since different type of avalanches may occur as a result of the interactions of different factors, the process of snow avalanche formation is inherently complex and with some degree of unpredictability. For this reason, although several models assess the risk of avalanche by accounting for all the involved processes with a great detail, a high margin of uncertainty invariably remains. In this work, we explicitly describe such an unpredictable behaviour with an intrinsic noise affecting the processes leading snow instability. Eventually, this sets the basis for a minimalist stochastic model, which allows us to investigate the avalanche dynamics and its statistical properties. We employ a continuous time process with stochastic jumps (snowfalls), deterministic decay (snowmelt and compaction) and state dependent avalanche occurrence (renewals) as a minimalist model for the determination of avalanche size and related intertime occurrence. The physics leading to avalanches is simplified to the extent where only meteorological data and terrain data are necessary to estimate avalanche danger. We explore the analytical formulation of the process and the properties of the probability density function of the avalanche process variables. We also discuss what is the probabilistic link between avalanche size and preceding snowfall event and
Vapor Compressor Driven Hybrid Two-Phase Loop, Phase I
National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project will demonstrate a vapor compressor driven hybrid two-phase loop technology. The hybrid two-phase loop...
Isentropic Compression of Argon
International Nuclear Information System (INIS)
Oona, H.; Solem, J.C.; Veeser, L.R.; Ekdahl, C.A.; Rodriquez, P.J.; Younger, S.M.; Lewis, W.; Turley, W.D.
1997-01-01
We are studying the transition of argon from an insulator to a conductor by compressing the frozen gas isentropically to pressures at which neighboring atomic orbitals overlap sufficiently to allow some electron motion between atoms. Argon and the other rare gases have closed electron shells and therefore remain montomic, even when they solidify. Their simple structure makes it likely that any measured change in conductivity is due to changes in the atomic structure, not in molecular configuration. As the crystal is compressed the band gap closes, allowing increased conductivity. We have begun research to determine the conductivity at high pressures, and it is our intention to determine the compression at which the crystal becomes a metal
International Nuclear Information System (INIS)
Wrobel, W.G.
1981-02-01
The electron-beam-pumped argon eximer laser is investigated and tuned for the first time. The electron beam is generated by means of an improved coaxial field emmision diode in which argon gas is excited with power densities of 0.3 GW/cm 3 for 18 ns. The processes in the excited gas of 20 to 65 bar are described in the context of a kinetic model as a sequence of stationary states. Investigations of the amplified spontaneous emission (superfluorescence) confirm the predictions of this model. Only the absorption due to the excited Ar atoms is anomalously high. Reproducible operation of the argon eximer laser was achieved in a wide pressure range with various resonator arrangements. The wavelength of this shortest wavelength of this shortest wavelength excimer laser is 126 nm, the laser line width approx. 1.7 nm, the pulse length 7 to 13 ns, and the laser power 250 kW. The laser emission is tuned from 123.2 nm to 128.4 nm by two different methods (diffraction grating and prism). This tunable laser is thus the one with the shortest wavelength at present. Its line width is 0.25 to 0.4 nm, and the power ue 1.7 kW. (orig.)
Thermo-fluid dynamics of two-phase flow
Ishii, Mamoru; Ishii, Mamoru; Ishii, M
2006-01-01
Provides a very systematic treatment of two phase flow problems from a theoretical perspectiveProvides an easy to follow treatment of modeling and code devlopemnt of two phase flow related phenomenaCovers new results of two phase flow research such as coverage of fuel cells technology.
One-dimensional transient unequal velocity two-phase flow by the method of characteristics
International Nuclear Information System (INIS)
Rasouli, F.
1981-01-01
An understanding of two-phase flow is important when one is analyzing the accidental loss of coolant or when analyzing industrial processes. If a pipe in the steam generator of a nuclear reactor breaks, the flow will remain critical (or choked) for almost the entire blowdown. For this reason the knowledge of the two-phase maximum (critical) flow rate is important. A six-equation model--consisting of two continuity equations, two energy equations, a mixture momentum equation, and a constitutive relative velocity equation--is solved numerically by the method of characteristics for one-dimensional, transient, two-phase flow systems. The analysis is also extended to the special case of transient critical flow. The six-equation model is used to study the flow of a nonequilibrium sodium-argon system in a horizontal tube in which the nonequilibrium sodium-argon system in a horizontal tube in which the critical flow condition is at the entrance. A four-equation model is used to study the pressure-pulse propagation rate in an isothermal air-water system, and the results that are found are compared with the experimental data. Proper initial and boundary conditions are obtained for the blowdown problem. The energy and mass exchange relations are evaluated by comparing the model predictions with results of void-fraction and heat-transfer experiments. A simplified two-equation model is obtained for the special case of two incompressible phases. This model is used in the preliminary analysis of batch sedimentation. It is also used to predict the shock formation in the gas-solid fluidized bed
Terrain Classification of Norwegian Slab Avalanche Accidents
Hallandvik, Linda; Aadland, Eivind; Vikene, Odd Lennart
2016-01-01
It is difficult to rely on snow conditions, weather, and human factors when making judgments about avalanche risk because these variables are dynamic and complex; terrain, however, is more easily observed and interpreted. Therefore, this study aimed to investigate (1) the type of terrain in which historical fatal snow avalanche accidents in Norway…
Spatial determination of magnetic avalanche ignition points
International Nuclear Information System (INIS)
Jaafar, Reem; McHugh, S.; Suzuki, Yoko; Sarachik, M.P.; Myasoedov, Y.; Zeldov, E.; Shtrikman, H.; Bagai, R.; Christou, G.
2008-01-01
Using time-resolved measurements of local magnetization in the molecular magnet Mn 12 -ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends
Spatial determination of magnetic avalanche ignition points
Energy Technology Data Exchange (ETDEWEB)
Jaafar, Reem; McHugh, S.; Suzuki, Yoko [Physics Department, City College of the City University of New York, New York, NY 10031 (United States); Sarachik, M.P. [Physics Department, City College of the City University of New York, New York, NY 10031 (United States)], E-mail: sarachik@sci.ccny.cuny.edu; Myasoedov, Y.; Zeldov, E.; Shtrikman, H. [Department Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Bagai, R.; Christou, G. [Department of Chemistry, University of Florida, Gainesville, FL 32611 (United States)
2008-03-15
Using time-resolved measurements of local magnetization in the molecular magnet Mn{sub 12}-ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends.
Avalanche photodiodes for ISABELLE detectors
International Nuclear Information System (INIS)
Strand, R.C.
1979-01-01
At ISABELLE some requirements for detecting bursts of photons are not met by standard photomultiplier tubes. The characteristics of immunity to magnetic fields, small size (few mm), low power consumption (approx. 100 mW), insensitivity to optical overloads, and wide dynamic range (approx. 60 dB) are achieved with difficulty, if at all, with PMTs. These are characteristics of the solid state avalanche photodiode (APD), the preferred detector for light-wave communications. Successful field tests with APD detectors stimulated the design of standard optical-fiber communication systems to replace wire carriers by the early 1980's. In other characteristics, i.e., counting rate, pulse-height resolution, effective quantum efficiency, detection efficiency, and reliability, bare APDs are equivalent to standard PMTs. APDs with currently available amplifiers cannot resolve single photoelectrons but they could provide reasonable detection efficiencies and pulse-height resolution for packets of approx. > 100 photons. Commercially available APDs can cost up to 100 times as much as PMTs per active area, but they are potentially much cheaper. Six topics are discussed: (1) detectors for light-wave communication and detectors for particles, (2) avalanche photodiodes, (3) commercially available APDs, (4) dynamic response of PMTs and bare APDs, (5) photon counting with cold APDs, and (6) conclusions and recommendations
Two-phase flow patterns and their relationship to two-phase heat transfer
International Nuclear Information System (INIS)
Hewitt, G.F.
1977-01-01
The objective of this lecture was to discuss the general nature of two phase flows, to define the various regimes of flow and to discuss the influence of these regimes on the heat transfer processes taking place. The methods of regime delineation are briefly described and regime descriptions introduced for both vertical and horizontal flows in tubes. ''Flow regime maps'' have been widely used as an aid to determination of the regime which occurs in a given situation. Some of the more widely used maps are described and the limitations of this approach discussed. There have been many attempts to obtain a better phenomenological description of two phase flow patterns. In this lecture, these attempts will be reviewed in the context of the bubble/plug, plug/churn and churn/annular flow transitions in vertical flow. The latter two transitions are related to the flooding/flow reversal phenomena. For horizontal flows, recent work on the onset of slugging will be reviewed. In flows with evaporation or condensation, the situation is influenced by departures from thermodynamic equilibrium and the types of departure observed are discuss briefly. Flow patterns and their relationships with heat transfer regimes are then reviewed for the case of condensation in horizontal tubes and evaporation in vertical tubes
The Argon Geochronology Experiment (AGE)
Swindle, T. D.; Bode, R.; Fennema, A.; Chutjian, A.; MacAskill, J. A.; Darrach, M. R.; Clegg, S. M.; Wiens, R. C.; Cremers, D.
2006-01-01
This viewgraph presentation reviews the Argon Geochronology Experiment (AGE). Potassium-Argon dating is shown along with cosmic ray dating exposure. The contents include a flow diagram of the Argon Geochronology Experiment, and schematic diagrams of the mass spectrometer vacuum system, sample manipulation mechanism, mineral heater oven, and the quadrupole ion trap mass spectrometer. The Laser-Induced Breakdown Spectroscopy (LIBS) Operation with elemental abundances is also described.
International Nuclear Information System (INIS)
Fabjan, C.W.
1989-01-01
In this paper the viability of liquid-argon calorimetric techniques in the experimental environment of the Superconducting Super Collider (SSC) is briefly analyzed. The authors compare the required and achievable energy resolution with benchmark figures obtained using practical instruments. Comments on the desirable (i.e. required) temporal performance are made and compared with the state of the art. Some of the major engineering challenges are listed, for which solutions will have to be developed if such instruments are to find a place in an SSC experimental area
System identification on two-phase flow stability
International Nuclear Information System (INIS)
Wu Shaorong; Zhang Youjie; Wang Dazhong; Bo Jinghai; Wang Fei
1996-01-01
The theoretical principle, experimental method and results of interrelation analysis identification for the instability of two-phase flow are described. A completely new concept of test technology and method on two-phase flow stability was developed by using he theory of information science on system stability and system identification for two-phase flow stability in thermo-physics field. Application of this method would make it possible to identify instability boundary of two-phase flow under stable operation conditions of two-phase flow system. The experiment was carried out on the thermohydraulic test system HRTL-5. Using reverse repeated pseudo-random sequences of heating power as input signal sources and flow rate as response function in the test, the two-phase flow stability and stability margin of the natural circulation system are investigated. The effectiveness and feasibility of identifying two-phase flow stability by using this system identification method were experimentally demonstrated. Basic data required for mathematics modeling of two-phase flow and analysis of two-phase flow stability were obtained, which are useful for analyzing, monitoring of the system operation condition, and forecasting of two-phase flow stability in engineering system
A review of damping of two-phase flows
International Nuclear Information System (INIS)
Hara, Fumio
1993-01-01
Damping of two-phase flows has been recognized as one of the most unknown parameters in analyzing vibrational characteristics of structures subjected to two-phase flows since it seems to be influenced by many physical parameters involved in the physics of dynamic energy dissipation of a vibrating structure, for example, liquid viscosity, surface tension, flow velocity, mass ratio, frequency, void fraction, flow regime and so forth. This paper deals with a review of scientific works done to date on the damping of two phase flows and discussions about what has been clarified and what has not been known to us, or what kinds of research are needed about two-phase flow damping. The emphasis is put on the definition of two-phase fluid damping, damping measurement techniques, damping characteristics in relation to two phase flow configurations, and damping generation mechanisms
Forced two phase helium cooling of large superconducting magnets
International Nuclear Information System (INIS)
Green, M.A.; Burns, W.A.; Taylor, J.D.
1979-08-01
A major problem shared by all large superconducting magnets is the cryogenic cooling system. Most large magnets are cooled by some variation of the helium bath. Helium bath cooling becomes more and more troublesome as the size of the magnet grows and as geometric constraints come into play. An alternative approach to cooling large magnet systems is the forced flow, two phase helium system. The advantages of two phase cooling in many magnet systems are shown. The design of a two phase helium system, with its control dewar, is presented. The paper discusses pressure drop of a two phase system, stability of a two phase system and the method of cool down of a two phase system. The results of experimental measurements at LBL are discussed. Included are the results of cool down and operation of superconducting solenoids
Gallium-based avalanche photodiode optical crosstalk
International Nuclear Information System (INIS)
Blazej, Josef; Prochazka, Ivan; Hamal, Karel; Sopko, Bruno; Chren, Dominik
2006-01-01
Solid-state single photon detectors based on avalanche photodiode are getting more attention in various areas of applied physics: optical sensors, quantum key distribution, optical ranging and Lidar, time-resolved spectroscopy, X-ray laser diagnostics, and turbid media imaging. Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAsP, and InGaP/InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Trends in demand are focused on detection array construction recently. Even extremely small arrays containing a few cells are of great importance for users. Electrical crosstalk between individual gating and quenching circuits and optical crosstalk between individual detecting cells are serious limitation for array design and performance. Optical crosstalk is caused by the parasitic light emission of the avalanche which accompanies the photon detection process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon- and gallium-based photodiodes. The timing properties and spectral distribution of the emitted light have been measured for different operating conditions to quantify optical crosstalk. We conclude that optical crosstalk is an inherent property of avalanche photodiode operated in Geiger mode. The only way to minimize optical crosstalk in avalanche photodiode array is to build active quenching circuit with minimum response time
Energy and dissipated work in snow avalanches
Bartelt, P.; Buser, O.
2004-12-01
Using the results of large scale avalanche experiments at the Swiss Vallée de la Sionne test site, the energy balance of several snow avalanches is determined. Avalanches convert approximately one-seventh of their potential energy into kinetic energy. The total potential energy depends strongly on the entrained snowcover, indicating that entrainment processes cannot be ignored when predicting terminal velocities and runout distances. We find energy dissipation rates on the order of 1 GW. Fluidization of the fracture slab can be identified in the experiments as an increase in dissipation rate, thereby explaining the initial and rapid acceleration of avalanches after release. Interestingly, the dissipation rates appear to be constant along the track, although large fluctuations in internal velocity exist. Thus, we can demonstrate within the context of non-equilibrium thermodynamics that -- in space -- granular snow avalanches are irreversible, dissipative systems that minimize entropy production because they appear to reach a steady-state non-equilibrium. A thermodynamic analysis reveals that fluctuations in velocity depend on the roughness of the flow surface and viscosity of the granular system. We speculate that this property explains the transition from flowing avalanches to powder avalanches.
Numerical method for two-phase flow discontinuity propagation calculation
International Nuclear Information System (INIS)
Toumi, I.; Raymond, P.
1989-01-01
In this paper, we present a class of numerical shock-capturing schemes for hyperbolic systems of conservation laws modelling two-phase flow. First, we solve the Riemann problem for a two-phase flow with unequal velocities. Then, we construct two approximate Riemann solvers: an one intermediate-state Riemann solver and a generalized Roe's approximate Riemann solver. We give some numerical results for one-dimensional shock-tube problems and for a standard two-phase flow heat addition problem involving two-phase flow instabilities
Argon solubility in liquid steel
Boom, R; Dankert, O; Van Veen, A; Kamperman, AA
2000-01-01
Experiments have been performed to establish the solubility of argon in liquid interstitial-free steel. The solubility appears to be lower than 0.1 at ppb, The results are in line with argon solubilities reported in the literature on liquid iron. Semiempirical theories and calculations based on the
Two-phase-flow cooling concept for fusion reactor blankets
International Nuclear Information System (INIS)
Bender, D.J.; Hoffman, M.A.
1977-01-01
The new two-phase heat transfer medium proposed is a mixture of potassium droplets and helium which permits blanket operation at hih temperature and low pressure, while maintaining acceptable pumping power requirements, coolant ducting size, and blanket structure fractions. A two-phase flow model is described. The helium pumping power and the primary heat transfer loop are discussed
Two-phase flow characterisation by nuclear magnetic resonance
International Nuclear Information System (INIS)
Leblond, J.; Javelot, S.; Lebrun, D.; Lebon, L.
1998-01-01
The results presented in this paper demonstrate the performance of the PFGSE-NMR to obtain a complete characterisation of two-phase flows. Different methods are proposed to characterise air-water flows in different regimes: stationary two-phase flows and flows in transient condition. Finally a modified PFGSE is proposed to analyse the turbulence of air-water bubbly flow. (author)
Unsteady State Two Phase Flow Pressure Drop Calculations
Ayatollahi, Shahaboddin
1992-01-01
A method is presented to calculate unsteady state two phase flow in a gas-liquid line based on a quasi-steady state approach. A computer program for numerical solution of this method was prepared. Results of calculations using the computer program are presented for several unsteady state two phase flow systems
A Complex Solar Coronal Jet with Two Phases
Energy Technology Data Exchange (ETDEWEB)
Chen, Jie; Su, Jiangtao; Deng, Yuanyong [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Priest, E. R., E-mail: chenjie@bao.ac.cn [Mathematical Institute, University of St Andrews, North Haugh, St Andrews, KY16 9SS (United Kingdom)
2017-05-01
Jets often occur repeatedly from almost the same location. In this paper, a complex solar jet was observed with two phases to the west of NOAA AR 11513 on 2012 July 2. If it had been observed at only moderate resolution, the two phases and their points of origin would have been regarded as identical. However, at high resolution we find that the two phases merge into one another and the accompanying footpoint brightenings occur at different locations. The phases originate from different magnetic patches rather than being one phase originating from the same patch. Photospheric line of sight (LOS) magnetograms show that the bases of the two phases lie in two different patches of magnetic flux that decrease in size during the occurrence of the two phases. Based on these observations, we suggest that the driving mechanism of the two successive phases is magnetic cancellation of two separate magnetic fragments with an opposite-polarity fragment between them.
Catastrophic avalanches and methods of their control
Directory of Open Access Journals (Sweden)
N. A. Volodicheva
2014-01-01
Full Text Available Definition of such phenomenon as “catastrophic avalanche” is presented in this arti-cle. Several situations with releases of catastrophic avalanches in mountains of Caucasus, Alps, and Central Asia are investigated. Materials of snow-avalanche ob-servations performed since 1960s at the Elbrus station of the Lomonosov Moscow State University (Central Caucasus were used for this work. Complex-valued measures of engineering protection demonstrating different efficiencies are consid-ered.
Statistics of Electron Avalanches and Streamers
Directory of Open Access Journals (Sweden)
T. Ficker
2007-01-01
Full Text Available We have studied the severe systematic deviations of populations of electron avalanches from the Furry distribution, which has been held to be the statistical law corresponding to them, and a possible explanation has been sought. A new theoretical concept based on fractal avalanche multiplication has been proposed and is shown to be a convenient candidate for explaining these deviations from Furry statistics.
The Argon Dark Matter Experiment
AUTHOR|(CDS)2071720
2009-01-01
The ArDM experiment, a 1 ton liquid argon TPC/Calorimeter, is designed for the detection of dark matter particles which can scatter off the spinless argon nucleus, producing nuclear recoils. These events will be discerned by their light to charge ratio, as well as the time structure of the scintillation light. The experiment is presently under construction and commissioning on surface at CERN. Cryogenic operation and light detection performance was recently confirmed in a test run of the full 1 ton liquid argon target under purely calorimetric operation and with a prototype light readout system. This note describes the experimental concept, the main detector components and presents some first results.
Industrial aspects of gas-liquid two-phase flow
International Nuclear Information System (INIS)
Hewitt, G.F.
1977-01-01
The lecture begins by reviewing the various types of plant in which two phase flow occurs. Specifically, boiling plant, condensing plant and pipelines are reviewed, and the various two phase flow problems occurring in them are described. Of course, many other kinds of chemical engineering plant involve two phase flow, but are somewhat outside the scope of this lecture. This would include distillation columns, vapor-liquid separators, absorption towers etc. Other areas of industrial two phase flow which have been omitted for space reasons from this lecture are those concerned with gas/solids, liquid/solid and liquid/liquid flows. There then follows a description of some of the two phase flow processes which are relevant in industrial equipment and where special problems occur. The topics chosen are as follows: (1) pressure drop; (2) horizontal tubes - separation effects non-uniformites in heat transfer coefficient, effect of bends on dryout; (3) multicomponent mixtures - effects in pool boiling, mass transfer effects in condensation and Marangoni effects; (4) flow distribution - manifold problems in single phase flow, separation effects at a single T-junction in two phase flow and distribution in manifolds in two phase flow; (5) instability - oscillatory instability, special forms of instability in cryogenic systems; (6) nucleate boiling - effect of variability of surface, unresolved problems in forced convective nucleate boiling; and (7) shell side flows - flow patterns, cross flow boiling, condensation in cross flow
Modeling two-phase flow in PEM fuel cell channels
Energy Technology Data Exchange (ETDEWEB)
Wang, Yun; Basu, Suman; Wang, Chao-Yang [Electrochemical Engine Center (ECEC), and Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
2008-05-01
This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-channels of a proton exchange membrane (PEM) fuel cell. Envisaging the mini-channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy's law and the M{sup 2} formalism, which allow estimate of the parameters key to fuel cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel cells are fully discussed: liquid water buildup towards the fuel cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-channels. (author)
Research on one-dimensional two-phase flow
International Nuclear Information System (INIS)
Adachi, Hiromichi
1988-10-01
In Part I the fundamental form of the hydrodynamic basic equations for a one-dimensional two-phase flow (two-fluid model) is described. Discussions are concentrated on the treatment of phase change inertial force terms in the equations of motion and the author's equations of motion which have a remarkable uniqueness on the following three points. (1) To express force balance of unit mass two-phase fluid instead of that of unit volume two-phase fluid. (2) To pick up the unit existing mass and the unit flowing mass as the unit mass of two-phase fluid. (3) To apply the kinetic energy principle instead of the momentum low in the evaluation of steady inertial force term. In these three, the item (1) is for excluding a part of momentum change or kinetic energy change due to mass change of the examined part of fluid, which is independent of force. The item (2) is not to introduce a phenomenological physical model into the evaluation of phase change inertial force term. And the item (3) is for correctly applying the momentum law taking into account the difference of representative velocities between the main flow fluid (vapor phase or liquid phase) and the phase change part of fluid. In Part II, characteristics of various kinds of high speed two-phase flow are clarified theoretically by the basic equations derived. It is demonstrated that the steam-water two-phase critical flow with violent flashing and the airwater two-phase critical flow without phase change can be described with fundamentally the same basic equations. Furthermore, by comparing the experimental data from the two-phase critical discharge test and the theoretical prediction, the two-phase discharge coefficient, C D , for large sharp-edged orifice is determined as the value which is not affected by the experimental facility characteristics, etc. (author)
Regimes of Two-Phase Flow in Short Rectangular Channel
Chinnov, Evgeny A.; Guzanov, Vladimir V.; Cheverda, Vyacheslav; Markovich, Dmitry M.; Kabov, Oleg A.
2009-08-01
Experimental study of two-phase flow in the short rectangular horizontal channel with height 440 μm has been performed. Characteristics of liquid motion inside the channel have been registered and measured by the Laser Induced Fluorescence technique. New information has allowed determining more precisely the characteristics of churn regime and boundaries between different regimes of two-phase flow. It was shown that formation of some two-phase flow regimes and transitions between them are determined by instability of the flow in the lateral parts of the channel.
What types of investors generate the two-phase phenomenon?
Ryu, Doojin
2013-12-01
We examine the two-phase phenomenon described by Plerou, Gopikrishnan, and Stanley (2003) [1] in the KOSPI 200 options market, one of the most liquid options markets in the world. By analysing a unique intraday dataset that contains information about investor type for each trade and quote, we find that the two-phase phenomenon is generated primarily by domestic individual investors, who are generally considered to be uninformed and noisy traders. In contrast, our empirical results indicate that trades by foreign institutions, who are generally considered informed and sophisticated investors, do not exhibit two-phase behaviour.
State of the art: two-phase flow calibration techniques
International Nuclear Information System (INIS)
Stanley, M.L.
1977-01-01
The nuclear community faces a particularly difficult problem relating to the calibration of instrumentation in a two-phase flow steam/water environment. The rationale of the approach to water reactor safety questions in the United States demands that accurate measurements of mass flows in a decompressing two-phase flow be made. An accurate measurement dictates an accurate calibration. This paper addresses three questions relating to the state of the art in two-phase calibration: (1) What do we mean by calibration. (2) What is done now. (3) What should be done
Two-phase-flow models and their limitations
International Nuclear Information System (INIS)
Ishii, M.; Kocamustafaogullari, G.
1982-01-01
An accurate prediction of transient two-phase flow is essential to safety analyses of nuclear reactors under accident conditions. The fluid flow and heat transfer encountered are often extremely complex due to the reactor geometry and occurrence of transient two-phase flow. Recently considerable progresses in understanding and predicting these phenomena have been made by a combination of rigorous model development, advanced computational techniques, and a number of small and large scale supporting experiments. In view of their essential importance, the foundation of various two-phase-flow models and their limitations are discussed in this paper
Thermo-Fluid Dynamics of Two-Phase Flow
Ishii, Mamrou
2011-01-01
"Thermo-fluid Dynamics of Two-Phase Flow, Second Edition" is focused on the fundamental physics of two-phase flow. The authors present the detailed theoretical foundation of multi-phase flow thermo-fluid dynamics as they apply to: Nuclear reactor transient and accident analysis; Energy systems; Power generation systems; Chemical reactors and process systems; Space propulsion; Transport processes. This edition features updates on two-phase flow formulation and constitutive equations and CFD simulation codes such as FLUENT and CFX, new coverage of the lift force model, which is of part
The Liquid Argon Purity Demonstrator
Energy Technology Data Exchange (ETDEWEB)
Adamowski, M.; Carls, B.; Dvorak, E.; Hahn, A.; Jaskierny, W.; Johnson, C.; Jostlein, H.; Kendziora, C.; Lockwitz, S.; Pahlka, B.; Plunkett, R.; Pordes, S.; Rebel, B.; Schmitt, R.; Stancari, M.; Tope, T.; Voirin, E.; Yang, T.
2014-07-01
The Liquid Argon Purity Demonstrator was an R&D test stand designed to determine if electron drift lifetimes adequate for large neutrino detectors could be achieved without first evacuating the cryostat. We describe here the cryogenic system, its operations, and the apparatus used to determine the contaminant levels in the argon and to measure the electron drift lifetime. The liquid purity obtained by this system was facilitated by a gaseous argon purge. Additionally, gaseous impurities from the ullage were prevented from entering the liquid at the gas-liquid interface by condensing the gas and filtering the resulting liquid before returning to the cryostat. The measured electron drift lifetime in this test was greater than 6 ms, sustained over several periods of many weeks. Measurements of the temperature profile in the argon, to assess convective flow and boiling, were also made and are compared to simulation.
Transient two-phase performance of LOFT reactor coolant pumps
International Nuclear Information System (INIS)
Chen, T.H.; Modro, S.M.
1983-01-01
Performance characteristics of Loss-of-Fluid Test (LOFT) reactor coolant pumps under transient two-phase flow conditions were obtained based on the analysis of two large and small break loss-of-coolant experiments conducted at the LOFT facility. Emphasis is placed on the evaluation of the transient two-phase flow effects on the LOFT reactor coolant pump performance during the first quadrant operation. The measured pump characteristics are presented as functions of pump void fraction which was determined based on the measured density. The calculated pump characteristics such as pump head, torque (or hydraulic torque), and efficiency are also determined as functions of pump void fractions. The importance of accurate modeling of the reactor coolant pump performance under two-phase conditions is addressed. The analytical pump model, currently used in most reactor analysis codes to predict transient two-phase pump behavior, is assessed
Two-phase systems. Fundamentals and industrial applications
International Nuclear Information System (INIS)
Woillez, Jacques
2014-01-01
Two-phase flows are omnipresent in industrial processes in different sectors with the behaviour and control of non-mixing mixtures of gas and liquids, of several liquids, of solids and fluids which are present in the production of raw materials, in the environment, in energy production, in chemistry, in pharmaceutical or food industry. The author presents the fundamentals elements which are needed to perform hardware predictive calculations and to understand typical phenomena associated with these flows. The chapters address fluids mechanics (movement equations, Bernoulli equation, load losses, turbulence, heat exchange coefficients, thermodynamics, compressible flows), two-phase systems (characteristic values, modes of appearance of two-phase flows, conduct flows, suspension mechanics, mass transfers, similarity, numerical simulation), the applications (energy production, agitation and mixing, phase separation, sprays), and peculiar phenomena (Marangoni effect, the tea cup effect, entry jets, water hammer effect, sound speed, two-phase pumping, fluidization)
Visual Analysis of Inclusion Dynamics in Two-Phase Flow.
Karch, Grzegorz Karol; Beck, Fabian; Ertl, Moritz; Meister, Christian; Schulte, Kathrin; Weigand, Bernhard; Ertl, Thomas; Sadlo, Filip
2018-05-01
In single-phase flow visualization, research focuses on the analysis of vector field properties. In two-phase flow, in contrast, analysis of the phase components is typically of major interest. So far, visualization research of two-phase flow concentrated on proper interface reconstruction and the analysis thereof. In this paper, we present a novel visualization technique that enables the investigation of complex two-phase flow phenomena with respect to the physics of breakup and coalescence of inclusions. On the one hand, we adapt dimensionless quantities for a localized analysis of phase instability and breakup, and provide detailed inspection of breakup dynamics with emphasis on oscillation and its interplay with rotational motion. On the other hand, we present a parametric tightly linked space-time visualization approach for an effective interactive representation of the overall dynamics. We demonstrate the utility of our approach using several two-phase CFD datasets.
Metrology of two-phase flow: different methods
International Nuclear Information System (INIS)
Delhaye, J.M.; Galaup, J.P.; Reocreux, M.; Ricque, R.
Nine papers are presented concerning different methods of measuring two-phase flow. Some of the methods and equipment discussed include: radiation absorption, electromagnetic flowmeter, anemometry, resistance probes, phase indicating microthermocouples, optical probes, sampling methods, and pitot tubes
Qualitative behaviour of incompressible two-phase flows with phase ...
Indian Academy of Sciences (India)
Jan Prüss
2017-11-07
Nov 7, 2017 ... Qualitative behaviour of incompressible two-phase flows with phase ... Germany. 2Graduate School of Human and Environmental Studies, Kyoto University, ... Note that j is a dummy variable as it can be eliminated from the ...
Two-phase flow patterns in horizontal rectangular minichannel
Directory of Open Access Journals (Sweden)
Ron’shin Fedor
2016-01-01
Full Text Available The two-phase flow in a short horizontal channel of rectangular cross-section of 1 × 19 mm2 has been studied experimentally. Five conventional two-phase flow patterns have been detected (bubble, churn, stratified, annular and jet and transitions between them have been determined. It is shown that a change in the width of the horizontal channels has a substantial effect on the boundaries between the flow regimes.
Refrigeration. Two-Phase Flow. Flow Regimes and Pressure Drop
DEFF Research Database (Denmark)
Knudsen, Hans-Jørgen Høgaard
2002-01-01
The note gives the basic definitions used in two-phase flow. Flow regimes and flow regimes map are introduced. The different contributions to the pressure drop are stated together with an imperical correlation from the litterature.......The note gives the basic definitions used in two-phase flow. Flow regimes and flow regimes map are introduced. The different contributions to the pressure drop are stated together with an imperical correlation from the litterature....
Stochastic modelling of two-phase flows including phase change
International Nuclear Information System (INIS)
Hurisse, O.; Minier, J.P.
2011-01-01
Stochastic modelling has already been developed and applied for single-phase flows and incompressible two-phase flows. In this article, we propose an extension of this modelling approach to two-phase flows including phase change (e.g. for steam-water flows). Two aspects are emphasised: a stochastic model accounting for phase transition and a modelling constraint which arises from volume conservation. To illustrate the whole approach, some remarks are eventually proposed for two-fluid models. (authors)
Two-phase cooling fluids; Les fluides frigoporteurs diphasiques
Energy Technology Data Exchange (ETDEWEB)
Lallemand, A. [Institut National des Sciences Appliquees (INSA), 69 - Lyon (France)
1997-12-31
In the framework of the diminution of heat transfer fluid consumption, the concept of indirect refrigerating circuits, using cooling intermediate fluids, is reviewed and the fluids that are currently used in these systems are described. Two-phase cooling fluids advantages over single-phase fluids are presented with their thermophysical characteristics: solid fraction, two-phase mixture enthalpy, thermal and rheological properties, determination of heat and mass transfer characteristics, and cold storage through ice slurry
Review on two-phase flow instabilities in narrow spaces
International Nuclear Information System (INIS)
Tadrist, L.
2007-01-01
Instabilities in two-phase flow have been studied since the 1950s. These phenomena may appear in power generation and heat transfer systems where two-phase flow is involved. Because of thermal management in small size systems, micro-fluidics plays an important role. Typical processes must be considered when the channel hydraulic diameter becomes very small. In this paper, a brief review of two-phase flow instabilities encountered in channels having hydraulic diameters greater than 10 mm are presented. The main instability types are discussed according to the existing experimental results and models. The second part of the paper examines two-phase flow instabilities in narrow spaces. Pool and flow boiling cases are considered. Experiments as well as theoretical models existing in the literature are examined. It was found that several experimental works evidenced these instabilities meanwhile only limited theoretical developments exist in the literature. In the last part of the paper an interpretation of the two-phase flow instabilities linked to narrow spaces are presented. This approach is based on characteristic time scales of the two-phase flow and bubble growth in the capillaries
A parallel plate avalanche chamber for relativistic heavy ions
International Nuclear Information System (INIS)
Burgei, R.
1989-01-01
In order to determine the interaction point of relativistic heavy ions in the Diogene target, we have built and tested an X-Y low pressure parallel plate avalanche chamber. It uses three thin metallized foils and is filled with isobutane. A preliminary study shows that it is the only detector with the required specifications: efficiency, accurate position determination and a small uniform amount of material for the particle beam to go through. The electronics system is designed for reliability, easy adjustments and high stability. The interaction point is given on delay-line read-out. This represents the optimum compromise between low price and good performance. Laboratory measurements of gain, efficiency and position accuracy are done with an alpha-particle source. Two of these detectors are working at the Saturne National Laboratory. They allow the trajectory of several tens of particles (among a million per second) to be reconstructed. With an argon beam at 400 MeV per nucleon, the position uncertainty in the target has been measured to be 0.5 mm (standard deviation). This uncertainty is 0.3 mm for each detector, with an efficiency of 94 per cent. Our set-up, which is now operational, improves the accuracy of the results and speed of analysis of Diogene experiments devoted to the study of central collisions between heavy ions [fr
Contribution to the theory of the two phase blowdown phenomenon
International Nuclear Information System (INIS)
Hutcherson, M.N.
1975-12-01
In order to accurately model the two phase portion of a pressure vessel blowdown, it becomes necessary to understand the bubble growth mechanism within the vessel during the early period of the decompression, the two phase flow behavior within the vessel, and the applicability of the available two phase critical flow models to the blowdown transient. To aid in providing answers to such questions, a small scale, separate effects, isothermal blowdown experiment has been conducted in a small pressure vessel. The tests simulated a full open, double ended, guillotine break in a large diameter, short exhaust duct from the vessel. The vaporization process at the initiation of the decompression is apparently that of thermally dominated bubble growth originating from the surface cavities inside the system. Thermodynamic equilibrium of the remaining fluid within the vessel existed in the latter portion of the decompression. A nonuniform distribution of fluid quality within the vessel was also detected in this experiment. By comparison of the experimental results from this and other similar transient, two phase critical flow studies with steady state, small duct, two phase critical flow data, it is shown that transient, two phase critical flow in large ducts appears to be similar to steady state, two phase critical flow in small ducts. Analytical models have been developed to predict the blowdown characteristics of a system during subcooled decompression, the bubble growth regime of blowdown, and also in the nearly dispersed period of depressurization. This analysis indicates that the system pressure history early in the blowdown is dependent on the internal vessel surface area, the internal vessel volume, and also on the exhaust flow area from the system. This analysis also illustrates that the later period of decompression can be predicted based on thermodynamic equilibrium
Fluid-elastic vibration in two-phase cross flow
International Nuclear Information System (INIS)
Sasakawa, T.; Serizawa, A.; Kawara, Z.
2003-01-01
The present work aims at clarifying the mechanisms of fluid elastic vibration of tube bundles in two-phase cross flow. The experiment is conducted using air-water two-phase flow under atmospheric pressure. The test section is a 1.03m long transparent acrylic square duct with 128 x 128 mm 2 cross section, which consists of 3 rod-rows with 5 rods in each row. The rods are 125mm long aluminum rods with 22 mm in diameter (p/D=1.45). The natural frequency of rod vibration is about 30Hz. The result indicated a diversion of observed trend in vibration behavior depending on two-phase flow patterns either bubbly flow or churn flow. Specifically, in churn flow, the fluid elastic vibration has been observed to occur when the frequency in void fraction fluctuation approached to the natural frequency of the rods, but this was not the case in fluid elastic vibration in bubbly flow. This fact suggests the existence of mechanisms closely coupled with two-phase flow structures depending on the flow patterns, that is, static two-phase character-controlled mechanism in bubbly flow and dynamic character- controlled in churn flow
Two-phase flow induced parametric vibrations in structural systems
International Nuclear Information System (INIS)
Hara, Fumio
1980-01-01
This paper is divided into two parts concerning piping systems and a nuclear fuel pin system. The significant experimental results concerning the random vibration induced in an L-shaped pipe by air-water two-phase flow and the theoretical analysis of the vibration are described in the first part. It was clarified for the first time that the parametric excitation due to the periodic changes of system mass, centrifugal force and Coriolis force was the mechanism of exciting the vibration. Moreover, the experimental and theoretical analyses of the mechanism of exciting vibration by air-water two-phase flow in a straight, horizontal pipe were carried out, and the first natural frequency of the piping system was strongly related to the dominant frequency of void signals. The experimental results on the vibration of a nuclear fuel pin model in parallel air-water two-phase flow are reported in the latter part. The relations between vibrational strain variance and two-phase flow velocity or pressure fluctuation, and the frequency characteristics of vibrational strain variance were obtained. The theoretical analysis of the dynamic interaction between air-water two-phase flow and a fuel pin structure, and the vibrational instability of fuel pins in alternate air and water slugs or in large bubble flow are also reported. (Kako, I.)
Experimental investigation two phase flow in direct methanol fuel cells
International Nuclear Information System (INIS)
Mat, M. D.; Kaplan, Y.; Celik, S.; Oeztural, A.
2007-01-01
Direct methanol fuel cells (DMFC) have received many attentions specifically for portable electronic applications since it utilize methanol which is in liquid form in atmospheric condition and high energy density of the methanol. Thus it eliminates the storage problem of hydrogen. It also eliminates humidification requirement of polymeric membrane which is a problem in PEM fuel cells. Some electronic companies introduced DMFC prototypes for portable electronic applications. Presence of carbon dioxide gases due to electrochemical reactions in anode makes the problem a two phase problem. A two phase flow may occur at cathode specifically at high current densities due to the excess water. Presence of gas phase in anode region and liquid phase in cathode region prevents diffusion of fuel and oxygen to the reaction sites thus reduces the performance of the system. Uncontrolled pressure buildup in anode region increases methanol crossover through membrane and adversely effect the performance. Two phase flow in both anode and cathode region is very effective in the performance of DMYC system and a detailed understanding of two phase flow for high performance DMFC systems. Although there are many theoretical and experimental studies available on the DMFC systems in the literature, only few studies consider problem as a two-phase flow problem. In this study, an experimental set up is developed and species distributions on system are measured with a gas chromatograph. System performance characteristics (V-I curves) is measured depending on the process parameters (temperature, fuel ad oxidant flow rates, methanol concentration etc)
Relating rock avalanche morphology to emplacement processes
Dufresne, Anja; Prager, Christoph; Bösmeier, Annette
2015-04-01
The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite
Criticality and avalanches in neural networks
International Nuclear Information System (INIS)
Zare, Marzieh; Grigolini, Paolo
2013-01-01
Highlights: • Temporal criticality is used as criticality indicator. • The Mittag–Leffler function is proposed as a proper form of temporal complexity. • The distribution of avalanche size becomes scale free in the supercritical state. • The scale-free distribution of avalanche sizes is an epileptic manifestation. -- Abstract: Experimental work, both in vitro and in vivo, reveals the occurrence of neural avalanches with an inverse power law distribution in size and time duration. These properties are interpreted as an evident manifestation of criticality, thereby suggesting that the brain is an operating near criticality complex system: an attractive theoretical perspective that according to Gerhard Werner may help to shed light on the origin of consciousness. However, a recent experimental observation shows no clear evidence for power-law scaling in awake and sleeping brain of mammals, casting doubts on the assumption that the brain works at criticality. This article rests on a model proposed by our group in earlier publications to generate neural avalanches with the time duration and size distribution matching the experimental results on neural networks. We now refine the analysis of the time distance between consecutive firing bursts and observe the deviation of the corresponding distribution from the Poisson statistics, as the system moves from the non-cooperative to the cooperative regime. In other words, we make the assumption that the genuine signature of criticality may emerge from temporal complexity rather than from the size and time duration of avalanches. We argue that the Mittag–Leffler (ML) exponential function is a satisfactory indicator of temporal complexity, namely of the occurrence of non-Poisson and renewal events. The assumption that the onset of criticality corresponds to the birth of renewal non-Poisson events establishes a neat distinction between the ML function and the power law avalanches generating regime. We find that
Phase avalanches in near-adiabatic evolutions
International Nuclear Information System (INIS)
Vertesi, T.; Englman, R.
2006-01-01
In the course of slow, nearly adiabatic motion of a system, relative changes in the slowness can cause abrupt and high magnitude phase changes, ''phase avalanches,'' superimposed on the ordinary geometric phases. The generality of this effect is examined for arbitrary Hamiltonians and multicomponent (>2) wave packets and is found to be connected (through the Blaschke term in the theory of analytic signals) to amplitude zeros in the lower half of the complex time plane. Motion on a nonmaximal circle on the Poincare-sphere suppresses the effect. A spectroscopic transition experiment can independently verify the phase-avalanche magnitudes
Beyond Critical Exponents in Neuronal Avalanches
Friedman, Nir; Butler, Tom; Deville, Robert; Beggs, John; Dahmen, Karin
2011-03-01
Neurons form a complex network in the brain, where they interact with one another by firing electrical signals. Neurons firing can trigger other neurons to fire, potentially causing avalanches of activity in the network. In many cases these avalanches have been found to be scale independent, similar to critical phenomena in diverse systems such as magnets and earthquakes. We discuss models for neuronal activity that allow for the extraction of testable, statistical predictions. We compare these models to experimental results, and go beyond critical exponents.
Real time avalanche detection for high risk areas.
2014-12-01
Avalanches routinely occur on State Highway 21 (SH21) between Lowman and Stanley, Idaho each winter. The avalanches pose : a threat to the safety of maintenance workers and the traveling public. A real-time avalanche detection system will allow the :...
Two-Phase Phenomena In Wet Flue Gas Desulfurization Process
International Nuclear Information System (INIS)
Minzer, U.; Moses, E.J.; Toren, M.; Blumenfeld, Y.
1998-01-01
In order to reduce sulfur oxides discharge, Israel Electric Corporation (IEC) is building a wet Flue Gas Desulfurization (FGD) facility at Rutenberg B power station. The primary objective of IEC is to minimize the occurrence of stack liquid discharge and avoid the discharge of large droplets, in order to prevent acid rain around the stack. Liquid discharge from the stack is the integrated outcome of two-phase processes, which are discussed in this work. In order to estimate droplets discharge the present investigation employs analytical models, empirical tests, and numerical calculations of two-phase phenomena. The two-phase phenomena are coupled and therefore cannot be investigated separately. The present work concerns the application of Computational Fluid Dynamic (CFD) as an engineering complementary tool in the IEC investigation
DISTRIBUTION OF TWO-PHASE FLOW IN A DISTRIBUTOR
Directory of Open Access Journals (Sweden)
AZRIDJAL AZIZ
2012-02-01
Full Text Available The flow configuration and distribution behavior of two-phase flow in a distributor made of acrylic resin have been investigated experimentally. In this study, air and water were used as two-phase flow working fluids. The distributor consists of one inlet and two outlets, which are set as upper and lower, respectively. The flow visualization at the distributor was made by using a high–speed camera. The flow rates of air and water flowing out from the upper and lower outlet branches were measured. Effects of inclination angle of the distributor were investigated. By changing the inclination angle from vertical to horizontal, uneven distributions were also observed. The distribution of two-phase flow through distributor tends even flow distribution on the vertical position and tends uneven distribution on inclined and horizontal positions. It is shown that even distribution could be achieved at high superficial velocities of both air and water.
