STOP-Bang Questionnaire in Patients with Rapid Eye Movement Sleep Behavior Disorder

Directory of Open Access Journals (Sweden)

Ki-Hwan Ji

2017-12-01

Full Text Available Background and Objective The snoring, tiredness, observed apnea, and high blood pressure– body mass index, age, neck circumference, and gender (STOP-Bang questionnaire is known as a simple but useful tool for the diagnosis of high-risk obstructive sleep apnea (OSA. However, the utility of STOP-Bang questionnaire in rapid eye movement (REM sleep behavior disorder (RBD populations is not validated. This study aimed to determine the diagnostic value of the STOP-Bang questionnaire in patients with RBD at high risk for OSA. Methods We collected data from 65 consecutive patients who were diagnosed with RBD in a tertiary sleep center (20 women; mean age, 64.3 ± 12.5 years. All the patients visited sleep center with complaints of abnormal behavior during sleep, and underwent testing with STOP-Bang questionnaire and polysomnography. The diagnosis of RBD was based on the International Classification of Sleep Disorders, second edition. We diagnosed OSA when apnea-hypopnea index (AHI was at least 5/h. The receiver operating characteristic (ROC curves were plotted. Results The mean AHI was 18.2 ± 16.5/h, and 75.4% (n = 49 had an AHI ≥ 5. The STOP-Bang (threshold ≥ 3 identified 70.7% of patients as high risk for OSA, and sensitivity, specificity, positive and negative predictive values were 81.6, 62.5, 87, and 52.6%, respectively. The area under the ROC curve (AUC was 0.79 (p < 0.001. The STOP (threshold ≥ 2 identified 70.7% of patients at high risk for OSA, and sensitivity, specificity, positive and negative predictive values were 75.5, 87.5, 94.9, and 53.8%, respectively. The AUC was 0.86 (p < 0.001. A pairwise comparison of ROC curve between STOP-Bang and STOP was insignificant (p = 0.145. Conclusions In RBD population, the STOP-Bang or STOP questionnaire is a useful screening tool to identify patients at high risk for OSA.

Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima.

Science.gov (United States)

Furch, Alexandra C U; Zimmermann, Matthias R; Will, Torsten; Hafke, Jens B; van Bel, Aart J E

2010-08-01

The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring approximately 10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca(2+)-dependent occlusion mechanisms is attributed to Ca(2+) influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca(2+) ions.

Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima

Science.gov (United States)

Furch, Alexandra C. U.; Zimmermann, Matthias R.; Will, Torsten; Hafke, Jens B.; van Bel, Aart J. E.

2010-01-01

The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring ∼10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30–40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca2+-dependent occlusion mechanisms is attributed to Ca2+ influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca2+ ions. PMID:20584788

Stopped-flow injection method for determination of phosphate in soils and fertilisers

Directory of Open Access Journals (Sweden)

Jaroon Jakmunee

2008-02-01

Full Text Available A stopped-flow injection system for the determination of phosphate has been developed. It involves the phosphate-molybdate-ascorbic acid reactions in the molybdenum blue method. The system is controlled by a semi-automatic stopped-FI analyser with a light emitting diode (LED-colorimeter for monitoring the absorbance change relating to the concentration of a reaction product formed during the stopping period while the injected zone of a standard or sample is being in the flow cell. The slope of the FIAgram obtained is linearly proportional to the reaction rate, which depends on the phosphate concentration. Effects of concentration of reagents, viz. sodium molybdate, ascorbic acid and nitric acid, on the slope of the FIAgram were studied. The suitable concentration is 0.02 M, 0.25 %w/v and 0.15 M, respectively. A linear calibration graph in the range of 0.3-6.0 mg P L-1 was employed for the determination of phosphate in soil and fertiliser samples. The results obtained agree well with those from a standard spectrophotometric method.

Flow analysis for efficient design of wavy structured microchannel mixing devices

Science.gov (United States)

Kanchan, Mithun; Maniyeri, Ranjith

2018-04-01

Microfluidics is a rapidly growing field of applied research which is strongly driven by demands of bio-technology and medical innovation. Lab-on-chip (LOC) is one such application which deals with integrating bio-laboratory on micro-channel based single fluidic chip. Since fluid flow in such devices is restricted to laminar regime, designing an efficient passive modulator to induce chaotic mixing for such diffusion based flow is a major challenge. In the present work two-dimensional numerical simulation of viscous incompressible flow is carried out using immersed boundary method (IBM) to obtain an efficient design for wavy structured micro-channel mixing devices. The continuity and Navier-Stokes equations governing the flow are solved by fractional step based finite volume method on a staggered Cartesian grid system. IBM uses Eulerian co-ordinates to describe fluid flow and Lagrangian co-ordinates to describe solid boundary. Dirac delta function is used to couple both these co-ordinate variables. A tether forcing term is used to impose the no-slip boundary condition on the wavy structure and fluid interface. Fluid flow analysis by varying Reynolds number is carried out for four wavy structure models and one straight line model. By analyzing fluid accumulation zones and flow velocities, it can be concluded that straight line structure performs better mixing for low Reynolds number and Model 2 for higher Reynolds number. Thus wavy structures can be incorporated in micro-channels to improve mixing efficiency.

Additional band broadening of peptides in the first size-exclusion chromatographic dimension of an automated stop-flow two-dimensional high performance liquid chromatography.

Science.gov (United States)

Xu, Jucai; Sun-Waterhouse, Dongxiao; Qiu, Chaoying; Zhao, Mouming; Sun, Baoguo; Lin, Lianzhu; Su, Guowan

2017-10-27

The need to improve the peak capacity of liquid chromatography motivates the development of two-dimensional analysis systems. This paper presented a fully automated stop-flow two-dimensional liquid chromatography system with size exclusion chromatography followed by reversed phase liquid chromatography (SEC×RPLC) to efficiently separate peptides. The effects of different stop-flow operational parameters (stop-flow time, peak parking position, number of stop-flow periods and column temperature) on band broadening in the first dimension (1 st D) SEC column were quantitatively evaluated by using commercial small proteins and peptides. Results showed that the effects of peak parking position and the number of stop-flow periods on band broadening were relatively small. Unlike stop-flow analysis of large molecules with a long running time, additional band broadening was evidently observed for small molecule analytes due to the relatively high effective diffusion coefficient (D eff ). Therefore, shorter analysis time and lower 1 st D column temperature were suggested for analyzing small molecules. The stop-flow two-dimensional liquid chromatography (2D-LC) system was further tested on peanut peptides and an evidently improved resolution was observed for both stop-flow heart-cutting and comprehensive 2D-LC analysis (in spite of additional band broadening in SEC). The stop-flow SEC×RPLC, especially heart-cutting analysis with shorter analysis time and higher 1 st D resolution for selected fractions, offers a promising approach for efficient analysis of complex samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Diffusion-limited mixing by incompressible flows

Science.gov (United States)

Miles, Christopher J.; Doering, Charles R.

2018-05-01

Incompressible flows can be effective mixers by appropriately advecting a passive tracer to produce small filamentation length scales. In addition, diffusion is generally perceived as beneficial to mixing due to its ability to homogenize a passive tracer. However we provide numerical evidence that, in cases where advection and diffusion are both actively present, diffusion may produce negative effects by limiting the mixing effectiveness of incompressible optimal flows. This limitation appears to be due to the presence of a limiting length scale given by a generalised Batchelor length (Batchelor 1959 J. Fluid Mech. 5 113–33). This length scale limitation may in turn affect long-term mixing rates. More specifically, we consider local-in-time flow optimisation under energy and enstrophy flow constraints with the objective of maximising the mixing rate. We observe that, for enstrophy-bounded optimal flows, the strength of diffusion may not impact the long-term mixing rate. For energy-constrained optimal flows, however, an increase in the strength of diffusion can decrease the mixing rate. We provide analytical lower bounds on mixing rates and length scales achievable under related constraints (point-wise bounded speed and rate-of-strain) by extending the work of Lin et al (2011 J. Fluid Mech. 675 465–76) and Poon (1996 Commun. PDE 21 521–39).

Safety impacts of platform tram stops on pedestrians in mixed traffic operation: A comparison group before-after crash study.

Science.gov (United States)

Naznin, Farhana; Currie, Graham; Logan, David; Sarvi, Majid

2016-01-01

Tram stops in mixed traffic environments present a variety of safety, accessibility and transport efficiency challenges. In Melbourne, Australia the hundred year-old electric tram system is progressively being modernized to improve passenger accessibility. Platform stops, incorporating raised platforms for level entry into low floor trams, are being retro-fitted system-wide to replace older design stops. The aim of this study was to investigate the safety impacts of platform stops over older design stops (i.e. Melbourne safety zone tram stops) on pedestrians in the context of mixed traffic tram operation in Melbourne, using an advanced before-after crash analysis approach, the comparison group (CG) method. The CG method evaluates safety impacts by taking into account the general trends in safety and the unobserved factors at treatment and comparison sites that can alter the outcomes of a simple before-after analysis. The results showed that pedestrian-involved all injury crashes reduced by 43% after platform stop installation. This paper also explores a concern that the conventional CG method might underestimate safety impacts as a result of large differences in passenger stop use between treatment and comparison sites, suggesting differences in crash risk exposure. To adjust for this, a modified analysis explored crash rates (crash counts per 10,000 stop passengers) for each site. The adjusted results suggested greater reductions in pedestrian-involved crashes after platform stop installation: an 81% reduction in pedestrian-involved all injury crashes and 86% reduction in pedestrian-involved FSI crashes, both are significant at the 95% level. Overall, the results suggest that platform stops have considerable safety benefits for pedestrians. Implications for policy and areas for future research are explored. Copyright © 2015 Elsevier Ltd. All rights reserved.

Development of rapid mixing fuel nozzle for premixed combustion

International Nuclear Information System (INIS)

Katsuki, Masashi; Chung, Jin Do; Kim, Jang Woo; Hwang, Seung Min; Kim, Seung Mo; Ahn, Chul Ju

2009-01-01

Combustion in high-preheat and low oxygen concentration atmosphere is one of the attractive measures to reduce nitric oxide emission as well as greenhouse gases from combustion devices, and it is expected to be a key technology for the industrial applications in heating devices and furnaces. Before proceeding to the practical applications, we need to elucidate combustion characteristics of non-premixed and premixed flames in high-preheat and low oxygen concentration conditions from scientific point of view. For the purpose, we have developed a special mixing nozzle to create a homogeneous mixture of fuel and air by rapid mixing, and applied this rapidmixing nozzle to a Bunsen-type burner to observe combustion characteristics of the rapid-mixture. As a result, the combustion of rapid-mixture exhibited the same flame structure and combustion characteristics as the perfectly prepared premixed flame, even though the mixing time of the rapid-mixing nozzle was extremely short as a few milliseconds. Therefore, the rapid-mixing nozzle in this paper can be used to create preheated premixed flames as far as the mixing time is shorter than the ignition delay time of the fuel

Thermoconvective flow velocity in a high-speed magnetofluid seal after it has stopped

Science.gov (United States)

Krakov, M. S.; Nikiforov, I. V.

2012-09-01

Convective flow is investigated in the high-speed (linear velocity of the shaft seal is more than 1 m/s) magnetofluid shaft seal after it has been stopped. Magnetic fluid is preliminarily heated due to viscous friction in the moving seal. After the shaft has been stopped, nonuniform heated fluid remains under the action of a high-gradient magnetic field. Numerical analysis has revealed that in this situation, intense thermomagnetic convection is initiated. The velocity of magnetic fluid depends on its viscosity. For the fluid with viscosity of 2 × 10-4 m2/s the maximum flow velocity within the volume of magnetic fluid with a characteristic size of 1 mm can attain a value of 10 m/s.

Thermoconvective flow velocity in a high-speed magnetofluid seal after it has stopped

OpenAIRE

Krakov, M. S.; Nikiforov, I. V.

2012-01-01

Convective flow is investigated in the high-speed (linear velocity of the shaft seal is more than 1 m/s) magnetofluid shaft seal after it has been stopped. Magnetic fluid is preliminarily heated due to viscous friction in the moving seal. After the shaft has been stopped, nonuniform heated fluid remains under the action of a high-gradient magnetic field. Numerical analysis has revealed that in this situation, intense thermomagnetic convection is initiated. The velocity of magnetic fluid depen...

Optimization of Orifice Geometry for Cross-Flow Mixing in a Cylindrical Duct

Science.gov (United States)

Kroll, J. T.; Sowa, W. A.; Samuelsen, G. S.

1996-01-01

Mixing of gaseous jets in a cross-flow has significant applications in engineering, one example of which is the dilution zone of a gas turbine combustor. Despite years of study, the design of the jet injection in combustors is largely based on practical experience. The emergence of NO(x) regulations for stationary gas turbines and the anticipation of aero-engine regulations requires an improved understanding of jet mixing as new combustor concepts are introduced. For example, the success of the staged combustor to reduce the emission of NO(x) is almost entirely dependent upon the rapid and complete dilution of the rich zone products within the mixing section. It is these mixing challenges to which the present study is directed. A series of experiments was undertaken to delineate the optimal mixer orifice geometry. A cross-flow to core-flow momentum-flux ratio of 40 and a mass flow ratio of 2.5 were selected as representative of a conventional design. An experimental test matrix was designed around three variables: the number of orifices, the orifice length-to- width ratio, and the orifice angle. A regression analysis was performed on the data to arrive at an interpolating equation that predicted the mixing performance of orifice geometry combinations within the range of the test matrix parameters. Results indicate that the best mixing orifice geometry tested involves eight orifices with a long-to-short side aspect ratio of 3.5 at a twenty-three degree inclination from the center-line of the mixing section.

Numerical simulation of internal flow in mixed-flow waterjet propulsion

International Nuclear Information System (INIS)

Wu, T T; Pan, Z Y; Zhang, D Q; Jia, Y Y

2012-01-01

In order to reveal the internal flow characteristic of a mixed-flow waterjet propulsion, a mixed-flow waterjet propulsion under different conditions was simulated based on multi-reference frame(MRF), the standard k − ε turbulent model and SIMPLEC algorithm. The relationship between pump performance instability and internal flow was obtained. The numerical results showed that characteristic instability occurred at 0.65-0.67Q BEP , the reason is that the backflow on the vaned diffuser hub-side blocks the downstream flow from the impeller. Therefore, the flow separates on the pressure surface of the impeller outlet and a strong vortex is generated, then the characteristic instability appeared due to the instability of internal flow. Backflow was found in diffuser passage at 0.65 Q BEP and 0.85 Q BEP , as flow rate decreases, the backflow region and velocity increases. Pressure fluctuation at diffuser inlet and diffuser passages was severe at at 0.65 Q BEP . According to the numerical simulation, the mixed-flow waterjet propulsion has characteristic instability at partial flow rate condition.

Experimental study of the influence of flow passage subtle variation on mixed-flow pump performance

Science.gov (United States)

Bing, Hao; Cao, Shuliang

2014-05-01

In the mixed-flow pump design, the shape of the flow passage can directly affect the flow capacity and the internal flow, thus influencing hydraulic performance, cavitation performance and operation stability of the mixed-flow pump. However, there is currently a lack of experimental research on the influence mechanism. Therefore, in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance, the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment. In this experiment, parameters, such as the head, the efficiency, and the shaft power, are measured, and the pressure fluctuation and the noise signal are also collected. The research results suggest that after processing the inlet flow passage, the head of the mixed-flow pump significantly goes down; the best efficiency of the mixed-flow pump drops by approximately 1.5%, the efficiency decreases more significantly under the large flow rate; the shaft power slightly increases under the large flow rate, slightly decreases under the small flow rate. In addition, the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump. At the same time, the noise dramatically increases. Overall speaking, the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance, thus suggesting a special attention to the optimization of flow passage. This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment, which will benefit the optimal design of the flow passage of the mixed-flow pump.

CFD simulation for thermal mixing of a SMART flow mixing header assembly

International Nuclear Information System (INIS)

Kim, Young In; Bae, Youngmin; Chung, Young Jong; Kim, Keung Koo

2015-01-01

Highlights: • Thermal mixing performance of a FMHA installed in SMART is investigated numerically. • Effects of operating condition and discharge hole configuration are examined. • FMHA performance satisfies the design requirements under various abnormal conditions. - Abstract: A flow mixing header assembly (FMHA) is installed in a system-integrated modular advanced reactor (SMART) to enhance the thermal mixing capability and create a uniform core flow distribution under both normal operation and accident conditions. In this study, the thermal mixing characteristics of the FMHA are investigated for various steam generator conditions using a commercial CFD code. Simulations include investigations for the effects of FMHA discharge flow rate differences, turbulence models, and steam generator conditions. The results of the analysis show that the FMHA works effectively for thermal mixing in various conditions and makes the temperature difference at the core inlet decrease noticeably. We verified that the mixing capability of the FMHA is excellent and satisfies the design requirement in all simulation cases tested here

CFD simulation on reactor flow mixing phenomena

International Nuclear Information System (INIS)

Kwon, T.S.; Kim, K.H.

2016-01-01

A pre-test calculation for multi-dimensional flow mixing in a reactor core and downcomer has been studied using a CFD code. To study the effects of Reactor Coolant Pump (RCP) and core zone on the boron mixing behaviors in a lower downcomer and core inlet, a 1/5-scale CFD model of flow mixing test facility for the APR+ reference plant was simulated. The flow paths of the 1/5-scale model were scaled down by the linear scaling method. The aspect ratio (L/D) of all flow paths was preserved to 1. To preserve a dynamic similarity, the ratio of Euler number was also preserved to 1. A single phase water flow at low pressure and temperature conditions was considered in this calculation. The calculation shows that the asymmetric effect driven by RCPs shifted the high velocity field to the failed pump's flow zone. The borated water flow zone at the core inlet was also shifted to the failed RCP side. (author)

Flow structure of steam-water mixed spray

International Nuclear Information System (INIS)

Sanada, Toshiyuki; Mitsuhashi, Yuki; Mizutani, Hiroya; Saito, Takayuki

2010-01-01

In this study, the flow structure of a steam-water mixed spray is studied both numerically and experimentally. The velocity and pressure profiles of single-phase flow are calculated using numerical methods. On the basis of the calculated flow fields, the droplet behavior is predicted by a one-way interaction model. This numerical analysis reveals that the droplets are accelerated even after they are sprayed from the nozzle. Experimentally, the mixed spray is observed using an ultra-high-speed video camera, and the velocity field is measured by using the oarticle image velocimetry (PIV) technique. Along with this PIV velocity field measurement, the velocities and diameters of droplets are measured by phase Doppler anemometry. Furthermore, the mixing process of steam and water and the atomization process of a liquid film are observed using a transparent nozzle. High-speed photography observations reveal that the flow inside the nozzle is annular flow and that most of the liquid film is atomized at the nozzle throat and nozzle outlet. Finally, the optimum mixing method for steam and water is determined.

Flow structure of steam-water mixed spray

Energy Technology Data Exchange (ETDEWEB)

Sanada, Toshiyuki, E-mail: ttsanad@ipc.shizuoka.ac.j [Department of Mechanical Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Shizuoka (Japan); Mitsuhashi, Yuki; Mizutani, Hiroya; Saito, Takayuki [Department of Mechanical Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Shizuoka (Japan)

2010-12-15

In this study, the flow structure of a steam-water mixed spray is studied both numerically and experimentally. The velocity and pressure profiles of single-phase flow are calculated using numerical methods. On the basis of the calculated flow fields, the droplet behavior is predicted by a one-way interaction model. This numerical analysis reveals that the droplets are accelerated even after they are sprayed from the nozzle. Experimentally, the mixed spray is observed using an ultra-high-speed video camera, and the velocity field is measured by using the oarticle image velocimetry (PIV) technique. Along with this PIV velocity field measurement, the velocities and diameters of droplets are measured by phase Doppler anemometry. Furthermore, the mixing process of steam and water and the atomization process of a liquid film are observed using a transparent nozzle. High-speed photography observations reveal that the flow inside the nozzle is annular flow and that most of the liquid film is atomized at the nozzle throat and nozzle outlet. Finally, the optimum mixing method for steam and water is determined.

Stopping times in cessation flows of Bingham plastics with slip at the wall

Science.gov (United States)

Philippou, Maria; Damianou, Yiolanda; Kaoullas, George; Georgiou, Georgios C.

2012-09-01

We solve numerically the cessation of axisymmetric Poiseuille flow of a Bingham plastic assuming that slip occurs along the wall. A power-law expression is used to relate the wall shear stress to the slip velocity. The numerical results show that the velocity becomes and remains uniform before complete cessation and that the stopping time is finite only when the exponent sBingham number and the volumetric flow rate decays exponentially. When s>1, the decay is much slower, i.e. polynomial. The asymptotic expressions for the volumetric flow rate in the case of full-slip are also derived.

Stop searches in flavourful supersymmetry

CERN Document Server

Crivellin, Andreas; Tunstall, Lewis C.

2016-01-01

Natural realisations of supersymmetry require light stops ${\\tilde t}_1$, making them a prime target of LHC searches for physics beyond the Standard Model. Depending on the kinematic region, the main search channels are ${\\tilde t_1}\\to t \\tilde \\chi^0_1$, ${\\tilde t_1}\\to W b \\tilde \\chi^0_1$ and ${\\tilde t_1}\\to c \\tilde \\chi^0_1$. We first examine the interplay of these decay modes with ${\\tilde c_1}\\to c \\tilde \\chi^0_1$ in a model-independent fashion, revealing the existence of large regions in parameter space which are excluded for any ${\\tilde t_1}\\to c \\tilde \\chi^0_1$ branching ratio. This effect is then illustrated for scenarios with stop-scharm mixing in the right-handed sector, where it has previously been observed that the stop mass limits can be significantly weakened for large mixing. Our analysis shows that once the LHC bounds from ${\\tilde c_1}\\to c \\tilde \\chi^0_1$ searches are taken into account, non-zero stop-scharm mixing leads only to a modest increase in the allowed regions of parameter...

Characterization of vertical mixing in oscillatory vegetated flows

Science.gov (United States)

Abdolahpour, M.; Ghisalberti, M.; Lavery, P.; McMahon, K.

2016-02-01

Seagrass meadows are primary producers that provide important ecosystem services, such as improved water quality, sediment stabilisation and trapping and recycling of nutrients. Most of these ecological services are strongly influenced by the vertical exchange of water across the canopy-water interface. That is, vertical mixing is the main hydrodynamic process governing the large-scale ecological and environmental impact of seagrass meadows. The majority of studies into mixing in vegetated flows have focused on steady flow environments whereas many coastal canopies are subjected to oscillatory flows driven by surface waves. It is known that the rate of mass transfer will vary greatly between unidirectional and oscillatory flows, necessitating a specific investigation of mixing in oscillatory canopy flows. In this study, we conducted an extensive laboratory investigation to characterise the rate of vertical mixing through a vertical turbulent diffusivity (Dt,z). This has been done through gauging the evolution of vertical profiles of concentration (C) of a dye sheet injected into a wave-canopy flow. Instantaneous measurement of the variance of the vertical concentration distribution ( allowed the estimation of a vertical turbulent diffusivity (). Two types of model canopies, rigid and flexible, with identical heights and frontal areas, were subjected to a wide and realistic range of wave height and period. The results showed two important mechanisms that dominate vertical mixing under different conditions: a shear layer that forms at the top of the canopy and wake turbulence generated by the stems. By allowing a coupled contribution of wake and shear layer mixing, we present a relationship that can be used to predict the rate of vertical mixing in coastal canopies. The results further showed that the rate of vertical mixing within flexible vegetation was always lower than the corresponding rigid canopy, confirming the impact of plant flexibility on canopy-flow

Design and fabrication of magnetically functionalized flexible micropillar arrays for rapid and controllable microfluidic mixing

KAUST Repository

Zhou, BingPu

2015-03-25

Magnetically functionalized PDMS-based micropillar arrays have been successfully designed, fabricated and implanted for controllable microfluidic mixing. The arrangement of PDMS micropillar arrays inside the microchannel can be flexibly controlled by an external magnetic field. As a consequence, the flow fields inside the microchannel can be regulated at will via magnetic activation conveniently. When a microchannel is implanted with such micropillar arrays, two microstreams can be mixed easily and controllably upon the simple application of an on/off magnetic signal. Mixing efficiencies based on micropillar arrays with different densities were investigated and compared. It was found that micropillar arrays with higher density (i.e. smaller pillar pitch) would render better mixing performance. Our microfluidic system is capable of generating highly reproducible results within many cycles of mixing/non-mixing conversion. We believe that the simple mixing-triggering method together with rapid and controllable mixing control will be extraordinarily valuable for various biological or chemical applications in the future. This journal is © The Royal Society of Chemistry 2015.

Design and fabrication of magnetically functionalized flexible micropillar arrays for rapid and controllable microfluidic mixing

KAUST Repository

Zhou, BingPu; Xu, Wei; Syed, Ahad; Chau, Yeungyeung; Chen, Longqing; Chew, Basil; Yassine, Omar; Wu, Xiaoxiao; Gao, Yibo; Zhang, Jingxian; Xiao, Xiao; Kosel, Jü rgen; Zhang, Xixiang; Yao, Zhaohui; Wen, Weijia

2015-01-01

Magnetically functionalized PDMS-based micropillar arrays have been successfully designed, fabricated and implanted for controllable microfluidic mixing. The arrangement of PDMS micropillar arrays inside the microchannel can be flexibly controlled by an external magnetic field. As a consequence, the flow fields inside the microchannel can be regulated at will via magnetic activation conveniently. When a microchannel is implanted with such micropillar arrays, two microstreams can be mixed easily and controllably upon the simple application of an on/off magnetic signal. Mixing efficiencies based on micropillar arrays with different densities were investigated and compared. It was found that micropillar arrays with higher density (i.e. smaller pillar pitch) would render better mixing performance. Our microfluidic system is capable of generating highly reproducible results within many cycles of mixing/non-mixing conversion. We believe that the simple mixing-triggering method together with rapid and controllable mixing control will be extraordinarily valuable for various biological or chemical applications in the future. This journal is © The Royal Society of Chemistry 2015.