Mathematical modeling of disperse two-phase flows
Morel, Christophe
2015-01-01
This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, a...
Two-phase flow characteristics analysis code: MINCS
International Nuclear Information System (INIS)
Watanabe, Tadashi; Hirano, Masashi; Akimoto, Masayuki; Tanabe, Fumiya; Kohsaka, Atsuo.
1992-03-01
Two-phase flow characteristics analysis code: MINCS (Modularized and INtegrated Code System) has been developed to provide a computational tool for analyzing two-phase flow phenomena in one-dimensional ducts. In MINCS, nine types of two-phase flow models-from a basic two-fluid nonequilibrium (2V2T) model to a simple homogeneous equilibrium (1V1T) model-can be used under the same numerical solution method. The numerical technique is based on the implicit finite difference method to enhance the numerical stability. The code structure is highly modularized, so that new constitutive relations and correlations can be easily implemented into the code and hence evaluated. A flow pattern can be fixed regardless of flow conditions, and state equations or steam tables can be selected. It is, therefore, easy to calculate physical or numerical benchmark problems. (author)
Assessing the importance of terrain parameters on glide avalanche release
Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.
2014-01-01
Glide snow avalanches are dangerous and difficult to predict. Despite recent research there is still a lack of understanding regarding the controls of glide avalanche release. Glide avalanches often occur in similar terrain or the same locations annually and observations suggest that topography may be critical. Thus, to gain an understanding of the terrain component of these types of avalanches we examined terrain parameters associated with glide avalanche release as well as areas of consistent glide crack formation but no subsequent avalanches. Glide avalanche occurrences visible from the Going-to-the-Sun Road corridor in Glacier National Park, Montana from 2003-2013 were investigated using an avalanche database derived of daily observations each year from April 1 to June 15. This yielded 192 glide avalanches in 53 distinct avalanche paths. Each avalanche occurrence was digitized in a GIS using satellite, oblique, and aerial imagery as reference. Topographical parameters such as area, slope, aspect, elevation and elevation were then derived for the entire dataset utilizing GIS tools and a 10m DEM. Land surface substrate and surface geology were derived from National Park Service Inventory and Monitoring maps and U.S. Geological Survey surface geology maps, respectively. Surface roughness and glide factor were calculated using a four level classification index. . Then, each avalanche occurrence was aggregated to general avalanche release zones and the frequencies were compared. For this study, glide avalanches released in elevations ranging from 1300 to 2700 m with a mean aspect of 98 degrees (east) and a mean slope angle of 38 degrees. The mean profile curvature for all glide avalanches was 0.15 and a plan curvature of -0.01, suggesting a fairly linear surface (i.e. neither convex nor concave). The glide avalanches occurred in mostly bedrock made up of dolomite and limestone slabs and talus deposits with very few occurring in alpine meadows. However, not all glide
Assessing the importance of terrain parameters on glide avalanche release
Peitzsch, E.; Hendrikx, J.; Fagre, D. B.
2013-12-01
Glide snow avalanches are dangerous and difficult to predict. Despite recent research there is still a lack of understanding regarding the controls of glide avalanche release. Glide avalanches often occur in similar terrain or the same locations annually and observations suggest that topography may be critical. Thus, to gain an understanding of the terrain component of these types of avalanches we examined terrain parameters associated with glide avalanche release as well as areas of consistent glide crack formation but no subsequent avalanches. Glide avalanche occurrences visible from the Going-to-the-Sun Road corridor in Glacier National Park, Montana from 2003-2013 were investigated using an avalanche database derived of daily observations each year from April 1 to June 15. This yielded 192 glide avalanches in 53 distinct avalanche paths. Each avalanche occurrence was digitized in a GIS using satellite, oblique, and aerial imagery as reference. Topographical parameters such as area, slope, aspect, elevation and elevation were then derived for the entire dataset utilizing GIS tools and a 10m DEM. Land surface substrate and surface geology were derived from National Park Service Inventory and Monitoring maps and U.S. Geological Survey surface geology maps, respectively. Surface roughness and glide factor were calculated using a four level classification index. . Then, each avalanche occurrence was aggregated to general avalanche release zones and the frequencies were compared. For this study, glide avalanches released in elevations ranging from 1300 to 2700 m with a mean aspect of 98 degrees (east) and a mean slope angle of 38 degrees. The mean profile curvature for all glide avalanches was 0.15 and a plan curvature of -0.01, suggesting a fairly linear surface (i.e. neither convex nor concave). The glide avalanches occurred in mostly bedrock made up of dolomite and limestone slabs and talus deposits with very few occurring in alpine meadows. However, not all glide
Behavior of pumps conveying two-phase liquid flow
International Nuclear Information System (INIS)
Grison, Pierre; Lauro, J.-F.
1979-01-01
Determination of the two-phase flow (critical or otherwise) through a pump is an essential requirement for complete description of a loss of primary coolant accident in a PWR plant. Theoretical and experimental research at Electricite de France on this subject is described and problems associated with the introduction of a two-phase fluid (with mass transfer) are discussed, with an attempt to single out new phenomena involved and establish their effect on pump behavior. A complementary experimental investigation is described and the results of tests at pressures and temperatures up to 120 bars and 320 0 C respectively are compared with the theoretical model data [fr
Behavior of pumps conveying two-phase liquid flow
Energy Technology Data Exchange (ETDEWEB)
Grison, P; Lauro, J F [Electricite de France, 78 - Chatou. Direction des Etudes et Recherches
1979-01-01
Determination of the two-phase flow (critical or otherwise) through a pump is an essential requirement for complete description of a loss of primary coolant accident in a PWR plant. Theoretical and experimental research at Electricite de France on this subject is described and problems associated with the introduction of a two-phase fluid (with mass transfer) are discussed, with an attempt to single out new phenomena involved and establish their effect on pump behavior. A complementary experimental investigation is described and the results of tests at pressures and temperatures up to 120 bars and 320/sup 0/C respectively are compared with the theoretical model data.
Dynamic Modeling of Phase Crossings in Two-Phase Flow
DEFF Research Database (Denmark)
Madsen, Søren; Veje, Christian; Willatzen, Morten
2012-01-01
by a high resolution finite difference scheme due to Kurganov and Tadmore. The homogeneous formulation requires a set of thermodynamic relations to cover the entire range from liquid to gas state. This leads a number of numerical challenges since these relations introduce discontinuities in the derivative...... of the variables and are usually very slow to evaluate. To overcome these challenges, we use an interpolation scheme with local refinement. The simulations show that the method handles crossing of the saturation lines for both liquid to two-phase and two-phase to gas regions. Furthermore, a novel result obtained...
Two-phase LMMHD mixer-development experiments
International Nuclear Information System (INIS)
Fabris, G.; Dunn, P.F.; Chow, J.C.F.
1978-01-01
The results of a series of experiments conducted to evaluate the fluid mechanical performance of various two-phase LMMHD mixer designs are presented. The results from both flow visualization studies of the local two-phase flows downstream from various mixer-element configurations and local measurements performed to characterize these flows are presented. A conceptual LMMHD mixer design is described that insures the generation of small bubbles, prevents the formation of gas slugs and separated regions, and favors the stabilization of a homogeneous foam flow
Shock wave of vapor-liquid two-phase flow
Institute of Scientific and Technical Information of China (English)
Liangju ZHAO; Fei WANG; Hong GAO; Jingwen TANG; Yuexiang YUAN
2008-01-01
The shock wave of vapor-liquid two-phase flow in a pressure-gain steam injector is studied by build-ing a mathematic model and making calculations. The results show that after the shock, the vapor is nearly com-pletely condensed. The upstream Mach number and the volume ratio of vapor have a great effect on the shock. The pressure and Mach number of two-phase shock con-form to the shock of ideal gas. The analysis of available energy shows that the shock is an irreversible process with entropy increase.
Two-phase flow model with nonequilibrium and critical flow
International Nuclear Information System (INIS)
Sureau, H.; Houdayer, G.
1976-01-01
The model proposed includes the three conservation equations (mass, momentum, energy) applied to the two phase flows and a fourth partial derivative equation which takes into account the nonequilibriums and describes the mass transfer process. With this model, the two phase critical flow tests performed on the Moby-Dick loop (CENG) with several geometries, are interpreted by a unique law. Extrapolations to industrial dimension problems show that geometry and size effects are different from those obtained with earlier models (Zaloudek, Moody, Fauske) [fr
A void fraction model for annular two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Tandon, T.N.; Gupta, C.P.; Varma, H.K.
1985-01-01
An analytical model has been developed for predicting void fraction in two-phase annular flow. In the analysis, the Lockhart-Martinelli method has been used to calculate two-phase frictional pressure drop and von Karman's universal velocity profile is used to represent the velocity distribution in the annular liquid film. Void fractions predicted by the proposed model are generally in good agreement with a available experimental data. This model appears to be as good as Smith's correlation and better than the Wallis and Zivi correlations for computing void fraction.
Mechanistic multidimensional analysis of horizontal two-phase flows
International Nuclear Information System (INIS)
Tselishcheva, Elena A.; Antal, Steven P.; Podowski, Michael Z.
2010-01-01
The purpose of this paper is to discuss the results of analysis of two-phase flow in horizontal tubes. Two flow situations have been considered: gas/liquid flow in a long straight pipe, and similar flow conditions in a pipe with 90 deg. elbow. The theoretical approach utilizes a multifield modeling concept. A complete three-dimensional two-phase flow model has been implemented in a state-of-the-art computational multiphase fluid dynamics (CMFD) computer code, NPHASE. The overall model has been tested parametrically. Also, the results of NPHASE simulations have been compared against experimental data for a pipe with 90 deg. elbow.
Energy Technology Data Exchange (ETDEWEB)
Sim, Woo Gun; Dagdan, Banzragch [Hannam Univ., Daejeon (Korea, Republic of)
2017-03-15
Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.
Modelling electroluminescence in liquid argon
International Nuclear Information System (INIS)
Stewart, D Y; Barker, G J; Bennieston, A J; Harrison, P F; McConkey, N; Morgan, B; Ramachers, Y A; Lightfoot, P K; Robinson, M; Spooner, N J C; Thompson, L
2010-01-01
We present Monte-Carlo simulations of electron transport through liquid argon motivated by our recent observation of electroluminescence light emanating from a thick gaseous electron multiplier (THGEM) in a liquid argon volume. All known elastic and inelastic reaction cross-sections have been accounted for, providing electroluminescence light yield predictions for arbitrary electrostatic fields. This study concludes that the large field gradients needed to produce electroluminescence cannot be accounted for by straightforward electrostatic field calculations based on ideal THGEM holes, suggesting that further experimental investigations are required.
Pre-breakdown light emission phenomena in low-pressure argon between parabolic electrodes
Energy Technology Data Exchange (ETDEWEB)
Wagenaars, E [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Perriens, N W B [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Brok, W J M [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Bowden, M D [Department of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA (United Kingdom); Veldhuizen, E M van [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Kroesen, G M W [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)
2006-09-07
An experimental study on pre-breakdown light emission in low-pressure argon gas was performed. In a pulsed discharge, pre-breakdown phenomena were observed for repetition rates between 100 and 2000 Hz and pulse duration of 100 {mu}s. These phenomena were studied with time-resolved emission imaging using an intensified charge coupled device camera. The origin of the pre-breakdown emission was identified as diffusion of volume charges left over from previous discharges. These charges were accelerated towards the anode in small electron avalanches causing excitation of argon atoms. Different spatial distributions of the pre-breakdown light emission for different times between discharges were measured and the effects of the pre-breakdown phenomena on the main breakdown phase were studied using a double voltage pulse. The observed effects were attributed to the distribution of volume charges, left over from previous discharges, in the discharge gap during the pre-breakdown phase.
Oscillatory regime of avalanche particle detectors
International Nuclear Information System (INIS)
Lukin, K.A.; Cerdeira, H.A.; Colavita, A.A.
1995-06-01
We describe the model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. We show that this detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out. (author). 15 refs, 7 figs
Avalanches in a Bose-Einstein condensate
Schuster, J.; Marte, A.; Amtage, S.; Sang, B.; Rempe, G.; Beijerinck, H.C.W.
2001-01-01
Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large 87Rb condensate. We show that the collisional opacity of an ultracold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under
Microgravity two-phase flow and heat transfer
Gabriel, Kamiel S
2007-01-01
Advances in understanding the behaviour of multiphase thermal systems could lead to higher efficiency energy production systems, but such advances have been greatly hindered by the strong effect of gravitational acceleration on the flow. This book presents a coverage of various aspects of two-phase flow behaviour in the virtual absence of gravity.
Approximate characteristics for one-dimensional two-phase flows
International Nuclear Information System (INIS)
Sarayloo, A.; Peddleson, J.
1985-01-01
An approximate method for determining the characteristics associated with one-dimensional particulate two-phase flow models is presented. The method is based on iteration and is valid for small particulate volume fractions. The method is applied to several special cases involving incompressible particles suspended in a gas. The influences of certain changes in the physical model are investigated
TWO-PHASE EJECTOR of CARBON DIOXIDE HEAT PUMP CALCULUS
Directory of Open Access Journals (Sweden)
Sit B.M.
2010-12-01
Full Text Available It is presented the calculus of the two-phase ejector for carbon dioxide heat pump. The method of calculus is based on the method elaborated by S.M. Kandil, W.E. Lear, S.A. Sherif, and is modified taking into account entrainment ratio as the input for the calculus.
Stability of equilibria for a two-phase osmosis model
Lippoth, F.; Prokert, G.
2012-01-01
For a two-phase moving boundary problem modelling the motion of a semipermeable membrane by osmotic pressure and surface tension, we prove that the manifold of equilibria is locally exponentially attractive. Our method relies on maximal regularity results for parabolic systems with relaxation type
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
Grandotto Biettoli, M.
2006-04-01
The report presents globally the works done by the author in the thermohydraulic applied to nuclear reactors flows. It presents the studies done to the numerical simulation of the two phase flows in the steam generators and a finite element method to compute these flows. (author)
Determination of bubble parameters in two-phase flow
International Nuclear Information System (INIS)
Oliveira Lira, C.A.B. de.
1980-01-01
A development of a probe-detector system for measurement of bubble parameters like size, rise velocity and void fraction in two-phase flow is presented. The method uses an electro resistivity probe and a compact electronic circuit has been developed for obtain this purpose. (author)
Thermalhydraulic instability analysis of a two phase natural circulation loop
International Nuclear Information System (INIS)
Sesini, Paula Aida
1998-01-01
This work presents an analysis of a loop operating in natural circulation regime. Experiments were done in a rectangular closed circuit in one and two-phase flows. Numerical analysis were performed initially with the CIRNAT code and afterwards with RELAP5/MOD2. The limitations of CIRNAT were studied and new developments for this code are proposed. (author)
Controlling two-phase flow in microfluidic systems using electrowetting
Gu, H.
2011-01-01
Electrowetting (EW)-based digital microfluidic systems (DMF) and droplet-based two-phase flow microfluidic systems (TPF) with closed channels are the most widely used microfluidic platforms. In general, these two approaches have been considered independently. However, integrating the two
One-dimensional two-phase thermal hydraulics (ENSTA course)
International Nuclear Information System (INIS)
Olive, J.
1995-11-01
This course is part of the ENSTA 3rd year thermal hydraulics program (nuclear power option). Its purpose is to provide the theoretical basis and main physical notions pertaining to two-phase flow, mainly focussed on water-steam flows. The introduction describes the physical specificities of these flows, emphasizing their complexity. The mathematical bases are then presented (partial derivative equations), leading to a one-dimensional type, simplified description. Balances drawn up for a pipe length volume are used to introduce the mass conservation. motion and energy equations for each phase. Various postulates used to simplify two-phase models are presented, culminating in homogeneous model definitions and equations, several common examples of which are given. The model is then applied to the calculation of pressure drops in two-phase flows. This involves presenting the models most frequently used to represent pressure drops by friction or due to pipe irregularities, without giving details (numerical values of parameters). This chapter terminates with a brief description of static and dynamic instabilities in two-phase flows. Finally, heat transfer conditions frequently encountered in liquid-steam flows are described, still in the context of a 1D model. This chapter notably includes reference to under-saturated boiling conditions and the various forms of DNB. The empirical heat transfer laws are not discussed in detail. Additional material is appended, some of which is in the form of corrected exercises. (author). 6 appends
Two-phase flow instrumentation and laser beams
International Nuclear Information System (INIS)
Delhaye, J.M.
1976-01-01
Some methods based on laser techniques in order to place emphasis on the relation between measured quantities and the primary variables entering the general equations of two-phase systems are reviewed and summarized. The case where the bubbles or droplets are so small that they act as individual scattering centers is excluded [fr
Two-phase flow instrumentation research at RPI
International Nuclear Information System (INIS)
Lahey, R.T. Jr.; Krycuk, G.
1979-01-01
Novel instrumentation for the measurement of void fraction and phase velocity was developed. An optical digital interferometer and a dual beam x-ray equipment were designed for detection of voids. Pitot tube measurements were made to understand two-phase flow phenomena in liquid phase velocity
Two Phase Flow Split Model for Parallel Channels | Iloeje | Nigerian ...
African Journals Online (AJOL)
The model and code are capable of handling single and two phase flows, steady states and transients, up to ten parallel flow paths, simple and complicated geometries, including the boilers of fossil steam generators and nuclear power plants. A test calculation has been made with a simplified three-channel system ...
A semi-empirical two phase model for rocks
International Nuclear Information System (INIS)
Fogel, M.B.
1993-01-01
This article presents data from an experiment simulating a spherically symmetric tamped nuclear explosion. A semi-empirical two-phase model of the measured response in tuff is presented. A comparison is made of the computed peak stress and velocity versus scaled range and that measured on several recent tuff events
Two-phase alkali-metal experiments in reduced gravity
International Nuclear Information System (INIS)
Antoniak, Z.I.
1986-06-01
Future space missions envision the use of large nuclear reactors utilizing either a single or a two-phase alkali-metal working fluid. The design and analysis of such reactors require state-of-the-art computer codes that can properly treat alkali-metal flow and heat transfer in a reduced-gravity environment. A literature search of relevant experiments in reduced gravity is reported on here, and reveals a paucity of data for such correlations. The few ongoing experiments in reduced gravity are noted. General plans are put forth for the reduced-gravity experiments which will have to be performed, at NASA facilities, with benign fluids. A similar situation exists regarding two-phase alkali-metal flow and heat transfer, even in normal gravity. Existing data are conflicting and indequate for the task of modeling a space reactor using a two-phase alkali-metal coolant. The major features of past experiments are described here. Data from the reduced-gravity experiments with innocuous fluids are to be combined with normal gravity data from the two-phase alkali-metal experiments. Analyses undertaken here give every expectation that the correlations developed from this data base will provide a valid representation of alkali-metal heat transfer and pressure drop in reduced gravity
Nano-multiplication region avalanche photodiodes and arrays
Zheng, Xinyu (Inventor); Pain, Bedabrata (Inventor); Cunningham, Thomas J. (Inventor)
2011-01-01
An avalanche photodiode with a nano-scale reach-through structure comprising n-doped and p-doped regions, formed on a silicon island on an insulator, so that the avalanche photodiode may be electrically isolated from other circuitry on other silicon islands on the same silicon chip as the avalanche photodiode. For some embodiments, multiplied holes generated by an avalanche reduces the electric field in the depletion region of the n-doped and p-doped regions to bring about self-quenching of the avalanche photodiode. Other embodiments are described and claimed.
High speed motion neutron radiography of two-phase flow
International Nuclear Information System (INIS)
Robinson, A.H.; Wang, S.L.
1983-01-01
Current research in the area of two-phase flow utilizes a wide variety of sensing devices, but some limitations exist on the information which can be obtained. Neutron radiography is a feasible alternative to ''see'' the two-phase flow. A system to perform neutron radiographic analysis of dynamic events which occur on the order of several milliseconds has been developed at Oregon State University. Two different methods have been used to radiograph the simulated two-phase flow. These are pulsed, or ''flash'' radiography, and high speed movie neutron radiography. The pulsed method serves as a ''snap-shot'' with an exposure time ranging from 10 to 20 milliseconds. In high speed movie radiography, a scintillator is used to convert neutrons into light which is enhanced by an optical intensifier and then photographed by a high speed camera. Both types of radiography utilize the pulsing capability of the OSU TRIGA reactor. The principle difficulty with this type of neutron radiography is the fogging of the image due to the large amount of scattering in the water. This difficulty can be overcome by using thin regions for the two-phase flow or using heavy water instead of light water. The results obtained in this paper demonstrate the feasibility of using neutron radiography to obtain data in two-phase flow situations. Both movies and flash radiographs have been obtained of air bubbles in water and boiling from a heater element. The neutron radiographs of the boiling element show both nucleate boiling and film boiling. (Auth.)
Modeling and numerical study of two phase flow
International Nuclear Information System (INIS)
Champmartin, A.
2011-01-01
This thesis describes the modelization and the simulation of two-phase systems composed of droplets moving in a gas. The two phases interact with each other and the type of model to consider directly depends on the type of simulations targeted. In the first part, the two phases are considered as fluid and are described using a mixture model with a drift relation (to be able to follow the relative velocity between the two phases and take into account two velocities), the two-phase flows are assumed at the equilibrium in temperature and pressure. This part of the manuscript consists of the derivation of the equations, writing a numerical scheme associated with this set of equations, a study of this scheme and simulations. A mathematical study of this model (hyperbolicity in a simplified framework, linear stability analysis of the system around a steady state) was conducted in a frame where the gas is assumed baro-tropic. The second part is devoted to the modelization of the effect of inelastic collisions on the particles when the time of the simulation is shorter and the droplets can no longer be seen as a fluid. We introduce a model of inelastic collisions for droplets in a spray, leading to a specific Boltzmann kernel. Then, we build caricatures of this kernel of BGK type, in which the behavior of the first moments of the solution of the Boltzmann equation (that is mass, momentum, directional temperatures, variance of the internal energy) are mimicked. The quality of these caricatures is tested numerically at the end. (author) [fr
Geminate recombination in liquid argon
International Nuclear Information System (INIS)
Freeman, G.R.
1984-01-01
The extended Onsager model for geminate neutralization is supported by the field dependence of the ionization yield in liquid argon irradiated by high energy electrons or x rays. Attempts to employ the model fail unless the distribution of initial separation distances between the thermalized electrons and their sibling ions (secondary electron thermalization ranges) is included. Data of Scalettar and co-workers are reanalyzed
Multiparticle imaging velocimetry measurements in two-phase flow
International Nuclear Information System (INIS)
Hassan, Y.A.
1998-01-01
The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in two and three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in global domain. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various two and three- dimensional, two-phase flow situations. (author)
Study of two-phase underexpanded jets by gas jet
International Nuclear Information System (INIS)
Uchida, Mitsunori; Someya, Satoshi; Okamoto, Koji
2008-01-01
When a heat exchange in a Fast Breeder Reactor cracks, a sodium-water reaction occurs. When a tube cracks, highly pressurized water or steam escapes into the surrounding liquid sodium and a sodium-water reaction occurs forming the disodium oxide. The disodium oxide caught in the steam jet strikes other tubes in the reactor. The struck disodium oxide can then cause these tubes to crack. The release of steam into the liquid sodium media is a two-phase flow involving underexpansion. In this paper qualitative measurement of the underexpanded gas jet which injected into water was carried our for the purpose of analyzing the behavior of the two-phase flow. (author)
Reactor vessel and core two-phase flow ultrasonic densitometer
International Nuclear Information System (INIS)
Arave, A.E.
1979-01-01
A local ultrasonic density (LUD) detector has been developed by EG and G Idaho, Inc., at the Idaho National Engineering Laboratory (INEL) for the Loss-of-Fluid Test (LOFT) reactor vessel and core two-phase flow density measurements. The principle of operating the sensor is the change in propagation time of a torsional ultrasonic wave in a metal transmission line as a function of the density of the surrounding media. A theoretical physics model is presented which represents the total propagation time as a function of the sensor modulus of elasticity and polar moment of inertia. Separate effects tests and two-phase flow tests have been conducted to characterize the detector. Tests show the detector can perform in a 343 0 C pressurized water reactor environment and measure the average density of the media surrounding the sensor
Stability of interfacial waves in two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Liu, W S [Ontario Hydro, Toronto, ON (Canada)
1996-12-31
The influence of the interfacial pressure and the flow distribution in the one-dimensional two-fluid model on the stability problems of interfacial waves is discussed. With a proper formulation of the interfacial pressure, the following two-phase phenomena can be predicted from the stability and stationary criteria of the interfacial waves: onset of slug flow, stationary hydraulic jump in a stratified flow, flooding in a vertical pipe, and the critical void fraction of a bubbly flow. It can be concluded that the interfacial pressure plays an important role in the interfacial wave propagation of the two-fluid model. The flow distribution parameter may enhance the flow stability range, but only plays a minor role in the two-phase characteristics. (author). 20 refs., 3 tabs., 4 figs.
Non-Darcy behavior of two-phase channel flow.
Xu, Xianmin; Wang, Xiaoping
2014-08-01
We study the macroscopic behavior of two-phase flow in porous media from a phase-field model. A dissipation law is first derived from the phase-field model by homogenization. For simple channel geometry in pore scale, the scaling relation of the averaged dissipation rate with the velocity of the two-phase flow can be explicitly obtained from the model which then gives the force-velocity relation. It is shown that, for the homogeneous channel surface, Dacry's law is still valid with a significantly modified permeability including the contribution from the contact line slip. For the chemically patterned surfaces, the dissipation rate has a non-Darcy linear scaling with the velocity, which is related to a depinning force for the patterned surface. Our result offers a theoretical understanding on the prior observation of non-Darcy behavior for the multiphase flow in either simulations or experiments.
Method and apparatus for monitoring two-phase flow. [PWR
Sheppard, J.D.; Tong, L.S.
1975-12-19
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Macroscopic balance equations for two-phase flow models
International Nuclear Information System (INIS)
Hughes, E.D.
1979-01-01
The macroscopic, or overall, balance equations of mass, momentum, and energy are derived for a two-fluid model of two-phase flows in complex geometries. These equations provide a base for investigating methods of incorporating improved analysis methods into computer programs, such as RETRAN, which are used for transient and steady-state thermal-hydraulic analyses of nuclear steam supply systems. The equations are derived in a very general manner so that three-dimensional, compressible flows can be analysed. The equations obtained supplement the various partial differential equation two-fluid models of two-phase flow which have recently appeared in the literature. The primary objective of the investigation is the macroscopic balance equations. (Auth.)
Numerical simulation for two-phase jet problem
International Nuclear Information System (INIS)
Lee, W.H.; Shah, V.L.
1981-01-01
A computer program TWOP was developed for obtaining the numerical solutions of three-dimensional, transient, two-phase flow system with nonequilibrium and nonhomogeneous conditions. TWOP employs two-fluid model and a set of the conservation equations formulated by Harlow and Amsden along with their Implicit Multi-Field (IMF) numerical technique that allows all degrees of couplings between the two fields. We have further extended the procedure of Harlow and Amsden by incorporating the implicit couplings of phase transition and interfacial heat transfer terms in the energy equations. Numerical results of two tested problems are presented to demonstrate the capabilities of the TWOP code. The first problem is the separation of vapor and liquid, showing that the code can handle the computational difficulties such as liquid packing and sharp interface phenomena. The second problem is the high pressure two-phase jet impinged on vertical plate, demonstrating the important role of the interfacial mass and momentum exchange
Mathematical modeling and the two-phase constitutive equations
International Nuclear Information System (INIS)
Boure, J.A.
1975-01-01
The problems raised by the mathematical modeling of two-phase flows are summarized. The models include several kinds of equations, which cannot be discussed independently, such as the balance equations and the constitutive equations. A review of the various two-phase one-dimensional models proposed to date, and of the constitutive equations they imply, is made. These models are either mixture models or two-fluid models. Due to their potentialities, the two-fluid models are discussed in more detail. To avoid contradictions, the form of the constitutive equations involved in two-fluid models must be sufficiently general. A special form of the two-fluid models, which has particular advantages, is proposed. It involves three mixture balance equations, three balance equations for slip and thermal non-equilibriums, and the necessary constitutive equations [fr
Turbine flow meter response in two-phase flows
International Nuclear Information System (INIS)
Shim, W.J.; Dougherty, T.J.; Cheh, H.Y.
1996-01-01
The purpose of this paper is to suggest a simple method of calibrating turbine flow meters to measure the flow rates of each phase in a two-phase flow. The response of two 50.8 mm (2 inch) turbine flow meters to air-water, two-phase mixtures flowing vertically in a 57 mm I.D. (2.25 inch) polycarbonate tube has been investigated for both upflow and downflow. The flow meters were connected in series with an intervening valve to provide an adjustable pressure difference between them. Void fractions were measured by two gamma densitometers, one upstream of the flow meters and the other downstream. The output signal of the turbine flow meters was found to depend only on the actual volumetric flow rate of the gas, F G , and liquid, F L , at the location of the flow meter
Visualization in cryogenic environment: Application to two-phase studies
Rousset, Bernard; Chatain, Denis; Puech, Laurent; Thibault, Pierre; Viargues, François; Wolf, Pierre-Etienne
2009-10-01
This paper reviews recent technical developments devoted to the study of cryogenic two-phase fluids. These techniques span from simple flow visualization to quantitative measurements of light scattering. It is shown that simple flow pattern configurations are obtained using classical optical tools (CCD cameras, endoscopes), even in most severe environments (high vacuum, high magnetic field). Quantitative measurements include laser velocimetry, particle sizing, and light scattering analysis. In the case of magnetically compensated gravity boiling oxygen, optical access is used to control the poistioning of a bubble subject to buoyancy forces in an experimental cell. Flow visualization on a two-phase superfluid helium pipe-flow, performed as a support of LHC cooldown studies, leads to flow pattern characterization. Visualization includes stratified and atomized flows. Thanks to the low refractive index contrast between the liquid and its vapor, quantitative results on droplet densities can be obtained even in a multiple scattering regime.
Study on flow instabilities in two-phase mixtures
International Nuclear Information System (INIS)
Ishii, M.
1976-03-01
Various mechanisms that can induce flow instabilities in two-phase flow systems are reviewed and their relative importance discussed. In view of their practical importance, the density-wave instabilities have been analyzed in detail based on the one-dimensional two-phase flow formulation. The dynamic response of the system to the inlet flow perturbations has been derived from the model; thus the characteristic equation that predicts the onset of instabilities has been obtained. The effects of various system parameters, such as the heat flux, subcooling, pressure, inlet velocity, inlet orificing, and exit orificing on the stability boundary have been analyzed. In addition to numerical solutions, some simple stability criteria under particular conditions have been obtained. Both results have been compared with various experimental data, and a satisfactory agreement has been demonstrated
Transition from boiling to two-phase forced convection
International Nuclear Information System (INIS)
Maroti, L.
1985-01-01
The paper presents a method for the prediction of the boundary points of the transition region between fully developed boiling and two-phase forced convection. It is shown that the concept for the determination of the onset of fully developed boiling can also be applied for the calculation of the point where the heat transfer is effected again by the forced convection. Similarly, the criterion for the onset of nucleate boiling can be used for the definition of the point where boiling is completely suppressed and pure two-phase forced convection starts. To calculate the heat transfer coefficient for the transition region, an equation is proposed that applies the boundary points and a relaxation function ensuring the smooth transition of the heat transfer coefficient at the boundaries
A new correlation for two-phase critical discharge coefficient
International Nuclear Information System (INIS)
Park, Jong Woon; Chun, Moon Hyun
1989-01-01
A new simple correlation for subcooled and two-phase critical flow discharge coefficient has been developed by stepwise regression technique. The new discharge coefficient has three independent variables and they are length to hydraulic diameter ratio, degree of subcooling, and stagnation temperature. The new discharge coefficient is applied as a multiplier to homogeneous equilibrium model and Abauf's single phase critical mass flux calculation equation. This method has been tested for its accuracy by comparing with experimental data. Results of the comparison show that the agreement between the predictions with new correlation and the experimental data is good for pipes and nozzles with vertical upward flow for subcooled upstream condition and nozzles with horizontal configuration for two-phase upstream condition
Peptide-tagged proteins in aqueous two-phase systems
Nilsson, Anna
2002-01-01
This thesis deals with proteins containing peptide tags for improved partitioning in aqueous two-phase systems. Qualitatively the peptide-tagged protein partitioning could be predicted from peptide data, i.e. partitioning trends found for peptides were also found for the peptide-tagged proteins. However, full effect of the tag as expected from peptide partitioning was not found in the tagged protein. When alkyl-ethylene oxide surfactant was included in a two-polymer system, almost full effect...
Computational methods for two-phase flow and particle transport
Lee, Wen Ho
2013-01-01
This book describes mathematical formulations and computational methods for solving two-phase flow problems with a computer code that calculates thermal hydraulic problems related to light water and fast breeder reactors. The physical model also handles the particle and gas flow problems that arise from coal gasification and fluidized beds. The second part of this book deals with the computational methods for particle transport.
Recent advances in two-phase flow numerics
International Nuclear Information System (INIS)
Mahaffy, J.H.; Macian, R.
1997-01-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques
Recent advances in two-phase flow numerics
Energy Technology Data Exchange (ETDEWEB)
Mahaffy, J.H.; Macian, R. [Pennsylvania State Univ., University Park, PA (United States)
1997-07-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques.
Two-phase titration of cerium(3) by permanganate
International Nuclear Information System (INIS)
Lazarev, A.I.; Lazareva, V.I.; Gerko, V.V.
1986-01-01
Reaction of cerium (3) and permanganate was investigated at a room temperature depending on PH, concentrations of pyrophosphate, cerium (3), tetraphenylphosphonium and foreign compounds. Selective method of two-phase titration determination of cerium (3) by permanganate without using silver compounds, preliminary separation of chlorides, nitrates, was developed. The method was tested using alloys based on iron, nickel, REE, copper, cobalt (S r ≤0.008). Correctness is proved with method of standard additives
Laser Doppler measurements in two-phase flows
International Nuclear Information System (INIS)
Durst, F.; Zare, M.
1976-01-01
Basic theory for laser-Doppler velocity measurements of large reflecting or refracting surfaces is provided. It is shown that the Doppler-signals contain information of the velocity and size of the large bodies, and relationships for transforming velocity and radius of curvature of moving spheres are presented. Preliminary experiments verified the analytical findings and demonstrated the applicability of the method to some two-phase flows
Two-phase flow instability and propagation of disturbances
International Nuclear Information System (INIS)
Yadigaroglu, G.
1984-01-01
Various mechanisms of static and dynamic macroinstabilities, appearing in two-phase flows, have been considered. Types of instabilities, conditioned by the form of hydraulic characteristics of the channel and density waves are analyzed in detail. Problems of instabilities in nuclear reactor circuits, in particular problems of instabilities, conditioned by water and steam mixing and vapour condensation, and problems of steam generator operation instability are discussed
Interfacial structures in downward two-phase bubbly flow
International Nuclear Information System (INIS)
Paranjape, S.S.; Kim, S.; Ishii, M.; Kelly, J.
2003-01-01
Downward two-phase flow was studied considering its significance in view of Light Water Reactor Accidents (LWR) such as Loss of Heat Sink (LOHS) by feed water loss or secondary pipe break. The flow studied, was an adiabatic, air-water, co-current, vertically downward two-phase flow. The experimental test sections had internal hydraulic diameters of 25.4 mm and 50.8 mm. Flow regime map was obtained using the characteristic signals obtained from an impedance void meter, employing neural network based identification methodology to minimize the subjective judgment in determining the flow regimes. A four sensor conductivity probe was used to measure the local two phase flow parameters, which characterize the interfacial structures. The local time averaged two-phase flow parameters measured were: void fraction (α), interfacial area concentration (a i ), bubble velocity (v g ), and Sauter mean diameter (D Sm ). The flow conditions were from the bubbly flow regime. The local profiles of these parameters as well as their axial development revealed the nature of the interfacial structures and the bubble interaction mechanisms occurring in the flow. Furthermore, this study provided a good database for the development of the interfacial area transport equation, which dynamically models the changes in the interfacial area along the flow field. An interfacial area transport equation was developed for downward flow based on that developed for the upward flow, with certain modifications in the bubble interaction terms. The area averaged values of the interfacial area concentration were compared with those predicted by the interfacial area transport model. (author)
Remediation in clay using two-phase vacuum extraction
International Nuclear Information System (INIS)
Lindhult, E.C.; Tarsavage, J.M.; Foukaris, K.A.
1995-01-01
Soil and groundwater contamination in a tight clay usually requires costly and/or time consuming remediation, due to the inherently low hydraulic conductivity of the soil. However, Dames and Moore is successfully using an innovative, cost-effective two-phase vacuum extraction (VE) technology at a former gasoline service station. Dramatic decreases in BTEX concentrations in onsite and downgradient monitoring wells are apparent
Phase separation and shape deformation of two-phase membranes
International Nuclear Information System (INIS)
Jiang, Y.; Lookman, T.; Saxena, A.
2000-01-01
Within a coupled-field Ginzburg-Landau model we study analytically phase separation and accompanying shape deformation on a two-phase elastic membrane in simple geometries such as cylinders, spheres, and tori. Using an exact periodic domain wall solution we solve for the shape and phase separating field, and estimate the degree of deformation of the membrane. The results are pertinent to preferential phase separation in regions of differing curvature on a variety of vesicles. (c) 2000 The American Physical Society
Two-phase computer codes for zero-gravity applications
International Nuclear Information System (INIS)
Krotiuk, W.J.
1986-10-01
This paper discusses the problems existing in the development of computer codes which can analyze the thermal-hydraulic behavior of two-phase fluids especially in low gravity nuclear reactors. The important phenomenon affecting fluid flow and heat transfer in reduced gravity is discussed. The applicability of using existing computer codes for space applications is assessed. Recommendations regarding the use of existing earth based fluid flow and heat transfer correlations are made and deficiencies in these correlations are identified
Fluid dynamics of cryogenic two-phase flows
International Nuclear Information System (INIS)
Verfondern, K.; Jahn, W.
2004-01-01
The objective of this study was to examine the flow behavior of a methane hydrate/methane-liquid hydrogen dispersed two-phase fluid through a given design of a moderator chamber for the ESS target system. The calculations under simplified conditions, e.g., taking no account of heat input from outside, have shown that the computer code used, CFX, was able to simulate the behavior of the two-phase flow through the moderator chamber, producing reasonable results up to a certain level of the solid phase fraction, that allowed a continuous flow process through the chamber. Inlet flows with larger solid phase fractions than 40 vol% were found to be a ''problem'' for the computer code. From the computer runs based on fractions between 20 and 40 vol%, it was observed that with increasing solid phase fraction at the inlet, the resulting flow pattern revealed a strong tendency for blockage within the chamber, supported by the ''heavy weight'' of the pellets compared to the carrying liquid. Locations which are prone to the development of such uneven flow behavior are the areas around the turning points in the semispheres and near the exit of the moderator. The considered moderator chamber with horizontal inlet and outlet flow for a solid-liquid two-phase fluid does not seem to be an appropriate design. (orig.)
Instrumentation for localized measurements in two-phase flow conditions
International Nuclear Information System (INIS)
Neff, G.G.; Averill, R.H.; Shurts, S.W.
1979-01-01
Three types of instrumentation that have been developed by EG and G Idaho, Inc., and its predecessor, Aerojet Nuclear company, at the Idaho National Engineering Laboratory to investigate two-phase flow phenomenon in a nuclear reactor at the Loss-of-Fluid Test (LOFT) facility are discussed: (a) a combination drag disc-turbine transducer (DTT), (b) a multibeam nuclear hardened gamma densitometer system, and (c) a conductivity sensitive liquid level transducer (LLT). The DTT obtains data on the complex problem of two-phase flow conditions in the LOFT primary coolant system during a loss-os-coolant experiment (LOCE). The discussion of the DTT describes how a turbine, measuring coolant velocity, and a drag disc, measuring coolant momentum flux, can provide valuable mass flow data. The nuclear hardened gamma densitometer is used to obtain density and flow regime information for two-phase flow in the LOFT primary coolant system during a LOCE. The LLT is used to measure water and steam conditions within the LOFT reactor core during a LOCE. The LLT design and the type of data obtained are described
An objective indicator for two-phase flow pattern transition
International Nuclear Information System (INIS)
Hervieua, E.; Seleghim, P. Jr.
1998-01-01
This work concerns the development of a methodology the objective of which is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. During the first time, the efforts focused on: (1) the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; (2) the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; and (3) the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. During the second time, in order to verify the fundamental assumption, a series of experiments were conducted, the objective of which was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (orig.)
An objective indicator for two-phase flow pattern transition
International Nuclear Information System (INIS)
Hervieu, E.; Seleghim, P. Jr.
1998-01-01
This work concerns the development of a methodology which objective is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. In a first time, the efforts focused on: the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. In a second time, in order to verify the fundamental assumption, a series of experiments were conducted, which objective was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (author)
Random signal tomographical analysis of two-phase flow
International Nuclear Information System (INIS)
Han, P.; Wesser, U.
1990-01-01
This paper reports on radiation tomography which is a useful tool for studying the internal structures of two-phase flow. However, general tomography analysis gives only time-averaged results, hence much information is lost. As a result, it is sometimes difficult to identify the flow regime; for example, the time-averaged picture does not significantly change as an annual flow develops from a slug flow. A two-phase flow diagnostic technique based on random signal tomographical analysis is developed. It extracts more information by studying the statistical variation of the measured signal with time. Local statistical parameters, including mean value, variance, skewness and flatness etc., are reconstructed from the information obtained by a general tomography technique. More important information are provided by the results. Not only the void fraction can be easily calculated, but also the flow pattern can be identified more objectively and more accurately. The experimental setup is introduced. It consisted of a two-phase flow loop, an X-ray system, a fan-like five-beam detector system and a signal acquisition and processing system. In the experiment, for both horizontal and vertical test sections (aluminum and steel tube with Di/Do = 40/45 mm), different flow situations are realized by independently adjusting air and water mass flow. Through a glass tube connected with the test section, some typical flow patterns are visualized and used for comparing with the reconstruction results
Two-phase flow measurement by pulsed neutron activation techniques
International Nuclear Information System (INIS)
Kehler, P.
1978-01-01
The Pulsed Neutron Activation (PNA) technique for measuring the mass flow velocity and the average density of two-phase mixtures is described. PNA equipment can be easily installed at different loops, and PNA techniques are non-intrusive and independent of flow regimes. These features of the PNA technique make it suitable for in-situ measurement of two-phase flows, and for calibration of more conventional two-phase flow measurement devices. Analytic relations governing the various PNA methods are derived. The equipment and procedures used in the first air-water flow measurement by PNA techniques are discussed, and recommendations are made for improvement of future tests. In the present test, the mass flow velocity was determined with an accuracy of 2 percent, and average densities were measured down to 0.08 g/cm 3 with an accuracy of 0.04 g/cm 3 . Both the accuracy of the mass flow velocity measurement and the lower limit of the density measurement are functions of the injected activity and of the total number of counts. By using a stronger neutron source and a larger number of detectors, the measurable density can be decreased by a factor of 12 to .007 g/cm 3 for 12.5 cm pipes, and to even lower ranges for larger pipes
Cold water injection into two-phase mixtures
International Nuclear Information System (INIS)
1989-07-01
This report presents the results of a review of the international literature regarding the dynamic loadings associated with the injection of cold water into two-phase mixtures. The review placed emphasis on waterhammer in nuclear power plants. Waterhammmer incidence data were reviewed for information related to thermalhydraulic conditions, underlying causes and consequential damage. Condensation induced waterhammer was found to be the most significant consequence of injecting cold water into a two-phase system. Several severe waterhammer incidents have been attributed to slug formation and steam bubble collapse under conditions of stratified steam and cold water flows. These phenomena are complex and not well understood. The current body of experimental and analytical knowledge is not large enough to establish maps of expected regimes of condensation induced waterhammer. The Electric Power Research Institute, in the United States, has undertaken a major research and development programme to develop the knowledge base for this area. The limited models and data currently available show that mechanical parameters are as important as thermodynamic conditions for the initiation of condensation induced waterhammer. Examples of bounds for avoiding two-phase waterhammer are given. These bounds are system specific and depend upon parameters such as pump capacity, pipe length and pipe orientation
Avalanches in Mn12-Acetate: ``Magnetic Burning"
McHugh, Sean; Suzuki, Y.; Graybill, D.; Sarachik, M. P.; Avraham, N.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Chakov, N. E.; Christou, G.
2006-03-01
From local time-resolved measurements of fast reversal of the magnetization in single crystals of the molecular magnet Mn12-acetate, we have shown[1] that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity roughly two orders of magnitude smaller than the speed of sound. This phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance. The propagation speed of the avalanche depends on the energy stored in each molecule, which can be controlled and tuned using an external magnetic field. We report studies of propagation speed with different external fields in Mn12-acetate. [1] Yoko Suzuki, M.P. Sarachik, E.M. Chudnovsky, S. McHugh, R. Gonzalez-Rubio, N. Avraham, Y. Myasoedov, H. Shtrikman, E. Zeldov, N.E. Chakov and G. Christou, Phys. Rev. Lett. 95, 147201 (2005).
Avalanches in functional materials and geophysics
Saxena, Avadh; Planes, Antoni
2017-01-01
This book provides the state-of-the art of the present understanding of avalanche phenomena in both functional materials and geophysics. The main emphasis of the book is analyzing these apparently different problems within the common perspective of out-of-equilibrium phenomena displaying spatial and temporal complexity that occur in a broad range of scales. Many systems, when subjected to an external force, respond intermittently in the form of avalanches that often span over a wide range of sizes, energies and durations. This is often related to a class of critical behavior characterized by the absence of characteristic scales. Typical examples are magnetization processes, plastic deformation and failure occuring in functional materials. These phenomena share many similarities with seismicity arising from the earth crust failure due to stresses that originate from plate tectonics.
Characterization of horizontal air–water two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Kong, Ran; Kim, Seungjin, E-mail: skim@psu.edu
2017-02-15
Highlights: • A visualization study is performed to develop flow regime map in horizontal flow. • Database in horizontal bubbly flow is extended using a local conductivity probe. • Frictional pressure drop analysis is performed in horizontal bubbly flow. • Drift flux analysis is performed in horizontal bubbly flow. - Abstract: This paper presents experimental studies performed to characterize horizontal air–water two-phase flow in a round pipe with an inner diameter of 3.81 cm. A detailed flow visualization study is performed using a high-speed video camera in a wide range of two-phase flow conditions to verify previous flow regime maps. Two-phase flows are classified into bubbly, plug, slug, stratified, stratified-wavy, and annular flow regimes. While the transition boundaries identified in the present study compare well with the existing ones (Mandhane et al., 1974) in general, some discrepancies are observed for bubbly-to-plug/slug, and plug-to-slug transition boundaries. Based on the new transition boundaries, three additional test conditions are determined in horizontal bubbly flow to extend the database by Talley et al. (2015a). Various local two-phase flow parameters including void fraction, interfacial area concentration, bubble velocity, and bubble Sauter mean diameter are obtained. The effects of increasing gas flow rate on void fraction, bubble Sauter mean diameter, and bubble velocity are discussed. Bubbles begin to coalesce near the gas–liquid layer instead of in the highly packed region when gas flow rate increases. Using all the current experimental data, two-phase frictional pressure loss analysis is performed using the Lockhart–Martinelli method. It is found that the coefficient C = 24 yields the best agreement with the data with the minimum average difference. Moreover, drift flux analysis is performed to predict void-weighted area-averaged bubble velocity and area-averaged void fraction. Based on the current database, functional
The Condensation effect on the two-phase flow stability
International Nuclear Information System (INIS)
Abdou Mohamed, Hesham Nagah
2005-01-01
A one-dimensional analytical model has been developed to be used for the linear analysis of density-wave oscillations in a parallel heated channel and a natural circulation loop.The heater and the riser sections are divided into a single-phase and a two-phase region.The two-phase region is represented by the drift-flux model. The model accounts for aphasic slip and subcooled boiling.The localized friction at the heater and the riser exit is treated considering the two-phase mixture.Also the effects of the condensation in the riser and the change in the system pressure have been studied.The exact equation for the heated channel and the total loop pressure drop is perturbed around the steady state.he stability characteristics of the heated channel and the loop are investigated using the Root finding method criterion.The results are summarized on instability maps in the plane of subcooled boiling number vs. phase change number (i.e., inlet subcooling vs. heater heat flux).The predictions of the model are compared with experimental results published in open literature. The results show that, the treatment effect of localized friction in two-phase mixtures stabilizes the system and improves the agreement of the calculations with the experimental results.For a parallel heated channel, the results indicate a more stable system with high inlet restriction, low outlet restriction, and high inlet velocity. And for a natural circulation loop, an increase in the inlet restriction broadened the range of the continuous circulation mode and stabilized the system, a decrease in the exit restriction or the liquid charging level shifted to the right the range of the continuous circulation mode and stabilized the system and an increase in the riser condensation shifted to the right the range of the continuous circulation mode and stabilized the system.The results show that the model agrees well with the available experimental data. In particular, the results show the significance of
A position sensitive parallel plate avalanche counter
International Nuclear Information System (INIS)
Lombardi, M.; Tan Jilian; Potenza, R.; D'amico, V.
1986-01-01
A position sensitive parallel plate avalanche counter with a distributed constant delay-line-cathode (PSAC) is described. The strips formed on the printed board were served as the cathode and the delay line for readout of signals. The detector (PSAC) was operated in isobutane gas at the pressure range from 10 to 20 torr. The position resolution is better than 1 mm and the time resolution is about 350 ps, for 252 Cf fission-spectrum source
International Nuclear Information System (INIS)
Yonomoto, Taisuke; Tasaka, Kanji
1988-01-01
A theoretical and experimental study was conducted to understand two-phase flow discharged from a stratified two-phase region through a small break. This problem is important for an analysis of a small break loss-of-coolant accident (LOCA) in a light water reactor (LWR). The present theoretical results show that a break quality is a function of h/h b , where h is the elevation difference between a bulk water level in the upstream region and break and b the suffix for entrainment initiation. This result is consistent with existing eperimental results in literature. An air-water experiment was also conducted changing a break orientation as an experimental parameter to develop and assess the model. Comparisons between the model and the experimental results show that the present model can satisfactorily predict the flow rate and the quality at the break without using any adjusting constant when liquid entrainment occurs in a stratified two-phase region. When gas entrainment occurs, the experimental data are correlated well by using a single empirical constant. (author)
Two-phase flow in volatile oil reservoir using two-phase pseudo-pressure well test method
Energy Technology Data Exchange (ETDEWEB)
Sharifi, M.; Ahmadi, M. [Calgary Univ., AB (Canada)
2009-09-15
A study was conducted to better understand the behaviour of volatile oil reservoirs. Retrograde condensation occurs in gas-condensate reservoirs when the flowing bottomhole pressure (BHP) lowers below the dewpoint pressure, thus creating 4 regions in the reservoir with different liquid saturations. Similarly, when the BHP of volatile oil reservoirs falls below the bubblepoint pressure, two phases are created in the region around the wellbore, and a single phase (oil) appears in regions away from the well. In turn, higher gas saturation causes the oil relative permeability to decrease towards the near-wellbore region. Reservoir compositional simulations were used in this study to predict the fluid behaviour below the bubblepoint. The flowing bottomhole pressure was then exported to a well test package to diagnose the occurrence of different mobility regions. The study also investigated the use of a two-phase pseudo-pressure method on volatile and highly volatile oil reservoirs. It was concluded that this method can successfully predict the true permeability and mechanical skin. It can also distinguish between mechanical skin and condensate bank skin. As such, the two-phase pseudo-pressure method is particularly useful for developing after-drilling well treatment and enhanced oil recovery process designs. However, accurate relative permeability and PVT data must be available for reliable interpretation of the well test in volatile oil reservoirs. 18 refs., 3 tabs., 9 figs.
Liquid Argon Barrel Cryostat Arrived
Pailler, P
Last week the first of three cryostats for the ATLAS liquid argon calorimeter arrived at CERN. It had travelled for 46 days over several thousand kilometers from Japan to CERN. During three years it has been fabricated by Kawasaki Heavy Industries Ltd. at Harima, close to Kobe, under contract from Brookhaven National Laboratory (BNL) of the U.S.. This cryostat consists of two concentric cylinders made of aluminium: the outer vacuum vessel with a diameter of 5.5 m and a length of 7 m, and the inner cold vessel which will contain the electromagnetic barrel calorimeter immersed in liquid argon. The total weight will be 270 tons including the detectors and the liquid argon. The cryostat is now located in building 180 where it will be equipped with 64 feed-throughs which serve for the passage of 122,880 electrical lines which will carry the signals of the calorimeter. After integration of the calorimeter, the solenoidal magnet of ATLAS will be integrated in the vacuum vessel. A final cold test of the cryostat inc...
New advances for modelling the debris avalanches
Cuomo, Sabatino; Cascini, Leonardo; Pastor, Manuel; Castorino, Giuseppe Claudio
2013-04-01
Flow-like landslides are a major global hazard and they occur worldwide causing a large number of casualties, significant structural damages to property and infrastructures as well as economic losses. When involving open slopes, these landslides often occur in triangular source areas where initial slides turn into avalanches through further failures and/or eventual soil entrainment. This paper deals with the numerical modelling of the propagation stage of debris avalanches which provides information such as the propagation pattern of the mobilized material, its velocity, thickness and run-out distance. In the paper, a "depth integrated" model is used which allows: i) adequately taking into account the irregular topography of real slopes which greatly affect the propagation stage and ii) using a less time consuming model than fully 3D approaches. The used model is named "GeoFlow_SPH" and it was formerly applied to theoretical, experimental and real case histories (Pastor et al., 2009; Cascini et al., 2012). In this work the behavior of debris avalanches is analyzed with special emphasis on the apical angle, one of the main features of this type of landslide, in relation to soil rheology, hillslope geometry and features of triggering area. Furthermore, the role of erosion has been investigated with reference to the uppermost parts of open slopes with a different steepness. These analyses are firstly carried out for simplified benchmark slopes, using both water-like materials (with no shear strength) and debris type materials. Then, three important case studies of Campania region (Cervinara, Nocera Inferiore e Sarno) are analyzed where debris avalanches involved pyroclastic soils originated from the eruptive products of Vesusius volcano. The results achieved for both benchmark slopes and real case histories outline the key role played by the erosion on the whole propagation stage of debris avalanches. The results are particularly satisfactory since they indicate the
Measurement of Two-Phase Flow Characteristics Under Microgravity Conditions
Keshock, E. G.; Lin, C. S.; Edwards, L. G.; Knapp, J.; Harrison, M. E.; Xhang, X.
1999-01-01
This paper describes the technical approach and initial results of a test program for studying two-phase annular flow under the simulated microgravity conditions of KC-135 aircraft flights. A helical coil flow channel orientation was utilized in order to circumvent the restrictions normally associated with drop tower or aircraft flight tests with respect to two-phase flow, namely spatial restrictions preventing channel lengths of sufficient size to accurately measure pressure drops. Additionally, the helical coil geometry is of interest in itself, considering that operating in a microgravity environment vastly simplifies the two-phase flows occurring in coiled flow channels under 1-g conditions for virtually any orientation. Pressure drop measurements were made across four stainless steel coil test sections, having a range of inside tube diameters (0.95 to 1.9 cm), coil diameters (25 - 50 cm), and length-to-diameter ratios (380 - 720). High-speed video photographic flow observations were made in the transparent straight sections immediately preceding and following the coil test sections. A transparent coil of tygon tubing of 1.9 cm inside diameter was also used to obtain flow visualization information within the coil itself. Initial test data has been obtained from one set of KC-135 flight tests, along with benchmark ground tests. Preliminary results appear to indicate that accurate pressure drop data is obtainable using a helical coil geometry that may be related to straight channel flow behavior. Also, video photographic results appear to indicate that the observed slug-annular flow regime transitions agree quite reasonably with the Dukler microgravity map.
Developing two-phase flow modelling concepts for rock fractures
Energy Technology Data Exchange (ETDEWEB)
Keto, V. (Fortum Nuclear Services Oy, Espoo (Finland))
2010-01-15
The Finnish nuclear waste disposal company, Posiva Oy, is planning an underground repository for spent nuclear fuel to be constructed on the island of Olkiluoto on the south-west coast of Finland. One element of the site investigations conducted at Olkiluoto is the excavation of the underground rock characterisation facility (ONKALO) that will be extended to the final disposal depth (approximately -400 m). The bedrock around the excavated tunnel volume is fully saturated with groundwater, which water commonly contains a mixture of dissolved gases. These gases remain dissolved due to the high hydrostatic pressure. During tunnel excavation work the natural hydrostatic pressure field is disturbed and the water pressure will decrease close to the atmospheric pressure in the immediate vicinity of the tunnel. During this pressure drop two-phase flow conditions (combined flow of both water and gas) may develop in the vicinity of the underground opening, as the dissolved gas is exsoluted under the low pressure (the term exsolution refers here to release of the dissolved gas molecules from the water phase into a separate gas phase). This report steers towards concept development for numerical two-phase flow modeling for fractured rock. The focus is on the description of gas phase formation process under disturbed hydraulic conditions by exsolution of dissolved gases from groundwater, and on understanding the effects of a possibly formed gas phase on groundwater flow conditions in rock fractures. A mathematical model of three mutually coupled nonlinear partial differential equations for two-phase flow is presented and corresponding constitutional relationships are introduced and discussed. Illustrative numerical simulations are performed in a simplified setting using COMSOL Multiphysics 3.5a - software package. Shortcomings and conceptual problems are discussed. (orig.)
Developing two-phase flow modelling concepts for rock fractures
International Nuclear Information System (INIS)
Keto, V.
2010-01-01
The Finnish nuclear waste disposal company, Posiva Oy, is planning an underground repository for spent nuclear fuel to be constructed on the island of Olkiluoto on the south-west coast of Finland. One element of the site investigations conducted at Olkiluoto is the excavation of the underground rock characterisation facility (ONKALO) that will be extended to the final disposal depth (approximately -400 m). The bedrock around the excavated tunnel volume is fully saturated with groundwater, which water commonly contains a mixture of dissolved gases. These gases remain dissolved due to the high hydrostatic pressure. During tunnel excavation work the natural hydrostatic pressure field is disturbed and the water pressure will decrease close to the atmospheric pressure in the immediate vicinity of the tunnel. During this pressure drop two-phase flow conditions (combined flow of both water and gas) may develop in the vicinity of the underground opening, as the dissolved gas is exsoluted under the low pressure (the term exsolution refers here to release of the dissolved gas molecules from the water phase into a separate gas phase). This report steers towards concept development for numerical two-phase flow modeling for fractured rock. The focus is on the description of gas phase formation process under disturbed hydraulic conditions by exsolution of dissolved gases from groundwater, and on understanding the effects of a possibly formed gas phase on groundwater flow conditions in rock fractures. A mathematical model of three mutually coupled nonlinear partial differential equations for two-phase flow is presented and corresponding constitutional relationships are introduced and discussed. Illustrative numerical simulations are performed in a simplified setting using COMSOL Multiphysics 3.5a - software package. Shortcomings and conceptual problems are discussed. (orig.)
Anthropogenic effect on avalanche and debris flow activity
S. A. Sokratov; Yu. G. Seliverstov; A. L. Shnyparkov; K. P. Koltermann
2013-01-01
The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoida...
Avalanche and streamer mode operation of resistive plate chambers
International Nuclear Information System (INIS)
Cardarelli, R.; Makeev, V.; Santonico, R.
1996-01-01
A resistive plate chamber was operated at voltages increasing in steps of 200 V over a 3 kV interval and the transition between the avalanche and streamer modes was studied. The avalanche amplitude was observed to be exponentially dependent on the operating voltage up to a value, characteristic of the gas, where the avalanche saturation occurs and delayed streamer signals start to appear. Signal waveforms, charge and timing distributions are reported. (orig.)
Two-phase exchangers with small temperature differences
International Nuclear Information System (INIS)
Moracchioli, R.; Marie, G.; Lallee, J. de.
1976-01-01
The possibility in using heat available at low temperature level is shown (industrial wastes, solar energy, geothermal energy, heat power from seas). Special emphasis is put on the importance of heat exchangers that commonly should be evaporators and condensors working with small temperature differences (20 to 100 deg C). The expansion of the so-called ''new'' energies or recovery processes will depend on the physical performance of exchangers (Rankine two-phase cycles) and cost of the elementary exchange interfaces and assembling technics [fr
Flow patterns in vertical two-phase flow
International Nuclear Information System (INIS)
McQuillan, K.W.; Whalley, P.B.
1985-01-01
This paper is concerned with the flow patterns which occur in upwards gas-liquid two-phase flow in vertical tubes. The basic flow patterns are described and the use of flow patter maps is discussed. The transition between plug flow and churn flow is modelled under the assumption that flooding of the falling liquid film limits the stability of plug flow. The resulting equation is combined with other flow pattern transition equations to produce theoretical flow pattern maps, which are then tested against experimental flow pattern data. Encouraging agreement is obtained
Two-phase flow measurement based on oblique laser scattering
Vendruscolo, Tiago P.; Fischer, Robert; Martelli, Cícero; Rodrigues, Rômulo L. P.; Morales, Rigoberto E. M.; da Silva, Marco J.
2015-07-01
Multiphase flow measurements play a crucial role in monitoring productions processes in many industries. To guarantee the safety of processes involving multiphase flows, it is important to detect changes in the flow conditions before they can cause damage, often in fractions of seconds. Here we demonstrate how the scattering pattern of a laser beam passing a two-phase flow under an oblique angle to the flow direction can be used to detect derivations from the desired flow conditions in microseconds. Applying machine-learning techniques to signals obtained from three photo-detectors we achieve a compact, versatile, low-cost sensor design for safety applications.
Flooding and flow reversal of two-phase annular flow
International Nuclear Information System (INIS)
Asahi, Y.
1978-01-01
The flooding and flow reversal conditions of two-phase annular flow are mathematically defined in terms of a characteristic function representing a force balance. Sufficiently below the flooding point in counter-current flow, the interface is smooth and the characteristic equation reduces to the Nusselt relationship. Just below flooding point and above the flow reversal point in cocurrent flow, the interface is 'wavy', so that the interfacial shear effect plays an important role. The theoretical analysis is compared with experimental results by others. It is suggested that the various length effects which have been experimentally observed may be accounted for by the spatial variation of the droplet entrainment. (Auth.)
A study of critical two-phase flow models
International Nuclear Information System (INIS)
Siikonen, T.
1982-01-01
The existing computer codes use different boundary conditions in the calculation of critical two-phase flow. In the present study these boundary conditions are compared. It is shown that the boundary condition should be determined from the hydraulic model used in the computer code. The use of a correlation, which is not based on the hydraulic model used, leads often to bad results. Usually a good agreement with data is obtained in the calculation as far as the critical mass flux is concerned, but the agreement is not so good in the pressure profiles. The reason is suggested to be mainly in inadequate modeling of non-equilibrium effects. (orig.)
Design and construction of two phases flow meter
International Nuclear Information System (INIS)
Nor Paiza Mohamad Hasan
2002-01-01
This paper deals with design of the gamma ray correlometer and flow loop system for measuring the velocity between two parallel cross-sections of a pipeline. In the laboratory, the radioisotope source and detector were collimated by brass with small beam slit respectively. The flow loop system consists of transparent pipeline, adjustable frequency pump and water container. As a result, when the construction of the flow loop and correlometer is completed, the velocity of two phases flow can be measured by the cross-correlation techniques. (Author)
Experimental and numerical investigation on two-phase flow instabilities
Energy Technology Data Exchange (ETDEWEB)
Ruspini, Leonardo Carlos
2013-03-01
Two-phase flow instabilities are experimentally and numerically studied within this thesis. In particular, the phenomena called Ledinegg instability, density wave oscillations and pressure drop oscillations are investigated. The most important investigations regarding the occurrence of two-phase flow instabilities are reviewed. An extensive description of the main contributions in the experimental and analytical research is presented. In addition, a critical discussion and recommendations for future investigations are presented. A numerical framework using a hp-adaptive method is developed in order to solve the conservation equations modelling general thermo-hydraulic systems. A natural convection problem is analysed numerically in order to test the numerical solver. Moreover, the description of an adaptive strategy to solve thermo-hydraulic problems is presented. In the second part of this dissertation, a homogeneous model is used to study Ledinegg, density wave and pressure drop oscillations phenomena numerically. The dynamic characteristics of the Ledinegg (flow excursion) phenomenon are analysed through the simulation of several transient examples. In addition, density wave instabilities in boiling and condensing systems are investigated. The effects of several parameters, such as the fluid inertia and compressibility volumes, on the stability limits of Ledinegg and density wave instabilities are studied, showing a strong influence of these parameters. Moreover, the phenomenon called pressure drop oscillations is numerically investigated. A discussion of the physical representation of several models is presented with reference to the obtained numerical results. Finally, the influence of different parameters on these phenomena is analysed. In the last part, an experimental investigation of these phenomena is presented. The designing methodology used for the construction of the experimental facility is described. Several simulations and a non
Laser doppler anemometry in single- and two-phase flows
International Nuclear Information System (INIS)
Durst, F.
1976-01-01
The present report gives an introduction into laser-Doppler anemometry and tries to explain the basic physical principles of this measuring technique. Moire fringe patterns are used in order to visually model LDA-signals and to explain the basic difference in optical systems. It is pointed out that LDA measurements in highly turbulent flows and in two-phase flows should be attempted with direction sensitive instruments only. Some of the optical systems developed by the author and his collaborators are introduced and their functioning in measurements is demonstrated. These measurements embrace investigations in a number of single-phase flows including flames. (orig.) [de
Current capabilities of transient two-phase flow instruments
International Nuclear Information System (INIS)
Solbrig, C.W.; Kondic, N.N.
1979-01-01
The measurement of two phase flow phenomena in transient conditions representative of a Loss-of-Coolant Accident requires the use of sophisticated instruments and the further development of other instruments. Measurements made in large size pipes are often flow regime dependent. The flow regimes encountered depend upon the system geometry, transient effects, heat transfer, etc. The geometries in which these measurements must be made, the instruments which are currently used, new instruments being developed, the facilities used to calibrate these instruments, and the improvements which must be made to measurement capabilities are described
Modulating patterns of two-phase flow with electric fields.
Liu, Dingsheng; Hakimi, Bejan; Volny, Michael; Rolfs, Joelle; Anand, Robbyn K; Turecek, Frantisek; Chiu, Daniel T
2014-07-01
This paper describes the use of electro-hydrodynamic actuation to control the transition between three major flow patterns of an aqueous-oil Newtonian flow in a microchannel: droplets, beads-on-a-string (BOAS), and multi-stream laminar flow. We observed interesting transitional flow patterns between droplets and BOAS as the electric field was modulated. The ability to control flow patterns of a two-phase fluid in a microchannel adds to the microfluidic tool box and improves our understanding of this interesting fluid behavior.
Dynamic modelling for two-phase flow systems
International Nuclear Information System (INIS)
Guerra, M.A.
1991-06-01
Several models for two-phase flow have been studied, developing a thermal-hydraulic analysis code with one of these models. The program calculates, for one-dimensional cases with variable flow area, the transient behaviour of system process variables, when the boundary conditions (heat flux, flow rate, enthalpy and pressure) are functions of time. The modular structure of the code, eases the program growth. In fact, the present work is the basis for a general purpose accident and transient analysis code in nuclear reactors. Code verification has been made against RETRAN-02 results. Satisfactory results have been achieved with the present version of the code. (Author) [es
Research on boiling and two-phase flow
International Nuclear Information System (INIS)
Marinsek, Z.; Gaspersic, B.; Pavselj, D.; Tomsic, M.
1977-01-01
Report consists of three contributions. Experimental apparatus with pressure chamber (up to 25 bar and 250 deg C) was constructed including optical bubble detection device, and test measurements of mutual influence of boiling bubbles from two adjacent nucleation sites were performed; for analyses, a computer programme package for coincidence analyses of events was made, including data acquisition hardware. Two-phase pressure drop in subcooled Vertical annular water flow was measured, for pressures up to 10 bar, mass velocity 500 to 760 kg/m 2 s and vapour quality 0 to .01. Results agree fairly well with Martinelli-Nelson model
Virtual mass effects in two-phase flow. Topical report
International Nuclear Information System (INIS)
Cheng, L.Y.; Drew, D.A.; Lahey, R.T. Jr.
1978-03-01
The effect of virtual mass on phase separation during the acceleration of a two-phase mixture was studied. Virtual mass can be regarded as an induced inertia on the dispersed phase which is accelerating relative to the continuous phase, and it was found that the virtual mass acceleration is objective, implying an invariance with respect to reference frame. An objective form of the virtual acceleration was derived and required parameters were determined for limiting cases. Analyses determined that experiments on single bubble nozzle/diffuser flow cannot readily discriminate between various virtual mass acceleration models
Interfacial area measurements in two-phase flow
International Nuclear Information System (INIS)
Veteau, J.-M.
1979-08-01
A thorough understanding of two-phase flow requires the accurate measurement of the time-averaged interfacial area per unit volume (also called the time-averaged integral specific area). The so-called 'specific area' can be estimated by several techniques described in the literature. These different methods are reviewed and the flow conditions which lead to a rigourous determination of the time-averaged integral specific area are clearly established. The probe technique, involving local measurements seems very attractive because of its large range of application [fr
Heat transfer in two-phase flow of helium
International Nuclear Information System (INIS)
Subbotin, V.I.; Deev, V.I.; Solodovnikov, V.V.; Arkhipov, V.V.
1986-01-01
The results of experimental study of heat transfer in two-phase helium flow are presented. The effect of operating parameters (pressure, mass velocity, heat flux and quality) on boiling heat transfer intensity was investigated. A significant influence of boiling process prehistory on heat transfer coefficients was demonstrated. On the basis of experimental data obtained three typical regimes of flow boiling heat transfer were found. Analogy of heat transfer in flow boiling and pool boiling of helium and noncryogenic liquids was established. Correlations were developed which are in close agreement with available heat transfer data
Two-phase flow boiling pressure drop in small channels
International Nuclear Information System (INIS)
Sardeshpande, Madhavi V.; Shastri, Parikshit; Ranade, Vivek V.
2016-01-01
Highlights: • Study of typical 19 mm steam generator tube has been undertaken in detail. • Study of two phase flow boiling pressure drop, flow instability and identification of flow regimes using pressure fluctuations is the main focus of present work. • Effect of heat and mass flux on pressure drop and void fraction was studied. • Flow regimes identified from pressure fluctuations data using FFT plots. • Homogeneous model predicted pressure drop well in agreement. - Abstract: Two-phase flow boiling in small channels finds a variety of applications in power and process industries. Heat transfer, boiling flow regimes, flow instabilities, pressure drop and dry out are some of the key issues related to two-phase flow boiling in channels. In this work, the focus is on pressure drop in two-phase flow boiling in tubes of 19 mm diameter. These tubes are typically used in steam generators. Relatively limited experimental database is available on 19 mm ID tube. Therefore, in the present work, the experimental set-up is designed for studying flow boiling in 19 mm ID tube in such a way that any of the different flow regimes occurring in a steam generator tube (from pre-heating of sub-cooled water to dry-out) can be investigated by varying inlet conditions. The reported results cover a reasonable range of heat and mass flux conditions such as 9–27 kW/m 2 and 2.9–5.9 kg/m 2 s respectively. In this paper, various existing correlations are assessed against experimental data for the pressure drop in a single, vertical channel during flow boiling of water at near-atmospheric pressure. A special feature of these experiments is that time-dependent pressures are measured at four locations along the channel. The steady-state pressure drop is estimated and the identification of boiling flow regimes is done with transient characteristics using time series analysis. Experimental data and corresponding results are compared with the reported correlations. The results will be
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
Grandotto Biettoli, M.
2006-04-01
The author gives an overview of his research activity since 1981. He first gives a detailed presentation of properties and equations of two-phase flows in heat exchangers, and of their mathematical and numerical investigation: semi-local equations (mass conservation, momentum conservation and energy conservation), homogenized conservation equations (mass, momentum and enthalpy conservation, boundary conditions), equation closures, discretization, resolution algorithm, computational aspects and applications. Then, he reports the works performed in the field of turbulent flows, hyperbolic methods, low Mach methods, the Neptune project, and parallel computing
Lattice Boltzmann model for simulating immiscible two-phase flows
International Nuclear Information System (INIS)
Reis, T; Phillips, T N
2007-01-01
The lattice Boltzmann equation is often promoted as a numerical simulation tool that is particularly suitable for predicting the flow of complex fluids. This paper develops a two-dimensional 9-velocity (D2Q9) lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio using a single relaxation time for each fluid. In the macroscopic limit, this model is shown to recover the Navier-Stokes equations for two-phase flows. This is achieved by constructing a two-phase component of the collision operator that induces the appropriate surface tension term in the macroscopic equations. A theoretical expression for surface tension is determined. The validity of this analysis is confirmed by comparing numerical and theoretical predictions of surface tension as a function of density. The model is also shown to predict Laplace's law for surface tension and Poiseuille flow of layered immiscible binary fluids. The spinodal decomposition of two fluids of equal density but different viscosity is then studied. At equilibrium, the system comprises one large low viscosity bubble enclosed by the more viscous fluid in agreement with theoretical arguments of Renardy and Joseph (1993 Fundamentals of Two-Fluid Dynamics (New York: Springer)). Two other simulations, namely the non-equilibrium rod rest and the coalescence of two bubbles, are performed to show that this model can be used to simulate two fluids with a large density ratio
Experimental study of two-phase natural circulation circuit
Energy Technology Data Exchange (ETDEWEB)
Lemos, Wanderley Freitas; Su, Jian, E-mail: wlemos@lasme.coppe.ufrj.br, E-mail: sujian@nuclear.ufrj.br [Coordenacao dos Programas de Pos-Graduacao em Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Faccini, Jose Luiz Horacio, E-mail: faccini@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), RIo de Janeiro, RJ (Brazil). Lab. de Termo-Hidraulica Experimental
2012-07-01
This paper reports an experimental study on the behavior of fluid flow in natural circulation under single-and two-phase flow conditions. The natural circulation circuit was designed based on concepts of similarity and scale in proportion to the actual operating conditions of a nuclear reactor. This test equipment has similar performance to the passive system for removal of residual heat presents in Advanced Pressurized Water Reactors (A PWR). The experiment was carried out by supplying water to primary and secondary circuits, as well as electrical power resistors installed inside the heater. Power controller has available to adjust the values for supply of electrical power resistors, in order to simulate conditions of decay of power from the nuclear reactor in steady state. Data acquisition system allows the measurement and control of the temperature at different points by means of thermocouples installed at several points along the circuit. The behavior of the phenomenon of natural circulation was monitored by a software with graphical interface, showing the evolution of temperature measurement points and the results stored in digital format spreadsheets. Besides, the natural circulation flow rate was measured by a flowmeter installed on the hot leg. A flow visualization technique was used the for identifying vertical flow regimes of two-phase natural circulation. Finally, the Reynolds Number was calculated for the establishment of a friction factor correlation dependent on the scale geometrical length, height and diameter of the pipe. (author)
Reduced order modeling of flashing two-phase jets
Energy Technology Data Exchange (ETDEWEB)
Gurecky, William, E-mail: william.gurecky@utexas.edu; Schneider, Erich, E-mail: eschneider@mail.utexas.edu; Ballew, Davis, E-mail: davisballew@utexas.edu
2015-12-01
Highlights: • Accident simulation requires ability to quickly predict two-phase flashing jet's damage potential. • A reduced order modeling methodology informed by experimental or computational data is described. • Zone of influence volumes are calculated for jets of various upstream thermodynamic conditions. - Abstract: In the event of a Loss of Coolant Accident (LOCA) in a pressurized water reactor, the escaping coolant produces a highly energetic flashing jet with the potential to damage surrounding structures. In LOCA analysis, the goal is often to evaluate many break scenarios in a Monte Carlo style simulation to evaluate the resilience of a reactor design. Therefore, in order to quickly predict the damage potential of flashing jets, it is of interest to develop a reduced order model that relates the damage potential of a jet to the pressure and temperature upstream of the break and the distance from the break to a given object upon which the jet is impinging. This work presents framework for producing a Reduced Order Model (ROM) that may be informed by measured data, Computational Fluid Dynamics (CFD) simulations, or a combination of both. The model is constructed by performing regression analysis on the pressure field data, allowing the impingement pressure to be quickly reconstructed for any given upstream thermodynamic condition within the range of input data. The model is applicable to both free and fully impinging two-phase flashing jets.
Analytical study of solids-gas two phase flow
International Nuclear Information System (INIS)
Hosaka, Minoru
1977-01-01
Fundamental studies were made on the hydrodynamics of solids-gas two-phase suspension flow, in which very small solid particles are mixed in a gas flow to enhance the heat transfer characteristics of gas cooled high temperature reactors. Especially, the pressure drop due to friction and the density distribution of solid particles are theoretically analyzed. The friction pressure drop of two-phase flow was analyzed based on the analytical result of the single-phase friction pressure drop. The calculated values of solid/gas friction factor as a function of solid/gas mass loading are compared with experimental results. Comparisons are made for Various combinations of Reynolds number and particle size. As for the particle density distribution, some factors affecting the non-uniformity of distribution were considered. The minimum of energy dispersion was obtained with the variational principle. The suspension density of particles was obtained as a function of relative distance from wall and was compared with experimental results. It is concluded that the distribution is much affected by the particle size and that the smaller particles are apt to gather near the wall. (Aoki, K.)
Droplets formation and merging in two-phase flow microfluidics.
Gu, Hao; Duits, Michel H G; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
CFD Simulations of Pb-Bi Two-Phase Flow
International Nuclear Information System (INIS)
Dostal, Vaclav; Zelezny, Vaclav; Zacha, Pavel
2008-01-01
In a Pb-Bi cooled direct contact steam generation fast reactor water is injected directly above the core, the produced steam is separated at the top and is send to the turbine. Neither the direct contact phenomenon nor the two-phase flow simulations in CFD have been thoroughly described yet. A first attempt in simulating such two-phase flow in 2D using the CFD code Fluent is presented in this paper. The volume of fluid explicit model was used. Other important simulation parameters were: pressure velocity relation PISO, discretization scheme body force weighted for pressure, second order upwind for momentum and CISCAM for void fraction. Boundary conditions were mass flow inlet (Pb-Bi 0 kg/s and steam 0.07 kg/s) and pressure outlet. The effect of mesh size (0.5 mm and 0.2 mm cells) was investigated as well as the effect of the turbulent model. It was found that using a fine mesh is very important in order to achieve larger bubbles and the turbulent model (k-ε realizable) is necessary to properly model the slug flow. The fine mesh and unsteady conditions resulted in computationally intense problem. This may pose difficulties in 3D simulations of the real experiments. (authors)
Numerical calculation of two-phase turbulent jets
Energy Technology Data Exchange (ETDEWEB)
Saif, A.A.
1995-05-01
Two-phase turbulent round jets were numerically simulated using a multidimensional two-phase CFD code based on the two-fluid model. The turbulence phenomena were treated with the standard k-{epsilon} model. It was modified to take into account the additional dissipation of turbulent kinetic energy by the dispersed phase. Within the context of the two-fluid model it is more appropriate and physically justified to treat the diffusion by an interfacial force in the momentum equation. In this work, the diffusion force and the additional dissipation effect by the dispersed phase were modeled starting from the classical turbulent energy spectrum analysis. A cut-off frequency was proposed to decrease the dissipation effect by the dispersed phase when large size particles are introduced in the flow. The cut-off frequency combined with the bubble-induced turbulence effect allows for an increase in turbulence for large particles. Additional care was taken in choosing the right kind of experimental data from the literature so that a good separate effect test was possible for their models. The models predicted the experimental data very closely and they were general enough to predict extreme limit cases: water-bubble and air-droplet jets.
Computer simulation of two-phase flow in nuclear reactors
International Nuclear Information System (INIS)
Wulff, W.
1993-01-01
Two-phase flow models dominate the requirements of economic resources for the development and use of computer codes which serve to analyze thermohydraulic transients in nuclear power plants. An attempt is made to reduce the effort of analyzing reactor transients by combining purpose-oriented modelling with advanced computing techniques. Six principles are presented on mathematical modeling and the selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited than the two-fluid model for the analysis of two-phase flow in nuclear reactors, because of the latter's closure problems. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost. (orig.)
Experimental study of two-phase natural circulation circuit
International Nuclear Information System (INIS)
Lemos, Wanderley Freitas; Su, Jian; Faccini, Jose Luiz Horacio
2012-01-01
This paper reports an experimental study on the behavior of fluid flow in natural circulation under single-and two-phase flow conditions. The natural circulation circuit was designed based on concepts of similarity and scale in proportion to the actual operating conditions of a nuclear reactor. This test equipment has similar performance to the passive system for removal of residual heat presents in Advanced Pressurized Water Reactors (A PWR). The experiment was carried out by supplying water to primary and secondary circuits, as well as electrical power resistors installed inside the heater. Power controller has available to adjust the values for supply of electrical power resistors, in order to simulate conditions of decay of power from the nuclear reactor in steady state. Data acquisition system allows the measurement and control of the temperature at different points by means of thermocouples installed at several points along the circuit. The behavior of the phenomenon of natural circulation was monitored by a software with graphical interface, showing the evolution of temperature measurement points and the results stored in digital format spreadsheets. Besides, the natural circulation flow rate was measured by a flowmeter installed on the hot leg. A flow visualization technique was used the for identifying vertical flow regimes of two-phase natural circulation. Finally, the Reynolds Number was calculated for the establishment of a friction factor correlation dependent on the scale geometrical length, height and diameter of the pipe. (author)
Two-phase flow in a diverging nozzle
International Nuclear Information System (INIS)
Wadle, M.
1986-05-01
Stationary two-phase flow experiments were performed with steam-water and air-water mixtures in a well-instrumented horizontal diverging nozzle. The test section consisted of a constant diameter tube, the friction-section, followed by an expansion, the diffusor, which has a tanh-contour and finally another constant diameter tube. The diameter ratio sigma=D1/D2 is 16/80. For the steam-water experiments the flow parameters were: 0 2 and for air-water mixtures (0 2 ). The initial conditions were varied to achieve subcritical and critical mass flow rates. A new model for the pressure recovery in an abrupt expansion is presented. It is based on the superficial velocity concept and agrees well with the steam-water and the water-air experimental data as well as with the experiments of other authors. The experiments were also calculated with the two-phase code DUESE. The Drift-Flux models in this code as well as the constitutive correlations and their empirical constants could be tested. It is shown, that a 1D Drift-Flux code can handle the highly transient flow in the diffusor if the proper drift model is used. In a 1D simulation it is only necessary that the computational flow area is expanded to its full width within an axial length which is equivalent to the real contour. (orig./GL) [de
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Directory of Open Access Journals (Sweden)
Hao Gu
2011-04-01
Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Digital video image processing applications to two phase flow measurements
International Nuclear Information System (INIS)
Biscos, Y.; Bismes, F.; Hebrard, P.; Lavergne, G.
1987-01-01
Liquid spraying is common in various fields (combustion, cooling of hot surfaces, spray drying,...). For two phase flows modeling, it is necessary to test elementary laws (vaporizing drops, equation of motion of drops or bubbles, heat transfer..). For example, the knowledge of the laws related to the behavior of vaporizing liquid drop in a hot airstream and impinging drops on a hot surface is important for two phase flow modeling. In order to test these different laws in elementary cases, the authors developed different measurement techniques, associating video and microcomputers. The test section (built in perpex or glass) is illuminated with a thin sheet of light generated by a 15mW He-Ne laser and appropriate optical arrangement. Drops, bubbles or liquid film are observed at right angle by a video camera synchronised with a microcomputer either directly or with an optical device (lens, telescope, microscope) providing sufficient magnification. Digitizing the video picture in real time associated with an appropriate numerical treatment allows to obtain, in a non interfering way, a lot of informations relative to the pulverisation and the vaporization as function of space and time (drop size distribution; Sauter mean diameter as function of main flow parameters: air velocity, surface tension, temperature; isoconcentration curves, size evolution relative to vaporizing drops, film thickness evolution spreading on a hot surface...)
The PDF method for Lagrangian two-phase flow simulations
International Nuclear Information System (INIS)
Minier, J.P.; Pozorski, J.
1996-04-01
A recent turbulence model put forward by Pope (1991) in the context of PDF modelling has been used. In this approach, the one-point joint velocity-dissipation pdf equation is solved by simulating the instantaneous behaviour of a large number of Lagrangian fluid particles. Closure of the evolution equations of these Lagrangian particles is based on stochastic models and more specifically on diffusion processes. Such models are of direct use for two-phase flow modelling where the so-called fluid seen by discrete inclusions has to be modelled. Full Lagrangian simulations have been performed for shear-flows. It is emphasized that this approach gives far more information than traditional turbulence closures (such as the K-ε model) and therefore can be very useful for situations involving complex physics. It is also believed that the present model represents the first step towards a complete Lagrangian-Lagrangian model for dispersed two-phase flow problems. (authors). 21 refs., 6 figs
Studying Suspended Sediment Mechanism with Two-Phase PIV
Matinpour, H.; Atkinson, J. F.; Bennett, S. J.; Guala, M.
2017-12-01
Suspended sediment transport affects soil erosion, agriculture and water resources quality. Turbulent diffusion is the most primary force to maintain sediments in suspension. Although extensive previous literature have been studying the interactions between turbulent motion and suspended sediment, mechanism of sediments in suspension is still poorly understood. In this study, we investigate suspension of sediments as two distinct phases: one phase of sediments and another phase of fluid with turbulent motions. We designed and deployed a state-of-the-art two-phase PIV measurement technique to discriminate these two phases and acquire velocities of each phase separately and simultaneously. The technique that we have developed is employing a computer-vision based method, which enables us to discriminate sediment particles from fluid tracer particles based on two thresholds, dissimilar particle sizes and different particle intensities. Results indicate that fluid turbulence decreases in the presence of suspended sediments. Obtaining only sediment phase consecutive images enable us to compute fluctuation sediment concentration. This result enlightens understanding of complex interaction between the fluctuation velocities and the fluctuation of associated mass and compares turbulent viscosity with turbulent eddy diffusivity experimentally.
DarkSide-20k: A 20 Tonne Two-Phase LAr TPC for Direct Dark Matter Detection at LNGS
Energy Technology Data Exchange (ETDEWEB)
Aalseth, C.E.; et al.
2017-07-25
Building on the successful experience in operating the DarkSide-50 detector, the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMP search detector using a two-phase Liquid Argon Time Projection Chamber (LArTPC) with an active (fiducial) mass of 23 t (20 t). The DarkSide-20k LArTPC will be deployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV) inside a cylindrical Water Cherenkov Veto (WCV). Operation of DarkSide-50 demonstrated a major reduction in the dominant $^{39}$Ar background when using argon extracted from an underground source, before applying pulse shape analysis. Data from DarkSide-50, in combination with MC simulation and analytical modeling, shows that a rejection factor for discrimination between electron and nuclear recoils of $\\gt3\\times10^9$ is achievable. This, along with the use of the veto system, is the key to unlocking the path to large LArTPC detector masses, while maintaining an "instrumental background-free" experiment, an experiment in which less than 0.1 events (other than $\
Investigation of Power Losses of Two-Stage Two-Phase Converter with Two-Phase Motor
Directory of Open Access Journals (Sweden)
Michal Prazenica
2011-01-01
Full Text Available The paper deals with determination of losses of two-stage power electronic system with two-phase variable orthogonal output. The simulation is focused on the investigation of losses in the converter during one period in steady-state operation. Modeling and simulation of two matrix converters with R-L load is shown in the paper. The simulation results confirm a very good time-waveform of the phase current and the system seems to be suitable for low-cost application in automotive/aerospace industries and in application with high frequency voltage sources.