Dynamic route guidance strategy in a two-route pedestrian-vehicle mixed traffic flow system

Science.gov (United States)

Liu, Mianfang; Xiong, Shengwu; Li, Bixiang

2016-05-01

With the rapid development of transportation, traffic questions have become the major issue for social, economic and environmental aspects. Especially, during serious emergencies, it is very important to alleviate road traffic congestion and improve the efficiency of evacuation to reduce casualties, and addressing these problems has been a major task for the agencies responsible in recent decades. Advanced road guidance strategies have been developed for homogeneous traffic flows, or to reduce traffic congestion and enhance the road capacity in a symmetric two-route scenario. However, feedback strategies have rarely been considered for pedestrian-vehicle mixed traffic flows with variable velocities and sizes in an asymmetric multi-route traffic system, which is a common phenomenon in many developing countries. In this study, we propose a weighted road occupancy feedback strategy (WROFS) for pedestrian-vehicle mixed traffic flows, which considers the system equilibrium to ease traffic congestion. In order to more realistic simulating the behavior of mixed traffic objects, the paper adopted a refined and dynamic cellular automaton model (RDPV_CA model) as the update mechanism for pedestrian-vehicle mixed traffic flow. Moreover, a bounded rational threshold control was introduced into the feedback strategy to avoid some negative effect of delayed information and reduce. Based on comparisons with the two previously proposed strategies, the simulation results obtained in a pedestrian-vehicle traffic flow scenario demonstrated that the proposed strategy with a bounded rational threshold was more effective and system equilibrium, system stability were reached.

Mixing and NO(x) Emission Calculations of Confined Reacting Jet Flows in a Cylindrical Duct

Science.gov (United States)

Holdeman, James D. (Technical Monitor); Oechsle, Victor L.

2003-01-01

Rapid mixing of cold lateral jets with hot cross-stream flows in confined configurations is of practical interest in gas turbine combustors as it strongly affects combustor exit temperature quality, and gaseous emissions in for example rich-lean combustion. It is therefore important to further improve our fundamental understanding of the important processes of dilution jet mixing especially when the injected jet mass flow rate exceeds that of the cross-stream. The results reported in this report describe some of the main flow characteristics which develop in the mixing process in a cylindrical duct. A 3-dimensional tool has been used to predict the mixing flow field characteristics and NOx emission in a quench section of an RQL combustor, Eighteen configurations have been analyzed in a circular geometry in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying three parameters: 1) jet-to-mainstream momentum-flux ratio (J), 2) orifice shape or orifice aspect ratio, and 3) slot slant angle. The results indicate that the mixing flow field significantly varies with the value of the jet penetration and subsequently, slanting elongated slots generally improve the mixing uniformity at high J conditions. Round orifices produce more uniform mixing and low NO(x) emissions at low J due to the strong and adequate jet penetration. No significant correlation was found between the NO(x) production rates and the mixing deviation parameters, however, strong correlation was found between NO(x) formation and jet penetration. In the computational results, most of the NO(x) formation occurred behind the orifice starting at the orifice wake region. Additional NO(x) is formed upstream of the orifice in certain configurations with high J conditions due to the upstream recirculation.

Effect of gas quantity on two-phase flow characteristics of a mixed-flow pump

OpenAIRE

Qiang Fu; Fan Zhang; Rongsheng Zhu; Xiuli Wang

2016-01-01

The inlet gas quantity has a great influence on the performance and inner flow characteristics of a mixed-flow pump. In this article, both numerical and experimental methods are used to carry out this research work. The effects under the steady gas volume fraction state and the transient gas quantity variation process on the mixed-flow pump are investigated and compared in detail. It could be concluded that the head of the mixed-flow pump shows slight decline at the low gas volume fraction st...

Mixing of high density solution in vertical upward flow

International Nuclear Information System (INIS)

Kumamaru, Hiroshige; Hosogi, Nobuyoshi; Komada, Toshiaki; Fujiwara, Yoshiki

1999-01-01

Experimental and analytical studies have been performed in order to provide fundamental data and a numerical calculation model on the mixing of boric acid solution, injected from the standby liquid control system (SLCS), under a low natural circulation flow during an ATWS in a BWR. First, fundamental experiments on the mixing of high-density solution in vertically-upward water flow have been performed by using a small apparatus. Mixing patterns observed in the experiments have been classified to two groups, i.e. complete mixing (entrainment) and incomplete mixing (entrainment). In the complete mixing, the injected high-density solution is mixed (entrained) completely into the vertically-upward water flow. From the experiments, the minimum water flow rates in which the complete mixing (entrainment) is achieved have been obtained for various solution densities and solution injection rates. Secondly, two-dimensional numerical calculations have been performed. A continuity equation for total fluid, momentum equations in two directions and a continuity equation for solute are solved by using the finite difference method for discretization method and by following the MAC method for solution procedure. The calculations have predicted nearly the minimum water flow rate in which the complete mixing is achieved, while the calculations have been performed only for one combination of the solution density and solution injection rate until now. (author)

Transient burnout under rapid flow reduction condition

International Nuclear Information System (INIS)

Iwamura, Takamichi

1987-01-01

Burnout characteristics were experimentally studied using uniformly heated tube and annular test sections under rapid flow reduction conditions. Observations indicated that the onset of burnout under a flow reduction transient is caused by the dryout of a liquid film on the heated surface. The decrease in burnout mass velocity at the channel inlet with increasing flow reduction rate is attributed to the fact that the vapor flow rate continues to increase and sustain the liquid film flow after the inlet flow rate reaches the steady-state burnout flow rate. This is because the movement of the boiling boundary cannot keep up with the rapid reduction of inlet flow rate. A burnout model for the local condition could be applied to the burnout phenomena with the flow reduction under pressures of 0.5 ∼ 3.9 MPa and flow reduction rates of 0.6 ∼ 35 %/s. Based on this model, a method to predict the burnout time under a flow reduction condition was presented. The calculated burnout times agreed well with experimental results obtained by some investigators. (author)

The Cross-Flow Mixing Analysis of Quasi-Static Pebble Flow in Pebble Bed Reactor

International Nuclear Information System (INIS)

Fang Xiang; Liu Zhiyong; Sun Yanfei; Yang Xingtuan; Jiang Shengyao

2014-01-01

In the pebble bed reactor, large number of fuel pebbles’ movement law and moving state can affect the reactor’s design, operation and safety directly. Therefore the pebble flow, which is based on the theory of particle streaming, is one of the most important research subjects of the pebble bed reactor engineering. The in-core pebble flow is a very slow particle flow (or called quasi-static particle flow), which is very different from the usual particle motion. How to accurately describe the characteristics of in-core pebble flow is a central issue for this subject. Due to the presence of random flow, the cross-mixing phenomenon will occur inevitably. In the present paper, the mixing phenomenon of pebble flow is generalized on the basis of experiment results. The pebble flow cross-mixing probability serves as the parameter which describes both the regularity and the randomness of pebble flow. The results are provided in the form of diagrammatic presentation. (author)

Electrogates for stop-and-go control of liquid flow in microfluidics

Science.gov (United States)

Arango, Y.; Temiz, Y.; Gökçe, O.; Delamarche, E.

2018-04-01

Diagnostics based on microfluidic devices necessitate specific reagents, flow conditions, and kinetics for optimal performance. Such an optimization is often achieved using assay-specific microfluidic chip designs or systems with external liquid pumps. Here, we present "electrogates" for stop-and-go control of flow of liquids in capillary-driven microfluidic chips by combining liquid pinning and electrowetting. Electrogates are simple to fabricate and efficient: a sample pipetted to a microfluidic chip flows autonomously in 15-μm-deep hydrophilic channels until the liquid meniscus is pinned at the edge of a 1.5-μm-deep trench patterned at the bottom of a rectangular microchannel. The flow can then be resumed by applying a DC voltage between the liquid and the trench via integrated electrodes. Using a trench geometry with a semicircular shape, we show that retention times longer than 30 min are achieved for various aqueous solutions such as biological buffers, artificial urine, and human serum. We studied the activation voltage and activation delay of electrogates using a chip architecture having 6 independent flow paths and experimentally showed that the flow can be resumed in less than 1 s for voltages smaller than 10 V, making this technique compatible with low-power and portable microfluidic systems. Electrogates therefore can make capillary-driven microfluidic chips very versatile by adding flow control in microfluidic channels in a flexible manner.

Rapid flow imaging method

International Nuclear Information System (INIS)

Pelc, N.J.; Spritzer, C.E.; Lee, J.N.

1988-01-01

A rapid, phase-contrast, MR imaging method of imaging flow has been implemented. The method, called VIGRE (velocity imaging with gradient recalled echoes), consists of two interleaved, narrow flip angle, gradient-recalled acquisitions. One is flow compensated while the second has a specified flow encoding (both peak velocity and direction) that causes signals to contain additional phase in proportion to velocity in the specified direction. Complex image data from the first acquisition are used as a phase reference for the second, yielding immunity from phase accumulation due to causes other than motion. Images with pixel values equal to MΔΘ where M is the magnitude of the flow compensated image and ΔΘ is the phase difference at the pixel, are produced. The magnitude weighting provides additional vessel contrast, suppresses background noise, maintains the flow direction information, and still allows quantitative data to be retrieved. The method has been validated with phantoms and is undergoing initial clinical evaluation. Early results are extremely encouraging

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

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations.

Science.gov (United States)

Toh, Ren Wei; Li, Jie Sheng; Wu, Jie

2018-01-04

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

Effect of gas quantity on two-phase flow characteristics of a mixed-flow pump

Directory of Open Access Journals (Sweden)

Qiang Fu

2016-04-01

Full Text Available The inlet gas quantity has a great influence on the performance and inner flow characteristics of a mixed-flow pump. In this article, both numerical and experimental methods are used to carry out this research work. The effects under the steady gas volume fraction state and the transient gas quantity variation process on the mixed-flow pump are investigated and compared in detail. It could be concluded that the head of the mixed-flow pump shows slight decline at the low gas volume fraction state, while it decreases sharply at the high gas volume fraction state and then decreases with the increasing gas quantity. There is an obvious asymmetric blade vapor density on the blade suction side under each cavitation state. The cavities can be weakened obviously by increasing the inlet gas volume fraction within a certain range. It has little influence on the internal unsteady flow of the mixed-flow pump when the gas volume fraction is less than 10%, but the pump starts to operate with a great unsteady characteristic when the inlet gas volume fraction increases to 15%.

Train Stop Scheduling in a High-Speed Rail Network by Utilizing a Two-Stage Approach

Directory of Open Access Journals (Sweden)

Huiling Fu

2012-01-01

Full Text Available Among the most commonly used methods of scheduling train stops are practical experience and various “one-step” optimal models. These methods face problems of direct transferability and computational complexity when considering a large-scale high-speed rail (HSR network such as the one in China. This paper introduces a two-stage approach for train stop scheduling with a goal of efficiently organizing passenger traffic into a rational train stop pattern combination while retaining features of regularity, connectivity, and rapidity (RCR. Based on a three-level station classification definition, a mixed integer programming model and a train operating tactics descriptive model along with the computing algorithm are developed and presented for the two stages. A real-world numerical example is presented using the Chinese HSR network as the setting. The performance of the train stop schedule and the applicability of the proposed approach are evaluated from the perspective of maintaining RCR.

Analysis of stratified flow mixing

International Nuclear Information System (INIS)

Soo, S.L.; Lyczkowski, R.W.

1985-01-01

The Creare 1/5-scale Phase II experiments which model fluid and thermal mixing of relatively cold high pressure injection (HPI) water into a cold leg of a full-scale pressurized water reactor (PWR) having loop flow are analyzed and found that they cannot achieve complete similarity with respect to characteristic Reynolds and Froude numbers and developing hydrodynamic entry length. Several analyses show that these experiments fall into two distinct regimes of mixing: momentum controlled and gravity controlled (stratification). 18 refs., 9 figs

Probing Light Stops with Stoponium

CERN Document Server

Batell, Brian

2015-01-01

We derive new limits on light stops from diboson resonance searches in the $\\gamma\\gamma$, $Z \\gamma$, $ZZ$, $WW$ and $hh$ channels from the first run of the LHC. If the two-body decays of the light stop are mildly suppressed or kinematically forbidden, stoponium bound states will form in $pp$ collisions and subsequently decay via the pair annihilation of the constituent stops to diboson final states, yielding striking resonance signatures. Remarkably, we find that stoponium searches are highly complementary to direct collider searches and indirect probes of light stops such as Higgs coupling measurements. Using an empirical quarkonia potential model and including the first two $S$-wave stoponium states, we find that in the decoupling limit $m_{\\widetilde t_1} \\lesssim 130$ GeV is excluded for any value of the stop mixing angle and heavy stop mass by the combination of the latest resonance searches and the indirect constraints. The $\\gamma \\gamma$ searches are the most complementary to the indirect constraint...

Analysis of impact of mixing flow on the pebble bed high temperature reactor

International Nuclear Information System (INIS)

Hao Chen; Li Fu; Guo Jiong

2014-01-01

The impact of the mixing flow in the pebble flow on pebble bed high temperature gas cooled reactor (HTR) was analyzed in the paper. New code package MFVSOP which can simulate the mixing flow was developed. The equilibrium core of HTR-PM was selected as reference case, the impact of the mixing flow on the core parameters such as core power peak factor, power distribution was analyzed with different degree of mixing flow, and uncertainty analysis was carried out. Numerical results showed that the mixing flow had little impact on key parameters of pebble bed HTR, and the multiple-pass-operation-mode in pebble bed HTR can reduce the uncertainty arouse from the mixing flow. (authors)

Fluid Mixing in the Eye Under Rapid Eye Movement

Science.gov (United States)

Huang, Jinglin; Gharib, Morteza

2017-11-01

Drug injection is an important technique in certain treatments of eye diseases. The efficacy of chemical mixing plays an important role in determining pharmacokinetics of injected drugs. In this study, we build a device to study the chemical mixing behavior in a spherical structure. The mixing process is visualized and analyzed qualitatively. We hope to understand the chemical convection and diffusion behaviors in correlation with controlled rapid mechanical movements. The results will have potential applications in treatment of eye diseases. Resnick Institute at Caltech.

Mixing and NOx Emission Calculations of Confined Reacting Jet Flows in Cylindrical and Annular Ducts

Science.gov (United States)

Oechsle, Victor L.; Connor, Christopher H.; Holdeman, James D. (Technical Monitor)

2000-01-01

Rapid mixing of cold lateral jets with hot cross-stream flows in confined configurations is of practical interest in gas turbine combustors as it strongly affects combustor exit temperature quality, and gaseous emissions in for example rich-lean combustion. It is therefore important to further improve our fundamental understanding of the important processes of dilution jet mixing especially when the injected jet mass flow rate exceeds that of the cross-stream. The results reported in this report describe some of the main flow characteristics which develop in the mixing process in a cylindrical duct. A three-dimensional computational fluid dynamics (CFD) code has been used to predict the mixing flow field characteristics and NOx emission in a quench section of a rich-burn/quick-mix/lean-burn (RQL) combustor. Sixty configurations have been analyzed in both circular and annular geometries in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying the number of orifices per row and orifice shape. Other parameters such as J (momentum-flux ratio), MR (mass flowrate ratio), DR (density ratio), and mixer sector orifice ACd (effective orifice area) were maintained constant throughout the entire study. The results indicate that the mixing flow field can be correlated with the NOx production if they are referenced with the stoichiometric equivalence ratio value and not the equilibrium value. The mixing flowfields in both circular and annular mixers are different. The penetration of equal jets in both annular and circular geometries is vastly different which significantly affects the performance of the mixing section. In the computational results with the circular mixer, most of the NOx formation occurred behind the orifice starting at the orifice wake region. General trends have been observed in the NOx production as the number of orifices is changed and this appears to be

Theoretical studies on the stopping power of deuterium-tritium mixed with uranium plasmas for α particles

International Nuclear Information System (INIS)

Wang, Zhigang; Fu, Zhen-Guo; Zhang, Ping

2014-01-01

The stopping power of a compressed and highly ionized deuterium-tritium (DT) and uranium (U) plasma for α particles at very high temperatures (T = 5 keV) is examined theoretically with the dimensional continuation method. We show that with increasing density of U, both the magnitude and width of the resonance peak in the stopping power (as a function of the α particle energy), increases because of the ions, while the penetration distance of the α particles decreases. A simple relation of decreasing penetration distance as a function of plasma density is observed, which may be useful for inertial confinement fusion experiments. Moreover, by comparing the results with the case of a DT plasma mixed with beryllium, we find that the effect of a higher Z plasma is stronger, with regard to energy loss as well as the penetration distance of α particles, than that of a lower Z plasma

Intermediate heat exchanger tube vibration induced by cross and parallel mixed flow

International Nuclear Information System (INIS)

Kawamura, Koji

1986-01-01

The characteristics of pool type LMFBR intermediate heat exchanger (IHX) tube vibrations induced by cross and parallel mixed flow were basically investigated. Secondary coolant in IHX tube bundle is mixed flow of parallel jit flow along the tube axis through flow holes in baffle plates and cross flow. By changing these two flow rate, flow distributions vary in the tube bundle. Mixed flow also induces vibrations which cause fretting wear and fatigue of tube. It is therefore very important to evaluate the tube vibration characteristics for estimating the tube integrity. The results show that the relationships between tube vibrations and flow distributions in the tube bundle were cleared, and mixed flow induced tube vibration could be evaluated on the base of the characteristics of both parallel and cross flow induced vibration. From these investigations it could be concluded that the characteristics of tube vibration for various flow distributions can be systematically evaluated. (author)

Optimized open-flow mixing: insights from microbubble streaming

Science.gov (United States)

Rallabandi, Bhargav; Wang, Cheng; Guo, Lin; Hilgenfeldt, Sascha

2015-11-01

Microbubble streaming has been developed into a robust and powerful flow actuation technique in microfluidics. Here, we study it as a paradigmatic system for microfluidic mixing under a continuous throughput of fluid (open-flow mixing), providing a systematic optimization of the device parameters in this practically important situation. Focusing on two-dimensional advective stirring (neglecting diffusion), we show through numerical simulation and analytical theory that mixing in steady streaming vortices becomes ineffective beyond a characteristic time scale, necessitating the introduction of unsteadiness. By duty cycling the streaming, such unsteadiness is introduced in a controlled fashion, leading to exponential refinement of the advection structures. The rate of refinement is then optimized for particular parameters of the time modulation, i.e. a particular combination of times for which the streaming is turned ``on'' and ``off''. The optimized protocol can be understood theoretically using the properties of the streaming vortices and the throughput Poiseuille flow. We can thus infer simple design principles for practical open flow micromixing applications, consistent with experiments. Current Address: Mechanical and Aerospace Engineering, Princeton University.

Intermediate flow mixing nonsupport grid for BWR fuel assembly

International Nuclear Information System (INIS)

Taleyarkhan, R.P.

1987-01-01

An intermediate flow mixing nonsupport grid is described for use in a nuclear reactor fuel assembly containing an array of elongated fuel rods. The grid comprises: (a) interleaved inner straps arranged in an egg-crate configuration to define inner cell openings for receiving respective ones of the fuel rods. The inner straps have outer terminal end portions; (b) an outer peripheral strap attached to the respective terminal end portions of the inner straps to define perimeter cell openings for receiving other ones of the fuel rods. The inner straps and outer strap together have opposite upstream and downstream sides; (c) a first group of mixing vanes disposed at the downstream side and being attached on portions of the outer strap and on respective portions of the inner straps. Together with the outer strap portions, they define the perimeter cell openings. Each of the mixing vanes of the first group extend generally in a downstream direction and inwardly toward the perimeter cell openings for deflecting coolant flowing; and (d) a second group of mixing vanes disposed at the downstream side and being attached on other portions of the inner straps. Together with the respective portions, they define the inner cell openings. Each of the mixing vanes of the second group extend generally in a downstream direction and inwardly toward the inner cell openings for deflecting coolant flowing therethrough; (e) the mixing vanes of the second group are substantially smaller in size than the mixing vanes of the first group so as to generate substantially less turbulence in the portions of the coolant flowing through the inner cell openings than in the portions of the coolant flowing through the perimeter cell openings

Stopped-flow studies of spectral changes in human serum albumin following an alkaline pH jump

DEFF Research Database (Denmark)

Honoré, B

1987-01-01

A stopped-flow technique was used to study the spectral changes occurring in albumin following a pH jump from 11.3 to 11.8 at 25 degrees C. Ultraviolet difference spectra between various albumin species participating in the process are reported. These spectra are similar in shape to the difference...

An experimental and numerical study of a jetfire stop material and a new helical flow heat exchanger

Energy Technology Data Exchange (ETDEWEB)

Austegard, Anders

1997-12-31

This thesis consists of two parts. Part 1: Experimental and numerical study of jetfire stop, and Part 2: Experimental and numerical study of a new kind of shell and tube heat exchanger with helical flow on shell side. Part 1 describes the development of the model for simulation of the temperature development through Viking jetfirestop. A simulation program is developed that calculates the temperature development through Viking jetfire stop. In the development of the model, measurements of reaction energy, pyrolysis and heat conductivity at low temperatures are made. The conductivity at higher temperatures and when pyrolysis reactions are going on is estimated experimentally and by numerical calculations. Full-scale jet fire test and small-scale xenon lamp experiments are made to test the simulation model. Part 2 contains the development of a model that simulate the fluid flow and heat transfer in a helical flow shell and tube heat exchanger. It consists of the development of a porosity model and a model for pressure drop and heat transfer as well as experiments in non-standard tube layouts. Results from the simulation program are compared with experiments on a helical flow shell and tube heat exchanger. There is a separate appendix volume. 62 refs., 152 figs., 22 tabs.

A microfluidics-based technique for automated and rapid labeling of cells for flow cytometry

International Nuclear Information System (INIS)

Patibandla, Phani K; Estrada, Rosendo; Kannan, Manasaa; Sethu, Palaniappan

2014-01-01

Flow cytometry is a powerful technique capable of simultaneous multi-parametric analysis of heterogeneous cell populations for research and clinical applications. In recent years, the flow cytometer has been miniaturized and made portable for application in clinical- and resource-limited settings. The sample preparation procedure, i.e. labeling of cells with antibodies conjugated to fluorescent labels, is a time consuming (∼45 min) and labor-intensive procedure. Microfluidics provides enabling technologies to accomplish rapid and automated sample preparation. Using an integrated microfluidic device consisting of a labeling and washing module, we demonstrate a new protocol that can eliminate sample handling and accomplish sample and reagent metering, high-efficiency mixing, labeling and washing in rapid automated fashion. The labeling module consists of a long microfluidic channel with an integrated chaotic mixer. Samples and reagents are precisely metered into this device to accomplish rapid and high-efficiency mixing. The mixed sample and reagents are collected in a holding syringe and held for up to 8 min following which the mixture is introduced into an inertial washing module to obtain ‘analysis-ready’ samples. The washing module consists of a high aspect ratio channel capable of focusing cells to equilibrium positions close to the channel walls. By introducing the cells and labeling reagents in a narrow stream at the center of the channel flanked on both sides by a wash buffer, the elution of cells into the wash buffer away from the free unbound antibodies is accomplished. After initial calibration experiments to determine appropriate ‘holding time’ to allow antibody binding, both modules were used in conjunction to label MOLT-3 cells (T lymphoblast cell line) with three different antibodies simultaneously. Results confirm no significant difference in mean fluorescence intensity values for all three antibodies labels (p < 0.01) between the

Continuous-Flow Detector for Rapid Pathogen Identification

Energy Technology Data Exchange (ETDEWEB)

Barrett, Louise M. [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Microfluidics; Skulan, Andrew J. [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Microfluidics; Singh, Anup K. [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Microfluidics; Cummings, Eric B. [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Microfluidics; Fiechtner, Gregory J. [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Microfluidics

2006-09-01

This report describes the continued development of a low-power, portable detector for the rapid identification of pathogens such as B. anthracis and smallpox. Based on our successful demonstration of the continuous filter/concentrator inlet, we believe strongly that the inlet section will enable differentiation between viable and non-viable populations, between types of cells, and between pathogens and background contamination. Selective, continuous focusing of particles in a microstream enables highly selective and sensitive identification using fluorescently labeled antibodies and other receptors such as peptides, aptamers, or small ligands to minimize false positives. Processes such as mixing and lysing will also benefit from the highly localized particle streams. The concentrator is based on faceted prisms to contract microfluidic flows while maintaining uniform flowfields. The resulting interfaces, capable of high throughput, serve as high-, low-, and band-pass filters to direct selected bioparticles to a rapid, affinity-based detection system. The proposed device is superior to existing array-based detectors as antibody-pathogen binding can be accomplished in seconds rather than tens of minutes or even hours. The system is being designed to interface with aerosol collectors under development by the National Laboratories or commercial systems. The focused stream is designed to be interrogated using diode lasers to differentiate pathogens by light scattering. Identification of particles is done using fluorescently labeled antibodies to tag the particles, followed by multiplexed laser-induced fluorescence (LIF) detection (achieved by labeling each antibody with a different dye).