Prospects for photosensitive dopants in liquid argon
International Nuclear Information System (INIS)
Anderson, D.F.
1990-12-01
Evidence is presented that the addition of a few ppM of a photosensitive dopant to a U/liquid argon or Pb/liquid argon calorimeter will make a substantial reduction in the e/π ratio. Previous results indicating high voltage problems and no change in the e/π ratio in tests of photosensitive dopants with the Fermilab D0 experiment's U/liquid argon tests calorimeter are also explained. 13 refs., 3 figs
Salazar-Campoy, María M.; Morales, R. D.; Nájera-Bastida, A.; Calderón-Ramos, Ismael; Cedillo-Hernández, Valentín; Delgado-Pureco, J. C.
2018-04-01
The effects of nozzle design on dispersed, two-phase flows of the steel-argon system in a slab mold are studied using a water-air model with particle image velocimetry and ultrasound probe velocimetry techniques. Three nozzle designs were tested with the same bore size and different port geometries, including square (S), special bottom design with square ports (U), and circular (C). The meniscus velocities of the liquid increase two- or threefold in two-phase flows regarding one-phase flows using low flow rates of the gas phase. This effect is due to the dragging effects on bubbles by the liquid jets forming two-way coupled flows. Liquid velocities (primary phase) along the narrow face of the mold also are higher for two-phase flows. Flows using nozzle U are less dependent on the effects of the secondary phase (air). The smallest bubble sizes are obtained using nozzle U, which confirms that bubble breakup is dependent on the strain rates of the fluid and dissipation of kinetic energy in the nozzle bottom and port edges. Through dimensionless analysis, it was found that the bubble sizes are inversely proportional to the dissipation rate of the turbulent kinetic energy, ɛ 0.4. A simple expression involving ɛ, surface tension, and density of metal is derived to scale up bubble sizes in water to bubble sizes in steel with different degrees of deoxidation. The validity of water-air models to study steel-argon flows is discussed. Prior works related with experiments to model argon bubbling in steel slab molds under nonwetting conditions are critically reviewed.
Two-phase flow induced vibrations in CANDU steam generators
International Nuclear Information System (INIS)
Gidi, A.
2009-01-01
The U-Bend region of nuclear steam generators tube bundles have suffered from two-phase cross flow induced vibrations. Tubes in this region have experienced high amplitude vibrations leading to catastrophic failures. Turbulent buffeting and fluid-elastic instability has been identified as the main causes. Previous investigations have focused on flow regime and two-phase flow damping ratio. However, tube bundles in steam generators have vapour generated on the surface of the tubes, which might affect the flow regime, void fraction distribution, turbulent intensity levels and tube-flow interaction, all of which have the potential to change the tube vibration response. A cantilevered tube bundle made of electric cartridges heaters was built and tested in a Freon-11 flow loop at McMaster University. Tubes were arranged in a parallel triangular configuration. The bundle was exposed to two-phase cross flows consisting of different combinations of void from two sources, void generated upstream of the bundle and void generated at the surface of the tubes. Tube tip vibration response was measured optically and void fraction was measured by gamma densitometry technique. It was found that tube vibration amplitude in the transverse direction was reduced by a factor of eight for void fraction generated at the tube surfaces only, when compared to the upstream only void generation case. The main explanation for this effect is a reduction in the correlation length of the turbulent buffeting forcing function. Theoretical calculations of the tube vibration response due to turbulent buffeting under the same experimental conditions predicted a similar reduction in tube amplitude. The void fraction for the fluid-elastic instability threshold in the presence of tube bundle void fraction generation was higher than that for the upstream void fraction generation case. The first explanation of this difference is the level of turbulent buffeting forces the tube bundle was exposed to
Mixed convection in a two-phase flow cooling loop
International Nuclear Information System (INIS)
Janssens-Maenhout, G.; Daubner, M.; Knebel, J.U.
2002-03-01
This report summarizes the numerical simulations using the CFD code CFX4.1 which has additional models for subcooled flow boiling phenomena and the interfacial forces. The improved CFX4.1 code can be applied to the design of boiling induced mixed convection cooling loops in a defined parameter range. The experimental part describes the geysering experiments and the instability effects on the two-phase natural circulation flow. An experimentally validated flow pattern map in the Phase Change Number - Subcooling Number (N PCh - N Sub ) diagram defines the operational range in which flow instabilities such as geysering can be expected. One important perspective of this combined experimental/numerical work, which is in the field of two-phase flow, is its application to the development of accelerator driven systems (ADS). The main objective on an ADS is its potential to transmute minor actinides and long-lived fission products, thus participating in closing the fuel cycle. The development of an ADS is an important issue within the Euratom Fifth FP on Partitioning and Transmutation. One concept of an ADS, which is investigated in more detail within the ''preliminary design study of an experimental ADS'' Project (PDS-XADS) of the Euratom Fifth FP, is the XADS lead-bismuth cooled Experimental ADS of ANSALDO. An essential feature of this concept is the natural circulation of the primary coolant within the reactor pool. The natural circulation, which is driven by the density differences between the blanket and the heat exchanger, is enhanced by the injection of the nitrogen cover gas through spargers located in a riser part just above the blanket. This so-called gas-lift pump system has not been investigated in more detail nor has this gas-lift pump system been numerically/experimentally confirmed. The knowledge gained within the SUCO Programe, i.e. the modelling of the interfacial forces, the experimental work on flow instabilities and the modelling of the interfacial area
Mixed convection in a two-phase flow cooling loop
Energy Technology Data Exchange (ETDEWEB)
Janssens-Maenhout, G.; Daubner, M.; Knebel, J.U.
2002-03-01
This report summarizes the numerical simulations using the CFD code CFX4.1 which has additional models for subcooled flow boiling phenomena and the interfacial forces. The improved CFX4.1 code can be applied to the design of boiling induced mixed convection cooling loops in a defined parameter range. The experimental part describes the geysering experiments and the instability effects on the two-phase natural circulation flow. An experimentally validated flow pattern map in the Phase Change Number - Subcooling Number (N{sub PCh} - N{sub Sub}) diagram defines the operational range in which flow instabilities such as geysering can be expected. One important perspective of this combined experimental/numerical work, which is in the field of two-phase flow, is its application to the development of accelerator driven systems (ADS). The main objective on an ADS is its potential to transmute minor actinides and long-lived fission products, thus participating in closing the fuel cycle. The development of an ADS is an important issue within the Euratom Fifth FP on Partitioning and Transmutation. One concept of an ADS, which is investigated in more detail within the ''preliminary design study of an experimental ADS'' Project (PDS-XADS) of the Euratom Fifth FP, is the XADS lead-bismuth cooled Experimental ADS of ANSALDO. An essential feature of this concept is the natural circulation of the primary coolant within the reactor pool. The natural circulation, which is driven by the density differences between the blanket and the heat exchanger, is enhanced by the injection of the nitrogen cover gas through spargers located in a riser part just above the blanket. This so-called gas-lift pump system has not been investigated in more detail nor has this gas-lift pump system been numerically/experimentally confirmed. The knowledge gained within the SUCO Programe, i.e. the modelling of the interfacial forces, the experimental work on flow instabilities and the
Dynamics of imploding argon plasmas
International Nuclear Information System (INIS)
Clark, W.; Richardson, R.; Brannon, J.; Wilkinson, M.; Katzenstein, J.
1982-01-01
The BLACKJACK 5 pulse generator has been used to implode annular argon plasmas to form dense Z pinches. Visible streak photography, framing photography, and laser shadowgraphy were used to observe the radial position and velocity of the plasmas as they imploded. The measured position and velocity of the imploding plasmas have been compared with the results of calculations based on a one-dimensional snowplow model. Good agreement is obtained between the snowplow calculations and the optical measurements. Empirically determined optimum implosion parameters are also found to agree with those predicted by the model
Radiation damage effect on avalanche photodiodes
Baccaro, S; Cavallari, F; Da Ponte, V; Deiters, K; Denes, P; Diemoz, M; Kirn, Th; Lintern, A L; Longo, E; Montecchi, M; Musienko, Y; Pansart, J P; Renker, D; Reucroft, S; Rosi, G; Rusack, R; Ruuska, D; Stephenson, R; Torbet, M J
1999-01-01
Avalanche Photodiodes have been chosen as photon sensors for the electromagnetic calorimeter of the CMS experiment at the LHC. These sensors should operate in the 4T magnetic field of the experiment. Because of the high neutron radiation in the detector extensive studies have been done by the CMS collaboration on the APD neutron radiation damage. The characteristics of these devices after irradiation have been analized, with particular attention to the quantum efficiency and the dark current. The recovery of the radiation induced dark current has been studied carefully at room temperature and at slightly lower and higher temperatures. The temperature dependence of the defects decay-time has been evaluated.
Lifetime of Bubble Rafts: Cooperativity and Avalanches
Ritacco, Hernán; Kiefer, Flavien; Langevin, Dominique
2007-06-01
We have studied the collapse of pseudo-bi-dimensional foams. These foams are made of uniformly sized soap bubbles packed in an hexagonal lattice sitting at the top of a liquid surface. The collapse process follows the sequence: (1) rupture of a first bubble, driven by thermal fluctuations and (2) a cascade of bursting bubbles. We present a simple numerical model which captures the main characteristics of the dynamics of foam collapse. We show that in a certain range of viscosities of the foaming solutions, the size distribution of the avalanches follows power laws as in self-organized criticality processes.
TCAD simulation of Low Gain Avalanche Detectors
Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti
2016-11-01
In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.
Tuning magnetization avalanches in Mn12-acetate
Wen, Bo; McHugh, S.; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.; Bagai, R.; Christou, G.
2009-03-01
We report the results of a systematic study of magnetic avalanches (abrupt magnetization reversals) in the molecular magnet Mn12-acetate using a micron-sized Hall sensor array. Measurements were taken for: (a) fixed magnetic field (constant barrier against spin reversal); and (b) fixed energy release obtained by adjusting the barrier and δM. A detailed comparison with the theory of magnetic deflagration of Garanin and Chudnovsky [1] will be presented and discussed. [1] D. A. Garanin and E. M. Chudnovsky, Phys. Rev. B 76, 054410 (2007)
TCAD simulation of Low Gain Avalanche Detectors
Energy Technology Data Exchange (ETDEWEB)
Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh, E-mail: ashutosh.bhardwaj@cern.ch; Ranjan, Kirti
2016-11-11
In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.
TCAD simulation of Low Gain Avalanche Detectors
International Nuclear Information System (INIS)
Dalal, Ranjeet; Jain, Geetika; Bhardwaj, Ashutosh; Ranjan, Kirti
2016-01-01
In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.
ESR imaging investigations of two-phase systems.
Herrmann, Werner; Stösser, Reinhard; Borchert, Hans-Hubert
2007-06-01
The possibilities of electron spin resonance (ESR) and electron spin resonance imaging (ESRI) for investigating the properties of the spin probes TEMPO and TEMPOL in two-phase systems have been examined in the systems water/n-octanol, Miglyol/Miglyol, and Precirol/Miglyol. Phases and regions of the phase boundary could be mapped successfully by means of the isotropic hyperfine coupling constants, and, moreover, the quantification of rotational and lateral diffusion of the spin probes was possible. For the quantitative treatment of the micropolarity, a simplified empirical model was established on the basis of the Nernst distribution and the experimentally determined isotropic hyperfine coupling constants. The model does not only describe the summarized micropolarities of coexisting phases, but also the region of the phase boundary, where solvent molecules of different polarities and tendencies to form hydrogen bonds compete to interact with the NO group of the spin probe. Copyright 2007 John Wiley & Sons, Ltd.
Characterization of the two-phase Taylor Couette flow
International Nuclear Information System (INIS)
Mehel A; Gabillet B; Djeridi H
2005-01-01
The focus of the present study concerns the effects of a dispersed phase on the structure of a quasi periodic Couette Taylor flow. The two phase flow patterns are investigated experimentally for the Taylor number Ta=780. Small bubbles (0.035 times as small as the gap) are generated by agitation of the upper free surface. Larger bubbles (0.15 times as small as the gap) are produced by injection at the bottom of the apparatus associated with a pressure drop. Void fraction, bubble size and velocity are measured, as well as the azimuthal and axial velocity components of the liquid. A premature transition to turbulence is pointed out and discussed according to the bubble size and their localization in the gap. (authors)
Response of two-phase droplets to intense electromagnetic radiation
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-01-01
The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii of 37, 55, and 80 microns) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.
Two-phase flow in beds of spherical particles
International Nuclear Information System (INIS)
Schulenberg, T.; Mueller, U.
1984-02-01
A refined model for two-phase flow in beds of uniform spherical particles is presented. It includes the influence of interfacial drag forces between liquid and gas, which are important in beds of coarse particles, and an incrase of porosity due to vapour channels or similiar irreversible bed disturbances, which occur in beds of fine particles. The model is based on the momentum equations for separated flow, which are closed with empirical relations for wall shear stress and interfacial drag. To improve this model it is applied to volumetrically heated beds on a adiabatic bottom, which are saturated and superimposed with a boiling liquid. In case of fine particles only an impermeable bottom is considered, whereas in case of coarse particles also beds on a permeable support are discussed. (orig.) [de
Particle clustering within a two-phase turbulent pipe jet
Lau, Timothy; Nathan, Graham
2016-11-01
A comprehensive study of the influence of Stokes number on the instantaneous distributions of particles within a well-characterised, two-phase, turbulent pipe jet in a weak co-flow was performed. The experiments utilised particles with a narrow size distribution, resulting in a truly mono-disperse particle-laden jet. The jet Reynolds number, based on the pipe diameter, was in the range 10000 developed technique. The results show that particle clustering is significantly influenced by the exit Stokes number. Particle clustering was found to be significant for 0 . 3 financial contributions by the Australian Research Council (Grant No. DP120102961) and the Australian Renewable Energy Agency (Grant No. USO034).
Unsteady interfacial coupling of two-phase flow models
International Nuclear Information System (INIS)
Hurisse, O.
2006-01-01
The primary coolant circuit in a nuclear power plant contains several distinct components (vessel, core, pipes,...). For all components, specific codes based on the discretization of partial differential equations have already been developed. In order to obtain simulations for the whole circuit, the interfacial coupling of these codes is required. The approach examined within this work consists in coupling codes by providing unsteady information through the coupling interface. The numerical technique relies on the use of an interface model, which is combined with the basic strategy that was introduced by Greenberg and Leroux in order to compute approximations of steady solutions of non-homogeneous hyperbolic systems. Three different coupling cases have been examined: (i) the coupling of a one-dimensional Euler system with a two-dimensional Euler system; (ii) the coupling of two distinct homogeneous two-phase flow models; (iii) the coupling of a four-equation homogeneous model with the standard two-fluid model. (author)
Mathematical model of two-phase flow in accelerator channel
Directory of Open Access Journals (Sweden)
О.Ф. Нікулін
2010-01-01
Full Text Available The problem of two-phase flow composed of energy-carrier phase (Newtonian liquid and solid fine-dispersed phase (particles in counter jet mill accelerator channel is considered. The mathematical model bases goes on the supposition that the phases interact with each other like independent substances by means of aerodynamics’ forces in conditions of adiabatic flow. The mathematical model in the form of system of differential equations of order 11 is represented. Derivations of equations by base physical principles for cross-section-averaged quantity are produced. The mathematical model can be used for estimation of any kinematic and thermodynamic flow characteristics for purposely parameters optimization problem solving and transfer functions determination, that take place in counter jet mill accelerator channel design.
Two-phase titration of cerium(III) by permanganate
International Nuclear Information System (INIS)
Lazarev, A.I.; Lazareva, V.I.; Gerko, V.V.
1987-01-01
This paper presents a method for the two-phase titrimetric determination of cerium(III) with permanganate which does not require an expenditure of sugar and preliminary removal of chlorides and nitrates. The interaction of cerium(III) with permanganate at room temperature was studied as a function of the pH, the concentration of pyrophosphate, tetraphenylphosphonium (TPP), permanganate, and extraneous compounds, the rate of titration, and the time of stay of the solution in air before titration. The investigations were conducted according to the following methodology: water, solution of cerium(III) pyrophosphate, and TPP were introduced into an Erlenmeyer flask with a side branch near the bottom for clearer observation of the color of the chloroform phase. The authors established the given pH value, poured the water into a volume of 50 ml, and added chloroform. The result was titrated with permanganate solutions of various concentrations until a violet color appeared in the chloroform phase
Interfacial shear modeling in two-phase annular flow
International Nuclear Information System (INIS)
Kumar, R.; Edwards, D.P.
1996-11-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment
Experiments in polydisperse two-phase turbulent flows
International Nuclear Information System (INIS)
Bachalo, W.D.; Houser, M.J.
1985-01-01
Aspects of turbulent two-phase flow measurements obtained with a laser Doppler velocimeter that was modified to also obtain particle size were investigated. Simultaneous measurements of the particle size and velocity allowed the determination of the lag characteristics of particles over a range of sizes. Relatively large particles were found to respond well to the turbulent fluctuations in low speed flows. Measurements of sprays were obtained at various points throughout the spray plume. Velocity measurements for each drop size class were obtained and revealed the relative velocity relaxation with downstream distance. The evolution of the rms velocities for each size class was also examined. Difficulties associated with seeding polydispersions to obtain gas phase turbulence data were discussed. Several approaches for mitigating the errors due to seed particle concentration bias were reviewed
Interfacial shear modeling in two-phase annular flow
International Nuclear Information System (INIS)
Kumar, R.; Edwards, D.P.
1996-07-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment
Numerical modeling of two-phase transonic flow
Czech Academy of Sciences Publication Activity Database
Halama, Jan; Benkhaldoun, F.; Fořt, Jaroslav
2010-01-01
Roč. 80, č. 88 (2010), s. 1624-1635 ISSN 0378-4754 Grant - others:GA ČR(CZ) GA201/08/0012 Program:GA Institutional research plan: CEZ:AV0Z20760514 Keywords : two - phase flow * condensation * fractional step method Subject RIV: BK - Fluid Dynamics Impact factor: 0.812, year: 2010 http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V0T-4VNK68X-2-R&_cdi=5655&_user=640952&_pii=S0378475409000421&_origin=search&_coverDate=04%2F30%2F2010&_sk=999199991&view=c&wchp=dGLzVlb-zSkWb&md5=5ba607428fac339a3e5f67035d3996d0&ie=/sdarticle.pdf
Two-phase flow instabilities in a vertical annular channel
Energy Technology Data Exchange (ETDEWEB)
Babelli, I.; Nair, S.; Ishii, M. [Purdue Univ., West Lafayette, IN (United States)
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Dynamics Coefficient for Two-Phase Soil Model
Directory of Open Access Journals (Sweden)
Wrana Bogumił
2015-02-01
Full Text Available The paper investigates a description of energy dissipation within saturated soils-diffusion of pore-water. Soils are assumed to be two-phase poro-elastic materials, the grain skeleton of which exhibits no irreversible behavior or structural hysteretic damping. Description of motion and deformation of soil is introduced as a system of equations consisting of governing dynamic consolidation equations based on Biot theory. Selected constitutive and kinematic relations for small strains and rotation are used. This paper derives a closed form of analytical solution that characterizes the energy dissipation during steady-state vibrations of nearly and fully saturated poro-elastic columns. Moreover, the paper examines the influence of various physical factors on the fundamental period, maximum amplitude and the fraction of critical damping of the Biot column. Also the so-called dynamic coefficient which shows amplification or attenuation of dynamic response is considered.
Two-phase flow experiments through intergranular stress corrosion cracks
International Nuclear Information System (INIS)
Collier, R.P.; Norris, D.M.
1984-01-01
Experimental studies of critical two-phase water flow, through simulated and actual intergranular stress corrosion cracks, were performed to obtain data to evaluate a leak flow rate model and investigate acoustic transducer effectiveness in detecting and sizing leaks. The experimental program included a parametric study of the effects of crack geometry, fluid stagnation pressure and temperature, and crack surface roughness on leak flow rate. In addition, leak detection, location, and leak size estimation capabilities of several different acoustic transducers were evaluated as functions of leak rate and transducer position. This paper presents flow rate data for several different cracks and fluid conditions. It also presents the minimum flows rate detected with the acoustic sensors and a relationship between acoustic signal strength and leak flow rate
Two-Phase Algorithm for Optimal Camera Placement
Directory of Open Access Journals (Sweden)
Jun-Woo Ahn
2016-01-01
Full Text Available As markers for visual sensor networks have become larger, interest in the optimal camera placement problem has continued to increase. The most featured solution for the optimal camera placement problem is based on binary integer programming (BIP. Due to the NP-hard characteristic of the optimal camera placement problem, however, it is difficult to find a solution for a complex, real-world problem using BIP. Many approximation algorithms have been developed to solve this problem. In this paper, a two-phase algorithm is proposed as an approximation algorithm based on BIP that can solve the optimal camera placement problem for a placement space larger than in current studies. This study solves the problem in three-dimensional space for a real-world structure.
Study on hydrodynamic crisis of two-phase flow
International Nuclear Information System (INIS)
Nigmatulin, B.I.; Ivandaev, A.I.
1977-01-01
The phenomenon of hydrodynamic crisis (locking) of a two-phase flow is investigated. A model of a disperseannular flow with an effective monodisperse nucleus is used for describing the motion of a mixture under near-critical conditions. Main differential equations of a flow in a channel are given; in particular, the differential laws of variation of the effective diameters of drops in the nucleus as a result of mass exchange between the mixture components are singled out. Questions of concretization of the model are discussed. The conditions for the attainment of the maximum rate of flow of the gas through the channel are studied, as well as the effect of the flow prehistory on the formation of critical conditions in the outlet cross-section
Study on hydrodynamic crisis of two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Nigmatulin, B I; Ivandaev, A I [Moskovskij Gosudarstvennyj Univ. (USSR). Nauchno-Issledovatel' skij Inst. Mekhaniki
1977-01-01
The phenomenon of hydrodynamic crisis (locking) of a two-phase flow is investigated. A model of a disperse annular flow with an effective monodisperse nucleus is used for describing the motion of a mixture under near-critical conditions. Main differential equations of a flow in a channel are given; in particular, the differential laws of variation of the effective diameters of drops in the nucleus as a result of mass exchange between the mixture components are singled out. Questions of concretization of the model are discussed. The conditions for the attainment of the maximum rate of flow of the gas through the channel are studied, as well as the effect of the flow prehistory on the formation of critical conditions in the outlet cross-section.
Gulping phenomena in transient countercurrent two-phase flow
International Nuclear Information System (INIS)
Tehrani, Ali A.K.
2001-04-01
Apart from previous work on countercurrent gas-liquid flow, transient tank drainage through horizontal off-take pipes is described, including experimental procedure, flow pattern on observations and countercurrent flow limitation results. A separate chapter is devoted to countercurrent two-phase flow in a pressurised water reactor hot-leg scaled model. Results concerning low head flooding, high head and loss of bowl flooding, transient draining of the steam generator and pressure variation and bubble detachment are presented. The following subjects are covered as well: draining of sealed tanks of vertical pipes, unsteady draining of closed vessel via vertical tube, unsteady filling of a closed vessel via vertical tube from a constant head reservoir. Practical significance of the results obtained is discussed
Measurement of two-phase flow momentum with force transducers
International Nuclear Information System (INIS)
Hardy, J.E.; Smith, J.E.
1990-01-01
Two strain-gage-based drag transducers were developed to measure two-phase flow in simulated pressurized water reactor (PWR) test facilities. One transducer, a drag body (DB), was designed to measure the bidirectional average momentum flux passing through an end box. The second drag sensor, a break through detector (BTD), was designed to sense liquid downflow from the upper plenum to the core region. After prototype sensors passed numerous acceptance tests, transducers were fabricated and installed in two experimental test facilities, one in Japan and one in West Germany. High-quality data were extracted from both the DBs and BTDs for a variety of loss-of-coolant accident (LOCA) scenarios. The information collected from these sensors has added to the understanding of the thermohydraulic phenomena that occur during the refill/reflood stage of a LOCA in a PWR. 9 refs., 15 figs
Flooding in counter-current two-phase flow
International Nuclear Information System (INIS)
Ragland, W.A.; Ganic, E.N.
1982-01-01
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding
Modeling two-phase ferroelectric composites by sequential laminates
International Nuclear Information System (INIS)
Idiart, Martín I
2014-01-01
Theoretical estimates are given for the overall dissipative response of two-phase ferroelectric composites with complex particulate microstructures under arbitrary loading histories. The ferroelectric behavior of the constituent phases is described via a stored energy density and a dissipation potential in accordance with the theory of generalized standard materials. An implicit time-discretization scheme is used to generate a variational representation of the overall response in terms of a single incremental potential. Estimates are then generated by constructing sequentially laminated microgeometries of particulate type whose overall incremental potential can be computed exactly. Because they are realizable, by construction, these estimates are guaranteed to conform with any material constraints, to satisfy all pertinent bounds and to exhibit the required convexity properties with no duality gap. Predictions for representative composite and porous systems are reported and discussed in the light of existing experimental data. (paper)
Two-phase flow and heat transfer under low gravity
Frost, W.
1981-01-01
Spacelab experiment to investigate two-phase flow patterns under gravity uses a water-air mixture experiment. Air and water are circulated through the system. The quality or the mixture or air-water is controlled. Photographs of the test section are made and at the same time pressure drop across the test section is measured. The data establishes a flow regime map under reduced gravity conditions with corresponding pressure drop correlations. The test section is also equipped with an electrical resistance heater in order to allow a flow boiling experiment to be carried out using Freon II. High-speed photographs of the test section are used to determine flow patterns. The temperature gradient and pressure drop along the duct can be measured. Thus, quality change can be measured, and heat transfer calculated.
Characteristics of two-phase flows in large diameter channels
Energy Technology Data Exchange (ETDEWEB)
Schlegel, J.P., E-mail: schlegelj@mst.edu [Department of Mining and Nuclear Engineering, Missouri University of Science and Technology, 301 W 14th St., Rolla, MO 65401 (United States); Hibiki, T.; Ishii, M. [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907 (United States)
2016-12-15
Two-phase flows in large diameter channels have a great deal of importance in a wide variety of industrial applications. Nuclear systems, petroleum refineries, and chemical processes make extensive use of larger systems. Flows in such channels have very different properties from flows in smaller channels which are typically used in experimental research. In this paper, the various differences between flows in large and small channels are highlighted using the results of previous experimental and analytical research. This review is followed by a review of recent experiments in and model development for flows in large diameter channels performed by the authors. The topics of these research efforts range from void fraction and interfacial area concentration measurement to flow regime identification and modeling, drift-flux modeling for high void fraction conditions, and evaluation of interfacial area transport models for large diameter channels.
Flooding in counter-current two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Ragland, W.A.; Ganic, E.N.
1982-01-01
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding.
The pdf approach to turbulent polydispersed two-phase flows
Minier, Jean-Pierre; Peirano, Eric
2001-10-01
The purpose of this paper is to develop a probabilistic approach to turbulent polydispersed two-phase flows. The two-phase flows considered are composed of a continuous phase, which is a turbulent fluid, and a dispersed phase, which represents an ensemble of discrete particles (solid particles, droplets or bubbles). Gathering the difficulties of turbulent flows and of particle motion, the challenge is to work out a general modelling approach that meets three requirements: to treat accurately the physically relevant phenomena, to provide enough information to address issues of complex physics (combustion, polydispersed particle flows, …) and to remain tractable for general non-homogeneous flows. The present probabilistic approach models the statistical dynamics of the system and consists in simulating the joint probability density function (pdf) of a number of fluid and discrete particle properties. A new point is that both the fluid and the particles are included in the pdf description. The derivation of the joint pdf model for the fluid and for the discrete particles is worked out in several steps. The mathematical properties of stochastic processes are first recalled. The various hierarchies of pdf descriptions are detailed and the physical principles that are used in the construction of the models are explained. The Lagrangian one-particle probabilistic description is developed first for the fluid alone, then for the discrete particles and finally for the joint fluid and particle turbulent systems. In the case of the probabilistic description for the fluid alone or for the discrete particles alone, numerical computations are presented and discussed to illustrate how the method works in practice and the kind of information that can be extracted from it. Comments on the current modelling state and propositions for future investigations which try to link the present work with other ideas in physics are made at the end of the paper.
Flashing liquid jets and two-phase droplet dispersion
International Nuclear Information System (INIS)
Cleary, Vincent; Bowen, Phil; Witlox, Henk
2007-01-01
The large-scale release of a liquid contained at upstream conditions above its local atmospheric boiling point is a scenario often given consideration in process industry risk analysis. Current-hazard quantification software often employs simplistic equilibrium two-phase approaches. Scaled water experiments have been carried out measuring droplet velocity and droplet size distributions for a range of exit orifice aspect ratios (L/d) and conditions representing low to high superheat. 2D Phase-Doppler Anemometry has been utilised to characterise droplet kinematics and spray quality. Droplet size correlations have been developed for non-flashing, the transition between non-flashing and flashing, and fully flashing jets. Using high-speed shadowography, transition between regimes is defined in terms of criteria identified in the external flow structure. An overview companion paper provides a wider overview of the problem and reports implementation of these correlations into consequence models and subsequent validation. The fluid utilised throughout is water, hence droplet correlations are developed in non-dimensional form to allow extrapolation to other fluids through similarity scaling, although verification of model performance for other fluids is required in future studies. Data is reduced via non-dimensionalisation in terms of the Weber number and Jakob number, essentially representing the fluid mechanics and thermodynamics of the system, respectively. A droplet-size distribution correlation has also been developed, conveniently presented as a volume undersize distribution based on the Rosin-Rammler distribution. Separate correlations are provided for sub-cooled mechanical break-up and fully flashing jets. This form of correlation facilitates rapid estimates of likely mass rainout quantities, as well as full distribution information for more rigorous two-phase thermodynamic modelling in the future
Construction of the two-phase critical flow test facility
International Nuclear Information System (INIS)
Chung, C. H.; Chang, S. K.; Park, H. S.; Min, K. H.; Choi, N. H.; Kim, C. H.; Lee, S. H.; Kim, H. C.; Chang, M. H.
2002-03-01
The two-phase critical test loop facility has been constructed in the KAERI engineering laboratory for the simulation of small break loss of coolant accident entrained with non-condensible gas of SMART. The test facility can operate at 12 MPa of pressure and 0 to 60 C of sub-cooling with 0.5 kg/s of non- condensible gas injection into break flow, and simulate up to 20 mm of pipe break. Main components of the test facility were arranged such that the pressure vessel containing coolant, a test section simulating break and a suppression tank inter-connected with pipings were installed vertically. As quick opening valve opens, high pressure/temperature coolant flows through the test section forming critical two-phase flow into the suppression tank. The pressure vessel was connected to two high pressure N2 gas tanks through a control valve to control pressure in the pressure vessel. Another N2 gas tank was also connected to the test section for the non-condensible gas injection. The test facility operation was performed on computers supported with PLC systems installed in the control room, and test data such as temperature, break flow rate, pressure drop across test section, gas injection flow rate were all together gathered in the data acquisition system for further data analysis. This test facility was classified as a safety related high pressure gas facility in law. Thus the loop design documentation was reviewed, and inspected during construction of the test loop by the regulatory body. And the regulatory body issued permission for the operation of the test facility
Psychological distress through immigration: the two-phase temporal pattern?
Ritsner, M; Ponizovsky, A
1999-01-01
A large community sample, cross-sectional and in part longitudinal design, and comparison groups was used to determine the timing of psychological distress among immigrants. A total of 2,378 adult immigrants from the former Soviet Union to Israel completed the self-administered questionnaire Talbieh Brief Distress Inventory. The aggregate levels of distress and six psychological symptoms--obsessiveness, hostility, interpersonal sensitivity, depression, anxiety, and paranoid ideation--were compared at 20 intervals covering 1 to 60 months after resettlement. The level of psychological distress was significantly higher in the immigrants than that of Israeli natives but not in the potential immigrant controls. A two-phase temporal pattern of development of psychological distress was revealed consisting of escalation and reduction phases. The escalation phase was characterized by an increase in distress levels until the 27th month after arrival (a peak) and the reduction phase led to a decline returning to normal levels. The 1-month prevalence rate was 15.6% for the total sample, and for highly distressed subjects it reached 24% at the 27th month after arrival, and it declined to 4% at the 44th month. The time pattern of distress shared males and females, married and divorced/widowed (but not singles), as well as subjects of all age groups (except for immigrants in their forties). The two-phase pattern of distress obtained according to cross-sectional data was indirectly confirmed through a longitudinal way. Claims of early euphoric or distress-free period followed by mental health crisis frequently referred to in the literature on migration was not supported by this study.
Two-phase flow heat transfer in nuclear reactor systems
International Nuclear Information System (INIS)
Koncar, Bostjan; Krepper, Eckhard; Bestion, Dominique; Song, Chul-Hwa; Hassan, Yassin A.
2013-01-01
Complete text of publication follows: Heat transfer and phase change phenomena in two-phase flows are often encountered in nuclear reactor systems and are therefore of paramount importance for their optimal design and safe operation.The complex phenomena observed especially during transient operation of nuclear reactor systems necessitate extensive theoretical and experimental investigations. This special issue brings seven research articles of high quality. Though small in number, they cover a wide range of topics, presenting high complexity and diversity of heat transfer phenomena in two-phase flow. In the last decades a vast amount of research has been devoted to theoretical work and computational simulations, yet the experimental work remains indispensable for understanding of two-phase flow phenomena and for model validation purposes. This is reflected also in this issue, where only one article is purely experimental, while three of them deal with theoretical modelling and the remaining three with numerical simulations. The experimental investigation of the critical heat flux (CHF) phenomena by means of photographic study is presented in the paper of J. Park et al. They have used a high-speed camera system to observe the transient boiling characteristics on a thin horizontal cylinder submerged in a pool of water or highly wetting liquid. Experiments show that the initial boiling process is strongly affected by the properties and wettability of the liquid. The authors have stressed the importance of the local scale observation leading to better understanding of the transient CHF phenomena. In the article of G. Espinosa-Paredes et al. a theoretical work concerning the derivation of transport equations for two-phase flow is presented. The author proposes a novel approach based on derivation of nonlocal volume averaged equations which contain new terms related to nonlocal transport effects. These non-local terms act as coupling elements between the phenomena
Electric field distribution and simulation of avalanche formation due ...
Indian Academy of Sciences (India)
Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel and crossed wire grid configurations are studied. It is found that the crossed ...
High voltage short plus generation based on avalanche circuit
International Nuclear Information System (INIS)
Hu Yuanfeng; Yu Xiaoqi
2006-01-01
Simulate the avalanche circuit in series with PSPICE module, design the high voltage short plus generation circuit by avalanche transistor in series for the sweep deflection circuit of streak camera. The output voltage ranges 1.2 KV into 50 ohm load. The rise time of the circuit is less than 3 ns. (authors)
Design and characterization of single photon avalanche diodes arrays
Neri, L.; Tudisco, S.; Lanzanò, L.; Musumeci, F.; Privitera, S.; Scordino, A.; Condorelli, G.; Fallica, G.; Mazzillo, M.; Sanfilippo, D.; Valvo, G.
2010-05-01
During the last years, in collaboration with ST-Microelectronics, we developed a new avalanche photo sensor, single photon avalanche diode (SPAD) see Ref.[S. Privitera, et al., Sensors 8 (2008) 4636 [1];S. Tudisco et al., IEEE Sensors Journal 8 (2008) 1324 [2
Measuring neuronal avalanches in disordered systems with absorbing states
Girardi-Schappo, M.; Tragtenberg, M. H. R.
2018-04-01
Power-law-shaped avalanche-size distributions are widely used to probe for critical behavior in many different systems, particularly in neural networks. The definition of avalanche is ambiguous. Usually, theoretical avalanches are defined as the activity between a stimulus and the relaxation to an inactive absorbing state. On the other hand, experimental neuronal avalanches are defined by the activity between consecutive silent states. We claim that the latter definition may be extended to some theoretical models to characterize their power-law avalanches and critical behavior. We study a system in which the separation of driving and relaxation time scales emerges from its structure. We apply both definitions of avalanche to our model. Both yield power-law-distributed avalanches that scale with system size in the critical point as expected. Nevertheless, we find restricted power-law-distributed avalanches outside of the critical region within the experimental procedure, which is not expected by the standard theoretical definition. We remark that these results are dependent on the model details.
Continuum radiation of argon plasma
International Nuclear Information System (INIS)
D'Yachkov, L.G.
1995-01-01
A simple completely analytical method of the calculation of radiative continuum of plasmas is derived and an analysis of experimental data on continuum radiation of argon plasma is made. The method is based on the semiclassical quantum defect theory. To calculate radial matrix elements of dipole transitions the asymptotic expansion in powers of E c /ω 2/3 , with an accuracy to the linear term, where E, is the arithmetic mean of the initial and final energies of the transition, is used. This expansion has the same form for free-free, free-bound and bound-bound transitions. If the quantum defects are also approximated by a linear function of energy, the integration over the electron energy (the Maxwell-Boltzmann distribution is assumed) can be performed in analytical form. For Rydberg states the sum of photoionization continua can be replaced by an integral. We have calculated the absorption coefficient pf argon plasma. The photoionization cross section is calculated for all the states of 4s, 5s, 6s, 4p, 5p, 3d, 4d, 4s', 5s', 6s', 4p', 5p', 3d' and 4d' configurations taking into account P-coupling and multiplet splitting (56 states). Other excited states are allowed for by the integral formula together with free-free transitions
Reducing financial avalanches by random investments
Biondo, Alessio Emanuele; Pluchino, Alessandro; Rapisarda, Andrea; Helbing, Dirk
2013-12-01
Building on similarities between earthquakes and extreme financial events, we use a self-organized criticality-generating model to study herding and avalanche dynamics in financial markets. We consider a community of interacting investors, distributed in a small-world network, who bet on the bullish (increasing) or bearish (decreasing) behavior of the market which has been specified according to the S&P 500 historical time series. Remarkably, we find that the size of herding-related avalanches in the community can be strongly reduced by the presence of a relatively small percentage of traders, randomly distributed inside the network, who adopt a random investment strategy. Our findings suggest a promising strategy to limit the size of financial bubbles and crashes. We also obtain that the resulting wealth distribution of all traders corresponds to the well-known Pareto power law, while that of random traders is exponential. In other words, for technical traders, the risk of losses is much greater than the probability of gains compared to those of random traders.
Avalanches of Singing Sand in the Laboratory
Dagois-Bohy, Simon; Courrech Du Pont, Sylvain; Douady, Stéphane
2011-03-01
The song of dunes is a natural phenomenon that has arisen travellers' curiosity for a long time, from Marco Polo to R.A. Bagnold. Scientific observations in the XXth century have shown that the sound is emitted during a shear flow of these particular grains, the free surface of the flow having coherent vibrations like a loud speaker. The sound emission is also submitted to a threshold effect with many parameters like humidity, flow speed, surface of the grains. The sound has been reproduced in laboratory avalanche experiments close to the natural phenomenon on field, but set in a channel with a hard bottom and a few centimeters of sand flowing, which contradicts explanations of the sound that involve a sand dune under the avalanche flow. Flow rates measurements also show the presence of a plug region in the flow above the sheared band, with the same characteristic length as the coherence zones of the sound. Finally we show experimentally that the Froude number, once modified to take into account the height of this plug band, is the parameter that sets the amplitude of the sound, and produces a threshold that depends on the grain type.
Townsend coefficients of gases in avalanche counters
International Nuclear Information System (INIS)
Brunner, G.
1978-01-01
Though much work has been done by many authors in the last few years in the development and application of avalanche counters for ion radiation, it is based upon values of the Townsend coefficients as the essential gas parameter, which were determined many years ago for much lower reduced field strengths F/p than prevail in such counters. Therefore absolute determinations of α in vapours of methyl alcohol, cyclohexane, acetone, and n-heptene were performed under original conditions of avalanche counters. The values obtained do not differ by more than 30%-50% from the former values indeed, extrapolated over F/p for the first three mentioned substances, but the amounts of A and B in the usual representation α/p=A exp(-B(F/p)) are much greater for the stronger reduced fields. This is of importance for such counter properties as the dependence of pulse heights on pressure, voltage, electrode distance etc., which are governed by other combinations of A and B than α/p itself. A comparison of results for different ionic radiations shows a marked influence of the primary ionization density along the particle tracks which is hard to explain. (Auth.)
Angle sensitive single photon avalanche diode
Energy Technology Data Exchange (ETDEWEB)
Lee, Changhyuk, E-mail: cl678@cornell.edu; Johnson, Ben, E-mail: bcj25@cornell.edu; Molnar, Alyosha, E-mail: am699@cornell.edu [Electrical and Computer Engineering, Cornell University, Ithaca, New York 14850 (United States)
2015-06-08
An ideal light sensor would provide exact information on intensity, timing, location, and angle of incoming photons. Single photon avalanche diodes (SPADs) provide such desired high (single photon) sensitivity with precise time information and can be implemented at a pixel-scale to form an array to extract spatial information. Furthermore, recent work has demonstrated photodiode-based structures (combined with micro-lenses or diffraction gratings) that are capable of encoding both spatial and angular information of incident light. In this letter, we describe the implementation of such a grating structure on SPADs to realize a pixel-scale angle-sensitive single photon avalanche diode (A-SPAD) built in a standard CMOS process. While the underlying SPAD structure provides high sensitivity, the time information of the two layers of diffraction gratings above offers angle-sensitivity. Such a unique combination of SPAD and diffraction gratings expands the sensing dimensions to pave a path towards lens-less 3-D imaging and light-field time-of-flight imaging.
International Nuclear Information System (INIS)
Briola, Stefano; Di Marco, Paolo; Gabbrielli, Roberto
2017-01-01
A novel Combined Cooling, Heating and Power (CCHP) cycle, operating with two-phase devices for the compression and expansion processes and a single-component wet working fluid, is proposed. A detailed sensitivity analysis of the novel CCHP cycle has been investigated in order to evaluate, in terms of energy performance indicators, its potentiality to serve typical trigenerative tertiary and industrial end-users with different fixed operating temperatures. In general, the novel CCHP cycle is characterized by higher energy performance indicators than a separated energy production system. The comparison between the novel CCHP cycle and several commercialized CCHP systems has been performed in the case studies related to tertiary and industrial end-users. The novel CCHP cycle shows a trigenerative capability in wide ranges of the end-users demands without surplus or deficit of the electric or thermal powers. Furthermore, the maximum allowable capital cost of the whole novel CCHP plant (BEPCC), that will assure the profitability of the investment, is calculated in the tertiary and industrial end-users case studies. For the tertiary end-user, the capital costs of the commercialized CCHP are between the minimum and maximum BEPCC values. On the contrary, for the industrial end-user, they are lower than the minimum and maximum BEPCC values. - Highlights: • Novel CCHP cycle with two-phase expanders and compressors has been conceived. • Novel CCHP cycle has higher performances than a separated energy production system. • Novel CCHP cycle satisfies the user demands in wide ranges without surplus/deficit. • Tertiary user: novel CCHP cycle is competitive against marketed CCHP systems. • Industrial user: novel CCHP cycle is not competitive against marketed CCHP systems.
Enhanced mixing in two-phase Taylor-Couette flows
International Nuclear Information System (INIS)
Dherbecourt, Diane
2015-01-01
In the scope of the nuclear fuel reprocessing, Taylor-Couette flows between two concentric cylinders (the inner one in rotation and the outer one at rest) are used at laboratory scale to study the performances of new liquid/liquid extraction processes. Separation performances are strongly related to the mixing efficiency, the quantification of the latter is therefore of prime importance. A previous Ph.D. work has related the mixing properties to the hydrodynamics parameters in single-phase flow, using both experimental and numerical investigations. The Reynolds number, flow state and vortices height (axial wavelength) impacts were thus highlighted. This Ph.D. work extends the previous study to two-phase configurations. For experimental simplification, and to avoid droplets coalescence or breakage, spherical solid particles of PMMA from 800 μm to 1500 μm diameter are used to model rigid droplets. These beads are suspended in an aqueous solution of dimethyl sulfoxide (DMSO) and potassium Thiocyanate (KSCN). The experimental setup uses coupled Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) to access simultaneously the hydrodynamic and the mixing properties. Although the two phases are carefully chosen to match in density and refractive index, these precautions are not sufficient to ensure a good measurement quality, and a second PLIF channel is added to increase the precision of the mixing quantification. The classical PLIF channel monitors the evolution of Rhodamine WT concentration, while the additional PLIF channel is used to map a Fluorescein dye, which is homogeneously concentrated inside the gap. This way, a dynamic mask of the bead positions can be created and used to correct the Rhodamine WT raw images. Thanks to this experimental setup, a parametric study of the particles size and concentration is achieved. A double effect of the dispersed phase is evidenced. On one hand, the particles affect the flow hydrodynamic properties
Liquid argon calorimetry for the SSC
International Nuclear Information System (INIS)
Gordon, H.A.
1990-01-01
Liquid argon calorimetry is a mature technique. However, adapting it to the challenging environment of the SSC requires a large amount of R ampersand D. The advantages of the liquid argon approach are summarized and the issues being addressed by the R ampersand D program are described. 18 refs
Creep of Two-Phase Microstructures for Microelectronic Applications
Energy Technology Data Exchange (ETDEWEB)
Reynolds, Heidi Linch [Univ. of California, Berkeley, CA (United States)
1998-12-01
The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a
The pressure effects on two-phase anaerobic digestion
International Nuclear Information System (INIS)
Chen, Yuling; Rößler, Benjamin; Zielonka, Simon; Lemmer, Andreas; Wonneberger, Anna-Maria; Jungbluth, Thomas
2014-01-01
Highlights: • The pressure effect on anaerobic digestion up to 9 bar was examined. • Increasing pressure decreased pH value in the anaerobic filter. • Increasing pressure increased methane content. • Increasing pressure decreased specific methane yield slightly. • The pressurized methane reactor was very stable and performed well. - Abstract: Two-phase pressurized anaerobic digestion is a novel process aimed at facilitating injection of the produced biogas into the natural gas grid by integrating the fermentative biogas production and upgrading it to substitute natural gas. In order to understand the mechanisms, knowledge of pressure effects on anaerobic digestion is required. To examine the effects of pressure on the anaerobic digestion process, a two-phase anaerobic digestion system was built up in laboratory scale, including three acidogenesis-leach-bed-reactors and one pressure-resistant anaerobic filter. Four different pressure levels (the absolute pressure of 1 bar, 3 bar, 6 bar and 9 bar) were applied to the methane reactor in sequence, with the organic loading rate maintained at approximately 5.1 kgCOD m −3 d −1 . Gas production, gas quality, pH value, volatile fatty acids, alcohol, ammonium-nitrogen, chemical oxygen demand (COD) and alkaline buffer capacity were analyzed. No additional caustic chemicals were added for pH adjustment throughout the experiment. With the pressure increasing from 1.07 bar to 8.91 bar, the pH value decreased from 7.2 to 6.5, the methane content increased from 66% to 75%, and the specific methane yield was slightly reduced from 0.33 l N g −1 COD to 0.31 l N g −1 COD. There was almost no acid-accumulation during the entire experiment. The average COD-degradation grade was always more than 93%, and the average alkaline buffering capacity (VFA/TIC ratio) did not exceed 0.2 at any pressure level. The anaerobic filter showed a very stable performance, regardless of the pressure variation
Statistical descriptions of polydisperse turbulent two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Minier, Jean-Pierre, E-mail: jean-pierre.minier@edf.fr
2016-12-15
Disperse two-phase flows are flows containing two non-miscible phases where one phase is present as a set of discrete elements dispersed in the second one. These discrete elements, or ‘particles’, can be droplets, bubbles or solid particles having different sizes. This situation encompasses a wide range of phenomena, from nano-particles and colloids sensitive to the molecular fluctuations of the carrier fluid to inertia particles transported by the large-scale motions of turbulent flows and, depending on the phenomenon studied, a broad spectrum of approaches have been developed. The aim of the present article is to analyze statistical models of particles in turbulent flows by addressing this issue as the extension of the classical formulations operating at a molecular or meso-molecular level of description. It has a three-fold purpose: (1) to bring out the thread of continuity between models for discrete particles in turbulent flows (above the hydrodynamical level of description) and classical mesoscopic formulations of statistical physics (below the hydrodynamical level); (2) to reveal the specific challenges met by statistical models in turbulence; (3) to establish a methodology for modeling particle dynamics in random media with non-zero space and time correlations. The presentation is therefore centered on organizing the different approaches, establishing links and clarifying physical foundations. The analysis of disperse two-phase flow models is developed by discussing: first, approaches of classical statistical physics; then, by considering models for single-phase turbulent flows; and, finally, by addressing current formulations for discrete particles in turbulent flows. This brings out that particle-based models do not cease to exist above the hydrodynamical level and offer great interest when combined with proper stochastic formulations to account for the lack of equilibrium distributions and scale separation. In the course of this study, general
Biogasification of solid wastes by two-phase anaerobic fermentation
International Nuclear Information System (INIS)
Ghosh, S.; Vieitez, E.R.; Liu, T.; Kato, Y.
1997-01-01
Municipal, industrial and agricultural solid wastes, and biomass deposits, cause large-scale pollution of land and water. Gaseous products of waste decomposition pollute the air and contribute to global warming. This paper describes the development of a two-phase fermentation system that alleviates methanogenic inhibition encountered with high-solids feed, accelerates methane fermentation of the solid bed, and captures methane (renewable energy) for captive use to reduce global warming. The innovative system consisted of a solid bed reactor packed with simulated solid waste at a density of 160 kg/m 3 and operated with recirculation of the percolated culture (bioleachate) through the bed. A rapid onset of solids hydrolysis, acidification, denitrification and hydrogen gas formation was observed under these operating conditions. However, these fermentative reactions stopped at a total fatty acids concentration of 13,000 mg/l (as acetic) at pH 5, with a reactor head-gas composition of 75 percent carbon dioxide, 20 percent nitrogen, 2 percent hydrogen and 3 percent methane. Fermentation inhibition was alleviated by moving the bioleachate to a separate methane-phase fermenter, and recycling methanogenic effluents at pH 7 to the solid bed. Coupled operation of the two reactors promoted methanogenic conversion of the high-solids feed. (author)
Two phases of the anyon gas and broken T symmetry
International Nuclear Information System (INIS)
Canright, G.S.; Rojo, A.G.
1991-01-01
This paper reports the first exact finite-temperature study of anyons. The authors' method is an extension to finite T of earlier numerical work with small numbers of anyons on a lattice. We study the spontaneous magnetization M 0 (T), since the signature has been identified as a key signature of broken T symmetry for anyon models. Our results confirm the two-phase picture suggested by earlier work: The authors find a low-temperature regime where M 0 is very small or zero, and a high-temperature regime where M 0 is of O(0.1 μ B ) per particle. In the high-temperature regime the authors can obtain an excellent estimate of M 0 (T) in the thermodynamic limit (which we call M 0 ∞ ). since our finite-size results extrapolate smoothly with little scatter. The authors' values for M 0 ∞ can then be compared with the results of μSR experiments on high-temperature superconductors, which set an upper experimental bound on the internal fields from such moments. The authors find that M 0 ∞ in a bulk material of many planes will almost certainly give a signal well above this threshold if (and only if) the planes are ordered ferromagnetically. In the antiferromagnetic case (which is strongly favored energetically) the signal from M 0 ∞ is probably undetectable. Finally, we estimate the transition temperature T c from our finite-size studies, obtaining a value on the order of a few hundred Kelvins
System for recording and displaying two-phase flow topographies
International Nuclear Information System (INIS)
Cary, C.N.; Block, J.A.
1979-01-01
A system of hardware and software has been developed and used to record and display in various forms details of the countercurrent flow topographies occurring in a scaled Pressurized Water Reactor downcomer annulus. An array of 288 conductivity sensors was mounted in a 1/15 scale PWR annulus. At each moment in time, the state of each probe indicates the presence or absence of water in this immediate vicinity. An electronic data acquisition system records the states of all probes 108 times per second on magnetic tape; software routines retrieve the data and reconstruct visual analogs of the flow topographies. The instantaneous two-phase state of the annulus at each instant can be displayed on a hard copy plotter or on a CRT screen. By synchronizing a camera drive with the CRT display, 16mm films have been made recreating the flow process at full speed and at various slow motion rates. All data obtained are stored in computer files in numerical form and can be subjected to various types of quantitative analysis to assist in advanced code development and verification
A turbulent two-phase flow model for nebula flows
International Nuclear Information System (INIS)
Champney, J.M.; Cuzzi, J.N.
1990-01-01
A new and very efficient turbulent two-phase flow numericaly model is described to analyze the environment of a protoplanetary nebula at a stage prior to the formation of planets. Focus is on settling processes of dust particles in flattened gaseous nebulae. The model employs a perturbation technique to improve the accuracy of the numerical simulations of such flows where small variations of physical quantities occur over large distance ranges. The particles are allowed to be diffused by gas turbulence in addition to settling under gravity. Their diffusion coefficients is related to the gas turbulent viscosity by the non-dimensional Schmidt number. The gas turbulent viscosity is determined by the means of the eddy viscosity hypothesis that assumes the Reynolds stress tensor proportional to the mean strain rate tensor. Zero- and two-equation turbulence models are employed. Modeling assumptions are detailed and discussed. The numerical model is shown to reproduce an existing analytical solution for the settling process of particles in an inviscid nebula. Results of nebula flows are presented taking into account turbulence effects of nebula flows. Diffusion processes are found to control the settling of particles. 24 refs
Passive Two-Phase Cooling of Automotive Power Electronics: Preprint
Energy Technology Data Exchange (ETDEWEB)
Moreno, G.; Jeffers, J. R.; Narumanchi, S.; Bennion, K.
2014-08-01
Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated, and tests were conducted using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator design that incorporates features to improve performance and reduce size was conceived. Simulation results indicate its thermal resistance can be 37% to 48% lower than automotive dual side cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers--plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.
Transient boiling in two-phase helium natural circulation loops
Furci, H.; Baudouy, B.; Four, A.; Meuris, C.
2014-01-01
Two-phase helium natural circulation loops are used for cooling large superconducting magnets, as CMS for LHC. During normal operation or in the case of incidents, transients are exerted on the cooling system. Here a cooling system of this type is studied experimentally. Sudden power changes are operated on a vertical-heated-section natural convection loop, simulating a fast increase of heat deposition on magnet cooling pipes. Mass flow rate, heated section wall temperature and pressure drop variations are measured as a function of time, to assess the time behavior concerning the boiling regime according to the values of power injected on the heated section. The boiling curves and critical heat flux (CHF) values have been obtained in steady state. Temperature evolution has been observed in order to explore the operating ranges where heat transfer is deteriorated. Premature film boiling has been observed during transients on the heated section in some power ranges, even at appreciably lower values than the CHF. A way of attenuating these undesired temperature excursions has been identified through the application of high enough initial heating power.
Two-phase flow characteristics of HFC and HCFC fluid
International Nuclear Information System (INIS)
Ueno, T.; Matsuda, K.; Kusakabe, T.
1998-01-01
Some two-phase flow characteristics of HFC and HCFC fluid have been investigated experimentally. Fluids used in this experiment are HCFC22 (hereinafter called 'R22'), HCFC123 (hereinafter called 'R123') and Mixture of HFC fluid (hereinafter called 'R407C'). The fluid R407C are mixture of HFC32, HFC134a and HFC125, and their concentrations are 23wt%, 52wt% and 25wt%, respectively. This paper presents main flow parameters such as void fraction, interfacial velocities, bubble diameter distribution and pressure drop multiplier, which can characterize flow behavior. The void fractions and interfacial velocities were measured at some local positions in the single pipe using the bi-optical probe(hereinafter called 'BOP'). The procedure to calculate the void fraction from the void signals obtained by BOP were adopted the so-called slice method. The effects of slice levels on the void fraction were discussed taking into account bubble diameter. The new correlation of slice level as the function of void fraction has been proposed. The area-averaged void fractions obtained from BOP's void signals using new correlation were compared with void fractions obtained from pressure drops. The area-averaged interfacial velocities were also compared with the superficial gas velocities. It was concluded that the accuracy of BOP measurements are 5% for void fraction and less than 8.5% for interfacial velocity
Two-phase flow field simulation of horizontal steam generators
Energy Technology Data Exchange (ETDEWEB)
Rabiee, Ataollah; Kamalinia, Amir Hossein; Hadad, Kamal [School of Mechanical Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of)
2017-02-15
The analysis of steam generators as an interface between primary and secondary circuits in light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailed thermal hydraulics investigation in order to predict their behavior during normal and transient operational conditions. Two phase flow field simulation on adjacent tube bundles is important in obtaining logical numerical results. However, the complexity of the tube bundles, due to geometry and arrangement, makes it complicated. Employment of porous media is suggested to simplify numerical modeling. This study presents the use of porous media to simulate the tube bundles within a general-purpose computational fluid dynamics code. Solved governing equations are generalized phase continuity, momentum, and energy equations. Boundary conditions, as one of the main challenges in this numerical analysis, are optimized. The model has been verified and tuned by simple two-dimensional geometry. It is shown that the obtained vapor volume fraction near the cold and hot collectors predict the experimental results more accurately than in previous studies.
Entrainment in vertical annular two-phase flow
International Nuclear Information System (INIS)
Sawant, Pravin; Ishii, Mamoru; Mori, Michitsugu
2009-01-01
Prediction of amount of entrained droplets or entrainment fraction in annular two-phase flow is essential for the estimation of dryout condition and analysis of post dryout heat transfer in light water nuclear reactors and steam boilers. In this study, air-water and organic fluid (Freon-113) annular flow entrainment experiments have been carried out in 9.4 and 10.2 mm diameter test sections, respectively. Both the experiments covered three distinct pressure conditions and wide range of liquid and gas flow conditions. The organic fluid experiments simulated high pressure steam-water annular flow conditions. In each of the experiments, measurements of entrainment fraction, droplet entrainment rate and droplet deposition rate have been performed by using a liquid film extraction method. A simple, explicit and non-dimensional correlation developed by Sawant et al. (2008a) for the prediction of entrainment fraction is further improved in this study in order to account for the existence of critical gas and liquid flow rates below which no entrainment is possible. Additionally, a new correlation is proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction condition. The improved correlation successfully predicted the newly collected air-water and Freon-113 entrainment fraction data. Furthermore, the correlations satisfactorily compared with the air-water, helium-water and air-genklene experimental data measured by Willetts (1987). (author)
A two-phase model of aquifer heterogeneity
International Nuclear Information System (INIS)
Moltyaner, G.L.
1994-11-01
A two-phase model of a fluid-saturated geologic medium is developed with groundwater velocity (rather than the hydraulic conductivity) as the primary model parameter. The model describes the groundwater flow, contaminant transport processes, and geologic medium structure at the local-scale of a continuum representation and relates structure to processes quantitatively. In this model, the heterogeneity of a geologic medium is characterized either in terms of the spatial variability in the bulk (local-scale) fluid density and sediment density, or in terms of variability in the local-scale porosity and effective grain diameter. The local-scale continuity equations resulting from these properties are derived for both phases. The effective grain diameter is employed to quantify the geologic structure. Velocity is employed to quantify the transport process. Since structure controls process, a high correlation is observed between the effective grain diameter and velocity. The observed correlation leads to a new formulation of Darcy's law without invoking the concept of a fictitious (Darcy's) velocity. The local-scale groundwater flow equation is developed on the basis of the new formulation. (author). 16 refs., 4 figs
Experimental investigation of a two-phase nozzle flow
International Nuclear Information System (INIS)
Kedziur, F.; John, H.; Loeffel, R.; Reimann, J.
1980-07-01
Stationary two-phase flow experiments with a convergent nozzle are performed. The experimental results are appropriate to validate advanced computer codes, which are applied to the blowdown-phase of a loss-of-coolant accident (LOCA). The steam-water experiments present a broad variety of initial conditions: the pressure varies between 2 and 13 MPa, the void fraction between 0 (subcooled) and about 80%, a great number of critical as well as subcritical experiments with different flow pattern is investigated. Additional air-water experiments serve for the separation of phase transition effects. The transient acceleration of the fluid in the LOCA-case is simulated by a local acceleration in the experiment. The layout of the nozzle and the applied measurement technique allow for a separate testing of blowdown-relevant, physical models and the determination of empirical model parameters, respectively. The measured quantities are essentially the mass flow rate, quality, axial pressure and temperature profiles as well as axial and radial density/void profiles obtained by a γ-ray absorption device. Moreover, impedance probes and a pitot probe are used. Observed phenomena like a flow contraction, radial pressure and void profiles as well as the appearance of two chocking locations are described, because their examination is rather instructive about the refinement of a program. The experimental facilities as well as the data of 36 characteristic experiments are documented. (orig.) [de
Dielectric barrier discharge in a two-phase mixture
Energy Technology Data Exchange (ETDEWEB)
Ye Qizheng; Zhang Ting; Lu Fei; Li Jin; He Zhenghao; Lin Fuchang [College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)
2008-01-21
This paper reports the experimental investigation of the dielectric barrier discharge in which the gap area is filled with a two-phase mixture (TPM), air and solid particles. We found that there are two kinds of discharges in the TPM. One is the surface discharge generated on the surface of the solid particles and the other is the filament discharge generated in the air void. For the case of low volume fraction of solid particles, the surface discharge starts to occur when the applied voltage is higher than the onset voltage. At a further voltage increase, the filament discharge takes place at the same time. For the case of high volume fraction, such as the packed-bed reactor, only the surface discharge exists. Under the condition of the same volume fraction, the larger the diameter of the solid particles, the lower the surface discharge onset voltage. As a conclusion, we think that the plasma reactor using the form of low volume fraction of solid particles may be a better choice for waste-gas treatment enhanced by catalysts.
A two-phase full-wave superconducting rectifier
International Nuclear Information System (INIS)
Ariga, T.; Ishiyama, A.
1989-01-01
A two-phase full-wave superconducting rectifier has been developed as a small cryogenic power supply of superconducting magnets for magnetically levitation trains. Those magnets are operated in the persistent current mode. However, small ohmic loss caused at resistive joints and ac loss induced by the vibration of the train cannot be avoided. Therefore, the low-power cryogenic power supply is required to compensate for the reduction in magnet current. The presented superconducting rectifier consists of two identical full-wave rectifiers connected in series. Main components of each rectifier are a troidal shape superconducting set-up transformer and two thermally controlled switches. The test results using a 47.5 mH load magnet at 0.2 Hz and 0.5 Hz operations are described. To estimate the characteristics of the superconducting rectifier, the authors have developed a simulation code. From the experiments and the simulations, the transfer efficiency is examined. Furthermore, the optimal design of thermally controlled switches based on the finite element analysis is also discussed
Acceleration of a two-phase flow by boiling, (3)
International Nuclear Information System (INIS)
Mori, Yasuo; Hijikata, Kunio; Iwata, Shoichiro
1976-01-01
Acceleration of two-component, two-phase flow has been studied, and a method using the volume expansion by boiling for accelerating fluid has been investigated. In this study, the phenomena of atomizing and boiling were separated, and the liquid with low boiling point was injected into water at lower than the saturation temperature, and was atomized. Then, this was mixed with high temperature liquid and was boiled. The uniform buffle flow was produced, and the phenomena were observed with a high speed camera. The process of acceleration and the acceleration performance were compared with the results of theoretical analysis described in the second report. The experiment was carried out with liquid R113, and at first, the mechanism of atomizing was studied. The atomizing was caused when the relative velocity between R113 and water was more than 4 m/s irrespective of water velocity. The distribution of the diameter of fine liquid drops was almost normal distribution. When the fine drops of R113 were mixed with the high temperature water, bubbles were produced, and the production rate showed definite dependence on the degree of overheating. The flow of bubbles was uniform. However, some of R113 did not become bubbles. The efficiency of acceleration was 1.0 which was independent of the degree of overheating. A further problem is to reduce the quantity of the liquid which does not boil. (Kato, T.)
Two phase flow problems in power station boilers
International Nuclear Information System (INIS)
Firman, E.C.
1974-01-01
The paper outlines some of the waterside thermal and hydrodynamic phenomena relating to design and operation of large boilers in central power stations. The associated programme of work is described with an outline of some results already obtained. By way of introduction, the principal features of conventional and nuclear drum boilers and once-through nuclear heat exchangers are described in so far as they pertain to this area of work. This is followed by discussion of the relevant physical phenomena and problems which arise. For example, the problem of steam entrainment from the drum into the tubes connecting it to the furnace wall tubes is related to its effects on circulation and possible mechanisms of tube failure. Other problems concern the transient associated with start-up or low load operation of plant. The requirement for improved mathematical representation of steady and dynamic performance is mentioned together with the corresponding need for data on heat transfer, pressure loss, hydrodynamic stability, consequences of deposits, etc. The paper concludes with reference to the work being carried out within the C.E.G.B. in relation to the above problems. The facilities employed and the specific studies being made on them are described: these range from field trials on operational boilers to small scale laboratory investigations of underlying two phase flow mechanisms and include high pressure water rigs and a freon rig for simulation studies
Vascular anastomosis by Argon Laser
International Nuclear Information System (INIS)
Gomes, O.M.; Macruz, R.; Armelin, E.; Brum, J.M.G.; Ribeiro, M.P.; Mnitentog, J.; Verginelli, G.; Pileggi, F.; Zerbini, E.J.
1982-01-01
Twenty four mongrel dogs, wheighing 13 to 24 kilograms were studied. After anesthesia, intubation and controlled ventilation, they were submitted to three types of vascular anastomosis: Group I - eight dogs with saphenous vein inter-carotid arteries by-pass: Group II - eight dogs with left mammary artery - left anterior descending coronary artery by-pass; Group III - eight dogs with venovenous anastomosis. In all groups 0.8 to 15 watts of Argon Laser power was applied to a total time of 90 to 300 seconds. The lower power for venovenous anastomosis and the greater for the arterial ones. The mean valves of resistence of the Laser anastomosis to pressure induced rupture was 730 mmHg in the immediate post operative study, and superior to 2.500 mmHg 30 days after. No signs of occlusion was demonstrated at the anastomosis sites by the angiographic and anathomo-patological study performed. (Author) [pt
Numerical methods for two-phase flow with contact lines
Energy Technology Data Exchange (ETDEWEB)
Walker, Clauido
2012-07-01
This thesis focuses on numerical methods for two-phase flows, and especially flows with a moving contact line. Moving contact lines occur where the interface between two fluids is in contact with a solid wall. At the location where both fluids and the wall meet, the common continuum descriptions for fluids are not longer valid, since the dynamics around such a contact line are governed by interactions at the molecular level. Therefore the standard numerical continuum models have to be adjusted to handle moving contact lines. In the main part of the thesis a method to manipulate the position and the velocity of a contact line in a two-phase solver, is described. The Navier-Stokes equations are discretized using an explicit finite difference method on a staggered grid. The position of the interface is tracked with the level set method and the discontinuities at the interface are treated in a sharp manner with the ghost fluid method. The contact line is tracked explicitly and its dynamics can be described by an arbitrary function. The key part of the procedure is to enforce a coupling between the contact line and the Navier-Stokes equations as well as the level set method. Results for different contact line models are presented and it is demonstrated that they are in agreement with analytical solutions or results reported in the literature.The presented Navier-Stokes solver is applied as a part in a multiscale method to simulate capillary driven flows. A relation between the contact angle and the contact line velocity is computed by a phase field model resolving the micro scale dynamics in the region around the contact line. The relation of the microscale model is then used to prescribe the dynamics of the contact line in the macro scale solver. This approach allows to exploit the scale separation between the contact line dynamics and the bulk flow. Therefore coarser meshes can be applied for the macro scale flow solver compared to global phase field simulations
Overspill avalanching in a dense reservoir network
Mamede, George L.; Araújo, Nuno A. M.; Schneider, Christian M.; de Araújo, José Carlos; Herrmann, Hans J.
2012-01-01
Sustainability of communities, agriculture, and industry is strongly dependent on an effective storage and supply of water resources. In some regions the economic growth has led to a level of water demand that can only be accomplished through efficient reservoir networks. Such infrastructures are not always planned at larger scale but rather made by farmers according to their local needs of irrigation during droughts. Based on extensive data from the upper Jaguaribe basin, one of the world’s largest system of reservoirs, located in the Brazilian semiarid northeast, we reveal that surprisingly it self-organizes into a scale-free network exhibiting also a power-law in the distribution of the lakes and avalanches of discharges. With a new self-organized-criticality-type model we manage to explain the novel critical exponents. Implementing a flow model we are able to reproduce the measured overspill evolution providing a tool for catastrophe mitigation and future planning. PMID:22529343
Numerical flow analyses of a two-phase hydraulic coupling
Energy Technology Data Exchange (ETDEWEB)
Hur, N.; Kwak, M.; Moshfeghi, M. [Sogang University, Seoul (Korea, Republic of); Chang, C.-S.; Kang, N.-W. [VS Engineering, Seoul (Korea, Republic of)
2017-05-15
We investigated flow characteristics in a hydraulic coupling at different charged water conditions and speed ratios. Hence, simulations were performed for three-dimensional two-phase flow by using the VOF method. The realizable k-ε turbulence model was adopted. To resolve the interaction of passing blades of the primary and secondary wheels, simulations were conducted in the unsteady framework using a sliding grid technique. The results show that the water-air distribution inside the wheel is strongly dependent upon both amount of charged water and speed ratio. Generally, air is accumulated in the center of the wheel, forming a toroidal shape wrapped by the circulating water. The results also show that at high speed ratios, the solid-body-like rotation causes dry areas on the periphery of the wheels and, hence, considerably decreases the circulating flow rate and the transmitted torque. Furthermore, the momentum transfer was investigated through the concept of a mass flux triangle based on the local velocity multiplied by the local mixture density instead of the velocity triangle commonly used in a single-phase turbomachine analysis. Also, the mass fluxes along the radius of the coupling in the partially charged and fully charged cases were found to be completely different. It is shown that the flow rate at the interfacial plane and also the transmitted torque are closely related and are strongly dependent upon both the amount of charged water and speed ratio. Finally, a conceptual categorization together with two comprehensive maps was provided for the torque transmission and also circulating flow rates. These two maps in turn exhibit valuable engineering information and can serve as bases for an optimal design of a hydraulic coupling.
Simulation of two-phase flows by domain decomposition
International Nuclear Information System (INIS)
Dao, T.H.
2013-01-01
This thesis deals with numerical simulations of compressible fluid flows by implicit finite volume methods. Firstly, we studied and implemented an implicit version of the Roe scheme for compressible single-phase and two-phase flows. Thanks to Newton method for solving nonlinear systems, our schemes are conservative. Unfortunately, the resolution of nonlinear systems is very expensive. It is therefore essential to use an efficient algorithm to solve these systems. For large size matrices, we often use iterative methods whose convergence depends on the spectrum. We have studied the spectrum of the linear system and proposed a strategy, called Scaling, to improve the condition number of the matrix. Combined with the classical ILU pre-conditioner, our strategy has reduced significantly the GMRES iterations for local systems and the computation time. We also show some satisfactory results for low Mach-number flows using the implicit centered scheme. We then studied and implemented a domain decomposition method for compressible fluid flows. We have proposed a new interface variable which makes the Schur complement method easy to build and allows us to treat diffusion terms. Using GMRES iterative solver rather than Richardson for the interface system also provides a better performance compared to other methods. We can also decompose the computational domain into any number of sub-domains. Moreover, the Scaling strategy for the interface system has improved the condition number of the matrix and reduced the number of GMRES iterations. In comparison with the classical distributed computing, we have shown that our method is more robust and efficient. (author) [fr
Development of two-phase Flow Model, 'SOBOIL', for Sodium
International Nuclear Information System (INIS)
Hahn, Do Hee; Chang, Won Pyo; Kim, In Chul; Kwon, Young Min; Lee, Yong Bum
2000-03-01
The objective of this research is to develop a sodium two-phase flow analysis model, 'SOBOIL', for the assessment of the initial stage of the KALIMER HCDA (Hypotherical Core Disruptive Accident). The 'SOBOIL' is basically similar to the multi-bubble slug ejection model used in SAS2A[1]. When a bubble is formed within the liquid slug, the bubble fills the whole cross section of the coolant channel except for a film left on the cladding or on the structure. Up to nine bubbles, separated by the liquid slugs, are allowed in the channel at any time. Each liquid slug flow rate in the model is performed in 2 steps. In the first step, the preliminary flow rate in the liquid slug is calculated neglecting the effect of changes in the vapor bubble pressures over the time step. The temperature and pressure distributions, and interface velocity at the interface between the liquid slug and vapor bubble are also calculated during this process. The new vapor temperature and pressure are then determined from the balance between the net energy transferred into the vapor and the change of the vapor energy. The liquid flow is finally calculated considering the change of the vapor pressure over a time step and the calculation is repeated until specified elapsed time is met. Continuous effort, therefore, must be made on the examination and improvement for the model to become reliable. To this end, much interest must be concentrated in the relevant international collaborations for access to a reference model or test data for the verification
Two-phase transformation of lepidocrocite to maghemite
Dekkers, M. J.; Gapeev, A. K.; Gendler, T. S.; Gribov, S. K.; Shcherbakov, V. P.
2003-04-01
A detailed investigation of CRM acquired at different stages of the transformation lepidocrocite -> maghemite -> hematite is carried out. Apparently, at least two-stage lepidocrocite maghemite transformation was revealed from: a) the two-peak Ms(T) curve; b) the observation of constricted hysteresis loops appearing after annealing fresh lepidocrocite samples at elevated temperatures; c) continuous monitoring (for 500 hrs) of CRM acquisition at elevated temperatures. For the latter two sets of CRM acquisition experiments at 12 temperatures from 175C to 550C in the presence of 0.1 mT magnetic field were performed: 1) with fine dispersed natural lepidocrocite grains in a kaolin matrix (about 1 volume % of lepidocrocite), 2) for lepidocrocite peaces 3x3x3 mm in size. In both cases the CRM was detected already at 175C after 1 day of annealing. Note that this temperature is lower than the temperature of the TGA peak of the lepidocrocite -> maghemite transformation. Mossbauer spectra obtained from the peaces after annealing at 225C during 6 and 14 hours, respectively, revealed significantly different patterns. Unexpectadly, fine dispersed maghemite grains formed due the lepidocrocite dehydration in the first peace (6 hrs of annealing) occurred to be more ordered than those of from the second peace. The samples are subjected to the X-ray analysis in an attempt to clarify the observed difference. The observed phenomena can be explained by the two-phase conception of the transformation lepidocrocite -> maghemite. First the precipitation of small superparamagnetic particles of maghemite takes place growing with time. Second, these grains coalesce with each other resulting in appearance of the antiphase boundaries decreasing the susceptibility, slowing down the process of CRM acquisition and generating the constricted hysteresis loops. The work is supported by INTAS 99-1273.
Emissive spectra of shock-heated argon
International Nuclear Information System (INIS)
Tang Jingyou; Gu Yan; Peng Qixian; Bai Yulin; Li Ping
2003-01-01
To study the radiant properties of argon under weak shock compression, an aluminum target filled with gaseous argon at ambient states was impacted by a tungsten alloy projectile which was launched from a two-stage light gun to 2.00 km/s. The radiant signals of single shock-compressed argon were recorded by a six-channel pyrometer and oscilloscopes, which varied with time linearly for the five channels from 405 nm to 700 nm and exponentially for the channel 800 nm, and the corresponding velocity of shock wave was determined to be 4.10 ± 0.09 km/s. By the present experiment, it has been shown that the absorbability of the shock-heated argon is low for visual light and the optical depths of argon gas turn from thin to thick as wavelengths gradually increase. The time-resolved spectra in the rising-front of the radiant signal in the re-shocked argon were recorded by means of an OMA, and strong emissive spectrum bands near 450 nm light-wave length but no linear spectrum were found. The emissive spectrum properties of shock-compression argon were qualitatively explained by the state parameters and ionization degree
Mergili, Martin; Fischer, Jan-Thomas; Krenn, Julia; Pudasaini, Shiva P.
2017-02-01
r.avaflow represents an innovative open-source computational tool for routing rapid mass flows, avalanches, or process chains from a defined release area down an arbitrary topography to a deposition area. In contrast to most existing computational tools, r.avaflow (i) employs a two-phase, interacting solid and fluid mixture model (Pudasaini, 2012); (ii) is suitable for modelling more or less complex process chains and interactions; (iii) explicitly considers both entrainment and stopping with deposition, i.e. the change of the basal topography; (iv) allows for the definition of multiple release masses, and/or hydrographs; and (v) serves with built-in functionalities for validation, parameter optimization, and sensitivity analysis. r.avaflow is freely available as a raster module of the GRASS GIS software, employing the programming languages Python and C along with the statistical software R. We exemplify the functionalities of r.avaflow by means of two sets of computational experiments: (1) generic process chains consisting in bulk mass and hydrograph release into a reservoir with entrainment of the dam and impact downstream; (2) the prehistoric Acheron rock avalanche, New Zealand. The simulation results are generally plausible for (1) and, after the optimization of two key parameters, reasonably in line with the corresponding observations for (2). However, we identify some potential to enhance the analytic and numerical concepts. Further, thorough parameter studies will be necessary in order to make r.avaflow fit for reliable forward simulations of possible future mass flow events.
Anthropogenic effect on avalanche and debris flow activity
Directory of Open Access Journals (Sweden)
S. A. Sokratov
2013-01-01
Full Text Available The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoidable changes of the natural environment as the result of a construction and of use of the constructed infrastructure to be account for in corresponding planning of the protection measures.
Avalanche localization and its effects in proportional counters
International Nuclear Information System (INIS)
Fischer, J.; Okuno, H.; Walenta, A.H.
1977-11-01
Avalanche development around the anode wire in a gas proportional counter is investigated. In the region of proportional gas amplification, the avalanche is found to be well localized on one side of the anode wire, where the electrons arrive along the field lines from the point of primary ionization. Induced signals on electrodes surrounding the anode wire are used to measure the azimuthal position of the avalanche on the anode wire. Practical applications of the phenomena such as left-right assignment in drift chambers and measurement of the angular direction of the primary ionization electrons drifting towards the anode wire are discussed
Argon cover gas purity control on LMFBR
Energy Technology Data Exchange (ETDEWEB)
Maeda, Hiroshi; Kobayashi, Takayoshi [PNC (Japan); Ishiyama, Satoshi [Toshiba (Japan); Motonaga, Tetsuji [Hitachi (Japan)
1987-07-01
Various control methods on chemical impurities and radioactive materials (fission products) in the primary argon gas of LMFBRs' have been studied based on experiences in Joyo and results of research and development. These results are reflected on MONJU design. On-line gas chromatographs are installed both in the Primary and in the Secondary Argon Gas Systems in JOYO. Also, chemical analysis has been done by batch sampling in JOYO. Though the rise of impurity concentration had been measured after periodical fuel exchange operation, impurity concentration has been controlled sufficiently under target control limits. In MONJU detailed design, the Rare Gas Removal and Recovery System which consisted of cryogenic distillation equipment had been eliminated and the capacity of Charcoal Beds in the Primary Argon Gas System has been improved to keep the concentration of radioactive materials sufficient low levels. The necessity to control the impurities in fresh argon gas which is supplied to the Primary Argon Gas System is now considered to keep the concentration of Kr and Xe isotopes in specified level, because their isotopes may make background rise for the Tagging Gas Failed Fuel Detection and Location System. Based on various investigations performed on sodium vapor trapping to obtain its detailed characteristics, design specifications and operating conditions of MONJU's Vapor Traps have been decided. To keep the level of radioactivity in gaseous effluents to the environment as low as reasonably achievable, the following means are now adopted in MONJU: the Primary Argon Gas System is composed of a closed recirculating path, but the exhaust gas discharged has different path after the Charcoal Beds; fresh argon gas is blown down to prevent Primary Argon Gas from releasing to the circumference during opening of the primary argon gas boundary, such as fuel exchange operations. (author)
Virial Coefficients for the Liquid Argon
Korth, Micheal; Kim, Saesun
2014-03-01
We begin with a geometric model of hard colliding spheres and calculate probability densities in an iterative sequence of calculations that lead to the pair correlation function. The model is based on a kinetic theory approach developed by Shinomoto, to which we added an interatomic potential for argon based on the model from Aziz. From values of the pair correlation function at various values of density, we were able to find viral coefficients of liquid argon. The low order coefficients are in good agreement with theoretical hard sphere coefficients, but appropriate data for argon to which these results might be compared is difficult to find.
Interfacial Instability in Two-Phase Flow: Manipulating Coalescence and Condensation
National Aeronautics and Space Administration — Two-phase flow under microgravity conditions presents a number of technical challenges ( and ). Life support and habitation depend on systems that use two-phase flow...
Stratified steady and unsteady two-phase flows between two parallel plates
International Nuclear Information System (INIS)
Sim, Woo Gun
2006-01-01
To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated
Two-phase flow structure in large diameter pipes
International Nuclear Information System (INIS)
Smith, T.R.; Schlegel, J.P.; Hibiki, T.; Ishii, M.
2012-01-01
Highlights: ► Local profiles of various quantities measured in large diameter pipe. ► Database for interfacial area in large pipes extended to churn-turbulent flow. ► Flow regime map confirms previous models for flow regime transitions. ► Data will be useful in developing interfacial area transport models for large pipes. - Abstract: Flow in large pipes is important in a wide variety of applications. In the nuclear industry in particular, understanding of flow in large diameter pipes is essential in predicting the behavior of reactor systems. This is especially true of natural circulation Boiling Water Reactor (BWR) designs, where a large-diameter chimney above the core provides the gravity head to drive circulation of the coolant through the reactor. The behavior of such reactors during transients and during normal operation will be predicted using advanced thermal–hydraulics analysis codes utilizing the two-fluid model. Essential to accurate two-fluid model calculations is reliable and accurate computation of the interfacial transfer terms. These interfacial transfer terms can be expressed as the product of one term describing the potential driving the transfer and a second term describing the available surface area for transfer, or interfacial area concentration. Currently, the interfacial area is predicted using flow regime dependent empirical correlations; however the interfacial area concentration is best computed through the use of the one-dimensional interfacial area transport equation (IATE). To facilitate the development of IATE source and sink term models in large-diameter pipes a fundamental understanding of the structure of the two-phase flow is essential. This understanding is improved through measurement of the local void fraction, interfacial area concentration and gas velocity profiles in pipes with diameters of 0.102 m and 0.152 m under a wide variety of flow conditions. Additionally, flow regime identification has been performed to
Experimental CFD grade data for stratified two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Vallee, Christophe, E-mail: c.vallee@fzd.d [Forschungszentrum Dresden-Rossendorf e.V., Institute of Safety Research, D-01314 Dresden (Germany); Lucas, Dirk; Beyer, Matthias; Pietruske, Heiko; Schuetz, Peter; Carl, Helmar [Forschungszentrum Dresden-Rossendorf e.V., Institute of Safety Research, D-01314 Dresden (Germany)
2010-09-15
Stratified two-phase flows were investigated at two test facilities with horizontal test-sections. For both, rectangular channel cross-sections were chosen to provide optimal observation possibilities for the application of optical measurement techniques. In order to show the local flow structure, high-speed video observation was applied, which delivers the high-resolution in space and time needed for CFD code validation. The first investigations were performed in the Horizontal Air/Water Channel (HAWAC), which is made of acrylic glass and allows the investigation of air/water co-current flows at atmospheric pressure and room temperature. At the channel inlet, a special device was designed for well-defined and adjustable inlet boundary conditions. For the quantitative analysis of the optical measurements performed at the HAWAC, an algorithm was developed to recognise the stratified interface in the camera frames. This allows to make statistical treatments for comparison with CFD calculation results. As an example, the unstable wave growth leading to slug flow is shown from the test-section inlet. Moreover, the hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was investigated in this closed channel. The structure of the hydraulic jump over time is revealed by the calculation of the probability density of the water level. A series of experiments show that the hydraulic jump profile and its position from the inlet vary substantially with the inlet boundary conditions due to the momentum exchange between the phases. The second channel is built in the pressure chamber of the TOPFLOW test facility, which is used to perform air/water and steam/water experiments at pressures of up to 5.0 MPa and temperatures of up to 264 {sup o}C, but under pressure equilibrium with the vessel inside. In the present experiment, the test-section represents a flat model of the hot leg of the German Konvoi pressurised water reactor scaled at
Experimental CFD grade data for stratified two-phase flows
International Nuclear Information System (INIS)
Vallee, Christophe; Lucas, Dirk; Beyer, Matthias; Pietruske, Heiko; Schuetz, Peter; Carl, Helmar
2010-01-01
Stratified two-phase flows were investigated at two test facilities with horizontal test-sections. For both, rectangular channel cross-sections were chosen to provide optimal observation possibilities for the application of optical measurement techniques. In order to show the local flow structure, high-speed video observation was applied, which delivers the high-resolution in space and time needed for CFD code validation. The first investigations were performed in the Horizontal Air/Water Channel (HAWAC), which is made of acrylic glass and allows the investigation of air/water co-current flows at atmospheric pressure and room temperature. At the channel inlet, a special device was designed for well-defined and adjustable inlet boundary conditions. For the quantitative analysis of the optical measurements performed at the HAWAC, an algorithm was developed to recognise the stratified interface in the camera frames. This allows to make statistical treatments for comparison with CFD calculation results. As an example, the unstable wave growth leading to slug flow is shown from the test-section inlet. Moreover, the hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was investigated in this closed channel. The structure of the hydraulic jump over time is revealed by the calculation of the probability density of the water level. A series of experiments show that the hydraulic jump profile and its position from the inlet vary substantially with the inlet boundary conditions due to the momentum exchange between the phases. The second channel is built in the pressure chamber of the TOPFLOW test facility, which is used to perform air/water and steam/water experiments at pressures of up to 5.0 MPa and temperatures of up to 264 o C, but under pressure equilibrium with the vessel inside. In the present experiment, the test-section represents a flat model of the hot leg of the German Konvoi pressurised water reactor scaled at 1
Study of the low-energy ER/NR discrimination and its electric-field dependence with liquid argon
Washimi, T.; Kikuchi, T.; Kimura, M.; Tanaka, M.; Yorita, K.
2018-02-01
A two-phase argon detector is generally suitable for the direct detection of weakly interacting massive particle (WIMP) dark matter owing to its high rejection power against electron recoil background events. However, ionization signal (S2) has not been effectively used for argon in current experiments because its basic properties and discrimination power from S2 signal in the low-energy region are not well known, as compared with xenon. The scope of this study is evaluation of S2 properties at a low-energy region of about 40 keVnr and its discrimination power between electron recoils and nuclear recoils based on results from a prototype LAr time projection chamber. The drift-field was varied from null to 3 kV/cm. The detection feasibility for low-mass WIMP with argon is also discussed.