Kinetic Spectrophotometric Method for the 1,4-Diionic Organophosphorus Formation in the Presence of Meldrum′s Acid: Stopped-Flow Approach

Directory of Open Access Journals (Sweden)

Fatemeh Ghodsi

2016-11-01

Full Text Available The kinetics of the reaction between triphenylphosphine (TPP and dimethyl acetylenedicarboxylate (DMAD in the presence of Meldrum’s acid (MA for the generation of the 1,4-diionic organophosphorus compound has been investigated using the stopped-flow and UV-VIS spectrophotometry techniques. The first step of the reaction between TPP and DMAD for the generation of (I1 in ethanol was followed by the stopped-flow apparatus. This step was recognized as a fast step. The reaction between the intermediate (I1 and MA showed first-order kinetics, and it was followed by the UV-VIS spectrophotometry technique. The activation parameters for the slow step of the proposed mechanism were determined using two linearized forms of the Eyring equation. From the temperature, concentration and solvent studies, the activation energy (Ea = 20.16 kJ·mol−1 and the related activation parameters (ΔG‡ = 71.17 ± 0.015 kJ·mol−1, ΔS‡ = −185.49 ± 0.026 J·mol−1 and ΔH‡ =17.72 ± 0.007 kJ·mol−1 were calculated. The experimental data indicated that the reaction was zero-order in MA and second-order overall. The proposed mechanism was confirmed with the observed kinetic data obtained from the UV-VIS and stopped-flow techniques.

A new algorithm for extended nonequilibrium molecular dynamics simulations of mixed flow

NARCIS (Netherlands)

Hunt, T.A.; Hunt, Thomas A.; Bernardi, Stefano; Todd, B.D.

2010-01-01

In this work, we develop a new algorithm for nonequilibrium molecular dynamics of fluids under planar mixed flow, a linear combination of planar elongational flow and planar Couette flow. To date, the only way of simulating mixed flow using nonequilibrium molecular dynamics techniques was to impose

Cavitation performance improvement of high specific speed mixed-flow pump

International Nuclear Information System (INIS)

Chen, T; Sun, Y B; Wu, D Z; Wang, L Q

2012-01-01

Cavitation performance improvement of large hydraulic machinery such as pump and turbine has been a hot topic for decades. During the design process of the pumps, in order to minimize size, weight and cost centrifugal and mixed-flow pump impellers are required to operate at the highest possible rotational speed. The rotational speed is limited by the phenomenon of cavitation. The hydraulic model of high-speed mixed-flow pump with large flow rate and high pumping head, which was designed based on the traditional method, always involves poor cavitation performance. In this paper, on the basis of the same hydraulic design parameters, two hydraulic models of high-speed mixed-flow pump were designed by using different methods, in order to investigate the cavitation and hydraulic performance of the two models, the method of computational fluid dynamics (CFD) was adopted for internal flow simulation of the high specific speed mixed-flow pump. Based on the results of numerical simulation, the influences of impeller parameters and three-dimensional configuration on pressure distribution of the blades' suction surfaces were analyzed. The numerical simulation results shows a better pressure distribution and lower pressure drop around the leading edge of the improved model. The research results could provide references to the design and optimization of the anti-cavitation blade.

Improving mixing efficiency in a closed circuit water flow rig for ...

African Journals Online (AJOL)

. ... pulse velocity method, indicating that the flow meters functioned correctly. The modified rig with scaled-up mixing techniques could serve as platform for training in evaluating mixing vessels and flow meters in industrial process plants.

GMSB with Light Stops

CERN Document Server

Delgado, Antonio; Quiros, Mariano

2015-01-01

Gauge mediated supersymmetry breaking (GMSB) is an elegant mechanism to transmit supersymmetry breaking from the hidden to the MSSM observable sector, which solves the supersymmetric flavor problem. However the smallness of the generated stop mixing requires superheavy stops to reproduce the experimental value of the Higgs mass. Two possible ways out are: i) To extend GMSB by direct superpotential messenger-MSSM Yukawa couplings to generate sizeable mixing, thus reintroducing the flavor problem; ii) To extend the MSSM Higgs sector with singlets and/or triplets providing extra tree-level corrections to the Higgs mass. Singlets will not get any soft mass from GMSB and triplets will contribute to the $\\rho$ parameter which could be an issue. In this paper we explore the second way by introducing extra supersymmetric triplets with hypercharges $Y=(0,\\pm 1)$, with a tree-level custodial $SU(2)_L\\otimes SU(2)_R$ global symmetry in the Higgs sector protecting the $\\rho$ parameter: a supersymmetric generalization of ...

Review of Mixed Convection Flow Regime Map of a Vertical pipe

International Nuclear Information System (INIS)

Chae, Myeong-Seon; Chung, Bum-Jin; Kang, Gyeong-Uk

2015-01-01

In a vertical pipe, the natural convective force due to buoyancy acts upward only, but forced convective force can be either upward or downward. This determines buoyancy-aided and buoyancy-opposed flows depending on the direction of forced flow with respect to the buoyancy forces. Furthermore, depending on the exchange mechanism, the flow condition is classified into laminar and turbulent. In laminar mixed convection, buoyancy-aided flow presents enhanced heat transfer compared to the pure forced convection and buoyancy-opposed flow shows impaired heat transfer as the flow velocity affected by the buoyancy forces. However, in turbulent mixed convection, buoyancy-aided flow shows an impairment of the heat transfer rate for small buoyancy, and a gradational enhancement for large buoyancy. In this study, the existing flow regime map on mixed convection in a vertical pipe was reviewed through an analysis of literatures. Using the investigated data and heat transfer correlations, the flow regime map was reconstructed independently, and compared with the existing one. This study reviewed the limitations of the classical mixed convection flow regime map. Using the existing data and heat transfer correlations by Martinelli and Boelter and Watzinger and Johnson, the flow regime map was reconstructed independently. The results revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime were not given. And the information about uncertainty analysis and the evidentiary data were given insufficiently. The flow regime map and investigator commonly used the diameter as the characteristic length for both Re and Gr in place of the height of the heated wall, though the buoyancy forces are proportional to the third power of the height of heated wall

Rapid mixing chemical oxidative polymerization: an easy route to ...

Indian Academy of Sciences (India)

Administrator

(SDCNTs)/PANI nanofibres (NFs) has been prepared using an easy in situ rapid mixing chemical ... SDCNTs thin film was obtained using thermal chemical vapour deposition method in ... In the next step, 250 mL of aqueous HCl was taken in a.

Groundwater flow system under a rapidly urbanizing coastal city as determined by hydrogeochemistry

Science.gov (United States)

Kagabu, Makoto; Shimada, Jun; Delinom, Robert; Tsujimura, Maki; Taniguchi, Makoto

2011-01-01

In the Jakarta area (Indonesia), excessive groundwater pumping due to the rapidly increasing population has caused groundwater-related problems such as brackish water contamination in coastal areas and land subsidence. In this study, we adopted multiple hydrogeochemical techniques to demonstrate the groundwater flow system in the Jakarta area. Although almost all groundwater existing in the Jakarta basin is recharged at similar elevations, the water quality and residence time demonstrates a clear difference between the shallow and deep aquifers. Due to the rapid decrease in the groundwater potential in urban areas, we found that the seawater intrusion and the shallow and deep groundwaters are mixing, a conclusion confirmed by major ions, Br -:Cl - ratios, and chlorofluorocarbon (CFC)-12 analysis. Spring water and groundwater samples collected from the southern mountainside area show younger age characteristics with high concentrations of 14C and Ca-HCO 3 type water chemistry. We estimated the residence times of these groundwaters within 45 years under piston flow conditions by tritium analysis. Also, these groundwater ages can be limited to 20-30 years with piston flow evaluated by CFCs. Moreover, due to the magnitude of the CFC-12 concentration, we can use a pseudo age indicator in this field study, because we found a positive correlation between the major type of water chemistry and the CFC-12 concentration.

Effect on Non-Newtonian Rheology on Mixing in Taylor-Couette Flow

Science.gov (United States)

Cagney, Neil; Balabani, Stavroula

2017-11-01

Mixing processes within many industry applications are strongly affected by the rheology of the working fluid. This is particularly relevant for pharmaceutical, food and waste treatment industries, where the working fluids are often strongly non-Newtonian, and significant variations in rheology between batches may occur. We approach the question of how rheology affects mixing by focussing on a the classical case of Taylor-Couette flow, which exhibits a number of instabilities and flow regimes as a function of Reynolds number. We examine Taylor-Couette flow generated for a range of aqueous solutions of xantham gum or corn starch, such that the rheology varies from shear-thinning to shear-thickening. For each case, we measure the power consumption using a torque meter and the flow field using high speed, time-resolved Particle-Image Velocimetry. The mixing characteristics are quantified using a number of Lagrangian and Eulerian approaches, including the coarse grained density method and vortex strength. By comparing these metrics to the power number, we discuss how the mixing efficiency (ratio of mixing effectiveness to power input) varies with the flow index of the fluid.

Mixing and axial dispersion in Taylor-Couette flow: experimental and numerical study

International Nuclear Information System (INIS)

Nemri, M.

2013-01-01

Taylor-Couette flows between two concentric cylinders have great potential applications in chemical engineering. They are particularly convenient for two-phase small scale devices enabling solvent extraction operations. An experimental device was designed with this idea in mind. It consists of two concentric cylinders with the inner one rotating and the outer one fixed. Taylor-Couette flows take place in the annular gap between them, and are known to evolve towards turbulence through a sequence of successive instabilities. Macroscopic quantities, such as axial dispersion and mixing index, are extremely sensitive to these flow structures, which may lead to flawed modelling of the coupling between hydrodynamics and mass transfer. This particular point has been studied both experimentally and numerically. The flow and mixing have been characterized by means of flow visualization and simultaneous PIV (Particle Imaging Velocimetry) and PLIF (Planar Laser Induced Fluorescence) measurements. PLIF visualizations showed clear evidences of different transport mechanisms including 'intra-vortex mixing' and 'inter-vortex mixing'. Under WVF and MWVF regimes, intra-vortex mixing is controlled by chaotic advection, due to the 3D nature of the flow, while inter-vortex transport occurs due to the presence of waves between neighboring vortices. The combination of these two mechanisms results in enhanced axial dispersion. We showed that hysteresis may occur between consecutive regimes depending on flow history and this may have a significant effect on mixing for a given Reynolds number. The axial dispersion coefficient Dx evolution along the successive flow states was investigated thanks to dye Residence Time Distribution measurements (RTD) and particle tracking (DNS). Both experimental and numerical results have confirmed the significant effect of the flow structure and history on axial dispersion. Our study confirmed that the commonly used 1-parameter chemical engineering models (e

Distributed simulation of mixing flow of dough

International Nuclear Information System (INIS)

Baloch, A.

2005-01-01

This paper reports on a study concerned with the numerical simulation of incompressible complex mixing flows of viscoelastic fluids is of industrial importance, particularly relevance in the food processing industry, such as occurs in dough mixing. The flows considered are in a complex domain setting. The present problem is one of this form, expressed as the flow between an outer rotating cylindrical vessel all and a stationary cylindrical/stirrers. The context is one of mixing with in a cylindrical vessel, where stirrers are located on the mixing vessel lid, and placed in a concentric/eccentric position with respect to the central cylindrical axis of the vessel. Here, the motion is considered as driven by the rotation of the outer vessel wall, with various stirrer locations. Two dough mixers at various rotation speeds are studied; one with one stirrer and the other with two stirrers. With a singular circular stirrer, an eccentric configuration is adopted. A further eccentric case with two circular stirrers is also contrasted against the above, where a symmetrical arrangement is assumed. Numerical simulations are based on two dimensions in the cylindrical polar co-ordinates system. The results reflected close agreement with the equivalent experimental results. The motivation for this work is to develop and advance technology to model the mixing of dough. The ultimate target is to predict and adjust the design of dough mixers, so that optimal dough processing may be achieved notably, with reference to work input on the dough. The hardware platform is a network combination of homogeneous Intel Linux clusters of workstations. A semi-implicit time-stepping Taylor-Galerkin scheme is employed with PVM (Parallel Virtual Machine) message passing libraries as the message passing protocol. Parallel results are compared against single processor (sequentially) solutions, using the parallelism paradigm of domain decomposition. Linear speed-up with the number of processors is

Stopped-flow kinetic studies of poly(amidoamine) dendrimer-calf thymus DNA to form dendriplexes.

Science.gov (United States)

Dey, Debabrata; Kumar, Santosh; Maiti, Souvik; Dhara, Dibakar

2013-11-07

Poly(amidoamine) (PAMAM) dendrimers are known to be highly efficient nonviral carriers in gene delivery. Dendrimer-mediated transfection is known to be a function of the dendrimer to DNA charge ratio as well as the size of the dendrimer. In the present study, the binding kinetics of four PAMAM dendrimers (G1, G2, G3, and G4) with calf thymus DNA (CT-DNA) has been studied using stopped-flow fluorescence spectroscopy. The effect of dendrimer-to-DNA charge ratio and dendrimer generation on the binding kinetics was investigated. In most cases, the results of dendrimer-CT-DNA binding can be explained by a two-step reaction mechanism: a rapid electrostatic binding between the dendrimer and DNA, followed by a conformational change of the dendrimer-DNA complex that ultimately leads to DNA condensation. It was observed that the charge ratio on the dendrimer and the DNA phosphate groups, as well as the dendrimer generation (size), has a marked effect on the kinetics of binding between the DNA and the dendrimers. The rate constant (k'1) of the first step was much higher compared to that of the second step (k'2), and both were found to increase with an increase in dendrimer concentration. Among the four generations of dendrimers, G4 exhibited significantly faster binding kinetics compared to the three smaller generation dendrimers.

PIV measurement of turbulent mixing layer flow with polymer additives

International Nuclear Information System (INIS)

Ning, T; Guo, F; Chen, B; Zhang, X

2009-01-01

Turbulent mixing layer flow with polymer additives was experimentally investigated by PIV in present paper. The velocity ratio between high and low speed is 4:1 and the Reynolds number for pure water case based on the velocity differences of two steams and hydraulic diameter of the channel ranges from 14667∼73333. Flow field and turbulent quantities of turbulent mixing layer with 200ppm polymer additives were measured and compared with pure water mixing layer flow. It is shown that the dynamic development of mixing layer is greatly influenced by polymer addictives. The smaller vortices are eliminated and the coherent structure is much clearer. Similar with pure water case, Reynolds stress and vorticity still concentrate in a coniform area of central part of mixing layer and the width will increase with the Reynolds number increasing. However, compared with pure water case, the coniform width of polymer additives case is larger, which means the polymer additives will lead to the diffusion of coherent structure. The peak value of vorticity in different cross section will decrease with the development of mixing layer. Compared with pure water case, the vorticity is larger at the beginning of the mixing layer but decreases faster in the case with polymer additives.

Neutronics of a mixed-flow gas-core reactor

International Nuclear Information System (INIS)

Soran, P.D.; Hansen, G.E.

1977-11-01

The study was made to investigate the neutronic feasibility of a mixed-flow gas-core reactor. Three reactor concepts were studied: four- and seven-cell radial reactors and a seven-cell scallop reactor. The reactors were fueled with UF 6 (either U-233 or U-235) and various parameters were varied. A four-cell reactor is not practical nor is the U-235 fueled seven-cell radial reactor; however, the 7-cell U-233 radial and scallop reactors can satisfy all design criteria. The mixed flow gas core reactor is a very attractive reactor concept and warrants further investigation

Powerful Swirl Generation of Flow-driven Rotating Mixing Vane for Enhancing CHF

International Nuclear Information System (INIS)

Seo, Han; Seo, Seok Bin; Heo, Hyo; Bang, In Cheol

2014-01-01

Mixing vanes are utilized to improve CHF and heat transfer performance in the rod bundle during normal operation. Experimental measurement of the swirling flow from a split vane pair was conducted using particle image velocimetry (PIV) and boroscope. The lateral velocity fields show that the swirling flow was initially centered in the subchannel and the computational fluid dynamics (CFD) analysis was performed based on the experiment. To visualize flow patterns in the 5Χ5 subchannel using PIV, matching the refraction between the working fluid and the structure was considered and the experiment aimed to develop the experimental data for providing fundamental information of the CFD analysis. The fixed split vane is the main mixing inducer in the fuel assembly. In a heat exchanger research, propeller type swirl generates at several pitch ratios and different blades angles were used to enhance heat transfer rate. Significant improvements of the heat transfer rate using the propellers were confirmed due to creation of tangential flow. In the present study, the mixing effect of rotation vane which has a shape of propeller was studied using PIV. A split vane was considered in the experiment to show the effect of rotation vane. Vertical and horizontal flow analyses were conducted to show the possible use of rotation vane in a subchannel. In the present work, the study of flow visualization using three types of vanes is conducted to show the mixing effect. The vertical flow and the horizontal flow distributions were analyzed in the two experimental facilities. For the vertical flow facility, flow distributions, flow profiles, and the turbulence kinetic energy are analyzed at the centerline of the channel. The results show that the rotation vane has the highest flow and turbulence kinetic intensity at the centerline of the channel. For the horizontal flow facility, the results indicate that lateral flow of the rotation vane is generated and maintained along with the flow

Mixed finite element simulations in two-dimensional groundwater flow problems

International Nuclear Information System (INIS)

Kimura, Hideo

1989-01-01

A computer code of groundwater flow in two-dimensional porous media based on the mixed finite element method was developed for accurate approximations of Darcy velocities in safety evaluation of radioactive waste disposal. The mixed finite element procedure solves for both the Darcy velocities and pressure heads simultaneously in the Darcy equation and continuity equation. Numerical results of a single well pumping at a constant rate in a uniform flow field showed that the mixed finite element method gives more accurate Darcy velocities nearly 50 % on average error than standard finite element method. (author)

Density effect on the mixing efficiency and flow modes in T-shaped micromixers

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Lobasov Alexander

2017-01-01

Full Text Available Flow patterns and mixing of liquids with different densities in T-shaped micromixers are numerically investigated at Reynolds number range from 1 to 250. The density ratio of the mixing media varies from 1 to 2; its effect on the flow structure and the mixing is studied. The dependences of the mixing efficiency and the pressure difference in this mixer on the density ratio and the Reynolds number are obtained. It is shown that the density ratio has a considerable effect on the flow structure, especially before the transition from the symmetric to the asymmetric flow pattern.

Effect of shock interactions on mixing layer between co-flowing supersonic flows in a confined duct

Science.gov (United States)

Rao, S. M. V.; Asano, S.; Imani, I.; Saito, T.

2018-03-01

Experiments are conducted to observe the effect of shock interactions on a mixing layer generated between two supersonic streams of Mach number M _{1} = 1.76 and M _{2} = 1.36 in a confined duct. The development of this mixing layer within the duct is observed using high-speed schlieren and static pressure measurements. Two-dimensional, compressible Reynolds averaged Navier-Stokes equations are solved using the k-ω SST turbulence model in Fluent. Further, adverse pressure gradients are imposed by placing inserts of small ( boundary layer thickness) thickness on the walls of the test section. The unmatched pressures cause the mixing layer to bend and lead to the formation of shock structures that interact with the mixing layer. The mixing layer growth rate is found to increase after the shock interaction (nearly doubles). The strongest shock is observed when a wedge insert is placed in the M _{2} flow. This shock interacts with the mixing layer exciting flow modes that produce sinusoidal flapping structures which enhance the mixing layer growth rate to the maximum (by 1.75 times). Shock fluctuations are characterized, and it is observed that the maximum amplitude occurs when a wedge insert is placed in the M _{2} flow.

Predicting the enhancement of mixing-driven reactions in nonuniform flows using measures of flow topology.

Science.gov (United States)

Engdahl, Nicholas B; Benson, David A; Bolster, Diogo

2014-11-01

The ability for reactive constituents to mix is often the key limiting factor for the completion of reactions across a huge range of scales in a variety of media. In flowing systems, deformation and shear enhance mixing by bringing constituents into closer proximity, thus increasing reaction potential. Accurately quantifying this enhanced mixing is key to predicting reactions and typically is done by observing or simulating scalar transport. To eliminate this computationally expensive step, we use a Lagrangian stochastic framework to derive the enhancement to reaction potential by calculating the collocation probability of particle pairs in a heterogeneous flow field accounting for deformations. We relate the enhanced reaction potential to three well known flow topology metrics and demonstrate that it is best correlated to (and asymptotically linear with) one: the largest eigenvalue of the (right) Cauchy-Green tensor.

Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

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Xiaojun Li

2013-01-01

Full Text Available Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.

Mixed Platoon Flow Dispersion Model Based on Speed-Truncated Gaussian Mixture Distribution

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Weitiao Wu

2013-01-01

Full Text Available A mixed traffic flow feature is presented on urban arterials in China due to a large amount of buses. Based on field data, a macroscopic mixed platoon flow dispersion model (MPFDM was proposed to simulate the platoon dispersion process along the road section between two adjacent intersections from the flow view. More close to field observation, truncated Gaussian mixture distribution was adopted as the speed density distribution for mixed platoon. Expectation maximum (EM algorithm was used for parameters estimation. The relationship between the arriving flow distribution at downstream intersection and the departing flow distribution at upstream intersection was investigated using the proposed model. Comparison analysis using virtual flow data was performed between the Robertson model and the MPFDM. The results confirmed the validity of the proposed model.

Stopped Flow Kinetics of MnII Catalysed Periodate Oxidation of 2, 3- dimethylaniline - Evaluation of Stability Constant of the Ternary Intermediate Complex

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Rajneesh Dutt Kaushik

2015-03-01

Full Text Available The formation of ternary intermediate unstable complex during the oxidation of aromatic amines by periodate ion catalysed by MnII has been proposed in case of some anilines. This paper is the first report on stopped-flow kinetic study and evaluation of stability constant of ternary complex forming in the MnII - catalysed periodate oxidation of 2, 3-dimethylaniline (D in acetone-water medium. Stop-flow spectrophotometric method was used to study the ternary complex formation and to determine its stability constant. The stop-flow trace shows the reaction to occur in two steps. The first step, which is presumably the formation of ternary complex, is relatively fast while the second stage is relatively quite slow. The stability constant evaluated for D - MnII - IO4- ternary complex by determining  equilibrium absorbance is (2.2 ± 1.0 × 105. Kinetics of ternary complex formation was defined by the rate law(A  under pseudo first order conditions. ln{[C2]eq / ( [C2]eq -[C2]} = kobs . t (A where, kobs is the pseudo first order rate constant, [C2] is concentration of ternary complex at given time t, and [C2]eq is the equilibrium concentration of ternary complex. © 2015 BCREC UNDIP. All rights reservedReceived: 3rd October 2014; Revised: 4th December 2014; Accepted: 15th December 2014How to Cite: Kaushik, R.D., Agarwal, R., Tyagi, P., Singh, O., Singh, J. (2015. Stopped Flow Kinetics of MnII Catalysed Periodate Oxidation of 2,3-dimethylaniline - Evaluation of Stability Constant of the Ternary Intermediate Complex. Bulletin of Chemical Reaction Engineering & Catalysis, 10 (1: 78-87. (doi:10.9767/bcrec.10.1.7621.78-87Permalink/DOI: http://dx.doi.org/10.9767/bcrec.10.1.7621.78-87

Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows

Science.gov (United States)

Kumar, Haribalan; Tawhai, Merryn H.; Hoffman, Eric A.; Lin, Ching-Long

2011-01-01

Study of mixing is important in understanding transport of submicron sized particles in the acinar region of the lung. In this article, we investigate transport in view of advective mixing utilizing Lagrangian particle tracking techniques: tracer advection, stretch rate and dispersion analysis. The phenomenon of steady streaming in an oscillatory flow is found to hold the key to the origin of kinematic mixing in the alveolus, the alveolar mouth and the alveolated duct. This mechanism provides the common route to folding of material lines and surfaces in any region of the acinar flow, and has no bearing on whether the geometry is expanding or if flow separates within the cavity or not. All analyses consistently indicate a significant decrease in mixing with decreasing Reynolds number (Re). For a given Re, dispersion is found to increase with degree of alveolation, indicating that geometry effects are important. These effects of Re and geometry can also be explained by the streaming mechanism. Based on flow conditions and resultant convective mixing measures, we conclude that significant convective mixing in the duct and within an alveolus could originate only in the first few generations of the acinar tree as a result of nonzero inertia, flow asymmetry, and large Keulegan–Carpenter (KC) number. PMID:21580803

Effect of flow rate distribution at the inlet on hydrodynamic mixing in narrow rectangular multi-channel

International Nuclear Information System (INIS)

Xu Jianjun; Chen Bingde; Wang Xiaojun

2008-01-01

Flow and heat transfer in the narrow rectangular multi-channel is widely en- countered in the engineering application, hydrodynamic mixing in the narrow rectangular multi-channel is one of the important concerns. With the help of the Computational Fluid Dynamics code CFX, the effect of flow rate distribution of the main channel at the inlet on hydrodynamic mixing in the narrow rectangular multi-channel is numerical simulated. The results show that the flow rate distributions at the inlet have a great effect on hydrodynamics mixing in multi-channel, the flow rate in the main channel doesn't change with increasing the axial mixing section when the average flow rate at the inlet is set. Hydrodynamic mixing will arise in the mixing section when the different ratio of the flow rate distribution at the inlet is set, and hydrodynamic mixing increases with the difference of the flow rate distribution at the inlet increase. The trend of the flow rate distribution of the main channel is consistent during the whole axial mixing section, and hydrodynamic mixing in former 4 mixing section is obvious. (authors)

The effect of mixing-vane arrangements in a subchannel turbulent flow

International Nuclear Information System (INIS)

Ikeno, Tsutomu; Murata, Tamotsu; Kajishima, Takeo

2006-01-01

Large eddy simulation (LES) of developed turbulent flows in a rod bundle was carried out for four spacer designs. The mixing-vanes attached at the spacer were inclined at 30degC or 20deg; they were arranged to promote the swirling or convective flow. These arrangements are possible elements to compose an actual rod bundle. Our LES technique with a consistent higher-order immersed boundary method and a one-equation dynamic sub-grid scale model contributed to an efficient treatment of the complex wall configurations of rods and spacers. The computational results reasonably reproduced experimental results for the drag coefficient and the decay rate of swirling flow. The profiles of the axial velocities and the turbulence intensities indicated reasonable trend for the turbulent flow in the rod bundle. The effect of mixing-vane arrangement on the lateral flows was successfully clarified: the cross flow took the longer way on the rod surface than the swirling flow and then was more significantly influenced by momentum diffusion at the no-slip wall. Therefore, the largely inclined mixing-vanes promoted the cross flow only in the neighborhood of the spacer, the swirling flow inside a subchannel could reach farther downstream than the cross flow. (author)

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)

Electron and Positron Stopping Powers of Materials

Science.gov (United States)

SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase)   The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.