Directory of Open Access Journals (Sweden)
V. P. Blagoveshchensky
2017-01-01
Full Text Available The calibration of the dry friction and turbulent friction coefficients is necessary for computer simulation of avalanches. The method of back calculation based on data on actual avalanches is used for this purpose. The article presents the results of the calibration of the Eglit’s and RAMMS models for Ile Alatau range condi‑ tions. The range is located in Kazakhstan. The data on six avalanches in the same avalanche site were used. Five avalanches were dry, and one avalanche was wet. Avalanches volume varied from 2000 to 12000 m3. Maximum speed avalanches were between 15 and 30 m/s, the flow height – from 3 to 10 m. Series of back calculations with different values of the friction coefficients was made to obtain the calibrated coeffi‑ cients. The calibrated coefficients were chosen under condition of the best fit with real avalanches. The cal‑ ibrated coefficients were following. For the Eglit’s model for dry avalanches of the volume 2000–5000 m3 μ = 0.46÷0.48, k = 0.005–0.006, and the volume 8000–12000 m3 μ = 0.38÷0.42, k = 0.002÷0.003. For RAMMS model for dry avalanches of the volume of 2000–5000 m3 μ (dry friction coefficient = 0.35÷0.4, ξ (viscous friction coefficient = 1500÷2000 m/s2, and the volume 8,000–12,000 m3 μ = 0.3÷0.35, ξ = 2000÷3000 m/s2. For wet avalanches of the volume 12,000 m3 μ = 0.35, ξ = 1500 m/s2. The work on the calibration will be con‑ tinued to obtain the friction coefficients for the Eglit’s and RAMMS models. The additional data on real ava‑ lanches will be needed for this purpose.
DarkSide-20k: A 20 tonne two-phase LAr TPC for direct dark matter detection at LNGS
Aalseth, C. E.; Acerbi, F.; Agnes, P.; Albuquerque, I. F. M.; Alexander, T.; Alici, A.; Alton, A. K.; Antonioli, P.; Arcelli, S.; Ardito, R.; Arnquist, I. J.; Asner, D. M.; Ave, M.; Back, H. O.; Barrado Olmedo, A. I.; Batignani, G.; Bertoldo, E.; Bettarini, S.; Bisogni, M. G.; Bocci, V.; Bondar, A.; Bonfini, G.; Bonivento, W.; Bossa, M.; Bottino, B.; Boulay, M.; Bunker, R.; Bussino, S.; Buzulutskov, A.; Cadeddu, M.; Cadoni, M.; Caminata, A.; Canci, N.; Candela, A.; Cantini, C.; Caravati, M.; Cariello, M.; Carlini, M.; Carpinelli, M.; Castellani, A.; Catalanotti, S.; Cataudella, V.; Cavalcante, P.; Cavuoti, S.; Cereseto, R.; Chepurnov, A.; Cicalò, C.; Cifarelli, L.; Citterio, M.; Cocco, A. G.; Colocci, M.; Corgiolu, S.; Covone, G.; Crivelli, P.; D'Antone, I.; D'Incecco, M.; D'Urso, D.; Da Rocha Rolo, M. D.; Daniel, M.; Davini, S.; de Candia, A.; De Cecco, S.; De Deo, M.; De Filippis, G.; De Guido, G.; De Rosa, G.; Dellacasa, G.; Della Valle, M.; Demontis, P.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Dionisi, C.; Dolgov, A.; Dormia, I.; Dussoni, S.; Empl, A.; Fernandez Diaz, M.; Ferri, A.; Filip, C.; Fiorillo, G.; Fomenko, K.; Franco, D.; Froudakis, G. E.; Gabriele, F.; Gabrieli, A.; Galbiati, C.; Garcia Abia, P.; Gendotti, A.; Ghisi, A.; Giagu, S.; Giampa, P.; Gibertoni, G.; Giganti, C.; Giorgi, M. A.; Giovanetti, G. K.; Gligan, M. L.; Gola, A.; Gorchakov, O.; Goretti, A. M.; Granato, F.; Grassi, M.; Grate, J. W.; Grigoriev, G. Y.; Gromov, M.; Guan, M.; Guerra, M. B. B.; Guerzoni, M.; Gulino, M.; Haaland, R. K.; Hallin, A.; Harrop, B.; Hoppe, E. W.; Horikawa, S.; Hosseini, B.; Hughes, D.; Humble, P.; Hungerford, E. V.; Ianni, An.; Jillings, C.; Johnson, T. N.; Keeter, K.; Kendziora, C. L.; Kim, S.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, A.; Kuss, M.; Kuźniak, M.; La Commara, M.; Lehnert, B.; Li, X.; Lissia, M.; Lodi, G. U.; Loer, B.; Longo, G.; Loverre, P.; Lussana, R.; Luzzi, L.; Ma, Y.; Machado, A. A.; Machulin, I. N.; Mandarano, A.; Mapelli, L.; Marcante, M.; Margotti, A.; Mari, S. M.; Mariani, M.; Maricic, J.; Martoff, C. J.; Mascia, M.; Mayer, M.; McDonald, A. B.; Messina, A.; Meyers, P. D.; Milincic, R.; Moggi, A.; Moioli, S.; Monroe, J.; Monte, A.; Morrocchi, M.; Mount, B. J.; Mu, W.; Muratova, V. N.; Murphy, S.; Musico, P.; Nania, R.; Navrer Agasson, A.; Nikulin, I.; Nosov, V.; Nozdrina, A. O.; Nurakhov, N. N.; Oleinik, A.; Oleynikov, V.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Palmas, S.; Pandola, L.; Pantic, E.; Paoloni, E.; Paternoster, G.; Pavletcov, V.; Pazzona, F.; Peeters, S.; Pelczar, K.; Pellegrini, L. A.; Pelliccia, N.; Perotti, F.; Perruzza, R.; Pesudo, V.; Piemonte, C.; Pilo, F.; Pocar, A.; Pollmann, T.; Portaluppi, D.; Pugachev, D. A.; Qian, H.; Radics, B.; Raffaelli, F.; Ragusa, F.; Razeti, M.; Razeto, A.; Regazzoni, V.; Regenfus, C.; Reinhold, B.; Renshaw, A. L.; Rescigno, M.; Retière, F.; Riffard, Q.; Rivetti, A.; Rizzardini, S.; Romani, A.; Romero, L.; Rossi, B.; Rossi, N.; Rubbia, A.; Sablone, D.; Salatino, P.; Samoylov, O.; Sánchez García, E.; Sands, W.; Sanfilippo, S.; Sant, M.; Santorelli, R.; Savarese, C.; Scapparone, E.; Schlitzer, B.; Scioli, G.; Segreto, E.; Seifert, A.; Semenov, D. A.; Shchagin, A.; Shekhtman, L.; Shemyakina, E.; Sheshukov, A.; Simeone, M.; Singh, P. N.; Skensved, P.; Skorokhvatov, M. D.; Smirnov, O.; Sobrero, G.; Sokolov, A.; Sotnikov, A.; Speziale, F.; Stainforth, R.; Stanford, C.; Suffritti, G. B.; Suvorov, Y.; Tartaglia, R.; Testera, G.; Tonazzo, A.; Tosi, A.; Trinchese, P.; Unzhakov, E. V.; Vacca, A.; Vázquez-Jáuregui, E.; Verducci, M.; Viant, T.; Villa, F.; Vishneva, A.; Vogelaar, B.; Wada, M.; Wahl, J.; Walding, J.; Wang, H.; Wang, Y.; Watson, A. W.; Westerdale, S.; Williams, R.; Wojcik, M. M.; Wu, S.; Xiang, X.; Xiao, X.; Yang, C.; Ye, Z.; Yllera de Llano, A.; Zappa, F.; Zappalà, G.; Zhu, C.; Zichichi, A.; Zullo, M.; Zullo, A.; Zuzel, G.
2018-03-01
Building on the successful experience in operating the DarkSide-50 detector, the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMP search detector using a two-phase Liquid Argon Time Projection Chamber (LAr TPC) with an active (fiducial) mass of 23 t (20 t). This paper describes a preliminary design for the experiment, in which the DarkSide-20k LAr TPC is deployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV) inside a cylindrical Water Cherenkov Veto (WCV). This preliminary design provides a baseline for the experiment to achieve its physics goals, while further development work will lead to the final optimization of the detector parameters and an eventual technical design. Operation of DarkSide-50 demonstrated a major reduction in the dominant 39Ar background when using argon extracted from an underground source, before applying pulse shape analysis. Data from DarkSide-50, in combination with MC simulation and analytical modeling, shows that a rejection factor for discrimination between electron and nuclear recoils of >3 × 109 is achievable. This, along with the use of the veto system and utilizing silicon photomultipliers in the LAr TPC, are the keys to unlocking the path to large LAr TPC detector masses, while maintaining an experiment in which less than < 0.1 events (other than ν-induced nuclear recoils) is expected to occur within the WIMP search region during the planned exposure. DarkSide-20k will have ultra-low backgrounds than can be measured in situ, giving sensitivity to WIMP-nucleon cross sections of 1.2 × 10^{-47} cm2 (1.1 × 10^{-46} cm2) for WIMPs of 1 TeV/c 2 (10 TeV/c 2) mass, to be achieved during a 5 yr run producing an exposure of 100 t yr free from any instrumental background.
Features of two-phase flow in a microchannel of 0.05×20 mm
Ronshin, Fedor
2017-10-01
We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.
Rolling effects on two-phase flow pattern and void fraction
International Nuclear Information System (INIS)
Yan Changqi; Yu Kaiqiu; Luan Feng; Cao Xiaxin
2008-01-01
The experimental and theoretical study was carried out for the upward gas-liquid two-phase explained reasonably through the analysis of slip ratio of two-phase flow and theoretical analysis using momentum equation of two-phase flow separating model. (authors)
Measurement of two phase flow properties using the nuclear reactor instruments
International Nuclear Information System (INIS)
Albrecht, R.W.; Washington Univ., Seattle; Crowe, R.D.; Dailey, D.J.; Kosaly, G.; Damborg, M.J.
1982-01-01
A procedure is introduced for characterizing one dimensional, two phase flow in terms of three properties; propagation, structure, and dynamics. It is shown that all of these properties can be measured by analyzing the response of the reactor neutron field to a two phase flow perturbation. Therefore, a nuclear reactor can be regarded as a two phase flow instrument. (author)
Relation of the runaway avalanche threshold to momentum space topology
McDevitt, Christopher J.; Guo, Zehua; Tang, Xian-Zhu
2018-02-01
The underlying physics responsible for the formation of an avalanche instability due to the generation of secondary electrons is studied. A careful examination of the momentum space topology of the runaway electron population is carried out with an eye toward identifying how qualitative changes in the momentum space of the runaway electrons is correlated with the avalanche threshold. It is found that the avalanche threshold is tied to the merger of an O and X point in the momentum space of the primary runaway electron population. Such a change of the momentum space topology is shown to be accurately described by a simple analytic model, thus providing a powerful means of determining the avalanche threshold for a range of model assumptions.
Discrimination capability of avalanche counters detecting different ionizing particles
International Nuclear Information System (INIS)
Prete, G.; Viesti, G.; Padua Univ.
1985-01-01
The discrimination capability of avalanche counters to detect different ionizing particles has been studied using a 252 Cf source. Pulse height, pulse-height resolution and timing properties have been measured as a function of the reduced applied voltage for parallel-plate and parallel-grid avalanche counters. At the highest applied voltages, space charge effects shift the pulse-height signal of the avalanche counter away from being linearly proportional to the stopping power of the detected particles and cause the pulse-height resolution to deteriorate. To optimize the avalanche counter capability, without loss of time resolution, it appears better to operate the detector at voltages well below the breakdown threshold. Measurements with 32 S ions are also reported. (orig.)
New method for determining avalanche breakdown voltage of silicon photomultipliers
International Nuclear Information System (INIS)
Chirikov-Zorin, I.
2017-01-01
The avalanche breakdown and Geiger mode of the silicon p-n junction is considered. A precise physically motivated method is proposed for determining the avalanche breakdown voltage of silicon photomultipliers (SiPM). The method is based on measuring the dependence of the relative photon detection efficiency (PDE rel ) on the bias voltage when one type of carriers (electron or hole) is injected into the avalanche multiplication zone of the p-n junction. The injection of electrons or holes from the base region of the SiPM semiconductor structure is performed using short-wave or long-wave light. At a low overvoltage (1-2 V) the detection efficiency is linearly dependent on the bias voltage; therefore, extrapolation to zero PDE rel value determines the SiPM avalanche breakdown voltage with an accuracy within a few millivolts. [ru
Transient events in bright debris discs: Collisional avalanches revisited
Thebault, P.; Kral, Q.
2018-01-01
Context. A collisional avalanche is set off by the breakup of a large planetesimal, releasing vast amounts of small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that could potentially create detectable transient structures. Aims: We investigate this mechanism, using for the first time a fully self-consistent code coupling dynamical and collisional evolutions. We also quantify for the first time the photometric evolution of the system and investigate whether or not avalanches could explain the short-term luminosity variations recently observed in some extremely bright debris discs. Methods: We use the state-of-the-art LIDT-DD code. We consider an avalanche-favoring A6V star, and two set-ups: a "cold disc" case, with a dust release at 10 au and an outer disc extending from 50 to 120 au, and a "warm disc" case with the release at 1 au and a 5-12 au outer disc. We explore, in addition, two key parameters: the density (parameterized by its optical depth τ) of the main outer disc and the amount of dust released by the initial breakup. Results: We find that avalanches could leave detectable structures on resolved images, for both "cold" and "warm" disc cases, in discs with τ of a few 10-3, provided that large dust masses (≳1020-5 × 1022 g) are initially released. The integrated photometric excess due to an avalanche is relatively limited, less than 10% for these released dust masses, peaking in the λ 10-20 μm domain and becoming insignificant beyond 40-50 μm. Contrary to earlier studies, we do not obtain stronger avalanches when increasing τ to higher values. Likewise, we do not observe a significant luminosity deficit, as compared to the pre-avalanche level, after the passage of the avalanche. These two results concur to make avalanches an unlikely explanation for the sharp luminosity drops observed in some extremely bright debris discs. The ideal configuration for observing an
La Carte de Localisation Probable des Avalanches (CPLA
Directory of Open Access Journals (Sweden)
Gilles BORREL
1994-12-01
Full Text Available La Carte de Localisation Probable des Avalanches (CPLA indique l’enveloppe des limites extrêmes connues atteintes par les avalanches, ainsi que les travaux de protection associés. Il s’agit d’un document informatif et non d’une carte de risque. Depuis 1990, les données thématiques sont numérisées.
Stretched exponentials and power laws in granular avalanching
Head, D. A.; Rodgers, G. J.
1999-02-01
We introduce a model for granular surface flow which exhibits both stretched exponential and power law avalanching over its parameter range. Two modes of transport are incorporated, a rolling layer consisting of individual particles and the overdamped, sliding motion of particle clusters. The crossover in behaviour observed in experiments on piles of rice is attributed to a change in the dominant mode of transport. We predict that power law avalanching will be observed whenever surface flow is dominated by clustered motion.
Broadband Ftmw Spectroscopy of the Urea-Argon and Thiourea-Argon Complexes
Medcraft, Chris; Bittner, Dror M.; Cooper, Graham A.; Mullaney, John C.; Walker, Nick
2017-06-01
The rotational spectra complexes of argon-urea, argon-thiourea and water-thiourea have been measured by chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. The sample was produced via laser vaporisation of a rod containing copper and the organic sample as a stream of argon was passed over the surface and subsequently expanded into the vacuum chamber cooling the sample. Argon was found to bind to π system of the carbonyl bond for both the urea and thiourea complexes.
Negative corona current pulses in argon and in mixture argon with SF6
International Nuclear Information System (INIS)
Zahoranova, A.; Zahoran, M.; Bucek, A.; Cernak, M.; Bosko, J.
2004-01-01
Waveforms of the first negative current pulses in a short negative point-to plane gap in pure argon and argon with SF 6 admixture have been investigated with a nanosecond time resolution at a gas pressure 50 kPa as a function of applied gap voltage and content of SF 6 in the mixture. We have made an attempt to explain the differences in the discharge development in pure argon and in argon with admixture of SF 6 based on the observed changes of the pulse shape. The experimental results obtained will be discussed in context with existing computer simulation models (Authors)
Emission spectra of gaseous avalanches and their time structure
International Nuclear Information System (INIS)
Fraga, M.M.; Lima, E.P. de; Marques, R.F.; Policarpo, A.J.P.L.; Alves, M.A.F.; Salete, M.; Leite, S.C.P.
1993-01-01
Following previous measurements in argon/methane mixtures, the authors now report on the emission spectra of argon/ethane and methane/ethane mixtures, in the region from 120 to 450 nm, for a single wire chamber working in the proportional and/or self-quenching streamer modes. Identification of radicals and fragments is attempted. The time evolution of VUV light, relevant to photon feedback processes, is presented for the CI lines at 156.1 and 165.7nm in argon/methane, argon/ethane and methane/ethane mixtures
Geiger mode avalanche photodiodes for microarray systems
Phelan, Don; Jackson, Carl; Redfern, R. Michael; Morrison, Alan P.; Mathewson, Alan
2002-06-01
New Geiger Mode Avalanche Photodiodes (GM-APD) have been designed and characterized specifically for use in microarray systems. Critical parameters such as excess reverse bias voltage, hold-off time and optimum operating temperature have been experimentally determined for these photon-counting devices. The photon detection probability, dark count rate and afterpulsing probability have been measured under different operating conditions. An active- quench circuit (AQC) is presented for operating these GM- APDs. This circuit is relatively simple, robust and has such benefits as reducing average power dissipation and afterpulsing. Arrays of these GM-APDs have already been designed and together with AQCs open up the possibility of having a solid-state microarray detector that enables parallel analysis on a single chip. Another advantage of these GM-APDs over current technology is their low voltage CMOS compatibility which could allow for the fabrication of an AQC on the same device. Small are detectors have already been employed in the time-resolved detection of fluorescence from labeled proteins. It is envisaged that operating these new GM-APDs with this active-quench circuit will have numerous applications for the detection of fluorescence in microarray systems.
Avalanche outbreaks emerging in cooperative contagions
Cai, Weiran; Chen, Li; Ghanbarnejad, Fakhteh; Grassberger, Peter
2015-11-01
The spreading of contagions can exhibit a percolation transition, which separates transitory prevalence from outbreaks that reach a finite fraction of the population. Such transitions are commonly believed to be continuous, but empirical studies have shown more violent spreading modes when the participating agents are not limited to one type. Striking examples include the co-epidemic of the Spanish flu and pneumonia that occurred in 1918 (refs , ), and, more recently, the concurrent prevalence of HIV/AIDS and a host of diseases. It remains unclear to what extent an outbreak in the presence of interacting pathogens differs from that due to an ordinary single-agent process. Here we study a mechanistic model for understanding contagion processes involving inter-agent cooperation. Our stochastic simulations reveal the possible emergence of a massive avalanche-like outbreak right at the threshold, which is manifested as a discontinuous phase transition. Such an abrupt change arises only if the underlying network topology supports a bottleneck for cascaded mutual infections. Surprisingly, all these discontinuous transitions are accompanied by non-trivial critical behaviours, presenting a rare case of hybrid transition. The findings may imply the origin of catastrophic occurrences in many realistic systems, from co-epidemics to financial contagions.
First approximations in avalanche model validations using seismic information
Roig Lafon, Pere; Suriñach, Emma; Bartelt, Perry; Pérez-Guillén, Cristina; Tapia, Mar; Sovilla, Betty
2017-04-01
Avalanche dynamics modelling is an essential tool for snow hazard management. Scenario based numerical modelling provides quantitative arguments for decision-making. The software tool RAMMS (WSL Institute for Snow and Avalanche Research SLF) is one such tool, often used by government authorities and geotechnical offices. As avalanche models improve, the quality of the numerical results will depend increasingly on user experience on the specification of input (e.g. release and entrainment volumes, secondary releases, snow temperature and quality). New model developments must continue to be validated using real phenomena data, for improving performance and reliability. The avalanches group form University of Barcelona (RISKNAT - UB), has studied the seismic signals generated from avalanches since 1994. Presently, the group manages the seismic installation at SLF's Vallée de la Sionne experimental site (VDLS). At VDLS the recorded seismic signals can be correlated to other avalanche measurement techniques, including both advanced remote sensing methods (radars, videogrammetry) and obstacle based sensors (pressure, capacitance, optical sender-reflector barriers). This comparison between different measurement techniques allows the group to address the question if seismic analysis can be used alone, on more additional avalanche tracks, to gain insight and validate numerical avalanche dynamics models in different terrain conditions. In this study, we aim to add the seismic data as an external record of the phenomena, able to validate RAMMS models. The seismic sensors are considerable easy and cheaper to install than other physical measuring tools, and are able to record data from the phenomena in every atmospheric conditions (e.g. bad weather, low light, freezing make photography, and other kind of sensors not usable). With seismic signals, we record the temporal evolution of the inner and denser parts of the avalanche. We are able to recognize the approximate position
Review of supershort avalanche electron beam during nanosecond-pulse discharges in some gases
Directory of Open Access Journals (Sweden)
Victor F. Tarasenko
2017-05-01
Full Text Available Supershort avalanche electron beam (SAEB plays an important role in nanosecond-pulse discharges. This paper aims at reviewing experiments results on characteritics of SAEB and its spectra in different gases in nanosecond-pulse discharges. All the joint experiments were carried in the Institute of High Current Electronics of the Russian Academy of Sciences and the Institute of Electrical Engineering of the Chinese Academy of Sciences. In these experiments, the generation of a SAEB in SF6 in an inhomogeneous electric field was studied on three generators with pulse rise times of 0.3, 0.5 and ∼2 ns. Firstly, the comparison of SAEB parameters in SF6 with those obtained in other gases (air, nitrogen, argon, and krypton is introduced. Secondly, the SAEB spectra in SF6 and air at pressures of 10 kPa (75 torr, and 0.1 MPa (750 torr are reviewed and discussed. Finally, 1.5-D theoretical simulation of the supershort pulse of the fast electron beam in a coaxial diode filled with SF6 at atmospheric pressure is described. The simulation was carried out in the framework of hybrid model for discharge and runaway electron kinetics. The above research progress can provide better understanding of the investigation into the mechanism of nanosecond-pulse discharges.
Using the New Two-Phase-Titan to Evaluate Potential Lahar Hazard at Villa la Angostura, Argentina
Sheridan, M. F.; Cordoba, G. A.; Viramonte, J. G.; Folch, A.; Villarosa, G.; Delgado, H.
2013-05-01
The 2011 eruption of Puyehue Volcano, located in the Cordon del Caulle volcanic complex, Chile, produced an ash plume that mainly affected downwind areas in Argentina. This plume forced air transport in the region to be closed for several weeks. Tephra fall deposits from this eruption affected many locations and pumice deposits on lakes killed most of the fish. As the ash emission occurred during the southern hemisphere winter (June), ash horizons were inter layered with layers of snow. This situation posed a potential threat for human settlements located downslope of the mountains. This was the case at Villa la Angostura, Neuquen province, Argentina, which sits on a series of fluvial deposits that originate in three major basins: Piedritas, Colorado, and Florencia. The Institute of Geological Survey of Argentina (SEGEMAR) estimated that the total accumulated deposit in each basin contains a ratio of approximately 30% ash and 70% snow. The CyTED-Ceniza Iberoamerican network worked together with Argentinean, Colombian and USA institutions in this hazard assessment. We used the program Two-Phase-Titan to model two scenarios in each of the basins. This computer code was developed at SUNY University at Buffalo supported by NSF Grant EAR 711497. Two-Phase-Titan is a new depth-averaged model for two phase flows that uses balance equations for multiphase mixtures. We evaluate the stresses using a Coulomb law for the solid phase and the typical hydraulic shallow water approach for the fluid phase. The linkage for compositions in the range between the pure end-member phases is accommodated by the inclusion of a phenomenological-based drag coefficient. The model is capable of simulating the whole range of particle volumetric fractions, from pure fluid flows to pure solid avalanches. The initial conditions, volume and solid concentration, required by Two-Phase-Titan were imposed using the SEGEMAR estimation of total deposited volume, assuming that the maximum volume that can
Intermittent flow under constant forcing: Acoustic emission from creep avalanches
Salje, Ekhard K. H.; Liu, Hanlong; Jin, Linsen; Jiang, Deyi; Xiao, Yang; Jiang, Xiang
2018-01-01
While avalanches in field driven ferroic systems (e.g., Barkhausen noise), domain switching of martensitic nanostructures, and the collapse of porous materials are well documented, creep avalanches (avalanches under constant forcing) were never observed. Collapse avalanches generate particularly large acoustic emission (AE) signals and were hence chosen to investigate crackling noise under creep conditions. Piezoelectric SiO2 has a strong piezoelectric response even at the nanoscale so that we chose weakly bound SiO2 spheres in natural sandstone as a representative for the study of avalanches under time-independent, constant force. We found highly non-stationary crackling noise with four activity periods, each with power law distributed AE emission. Only the period before the final collapse shows the mean field behavior (ɛ near 1.39), in agreement with previous dynamic measurements at a constant stress rate. All earlier event periods show collapse with larger exponents (ɛ = 1.65). The waiting time exponents are classic with τ near 2.2 and 1.32. Creep data generate power law mixing with "effective" exponents for the full dataset with combinations of mean field and non-mean field regimes. We find close agreement with the predicted time-dependent fiber bound simulations, including events and waiting time distributions. Båth's law holds under creep conditions.
Features of two-phase flow in a microchannel of 0.05×20 mm
Directory of Open Access Journals (Sweden)
Ronshin Fedor
2017-01-01
Full Text Available We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.
Two-Phase Annular Flow in Helical Coil Flow Channels in a Reduced Gravity Environment
Keshock, Edward G.; Lin, Chin S.
1996-01-01
A brief review of both single- and two-phase flow studies in curved and coiled flow geometries is first presented. Some of the complexities of two-phase liquid-vapor flow in curved and coiled geometries are discussed, and serve as an introduction to the advantages of observing such flows under a low-gravity environment. The studies proposed -- annular two-phase air-water flow in helical coil flow channels are described. Objectives of the studies are summarized.
Trapping cold ground state argon atoms.
Edmunds, P D; Barker, P F
2014-10-31
We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2](2) state to be (7.3±1.1)×10(-39) C m(2)/V. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be (3.3±0.8)×10(-10) cm(3) s(-1).
Sodium evaporation into a forced argon flow
International Nuclear Information System (INIS)
Kumada, Toshiaki; Kasahara, Fumio; Ishiguro, Ryoji
1975-01-01
Evaporation from a rectangular sodium free surface into an argon flow was measured. Tests were carried out with varying sodium temperature, argon velocity and argon temperature respectively under conditions of fog formation being possible. In order to clarify the enhancement of evaporation by fog formation, convection heat transfer from a plate of the same geometry into an air flow was also measured. The evaporation rate and Sherwood number were compared with those predicted by both the heat transfer experiment and the theory proposed by Hill and Szekely, and also a comparison was run with the previously reported experimental results of sodium evaporation. As a result it was shown that the sodium evaporation rate in this experiment is at least four times as large as that predicted by the heat transfer experiment and varies almost linearly with the heat transfer rate and the sodium vapour pressure. (auth.)
Characteristics of low-mass-velocity vertical gas-liquid two-phase flow
International Nuclear Information System (INIS)
Adachi, Hiromichi; Abe, Yutaka; Kimura, Ko-ji
1995-01-01
In the present paper, characteristics of low mass velocity two-phase flow was analyzed based on a concept that pressure energy of two-phase flow is converted into acceleration work, gravitational work and frictional work, and the pressure energy consumption rate should be minimum at the stable two-phase flow condition. Experimental data for vertical upward air-water two-phase flow at atmospheric pressure was used to verify this concept and the turbulent model used in this method is optimized with the data. (author)
Models for assessing the relative phase velocity in a two-phase flow. Status report
International Nuclear Information System (INIS)
Schaffrath, A.; Ringel, H.
2000-06-01
The knowledge of slip or drift flux in two phase flow is necessary for several technical processes (e.g. two phase pressure losses, heat and mass transfer in steam generators and condensers, dwell period in chemical reactors, moderation effectiveness of two phase coolant in BWR). In the following the most important models for two phase flow with different phase velocities (e.g. slip or drift models, analogy between pressure loss and steam quality, ε - ε models and models for the calculation of void distribution in reposing fluids) are classified, described and worked up for a further comparison with own experimental data. (orig.)
Two-photon excitation of argon
International Nuclear Information System (INIS)
Pindzola, P.S.; Payne, M.C.
1982-01-01
The authors calculate two photon excitation parameters for various excited states of argon assuming the absorption of near resonance broad-bandwidth laser radiation. Results are given for the case of two photons absorbed for the same laser beam as well as the case of absorbing photons of different frequency from each of two laser beams. The authors use multiconfiguration Hartree-Fock wave functions to evaluate the second-order sums over matrix elements. Various experimental laser schemes are suggested for the efficient excitation and subsequent ionization of argon
Argon isotopes as recorders of magmatic processes
Layer, P. W.; Gardner, J. E.; Mora Chaparro, J. C.; Arce, J. L.
2003-12-01
Argon isotopic ratios vary enough between different reservoirs (atmosphere, crust, mantle) and diffuse fast enough through most minerals at magmatic temperatures (700-1200 C) to make them ideal for looking at magma chamber dynamics. Indeed, diffusion is sufficiently fast to allow short time scales to be deciphered, setting argon apart from many other isotopic methods. A mineral's ability to retain "excess" argon (40Ar/36Ar ratios greater than the atmospheric value and apparent ages older than the known eruption age) during post-eruption cooling is key to Ar studies. Previous work shows that both phenocrysts (crystallizing in the magma chamber; e.g. Mt St. Helens; Layer and Gardner, 2001) and xenocrysts (introduced into the magma chamber; e.g Toba; Gardner et al., 2002) preserve excess argon, which enables magma chamber processes to be deciphered through the variable diffusion rates between crystal phases. Single crystal 40Ar/39Ar step-heating of biotite from the 10.5 ka eruption of Nevado de Toluca volcano, Mexico indicates that they are xenocrystic and resided for only a short (< 1 year) time in the magma before it erupted. The biotite has reaction rims of hornblende, orthopyroxene and plagioclase, and failed to grow experimentally at pressure-temperature conditions of the magma, confirming the xenocrystic nature of this phase. Single-step fusion of plagioclase phenocrysts from eruptions of El Chichon volcano, Mexico, shows evidence of excess (mantle) argon, whereas hornblende from the same eruptions contains little or none. In this case, faster diffusion of Ar in plagioclase than in hornblende allow plagioclase to incorporate excess argon during magma recharge; hornblende does not. Combining such results with other isotopic systems may in fact better determine magma chamber processes. At El Chichon, Sr isotopes suggest magma recharges ocurred (Tepley et al., 2000), whereas the argon isotopes suggest such pulses occurred just before each eruption. The fast and
Avalanches and plastic flow in crystal plasticity: an overview
Papanikolaou, Stefanos; Cui, Yinan; Ghoniem, Nasr
2018-01-01
Crystal plasticity is mediated through dislocations, which form knotted configurations in a complex energy landscape. Once they disentangle and move, they may also be impeded by permanent obstacles with finite energy barriers or frustrating long-range interactions. The outcome of such complexity is the emergence of dislocation avalanches as the basic mechanism of plastic flow in solids at the nanoscale. While the deformation behavior of bulk materials appears smooth, a predictive model should clearly be based upon the character of these dislocation avalanches and their associated strain bursts. We provide here a comprehensive overview of experimental observations, theoretical models and computational approaches that have been developed to unravel the multiple aspects of dislocation avalanche physics and the phenomena leading to strain bursts in crystal plasticity.
Parallel two-phase-flow-induced vibrations in fuel pin model
International Nuclear Information System (INIS)
Hara, Fumio; Yamashita, Tadashi
1978-01-01
This paper reports the experimental results of vibrations of a fuel pin model -herein meaning the essential form of a fuel pin from the standpoint of vibration- in a parallel air-and-water two-phase flow. The essential part of the experimental apparatus consisted of a flat elastic strip made of stainless steel, both ends of which were firmly supported in a circular channel conveying the two-phase fluid. Vibrational strain of the fuel pin model, pressure fluctuation of the two-phase flow and two-phase-flow void signals were measured. Statistical measures such as power spectral density, variance and correlation function were calculated. The authors obtained (1) the relation between variance of vibrational strain and two-phase-flow velocity, (2) the relation between variance of vibrational strain and two-phase-flow pressure fluctuation, (3) frequency characteristics of variance of vibrational strain against the dominant frequency of the two-phase-flow pressure fluctuation, and (4) frequency characteristics of variance of vibrational strain against the dominant frequency of two-phase-flow void signals. The authors conclude that there exist two kinds of excitation mechanisms in vibrations of a fuel pin model inserted in a parallel air-and-water two-phase flow; namely, (1) parametric excitation, which occurs when the fundamental natural frequency of the fuel pin model is related to the dominant travelling frequency of water slugs in the two-phase flow by the ratio 1/2, 1/1, 3/2 and so on; and (2) vibrational resonance, which occurs when the fundamental frequency coincides with the dominant frequency of the two-phase-flow pressure fluctuation. (auth.)
Experimental method to predict avalanches based on neural networks
Directory of Open Access Journals (Sweden)
V. V. Zhdanov
2016-01-01
Full Text Available The article presents results of experimental use of currently available statistical methods to classify the avalanche‑dangerous precipitations and snowfalls in the Kishi Almaty river basin. The avalanche service of Kazakhstan uses graphical methods for prediction of avalanches developed by I.V. Kondrashov and E.I. Kolesnikov. The main objective of this work was to develop a modern model that could be used directly at the avalanche stations. Classification of winter precipitations into dangerous snowfalls and non‑dangerous ones was performed by two following ways: the linear discriminant function (canonical analysis and artificial neural networks. Observational data on weather and avalanches in the gorge Kishi Almaty in the gorge Kishi Almaty were used as a training sample. Coefficients for the canonical variables were calculated by the software «Statistica» (Russian version 6.0, and then the necessary formula had been constructed. The accuracy of the above classification was 96%. Simulator by the authors L.N. Yasnitsky and F.М. Cherepanov was used to learn the neural networks. The trained neural network demonstrated 98% accuracy of the classification. Prepared statistical models are recommended to be tested at the snow‑avalanche stations. Results of the tests will be used for estimation of the model quality and its readiness for the operational work. In future, we plan to apply these models for classification of the avalanche danger by the five‑point international scale.
Investigations of single-electron avalanches in a proportional drift tube
International Nuclear Information System (INIS)
Anderson, W.S.; Armitage, J.C.; Chevreau, P.; Heinrich, J.G.; Lu, C.; McDonald, I.; McDonald, K.T.; Miller, B.; Secrest, D.; Weckel, J.
1990-01-01
Detailed information on single-electron drift and avalanche behavior has a basic interest in an investigation of gas-chamber performance. Its timing, avalanche distribution, attachment by the working gas mixtures, etc., provide various criteria for choosing the best suitable gas mixture under a specific experimental circumstance. Investigations of single-electron avalanches in a proportional drift tube have been carried out with a pulsed N 2 laser. The study consists of two aspects: timing properties, and fluctuations in the gas avalanche
Avalanche effect in the planar array of superheated superconductors
International Nuclear Information System (INIS)
Meagher, G.; Pond, J.; Kotlicki, A.; Turrell, B.G.; Eska, G.; Drukier, A.K.
1996-01-01
An avalanche effect has been observed in a cryogenic detector based on the planar array of superheated superconductors (PASS). The indium PASS, fabricated by photolithography on a mylar substrate, consisted of 40 well-separated lines each containing about 175 spheres of diameter 18 μm and separation 20 μm with those at the end being shielded by superconducting wire. The magnetic field was applied in the PASS plane parallel to the lines. Avalanche events in which several granules changed their state from superconducting to normal were triggered by the nucleation of the transition in a single grain by an alpha particle. (author)
High gain multigap avalanche detectors for Cerenkov ring imaging
Energy Technology Data Exchange (ETDEWEB)
Gilmore, R.S.; Lavender, W.M.; Leith, D.W.G.S.; Williams, S.H.
1980-10-01
We report on a continuing study of multigap parallel plate avalanche chambers, primarily as photoelectron detectors for use with Cerenkov ring imaging counters. By suitable control of the fields in successive gaps and by introducing screens to reduce photon feedback to the cathode the gain many be increased considerably. We have obtained gains in excess of 6 x 10/sup 7/ for photoelectrons with a good pulse height spectrum and expect to increase this further. We discuss the use of resistive anodes to give avalanche positions in two dimensions by charge division.
Avalanche size scaling in sheared three-dimensional amorphous solid
DEFF Research Database (Denmark)
Bailey, Nicholas; Schiøtz, Jakob; Lemaître, A.
2007-01-01
We study the statistics of plastic rearrangement events in a simulated amorphous solid at T=0. Events are characterized by the energy release and the "slip volume", the product of plastic strain and system volume. Their distributions for a given system size L appear to be exponential......, but a characteristic event size cannot be inferred, because the mean values of these quantities increase as L-alpha with alpha similar to 3/2. In contrast with results obtained in 2D models, we do not see simply connected avalanches. The exponent suggests a fractal shape of the avalanches, which is also evidenced...
2018-01-01
Set IV is a new addition to the previous Sets I, II and III. It contains 23 invited chapters from international specialists on the topics of numerical modeling of pulsating heat pipes and of slug flows with evaporation; lattice Boltzmann modeling of pool boiling; fundamentals of boiling in microchannels and microfin tubes, CO2 and nanofluids; testing and modeling of micro-two-phase cooling systems for electronics; and various special topics (flow separation in microfluidics, two-phase sensors, wetting of anisotropic surfaces, ultra-compact heat exchangers, etc.). The invited authors are leading university researchers and well-known engineers from leading corporate research laboratories (ABB, IBM, Nokia Bell Labs). Numerous "must read" chapters are also included here for the two-phase community. Set IV constitutes a "must have" engineering and research reference together with previous Sets I, II and III for thermal engineering researchers and practitioners.
Contraction ionization waves in the argon contracted discharge
International Nuclear Information System (INIS)
Golubovskij, Yu.B.; Kulikov, V.V.; Nekutchaev, V.O.
1985-01-01
An investigation of ionization waves in the argon contracted discharge and a definition of their arising propagation mechanism accounting for the specificity of elementary pocesses characteristic of argon are presented. (author)
Chiaramonte, Francis; Motil, Brian; McQuillen, John
2014-01-01
The Two-phase Heat Transfer International Topical Team consists of researchers and members from various space agencies including ESA, JAXA, CSA, and RSA. This presentation included descriptions various fluid experiments either being conducted by or planned by NASA for the International Space Station in the areas of two-phase flow, flow boiling, capillary flow, and crygenic fluid storage.
Analytic approximations for the elastic moduli of two-phase materials
DEFF Research Database (Denmark)
Zhang, Z. J.; Zhu, Y. K.; Zhang, P.
2017-01-01
Based on the models of series and parallel connections of the two phases in a composite, analytic approximations are derived for the elastic constants (Young's modulus, shear modulus, and Poisson's ratio) of elastically isotropic two-phase composites containing second phases of various volume...
Strong enhancement of streaming current power by application of two phase flow
Xie, Yanbo; Sherwood, John D.; Shui, Lingling; van den Berg, Albert; Eijkel, Jan C.T.
2011-01-01
We show that the performance of a streaming-potential based microfluidic energy conversion system can be strongly en-hanced by the use of two phase flow. In single-phase systems, the internal conduction current induced by the streaming poten-tial limits the output power, while in a two-phase system
Numerical simulation for gas-liquid two-phase flow in pipe networks
International Nuclear Information System (INIS)
Li Xiaoyan; Kuang Bo; Zhou Guoliang; Xu Jijun
1998-01-01
The complex pipe network characters can not directly presented in single phase flow, gas-liquid two phase flow pressure drop and void rate change model. Apply fluid network theory and computer numerical simulation technology to phase flow pipe networks carried out simulate and compute. Simulate result shows that flow resistance distribution is non-linear in two phase pipe network
Mass flow rate measurements in two-phase mixtrues with stagnation probes
International Nuclear Information System (INIS)
Fincke, J.R.; Deason, V.A.
1979-01-01
Applications of stagnation probes to the measurement of mass flow rate in two-phase flows are discussed. Descriptions of several stagnation devices, which have been evaluated at the Idaho National Engineering Laboratory, are presented along with modeling techniques and two-phase flow data
Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows
Sihao, L. V.; Yang, Weihua; Li, Xiangli; Li, Guohui
2013-01-01
A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent
Symmetrical components and power analysis for a two-phase microgrid system
DEFF Research Database (Denmark)
Alibeik, M.; Santos Jr., E. C. dos; Blaabjerg, Frede
2014-01-01
This paper presents a mathematical model for the symmetrical components and power analysis of a new microgrid system consisting of three wires and two voltages in quadrature, which is designated as a two-phase microgrid. The two-phase microgrid presents the following advantages: 1) constant power...
Modeling and Performance of a Self-Excited Two-Phase Reluctance ...
African Journals Online (AJOL)
A self-excited two-phase reluctance generator (SETPRG) with balanced stator winding is presented. A unique balanced two-phase stator winding was designed with emphasis on obtaining a stator MMF waveform with minimum space harmonics. Then a mathematical model by which the dynamic behavior of the generator ...
Design and development of drag-disc flowmeter for measurement of transient two-phase flow
International Nuclear Information System (INIS)
Sreenivas Rao, G.; Kukreja, V.; Dolas, P.K.; Venkat Raj, V.
1990-01-01
Experiments have been carried out to test the suitability of drag-disc flowmeter for measuring two-phase flow. Calibration tests carried out under single-phase and two-phase flow conditions have confirmed the suitability of the drag-disc flowmeter. The experimental work and the results obtained are presented and discussed in the paper. (author). 3 refs., 6 figs
Numerical simulation and experimental verification of a flat two-phase thermosyphon
International Nuclear Information System (INIS)
Zhang Ming; Liu Zhongliang; Ma Guoyuan; Cheng Shuiyuan
2009-01-01
The flat two-phase thermosyphon is placed between the heat source and the heat sink, which can achieve the uniform heat flux distribution and improve the performance of heat sink. In this paper, a two-dimensional heat and mass transfer model for a disk-shaped flat two-phase thermosyphon is developed. By solving the equations of continuity, momentum and energy numerically, the vapor velocity and temperature distributions of the flat two-phase thermosyphon are obtained. An analysis is also carried out on the ability of flat two-phase thermosyphon to spread heat and remove hot spots. In order to observe boiling and condensation phenomena, a transparent flat two-phase thermosyphon is manufactured and studied experimentally. The experimental results are compared with numerical results, which verify the physical and mathematical model of the flat two-phase thermosyphon. In order to study the main factors affecting the axial thermal resistance of two-phase thermosyphon, the temperatures inside the flat two-phase thermosyphon are measured and analyzed
SNOW AVALANCHE ACTIVITY IN PARÂNG SKI AREA REVEALED BY TREE-RINGS
Directory of Open Access Journals (Sweden)
F. MESEȘAN
2014-11-01
Full Text Available Snow Avalanche Activity in Parâng Ski Area Revealed by Tree-Rings. Snow avalanches hold favorable conditions to manifest in Parâng Mountains but only one event is historically known, without destructive impact upon infrastructure or fatalities and this region wasn’t yet the object of avalanche research. The existing ski infrastructure of Parâng resort located in the west of Parâng Mountains is proposed to be extended in the steep slopes of subalpine area. Field evidence pinpoints that these steep slopes were affected by snow avalanches in the past. In this study we analyzed 11 stem discs and 31 increment cores extracted from 22 spruces (Picea abies (L. Karst impacted by avalanches, in order to obtain more information about past avalanches activity. Using the dendrogeomorphological approach we found 13 avalanche events that occurred along Scărița avalanche path, since 1935 until 2012, nine of them produced in the last 20 years. The tree-rings data inferred an intense snow avalanche activity along this avalanche path. This study not only calls for more research in the study area but also proves that snow avalanches could constitute an important restrictive factor for the tourism infrastructure and related activities in the area. It must be taken into consideration by the future extension of tourism infrastructure. Keywords: snow avalanche, Parâng Mountains, dendrogeomorphology, ski area.
Characterizing the nature and variability of avalanche hazard in western Canada
Shandro, Bret; Haegeli, Pascal
2018-04-01
The snow and avalanche climate types maritime, continental and transitional are well established and have been used extensively to characterize the general nature of avalanche hazard at a location, study inter-seasonal and large-scale spatial variabilities and provide context for the design of avalanche safety operations. While researchers and practitioners have an experience-based understanding of the avalanche hazard associated with the three climate types, no studies have described the hazard character of an avalanche climate in detail. Since the 2009/2010 winter, the consistent use of Statham et al. (2017) conceptual model of avalanche hazard in public avalanche bulletins in Canada has created a new quantitative record of avalanche hazard that offers novel opportunities for addressing this knowledge gap. We identified typical daily avalanche hazard situations using self-organizing maps (SOMs) and then calculated seasonal prevalence values of these situations. This approach produces a concise characterization that is conducive to statistical analyses, but still provides a comprehensive picture that is informative for avalanche risk management due to its link to avalanche problem types. Hazard situation prevalence values for individual seasons, elevations bands and forecast regions provide unprecedented insight into the inter-seasonal and spatial variability of avalanche hazard in western Canada.
The potential of cloud point system as a novel two-phase partitioning system for biotransformation.
Wang, Zhilong
2007-05-01
Although the extractive biotransformation in two-phase partitioning systems have been studied extensively, such as the water-organic solvent two-phase system, the aqueous two-phase system, the reverse micelle system, and the room temperature ionic liquid, etc., this has not yet resulted in a widespread industrial application. Based on the discussion of the main obstacles, an exploitation of a cloud point system, which has already been applied in a separation field known as a cloud point extraction, as a novel two-phase partitioning system for biotransformation, is reviewed by analysis of some topical examples. At the end of the review, the process control and downstream processing in the application of the novel two-phase partitioning system for biotransformation are also briefly discussed.
Operation of a forced two phase cooling system on a large superconducting magnet
International Nuclear Information System (INIS)
Green, M.A.; Burns, W.A.; Eberhard, P.H.; Gibson, G.H.; Pripstein, M.; Ross, R.R.; Smits, R.G.; Taylor, J.D.; Van Slyke, H.
1980-05-01
This paper describes the operation of a forced two phase cooling system on a two meter diameter superconducting solenoid. The magnet is a thin high current density superconducting solenoid which is cooled by forced two phase helium in tubes around the coil. The magnet, which is 2.18 meters in diameter and 3.4 meters long, has a cold mass of 1700 kg. The two phase cooling system contains less than 300 liters of liquid helium, most of which is contained in a control dewar. This paper describes the operating characteristics of the LBL two phase forced cooling system during cooldown and warm up. The paper presents experimental data on operations of the magnet using either a helium pump or the refrigerator compressor to circulate two phase helium through the superconducting coil cooling tubes
Two phase flow measurement and visualization using Wire Mesh Sensors (WMS)
International Nuclear Information System (INIS)
Rajalakshmi, R.; Robin, Roshini; Rama Rao, A.
2016-01-01
Two phase flow behavior studies have gained importance in nuclear power plants to enhance fuel performance and safety. In this paper, taking into consideration low cost, high space-time resolution and instantaneous mapping, electrical sensors such as wire mesh sensors (WMS) is proposed for measurement of void distribution and its visualization. The sensor works on the conductivity principle and by measuring the variations in conductivity values of the two phases, the flow distributions can be identified. This paper describes the conceptual design of the WMS for two phase void measurements, Mathematical modeling of the sensor for data evaluation, modeling of the sensor geometry and FEM simulation studies for optimizing sensor geometry and excitation parameters, CFD two phase flows simulations, development of suitable algorithm and programming for two phase visualization and void distribution studies, prototype sensor fabrication and testing
Phenomenological studies of two-phase flow processes for nuclear waste isolation
International Nuclear Information System (INIS)
Pruess, K.; Finsterle, S.; Persoff, P.; Oldenburg, C.
1994-01-01
The US civilian radioactive waste management program is unique in its focus on a site in the unsaturated zone, at Yucca Mountain, Nevada. Two-phase flow phenomena can also play an important role in repositories beneath the water table where gas is generated by corrosion, hydrolysis, and biological degradation of the waste packages. An integrated program has been initiated to enhance our understanding of two-phase flow behavior in fractured rock masses. The studies include two-phase (gas-liquid) flow experiments in laboratory specimens of natural rock fractures, analysis and modeling of heterogeneity and instability effects in two-phase flow, and design and interpretation of field experiments by means of numerical simulation. We present results that identify important aspects of two-phase flow behavior on different space and time scales which are relevant to nuclear waste disposal in both unsaturated and saturated formations
Argon-ion contamination of the plasmasphere
International Nuclear Information System (INIS)
Chiu, Y.T.; Cornwall, J.M.; Luhmann, J.G.; Schulz, M.
1979-01-01
This paper applies present observational and analytic knowledge on effects of plasma beam interaction wth the magnetosphere to the plasmasphere contamination problem of the argon ion engine exhaust expected to be deposited in the magnetosphere during the construction phase of the Satellite Power System. Effects of plasmasphere, ionosphere, and radiation belt modifications are discussed
Silicon compounds of neon and argon
Czech Academy of Sciences Publication Activity Database
Roithová, J.; Schröder, Detlef
-, č. 46 (2009), s. 8788-8790 ISSN 1433-7851 R&D Projects: GA ČR GA203/09/1223 Grant - others: ERC (XE) Adg HORIZOMS Institutional research plan: CEZ:AV0Z40550506 Keywords : argon * bond formation * dications * neon Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 11.829, year: 2009
Performance of a uranium liquid argon calorimeter
International Nuclear Information System (INIS)
Tuts, P.M.
1987-01-01
The author presents results on the performance of a uranium and liquid argon colorimeter in the NW test beam at Fermilab. This study describes the calorimeter, and discusses its performance with electrons, pions and muons from 10 GeV to 150 GeV. The performance parameters measure response, linearity, resolution, compensation, and e/π separation
SLD liquid argon calorimeter prototype test results
International Nuclear Information System (INIS)
Dubois, R.; Eigen, G.; Au, Y.
1985-10-01
The results of the SLD test beam program for the selection of a calorimeter radiator composition within a liquid argon system are described, with emphasis on the study of the use of uranium to obtain equalization of pion and electron responses
Commissioning of the ATLAS Liquid Argon Calorimeters
Cooke, Mark S
2009-01-01
A selection of ATLAS liquid argon (LAr) calorimeter commissioning studies are presented. These include a coherent noise study, a measurement of the quality of the physics pulse shape prediction, and energy and time reconstruction analyses with cosmic and single beam signals.
Thermal decomposition of barium valerate in argon
DEFF Research Database (Denmark)
Torres, P.; Norby, Poul; Grivel, Jean-Claude
2015-01-01
The thermal decomposition of barium valerate (Ba(C4H9CO2)(2)/Ba-pentanoate) was studied in argon by means of thermogravimetry, differential thermal analysis, IR-spectroscopy, X-ray diffraction and hot-stage optical microscopy. Melting takes place in two different steps, at 200 degrees C and 280...
46 CFR 151.50-36 - Argon or nitrogen.
2010-10-01
... 46 Shipping 5 2010-10-01 2010-10-01 false Argon or nitrogen. 151.50-36 Section 151.50-36 Shipping... BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-36 Argon or nitrogen. (a) A cargo tank that contains argon or nitrogen and that has a maximum allowable working pressure of 172 kPa (25...
Critical state transformation in hard superconductors resulting from thermomagnetic avalanches
International Nuclear Information System (INIS)
Chabanenko, V.V.; Kuchuk, E.I.; Rusakov, V.F.; Abaloszewa, I.; Nabialek, A.; Perez-Rodriguez, F.
2016-01-01
The results of experimental investigations of magnetic flux dynamics in finite superconductors, obtained using integral and local measurements methods, are presented. Local methods were aimed at clarifying the role of demagnetizing factor in dynamic formation of a complex magnetic structure of the critical state of hard superconductors. To understand the reasons for cardinal restructuring of the induction, we further analyzed the literature data of flux dynamics visualization during avalanches, obtained by magneto-optical methods. New features in the behavior of the magnetic flux during and after the avalanche were discovered. Two stages of the formation of the induction structures in the avalanche area were established, i.e. of homogeneous and heterogeneous filling with the magnetic flux. The mechanism of the inversion of the induction profile was considered. Oscillations in the speed of the front of the magnetic flux were revealed. Transformation of the critical state near the edge of the sample was analyzed. The role of thermal effects and of de-magnetizing factor in the dissipative flux dynamics was shown. Generalized information allowed, in the framework of the Bean concept, to present a model the transformation of the picture of the induction of the critical state and of the superconducting currents of a finite superconductor as a result of flux avalanches for two regimes - of screening and trapping of the magnetic flux.
Group Dynamics and Decision Making: Backcountry Recreationists in Avalanche Terrain
Bright, Leslie Shay
2010-01-01
The purpose of this study was to describe and determine the prevalence of decision-making characteristics of recreational backcountry groups when making a decision of where to travel and ride in avalanche terrain from the perspective of individuals. Decision-making characteristics encompassed communication, decision-making processes, leadership,…
heat flow in a finite isolated pulsed avalanche semiconductor diode
African Journals Online (AJOL)
ES Obe
1981-03-01
Mar 1, 1981 ... high-power high-efficiency avalanche semiconductor devices. The ... computed, and useful practical design curves for a specified operation .... iv. For spherical shells of radius, ρ(x,y,z) = √x2+y2+z2. > R, the heat source.
Current oscillations in avalanche particle detectors with PNIPN-structure
International Nuclear Information System (INIS)
Lukin, K.A.
1995-08-01
The model of an avalanche high energy particle detector consisting of two pn-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. This detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behaviour is pointed out
Hybrid phase transition into an absorbing state: Percolation and avalanches
Lee, Deokjae; Choi, S.; Stippinger, M.; Kertész, J.; Kahng, B.
2016-04-01
Interdependent networks are more fragile under random attacks than simplex networks, because interlayer dependencies lead to cascading failures and finally to a sudden collapse. This is a hybrid phase transition (HPT), meaning that at the transition point the order parameter has a jump but there are also critical phenomena related to it. Here we study these phenomena on the Erdős-Rényi and the two-dimensional interdependent networks and show that the hybrid percolation transition exhibits two kinds of critical behaviors: divergence of the fluctuations of the order parameter and power-law size distribution of finite avalanches at a transition point. At the transition point global or "infinite" avalanches occur, while the finite ones have a power law size distribution; thus the avalanche statistics also has the nature of a HPT. The exponent βm of the order parameter is 1 /2 under general conditions, while the value of the exponent γm characterizing the fluctuations of the order parameter depends on the system. The critical behavior of the finite avalanches can be described by another set of exponents, βa and γa. These two critical behaviors are coupled by a scaling law: 1 -βm=γa .
Positron camera with high-density avalanche chambers
International Nuclear Information System (INIS)
Manfrass, D.; Enghardt, W.; Fromm, W.D.; Wohlfarth, D.; Hennig, K.
1988-01-01
The results of an extensive investigation of the properties of high-density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC detectors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction. (author)
A high current, high speed pulser using avalanche transistors
International Nuclear Information System (INIS)
Hosono, Yoneichi; Hasegawa, Ken-ichi
1985-01-01
A high current, high speed pulser for the beam pulsing of a linear accelerator is described. It uses seven avalanche transistors in cascade. Design of a trigger circuit to obtain fast rise time is discussed. The characteristics of the pulser are : (a) Rise time = 0.9 ns (FWHM) and (d) Life time asymptotically equals 2000 -- 3000 hr (at 50 Hz). (author)
Snow avalanche hazard of the Krkonose National Park, Czech Republic
Czech Academy of Sciences Publication Activity Database
Blahůt, Jan; Klimeš, Jan; Balek, Jan; Hájek, P.; Červená, L.; Lysák, J.
2017-01-01
Roč. 13, č. 2 (2017), s. 86-90 ISSN 1744-5647 R&D Projects: GA MV VG20132015115 Institutional support: RVO:67985891 Keywords : snow avalanches * hazard * inventory * hazard mitigation * Krkonoše Subject RIV: DE - Earth Magnetism, Geodesy, Geography OBOR OECD: Physical geography Impact factor: 2.174, year: 2016
Optical fibers and avalanche photodiodes for scintillator counters
International Nuclear Information System (INIS)
Borenstein, S.R.; Palmer, R.B.; Strand, R.C.
1980-01-01
Fine hodoscopes can be made of new scintillating optical fibers and one half inch end-on PMT's. An avalanche photodiode with small size and immunity to magnetic fields remains as a tempting new device to be proven as a photodetector for the fibers
Rock avalanches clusters along the northern Chile coastal scarp
Crosta, G. B.; Hermanns, R. L.; Dehls, J.; Lari, S.; Sepulveda, S.
2017-07-01
Rock avalanche clusters can be relevant indicators of the evolution of specific regions. They can be used to define: the type and intensity of triggering events, their recurrence and potential probability of occurrence, the progressive damage of the rock mass, the mechanisms of transport and deposition, as well as the environmental conditions at the time of occurrence. This paper tackles these subjects by analyzing two main clusters of rock avalanches (each event between 0.6 and 30 Mm3), separated by few kilometers and located along the coastal scarp of Northern Chile, south of Iquique. It lies, hence, within a seismic area characterized by a long seismic gap that ended on April 1st, 2014 with a Mw 8.2 earthquake. The scar position, high along the coastal cliff, supports seismic triggering for these clusters. The deposits' relative positions are used to obtain the sequence of rock avalanching events for each cluster. The progressive decrease of volume in the sequence of rock avalanches forming each cluster fits well the theoretical models for successive slope failures. These sequences seem to agree with those derived by dating the deposits with ages spanning between 4 kyr and 60 kyr. An average uplift rate of 0.2 mm/yr in the last 40 kyr is estimated for the coastal plain giving a further constraint to the rock avalanche deposition considering the absence of reworking of the deposits. Volume estimates and datings allow the estimation of an erosion rate contribution of about 0.098-0.112 mm km- 2 yr- 1 which is well comparable to values presented in the literature for earthquake induced landslides. We have carried out numerical modeling in order to analyze the mobility of the rock avalanches and examine the environmental conditions that controlled the runout. In doing so, we have considered the sequence of individual rock avalanches within the specific clusters, thus including in the models the confining effect caused by the presence of previous deposits. Bingham
Fluid-elastic force measurements acting on a tube bundle in two-phase cross flow
International Nuclear Information System (INIS)
Inada, Fumio; Kawamura, Koji; Yasuo, Akira
1996-01-01
Fluid-elastic force acting on a square tube bundle of P/D = 1.47 in air-water two-phase cross flow was measured to investigate the characteristics and to clarify whether the fluid elastic vibration characteristics could be expressed using two-phase mixture characteristics. Measured fluid elastic forces were separated into fluid-elastic force coefficients such as added mass, added stiffness, and added damping coefficient. The added damping coefficient was separated into a two-phase damping and a flow-dependent component as in previous research (Carlucci, 1981 and 1983; Pettigrew, 1994). These coefficients were nondimensionalized with two-phase mixture characteristics such as void fraction, mixture density and mixture velocity, which were obtained using the drift-flux model with consideration given to the model. The result was compared with the result obtained with the homogeneous model. It was found that fluid-elastic force coefficients could be expressed with two-phase flow mixture characteristics very well in the experimental result, and that better result can be derived using the slip model as compared to the homogeneous model. Added two-phase flow, which could be expressed as a function of void fraction, where two-phase damping was nondimensionalized with the relative velocity between the gas and liquid phases used as a reference velocity. Using these, the added stiffness coefficient and flow-dependent component of damping could be expressed very well as a function of nondimensional mixture velocity
Two-phase aqueous micellar systems: an alternative method for protein purification
Directory of Open Access Journals (Sweden)
Rangel-Yagui C. O.
2004-01-01
Full Text Available Two-phase aqueous micellar systems can be exploited in separation science for the extraction/purification of desired biomolecules. This article reviews recent experimental and theoretical work by Blankschtein and co-workers on the use of two-phase aqueous micellar systems for the separation of hydrophilic proteins. The experimental partitioning behavior of the enzyme glucose-6-phosphate dehydrogenase (G6PD in two-phase aqueous micellar systems is also reviewed and new results are presented. Specifically, we discuss very recent work on the purification of G6PD using: i a two-phase aqueous micellar system composed of the nonionic surfactant n-decyl tetra(ethylene oxide (C10E4, and (ii a two-phase aqueous mixed micellar system composed of C10E4 and the cationic surfactant decyltrimethylammonium bromide (C10TAB. Our results indicate that the two-phase aqueous mixed (C10E4/C10TAB micellar system can improve significantly the partitioning behavior of G6PD relative to that observed in the two-phase aqueous C10E4 micellar system.
Pressure distribution over tube surfaces of tube bundle subjected to two phase cross flow
International Nuclear Information System (INIS)
Sim, Woo Gun
2013-01-01
Two phase vapor liquid flows exist in many shell and tube heat exchangers such as condensers, evaporators and nuclear steam generators. To understand the fluid dynamic forces acting on a structure subjected to a two phase flow, it is essential to obtain detailed information about the characteristics of a two phase flow. The characteristics of a two phase flow and the flow parameters were introduced, and then, an experiment was performed to evaluate the pressure loss in the tube bundles and the fluid dynamic force acting on the cylinder owing to the pressure distribution. A two phase flow was pre mixed at the entrance of the test section, and the experiments were undertaken using a normal triangular array of cylinders subjected to a two phase cross flow. The pressure loss along the flow direction in the tube bundles was measured to calculate the two phase friction multiplier, and the multiplier was compared with the analytical value. Furthermore, the circular distributions of the pressure on the cylinders were measured. Based on the distribution and the fundamental theory of two phase flow, the effects of the void fraction and mass flux per unit area on the pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure on the tube by a numerical method. It was found that for low mass fluxes, the measured two phase friction multipliers agree well with the analytical results, and good agreement for the effect of the void fraction on the drag coefficients, as calculated by the measured pressure distributions, is shown qualitatively, as compared to the existing experimental results
Preferential site occupancy observed in coexpanded argon-krypton clusters
International Nuclear Information System (INIS)
Lundwall, M.; Bergersen, H.; Lindblad, A.; Oehrwall, G.; Svensson, S.; Bjoerneholm, O.; Tchaplyguine, M.
2006-01-01
Free heterogeneous argon-krypton clusters have been produced by coexpansion and investigated by means of x-ray photoelectron spectroscopy. By examining cluster surface and bulk binding energy shifts, relative intensities, and peak widths, we show that in the mixed argon-krypton clusters the krypton atoms favor the bulk and argon atoms are pushed to the surface. Furthermore, we show that krypton atoms in the surface layer occupy high-coordination sites and that heterogeneous argon-krypton clusters produced by coexpansion show the same surface structure as argon host clusters doped with krypton. These observations are supported by site-dependent calculations of chemical shifts
The development of structures in analogue and natural debris avalanches
Paguican, Engielle Mae; van Wyk de Vries, Benjamin; Mahar Francisco Lagmay, Alfredo; Grosse, Pablo
2010-05-01
All types of rockslide-debris avalanches present a plethora of internal structures that are also well observed on the surface. Many of these are seen as faults and folds that can be used to determine deformation history and kinematics. We present two sets of simple and well-constrained experiments of reduced basal friction laboratory rockslides, equivalent to a highly deformed simple shear layer, with plug-flow. These follow the original ramp-slide work of Shea and van Wyk de Vries (Geosphere, 2008). The experiments used a curved ramp where materials accelerate until reaching a gently-sloped depositional surface and a constantly inclined ramp with a more regular slope and longer slides. A detailed description of deposit structures, their sequential formation and morphology is then used to investigate the transport type and deformation chronology from slide initiation to runout stopping of avalanches. Results using a curved ramp show accumulation and thickening at where the slope decreases. The thickened mass then further remobilises and advances by secondary collapse of the mass. Such a stop-start process may be important in many mountainous avalanches where there are rapid changes in slope. The constantly inclined ramp shows shearing and extensional structures at the levees and a set of compression and extension structures in the middle. We noted that frontal accumulation during flow occurs as materials at the front move slower relative to those in the medial and proximal zones. This also leads to secondary frontal collapse, and helps to maintain a thicker mass that can flow further. Descriptions and analyses of these structures are then applied to the kinematics and dynamics of natural examples. We study the 2006 Guinsaugon Rockslide event in the Philippines and find that frontal accumulation and secondary avalanching had also occurred and were important in determining the distribution and runout of the mass. Frontal bulking and collapse may also have occurred at
Summary on experimental methods for statistical transient analysis of two-phase gas-liquid flow
International Nuclear Information System (INIS)
Delhaye, J.M.; Jones, O.C. Jr.
1976-06-01
Much work has been done in the study of two-phase gas-liquid flows. Although it has been recognized superficially that such flows are not homogeneous in general, little attention has been paid to the inherent discreteness of the two-phase systems. Only relatively recently have fluctuating characteristics of two-phase flows been studied in detail. As a result, new experimental devices and techniques have been developed for use in measuring quantities previously ignored. This report reviews and summarizes most of these methods in an effort to emphasize the importance of the fluctuating nature of these flows and as a guide to further research in this field
Two-phase flow and cross-mixing measurements in a rod bundle
International Nuclear Information System (INIS)
Yloenen, A.; Prasser, H.-M.
2011-01-01
The wire-mesh sensor technique has been used for the first time to study two-phase flow and liquid mixing in a rod bundle. A dedicated test facility (SUBFLOW) was constructed at Paul Scherrer Institut (PSI) in a co-operation with the Swiss Federal Institute of Technology (ETH Zurich). Simultaneous injection of salt water as tracer and air bubbles can be used to quantify the enhancement of liquid mixing in two-phase flow when the results are compared with the single-phase mixing experiment with the same test parameters. The second aspect in the current experiments is the two-phase flow in bundle geometry. (author)
A study of water hammer phenomena in a one-component two-phase bubbly flow
International Nuclear Information System (INIS)
Fujii, Terushige; Akagawa, Koji
2000-01-01
Water hammer phenomena caused by a rapid valve closure, that is, shock phenomena in two-phase flows, are an important problem for the safety assessment of a hypothetical LOCA. This paper presents the results of experimental and analytical studies of the water hammer phenomena in a one-component tow-phase bubbly flow. In order to clarify the characteristics of water hammer phenomena, experiments for a one-component two-phase flow of Freon R-113 were conducted and a numerical simulation of pressure transients was developed. An overall picture of the water hammer phenomena in a one-component two-phase flow is presented an discussed. (author)
Two-phase flow measurements with advanced instrumented spool pieces and local conductivity probes
International Nuclear Information System (INIS)
Turnage, K.G.; Davis, C.E.
1979-01-01
A series of two-phase, air-water and steam-water tests performed with instrumented spool pieces and with conductivity probes obtained from Atomic Energy of Canada, Ltd. is described. The behavior of the three-beam densitometer, turbine meter, and drag flowmeter is discussed in terms of two-phase models. Application of some two-phase mass flow models to the recorded spool piece data is made and preliminary results are shown. Velocity and void fraction information derived from the conductivity probes is presented and compared to velocities and void fractions obtained using the spool piece instrumentation
Dealing with the white death: avalanche risk management for traffic routes.
Rheinberger, Christoph M; Bründl, Michael; Rhyner, Jakob
2009-01-01
This article discusses mitigation strategies to protect traffic routes from snow avalanches. Up to now, mitigation of snow avalanches on many roads and railways in the Alps has relied on avalanche sheds, which require large initial investments resulting in high opportunity costs. Therefore, avalanche risk managers have increasingly adopted organizational mitigation measures such as warning systems and closure policies instead. The effectiveness of these measures is, however, greatly dependent on human decisions. In this article, we present a method for optimizing avalanche mitigation for traffic routes in terms of both their risk reduction impact and their net benefit to society. First, we introduce a generic framework for assessing avalanche risk and for quantifying the impact of mitigation. This allows for sound cost-benefit comparisons between alternative mitigation strategies. Second, we illustrate the framework with a case study from Switzerland. Our findings suggest that site-specific characteristics of avalanche paths, as well as the economic importance of a traffic route, are decisive for the choice of optimal mitigation strategies. On routes endangered by few avalanche paths with frequent avalanche occurrences, structural measures are most efficient, whereas reliance on organizational mitigation is often the most appropriate strategy on routes endangered by many paths with infrequent or fuzzy avalanche risk. Finally, keeping a traffic route open may be very important for tourism or the transport industry. Hence, local economic value may promote the use of a hybrid strategy that combines organizational and structural measures to optimize the resource allocation of avalanche risk mitigation.
International Nuclear Information System (INIS)
Baksht, E Kh; Lomaev, Mikhail I; Rybka, D V; Tarasenko, Viktor F
2006-01-01
The emission properties of a volume nanosecond discharge plasma produced in xenon, krypton and argon at high pressures in a discharge gap with a cathode having a small radius of curvature are studied. Spectra in the range 120-850 nm and amplitude-time characteristics of xenon emission at different regimes and excitation techniques are recorded and analysed. It is shown that upon excitation of the volume discharge initiated by a beam of avalanche electrons, at least 90% of the energy in the spectral range 120-850 nm is emitted by xenon dimers. For xenon at a pressure of 1.2 atm, ∼45 mJ of the spontaneous emission energy was obtained in the full solid angle in a pulse with the full width at half-maximum ∼130 ns. (laser applications and other topics in quantum electronics)
Automated identification of potential snow avalanche release areas based on digital elevation models
Bühler, Y.; Kumar, S.; Veitinger, J.; Christen, M.; Stoffel, A.; Snehmani
2013-05-01
The identification of snow avalanche release areas is a very difficult task. The release mechanism of snow avalanches depends on many different terrain, meteorological, snowpack and triggering parameters and their interactions, which are very difficult to assess. In many alpine regions such as the Indian Himalaya, nearly no information on avalanche release areas exists mainly due to the very rough and poorly accessible terrain, the vast size of the region and the lack of avalanche records. However avalanche release information is urgently required for numerical simulation of avalanche events to plan mitigation measures, for hazard mapping and to secure important roads. The Rohtang tunnel access road near Manali, Himachal Pradesh, India, is such an example. By far the most reliable way to identify avalanche release areas is using historic avalanche records and field investigations accomplished by avalanche experts in the formation zones. But both methods are not feasible for this area due to the rough terrain, its vast extent and lack of time. Therefore, we develop an operational, easy-to-use automated potential release area (PRA) detection tool in Python/ArcGIS which uses high spatial resolution digital elevation models (DEMs) and forest cover information derived from airborne remote sensing instruments as input. Such instruments can acquire spatially continuous data even over inaccessible terrain and cover large areas. We validate our tool using a database of historic avalanches acquired over 56 yr in the neighborhood of Davos, Switzerland, and apply this method for the avalanche tracks along the Rohtang tunnel access road. This tool, used by avalanche experts, delivers valuable input to identify focus areas for more-detailed investigations on avalanche release areas in remote regions such as the Indian Himalaya and is a precondition for large-scale avalanche hazard mapping.
Automated identification of potential snow avalanche release areas based on digital elevation models
Directory of Open Access Journals (Sweden)
Y. Bühler
2013-05-01
Full Text Available The identification of snow avalanche release areas is a very difficult task. The release mechanism of snow avalanches depends on many different terrain, meteorological, snowpack and triggering parameters and their interactions, which are very difficult to assess. In many alpine regions such as the Indian Himalaya, nearly no information on avalanche release areas exists mainly due to the very rough and poorly accessible terrain, the vast size of the region and the lack of avalanche records. However avalanche release information is urgently required for numerical simulation of avalanche events to plan mitigation measures, for hazard mapping and to secure important roads. The Rohtang tunnel access road near Manali, Himachal Pradesh, India, is such an example. By far the most reliable way to identify avalanche release areas is using historic avalanche records and field investigations accomplished by avalanche experts in the formation zones. But both methods are not feasible for this area due to the rough terrain, its vast extent and lack of time. Therefore, we develop an operational, easy-to-use automated potential release area (PRA detection tool in Python/ArcGIS which uses high spatial resolution digital elevation models (DEMs and forest cover information derived from airborne remote sensing instruments as input. Such instruments can acquire spatially continuous data even over inaccessible terrain and cover large areas. We validate our tool using a database of historic avalanches acquired over 56 yr in the neighborhood of Davos, Switzerland, and apply this method for the avalanche tracks along the Rohtang tunnel access road. This tool, used by avalanche experts, delivers valuable input to identify focus areas for more-detailed investigations on avalanche release areas in remote regions such as the Indian Himalaya and is a precondition for large-scale avalanche hazard mapping.
Turchaninova, A.
2012-04-01
The estimation of extreme avalanche runout distances, flow velocities, impact pressures and volumes is an essential part of snow engineering in mountain regions of Russia. It implies the avalanche hazard assessment and mapping. Russian guidelines accept the application of different avalanche models as well as approaches for the estimation of model input parameters. Consequently different teams of engineers in Russia apply various dynamics and statistical models for engineering practice. However it gives more freedom to avalanche practitioners and experts but causes lots of uncertainties in case of serious limitations of avalanche models. We discuss these problems by presenting the application results of different well known and widely used statistical (developed in Russia) and avalanche dynamics models for several avalanche test sites in the Khibini Mountains (The Kola Peninsula) and the Caucasus. The most accurate and well-documented data from different powder and wet, big rare and small frequent snow avalanche events is collected from 1960th till today in the Khibini Mountains by the Avalanche Safety Center of "Apatit". This data was digitized and is available for use and analysis. Then the detailed digital avalanche database (GIS) was created for the first time. It contains contours of observed avalanches (ESRI shapes, more than 50 years of observations), DEMs, remote sensing data, description of snow pits, photos etc. Thus, the Russian avalanche data is a unique source of information for understanding of an avalanche flow rheology and the future development and calibration of the avalanche dynamics models. GIS database was used to analyze model input parameters and to calibrate and verify avalanche models. Regarding extreme dynamic parameters the outputs using different models can differ significantly. This is unacceptable for the engineering purposes in case of the absence of the well-defined guidelines in Russia. The frequency curves for the runout distance
ATLAS Liquid Argon Calorimeter Module Zero
1993-01-01
This module was built and tested with beam to validate the ATLAS electromagnetic calorimeter design. One original design feature is the folding. 10 000 lead plates and electrodes are folded into an accordion shape and immersed in liquid argon. As they cross the folds, particles are slowed down by the lead. As they collide with the lead atoms, electrons and photons are ejected. There is a knock-on effect and as they continue on into the argon, a whole shower is produced. The electrodes collect up all the electrons and this signal gives a measurement of the energy of the initial particle. The M0 was fabricated by French institutes (LAL, LAPP, Saclay, Jussieu) in the years 1993-1994. It was tested in the H6/H8 beam lines in 1994, leading to the Technical Design Report in 1996.
Diffusion of lithium ions in argon
International Nuclear Information System (INIS)
Stefansson, T.
1983-01-01
Published measurements of transport coefficients for Li + ions in argon seem to be limited to the mobility and the longitudinal diffusion coefficient in the field-to-density ratio range at and below 200 Td 1-5 . In this paper results are presented from measurements of the transverse diffusion coefficient to mobility ratio (Dsub(T)/μ) for Li + ions in argon in the field-to-density ratio range 10 < E/n < 800 Td. The measurements were made with a drift tube mass spectrometer at a gas temperature of 295 +- 1 K using the modified Townsend method of Skullerud. The experimental curve is compared to a calculation by H.R. Skullerud in the same proceedings. (G.Q.)
Argon laser irradiation of the otolithic organ
Energy Technology Data Exchange (ETDEWEB)
Okuno, T.; Nomura, Y.; Young, Y.H.; Hara, M. (Univ. of Tokyo (Japan))
1990-12-01
An argon laser was used to irradiate the otolithic organs of guinea pigs and cynomolgus monkeys. After stapedectomy, the argon laser (1.5 W x 0.5 sec/shot) irradiated the utricle or saccule without touching the sensory organs. The stapes was replaced over the oval window after irradiation. The animals used for acute observation were killed immediately for morphologic studies; those used for long-term observation were kept alive for 2, 4, or 10 weeks. Acute observation revealed that sensory and supporting cells were elevated from the basement membrane only in the irradiated area. No rupture of the membranous labyrinth was observed. Long-term observation revealed that the otolith of the macula utriculi had disappeared in 2-week specimens. The entire macula utricili had disappeared in 10-week specimens. No morphologic changes were observed in cochlea, semicircular canals, or membranous labyrinth. The saccule showed similar changes.
International Nuclear Information System (INIS)
Sauter, H.; Meyder, R.; Philipp, P.; Samstag, M.
1995-01-01
The NOVA program was continued with turbulent, vertical, upward two-phase flow experiments. The development of a local gas distribution along the test section was visualized by X-ray tomography. (orig.)
Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary
2014-06-10
A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.
Ross, Michelle; Wakefield, Jon
2015-10-01
Two-phase study designs are appealing since they allow for the oversampling of rare sub-populations which improves efficiency. In this paper we describe a Bayesian hierarchical model for the analysis of two-phase data. Such a model is particularly appealing in a spatial setting in which random effects are introduced to model between-area variability. In such a situation, one may be interested in estimating regression coefficients or, in the context of small area estimation, in reconstructing the population totals by strata. The efficiency gains of the two-phase sampling scheme are compared to standard approaches using 2011 birth data from the research triangle area of North Carolina. We show that the proposed method can overcome small sample difficulties and improve on existing techniques. We conclude that the two-phase design is an attractive approach for small area estimation.
Non-local two phase flow momentum transport in S BWR
International Nuclear Information System (INIS)
Espinosa P, G.; Salinas M, L.; Vazquez R, A.
2015-09-01
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Reversible, on-demand generation of aqueous two-phase microdroplets
Collier, Charles Patrick; Retterer, Scott Thomas; Boreyko, Jonathan Barton; Mruetusatorn, Prachya
2017-08-15
The present invention provides methods of on-demand, reversible generation of aqueous two-phase microdroplets core-shell microbeads, microparticle preparations comprising the core-shell microbeads, and drug delivery formulation comprising the microparticle preparations. Because these aqueous microdroplets have volumes comparable to those of cells, they provide an approach to mimicking the dynamic microcompartmentation of biomaterial that naturally occurs within the cytoplasm of cells. Hence, the present methods generate femtoliter aqueous two-phase droplets within a microfluidic oil channel using gated pressure pulses to generate individual, stationary two-phase microdroplets with a well-defined time zero for carrying out controlled and sequential phase transformations over time. Reversible phase transitions between single-phase, two-phase, and core-shell microbead states are obtained via evaporation-induced dehydration and water rehydration.
Prediction of two-phase choked-flow through safety valves
International Nuclear Information System (INIS)
Arnulfo, G; Bertani, C; De Salve, M
2014-01-01
Different models of two-phase choked flow through safety valves are applied in order to evaluate their capabilities of prediction in different thermal-hydraulic conditions. Experimental data available in the literature for two-phase fluid and subcooled liquid upstream the safety valve have been compared with the models predictions. Both flashing flows and non-flashing flows of liquid and incondensable gases have been considered. The present paper shows that for flashing flows good predictions are obtained by using the two-phase valve discharge coefficient defined by Lenzing and multiplying it by the critical flow rate in an ideal nozzle evaluated by either Omega Method or the Homogeneous Non-equilibrium Direct Integration. In case of non-flashing flows of water and air, Leung/Darby formulation of the two-phase valve discharge coefficient together with the Omega Method is more suitable to the prediction of flow rate.
Single and two-phase flow pressure drop for CANFLEX bundle
Energy Technology Data Exchange (ETDEWEB)
Park, Joo Hwan; Jun, Ji Su; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G R; Bullock, D E [Atomic Energy of Canada Limited, Ontario (Canada)
1999-12-31
Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-134a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLEX bundle is found to be about 20% higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within {+-} 5% error. 11 refs., 5 figs. (Author)
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries
Dong, S.; Wang, X.
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries. PMID:27163909
Identification of two-phase flow regimes by time-series modeling
International Nuclear Information System (INIS)
King, C.H.; Ouyang, M.S.; Pei, B.S.
1987-01-01
The identification of two-phase flow patterns in pipes or ducts is important to the design and operation of thermal-hydraulic systems, especially in the nuclear reactor cores of boiling water reactors or in the steam generators of pressurized water reactors. Basically, two-phase flow shows some fluctuating characteristics even at steady-state conditions. These fluctuating characteristics can be analyzed by statistical methods for obtaining flow signatures. There have been a number of experimental studies conducted that are concerned with the statistical properties of void fraction or pressure pulsation in two-phase flow. In this study, the authors propose a new technique of identifying the patterns of air-water two-phase flow in a vertical pipe. This technique is based on analyzing the statistic characteristics of the pressure signals of the test loop by time-series modeling
A New Appraoch to Modeling Immiscible Two-phase Flow in Porous Media
DEFF Research Database (Denmark)
Yuan, Hao; Shapiro, Alexander; Stenby, Erling Halfdan
In this work we present a systematic literature review regarding the macroscopic approaches to modeling immiscible two-phase flow in porous media, the formulation process of the incorporate PDE based on Film Model(viscous coupling), the calculation of saturation profile around the transition zone...... to modeling immiscible two-phase flow in porous media. The suggested approach to immiscible two-phase flow in porous media describes the dispersed mesoscopic fluids’ interfaces which are highly influenced by the injected interfacial energy and the local interfacial energy capacity. It reveals a new...... possibility of modeling two-phase flow through energy balance. The saturation profile generated through the suggested approach is different from those through other approaches....
Development of One Dimensional Hyperbolic Coupled Solver for Two-Phase Flows
International Nuclear Information System (INIS)
Kim, Eoi Jin; Kim, Jong Tae; Jeong, Jae June
2008-08-01
The purpose of this study is a code development for one dimensional two-phase two-fluid flows. In this study, the computations of two-phase flow were performed by using the Roe scheme which is one of the upwind schemes. The upwind scheme is widely used in the computational fluid dynamics because it can capture discontinuities clearly such as a shock. And this scheme is applicable to multi-phase flows by the extension methods which were developed by Toumi, Stadtke, etc. In this study, the extended Roe upwind scheme by Toumi for two-phase flow was implemented in the one-dimensional code. The scheme was applied to a shock tube problem and a water faucet problem. This numerical method seems efficient for non oscillating solutions of two phase flow problems, and also capable for capturing discontinuities
Development of One Dimensional Hyperbolic Coupled Solver for Two-Phase Flows
Energy Technology Data Exchange (ETDEWEB)
Kim, Eoi Jin; Kim, Jong Tae; Jeong, Jae June
2008-08-15
The purpose of this study is a code development for one dimensional two-phase two-fluid flows. In this study, the computations of two-phase flow were performed by using the Roe scheme which is one of the upwind schemes. The upwind scheme is widely used in the computational fluid dynamics because it can capture discontinuities clearly such as a shock. And this scheme is applicable to multi-phase flows by the extension methods which were developed by Toumi, Stadtke, etc. In this study, the extended Roe upwind scheme by Toumi for two-phase flow was implemented in the one-dimensional code. The scheme was applied to a shock tube problem and a water faucet problem. This numerical method seems efficient for non oscillating solutions of two phase flow problems, and also capable for capturing discontinuities.
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
International Nuclear Information System (INIS)
Wu, Hao; Dong, Feng
2014-01-01
Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model
Development of an Enhanced Two-Phase Production System at the Geysers Geothermal Field; FINAL
International Nuclear Information System (INIS)
Steven Enedy
2001-01-01
A method was developed to enhance geothermal steam production from two-phase wells at THE Geysers Geothermal Field. The beneficial result was increased geothermal production that was easily and economically delivered to the power plant
A Variational Model for Two-Phase Immiscible Electroosmotic Flow at Solid Surfaces
Shao, Sihong; Qian, Tiezheng
2012-01-01
We develop a continuum hydrodynamic model for two-phase immiscible flows that involve electroosmotic effect in an electrolyte and moving contact line at solid surfaces. The model is derived through a variational approach based on the Onsager
Single and two-phase flow pressure drop for CANFLEX bundle
Energy Technology Data Exchange (ETDEWEB)
Park, Joo Hwan; Jun, Ji Su; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G. R.; Bullock, D. E. [Atomic Energy of Canada Limited, Ontario (Canada)
1998-12-31
Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-134a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLEX bundle is found to be about 20% higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within {+-} 5% error. 11 refs., 5 figs. (Author)
Non-local two phase flow momentum transport in S BWR
Energy Technology Data Exchange (ETDEWEB)
Espinosa P, G.; Salinas M, L.; Vazquez R, A., E-mail: gepe@xanum.uam.mx [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Apdo. Postal 55-535, 09340 Ciudad de Mexico (Mexico)
2015-09-15
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Two-phase flow boiling in small channels: A brief review
Indian Academy of Sciences (India)
fer coefficients, reduced inventory requirements, low capital cost etc. ... lot of work has been done to understand the fundamental aspects of two-phase flow and ... occurrence would facilitate optimal and safe operation of the involved systems.
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Energy Technology Data Exchange (ETDEWEB)
Staedtke, H.; Franchello, G.; Worth, B. [Joint Research Centre - Ispra Establishment (Italy)
1995-09-01
This paper describes a new approach to the numerical simulation of transient, multidimensional two-phase flow. The development is based on a fully hyperbolic two-fluid model of two-phase flow using separated conservation equations for the two phases. Features of the new model include the existence of real eigenvalues, and a complete set of independent eigenvectors which can be expressed algebraically in terms of the major dependent flow parameters. This facilitates the application of numerical techniques specifically developed for high speed single-phase gas flows which combine signal propagation along characteristic lines with the conservation property with respect to mass, momentum and energy. Advantages of the new model for the numerical simulation of one- and two- dimensional two-phase flow are discussed.
A new treatment of capillarity to improve the stability of IMPES two-phase flow formulation
Kou, Jisheng; Sun, Shuyu
2010-01-01
In this paper, we present an efficient numerical method for two-phase immiscible flow in porous media with different capillarity pressures. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressure
Experimental and analytical study of two-phase pressure drops during evaporation in horizontal tubes
Moreno Quibén, Jesús; Thome, John Richard
2007-01-01
Two-phase flow of gases and liquids or vapors and liquids in pipes, channels, equipment, etc. is frequently encountered in industry and has been studied intensively for many years. The reliable prediction of pressure drop in two-phase flow is thereby an important aim. Because of the complexity of these types of flow, empirical or semiempirical relationships are only of limited reliability and pressure drops predicted using leading methods may differ by up to 100%. In order to improve predicti...
Personal view of educating two-phase flow and human resource development as a nuclear engineer
International Nuclear Information System (INIS)
Hotta, Akitoshi
2010-01-01
As an engineer who has devoted himself in the nuclear industry for almost three decades, the author gave a personal view on educating two-phase flow and developing human resources. An expected role of universities in on-going discussions of collaboration among industry-government-academia is introduced. Reformation of two-phase flow education is discussed from two extreme viewpoints, the basic structure of physics and the practical system analysis. (author)
Experimental investigation on passive heat transfer by long closed two-phase thermosiphons
Energy Technology Data Exchange (ETDEWEB)
Grass, Claudia; Kulenovic, Rudi; Starflinger, Joerg [Stuttgart Univ. (Germany). Inst. fuer Kernenergetik und Energiesysteme (IKE)
2017-07-15
The removal of decay heat from spent fuel pools is presently realized by active cooling systems. In case of a station black out, a passive heat removal based on closed two-phase thermosiphons can contribute to the power plant safety. In this paper, the basic laboratory setup for closed two-phase thermosiphons and first experimental results are presented. Depending on the driving temperature difference and the heat input, steady-state and pulsating operation of the thermosiphons are investigated.
Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code
International Nuclear Information System (INIS)
Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.
1992-01-01
FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime
Water property lookup table (sanwat) for use with the two-phase computational code shaft
International Nuclear Information System (INIS)
Sherman, M.P.; Eaton, R.R.
1980-10-01
A lookup table for water thermodynamic and transport properties (SANWAT) has been constructed for use with the two-phase computational code, SHAFT. The table, which uses density and specific internal energy as independent variables, covers the liquid, two-phase, and vapor regions. The liquid properties of water are contained in a separate subtable in order to obtain high accuracy for this nearly incompressible region that is frequently encountered in studies of the characteristics of nuclear-waste repositories
Treatment technologies of liquid and solid wastes from two-phase olive oil mills
Borja Padilla, Rafael; Raposo Bejines, Francisco; Rincón, Bárbara
2006-01-01
Over the last 10 years the manufacture of olive oil has undergone important evolutionary changes in the equipment used for the separation of olive oil from the remaining components. The latest development has been the introduction of a two-phase centrifugation process in which a horizontally-mounted centrifuge is used for a primary separation of the olive oil fraction from the vegetable solid material and vegetation water. Therefore, the new two-phase olive oil mills produce three ident...