A Modified Cellular Automaton Approach for Mixed Bicycle Traffic Flow Modeling

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Xiaonian Shan

2015-01-01

Full Text Available Several previous studies have used the Cellular Automaton (CA for the modeling of bicycle traffic flow. However, previous CA models have several limitations, resulting in differences between the simulated and the observed traffic flow features. The primary objective of this study is to propose a modified CA model for simulating the characteristics of mixed bicycle traffic flow. Field data were collected on physically separated bicycle path in Shanghai, China, and were used to calibrate the CA model using the genetic algorithm. Traffic flow features between simulations of several CA models and field observations were compared. The results showed that our modified CA model produced more accurate simulation for the fundamental diagram and the passing events in mixed bicycle traffic flow. Based on our model, the bicycle traffic flow features, including the fundamental diagram, the number of passing events, and the number of lane changes, were analyzed. We also analyzed the traffic flow features with different traffic densities, traffic components on different travel lanes. Results of the study can provide important information for understanding and simulating the operations of mixed bicycle traffic flow.

Effects of the in-medium nucleon-nucleon cross section on collective flow and nuclear stopping in heavy-ion collisions in the Fermi-energy domain

Science.gov (United States)

Li, Pengcheng; Wang, Yongjia; Li, Qingfeng; Guo, Chenchen; Zhang, Hongfei

2018-04-01

With the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, a systematic investigation of the effects of in-medium nucleon-nucleon (NN ) elastic cross section on the collective flow and the stopping observables in 197Au+197Au collisions at beam energies from 40 to 150 MeV/nucleon is performed. Simulations with the medium correction factors F =σNN in -medium/σNN free=0.2 ,0.3 ,0.5 and the one obtained with the FU3FP1 parametrization which depends on both the density and the momentum are compared to the FOPI and INDRA experimental data. It is found that, to best fit the experimental data of the slope of the directed flow and the elliptic flow at midrapidity as well as the nuclear stopping, the correction factors of F =0.2 and 0.5 are required for reactions at beam energies of 40 and 150 MeV/nucleon, respectively. Whereas calculations with the FU3FP1 parametrization can simultaneously reproduce these experimental data reasonably well. And, the observed increasing nuclear stopping with increasing beam energy in experimental data can also be reproduced by using the FU3FP1 parametrization, whereas the calculated stopping power in Au + Au collisions with beam energies from 40 to 150 MeV /nucleon almost remains constant when taking F equal to a fixed value.

Filtered Rayleigh scattering mixing measurements of merging and non-merging streamwise vortex interactions in supersonic flow

Science.gov (United States)

Ground, Cody R.; Gopal, Vijay; Maddalena, Luca

2018-04-01

By introducing large-scale streamwise vortices into a supersonic flow it is possible to enhance the rate of mixing between two fluid streams. However, increased vorticity content alone does not explicitly serve as a predictor of mixing enhancement. Additional factors, particularly the mutual interactions occurring between neighboring vortical structures, affect the underlying fundamental physics that influence the rate at which the fluids mix. As part of a larger systematic study on supersonic streamwise vortex interactions, this work experimentally quantifies the average rate of mixing of helium and air in the presence of two separate modes of vortex interaction, the merging and non-merging of a pair of co-rotating vortices. In these experiments vortex-generating expansion ramps are placed on a strut injector. The freestream Mach number is set at 2.5 and helium is injected as a passive scalar. Average injectant mole fractions at selected flow planes downstream of the injector are measured utilizing the filtered Rayleigh scattering technique. The filtered Rayleigh scattering measurements reveal that, in the domain surveyed, the merging vortex interaction strongly displaces the plume from its initial horizontal orientation while the non-merging vortex interaction more rapidly mixes the helium and air. The results of the current experiments are consistent with associated knowledge derived from previous analyses of the two studied configurations which have included the detailed experimental characterization of entrainment, turbulent kinetic energy, and vorticity of both modes of vortex interaction.

Laminar/transition sweeping flow-mixing model for wire-wrapped LMFBR assemblies

International Nuclear Information System (INIS)

Burns, K.F.; Rohsenow, W.M.; Todreas, N.E.

1980-07-01

Recent interest in analyzing the thermal hydraulic characteristics of LMFBR assemblies operating in the mixed convection regime motivates the extension of the aforementioned turbulent sweeping flow model to low Reynolds number flows. The accuracy to which knowledge of the mixing parameters is required has not been well determined, due to the increased influence of conduction and buoyancy effects with respect to energy transport at low Reynolds numbers. This study represents a best estimate attempt to correlate the existing low Reynolds number sweeping flow data. The laminar/transition model which is presented is expected to be useful in anayzing mixed convection conditions. However, the justification for making additional improvemements is contingent upon two factors. First, the ability of the proposed laminar/transition model to predict additional low Reynolds number sweeping flow data for other geometries needs to be investigated. Secondly, the sensitivity of temperature predictions to uncertainties in the values of the sweeping flow parameters should be quantified

Mixing enhancement strategies and their mechanisms in supersonic flows: A brief review

Science.gov (United States)

Huang, Wei

2018-04-01

Achieving efficient fuel-air mixing is a crucial issue in the design of the scramjet engine due to the compressibility effect on the mixing shear layer growth and the stringent flow residence time limitation induced by the high-speed crossflow, and the potential solution is to enhance mixing between air and fuel by introducing of streamwise vortices in the flow field. In this survey, some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years, as well as their mixing augmentation mechanisms, were reviewed in detail, namely the pulsed transverse injection scheme, the traditional transverse injection coupled with the vortex generator, and the dual transverse injection system with a front porthole and a rear air porthole arranged in tandem. The streamwise vortices, through the large-scale stirring motion that they introduce, are responsible for the extraction of large amounts of energy from the mean flow that can be converted into turbulence, ultimately leading to increased mixing effectiveness. The streamwise vortices may be obtained by taking advantage of the shear layer between a jet and the cross stream or by employing intrusive physical devices. Finally, a promising mixing enhancement strategy in supersonic flows was proposed, and some remarks were provided.

Stop Flow Lithography Synthesis and Characterization of Structured Microparticles

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David Baah

2014-01-01

Full Text Available In this study, the synthesis of nonspherical composite particles of poly(ethylene glycol diacrylate (PEG-DA/SiO2 and PEG-DA/Al2O3 with single or multiple vias and the corresponding inorganic particles of SiO2 and Al2O3 synthesized using the Stop Flow Lithography (SFL method is reported. Precursor suspensions of PEG-DA, 2-hydroxy-2-methylpropiophenone, and SiO2 or Al2O3 nanoparticles were prepared. The precursor suspension flows through a microfluidic device mounted on an upright microscope and is polymerized in an automated process. A patterned photomask with transparent geometric features masks UV light to synthesize the particles. Composite particles with vias were synthesized and corresponding inorganic SiO2 and Al2O3 particles were obtained through polymer burn-off and sintering of the composites. The synthesis of porous inorganic particles of SiO2 and Al2O3 with vias and overall dimensions in the range of ~35–90 µm was achieved. BET specific surface area measurements for single via inorganic particles were 56–69 m2/g for SiO2 particles and 73–81 m2/g for Al2O3 particles. Surface areas as high as 114 m2/g were measured for multivia cubic SiO2 particles. The findings suggest that, with optimization, the particles should have applications in areas where high surface area is important such as catalysis and sieving.

Turbulent mixing between subchannels in a gas-liquid two-phase flow. For the equilibrium flow without net fluid transfer between subchannels

International Nuclear Information System (INIS)

Kawahara, Akimaro; Sadatomi, Michio; Sato, Yoshifusa; Saito, Hidetoshi.

1995-01-01

To provide data necessary for modeling turbulent mixing between subchannels in a nuclear fuel rod bundle, three experiments were made in series for equilibrium two-phase flows, in which net mass exchange does not occur between subchannels for each phase. The first one was the measurement of turbulent mixing rates of both gas and liquid phases by a tracer technique, using air and water as the working fluids. Three kinds of vertical test channels consisting of two subchannels were used. The data have shown that the turbulent mixing rate of each phase in a two-phase flow is strongly dependent on flow regime. So, to see the relation between turbulent mixing and two-phase flow configuration in the subchannels, the second experiment, flow visualization, was made. It was observed in slug and churn flows that a lateral inter-subchannel liquid flow of a large scale is caused by the successive axial transit of large gas bubbles in each subchannel, and the turbulent mixing for the liquid phase is dominated by this lateral flow. To investigate a driving force of such large scale lateral flow, the third experiment, the measurement of an instantaneous pressure differential between the subchannels, was made. The result showed that there is a close relationship between the liquid phase mixing rate and the magnitude of the pressure differential fluctuation. (author)

Extreme concentration fluctuations due to local reversibility of mixing in turbulent flows

Science.gov (United States)

Xia, Hua; Francois, Nicolas; Punzmann, Horst; Szewc, Kamil; Shats, Michael

2018-05-01

Mixing of a passive scalar in a fluid (e.g. a radioactive spill in the ocean) is the irreversible process towards homogeneous distribution of a substance. In a moving fluid, due to the chaotic advection [H. Aref, J. Fluid Mech. 143 (1984) 1; J. M. Ottino, The Kinematics of Mixing: Stretching,Chaos and Transport (Cambridge University Press, Cambridge, 1989)] mixing is much faster than if driven by molecular diffusion only. Turbulence is known as the most efficient mixing flow [B. I. Shraiman and E. D. Siggia, Nature 405 (2000) 639]. We show that in contrast to spatially periodic flows, two-dimensional turbulence exhibits local reversibility in mixing, which leads to the generation of unpredictable strong fluctuations in the scalar concentration. These fluctuations can also be detected from the analysis of the fluid particle trajectories of the underlying flow.

Mixing-induced quantum non-Markovianity and information flow

Science.gov (United States)

Breuer, Heinz-Peter; Amato, Giulio; Vacchini, Bassano

2018-04-01

Mixing dynamical maps describing open quantum systems can lead from Markovian to non-Markovian processes. Being surprising and counter-intuitive, this result has been used as argument against characterization of non-Markovianity in terms of information exchange. Here, we demonstrate that, quite the contrary, mixing can be understood in a natural way which is fully consistent with existing theories of memory effects. In particular, we show how mixing-induced non-Markovianity can be interpreted in terms of the distinguishability of quantum states, system-environment correlations and the information flow between system and environment.

Development and numerical analysis of low specific speed mixed-flow pump

International Nuclear Information System (INIS)

Li, H F; Huo, Y W; Pan, Z B; Zhou, W C; He, M H

2012-01-01

With the development of the city, the market of the mixed flow pump with large flux and high head is prospect. The KSB Shanghai Pump Co., LTD decided to develop low speed specific speed mixed flow pump to meet the market requirements. Based on the centrifugal pump and axial flow pump model, aiming at the characteristics of large flux and high head, a new type of guide vane mixed flow pump was designed. The computational fluid dynamics method was adopted to analyze the internal flow of the new type model and predict its performances. The time-averaged Navier-Stokes equations were closed by SST k-ω turbulent model to adapt internal flow of guide vane with larger curvatures. The multi-reference frame(MRF) method was used to deal with the coupling of rotating impeller and static guide vane, and the SIMPLEC method was adopted to achieve the coupling solution of velocity and pressure. The computational results shows that there is great flow impact on the head of vanes at different working conditions, and there is great flow separation at the tailing of the guide vanes at different working conditions, and all will affect the performance of pump. Based on the computational results, optimizations were carried out to decrease the impact on the head of vanes and flow separation at the tailing of the guide vanes. The optimized model was simulated and its performance was predicted. The computational results show that the impact on the head of vanes and the separation at the tailing of the guide vanes disappeared. The high efficiency of the optimized pump is wide, and it fit the original design destination. The newly designed mixed flow pump is now in modeling and its experimental performance will be getting soon.

Development and numerical analysis of low specific speed mixed-flow pump

Science.gov (United States)

Li, H. F.; Huo, Y. W.; Pan, Z. B.; Zhou, W. C.; He, M. H.

2012-11-01

With the development of the city, the market of the mixed flow pump with large flux and high head is prospect. The KSB Shanghai Pump Co., LTD decided to develop low speed specific speed mixed flow pump to meet the market requirements. Based on the centrifugal pump and axial flow pump model, aiming at the characteristics of large flux and high head, a new type of guide vane mixed flow pump was designed. The computational fluid dynamics method was adopted to analyze the internal flow of the new type model and predict its performances. The time-averaged Navier-Stokes equations were closed by SST k-ω turbulent model to adapt internal flow of guide vane with larger curvatures. The multi-reference frame(MRF) method was used to deal with the coupling of rotating impeller and static guide vane, and the SIMPLEC method was adopted to achieve the coupling solution of velocity and pressure. The computational results shows that there is great flow impact on the head of vanes at different working conditions, and there is great flow separation at the tailing of the guide vanes at different working conditions, and all will affect the performance of pump. Based on the computational results, optimizations were carried out to decrease the impact on the head of vanes and flow separation at the tailing of the guide vanes. The optimized model was simulated and its performance was predicted. The computational results show that the impact on the head of vanes and the separation at the tailing of the guide vanes disappeared. The high efficiency of the optimized pump is wide, and it fit the original design destination. The newly designed mixed flow pump is now in modeling and its experimental performance will be getting soon.

Problems of mixed convection flow regime map in a vertical cylinder

International Nuclear Information System (INIS)

Kang, Gyeong Uk; Chung, Bum Jin

2012-01-01

One of the technical issues by the development of the VHTR is the mixed convection, which is the regime of heat transfer that occurs when the driving forces of both forced and natural convection are of comparable orders of magnitude. In vertical internal flows, the buoyancy force acts upward only, but forced flows can move either upward or downward. Thus, there are two types of mixed convection flows, depending on the direction of the forced flow. When the directions of the forced flow and buoyancy are the same, the flow is a buoyancy aided flow; when they are opposite, the flow is a buoyancy opposed flow. In laminar flows, buoyancy aided flow shows enhanced heat transfer compared to the pure forced convection and buoyancy opposed flow shows impaired heat transfer due to the flow velocity affected by the buoyancy forces. In turbulent flows, however, buoyancy opposed flows shows enhanced heat transfer due to increased turbulence production and buoyancy aided flow shows impaired heat transfer at low buoyancy forces and as the buoyancy increases, the heat transfer restores and at further increases of the buoyancy forces, the heat transfer is enhanced. It is of primary interests to classify which convection regime is mainly dominant. The methods most used to classify between forced, mixed and natural convection have been to refer to the classical flow regime map suggested by Meta is and Eckert. During the course of fundamental literature studies on this topic, it is found that there are some problems on the flow regime map in a vertical cylinder. This paper is to discuss problems identified through reviewing the papers composed in the classical flow regime map. We have tried to reproduce the flow regime map independently using the data obtained from the literatures and compared with the classical flow regime map and finally, the problems on this topic were discussed

Presidential Rapid Commercialization Initiative for mixed waste solvent extraction

International Nuclear Information System (INIS)

Honigford, L.; Dilday, D.; Cook, D.

1997-01-01

Recently, the Fernald Environmental Management Project (FEMP) has made some major steps in mixed waste treatment which have taken it closer to meeting final remediation goals. However, one major hurdle remains for the FEMP mixed waste treatment program, and that hurdle is tri-mixed waste. Tri-mixed is a term coined to describe low-level waste containing RCRA hazardous constituents along with polychlorinated biphenyls (PCB). The prescribed method for disposal of PCBs is incineration. In mixed waste treatment plans developed by the FEMP with public input, the FEMP committed to pursue non-thermal treatment methods and avoid the use of incineration. Through the SITE Program, the FEMP identified a non-thermal treatment technology which uses solvents to extract PCBs. The technology belongs to a small company called Terra-Kleen Response Group, Inc. A question arose as to how can this new and innovative technology be implemented by a small company at a Department of Energy (DOE) facility. The answer came in the form of the Rapid Commercialization Initiative (RCI) and the Mixed Waste Focus Area (MWFA). RCI is a program sponsored by the Department of commerce (DOC), DOE, Department of Defense (DOD), US EPA and various state agencies to aid companies to market new and innovative technologies

LES analysis of the flow in a simplified PWR assembly with mixing grid

Science.gov (United States)

Bieder, Ulrich; Falk, Francois

2014-06-01

The flow in fuel assemblies of PWRs with mixing grids has been analyzed with CFD calculations by numerous authors. The comparisons between calculation and experiment are focused on the flow in the near wake of the mixing grid, i.e. on the flow in the first 10 to 20 hydraulic diameters (dh) downstream of the grid. In the study presented here, the comparison between the measurements in the AGATE facility (5x5 tube bundle) and TrioU calculations is done for the whole distance between two successive mixing grids that is up to 0.6m downstream of the grid. The AGATE experiments have originally not been designed for CFD validation but to characterize different types of mixing grids. Nevertheless, the quality of the experimental data allows the quantitative comparison between measurement and calculation. The conclusions of the comparison are summarized below: Linear turbulent viscosity models seem to work rather well as long as the cross flow velocity in the rod gaps is advection controlled, that is directly downstream of the mixing grid, Further downstream, when the cross flow velocity is reduced and isotropic turbulence becomes a more and more important mixing phenomena, linear viscosity models will fail, The mixing grid affects the cross flow velocity up to the successive grid at a distance of about 50dh. The flow in fuel assemblies is never similar to that in undisturbed rod bundles. The test section of the AGATE facility has been discretized on 300 million control volumes by using a staggered grid approach on tetrahedral meshes. 20 days of CPU on 4600 nodes of the HPC machine CURIE of the CCRT was necessary to calculate the statistics of the turbulent flow, in particular the mean velocity and the RMS of the turbulent fluctuations.

LES analysis of the flow in a simplified PWR assembly with mixing grid

International Nuclear Information System (INIS)

Bieder, U.; Falk, F.

2013-01-01

The flow in fuel assemblies of PWRs with mixing grids has been analyzed with CFD calculations by numerous authors. The comparisons between calculation and experiment are focused on the flow in the near wake of the mixing grid, i.e. on the flow in the first 10 to 20 hydraulic diameters (d h ) downstream of the grid. In the study presented here, the comparison between the measurements in the AGATE facility (5*5 tube bundle) and Trio U calculations is done for the whole distance between two successive mixing grids that is up to 0.6 m downstream of the grid. The AGATE experiments have originally not been designed for CFD validation but to characterize different types of mixing grids. Nevertheless, the quality of the experimental data allows the quantitative comparison between measurement and calculation. The conclusions of the comparison are summarized below. First, the linear turbulent viscosity models seem to work rather well as long as the cross flow velocity in the rod gaps is advection controlled, that is directly downstream of the mixing grid. Secondly, further downstream, when the cross flow velocity is reduced and isotropic turbulence becomes a more and more important mixing phenomena, linear viscosity models will fail. Thirdly, the mixing grid affects the cross flow velocity up to the successive grid at a distance of about 50 d h . The flow in fuel assemblies is never similar to that in undisturbed rod bundles. The test section of the AGATE facility has been discretized on 300 million control volumes by using a staggered grid approach on tetrahedral meshes. 20 days of CPU on 4600 nodes of the HPC machine CURIE of the CCRT (Computer Center for Research and Technology - France) was necessary to calculate the statistics of the turbulent flow, in particular the mean velocity and the RMS of the turbulent fluctuations. (authors)

Mixing of stratified flow around bridge piers in steady current

DEFF Research Database (Denmark)

Jensen, Bjarne; Carstensen, Stefan; Christensen, Erik Damgaard

2018-01-01

This paper presents the results of an experimental and numerical investigation of the mixing of stratified flow around bridge pier structures. In this study, which was carried out in connection with the Fehmarnbelt Fixed Link environmental impact assessment, the mixing processes of two-layer stra......This paper presents the results of an experimental and numerical investigation of the mixing of stratified flow around bridge pier structures. In this study, which was carried out in connection with the Fehmarnbelt Fixed Link environmental impact assessment, the mixing processes of two......-layer stratification was studied in which the lower level had a higher salinity than the upper layer. The physical experiments investigated two different pier designs. A general study was made regarding forces on the piers in which the effect of the current angle relative to the structure was also included...

Collective flow of pions in relativistic heavy-ion collisions

International Nuclear Information System (INIS)

Russkikh, V.N.; Ivanov, Yu.B.

1995-02-01

The transverse-momentum distributions of pions in the Au(1 GeV/nucleon)+Au collisions are analyzed. The calculations are carried out within relativistic meanfield one- and two-fluid models. The rapidity distributions of the mean transverse momentum of pions are found to be fairly sensitive to the nuclear equation of state and, especially, to the stopping power. It is shown that the collective flow of pions in the reaction plane always correlates with the 'hot' flow of nucleons (i.e. those emitted from hot regions of nuclear system), while not always, with the total nucleon flow. This 'hot' nucleon flow can be experimentally singled out by selecting nucleons with sufficiently high transverse momenta. We predict that the 'hot' nucleon flow selected in this way will always correlate with the pion flow. Available experimental data on transverse-momentum spectra of pions are compared with calculations employing various equations of state and stopping power. (orig.)

Visualization of diffusion mixing in a micro-mixer with flow paths fabricated by photolithography

Science.gov (United States)

Horiuchi, Toshiyuki; Morizane, Yuta

2017-09-01

Mixing processes of two liquids were investigated by visualizing the mixing when they were simultaneously injected in a micro-mixer with lithographically fabricated Y-shape flow paths, and the mixing phenomena was analyzed in detail. To visualize the mixing, flows were observed by an optical microscope, and a clearly detectable chemical reaction was utilized. As the two liquids, a transparent aqueous solution of a strong alkali and a phenolphthalein ethanol solution were used. When they were simultaneously injected in Y-shape flow paths of a micro-mixer, they flowed at first in parallel along the joined path as laminar flows. This is because the Reynolds' number became very small caused by the narrow flow-path widths of 50-100 μm. However, because two liquids were always contacted at the boundary, they were gradually mixed by diffusion, and the color of the mixed parts changed to vivid red. For this reason, it was able to measure the diffusion distance from the flow path center. Because the flow speeds were much faster than the diffusion speeds, the area colored in red did not depend on the time but depended on the distance from the joint point. It was known that the distance from the joint point corresponded to the time for mixing the liquids by the diffusion. It was clarified that the diffusion distance x was proportional to the square root of the diffusion time t or the distance from the joint point. The calculated diffusion coefficient D was (0.87-1.00)×10-9 m2/s.

Simulation of Turbulent Wake at Mixing of Two Confined Horizontal Flows

Directory of Open Access Journals (Sweden)

Rok Krpan

2018-01-01

Full Text Available The development of a turbulent mixing layer at mixing of two horizontal water streams with slightly different densities is studied by the means of numerical simulation. The mixing of such flows can be modelled as the flow of two components, where the concentration of one component in the mixing region is described as a passive scalar. The velocity field remains common over the entire computational domain, where the density and viscosity difference due to the concentration mainly affects the turbulent fluctuations in the mixing region. The numerical simulations are performed with the open source code OpenFOAM using two different approaches for turbulence modelling, Reynolds Averaged Navier Stokes equations (RANS and Large Eddy Simulation (LES. The simulation results are discussed and compared with the benchmark experiment obtained within the frame of OECD/NEA benchmark test. A good agreement with experimental results is obtained in the case of the single liquid experiment. A high discrepancy between the simulated and the experimental velocity fluctuations in the case of mixing of the flows with the slightly different densities and viscosities triggered a systematic investigation of the modelling approaches that helped us to find out and interpret the main reasons for the disagreement.

Extracting a mix parameter from 2D radiography of variable density flow

Science.gov (United States)

Kurien, Susan; Doss, Forrest; Livescu, Daniel

2017-11-01

A methodology is presented for extracting quantities related to the statistical description of the mixing state from the 2D radiographic image of a flow. X-ray attenuation through a target flow is given by the Beer-Lambert law which exponentially damps the incident beam intensity by a factor proportional to the density, opacity and thickness of the target. By making reasonable assumptions for the mean density, opacity and effective thickness of the target flow, we estimate the contribution of density fluctuations to the attenuation. The fluctuations thus inferred may be used to form the correlation of density and specific-volume, averaged across the thickness of the flow in the direction of the beam. This correlation function, denoted by b in RANS modeling, quantifies turbulent mixing in variable density flows. The scheme is tested using DNS data computed for variable-density buoyancy-driven mixing. We quantify the deficits in the extracted value of b due to target thickness, Atwood number, and modeled noise in the incident beam. This analysis corroborates the proposed scheme to infer the mix parameter from thin targets at moderate to low Atwood numbers. The scheme is then applied to an image of counter-shear flow obtained from experiments at the National Ignition Facility. US Department of Energy.

Investigation of effect of stopping supply flow into the cell on the confinement of the radioactive materials under fire accident

International Nuclear Information System (INIS)

Abe, Hitoshi; Watanabe, Koji

1999-03-01

On November 20th 1997, a fire accident happened at Uranium Enrichment Research Laboratory, Tokai, Japan Atomic Energy Research Institute and ventilation filters in the laboratory clogged. When fire accident occurs in a controlled area, a large quantity of smoke generates in the area and dropping exhaust flow from the area by the clogging of ventilation filters and rising pressure in the area are caused. Moreover, leakage of smoke including radioactive materials from the area by the pressure rising is expected. To prevent the leakage, it is expected that stopping supply flow to the area during a fire accident is effective, however, quantitative evaluation about this effect has not been performed. By using CELVA-1D code, one-dimensional thermofluid analysis code, this effect is evaluated quantitatively by modeling the laboratory and estimating source terms released during the fire accident. As the results, it has been found that the efficiency of confinement of the radioactive materials into the area is preserved in the slightly long period of time in case of stopping supply flow to the area, however, this effect can be neglected in case that scale of fire accident is relatively large. (author)

Time-resolved Fourier transform infrared spectrometry using a microfabricated continuous flow mixer: application to protein conformation study using the example of ubiquitin.

Science.gov (United States)

Kakuta, Masaya; Hinsmann, Peter; Manz, Andreas; Lendl, Bernhard

2003-05-01

We report on the use of time-resolved Fourier transform infrared spectroscopy (FT-IR) to study chemically induced conformational changes of proteins using the example of ubiquitin. For this purpose a micromachined mixer is coupled to a conventional IR transmission cell with a pathlength of 25 microm and operated in both the continuous and the stopped-flow mode. This experimental set-up allows the elucidation of reaction pathways in the time frame of about 500 milliseconds to seconds with little reagent consumption and low pressure. For continuous flow measurements employed in the time frame from 0.5 to 1.4 s the reaction time is determined by the flow rate used as the connection between the point of confluence in the micromixer and the flow cell was kept constant in all experiments. For stopped-flow experiments (>1.4 s) the time is determined by data acquisition of the rapid scanning infrared spectrometer. Ubiquitin, a small well-known protein with 76 amino acid residues, changes its conformation from native to A-state with the addition of methanol under low pH conditions. We investigated the conformational change in the time frame from 0.5 to 10 s by mixing ubiquitin (20% methanol-d(4)) with an 80% methanol-d(4) solution at pD 2 by evaluating the time dependent changes in the amide I band of the protein.

Treatment of two-phase turbulent mixing, void drift and diversion cross-flow in a hydraulically non-equilibrium subchannel flow

International Nuclear Information System (INIS)

Sadatomi, Michio; Kawahara, Akimaro; Sato, Yoshifusa

1997-01-01

A practical way of treating two-phase turbulent mixing, void drift and diversion cross-flow on a subchannel analysis has been studied. Experimental data on the axial variations of subchannel flow parameters, such as flow rates of both phases, pressure, void fraction and concentrations of tracers for both phases, were obtained for hydraulically non-equilibrium two-phase subchannel flows in a vertical multiple channel made up of two-identical circular subchannels. These data were analyzed on the basis of the following four assumptions: (1) the turbulent mixing is independent of both the void drift and the diversion cross-flow; (2) the turbulent mixing rates of both phases in a non-equilibrium flow are equal to those in the equilibrium flow that the flow under consideration will attain; (3) the void drift is independent of the diversion cross-flow; and (4) the lateral gas velocity due to the void drift is predictable from Lahey et al.'s void settling model even in a non-equilibrium flow with the diversion cross-flow. The validity of the assumptions (1) and (2) was assured by comparing the concentration distribution data with the calculations, and that of the assumptions (3) and (4) by analyzing the data on flow rates of both phases, pressure and void fraction (author)

LES analysis of the flow in a simplified PWR assembly with mixing grid

International Nuclear Information System (INIS)

Bieder, Ulrich; Fauchet, Gauthier; Falk, Francois

2014-01-01

The flow in fuel assemblies of Pressurized Water Reactors (PWR) with mixing grids has been analysed with Computational Fluid Dynamics (CFD) by numerous authors. The comparisons between calculation and experiment are mostly focused on the flow in the near wake of the mixing grid, i.e. on the flow in the first 5 to 10 hydraulic diameters (dh) downstream of the grid. In the study presented here, the comparison between the measurements in the AGATE facility (5 * 5 tube bundle) and Trio-U calculations is done for the whole distance between two successive mixing grids that is up to about 50 d h downstream of the grid. The AGATE experiments have originally not been designed for CFD validation but to characterize different types of mixing grids. Nevertheless, the quality of the experimental data allows the quantitative comparison between measurement and calculation. The conclusions of the comparison are summarized below: Linear turbulent viscosity models seem to work rather well as long as the cross flow velocity in the rod gaps is advection controlled, that is directly downstream of the mixing grid, Further downstream, when the cross flow velocity is reduced and anisotropic turbulence becomes a more and more important mixing phenomena, linear viscosity models can fail, The mixing grid affects the cross flow velocity up to the successive grid. The flow in fuel assemblies is never similar to that in undisturbed rod bundles. The test section of the AGATE facility has been discretized on 300 million control volumes by using a staggered grid approach on tetrahedral meshes. 20 days of CPU on 4600 cores of the High Performance Computer (HPC) cluster CURIE of the Centre de Calcul, Recherche et Technologie (CCRT) were necessary to converge the statistics of the turbulent fluctuations, completely converge the mean velocity and incompletely converge the RMS of the turbulent fluctuations. (authors)

Biobjective Optimization and Evaluation for Transit Signal Priority Strategies at Bus Stop-to-Stop Segment

Directory of Open Access Journals (Sweden)

Rui Li

2016-01-01

Full Text Available This paper proposes a new optimization framework for the transit signal priority strategies in terms of green extension, red truncation, and phase insertion at the stop-to-stop segment of bus lines. The optimization objective is to minimize both passenger delay and the deviation from bus schedule simultaneously. The objective functions are defined with respect to the segment between bus stops, which can include the adjacent signalized intersections and downstream bus stops. The transit priority signal timing is optimized by using a biobjective optimization framework considering both the total delay at a segment and the delay deviation from the arrival schedules at bus stops. The proposed framework is evaluated using a VISSIM model calibrated with field traffic volume and traffic signal data of Caochangmen Boulevard in Nanjing, China. The optimized TSP-based phasing plans result in the reduced delay and improved reliability, compared with the non-TSP scenario under the different traffic flow conditions in the morning peak hour. The evaluation results indicate the promising performance of the proposed optimization framework in reducing the passenger delay and improving the bus schedule adherence for the urban transit system.

Isospin effects on the system mass dependence of nuclear stopping around the energy of vanishing flow

Science.gov (United States)

Jain, Anupriya; Kumar, Suneel

2014-10-01

We study the effect of isospin degree of freedom on nuclear stopping throughout the mass range 50 and 350 for two sets of isotopic systems with N/Z ≈ 1.5 and 1.8, as well as isobaric systems with N/Z = 1.0 and 1.4. Analysis is carried out at incident energies below, at, and above the energy of vanishing flow (EVF) using the isospin-dependent quantum molecular dynamics model. Our findings reveal that nuclear stopping does not show any particular behavior at the EVF. Moreover, system size effects dominate the isospin effects throughout the range of colliding geometry. The Coulomb effects, however, become important at peripheral geometry. The comparative study of the counterbalancing of Coulomb and mean field by removing the nucleon-nucleon collisions and symmetry potential clearly indicates the dominance of nucleon-nucleon cross-section over the Coulomb repulsions. Moreover, the theoretical results presented in this manuscript for the set of reactions can be experimentally verified.

Isospin effects on the system mass dependence of nuclear stopping around the energy of vanishing flow

International Nuclear Information System (INIS)

Jain, Anupriya; Kumar, Suneel

2014-01-01

We study the effect of isospin degree of freedom on nuclear stopping throughout the mass range 50 and 350 for two sets of isotopic systems with N/Z ≈ 1.5 and 1.8, as well as isobaric systems with N/Z = 1.0 and 1.4. Analysis is carried out at incident energies below, at, and above the energy of vanishing flow (EVF) using the isospin-dependent quantum molecular dynamics model. Our findings reveal that nuclear stopping does not show any particular behavior at the EVF. Moreover, system size effects dominate the isospin effects throughout the range of colliding geometry. The Coulomb effects, however, become important at peripheral geometry. The comparative study of the counterbalancing of Coulomb and mean field by removing the nucleon–nucleon collisions and symmetry potential clearly indicates the dominance of nucleon–nucleon cross-section over the Coulomb repulsions. Moreover, the theoretical results presented in this manuscript for the set of reactions can be experimentally verified. (paper)

Design and optimization of mixed flow pump impeller blades by varying semi-cone angle

Science.gov (United States)

Dash, Nehal; Roy, Apurba Kumar; Kumar, Kaushik

2018-03-01

The mixed flow pump is a cross between the axial and radial flow pump. These pumps are used in a large number of applications in modern fields. For the designing of these mixed flow pump impeller blades, a lot number of design parameters are needed to be considered which makes this a tedious task for which fundamentals of turbo-machinery and fluid mechanics are always prerequisites. The semi-cone angle of mixed flow pump impeller blade has a specified range of variations generally between 45o to 60o. From the literature review done related to this topic researchers have considered only a particular semi-cone angle and all the calculations are based on this very same semi-cone angle. By varying this semi-cone angle in the specified range, it can be verified if that affects the designing of the impeller blades for a mixed flow pump. Although a lot of methods are available for designing of mixed flow pump impeller blades like inverse time marching method, the pseudo-stream function method, Fourier expansion singularity method, free vortex method, mean stream line theory method etc. still the optimized design of the mixed flow pump impeller blade has been a cumbersome work. As stated above since all the available research works suggest or propose the blade designs with constant semi-cone angle, here the authors have designed the impeller blades by varying the semi-cone angle in a particular range with regular intervals for a Mixed-Flow pump. Henceforth several relevant impeller blade designs are obtained and optimization is carried out to obtain the optimized design (blade with optimal geometry) of impeller blade.

The effect of rapid decompression on femur blood flow of rabbits

International Nuclear Information System (INIS)

Yu Shaoning; Tian Wuxun; Zhu Xiangqi

1997-01-01

PURPOSE: To study the influence of regional blood flow in femur trochanter (FT) of rabbits' under rapid decompression after exposure to hyperbaric air. METHODS: Rabbits were placed in a hyperbaric chamber and exposed to the pressure of 0.5 MPa for 1.5 h, and the pressure was reduced to the atmosphere pressure at a uniform rate of 0.03 mPa/min. The regional blood flow of FT in rabbits were measured with 133 Xe washout methods. RESULTS: The normal average regional blood flow in left and right FT were 14.5 +- 1.7 and 14.1 +- 1.9 ml/(min·100g) respectively. After exposure to hyperbaric air with rapid decompression, the average regional blood flow of left and right FT were 11.1 +- 1.2 and 10.5 +- 1.6 ml/(min·100g) respectively. But the symptoms of dysbarism in these rabbits were various each other. CONCLUSIONS: After being exposed to hyperbaric air with rapid decompression, the blood flow of rabbits' femur trochanter were noticeably reduced

CFD analysis of supercritical water flow and heat transfer in single channel with mixing vane

International Nuclear Information System (INIS)

Zuo Guoping; Xie Hongyan; Yu Tao

2012-01-01

Three-dimensional rectangular channel with the mixing wane in supercritical water reactor is investigated with CFX. The mixing vane elevation influenced on temperature distribution and flow field are simulated in the model. The results showed the mixing vane cause fluid circumferential flow, making flow hot and cold fluids mixed and fluid temperature uniform distribution, effectively improve the fuel rod surface temperature distribution and reduced hot temperature. Among the mixing wing elevation of 15, 30, 45, 50, 60 and 70 angle, the 30 angle is the best case in improving temperature distribution. (authors)

Formation of coherent structures in 3D laminar mixing flows

NARCIS (Netherlands)

Speetjens, M.F.M.; Clercx, H.J.H.

2009-01-01

Mixing under laminar flow conditions is key to a wide variety of industrial systems of size extending from microns to meters. Examples range from the traditional (and still very relevant) mixing of viscous fluids via compact processing equipment down to emerging micro-fluidics applications. Profound

Adaptive mixed finite element methods for Darcy flow in fractured porous media

KAUST Repository

Chen, Huangxin; Salama, Amgad; Sun, Shuyu

2016-01-01

In this paper, we propose adaptive mixed finite element methods for simulating the single-phase Darcy flow in two-dimensional fractured porous media. The reduced model that we use for the simulation is a discrete fracture model coupling Darcy flows in the matrix and the fractures, and the fractures are modeled by one-dimensional entities. The Raviart-Thomas mixed finite element methods are utilized for the solution of the coupled Darcy flows in the matrix and the fractures. In order to improve the efficiency of the simulation, we use adaptive mixed finite element methods based on novel residual-based a posteriori error estimators. In addition, we develop an efficient upscaling algorithm to compute the effective permeability of the fractured porous media. Several interesting examples of Darcy flow in the fractured porous media are presented to demonstrate the robustness of the algorithm.

Adaptive mixed finite element methods for Darcy flow in fractured porous media

KAUST Repository

Chen, Huangxin

2016-09-21

In this paper, we propose adaptive mixed finite element methods for simulating the single-phase Darcy flow in two-dimensional fractured porous media. The reduced model that we use for the simulation is a discrete fracture model coupling Darcy flows in the matrix and the fractures, and the fractures are modeled by one-dimensional entities. The Raviart-Thomas mixed finite element methods are utilized for the solution of the coupled Darcy flows in the matrix and the fractures. In order to improve the efficiency of the simulation, we use adaptive mixed finite element methods based on novel residual-based a posteriori error estimators. In addition, we develop an efficient upscaling algorithm to compute the effective permeability of the fractured porous media. Several interesting examples of Darcy flow in the fractured porous media are presented to demonstrate the robustness of the algorithm.

Thermal and hydrodynamic characteristics of forced and mixed convection flow through vertical rectangular channels

Directory of Open Access Journals (Sweden)

Hanafi Abdalla S.

2008-01-01

Full Text Available This paper presents experimental and numerical studies for the case of turbulent forced and mixed convection flow of water through narrow vertical rectangular channel. The channel is composed of two parallel plates which are heated at a uniform heat flux, whereas, the other two sides of the channel are thermally insulated. The plates are of 64 mm in width, 800 mm in height, and separated from each other at a narrow gap of 2.7 mm. The Nusselt number distribution along the flow direction normalized by the Nusselt number for the case of turbulent forced convection flow is obtained experimentally with a comparison with the numerical results obtained from a commercial computer code. The quantitative determination of the nor- malized Nusselt number with respect to the dimension-less number Z = (Gr/Re21/8Pr0.5 is presented with a comparison with previous experimental results. Qualitative results are presented for the normalized temperature and velocity profiles in the transverse direction with a comparison between the forced and mixed convection flow for both the cases of upward and downward flow directions. The effect of the axial locations and the parameter Gr/Re on the variation of the normalized temperature profiles in the transverse direction for both the regions of forced and mixed convection and for both of the upward and downward flow directions are obtained. The normalized velocity profiles in the transverse directions are also determined at different inlet velocity and heat fluxes for the previous cases. It is found that the normalized Nusselt number is greater than one in the mixed convection region for both the cases of upward and downward flow and correlated well with the dimension-less parameter Z for both of the forced and mixed convection regions. The temperature profiles increase with increasing the axial location along the flow direction or the parameter Gr/Re for both of the forced and mixed convection regions, but this increase is

Mixed convection flow past a horizontal plate

Directory of Open Access Journals (Sweden)

Savić Lj.

2005-01-01

Full Text Available The mixed convection flow past a horizontal plate being aligned through a small angle of attack to a uniform free stream will be considered in the limit of large Reynolds number and small Richardson number. Even a small angle of inclination of the wake is sufficient for the buoyancy force to accelerate the flow in the wake which causes a velocity overshoot in the wake. Moreover a hydrostatic pressure difference across the wake induces a correction to the potential flow which influences the inclination of the wake. Thus the wake and the correction of the potential flow have to be determined simultaneously. However, it turns out that solutions exist only if the angle of attack is sufficiently large. Solutions are computed numerically and the influence of the buoyancy on the lift coefficient is determined.

The structure of turbulence in a rapid tidal flow.

Science.gov (United States)

Milne, I A; Sharma, R N; Flay, R G J

2017-08-01

The structure of turbulence in a rapid tidal flow is characterized through new observations of fundamental statistical properties at a site in the UK which has a simple geometry and sedate surface wave action. The mean flow at the Sound of Islay exceeded 2.5 m s -1 and the turbulent boundary layer occupied the majority of the water column, with an approximately logarithmic mean velocity profile identifiable close to the seabed. The anisotropic ratios, spectral scales and higher-order statistics of the turbulence generally agree well with values reported for two-dimensional open channels in the laboratory and other tidal channels, therefore providing further support for the application of universal models. The results of the study can assist in developing numerical models of turbulence in rapid tidal flows such as those proposed for tidal energy generation.

Conductive solar wind models in rapidly diverging flow geometries

International Nuclear Information System (INIS)

Holzer, T.E.; Leer, E.

1980-01-01

A detailed parameter study of conductive models of the solar wind has been carried out, extending the previous similar studies of Durney (1972) and Durney and Hundhausen (1974) by considering collisionless inhibition of thermal conduction, rapidly diverging flow geometries, and the structure of solutions for the entire n 0 -T 0 plane (n 0 and T 0 are the coronal base density and temperature). Primary emphasis is placed on understanding the complex effects of the physical processes operative in conductive solar wind models. There are five points of particular interest that have arisen from the study: (1) neither collisionless inhibition of thermal conduction nor rapidly diverging flow geometries can significantly increase the solar wind speed at 1 AU; (2) there exists a firm upper limit on the coronal base temperature consistent with observed values of the coronal base pressure and solar wind mass flux density; (3) the principal effect of rapidly diverging flow geometries is a decrease in the solar wind mass flux density at 1 AU and an increase in the mass flux density at the coronal base; (4) collisionless inhibition of thermal conduction can lead to a solar wind flow speed that either increases or decreases with increasing coronal base density (n 0 ) and temperature (T 0 , depending on the region of the n 0 -T 0 plane considered; (5) there is a region of the n 0 -T/sub o/ plane at high coronal base densities where low-speed, high-mass-flux, transonic solar wind flows exist: a region not previously considered

Pressure fluctuation characteristics of flow field of mixed flow nuclear primary pump

International Nuclear Information System (INIS)

Wang Chunlin; Yang Xiaoyong; Li Changjun; Jia Fei; Zhao Binjuan

2013-01-01

In order to research the pressure fluctuation characteristics of flow field of mixed flow nuclear primary pump, this study used the technique of ANSYS-Workbench and CFX fluid solid heat coupling to do numerical simulation analysis for model pump. According to the situation of pressure fluctuation of time domain and frequency domain, the main cause of pressure fluctuation was discussed. For different flow, the pressure fluctuations were compared. This study shows it is feasible that large eddy simulation method is used for the research of pressure fluctuation. The pressure fluctuation amplitudes of four sections are increasing from wheel hub to wheel rim. The pressure fluctuation of inlet and outlet of impeller depends on the rotational frequency of impeller. Along with the fluid flowing away from the impeller, the effect of the impeller on the fluid pressure fluctuation weakens gradually. Comparing the different results of three flow conditions, the pressure fluctuation in design condition flow is superior to the others. (authors)

Area law for fixed points of rapidly mixing dissipative quantum systems

Energy Technology Data Exchange (ETDEWEB)

Brandão, Fernando G. S. L. [Quantum Architectures and Computation Group, Microsoft Research, Redmond, Washington 98052 (United States); Department of Computer Science, University College London, Gower Street, London WC1E 6BT (United Kingdom); Cubitt, Toby S. [Department of Computer Science, University College London, Gower Street, London WC1E 6BT (United Kingdom); DAMTP, University of Cambridge, Cambridge (United Kingdom); Lucia, Angelo, E-mail: anlucia@ucm.es [Departamento de Análisis Matemático, Universidad Complutense de Madrid, Madrid (Spain); Michalakis, Spyridon [Institute for Quantum Information and Matter, Caltech, California 91125 (United States); Perez-Garcia, David [Departamento de Análisis Matemático, Universidad Complutense de Madrid, Madrid (Spain); IMI, Universidad Complutense de Madrid, Madrid (Spain); ICMAT, C/Nicolás Cabrera, Campus de Cantoblanco, 28049 Madrid (Spain)

2015-10-15

We prove an area law with a logarithmic correction for the mutual information for fixed points of local dissipative quantum system satisfying a rapid mixing condition, under either of the following assumptions: the fixed point is pure or the system is frustration free.

PIV measurement of turbulent bubbly mixing layer flow with polymer additives

International Nuclear Information System (INIS)

Ning, T; Guo, F; Chen, B; Zhang, X

2009-01-01

Based on experimental investigation of single-phase turbulent mixing layer flow with polymer additives, bubbly mixing layer was experimentally investigated by PIV. The velocity ratio between high and low speed is 4:1 and the Reynolds number based on the velocity difference of two steams and hydraulic diameter of the channel ranges is 73333. Gas bubbles with about 0.5% gas fraction were injected into pure water mixing layer with/without polymer additives from three different parts at the end of the splitter plate. The comparison between single phase and bubbly mixing layer shows clearly that the dynamic development of mixing layer is great influenced by the bubble injection. Similar with single phase, the Reynolds stress and vorticity still concentrate in a coniform area of central mixing flow field part and the width will increase with increasing the Reynolds number. Mean Reynolds stress will decrease with bubble injection in high Reynolds numbers and the decreasing of Reynolds stress with polymer additives is much more than pure water case.

Hypervapotron flow testing with rapid prototype models

International Nuclear Information System (INIS)

Driemeyer, D.; Hellwig, T.; Kubik, D.; Langenderfer, E.; Mantz, H.; McSmith, M.; Jones, B.; Butler, J.

1995-01-01

A flow test model of the inlet section of a three channel hypervapotron plate that has been proposed as a heat sink in the ITER divertor was prepared using a rapid prototyping stereolithography process that is widely used for component development in US industry. An existing water flow loop at the University of Illinois is being used for isothermal flow tests to collect pressure drop data for comparison with proposed vapotron friction factor correlations. Differential pressure measurements are taken, across the test section inlet manifold, the vapotron channel (about a seven inch length), the outlet manifold and the inlet-to-outlet. The differential pressures are currently measured with manometers. Tests were conducted at flow velocities from 1--10 m/s to cover the full range of ITER interest. A tap was also added for a small hypodermic needle to inject dye into the flow channel at several positions to examine the nature of the developing flow field at the entrance to the vapotron section. Follow-on flow tests are planned using a model with adjustable flow channel dimensions to permit more extensive pressure drop data to be collected. This information will be used to update vapotron design correlations for ITER

The influence of tributary flow density differences on the hydrodynamic behavior of a confluent meander bend and implications for flow mixing

Science.gov (United States)

Herrero, Horacio S.; Díaz Lozada, José M.; García, Carlos M.; Szupiany, Ricardo N.; Best, Jim; Pagot, Mariana

2018-03-01

The goal of this study is to evaluate the influence of tributary flow density differences on hydrodynamics and mixing at a confluent meander bend. A detailed field characterization is performed using an Acoustic Doppler Current Profiler (ADCP) for quantification of the 3D flow field, flow discharge and bathymetry, as well as CTD measurements (conductivity, temperature, depth) to characterize the patterns of mixing. Satellite images of the confluence taken at complementary times to the field surveys were analyzed to evaluate the confluence hydrodynamics at different flow conditions. The results illustrate the differences in hydrodynamics and mixing length in relation to confluences with equal density tributaries. At low-density differences, and higher discharge ratio (Qr) between the two rivers, the flow is similar to equi-density confluent meander bends. In contrast, at high-density differences (low Qr), the tributary flow is confined to near the confluence but the density difference causes the flow to move across channel. In this case, the density difference causes the lateral spread of the tributary flow to be greater than at a greater Qr when the density difference is less. These results illustrate the potential importance of density differences between tributaries in determining the rate and spatial extent of mixing and sediment dispersal at confluent meander bends.

Effect of flow and active mixing on bacterial growth in a colon-like geometry

Science.gov (United States)

Cremer, Jonas; Segota, Igor; Arnoldini, Markus; Groisman, Alex; Hwa, Terence

The large intestine harbors bacteria from hundreds of species, with bacterial densities reaching up to 1012 cells per gram. Many different factors influence bacterial growth dynamics and thus bacterial density and microbiota composition. One dominant force is flow which can in principle lead to a washout of bacteria from the proximal colon. Active mixing by Contractions of the colonic wall together with bacterial growth might counteract such flow-forces and allow high bacterial densities to occur. As a step towards understanding bacterial growth in the presence of mixing and flow, we constructed an in-vitro setup where controlled wall-deformations of a channel emulate Contractions. We investigate growth along the channel under a steady nutrient inflow. In the limits of no or very frequent Contractions, the device behaves like a plug-flow reactor and a chemostat respectively. Depending on mixing and flow, we observe varying spatial gradients in bacterial density along the channel. Active mixing by deformations of the channel wall is shown to be crucial in maintaining a steady-state bacterial population in the presence of flow. The growth-dynamics is quantitatively captured by a simple mathematical model, with the effect of mixing described by an effective diffusion term.

Lifespan changes in global and selective stopping and performance adjustments

Directory of Open Access Journals (Sweden)

Maria Christina Van De Laar

2011-12-01

Full Text Available This study examined stopping and performance adjustments in four age groups (M ages: 8, 12, 21, and 76 years. All participants performed on three tasks, a standard two-choice task and the same task in which stop-signal trials were inserted requiring either the suppression of the response activated by the choice stimulus (global stop task or the suppression of the response when one stop signal was presented but not when the other stop signal occurred (selective stop task. The results showed that global stopping was faster than selective stopping in all age groups. Global stopping matured more rapidly than selective stopping. The developmental gain in stopping was considerably more pronounced compared to the loss observed during senescence. All age groups slowed the response on trials without a stop signal in the stop task compared to trials in the choice task, the elderly in particular. In addition, all age groups slowed on trials following stop-signal trials, except the elderly who did not slow following successful inhibits. By contrast, the slowing following failed inhibits was disproportionally larger in the elderly compared to young adults. Finally, sequential effects did not alter the pattern of performance adjustments. The results were interpreted in terms of developmental change in the balance between proactive and reactive control.

Lifespan Changes in Global and Selective Stopping and Performance Adjustments

Science.gov (United States)

van de Laar, Maria C.; van den Wildenberg, Wery P. M.; van Boxtel, Geert J. M.; van der Molen, Maurits W.