Treatment technologies of liquid and solid wastes from two-phase olive oil mills
Rincón, Bárbara; Raposo, Francisco; Borja, Rafael
2006-01-01
Over the last 10 years the manufacture of olive oil has undergone important evolutionary changes in the equipment used for the separation of olive oil from the remaining components. The latest development has been the introduction of a two-phase centrifugation process in which a horizontally-mounted centrifuge is used for a primary separation of the olive oil fraction from the vegetable solid material and vegetation water. Therefore, the new two-phase olive oil mills produce three identifiabl...
Bioconversion of apigenin-7-O-β-glucoside in aqueous two-phase system
Directory of Open Access Journals (Sweden)
Ilić Sanja M.
2005-01-01
Full Text Available The study is concerned with the conversion of apigenin-7-O-β-glucoside into apigenin in polyethylene glycol 6000 / dextran 20000 aqueous two-phase system by β-glucosidase. Apigenin was separated from apigenin-7-O-β-glucoside and β-glucosidase by their partition into opposite phases. In 14% PEG / 22.5% DEX aqueous two-phase system obtained yield of apigenin in top phase was 108%.
Estimation of the sugar cane cultivated area from LANDSAT images using the two phase sampling method
Parada, N. D. J. (Principal Investigator); Cappelletti, C. A.; Mendonca, F. J.; Lee, D. C. L.; Shimabukuro, Y. E.
1982-01-01
A two phase sampling method and the optimal sampling segment dimensions for the estimation of sugar cane cultivated area were developed. This technique employs visual interpretations of LANDSAT images and panchromatic aerial photographs considered as the ground truth. The estimates, as a mean value of 100 simulated samples, represent 99.3% of the true value with a CV of approximately 1%; the relative efficiency of the two phase design was 157% when compared with a one phase aerial photographs sample.
Determination of drift-flux velocity as a function of two-phase flow patterns
International Nuclear Information System (INIS)
Austregesilo Filho, H.
1986-01-01
A method is suggested for the calculation of drift-flux velocity as a function of two-phase flow patterns determined analytically. This model can be introduced in computer codes for thermal hydraulic analyses based mainly on homogeneous assumptions, in order to achieve a more realis tic description of two-phase flow phenomena, which is needed for the simulation of accidents in nuclear power plants for which phase separation effects are dominant, e.g., small break accidents. (Author) [pt
Coe, Jeffrey A.; Baum, Rex L.; Allstadt, Kate E.; Kochevar, Bernard; Schmitt, Robert G.; Morgan, Matthew L.; White, Jonathan L.; Stratton, Benjamin T.; Hayashi, Timothy A.; Kean, Jason W.
2016-01-01
On 25 May 2014, a rain-on-snow–induced rock avalanche occurred in the West Salt Creek valley on the northern flank of Grand Mesa in western Colorado (United States). The avalanche mobilized from a preexisting rock slide in the Green River Formation and traveled 4.6 km down the confined valley, killing three people. The avalanche was rare for the contiguous United States because of its large size (54.5 Mm3) and high mobility (height/length = 0.14). To understand the avalanche failure sequence, mechanisms, and mobility, we conducted a forensic analysis using large-scale (1:1000) structural mapping and seismic data. We used high-resolution, unmanned aircraft system imagery as a base for field mapping, and analyzed seismic data from 22 broadband stations (distances earth and tracked these forces using curves in the avalanche path. Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure. The sequence began with an early morning landslide/debris flow that started ∼10 h before the main avalanche. The main avalanche lasted ∼3.5 min and traveled at average velocities ranging from 15 to 36 m/s. For at least two hours after the avalanche ceased movement, a central, hummock-rich core continued to move slowly. Since 25 May 2014, numerous shallow landslides, rock slides, and rock falls have created new structures and modified avalanche topography. Mobility of the main avalanche and central core was likely enhanced by valley floor material that liquefied from undrained loading by the overriding avalanche. Although the base was likely at least partially liquefied, our mapping indicates that the overriding avalanche internally deformed predominantly by sliding along discrete shear surfaces in material that was nearly dry and had substantial frictional strength. These results indicate that the West Salt Creek avalanche, and probably other long-traveled avalanches, could be modeled as two layers: a thin, liquefied
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe.
Park, Yu Sun; Chang, Soon Heung
2011-04-04
A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.
Numerical study for two phase flow in the near nozzle region of turbine combustors
International Nuclear Information System (INIS)
Pervez, K.; Mushtaq, S.
1999-01-01
In the present study flow conditions in the near nozzle region of the combustion chamber have been investigated. There exists two-phase flow in this region. The overall performance and pollutant formation in the combustion chamber have been investigated. There exists two-phase flow in this region. The overall performance and pollutant formation in the combustion zone largely depends on the spray field in the near nozzle region the studies are conducted to determined the effects of multi jets on the flow pattern in the near nozzle region The phase doppler particle analyzer (PDPA) has been used to measure the velocities and sizes of the droplets. The flow field of two-phase liquid drop-air jets is formed from three injectors arranged in t line. Furthermore the two-phase flow field has been analyzed numerically also. The numerical analysis consists of two computational models, namely (i) 3 non-evaporating two-phase jets, (II) 3 evaporating two phase jets. The Eulerian-Eulerian approach in incorporated in both the numerical models. Since the flow is turbulent, a two-equation model (k-Epsilon) is implemented in the numerical analysis. Numerical solution of the conservation equation is obtained using PHOENICS computer code. Boundary conditions are provided from the experimental measurements. Numerical domain for the two models of the analysis starts at some distance (about 10 diameters of the injector orifice) where the atomization process is complete and droplet size and velocity could be measured experimentally. (author)
Application of non-equilibrium thermodynamics to two-phase flows with a change of phase
International Nuclear Information System (INIS)
Delhaye, J.M.
1969-01-01
In this report we use the methods of non-equilibrium thermodynamics in two-phase flows. This paper follows a prior one in which we have studied the conservation laws and derived the general equations of two-phase flow. In the first part the basic ideas of thermodynamics of irreversible systems are given. We follow the classical point of view. The second part is concerned with the derivation of a closed set of equations for the two phase elementary volume model. In this model we assume that the elementary volume contains two phases and that it is possible to define a volumetric local concentration. To obtain the entropy balance we can choose either the reversibility of the barycentric motion or the reversibility of each phase. We adopt the last assumption and our derivation is the same as this of I.Prigogine and P. Mazur about the hydrodynamics of liquid helium. The scope of this work is not to find a general solution to the problems of two phase flows but to obtain a new set of equations which may be used to explain some characteristic phenomena of two-phase flow such as wave propagation or critical states. (author) [fr
International Nuclear Information System (INIS)
Boucker, M.; Laviaville, J.; Martin, A.; Bechaud, C.; Bestion, D.; Coste, P.
2004-01-01
The objective of this communication is to present some preliminary applications to pressurized thermal shock (PTS) investigations of the CFD (Computational Fluid Dynamics) two-phase flow solver of the new NEPTUNE thermal-hydraulics platform. In the framework of plant life extension, the Reactor Pressure Vessel (RPV) integrity is a major concern, and an important part of RPV integrity assessment is related to PTS analysis. In the case where the cold legs are partially filled with steam, it becomes a two-phase problem and new important effects occur, such as condensation due to the Emergency Core Cooling (ECC) injections of sub-cooled water. Thus, an advanced prediction of RPV thermal loading during these transients requires sophisticated two-phase, local scale, 3-dimensional codes. In that purpose, a program has been set up to extend the capabilities of the NEPTUNE two-phase CFD solver. A simple set of turbulence and condensation model for free surface steam-water flow has been tested in simulation of an ECC high pressure injection representing facility, using a full 3-dimensional mesh and the new NEPTUNE solver. Encouraging results have been obtained but it should be noticed that several sources of error can compensate for one another. Nevertheless, the computation presented here allows to be reasonable confident in the use of two-phase CFD in order to carry out refined analysis of two-phase PTS scenarios within the next years
Magnetic avalanches in manganese-acetate, "magnetic deflagration"
Suzuki, Yoko
Mn12-acetate, first synthesized in 1980 by Lis, is one example of a class of many molecules called single molecule magnets (SMMs) or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule. They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mn12-acetate in 1996 by Friedman, et al. , and Berry phase oscillations which were measured in Fe8 (another SMM) in 1999 by Wernsdorfer, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions. Mn12-acetate has twelve Mn ions magnetically coupled in the center of the molecule yielding a giant spin of S = 10 at low temperature. It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches, first detected by Paulsen et al., also occur for some samples only at low temperature, leading to a very fast single-step reversal of the full magnetization, which clearly differs from relaxation by tunneling. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches" and "propagation of the avalanche front". In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread
Teich, M.; Feistl, T.; Fischer, J.; Bartelt, P.; Bebi, P.; Christen, M.; Grêt-Regamey, A.
2013-12-01
Two-dimensional avalanche simulation software operating in three-dimensional terrain are widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. This varying decelerating effect has rarely been addressed or implemented in avalanche simulation. We present an evaluation and operationalization of a novel forest detrainment modeling approach implemented in the avalanche simulation software RAMMS. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The extracted avalanche mass caught behind trees stops immediately and, therefore, is instantly subtracted from the flow and the momentum of the stopped mass is removed from the total momentum of the avalanche flow. This relationship is parameterized by the empirical detrainment coefficient K [Pa] which accounts for the braking power of different forest types per unit area. To define K dependent on specific forest characteristics, we simulated 40 well-documented small- to medium-scale avalanches which released in and ran through forests with varying K-values. Comparing two-dimensional simulation results with one-dimensional field observations for a high number of avalanche events and simulations manually is however time consuming and rather subjective. In order to process simulation results in a comprehensive and standardized way, we used a recently developed automatic evaluation and comparison method defining runout distances based on a pressure
Charge transfer cross-sections of argon ions colliding on argon atoms
International Nuclear Information System (INIS)
Aubert, J.; Bliman, S.; Chan-Tung, N.; Geller, R.; Jacquot, B.; Van Houtte, D.
1980-04-01
A device has been built to measure charge changing cross-sections of Argon ions colliding on argon atoms. It consists of an E.C.R. ion source (Micromafios) that delivers argon ions up to charge + 13. The ion source potential may be varied from 1 up to 10 kVolts. A first magnet is used to charge analyze the extracted beam. For a given separated charge state, the ion beam is passed in a collision cell whose pressure may be varied. The ions undergoing collisions on the target are analyzed by a second magnet and collected. The pressure is varied in the collision cell in order to check that the single collision condition is satisfied. It is shown that the ions do two types of collisions: charge exchange and stripping whose cross-sections are measured. Interpretation of charge exchange is proposed along yet classic theoretical approaches. As to stripping no available theory allows interpretation
A new web-based system to improve the monitoring of snow avalanche hazard in France
Bourova, Ekaterina; Maldonado, Eric; Leroy, Jean-Baptiste; Alouani, Rachid; Eckert, Nicolas; Bonnefoy-Demongeot, Mylene; Deschatres, Michael
2016-05-01
Snow avalanche data in the French Alps and Pyrenees have been recorded for more than 100 years in several databases. The increasing amount of observed data required a more integrative and automated service. Here we report the comprehensive web-based Snow Avalanche Information System newly developed to this end for three important data sets: an avalanche chronicle (Enquête Permanente sur les Avalanches, EPA), an avalanche map (Carte de Localisation des Phénomènes d'Avalanche, CLPA) and a compilation of hazard and vulnerability data recorded on selected paths endangering human settlements (Sites Habités Sensibles aux Avalanches, SSA). These data sets are now integrated into a common database, enabling full interoperability between all different types of snow avalanche records: digitized geographic data, avalanche descriptive parameters, eyewitness reports, photographs, hazard and risk levels, etc. The new information system is implemented through modular components using Java-based web technologies with Spring and Hibernate frameworks. It automates the manual data entry and improves the process of information collection and sharing, enhancing user experience and data quality, and offering new outlooks to explore and exploit the huge amount of snow avalanche data available for fundamental research and more applied risk assessment.
Interaction between local parameters of two-phase flow and random forces on a cylinder
International Nuclear Information System (INIS)
Sylviane Pascal-Ribot; Yves Blanchet; Franck Baj; Phillippe Piteau
2005-01-01
Full text of publication follows: In the frame of assessments of steam generator tube bundle vibrations, a study was conducted in order to investigate the effects of an air/water flow on turbulent buffeting forces induced on a cylinder. The main purpose is to relate the physical parameters characterizing an air/water two-phase crossflow with the structural loading of a fixed cylindrical tube. In this first approach, the experiments are carried out in a rectangular acrylic test section supplied with a vertical upward bubbly flow. This flow is transversally impeded by a fixed rigid 12,15 mm diameter cylinder. Different turbulence grids are used in order to modify two-phase characteristics such as bubble diameter, void fraction profile, fluctuation parameters. Preliminarily, a dimensional analysis of fluid-structure interaction under two-phase turbulent solicitations has enabled to identify a list of physically relevant variables which must be measured to evaluate the random forces. The meaning of these relevant parameters as well as the effect of flow patterns are discussed. Direct measurements of two-phase flow parameters are performed simultaneously with measurements of forces exerted on the cylinder. The main descriptive parameters of a two-phase flow are measured using a bi-optical probe, in particular void fraction profiles, interfacial velocities, bubble diameters, void fraction fluctuations. In the same time, the magnitude of random forces caused by two-phase flow is measured with a force transducer. A thorough analysis of the experimental data is then undertaken in order to correlate physical two-phase mechanisms with the random forces exerted on the cylinder. The hypotheses made while applying the dimensional analysis are verified and their pertinence is discussed. Finally, physical parameters involved in random buffeting forces applied on a transverse tube are proposed to scale the spectral magnitude of these forces and comparisons with other authors
Athermal avalanche in bilayer superconducting nanowire single-photon detectors
Energy Technology Data Exchange (ETDEWEB)
Verma, V. B., E-mail: verma@nist.gov; Lita, A. E.; Stevens, M. J.; Mirin, R. P.; Nam, S. W. [National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)
2016-03-28
We demonstrate that two superconducting nanowires separated by a thin insulating barrier can undergo an avalanche process. In this process, Joule heating caused by a photodetection event in one nanowire and the associated production of athermal phonons which are transmitted through the barrier cause the transition of the adjacent nanowire from the superconducting to the normal state. We show that this process can be utilized in the fabrication of superconducting nanowire single photon detectors to improve the signal-to-noise ratio, reduce system jitter, maximize device area, and increase the external efficiency over a very broad range of wavelengths. Furthermore, the avalanche mechanism may provide a path towards a superconducting logic element based on athermal gating.
Study of an avalanche-mode resistive plate chamber
International Nuclear Information System (INIS)
Ying, J.; Ban, Y.; Liu, H.T.; Zhu, Z.M.; Zhu, Z.Y.; Chen, T.; Ma, J.G.; Ye, Y.L.
2000-01-01
Resistive plate chambers (RPCs) are widely used to detect high-energy charged particles, especially muons, due to the high gain, moderate time and spatial resolution, simple design and low cost of these detectors. While the simple streamer mode is adequate for cosmic-ray and low-rate accelerator experiments, the avalanche mode is required for high-rate experiments such as CMS at LHC. In this paper construction of a medium-sized double-gap RPC made of Chinese materials is reported. The experimental set-up of cosmic-ray and muon beam tests are introduced. The avalanche mode was clearly observed. Good efficiency and time resolution were obtained from the beam test at CERN under normal irradiation conditions. At very high radiation background the chamber efficiency decreases, indicating the necessity to change the resistivity value of the Chinese bakelites. (author)
Stability of the discretization of the electron avalanche phenomenon
Energy Technology Data Exchange (ETDEWEB)
Villa, Andrea, E-mail: andrea.villa@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Barbieri, Luca, E-mail: luca.barbieri@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Gondola, Marco, E-mail: marco.gondola@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy); Leon-Garzon, Andres R., E-mail: andresricardo.leon@polimi.it [CMIC Department “Giulio Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano (Italy); Malgesini, Roberto, E-mail: roberto.malgesini@rse-web.it [Ricerca Sul Sistema Energetico (RSE), Via Rubattino 50, 20134, Milano (Italy)
2015-09-01
The numerical simulation of the discharge inception is an active field of applied physics with many industrial applications. In this work we focus on the drift-reaction equation that describes the electron avalanche. This phenomenon is one of the basic building blocks of the streamer model. The main difficulty of the electron avalanche equation lies in the fact that the reaction term is positive when a high electric field is applied. It leads to exponentially growing solutions and this has a major impact on the behavior of numerical schemes. We analyze the stability of a reference finite volume scheme applied to this latter problem. The stability of the method may impose a strict mesh spacing, therefore a proper stabilized scheme, which is stable whatever spacing is used, has been developed. The convergence of the scheme is treated as well as some numerical experiments.
Plasma simulation of electron avalanche in a linear thyratron
International Nuclear Information System (INIS)
Kushner, M.J.
1985-01-01
Thyratrons typically operate at sufficiently small PD (pressure x electrode separation) that holdoff is obtained by operating on the near side of the Paschen curve, and by shielding the slot in the control grid so there is no straight line path for electrons to reach the anode from the cathode. Electron avalanche is initiated by pulsing the control grid to a high voltage. Upon collapse of voltage in the cathode-control grid space, the discharge is sustained by penetration of potential through the control grid slot into the cathode-control grid region. To better understand the electron avalanche process in multi-grid and slotted structures such as thyratrons, a plasma simulation code has been constructed. This effort is in support of a companion program in which a linear thyratron is being electrically and spectroscopically characterized
Universal Critical Dynamics in High Resolution Neuronal Avalanche Data
Friedman, Nir; Ito, Shinya; Brinkman, Braden A. W.; Shimono, Masanori; DeVille, R. E. Lee; Dahmen, Karin A.; Beggs, John M.; Butler, Thomas C.
2012-05-01
The tasks of neural computation are remarkably diverse. To function optimally, neuronal networks have been hypothesized to operate near a nonequilibrium critical point. However, experimental evidence for critical dynamics has been inconclusive. Here, we show that the dynamics of cultured cortical networks are critical. We analyze neuronal network data collected at the individual neuron level using the framework of nonequilibrium phase transitions. Among the most striking predictions confirmed is that the mean temporal profiles of avalanches of widely varying durations are quantitatively described by a single universal scaling function. We also show that the data have three additional features predicted by critical phenomena: approximate power law distributions of avalanche sizes and durations, samples in subcritical and supercritical phases, and scaling laws between anomalous exponents.
A micropixel avalanche phototransistor for time of flight measurements
Energy Technology Data Exchange (ETDEWEB)
Sadigov, A., E-mail: saazik@yandex.ru [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Suleymanov, S. [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Ahmadov, F. [National Nuclear Research Center, Baku (Azerbaijan); Ahmadov, G. [National Nuclear Research Center, Baku (Azerbaijan); Joint Institute for Nuclear Research, Dubna (Russian Federation); Abdullayev, K. [National Aviation Academy, Baku (Azerbaijan); Akberov, R. [National Nuclear Research Center, Baku (Azerbaijan); Institute of Radiation Problems, Baku (Azerbaijan); Heydarov, N. [National Nuclear Research Center, Baku (Azerbaijan); Madatov, R. [Institute of Radiation Problems, Baku (Azerbaijan); Mukhtarov, R. [National Aviation Academy, Baku (Azerbaijan); Nazarov, M.; Valiyev, R. [National Nuclear Research Center, Baku (Azerbaijan)
2017-02-11
This paper presents results of studies of the silicon based new micropixel avalanche phototransistor (MAPT). MAPT is a modification of well-known silicon photomultipliers (SiPMs) and differs since each photosensitive pixel of the MAPT operates in Geiger mode and comprises an individual micro-transistor operating in binary mode. This provides a high amplitude single photoelectron signal with significantly shorter rise time. The obtained results are compared with appropriate parameters of known SiPMs. - Highlights: • A new photo detector – micropixel avalanche phototransistor was developed. • MAPT has a matrix of microtransistors with fast output. • In these modules the duration of the leading edge of the signal from the photodetectors are not worse than 50–100 ps.
Tuning magnetic avalanches in the molecular magnet Mn12 -acetate
McHugh, S.; Wen, Bo; Ma, Xiang; Sarachik, M. P.; Myasoedov, Y.; Zeldov, E.; Bagai, R.; Christou, G.
2009-05-01
Using micron-sized Hall sensor arrays to obtain time-resolved measurements of the local magnetization, we report a systematic study in the molecular magnet Mn12 acetate of magnetic avalanches controllably triggered in different fixed external magnetic fields and for different values of the initial magnetization. The speeds of propagation of the spin-reversal fronts are in good overall agreement with the theory of magnetic deflagration of Garanin and Chudnovsky [Phys. Rev. B 76, 054410 (2007)].
Propagation of avalanches in Mn12-acetate: magnetic deflagration.
Suzuki, Yoko; Sarachik, M P; Chudnovsky, E M; McHugh, S; Gonzalez-Rubio, R; Avraham, Nurit; Myasoedov, Y; Zeldov, E; Shtrikman, H; Chakov, N E; Christou, G
2005-09-30
Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.
Large area avalanche MRS-photodiodes for nuclear spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Ermalitski, F A; Zalesski, V B
1996-12-31
Problems of application of avalanche photodiodes (APD) in readout systems of nuclear spectrometers are considered. APD`s with a large sensitive area of a diameter 1-5 mm and a high multiplication coefficient 200-1000 are created. MPS-photodiodes provide for the energy resolution 80% at temperature 231 K for detecting gamma-quanta with energy 662 keV. 4 refs.
Azimuthal spread of the avalanche in proportional chambers
International Nuclear Information System (INIS)
Okuno, H.; Fischer, J.; Radeka, V.; Walenta, A.H.
1978-10-01
The angular distribution of the avalanche around the anode wire in the gas proportional counter is determined by measuring the distribution of positive ions arriving on cathode strips surrounding the anode wire for each single event. The shape and width of the distribution depend on such factors as the gas gain, the anode diameter, the counting gas and the primary ionization density. Effects of these factors are studied systematically, and their importance for practical counter applications is discussed
Avalanche fluctuations within the multigap resistive plate chamber
International Nuclear Information System (INIS)
Cerron Zeballos, E.; Crotty, I.; Lamas Valverde, J.; Veenhof, R.J.; Williams, M.C.S.; Zichichi, A.
1996-01-01
The multigap resistive plate chamber (MRPC) was originally designed to have improved time resolution (compared to the wide gap RPC), but also to keep the good high rate behaviour and ease of construction associated with the wide gap RPC. However in addition we observed a very long efficiency plateau, even at high rates. Here we consider fluctuations in avalanche growth, and show that the inherent ''averaging'' of these fluctuations can account for the enhanced performance of the multigap RPC. (orig.)
Kinetic modelling of runaway electron avalanches in tokamak plasmas.
Czech Academy of Sciences Publication Activity Database
Nilsson, E.; Decker, J.; Peysson, Y.; Granetz, R.S.; Saint-Laurent, F.; Vlainic, Milos
2015-01-01
Roč. 57, č. 9 (2015), č. článku 095006. ISSN 0741-3335 EU Projects: European Commission(XE) 633053 - EUROfusion Institutional support: RVO:61389021 Keywords : plasma physics * runaway electrons * knock-on collisions * tokamak * Fokker-Planck * runaway avalanches Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.404, year: 2015
High-Gain Avalanche Rushing amorphous Photoconductor (HARP) detector
Energy Technology Data Exchange (ETDEWEB)
Tanioka, K. [NHK Science and Technical Research Laboratories, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan)], E-mail: tanioka.k-jg@nhk.or.jp
2009-09-01
We have been studying a very sensitive image sensor since the early 1980s. In 1985, the author found for the first time that an experimental pickup tube with an amorphous selenium photoconductive target exhibits high sensitivity with excellent picture quality because of a continuous and stable avalanche multiplication phenomenon. We named the pickup tube with an amorphous photoconductive layer operating in the avalanche-mode 'HARP': High-gain Avalanche Rushing amorphous Photoconductor. A color camera equipped with the HARP pickup tubes has a maximum sensitivity of 11 lx at F8. This means that the HARP camera is about 100 times as sensitive as that of CCD camera for broadcasting. This ultrahigh-sensitivity HARP pickup tube is a powerful tool for reporting breaking news at night and other low-light conditions, the production of scientific programs, and numerous other applications, including medical diagnoses, biotech research, and nighttime surveillance. In addition, since the HARP target can convert X-rays into electrons directly, it should be possible to exploit this capability to produce X-ray imaging devices with unparalleled levels of resolution and sensitivity.
First Townsend coefficient of organic vapour in avalanche counters
International Nuclear Information System (INIS)
Sernicki, J.
1990-01-01
A new concept is presented in the paper for implementing the proven method of determining the first Townsend coefficient (α) of gases using an avalanche counter. The A and B gas constants, interrelated by the expression α/p=A exp[-B/(K/p)], are analyzed. Parallel-plate avalanche counters (PPAC) with an electrode spacing d from 0.1 to 0.4 cm have been employed for the investigation, arranged to register low-energy alpha particles at n-heptane vapour pressures of p≥5 Torr. An in-depth discussion is given, covering the veracity and the behaviour vs K/p, of the n-heptane A and B constants determined at reduced electric-field intensity values ranging from 173.5 to 940 V/cm Torr; the constants have been found to depend upon d. The results of the investigation are compared to available data of the α coefficient of organic vapours used in avalanche counters. The PPAC method of determining α reveals some imperfections at very low values of the pd product. (orig.)
AN MHD AVALANCHE IN A MULTI-THREADED CORONAL LOOP
Energy Technology Data Exchange (ETDEWEB)
Hood, A. W.; Cargill, P. J.; Tam, K. V. [School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife, KY16 9SS (United Kingdom); Browning, P. K., E-mail: awh@st-andrews.ac.uk [School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)
2016-01-20
For the first time, we demonstrate how an MHD avalanche might occur in a multithreaded coronal loop. Considering 23 non-potential magnetic threads within a loop, we use 3D MHD simulations to show that only one thread needs to be unstable in order to start an avalanche even when the others are below marginal stability. This has significant implications for coronal heating in that it provides for energy dissipation with a trigger mechanism. The instability of the unstable thread follows the evolution determined in many earlier investigations. However, once one stable thread is disrupted, it coalesces with a neighboring thread and this process disrupts other nearby threads. Coalescence with these disrupted threads then occurs leading to the disruption of yet more threads as the avalanche develops. Magnetic energy is released in discrete bursts as the surrounding stable threads are disrupted. The volume integrated heating, as a function of time, shows short spikes suggesting that the temporal form of the heating is more like that of nanoflares than of constant heating.
Avalanches in the Bean critical-state model
International Nuclear Information System (INIS)
Barford, W.
1997-01-01
A macroscopic equation of motion for the flux density in dirty type-II superconductors is introduced. The flux density is subject to various types of spatially varying pinning force. When there is no stick-slip dynamics, i.e., when the static pinning force equals the dynamic pinning force, it is shown that in both one and two dimensions an increase in the surface magnetic field leads to an overall height change and hence to a change in magnetization equal to the change in the surface magnetic field. More interesting behavior occurs on introducing stick-slip dynamics, i.e., when the static pinning force exceeds the dynamic pinning force. In this limit a distribution of avalanche sizes over four orders of magnitude is found for a 100x100 lattice. Apart from the anomalous behavior at large sizes, this is shown to fit a distribution of the form P(s)∼s -ν exp(-s/α), where s is the avalanche size. The anomalous behavior for large sizes corresponds to avalanches which involve most of the lattice and, hence, cause the flux to open-quotes slide over the edge,close quotes as detected by a change in the edge magnetization. copyright 1997 The American Physical Society
Inlet effects on vertical-downward air–water two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Qiao, Shouxu; Mena, Daniel; Kim, Seungjin, E-mail: skim@psu.edu
2017-02-15
Highlights: • Inlet effects on two-phase flow parameters in vertical-downward flow are studied. • Flow regimes in the vertical-downward two-phase flow are defined. • Vertical-downward flow regime maps for three inlet configurations are developed. • Frictional pressure loss analysis for three different inlets is performed. • Database of local two-phase flow parameters for each inlet configuration. - Abstract: This paper focuses on investigating the geometric effects of inlets on global and local two-phase flow parameters in vertical-downward air–water two-phase flow. Flow visualization, frictional pressure loss analysis, and local experiments are performed in a test facility constructed from 50.8 mm inner diameter acrylic pipes. Three types of inlets of interest are studied: (1) two-phase flow injector without a flow straightener (Type A), (2) two-phase flow injector with a flow straightener (Type B), and (3) injection through a horizontal-to-vertical-downward 90° vertical elbow (Type C). A detailed flow visualization study is performed to characterize flow regimes including bubbly, slug, churn-turbulent, and annular flow. Flow regime maps for each inlet are developed and compared to identify the effects of each inlet. Frictional pressure loss analysis shows that the Lockhart–Martinelli method is capable of correlating the frictional loss data acquired for Type B and Type C inlets with a coefficient value of C = 25, but additional data may be needed to model the Type A inlet. Local two-phase flow parameters measured by a four-sensor conductivity probe in four bubbly and near bubbly flow conditions are analyzed. It is observed that vertical-downward two-phase flow has a characteristic center-peaked void profile as opposed to a wall-peaked profile as seen in vertical-upward flow. Furthermore, it is shown that the Type A inlet results in the most pronounced center-peaked void fraction profile, due to the coring phenomenon. Type B and Type C inlets
Development of a low-cost inductively coupled argon plasma
International Nuclear Information System (INIS)
Ripson, P.A.M.
1983-01-01
The aim of this investigation is to drastically reduce running costs of an inductively coupled plasma. This is done by reducing the argon consumption from 20 l/min to about 1 l/min. First, a sample introduction system operating on 0.1 l/min of carrier argon is described. This system ensures a high ratio of plasma argon and carrier argon even at the low total argon consumptions intended. Next, the developed low consumption plasma is presented. In the proposed design, air is blown perpendicularly against the outside of the torch. A different coil has been developed to make air-cooling efficient. Preliminary data on coupling efficiency for the air-cooled plasma are presented. A similarly low argon consumption has been achieved with water as an external coolant medium. It is concluded that a cheaper alternative to the current ICP has become available. (Auth.)
International Nuclear Information System (INIS)
Cacuci, D.G.
1984-07-01
This report presents a self-contained mathematical formalism for deterministic sensitivity analysis of two-phase flow systems, a detailed application to sensitivity analysis of the homogeneous equilibrium model of two-phase flow, and a representative application to sensitivity analysis of a model (simulating pump-trip-type accidents in BWRs) where a transition between single phase and two phase occurs. The rigor and generality of this sensitivity analysis formalism stem from the use of Gateaux (G-) differentials. This report highlights the major aspects of deterministic (forward and adjoint) sensitivity analysis, including derivation of the forward sensitivity equations, derivation of sensitivity expressions in terms of adjoint functions, explicit construction of the adjoint system satisfied by these adjoint functions, determination of the characteristics of this adjoint system, and demonstration that these characteristics are the same as those of the original quasilinear two-phase flow equations. This proves that whenever the original two-phase flow problem is solvable, the adjoint system is also solvable and, in principle, the same numerical methods can be used to solve both the original and adjoint equations
Experiments of steady state head and torque of centrifugal pumps in two-phase flow
International Nuclear Information System (INIS)
Minato, Akihiko; Tominaga, Kenji.
1988-01-01
Circulation pump behavior has large effect on coolant discharge flow rate in case of reactor pipe break. Experiment of two-phase pump performance was conducted as a joint study of Japanese BWR user utilities and makers. Two-phase head and torque of three centrifugal pumps in high temperature and high pressure (around 6 MPa) steam/water were measured. Head was decreased from single-phase characteristics when gas was mixed in liquid flow in condition with normal flow and normal rotation directions. When flow rate was large enough, two-phase head was about the same as single-phase one in reversal flow conditions. Two-phase head was smoothly increased as flowing steam volumetic concentration increased when flow rate was small and flow direction was reversal. Changes of torque with gas concentration were correspondent to those of head. This suggested that changes of interaction between flow and impellers due to phase slip effected on torque which caused head differences between single- and two-phase flows. Dependence of dimensionless head and torque of three test pumps on steam concentration were almost the same as each other. (author)
Complex network analysis in inclined oil–water two-phase flow
International Nuclear Information System (INIS)
Zhong-Ke, Gao; Ning-De, Jin
2009-01-01
Complex networks have established themselves in recent years as being particularly suitable and flexible for representing and modelling many complex natural and artificial systems. Oil–water two-phase flow is one of the most complex systems. In this paper, we use complex networks to study the inclined oil–water two-phase flow. Two different complex network construction methods are proposed to build two types of networks, i.e. the flow pattern complex network (FPCN) and fluid dynamic complex network (FDCN). Through detecting the community structure of FPCN by the community-detection algorithm based on K-means clustering, useful and interesting results are found which can be used for identifying three inclined oil–water flow patterns. To investigate the dynamic characteristics of the inclined oil–water two-phase flow, we construct 48 FDCNs under different flow conditions, and find that the power-law exponent and the network information entropy, which are sensitive to the flow pattern transition, can both characterize the nonlinear dynamics of the inclined oil–water two-phase flow. In this paper, from a new perspective, we not only introduce a complex network theory into the study of the oil–water two-phase flow but also indicate that the complex network may be a powerful tool for exploring nonlinear time series in practice. (general)
International Nuclear Information System (INIS)
Gao Zhong-Ke; Hu Li-Dan; Jin Ning-De
2013-01-01
We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas—liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitative characterization of the dynamic flow behavior in the transitions among different gas—liquid flow patterns. (general)
Thermodynamic analysis of the two-phase ejector air-conditioning system for buses
International Nuclear Information System (INIS)
Ünal, Şaban; Yilmaz, Tuncay
2015-01-01
Air-conditioning compressors of the buses are usually operated with the power taken from the engine of the buses. Therefore, an improvement in the air-conditioning system will reduce the fuel consumption of the buses. The improvement in the coefficient of performance (COP) of the air-conditioning system can be provided by using the two-phase ejector as an expansion valve in the air-conditioning system. In this study, the thermodynamic analysis of bus air-conditioning system enhanced with a two-phase ejector and two evaporators is performed. Thermodynamic analysis is made assuming that the mixing process in ejector occurs at constant cross-sectional area and constant pressure. The increase rate in the COP with respect to conventional system is analyzed in terms of the subcooling, condenser and evaporator temperatures. The analysis shows that COP improvement of the system by using the two phase ejector as an expansion device is 15% depending on design parameters of the existing bus air-conditioning system. - Highlights: • Thermodynamic analysis of the two-phase ejector refrigeration system. • Analysis of the COP increase rate of bus air-conditioning system. • Analysis of the entrainment ratio of the two-phase ejector refrigeration system
DSMC simulation of two-phase plume flow with UV radiation
Energy Technology Data Exchange (ETDEWEB)
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073 (China)
2014-12-09
Rarefied gas-particle two-phase plume in which the phase of particles is liquid or solid flows from a solid propellant rocket of hypersonic vehicle flying at high altitudes, the aluminum oxide particulates not only impact the rarefied gas flow properties, but also make a great difference to plume radiation signature, so the radiation prediction of the rarefied gas-particle two-phase plume flow is very important for space target detection of hypersonic vehicles. Accordingly, this project aims to study the rarefied gas-particle two-phase flow and ultraviolet radiation (UV) characteristics. Considering a two-way interphase coupling of momentum and energy, the direct simulation Monte Carlo (DSMC) method is developed for particle phase change and the particle flow, including particulate collision, coalescence as well as separation, and a Monte Carlo ray trace model is implemented for the particulate UV radiation. A program for the numerical simulation of the gas-particle two-phase flow and radiation in which the gas flow nonequilibrium is strong is implemented as well. Ultraviolet radiation characteristics of the particle phase is studied based on the calculation of the flow field coupled with the radiation calculation, the radiation model for different size particles is analyzed, focusing on the effects of particle emission, absorption, scattering as well as the searchlight emission of the nozzle. A new approach may be proposed to describe the rarefied gas-particle two-phase plume flow and radiation transfer characteristics in this project.
Experimental study on local resistance of two-phase flow through spacer grid with rod bundle
International Nuclear Information System (INIS)
Yan Chaoxing; Yan Changqi; Sun Licheng; Tian Qiwei
2015-01-01
The experimental study on local resistance of single-phase and two-phase flows through a spacer grid in a vertical channel with 3 × 3 rod bundle was carried out under the normal temperature and pressure. For the case of single-phase flow, the liquid Reynolds number covered the range of 290-18 007. For the case of two-phase flow, the ranges of gas and liquid superficial velocities were 0.013-3.763 m/s and 0.076-1.792 m/s, respectively. A correlation for predicting local resistance of single-phase flow was given based on experimental results. Eight classical two-phase viscosity formulae for homogeneous model were evaluated against the experimental data of two-phase flow. The results show that Dukler model predicts the experimental data well in the range of Re 1 < 9000 while McAdams correlation is the best one for Re 1 ≥ 9000. For all experimental data, Dukler model provides the best prediction with the mean relative error of 29.03%. A new correlation is fitted for the range of Re 1 < 9000 by considering mass quality, two- phase Reynolds number and liquid and gas densities, resulting in a good agreement with the experimental data. (authors)
Present status of numerical analysis on transient two-phase flow
International Nuclear Information System (INIS)
Akimoto, Masayuki; Hirano, Masashi; Nariai, Hideki.
1987-01-01
The Special Committee for Numerical Analysis of Thermal Flow has recently been established under the Japan Atomic Energy Association. Here, some methods currently used for numerical analysis of transient two-phase flow are described citing some information given in the first report of the above-mentioned committee. Many analytical models for transient two-phase flow have been proposed, each of which is designed to describe a flow by using differential equations associated with conservation of mass, momentum and energy in a continuous two-phase flow system together with constructive equations that represent transportation of mass, momentum and energy though a gas-liquid interface or between a liquid flow and the channel wall. The author has developed an analysis code, called MINCS, that serves for systematic examination of conservation equation and constructive equations for two-phase flow models. A one-dimensional, non-equilibrium two-liquid flow model that is used as the basic model for the code is described. Actual procedures for numerical analysis is shown and some problems concerning transient two-phase analysis are described. (Nogami, K.)
On the use of nuclear magnetic resonance to characterize vertical two-phase bubbly flows
International Nuclear Information System (INIS)
Lemonnier, H.; Jullien, P.
2011-01-01
Research highlights: → We provide a complete theory of the PGSE measurement in single and two-phase flow. → Friction velocity can be directly determinated from measured velocity distributions. → Fast determination of moments shorten PGSE process with small loss of accuracy. → Turbulent diffusion measurements agree well with known trends and existing models. → We think NMR can be a tool to benchmark thermal anemometry in two-phase flow. - Abstract: Since the pioneering work of who showed that NMR can be used to measure accurately the mean liquid velocity and void fraction in two-phase pipe flow, it has been shown that NMR signal can also characterize the turbulent eddy diffusivity and velocity fluctuations. In this paper we provide an in depth validation of these statements together with a clarification of the nature of the mean velocity that is actually measured by NMR PFGSE sequence. The analysis shows that the velocity gradient at the wall is finely space-resolved and allows the determination of the friction velocity in single-phase flows. Next turbulent diffusion measurements in two-phase flows are presented, analyzed and compared to existing data and models. It is believed that NMR velocity measurement is sufficiently understood that it can be utilized to benchmark thermal anemometry in two-phase flows. Theoretical results presented in this paper also show how this can be undertaken.
Measurement of void fraction and bubble size distribution in two-phase flow system
International Nuclear Information System (INIS)
Huahun, G.
1987-01-01
The importance of study two phase flow parameter and microstructure has appeared increasingly, with the development of two-phase flow discipline. In the paper, the measurement methods of several important microstructure parameter in a two phase flow vertical channel have been studied. Using conductance probe the two phase flow pattern and the average void fraction have been measured previously by the authors. This paper concerns microstructure of the bubble size distribution and local void fraction. The authors studied the methods of measuring bubble velocity, size distribution and local void fraction using double conductance probes and a set of apparatus. Based on our experiments and Yoshihiro work, a formula of calculated local void fraction has been deduced by using the statistical characteristics of bubbles in two phase flow and the relation between calculated bubble size and voltage has been determined. Finally the authors checked by using photograph and fast valve, which is classical but reliable. The results are the same with what has been studied before
Post Analysis of Two Phase Natural Circulation Mass Flow Rate for CE-PECS
Energy Technology Data Exchange (ETDEWEB)
Park, R. J.; Ha, K. S.; Rhee, B. W.; Kim, H. Y. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
The coolant in the inclined channel absorbs the decay heat and sensible heat transferred from the corium through the structure of the core catcher body and flows up to the pool as a two phase mixture. On the other hand, some of the pool water will flow into the inlet of the downcomer piping, and will flow into the inclined cooling channel of the core catcher by gravity. The engineered cooling channel is designed to provide effective long-term cooling and stabilization of the corium mixture in the core catcher body while facilitating steam venting. To maintain the integrity of the ex-vessel core catcher, however, it is required that the coolant be circulated at a rate along the inclined cooling channel sufficient to avoid CHF (Critical Heat Flux) on the heating surface of the cooling channel. In this study, post simulations of two phase natural circulation in the CEPECS have been performed to evaluate two phase flow characteristics and the natural circulation mass flow rate in the flow channel using the RELAP5/MOD3 computer code. Post simulations of two phase natural circulation in the CE-PECS have been conducted to evaluate two phase flow characteristics and the natural circulation mass flow rate in the flow channel using the RELAP5/MOD3 computer code. The RELAP5/MOD3 results have shown that the water circulation mass flow rate is approximately 8.7 kg/s in the base case.
Zero-G two phase flow regime modeling in adiabatic flow
International Nuclear Information System (INIS)
Reinarts, T.R.; Best, F.R.; Wheeler, M.; Miller, K.M.
1993-01-01
Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with microgravity, two-phase flow regime analysis. The data come from a recent sets of experiments. The experiments were funded by NASA Johnson Space Center (JSC) and conducted by NASA JSC with Texas A ampersand M University. The experiment was on loan to NASA JSC from Foster-Miller, Inc., who constructed it with funding from the Air Force Phillips Laboratory. The experiment used R12 as the working fluid. A Foster-Miller two phase pump was used to circulate the two phase mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown 19 times for 577 parabolas aboard the NASA KC-135 aircraft which simulates zero-G conditions by its parabolic flight trajectory. Test conditions included bubbly, slug and annular flow regimes in 0-G. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes and several flow regime transition predictions. None of the predictions completely describe the transitions as indicated by the data
Post Analysis of Two Phase Natural Circulation Mass Flow Rate for CE-PECS
International Nuclear Information System (INIS)
Park, R. J.; Ha, K. S.; Rhee, B. W.; Kim, H. Y.
2015-01-01
The coolant in the inclined channel absorbs the decay heat and sensible heat transferred from the corium through the structure of the core catcher body and flows up to the pool as a two phase mixture. On the other hand, some of the pool water will flow into the inlet of the downcomer piping, and will flow into the inclined cooling channel of the core catcher by gravity. The engineered cooling channel is designed to provide effective long-term cooling and stabilization of the corium mixture in the core catcher body while facilitating steam venting. To maintain the integrity of the ex-vessel core catcher, however, it is required that the coolant be circulated at a rate along the inclined cooling channel sufficient to avoid CHF (Critical Heat Flux) on the heating surface of the cooling channel. In this study, post simulations of two phase natural circulation in the CEPECS have been performed to evaluate two phase flow characteristics and the natural circulation mass flow rate in the flow channel using the RELAP5/MOD3 computer code. Post simulations of two phase natural circulation in the CE-PECS have been conducted to evaluate two phase flow characteristics and the natural circulation mass flow rate in the flow channel using the RELAP5/MOD3 computer code. The RELAP5/MOD3 results have shown that the water circulation mass flow rate is approximately 8.7 kg/s in the base case