2011-01-01

This study examined stopping and performance adjustments in four age groups (M ages: 8, 12, 21, and 76 years). All participants performed on three tasks, a standard two-choice task and the same task in which stop-signal trials were inserted requiring either the suppression of the response activated by the choice stimulus (global stop task) or the suppression of the response when one stop-signal was presented but not when the other stop-signal occurred (selective stop task). The results showed that global stopping was faster than selective stopping in all age groups. Global stopping matured more rapidly than selective stopping. The developmental gain in stopping was considerably more pronounced compared to the loss observed during senescence. All age groups slowed the response on trials without a stop-signal in the stop task compared to trials in the choice task, the elderly in particular. In addition, all age groups slowed on trials following stop-signal trials, except the elderly who did not slow following successful inhibits. By contrast, the slowing following failed inhibits was disproportionally larger in the elderly compared to young adults. Finally, sequential effects did not alter the pattern of performance adjustments. The results were interpreted in terms of developmental change in the balance between proactive and reactive control. PMID:22180746

Estimation of Flow Channel Parameters for Flowing Gas Mixed with Air in Atmospheric-pressure Plasma Jets

Science.gov (United States)

Yambe, Kiyoyuki; Saito, Hidetoshi

2017-12-01

When the working gas of an atmospheric-pressure non-equilibrium (cold) plasma flows into free space, the diameter of the resulting flow channel changes continuously. The shape of the channel is observed through the light emitted by the working gas of the atmospheric-pressure plasma. When the plasma jet forms a conical shape, the diameter of the cylindrical shape, which approximates the conical shape, defines the diameter of the flow channel. When the working gas flows into the atmosphere from the inside of a quartz tube, the gas mixes with air. The molar ratio of the working gas and air is estimated from the corresponding volume ratio through the relationship between the diameter of the cylindrical plasma channel and the inner diameter of the quartz tube. The Reynolds number is calculated from the kinematic viscosity of the mixed gas and the molar ratio. The gas flow rates for the upper limit of laminar flow and the lower limit of turbulent flow are determined by the corresponding Reynolds numbers estimated from the molar ratio. It is confirmed that the plasma jet length and the internal plasma length associated with strong light emission increase with the increasing gas flow rate until the rate for the upper limit of laminar flow and the lower limit of turbulent flow, respectively. Thus, we are able to explain the increasing trend in the plasma lengths with the diameter of the flow channel and the molar ratio by using the cylindrical approximation.

Effects of elevated line sources on turbulent mixing in channel flow

Science.gov (United States)

Nguyen, Quoc; Papavassiliou, Dimitrios

2016-11-01

Fluids mixing in turbulent flows has been studied extensively, due to the importance of this phenomena in nature and engineering. Convection effects along with motion of three-dimensional coherent structures in turbulent flow disperse a substance more efficiently than molecular diffusion does on its own. We present here, however, a study that explores the conditions under which turbulent mixing does not happen, when different substances are released into the flow field from different vertical locations. The study uses a method which combines Direct Numerical Simulation (DNS) with Lagrangian Scalar Tracking (LST) to simulate a turbulent channel flow and track the motion of passive scalars with different Schmidt numbers (Sc). The particles are released from several instantaneous line sources, ranging from the wall to the center region of the channel. The combined effects of mean velocity difference, molecular diffusion and near-wall coherent structures lead to the observation of different concentrations of particles downstream from the source. We then explore in details the conditions under which particles mixing would not happen. Results from numerical simulation at friction Reynolds number of 300 and 600 will be discussed and for Sc ranging from 0.1 to 2,400.

Rapid detection of the positive side reactions in vanadium flow batteries

International Nuclear Information System (INIS)

Liu, Le; Li, Zhaohua; Xi, Jingyu; Zhou, Haipeng; Wu, Zenghua; Qiu, Xinping

2017-01-01

Highlights: • A method for rapid measurement of the positive side reactions in VFB is presented. • The SOC of positive electrolytes can be detected with resolution of 0.002%. • Side reaction ratios at different charge currents, flow rates are obtained. - Abstract: We present an optical detection method for rapid measurement of the positive side reactions in vanadium flow batteries (VFB). By measuring the transmittance of the positive electrolytes in VFB, the states of charge (SOC) of the positive electrolytes can be detected at very high resolution (better than 0.002% in the SOC range from 98% to 100%), due to the nonlinear transmittance spectra caused by the interactions between V(IV) and V(V) ions. The intensity of the positive side reactions of a VFB can be rapidly measured by a few steps, attributing to the fact that the positive side reactions occur only during the high voltage charging process. The ratios of the positive side reactions at different charge currents and different flow rates are obtained while causing no damage to the battery. This optical detection method can rapidly determine the optimal parameters of the VFB system, providing new means for studying the electrochemical reactions in the VFB system and rapid test in industrial production of VFBs.

Study on transient hydrodynamic performance and cavitation characteristic of high-speed mixed-flow pump

International Nuclear Information System (INIS)

Chen, T; Liu, Y L; Sun, Y B; Wang, L Q; Wu, D Z

2013-01-01

In order to analyse the hydrodynamic performance and cavitation characteristic of a high-speed mixed-flow pump during transient operations, experimental studies were carried out. The transient hydrodynamic performance and cavitation characteristics of the mixed-flow pump with guide vane during start-up operation processes were tested on the pump performance test-bed. Performance tests of the pump were carried out under various inlet pressures and speed-changing operations. The real-time instantaneous external characteristics such as rotational speed, hydraulic head, flow rate, suction pressure and discharge pressure of the pump were measured. Based on the experimental results, the effect of fluid acceleration on the hydrodynamic performances and cavitation characteristics of the mixed-flow pump were analysed and evaluated

Study on flow phenomena at a mixing tee pipe in plants

International Nuclear Information System (INIS)

Maeda, Shogo; Kubota, Hiroki; Sugimoto, Katsumi; Takenaka, Nobuyuki; Miyoshi, Koji

2016-01-01

Thermal fatigue cracking may initiate at a tee pipe in plants where high and low temperature fluids flow in. The thermal stress fluctuation is caused by the wall temperature fluctuation due to heat transfer of the fluid temperature fluctuation near the wall. In order to elucidate the flow phenomena at a mixing tee pipe to cause temperature fluctuation, a visualization experiment of the flow in mixing section was conducted using a rectangular test section made of acrylic. As a result, the flow pattern was classified by momentum ratio M_R of the main and branch pipes, and it changed from wall jet to deflecting jet on M_R=3.70, and from deflecting jet to impinging jet on M_R=0.64. The jet flow from the branch pipe is swaying at a period of from about 5 s to 10 s. The relationship between the periods of fluctuation and M_R was investigated. The period decreased as M_R increased. (author)

Signs of tops from highly mixed stops

Energy Technology Data Exchange (ETDEWEB)

Backović, Mihailo [Center for Cosmology, Particle Physics and Phenomenology - CP3,Universite Catholique de Louvain, Louvain-la-neuve (Belgium); Mariotti, Alberto [Theoretische Natuurkunde and IIHE/ELEM, Vrije Universiteit Brussel,and International Solvay Institutes, Pleinlaan 2, B-1050 Brussels (Belgium); Spannowsky, Michael [Institute for Particle Physics Phenomenology, Department of Physics,Durham University, Durham DH1 3LE (United Kingdom)

2015-06-17

Supersymmetric extensions of the Standard Model with highly mixed squark flavours beyond minimal flavour violation provide interesting scenarios of new physics, which have so far received limited attention. We propose a calculable realization of such scenarios in models of gauge mediation augmented with an extra interaction between the messengers and the up type squark. We compute the supersymmetric spectrum and analyze the flavour physics constraints on such models. In a simplified model approach, we show that scenarios with maximal squark flavour mixing result in interesting phenomenological signatures at the LHC. We show that the model can be probed up to masses of m{sub ũ}≲950 GeV in the single-top event topology at LHC14 with as little as 300 fb{sup −1}. The most distinctive signature of highly mixed scenarios, the same sign positive charge di-top, can be also probed to comparable squark masses at high luminosity LHC14.

Leptonic mono-top from single stop production at the LHC

Energy Technology Data Exchange (ETDEWEB)

Duan, Guang Hua [CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,Chinese Academy of Sciences,Beijing 100190 (China); Hikasa, Ken-ichi [Department of Physics, Tohoku University,Sendai 980-8578 (Japan); Wu, Lei [Department of Physics and Institute of Theoretical Physics, Nanjing Normal University,Nanjing, Jiangsu 210023 (China); ARC Centre of Excellence for Particle Physics at the Terascale,School of Physics, The University of Sydney,NSW 2006 (Australia); Yang, Jin Min [CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,Chinese Academy of Sciences,Beijing 100190 (China); Department of Physics, Tohoku University,Sendai 980-8578 (Japan); Zhang, Mengchao [Center for Theoretical Physics and Universe, Institute for Basic Science (IBS),Daejeon 34051 (Korea, Republic of)

2017-03-16

Top squark (stop) can be produced via QCD interaction but also the electroweak interaction at the LHC. In this paper, we investigate the observability of the associated production of stop and chargino, pp→t̃{sub 1}χ̃{sub 1}{sup −}, in compressed electroweakino scenarios at 14 TeV LHC. Due to small mass splitting between the lightest neutralino (χ̃{sub 1}{sup 0}) and chargino (χ̃{sub 1}{sup −}), the single stop production can give the mono-top signature through the stop decay t̃{sub 1}→tχ̃{sub 1}{sup 0}. We analyze the leptonic mono-top channel of the single stop production and propose a lab-frame observable cos θ{sub bℓ} to reduce the SM backgrounds. We find that such leptonic mono-top events from the single stop production can be probed at 2σ level at the HL-LHC if m{sub t̃{sub 1}}<760 GeV and m{sub χ̃{sub 1{sup 0}}}<150 GeV. Given a discovery of the stop and a measurement of the single stop production cross section, the stop mixing angle can also be determined from the single stop production at the HL-LHC.

Role of alveolar topology on acinar flows and convective mixing.

Science.gov (United States)

Hofemeier, Philipp; Sznitman, Josué

2014-06-01

Due to experimental challenges, computational simulations are often sought to quantify inhaled aerosol transport in the pulmonary acinus. Commonly, these are performed using generic alveolar topologies, including spheres, toroids, and polyhedra, to mimic the complex acinar morphology. Yet, local acinar flows and ensuing particle transport are anticipated to be influenced by the specific morphological structures. We have assessed a range of acinar models under self-similar breathing conditions with respect to alveolar flow patterns, convective flow mixing, and deposition of fine particles (1.3 μm diameter). By tracking passive tracers over cumulative breathing cycles, we find that irreversible flow mixing correlates with the location and strength of the recirculating vortex inside the cavity. Such effects are strongest in proximal acinar generations where the ratio of alveolar to ductal flow rates is low and interalveolar disparities are most apparent. Our results for multi-alveolated acinar ducts highlight that fine 1 μm inhaled particles subject to alveolar flows are sensitive to the alveolar topology, underlining interalveolar disparities in particle deposition patterns. Despite the simplicity of the acinar models investigated, our findings suggest that alveolar topologies influence more significantly local flow patterns and deposition sites of fine particles for upper generations emphasizing the importance of the selected acinar model. In distal acinar generations, however, the alveolar geometry primarily needs to mimic the space-filling alveolar arrangement dictated by lung morphology.

Unsteady single-phase natural circulation flow mixing prediction using CATHARE three-dimensional capabilities

Energy Technology Data Exchange (ETDEWEB)

Salah, Anis Bousbia; Vlassenbroeck, Jacques [Bel V - Subsidiary of the Belgian Federal Agency for Nuclear Contro, Brussels (Belize)

2017-04-15

Coolant mixing under natural circulation flow regime constitutes a key parameter that may play a role in the course of an accidental transient in a nuclear pressurized water reactor. This issue has motivated some experimental investigations carried out within the OECD/NEA PKL projects. The aim was to assess the coolant mixing phenomenon in the reactor pressure vessel downcomer and the core lower plenum under several asymmetric steady and unsteady flow conditions, and to provide experimental data for code validations. Former studies addressed the mixing phenomenon using, on the one hand, one-dimensional computational approaches with cross flows that are not fully validated under transient conditions and, on the other hand, expensive computational fluid dynamic tools that are not always justified for large-scale macroscopic phenomena. In the current framework, an unsteady coolant mixing experiment carried out in the Rossendorf coolant mixing test facility is simulated using the three-dimensional porous media capabilities of the thermal–hydraulic system CATHARE code. The current study allows highlighting the current capabilities of these codes and their suitability for reproducing the main phenomena occurring during asymmetric transient natural circulation mixing conditions.

Comparative study of turbulent mixing in jet in cross-flow configurations using LES

International Nuclear Information System (INIS)

Wegner, B.; Huai, Y.; Sadiki, A.

2004-01-01

Mixing processes in turbulent fluid motion are of fundamental interest in many situations in engineering practice. Due to its practical importance in a vast number of applications, the generic configuration of the jet in cross-flow has been studied extensively in the past. Recently, the question has received a lot of attention, whether the unsteady behavior of the jet in cross-flow can be influenced by either active or passive means in order to control and enhance the mixing process. In the present paper, we use the large eddy simulation (LES) methodology to investigate how turbulent mixing can be enhanced by varying the angle between the jet and the oncoming cross-flow. After validating the computations against measurements by Andreopoulos and Rodi, we analyze qualitatively and quantitatively the mixing process for three configurations with different angles. It is shown that the inclination influences the characteristics of vortical structures and secondary motion which in turn have an effect on the mixing process. Besides a PDF of the passive scalar and a scalar energy spectrum, a mixedness parameter is used to provide information with respect to the quality and rate of mixing

Microfluidic mixing in a Y-junction open channel

Directory of Open Access Journals (Sweden)

Jue Nee Tan

2012-09-01

Full Text Available In the laminar regimes typical of microfluidic systems’, mixing is governed by molecular diffusion; however this process is slow in nature. Consequently, passive or active methods are usually sought for effective mixing. In this work, open fluidic channels will be investigated; these channels are bounded on all but one face by an air/fluid interface. Firstly, it will be shown that flow in open channels can merge at a Y-junction in a stable manner; hence two fluids can be brought into contact with each other. Secondly, the mixing of these two fluids will be studied. At high flow rates (>300 μl/min mixing occurs at the junction without need for additional intervention, this mixing is far swifter than can be expected from molecular diffusion. At lower flow rates, intervention is required. A major motivation for open fluidic channels is the ability to interact with the surrounding air environment; this feature is used to effect the desired mixing. It is shown that by blowing an air jet across the junction, shear stresses at the air/fluid interface causes a flow profile within the fluid inductive to rapid mixing of the fluids.

Morphometric differences in debris flow and mixed flow fans in eastern Death Valley, CA

Science.gov (United States)

Wasklewicz, T. A.; Whitworth, J.

2004-12-01

Geomorphological features are best examined through direct measurement and parameterization of accurate topographic data. Fine-scale data are therefore required to produce a complete set of elevation data. Airborne Laser Swath Mapping (ALSM) data provide high-resolution data over large spatially continuous areas. The National Center for Advanced Laser Mapping (NCALM) collected ALSM data for an area along the eastern side of Death Valley extending from slightly north of Badwater to Mormon Point. The raw ALSM data were post-processed and delivered by NCALM in one-meter grid nodes that we converted to one-meter raster data sets. ALSM data are used to assess variations in the dimensions of surficial features found in 32 alluvial fans (21 debris flow and 11 mixed flow fans). Planimetric curvature of the fan surfaces is used to develop a topographic signature to distinguish debris flow from mixed flow fans. These two groups of fans are identified from field analysis of near vertical exposures along channels as well as surficial exposures at proximal, medial, and distal fan locations. One group of fans exhibited debris flow characteristics (DF), while the second group contained a mixture of fluid and debris flows (MF). Local planimetric curvature of the alluvial fan surfaces was derived from the one-meter DEM. The local curvature data were reclassified into concave and convex features. This sequence corresponds to two broad classes of fan features: channels and interfluves. Thirty random points were generated inside each fan polygon. The length of the nearest concave-convex (channel-interfluve) couplet was measured at each point and the percentage of convex and concave pixels in a 10m box centered on the random point was also recorded. Plots and statistical analyses of the data show clear indication that local planimetric curvature can be used as a topographic signature to distinguish between the varying formative processes in alluvial fans. Significant differences in the

Stopped-flow studies of spectral changes in bilirubin-human serum albumin following an alkaline pH jump and following binding of bilirubin

DEFF Research Database (Denmark)

Honoré, B

1987-01-01

A stopped-flow technique was used to study the spectral changes occurring in bilirubin-albumin following a pH jump as well as following binding of bilirubin at 25 degrees C. The changes were studied in two wavelength ranges, 280-310 nm (tyrosine residues) and 400-510 nm (bound bilirubin). The cha......A stopped-flow technique was used to study the spectral changes occurring in bilirubin-albumin following a pH jump as well as following binding of bilirubin at 25 degrees C. The changes were studied in two wavelength ranges, 280-310 nm (tyrosine residues) and 400-510 nm (bound bilirubin......). The changes were analyzed according to a scheme of consecutive unimolecular reactions. Spectral monitoring of a pH jump from 11.3 to 11.8 reveals that the bilirubin-albumin complex changes its structure in several steps. The UV absorption spectra show that 3.8 tyrosine residues ionize in the first step, 2...

Influence of Boussinesq coefficient on depth-averaged modelling of rapid flows

Science.gov (United States)

Yang, Fan; Liang, Dongfang; Xiao, Yang

2018-04-01

The traditional Alternating Direction Implicit (ADI) scheme has been proven to be incapable of modelling trans-critical flows. Its inherent lack of shock-capturing capability often results in spurious oscillations and computational instabilities. However, the ADI scheme is still widely adopted in flood modelling software, and various special treatments have been designed to stabilise the computation. Modification of the Boussinesq coefficient to adjust the amount of fluid inertia is a numerical treatment that allows the ADI scheme to be applicable to rapid flows. This study comprehensively examines the impact of this numerical treatment over a range of flow conditions. A shock-capturing TVD-MacCormack model is used to provide reference results. For unsteady flows over a frictionless bed, such as idealised dam-break floods, the results suggest that an increase in the value of the Boussinesq coefficient reduces the amplitude of the spurious oscillations. The opposite is observed for steady rapid flows over a frictional bed. Finally, a two-dimensional urban flooding phenomenon is presented, involving unsteady flow over a frictional bed. The results show that increasing the value of the Boussinesq coefficient can significantly reduce the numerical oscillations and reduce the predicted area of inundation. In order to stabilise the ADI computations, the Boussinesq coefficient could be judiciously raised or lowered depending on whether the rapid flow is steady or unsteady and whether the bed is frictional or frictionless. An increase in the Boussinesq coefficient generally leads to overprediction of the propagating speed of the flood wave over a frictionless bed, but the opposite is true when bed friction is significant.

Gas flow and thermal mixing in a helically wound tube bundle

International Nuclear Information System (INIS)

Chiger, H.D.

1980-07-01

The thermal dissipation of a hot gas streak flowing across a segment of a helically wound tube bundle and the bypass flow streaming between the tubes and the bundle wall were investigated experimentally in the range of 8000 < Re < 50,000. Two different modes of creating a hot streak were employed. A planar hot streak was (1) injected at the entrance to the tube bundle and (2) generated by electrically heating several tubes past the bundle inlet. In the first case the mixing occurs in a region of lower turbulence since it occurs near the bundle inlet. In the second case the mixing occurs in a region of higher turbulence since the flow has already passed over several tube rows before the hot streak is generated

Experimental investigation of transverse mixing in porous media under helical flow conditions

DEFF Research Database (Denmark)

Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A.

2016-01-01

Plume dilution and transverse mixing can be considerably enhanced by helical flow occurring in three-dimensional heterogeneous anisotropic porous media. In this study, we perform tracer experiments in a fully three-dimensional flow-through chamber to investigate the effects of helical flow on plume...

Hydrochemical evidence for mixing of river water and groundwater during high-flow conditions, lower Suwannee River basin, Florida, USA

Science.gov (United States)

Crandall, C.A.; Katz, B.G.; Hirten, J.J.

1999-01-01

Karstic aquifers are highly susceptible to rapid infiltration of river water, particularly during periods of high flow. Following a period of sustained rainfall in the Suwannee River basin, Florida, USA, the stage of the Suwannee River rose from 3.0 to 5.88 m above mean sea level in April 1996 and discharge peaked at 360 m3/s. During these high-flow conditions, water from the Suwannee River migrated directly into the karstic Upper Floridan aquifer, the main source of water supply for the area. Changes in the chemical composition of groundwater were quantified using naturally occurring geochemical tracers and mass-balance modeling techniques. Mixing of river water with groundwater was indicated by a decrease in the concentrations of calcium, silica, and 222Rn; and by an increase in dissolved organic carbon (DOC), tannic acid, and chloride, compared to low-flow conditions in water from a nearby monitoring well, Wingate Sink, and Little River Springs. The proportion (fraction) of river water in groundwater ranged from 0.13 to 0.65 at Wingate Sink and from 0.5 to 0.99 at well W-17258, based on binary mixing models using various tracers. The effectiveness of a natural tracer in quantifying mixing of river water and groundwater was related to differences in tracer concentration of the two end members and how conservatively the tracer reacted in the mixed water. Solutes with similar concentrations in the two end-member waters (Na, Mg, K, Cl, SO4, SiO2) were not as effective tracers for quantifying mixing of river water and groundwater as those with larger differences in end-member concentrations (Ca, tannic acid, DOC, 222Rn, HCO3). ?? Springer-Verlag.

Using Flow Electrodes in Multiple Reactors in Series for Continuous Energy Generation from Capacitive Mixing

KAUST Repository

Hatzell, Marta C.

2014-12-09

Efficient conversion of “mixing energy” to electricity through capacitive mixing (CapMix) has been limited by low energy recoveries, low power densities, and noncontinuous energy production resulting from intermittent charging and discharging cycles. We show here that a CapMix system based on a four-reactor process with flow electrodes can generate constant and continuous energy, providing a more flexible platform for harvesting mixing energy. The power densities were dependent on the flow-electrode carbon loading, with 5.8 ± 0.2 mW m–2 continuously produced in the charging reactor and 3.3 ± 0.4 mW m–2 produced in the discharging reactor (9.2 ± 0.6 mW m–2 for the whole system) when the flow-electrode carbon loading was 15%. Additionally, when the flow-electrode electrolyte ion concentration increased from 10 to 20 g L–1, the total power density of the whole system (charging and discharging) increased to 50.9 ± 2.5 mW m–2.

Determination of myoglobin based on its enzymatic activity by stopped-flow spectrophotometry

Science.gov (United States)

Zheng, Qi; Liu, Zhihong; Cai, Ruxiu

2005-04-01

A new method has been developed for the determination of myoglobin (Mb) based on its enzymatic activity for the oxidation of o-phenylenediamine (OPDA) with hydrogen peroxide. Stopped-flow spectrophotometry was used to study the kinetic behavior of the oxidation reaction. The catalytic activity of Mb was compared to other three kinds of catalyst. The time dependent absorbance of the reaction product, 2,3-diamimophenazine (DAPN), at a wavelength of 426 nm was recorded. The initial reaction rate obtained at 40 °C was found to be proportional to the concentration of Mb in the range of 1.0 × 10 -6 to 4.0 × 10 -9 mol L -1. The detection limit of Mb was found to be 9.93 × 10 -10 mol L -1. The relative standard deviations were within 5% for the determination of different concentrations of Mb. Excess of bovine serum albumin (BSA), Ca(II), Mg(II), Cu(II), glucose, caffeine, lactose and uric acid did not interfere.

Modeling molecular mixing in a spatially inhomogeneous turbulent flow

Science.gov (United States)

Meyer, Daniel W.; Deb, Rajdeep

2012-02-01

Simulations of spatially inhomogeneous turbulent mixing in decaying grid turbulence with a joint velocity-concentration probability density function (PDF) method were conducted. The inert mixing scenario involves three streams with different compositions. The mixing model of Meyer ["A new particle interaction mixing model for turbulent dispersion and turbulent reactive flows," Phys. Fluids 22(3), 035103 (2010)], the interaction by exchange with the mean (IEM) model and its velocity-conditional variant, i.e., the IECM model, were applied. For reference, the direct numerical simulation data provided by Sawford and de Bruyn Kops ["Direct numerical simulation and lagrangian modeling of joint scalar statistics in ternary mixing," Phys. Fluids 20(9), 095106 (2008)] was used. It was found that velocity conditioning is essential to obtain accurate concentration PDF predictions. Moreover, the model of Meyer provides significantly better results compared to the IECM model at comparable computational expense.

Design and aerodynamic performance evaluation of a high-work mixed flow turbine stage

Science.gov (United States)

Neri, Remo N.; Elliott, Thomas J.; Marsh, David N.; Civinskas, Kestutis C.

1994-01-01

As axial and radial turbine designs have been pushed to their aerothermodynamic and mechanical limits, the mixed-flow turbine (MFT) concept has been projected to offer performance and durability improvements, especially when ceramic materials are considered. The objective of this NASA/U.S. Army sponsored mixed-flow turbine (AMFT) program was to determine the level of performance attainable with MFT technology within the mechanical constraints of 1997 projected ceramic material properties. The MFT geometry is similar to a radial turbine, exhibiting a large radius change from inlet to exit, but differing in that the inlet flowpath is not purely radial, nor axial, but mixed; it is the inlet geometry that gives rise to the name 'mixed-flow'. The 'mixed' orientation of the turbine inlet offers several advantages over radial designs by allowing a nonzero inlet blade angle yet maintaining radial-element blades. The oblique inlet not only improves the particle-impact survivability of the design, but improves the aerodynamic performance by reducing the incidence at the blade inlet. The difficulty, however, of using mixed-flow geometry lies in the scarcity of detailed data and documented design experience. This paper reports the design of a MFT stage designed with the intent to maximize aerodynamic performance by optimizing design parameters such as stage reaction, rotor incidence, flowpath shape, blade shape, vane geometry, and airfoil counts using 2-D, 3-D inviscid, and 3-D viscous computational fluid dynamics code. The aerodynamic optimization was accomplished while maintaining mechanical integrity with respect to vibration and stress levels in the rotor. A full-scale cold-flow rig test was performed with metallic hardware fabricated to the specifications of the hot ceramic geometry to evaluate the stage performance.

Influence of Auroral Streamers on Rapid Evolution of Ionospheric SAPS Flows

Science.gov (United States)

Gallardo-Lacourt, Bea; Nishimura, Y.; Lyons, L. R.; Mishin, E. V.; Ruohoniemi, J. M.; Donovan, E. F.; Angelopoulos, V.; Nishitani, N.

2017-12-01

Subauroral polarization streams (SAPS) often show large, rapid enhancements above their slowly varying component. We present simultaneous observations from ground-based all-sky imagers and flows from the Super Dual Auroral Radar Network radars to investigate the relationship between auroral phenomena and flow enhancement. We first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased. We also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions. In the forward study, 98% of the streamers approaching the equatorward boundary were associated with SAPS flow enhancements reaching 700 m/s and typically hundreds of m/s above background speeds. The reverse study reveals that flow enhancements associated with streamers (60%) and enhanced larger-scale convection (37%) contribute to SAPS flow enhancements. The strong correlation of auroral streamers with rapid evolution (approximately minutes) of SAPS flows suggests that transient fast earthward plasma sheet flows can often lead to westward SAPS flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions. We also found a strong correlation between flow duration and streamer duration and a weak correlation between SAPS flow velocity and streamer intensity. This result suggests that intense flow bursts in the plasma sheet (which correlate with intense streamers) are associated with intense SAPS ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to Earth.

Asymptotic behavior of the mixed mass in Rayleigh–Taylor and Richtmyer–Meshkov instability induced flows

Energy Technology Data Exchange (ETDEWEB)

Zhou, Ye; Cabot, William H. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Thornber, Ben [The University of Sydney, School of Aerospace, Mechanical and Mechatronic Engineering, New South Wales 2006, Sydney (Australia)

2016-05-15

Rayleigh–Taylor instability (RTI) and Richtmyer–Meshkov instability (RMI) are serious practical issues in inertial confinement fusion research, and also have relevance to many cases of astrophysical fluid dynamics. So far, much of the attention has been paid to the late-time scaling of the mixed width, which is used as a surrogate to how well the fluids have been mixed. Yet, the actual amount of mixed mass could be viewed as a more direct indicator on the evolution of the mixing layers due to hydrodynamic instabilities. Despite its importance, there is no systematic study as yet on the scaling of the mixed mass for either the RTI or the RMI induced flow. In this article, the normalized mixed mass (Ψ) is introduced for measuring the efficiency of the mixed mass. Six large numerical simulation databases have been employed: the RTI cases with heavy-to-light fluid density ratios of 1.5, 3, and 9; the single shock RMI cases with density ratios of 3 and 20; and a reshock RMI case with density ratio of 3. Using simulated flow fields, the normalized mixed mass Ψ is shown to be more sensitive in discriminating the variation with Atwood number for the RTI flows. Moreover, Ψ is demonstrated to provide more consistent results for both the RTI and RMI flows when compared with the traditional mixedness parameters, Ξ and Θ.

Measurements of Flow Mixing at Subchannels in a Wire-Wrapped 37-Rod Bundle for a Sodium Cooled Fast Reactor

International Nuclear Information System (INIS)

Kim, Hyungmo; Bae, Hwang; Chang, Seok-Kyu; Choi, Sun Rock; Lee, Dong Won; Ko, Yung Joo; Choi, Hae Seob; Euh, Dong-Jin; Lee, Hyeong-Yeon

2014-01-01

For a safety analysis in a core thermal design of a sodium-cooled fast reactor (SFR), flow mixing characteristics at subchannels in a wire-wrapped rod bundle are very important. Wrapped wires make a cross flow in a around the fuel rod) of the fuel rod, and this effect lets flow be mixed. Experimental results of flow mixing can be meaningful for verification and validation of thermal mixing correlation in a reactor core thermo-hydraulic design code. A wire mesh sensing technique can be useful method for measuring of flow mixing characteristics. A wire mesh sensor has been traditionally used to measure the void fraction of a two-phase flow field, i.e. gas and liquid. However, it has been recently reported that the wire mesh sensor can be used successfully to recognize the flow field in liquid phase by injecting a tracing liquid with a different level of electric conductivity. This can be powerfully adapted to recognize flow mixing characteristics by wrapped wires in SFR core thermal design. In this work, we conducted the flow mixing experiments using a custom designed wire mesh sensor. To verify and validate computer codes for the SFR core thermal design, mixing experiments were conducted at a hexagonally arrayed 37-pin wire-wrapped fuel rod bundle test section. The well-designed wire mesh sensor was used to measure flow mixing characteristics. The developed post-processing method has its own merits, and flow mixing results were reasonable. In addition, by uncertainty analysis, the system errors and the random error were estimated in experiments. Therefore, the present results and methods can be used for design code verification and validation

Groundwater flow analysis using mixed hybrid finite element method for radioactive waste disposal facilities

International Nuclear Information System (INIS)

Aoki, Hiroomi; Shimomura, Masanori; Kawakami, Hiroto; Suzuki, Shunichi

2011-01-01

In safety assessments of radioactive waste disposal facilities, ground water flow analysis are used for calculating the radionuclide transport pathway and the infiltration flow rate of groundwater into the disposal facilities. For this type of calculations, the mixed hybrid finite element method has been used and discussed about the accuracy of ones in Europe. This paper puts great emphasis on the infiltration flow rate of groundwater into the disposal facilities, and describes the accuracy of results obtained from mixed hybrid finite element method by comparing of local water mass conservation and the reliability of the element breakdown numbers among the mixed hybrid finite element method, finite volume method and nondegenerated finite element method. (author)

Nonlinear effects contributing to hand-stopping tones in a horn.

Science.gov (United States)

Ebihara, Takayasu; Yoshikawa, Shigeru

2013-05-01

Hand stopping is a technique for playing the French horn while closing the bell relatively tightly using the right hand. The resulting timbre is called "penetrating" and "metallic." The effect of hand stopping on the horn input impedance has been studied, but the tone quality has hardly ever been considered. In the present paper, the dominant physical cause of the stopped-tone quality is discussed in detail. Numerical calculations of the transmission function of the stopped-horn model and the measurements of both sound pressure and wall vibration in hand stopping are carried out. They strongly suggest that the metallicness of the stopped tone is characterized by the generation of higher harmonics extending over 10 kHz due to the rapidly corrugating waveform and that the associated wall vibration on the bell may be responsible for this higher harmonic generation. However, excitation experiments and immobilization experiments performed to elucidate the relationship between sound radiation and wall vibration deny their correlation. Instead, the measurement result of the mouthpiece pressure in hand stopping suggests that minute wave corrugations peculiar to the metallic stopped tones are probably formed by nonlinear sound propagation along the bore.

Mixed convection flow and heat transfer in a vertical wavy channel ...

African Journals Online (AJOL)

Mixed convection flow and heat transfer in a vertical wavy channel filled with porous and fluid layers is studied analytically. The flow in the porous medium is modeled using Darcy-Brinkman equation. The coupled non-linear partial differential equations describing the conservation of mass, momentum and energy are solved ...

Experiments on mixing and combustion with low heat release in a turbulent shear flow

International Nuclear Information System (INIS)

Mungel, M.G.

1983-01-01

A new blowdown facility was built to study mixing and combustion in a turbulent shear layer. The system is capable of 100 m/s for three seconds in a 5 x 20 cm exit area on the high speed side, and 50 m/s in a 10 x 20 cm exit area on the low speed side. Dilute concentrations of hydrogen and fluorine, carried in an inert gas, react when both fluid streams meet at the tip of a splitter plate. The reaction is spontaneous, rapid, and highly exothermic. The resulting temperature field was studied using a rake of eight fast response thermometers placed across the width of the layer. Runs were performed for low heat release over a wide range of equivalence (concentration) ratios, at a Reynolds number of 30,800 based on velocity difference and vorticity thickness. The heat release is sufficiently low so that the overall properties of the mixing layer are not significantly changed from the cold case. The results show the presence of large, hot structures within the flow together with cool, irrotational tongues of freestream fluid that penetrate deep into the layer. Thus, it is possible for the entire width of the layer to be quite hot, owing to the passage of a large structure, or for the layer to be quite cool, owing to the presence of the cool fluid tongues. The mean temperature results from a duty cycle whereby a given point in the flow sees alternating hot and cool fluid which averages into the local mean. The results compare favorably with the recent theoretical model of Broadwell and Breidenthal for mixing and chemical reaction in a turbulent shear layer. With this model it is possible to bring the results for gases and liquids into quantitative agreement

Swirl effect on flow structure and mixing in a turbulent jet

Science.gov (United States)

Kravtsov, Z. D.; Sharaborin, D. K.; Dulin, V. M.

2018-03-01

The paper reports on experimental study of turbulent transport in the initial region of swirling turbulent jets. The particle image velocimetry and planar laser-induced fluorescence techniques are used to investigate the flow structure and passive scalar concentration, respectively, in free air jet with acetone vapor. Three flow cases are considered, viz., non-swirling jets and swirling jets with and without vortex breakdown and central recirculation zone. Without vortex breakdown, the swirl is shown to promote jet mixing with surrounding air and to decrease the jet core length. The vortex core breakdown further enhances mixing as the jet core disintegrates at the nozzle exit.

Experimental study of unsteady thermally stratified flow

International Nuclear Information System (INIS)

Lee, Sang Jun; Chung, Myung Kyoon

1985-01-01

Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objectives were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT(Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer of heat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field. (Author)

Controlling mixing and segregation in time periodic granular flows

Science.gov (United States)

Bhattacharya, Tathagata

Segregation is a major problem for many solids processing industries. Differences in particle size or density can lead to flow-induced segregation. In the present work, we employ the discrete element method (DEM)---one type of particle dynamics (PD) technique---to investigate the mixing and segregation of granular material in some prototypical solid handling devices, such as a rotating drum and chute. In DEM, one calculates the trajectories of individual particles based on Newton's laws of motion by employing suitable contact force models and a collision detection algorithm. Recently, it has been suggested that segregation in particle mixers can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. Further, it has been hypothesized that, for a rotating drum, the effectiveness of this technique can be linked to the probability distribution of the number of times a particle passes through the flowing layer per rotation of the drum. In the first portion of this work, various configurations of solid mixers are numerically and experimentally studied to investigate the conditions for improved mixing in light of these hypotheses. Besides rotating drums, many studies of granular flow have focused on gravity driven chute flows owing to its practical importance in granular transportation and to the fact that the relative simplicity of this type of flow allows for development and testing of new theories. In this part of the work, we observe the deposition behavior of both mono-sized and polydisperse dry granular materials in an inclined chute flow. The effects of different parameters such as chute angle, particle size, falling height and charge amount on the mass fraction distribution of granular materials after deposition are investigated. The simulation results obtained using DEM are compared with the experimental findings and a high degree of agreement is observed. Tuning of the underlying contact force parameters allows the achievement

Rayleigh-Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. I

Science.gov (United States)

Zhou, Ye

2017-12-01

Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities play an important role in a wide range of engineering, geophysical, and astrophysical flows. They represent a triggering event that, in many cases, leads to large-scale turbulent mixing. Much effort has been expended over the past 140 years, beginning with the seminal work of Lord Rayleigh, to predict the evolution of the instabilities and of the instability-induced mixing layers. The objective of Part I of this review is to provide the basic properties of the flow, turbulence, and mixing induced by RT, RM, and Kelvin-Helmholtz (KH) instabilities. Historical efforts to study these instabilities are briefly reviewed, and the significance of these instabilities is discussed for a variety of flows, particularly for astrophysical flows and for the case of inertial confinement fusion. Early experimental efforts are described, and analytical attempts to model the linear, and nonlinear regimes of these mixing layers are examined. These analytical efforts include models for both single-mode and multi-mode initial conditions, as well as multi-scale models to describe the evolution. Comparisons of these models and theories to experimental and simulation studies are then presented. Next, attention is paid to the issue of the influence of stabilizing mechanisms (e.g., viscosity, surface tension, and diffuse interface) on the evolution of these instabilities, as well as the limitations and successes of numerical methods. Efforts to study these instabilities and mixing layers using group-theoretic ideas, as well as more formal notions of turbulence cascade processes during the later stages of the induced mixing layers, are inspected. A key element of the review is the discussion of the late-time self-similar scaling for the RT and RM growth factors, α and θ. These parameters are influenced by the initial conditions and much of the observed variation can be explained by this. In some cases, these instabilities

Effect of exercise on patient specific abdominal aortic aneurysm flow topology and mixing.

Science.gov (United States)

Arzani, Amirhossein; Les, Andrea S; Dalman, Ronald L; Shadden, Shawn C

2014-02-01

Computational fluid dynamics modeling was used to investigate changes in blood transport topology between rest and exercise conditions in five patient-specific abdominal aortic aneurysm models. MRI was used to provide the vascular anatomy and necessary boundary conditions for simulating blood velocity and pressure fields inside each model. Finite-time Lyapunov exponent fields and associated Lagrangian coherent structures were computed from blood velocity data and were used to compare features of the transport topology between rest and exercise both mechanistically and qualitatively. A mix-norm and mix-variance measure based on fresh blood distribution throughout the aneurysm over time were implemented to quantitatively compare mixing between rest and exercise. Exercise conditions resulted in higher and more uniform mixing and reduced the overall residence time in all aneurysms. Separated regions of recirculating flow were commonly observed in rest, and these regions were either reduced or removed by attached and unidirectional flow during exercise, or replaced with regional chaotic and transiently turbulent mixing, or persisted and even extended during exercise. The main factor that dictated the change in flow topology from rest to exercise was the behavior of the jet of blood penetrating into the aneurysm during systole. Copyright © 2013 John Wiley & Sons, Ltd.

Flow and active mixing have a strong impact on bacterial growth dynamics in the proximal large intestine

Science.gov (United States)

Cremer, Jonas; Segota, Igor; Yang, Chih-Yu; Arnoldini, Markus; Groisman, Alex; Hwa, Terence

2016-11-01

More than half of fecal dry weight is bacterial mass with bacterial densities reaching up to 1012 cells per gram. Mostly, these bacteria grow in the proximal large intestine where lateral flow along the intestine is strong: flow can in principal lead to a washout of bacteria from the proximal large intestine. Active mixing by contractions of the intestinal wall together with bacterial growth might counteract such a washout and allow high bacterial densities to occur. As a step towards understanding bacterial growth in the presence of mixing and flow, we constructed an in-vitro setup where controlled wall-deformations of a channel emulate contractions. We investigate growth along the channel under a steady nutrient inflow. Depending on mixing and flow, we observe varying spatial gradients in bacterial density along the channel. Active mixing by deformations of the channel wall is shown to be crucial in maintaining a steady-state bacterial population in the presence of flow. The growth-dynamics is quantitatively captured by a simple mathematical model, with the effect of mixing described by an effective diffusion term. Based on this model, we discuss bacterial growth dynamics in the human large intestine using flow- and mixing-behavior having been observed for humans.

Water excretion mechanisms of the kidney studied in the rabbit using tritiated water during the stop-flow assay

International Nuclear Information System (INIS)

Morel, F.; Amiel, CI.; Falbriard, A.

1960-01-01

The pattern of water turnover in the kidney and the mechanisms of water transfer into the urine have been studied in the rabbit using tritiated water as a tracer and the stop-flow technique. The experiments have given the following results: a) During the interruption of the diuresis, the injected tritiated water is completely exchanged with the water of the renal cortex, but the tracer does not reach the deep regions of the kidney, despite the fact that the blood circulation is maintained in these regions; this suggests that the vascular loops of the vasa recta function as a mechanism of water exchange by countercurrent. b) During the osmotic polyuria following the stop-flow period, the concentration gradient of tritiated water inside the kidney diminishes progressively. The concentration of the tracer in the urine is at all time similar to that existing in the deep medulla and the renal papilla and markedly different from that of the cortex or arterial blood. This fact shows that the molecules of water in the urine excreted do not come from either the glomerular filtrate or the convoluted tubules but from the water contained in the deep regions of the kidney. Also these results indicate that the walls of the collecting ducts have a very high permeability to water diffusion. Reprint of a paper published in Revue francaise d'etudes cliniques et biologiques, Vol. IV, no. 8, p. 773-779, 1959 [fr

Doubly stratified mixed convection flow of Maxwell nanofluid with heat generation/absorption

Energy Technology Data Exchange (ETDEWEB)

Abbasi, F.M., E-mail: abbasisarkar@gmail.com [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Hayat, T. [Department of Mathematics, Quaid-i-Azam University, 45320, Islamabad 44000 (Pakistan); NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Ahmad, B. [NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)

2016-04-15

Magnetohydrodynamic (MHD) doubly stratified flow of Maxwell nanofluid in presence of mixed convection is analyzed in this article. Effects of thermophoresis, Brownian motion and heat generation/absorption are present. The flow is induced due to linear stretching of sheet. Mathematical formulation is made under boundary layer approach. Expressions of velocity, temperature and nanoparticles concentration are developed. The obtained results are plotted and discussed to examine the variations in temperature and nanoparticles concentration due to different physical parameters. Numerical computations are made to obtain the values of local Nusselt and Sherwood numbers. Impact of sundry parameters on the flow quantities is analyzed graphically. - Highlights: • Double stratified flow of Maxwell nanofluid with mixed convection is modeled. • Thermophoresis and Brownian motion effects are encountered. • Computations are made to obtain the solution expressions. • Numerical values of local Nusselt and Sherwood numbers are computed and examined.

Transport, mixing and stretching in a chaotic Stokes flow: The two-roll mill

International Nuclear Information System (INIS)

Kaper, T.J.; Wiggins, S.

1989-01-01

We present the outline and preliminary results of an analytical and numerical study of transport, mixing, and stretching in a chaotic Stokes' flow in a two-roll mill apparatus. We use the theory of dynamical systems to describe the rich behavior and structure exhibited by these flows. The main features are the homoclinic tangle which functions as the backbone of the chaotic mixing region, the Smale horseshoe, and the island chains. We then use our detailed knowledge of these structures to develop a theory of transport and stretching of fluid in the chaotic regime. In particular, we show how a specific set of tools for adiabatic chaos- the adiabatic Melnikov function lobe area and flux computations and the adiabatic switching method is ideally suited to develop this theory of transport, mixing and stretching in time-dependent two-dimensional Stokes' flows. 19 refs., 8 figs

Simulation and Visualization of Flows Laden with Cylindrical Nanoparticles in a Mixing Layer

Directory of Open Access Journals (Sweden)

Wenqian Lin

2018-01-01

Full Text Available The motion of cylindrical particles in a mixing layer is studied using the pseudospectral method and discrete particle model. The effect of the Stokes number and particle aspect ratio on the mixing and orientation distribution of cylindrical particles is analyzed. The results show that the rollup of mixing layer drives the particles to the edge of the vortex by centrifugal force. The cylindrical particles with the small Stokes number almost follow fluid streamlines and are mixed thoroughly, while those with the large Stokes number, centrifugalized and accumulated at the edge of the vortex, are poorly mixed. The mixing degree of particles becomes worse as the particle aspect ratio increases. The cylindrical particles would change their orientation under two torques and rotate around their axis of revolution aligned to the vorticity direction when the shear rate is low, while aligning on the flow-gradient plane beyond a critical shear rate value. More particles are oriented with the flow direction, and this phenomenon becomes more obvious with the decrease of the Stokes number and particle aspect ratio.

A review on the analysis and experiment of fluid flow and mixing in micro-channels

International Nuclear Information System (INIS)

Kang, Sang Mo; Suh, Yong Kweon; Jayaraj, Simon

2007-01-01

The studies with respect to micro-channels and micro-mixers are expanding in many dimensions. Most significant area of micro-mixer study is the flow analysis in various micro-channel configurations. The flow phenomena in microchannel devices are quite different from that of the macro-scale devices. An attempt is made here to review the important recent literature available in the area of micro-channel flow analysis and mixing. The topics covered include the physics of flow in micro-channels and integrated simulation of the micro-channel flow. Also, the flow control models and electro-kinetically driven micro-channel flows are dealt in detail. A survey of important numerical methods, which are currently popular for micro-channel flow analysis, is carried out. Different options for mixing in microchannels are provided, in sufficient detail

Analysis of mixed traffic flow with human-driving and autonomous cars based on car-following model

Science.gov (United States)

Zhu, Wen-Xing; Zhang, H. M.

2018-04-01

We investigated the mixed traffic flow with human-driving and autonomous cars. A new mathematical model with adjustable sensitivity and smooth factor was proposed to describe the autonomous car's moving behavior in which smooth factor is used to balance the front and back headway in a flow. A lemma and a theorem were proved to support the stability criteria in traffic flow. A series of simulations were carried out to analyze the mixed traffic flow. The fundamental diagrams were obtained from the numerical simulation results. The varying sensitivity and smooth factor of autonomous cars affect traffic flux, which exhibits opposite varying tendency with increasing parameters before and after the critical density. Moreover, the sensitivity of sensors and smooth factors play an important role in stabilizing the mixed traffic flow and suppressing the traffic jam.

Investigation of RADTRAN Stop Model input parameters for truck stops

International Nuclear Information System (INIS)

Griego, N.R.; Smith, J.D.; Neuhauser, K.S.

1996-01-01

RADTRAN is a computer code for estimating the risks and consequences as transport of radioactive materials (RAM). RADTRAN was developed and is maintained by Sandia National Laboratories for the US Department of Energy (DOE). For incident-free transportation, the dose to persons exposed while the shipment is stopped is frequently a major percentage of the overall dose. This dose is referred to as Stop Dose and is calculated by the Stop Model. Because stop dose is a significant portion of the overall dose associated with RAM transport, the values used as input for the Stop Model are important. Therefore, an investigation of typical values for RADTRAN Stop Parameters for truck stops was performed. The resulting data from these investigations were analyzed to provide mean values, standard deviations, and histograms. Hence, the mean values can be used when an analyst does not have a basis for selecting other input values for the Stop Model. In addition, the histograms and their characteristics can be used to guide statistical sampling techniques to measure sensitivity of the RADTRAN calculated Stop Dose to the uncertainties in the stop model input parameters. This paper discusses the details and presents the results of the investigation of stop model input parameters at truck stops

Calculation of external-internal flow fields for mixed-compression inlets

Science.gov (United States)

Chyu, W. J.; Kawamura, T.; Bencze, D. P.

1987-01-01

Supersonic inlet flows with mixed external-internal compressions were computed using a combined implicit-explicit (Beam-Warming-Steger/MacCormack) method for solving the three-dimensional unsteady, compressible Navier-Stokes equations in conservation form. Numerical calculations were made of various flows related to such inlet operations as the shock-wave intersections, subsonic spillage around the cowl lip, and inlet started versus unstarted conditions. Some of the computed results were compared with wind tunnel data.

The initial study on supercritical water flow and heat transfer in square rod bundle channel with mixing vane

International Nuclear Information System (INIS)

Zuo Guoping; Cao Can; Yu Tao

2010-01-01

Three-dimensional rectangular channel with the mixing wine in supercritical water reactor was studied in the paper using the FLUENT software. The mixing wing elevation influence on temperature distribution and flow field were studied in the model. The results showed the mixing wing caused fluid circumferential flow, making flow hot and cold fluids mixed and fluid temperature uniform distribution, effectively improved the fuel rod surface temperature distribution and reduced hot temperature. Among the four cases of mixing wing elevation of 15, 30, 45 and 50 angle, 30 angle is the best case in improving temperature distribution. (authors)

Experimental research on pressure fluctuation and vibration in a mixed flow pump

Energy Technology Data Exchange (ETDEWEB)

Wang, Kai; Liu, Houlin; Wang, Wenbo [National Research Center of Pumps and Pumping System Engineering and Technology, Jiangsu University, Zhenjiang (China); Zhou, Xiaohua [Gree Electric Appliance Inc. of Zhuhai, Zhuhai (China)

2016-01-15

To study the pressure fluctuation and vibration in mixed flow pumps, we chose a mixed flow pump with specific speed of 436.1 to measure. The time domains and frequency domain at each monitoring point on diffuser and outlet elbow were analyzed, as well as the vibration frequency domain characteristics at the impeller outlet and near the motor. The results show that the peak value of pressure fluctuation peak decreased gradually with the increase of flow rate. The pressure fluctuation of each monitoring point had periodicity, and the frequency domain dominated by blade passing frequency and multiple shaft frequency. The vibration frequency of each monitoring point occurred at shaft frequency and its multiple shaft frequency. The dominant frequency and the second frequency were distributed in shaft frequency and double shaft frequency.

Ion-beam mixed ultra-thin cobalt suicide (CoSi2) films by cobalt sputtering and rapid thermal annealing

Science.gov (United States)

Kal, S.; Kasko, I.; Ryssel, H.

1995-10-01

The influence of ion-beam mixing on ultra-thin cobalt silicide (CoSi2) formation was investigated by characterizing the ion-beam mixed and unmixed CoSi2 films. A Ge+ ion-implantation through the Co film prior to silicidation causes an interface mixing of the cobalt film with the silicon substrate and results in improved silicide-to-silicon interface roughness. Rapid thermal annealing was used to form Ge+ ion mixed and unmixed thin CoSi2 layer from 10 nm sputter deposited Co film. The silicide films were characterized by secondary neutral mass spectroscopy, x-ray diffraction, tunneling electron microscopy (TEM), Rutherford backscattering, and sheet resistance measurements. The experi-mental results indicate that the final rapid thermal annealing temperature should not exceed 800°C for thin (micrographs of the ion-beam mixed and unmixed CoSi2 films reveals that Ge+ ion mixing (45 keV, 1 × 1015 cm-2) produces homogeneous silicide with smooth silicide-to-silicon interface.

Lagrangian transport characteristics of a class of three-dimensional inline-mixing flows with fluid inertia

International Nuclear Information System (INIS)

Speetjens, M. F. M.; Demissie, E. A.; Metcalfe, G.; Clercx, H. J. H.

2014-01-01

Laminar mixing by the inline-mixing principle is a key to many industrial fluids-engineering systems of size extending from micrometers to meters. However, insight into fundamental transport phenomena particularly under the realistic conditions of three-dimensionality (3D) and fluid inertia remains limited. This study addresses these issues for inline mixers with cylindrical geometries and adopts the Rotated Arc Mixer (RAM) as a representative system. Transport is investigated from a Lagrangian perspective by identifying and examining coherent structures that form in the 3D streamline portrait. 3D effects and fluid inertia introduce three key features that are not found in simplified configurations: transition zones between consecutive mixing cells of the inline-mixing flow; local upstream flow (in certain parameter regimes); transition/inertia-induced breaking of symmetries in the Lagrangian equations of motion (causing topological changes in coherent structures). Topological considerations strongly suggest that there nonetheless always exists a net throughflow region between inlet and outlet of the inline-mixing flow that is strictly separated from possible internal regions. The Lagrangian dynamics in this region admits representation by a 2D time-periodic Hamiltonian system. This establishes one fundamental kinematic structure for the present class of inline-mixing flows and implies universal behavior in that all states follow from the Hamiltonian breakdown of one common integrable state. A so-called period-doubling bifurcation is the only way to eliminate transport barriers originating from this state and thus is a necessary (yet not sufficient) condition for global chaos. Important in a practical context is that a common simplification in literature, i.e., cell-wise fully-developed Stokes flow (“2.5D approach”), retains these fundamental kinematic properties and deviates from the generic 3D inertial case only in a quantitative sense. This substantiates its

A staggered conservative scheme for every Froude number in rapidly varied shallow water flows

Science.gov (United States)

Stelling, G. S.; Duinmeijer, S. P. A.

2003-12-01

This paper proposes a numerical technique that in essence is based upon the classical staggered grids and implicit numerical integration schemes, but that can be applied to problems that include rapidly varied flows as well. Rapidly varied flows occur, for instance, in hydraulic jumps and bores. Inundation of dry land implies sudden flow transitions due to obstacles such as road banks. Near such transitions the grid resolution is often low compared to the gradients of the bathymetry. In combination with the local invalidity of the hydrostatic pressure assumption, conservation properties become crucial. The scheme described here, combines the efficiency of staggered grids with conservation properties so as to ensure accurate results for rapidly varied flows, as well as in expansions as in contractions. In flow expansions, a numerical approximation is applied that is consistent with the momentum principle. In flow contractions, a numerical approximation is applied that is consistent with the Bernoulli equation. Both approximations are consistent with the shallow water equations, so under sufficiently smooth conditions they converge to the same solution. The resulting method is very efficient for the simulation of large-scale inundations.

Instabilities in rapid directional solidification under weak flow

Science.gov (United States)

Kowal, Katarzyna N.; Davis, Stephen H.; Voorhees, Peter W.

2017-12-01

We examine a rapidly solidifying binary alloy under directional solidification with nonequilibrium interfacial thermodynamics viz. the segregation coefficient and the liquidus slope are speed dependent and attachment-kinetic effects are present. Both of these effects alone give rise to (steady) cellular instabilities, mode S , and a pulsatile instability, mode P . We examine how weak imposed boundary-layer flow of magnitude |V | affects these instabilities. For small |V | , mode S becomes a traveling and the flow stabilizes (destabilizes) the interface for small (large) surface energies. For small |V | , mode P has a critical wave number that shifts from zero to nonzero giving spatial structure. The flow promotes this instability and the frequencies of the complex conjugate pairs each increase (decrease) with flow for large (small) wave numbers. These results are obtained by regular perturbation theory in powers of V far from the point where the neutral curves cross, but requires a modified expansion in powers of V1 /3 near the crossing. A uniform composite expansion is then obtained valid for all small |V | .

The effect of starting or stopping skin cooling on the thermoregulatory responses during leg exercise in humans.

Science.gov (United States)

Demachi, K; Yoshida, T; Kume, M; Tsuneoka, H

2012-07-01

To assess the effects of starting or stopping leg cooling on the thermoregulatory responses during exercise, 60 min of cycling exercise at 30% of maximal oxygen uptake was performed under 4 conditions using tube trouser perfused with water at 10 °C; no leg cooling (NC), starting of leg cooling after 30 min of exercise (delayed cooling, DC), continuous leg cooling (CC), and stopping of continuous leg cooling after 30 min of exercise (SC) at an environmental temperature of 28.5 °C. During exercise under the DC conditions, an instantaneous increase in the esophageal temperature (Tes), a suppression of the cutaneous vascular conductance at the forearm (%CVC), and a decrease in the mean skin temperature (Tsk) were observed after leg cooling. The total sweat loss (Δm sw,tot) was lower under the DC than the NC condition. In the SC study, however, the Tes remained constant, while the %CVC increased gradually after leg cooling was stopped, and the Δm sw,tot was greater than that under the CC condition. These results suggest that during exercise, rapid skin cooling of the leg may cause an increase in core temperature, while also enhancing thermal stress. However, stopping skin cooling did not significantly affect the core temperature long-term, because the skin blood flow and sweat rate subsequently increased. © Georg Thieme Verlag KG Stuttgart · New York.

Stereo Imaging Velocimetry of Mixing Driven by Buoyancy Induced Flow Fields

Science.gov (United States)

Duval, W. M. B.; Jacqmin, D.; Bomani, B. M.; Alexander, I. J.; Kassemi, M.; Batur, C.; Tryggvason, B. V.; Lyubimov, D. V.; Lyubimova, T. P.

2000-01-01

Mixing of two fluids generated by steady and particularly g-jitter acceleration is fundamental towards the understanding of transport phenomena in a microgravity environment. We propose to carry out flight and ground-based experiments to quantify flow fields due to g-jitter type of accelerations using Stereo Imaging Velocimetry (SIV), and measure the concentration field using laser fluorescence. The understanding of the effects of g-jitter on transport phenomena is of great practical interest to the microgravity community and impacts the design of experiments for the Space Shuttle as well as the International Space Station. The aim of our proposed research is to provide quantitative data to the community on the effects of g-jitter on flow fields due to mixing induced by buoyancy forces. The fundamental phenomenon of mixing occurs in a broad range of materials processing encompassing the growth of opto-electronic materials and semiconductors, (by directional freezing and physical vapor transport), to solution and protein crystal growth. In materials processing of these systems, crystal homogeneity, which is affected by the solutal field distribution, is one of the major issues. The understanding of fluid mixing driven by buoyancy forces, besides its importance as a topic in fundamental science, can contribute towards the understanding of how solutal fields behave under various body forces. The body forces of interest are steady acceleration and g-jitter acceleration as in a Space Shuttle environment or the International Space Station. Since control of the body force is important, the flight experiment will be carried out on a tunable microgravity vibration isolation mount, which will permit us to precisely input the desired forcing function to simulate a range of body forces. To that end, we propose to design a flight experiment that can only be carried out under microgravity conditions to fully exploit the effects of various body forces on fluid mixing. Recent

Experiments on scalar mixing and transport

International Nuclear Information System (INIS)

Warhaft, Z.

1993-01-01

The author provides an overview of his recent work on passive (temperature) scalar mixing in both homogeneous and inhomogeneous turbulent flows. He shows that for homogeneous grid generated turbulence, in the presence of a linear temperature profile, the probability density function (pdf) of the temperature fluctuations has broad exponential tails, while the pdf of velocity is Gaussian. However, in the absence of a scalar gradient the pdf of temperature is Gaussian. This new result sheds insight into the fundamentals of turbulent mixing as well as to the nature of the velocity field. It is also shown that the spectrum of the temperature fluctuations has a scaling region that is consistent with Kolmogorov scaling although a similar scaling region is absent for the velocity field in this low Reynolds number flow. Finally, results concerning the mixing and dispersion of scalars in a jet are shown. Although initially the scalar mixing is strongly dependent on input conditions, the mixing is shown to be rapid and the correlation coefficient asymptotes to unity by x/D ∼ 20

Lateral Mixing Mechanisms in Vertical and Horizontal Interconnected Subchannel Two-Phase Flows

International Nuclear Information System (INIS)

Gencay, Sarman; Teyssedou, Alberto; Tye, Peter

2002-01-01

A lateral mixing model based on equal volume exchange between two laterally interconnected subchannels is presented. The following mixing mechanisms are taken into account in this model: (a) diversion cross flow, caused by the lateral pressure difference between adjacent subchannels; (b) turbulent void diffusion, which is governed by the lateral void fraction difference between the subchannels; (c) void drift, responsible for the tendency of the vapor phase to drift toward unobstructed regions; and (d) buoyancy drift, which takes into account the effect of gravity in horizontal flows. Experimental two-phase air-water data obtained using two test sections having different geometries and orientations are used to determine the diffusion coefficients required by the mixing model. Under the absence of diversion crossflow, i.e., negligible lateral pressure difference between the subchannels, it is observed that the diffusion coefficient increases with increasing average void fraction in the subchannels. Moreover, for vertical flows turbulent void diffusion seems to be considerably affected by the geometry of the subchannels. For horizontal flows under nonsymmetric inlet void fraction conditions, even though the interconnected subchannels have the same geometry, different turbulent void diffusion and void drift coefficients are required to satisfy the conditions of hydrodynamic equilibrium. In the present study this condition is achieved by introducing a new void drift coefficient expressed as a correction term applied to the turbulent void drift term

The benefits and limitations of electrolyte mixing in vanadium flow batteries

International Nuclear Information System (INIS)

Zhang, Yunong; Liu, Le; Xi, Jingyu; Wu, Zenghua; Qiu, Xinping

2017-01-01

Highlights: •The benefits and limitations of electrolyte mixing method are studied in this work. •Different current densities and mix times are studied. •The VFB cycle number increases from 145 to 598 at 160 mA cm −2 by mixing the electrolytes. -- Abstract: Cycle life prolongation and discharge capacity regeneration have drawn enormous attention in the field of vanadium flow batteries (VFBs). Among all the methods, mixing the positive and negative electrolytes is the most efficient, but the study about the proper time and the effect of the mix method is relatively deficient. In this study, different mix times and current densities are chosen to explore the benefits and limitations of the mix method, also the mechanism of discharge capacity behavior is discussed. Through the mix method, not only the cycle number has been extended significantly, but also the voltage and energy efficiencies are recovered. Although the contribution of the mix method is restrained by the average valence of the mixed electrolytes, it can be alleviated by electrolysis. The mix method is economic, uncomplicated and can be employed in industrial applications.

Preliminary Investigation on Turbulent Flow in Tight-lattice Rod Bundle with Twist-mixing Vane Spacer Grid

International Nuclear Information System (INIS)

Lee, Chiyoung; Kwack, Youngkyun; Park, Juyong; Shin, Changhwan; In, Wangkee

2013-01-01

Our research group has investigated the effect of P/D difference on the behavior of turbulent rod bundle flow without the mixing vane spacer grid, using PIV (Particle Image Velocimetry) and MIR (Matching Index of Refraction) techniques for tight lattice fuel rod bundle application. In this work, using the tight-lattice rod bundle with a twist-mixing vane spacer grid, the turbulent rod bundle flow is preliminarily examined to validate the PIV measurement and CFD (Computational Fluid Dynamics) simulation. The turbulent flow in the tight-lattice rod bundle with a twist-mixing vane spacer grid was preliminarily examined to validate the PIV measurement and CFD simulation. Both were in agreement with each other within a reasonable degree of accuracy. Using PIV measurement and CFD simulation tested in this work, the detailed investigations on the behavior of turbulent rod bundle flow with the twist-mixing vane spacer grid will be performed at various conditions, and reported in the near future

Measurements of Flow Mixing at Subchannels in a Wire-Wrapped 61-Rod Bundle for a Sodium Cooled Fast Reactor

International Nuclear Information System (INIS)

Lee, Dong Won; Kim, Hyungmo; Ko, Yung Joo; Choi, Hae Seob; Euh, Dong-Jin; Jeong, Ji-Young; Lee, Hyeong-Yeon

2015-01-01

For a safety analysis in a core thermal design of a sodium-cooled fast reactor (SFR), flow mixing characteristics at subchannels in a wire-wrapped rod bundle are crucial factor for the design code verification and validation. Wrapped wires make a cross flow in a circumference of the fuel rod, and this effect lets flow be mixed. Therefore the sub-channel analysis method is commonly used for thermal hydraulic analysis of a SFR, a wire wrapped sub-channel type. To measure flow mixing characteristics, a wire mesh sensing technique can be useful method. A wire mesh sensor has been traditionally used to measure the void fraction of a two-phase flow field, i.e. gas and liquid. However, the recent reports that the wire mesh sensor can be used successfully to recognize the flow field in liquid phase by injecting a tracing liquid with a different level of electric conductivity. The subchannel flow characteristics analysis method is commonly used for the thermal hydraulic analysis of a SFR, a wire wrapped subchannel type. In this study, mixing experiments were conducted successfully at a hexagonally arrayed 61-pin wire-wrapped fuel rod bundle test section. Wire mesh sensor was used to measure flow mixing characteristics. The developed post-processing method has its own merits, and flow mixing results were reasonable

A rapid-mix study on the effect of lipophilicity of nitroimidazoles on the radiosensitization of mammalian cells in vitro

International Nuclear Information System (INIS)

Watts, M.E.; Hodgkiss, R.J.; Jones, N.R.; Sehmi, D.S.; Woodcock, M.

1983-01-01

A liquid flow rapid-mixing apparatus has been used to study the role of lipophilicity (octanol: water partition coefficient, P) in the sensitization of hypoxic V79 cells by nitroimidazoles. Sensitization by seven neutral 2-nitroimidazoles of similar reduction potential but widely differing partition (0.11-77) and one basic 2-nitroimidazole (pKsub(a) = 8.9; p = 8.5 (of free base)) was studied as a function of pre-irradiated contact time ca. 3-40 ms. With increasing P, sensitization occurs at increasingly shorter pre-irradiated contact times. The results suggest that even though factors other than passive diffusion control the sensitization observed with the base Ro 03-8799 it is able to diffuse to the target site faster than misonidazole. (author)

Unscrambling the Omlette: a New Bubble and Crystal Clustering Mechanism in Chaotically Mixed Magma Flows

Science.gov (United States)

Robertson, J.; Metcalfe, G.; Wang, S.; Barnes, S. J.

2014-12-01

The concentration of bubbles, crystals or droplets into small volumes of magma is a key trigger for many interesting magmatic processes. For example, gas slugs driving Strombolian eruptions form from the coalesence of exsolved bubbles within a volcanic conduit, while Ni-Cu-PGE magmatic sulfide deposits require a concentration of dense sulfide droplets from a large volume of magma to form a massive ore body. However the physical mechanism for this clustering remains unresolved - especially since small particles in active magma flows are expected to mostly track flow streamlines rather than clustering. We have uncovered a previously unreported clustering mechanism which is applicable to magmatic flows. This mechanism involves the interaction of particles with two kinds of chaotic flow structure: (a) high-strain regions within the well-mixed chaotic zones of the flow, and (b) unmixed islands of stability within the chaotic flow, known as Kolmogorov-Arnold-Moser (KAM) regions. The first figure shows the difference between chaotic and KAM regions in a chaotic laminar pipe flow. Trapping occurs when particles are scattered from high-strain regions in the chaotic zones and become trapped in the KAM regions, leading to a rapid concentration of particles relative to their original distribution (shown in the second series of figures). Using a combination of these analogue experiments and theoretical analysis we outline the conditions under which this clustering process can occur. We examine the onset of secondary density-related instabilities and the effects of increased particle-particle interaction within the clustered particles, and highlight the impact of particle clustering on the dynamics of magma ascent and emplacement.

Effect of sweet yeast bread formula on evaluating rapid mix test

Directory of Open Access Journals (Sweden)

Petra Dvořáková

2011-01-01

Full Text Available The aim of this work was to detect how different sweet yeast bread formulas influence results of rapid mix test and by the help of sensory analysis to discover consumer preferences and possible benefit and use in bakery industry. Applied raw materials (ground wheat flour T 530, yeast, sugar, salt, oil, egg, improver Hit along with basic formula were taken from the Varmužova bakery in Boršice by Buchlovice. The basic formula served as a standard (I, other six formulas were then determined (II–VII. In each formula, the rate of yeast, sugar or oil was altered in the range of ± 10% compared with the standard. Flour bread-making quality – Hagberg Falling number [s], Sedimentation index [ml], wet gluten [%], ash [%], moisture [%], binding capacity [%], granulation [%], alveographic energy [10−4J] and alveographic rate P/L – was measured. Rapid mix test and parameters like pastry weight, volume, shape, dough yield, pastry yield, baking loss, penetration and sensory analysis were determined. To establish yeast fermentation activity, Engelke fermentation test was applied. The most evident differences among the samples appeared in the volume and shape. The results of sensory analysis showed that the samples with higher rate of altered raw materials were evaluated as the best.

T-junction cross-flow mixing with thermally driven density stratification

Energy Technology Data Exchange (ETDEWEB)

Kickhofel, John, E-mail: jkickhofel@gmail.com [Laboratory of Nuclear Energy Systems, ETH Zurich, Sonneggstrasse 3, 8057 Zurich (Switzerland); Prasser, Horst-Michael, E-mail: prasser@lke.mavt.ethz.ch [Laboratory of Nuclear Energy Systems, ETH Zurich, Sonneggstrasse 3, 8057 Zurich (Switzerland); Selvam, P. Karthick, E-mail: karthick.selvam@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany); Laurien, Eckart, E-mail: eckart.laurien@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany); Kulenovic, Rudi, E-mail: rudi.kulenovic@ike.uni-stuttgart.de [Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart (Germany)

2016-12-01

Highlights: • Mesh sensor for realistic nuclear thermal hydraulic scenarios is demonstrated. • Flow temperature behavior across a wide range of Richardson numbers measured. • Upstream stratified flow in the T-junction results in a thermal shock scenario. • Large, stable near-wall thermal gradients exist in spite of turbulent flows. - Abstract: As a means of further elucidating turbulence- and stratification-driven thermal fatigue in the vicinity of T-junctions in nuclear power plants, a series of experiments have been conducted at the high temperature high pressure fluid–structure interaction T-junction facility of the University of Stuttgart with novel fluid measurement instrumentation. T-junction mixing with large fluid temperature gradients results in complex flow behavior, the result of density driven effects. Deionized water mixing at temperature differences of up to 232 K at 7 MPa pressure have been investigated in a T-junction with main pipe diameter 71.8 mm and branch line diameter 38.9 mm. The experiments have been performed with fixed flow rates of 0.4 kg/s in the main pipe and 0.1 kg/s in the branch line. A novel electrode-mesh sensor compatible with the DN80 PN100 pipeline upstream and downstream of the T-junction has been utilized as a temperature sensor providing a high density information in the pipe cross-section in both space and time. Additionally, in-flow and in-wall thermocouples quantify the damping of thermal fluctuations by the wall material. The results indicate that large inflow temperature differences lead to strong turbulence damping, and ultimately stable stratification extending both downstream and upstream of the T-junction resulting in large local thermal gradients.

Impacts of a jet's exit flow pattern on mixing and combustion performance

Energy Technology Data Exchange (ETDEWEB)

Nathan, G J; Mi, J; Newbold, G J.R.; Nobes, D S [Turbulence, Energy and Combustion Group, School of Mechanical Engineering, The University of Adelaide, South Australia 5005 (Australia); Alwahabi, Z T [Turbulence, Energy and Combustion Group, Chemical Engineering, The University of Adelaide, South Australia 5005 (Australia)

2006-09-15

The influence of modifying a jet's exit flow pattern on both the near and far-field turbulent mixing processes and on the resulting combustion performance, is explored. This reveals that, in contradiction to some common assumptions, increasing the coherence of large-scale motions can decrease molecular mixing rates, and yet can still be beneficial in some applications. Even relatively minor changes to the exit flow pattern of a non-reacting round jet, through changes to the nozzle profile are found to propagate downstream into the far field, apparently through the underlying turbulent structure. Importantly, while a jet from a smoothly contracting nozzle is found to have higher rates of entrainment, mean spread and mean decay of the scalar field than does a long pipe jet, it has a lower rate of molecular mixing. That is, increased large-scale mixing does not necessarily result in increased fine-scale mixing. A range of devices are reviewed which enhance, or stimulate the large-scale, coherent motions in an emerging jet using acoustic, mechanical or fluidic methods. The available evidence suggests that those methods which induce instantaneously asymmetric flow structure are more effective at increasing the near-field spreading than are those which induce instantaneously axisymmetric flow structure. Only limited data are available of the effects of such near-field changes on the far-field properties. Nevertheless, the available data reveal a clear trend that this near-field flow undergoes a transition to a far-field state whose spread and decay is comparable with that of a steady jet, albeit being indelibly altered by the near-field excitation. It also suggests that 'self-exciting' devices (i.e. that are not externally forced), cause a net reduction in the total entrainment relative to the unexcited jet, due to the losses induced by the device itself. Nevertheless, the changes which they can impart to the flow, such as redistributing the turbulent energy from the

Study on effect of mixing mechanism by the transverse gaseous injection flow in scramjet engine with variable parameters

Science.gov (United States)

Yadav, Siddhita; Pandey, K. M.

2018-04-01

In scramjet engine the mixing mechanism of fuel and atmospheric air is very complicated, because the fuel have time in milliseconds for mixing with atmospheric air in combustion chamber having supersonic speed. Mixing efficiency of fuel and atmospheric air depends on mainly these parameters: Aspect ratio of injector, vibration amplitude, shock type, number of injector, jet to transverse flow momentum flux ratio, injector geometry, injection angle, molecular weight, incoming air stream angle, jet to transverse flow pressure ratio, spacing variation, mass flow rate of fuel etc. here is a very brief study of these parameters from previously done research on these parameters for the improvement of mixing efficiency. The mixing process have the significant role for the working of engine, and mixing between the atmospheric air and the jet fuel is significant factor for improving the overall thrust of the engine. The results obtained by study of papers are obtained by the 3D-Reynolds Average-Nervier-Stokes(RANS) equations along with the 2-equation k-ω shear-stress-transport (SST) turbulence model. Engine having multi air jets have 60% more mixing efficiency than single air jet, thus if the jets are increased, the mixing efficiency of engine can also be increased up to 150% by changing jet from 1 to 16. When using delta shape of injector the mixing efficiency is inversely proportional to the pressure ratio. When the fuel is injected inside the combustor from the top and bottom walls of the engine efficiency of mixing in reacting zone is higher than the single wall injection and in comparison to parallel flow, the transverse type flow is better as the atmospheric air jet can penetrate smoothly in the fuel jets and mixes well in less time. Hence this study of parameters and their effects on mixing can enhance the efficiency of mixing in engine.

Quantitative Analysis of Piroxicam Using Temperature-Controlled Ionic Liquid Dispersive Liquid Phase Microextraction Followed By Stopped-Flow Injection Spectrofluorimetry

Directory of Open Access Journals (Sweden)

Mohammad Reza Ganjali

2013-07-01

Full Text Available Background:Piroxicam (PXM belongs to the wide class of non-steroidal anti-inflammatory drugs (NSAIDs. PXM has been widely applied in the treatment of rheumatoid arthritis, gonarthrosis, osteoarthritis, backaches, neuralgia, mialgia. In the presented work, a green and benign sample pretreatment method called temperature-controlled ionic liquid dispersive liquid phase microextraction (TCIL-DLPME was followed with stopped-flow injection spectrofluorimetry (SFIS for quantitation of PXM in pharmaceutical formulations and biological samples.Methods:Temperature-controlled ionic liquid dispersive liquid phase microextraction (TCIL-DLPME was applied as an environmentally friendly sample enrichment method to extract and isolate PXM prior to quantitation. Dispersion of 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6] ionic liquid (IL through the sample aqueous solution was performed by applying a relatively high temperature. PXM was extracted into the extractor, and after phase separation, PXM in the final solution was determined by stopped-flow injection spectrofluorimetry (SFIS.Results and Major Conclusion:Different factors affecting the designed method such as IL amount, diluting agent, pH and temperature were investigated in details and optimized. The method provided a linear dynamic range of 0.2-150 μg l-1, a limit of detection (LOD of 0.046 μg l-1 and a relative standard deviation (RSD of 3.1%. Furthermore, in order to demonstrate the analytical applicability of the recommended method, it was applied for quantitation of PXM in real samples.

Thermal and solutal stratification in mixed convection three-dimensional flow of an Oldroyd-B nanofluid

Directory of Open Access Journals (Sweden)

Tasawar Hayat

Full Text Available This paper investigates the double stratified effects in mixed convection three-dimensional flow of an Oldroyd-B nanofluid. The flow is due to a bidirectional stretching surface. Mathematical analysis is carried out using the temperature and concentration stratification effects. Brownian motion, thermophoresis and chemical reaction effects are also considered. The governing nonlinear boundary layer equations are first converted into the dimensionless ordinary differential equations and then solved for the convergent series solutions of velocity, temperature and nanoparticles concentration. Convergence analysis of the obtained series solutions is also checked and verified. Effects of various emerging parameters are studied in details. Numerical values of local Nusselt and Sherwood numbers are tabulated and analyzed. It is noticed that the impact of mixed convection parameter on temperature and nanoparticles concentration is quite similar. Both temperature and nanoparticles concentration are reduced for larger mixed convection parameter. Keywords: Three-dimensional flow, Oldroyd-B fluid, Nanoparticles, Mixed convection, Thermal and solutal stratification, Chemically reactive species

Mixing driven by transient buoyancy flows. I. Kinematics

Science.gov (United States)

Duval, W. M. B.; Zhong, H.; Batur, C.

2018-05-01

Mixing of two miscible liquids juxtaposed inside a cavity initially separated by a divider, whose buoyancy-driven motion is initiated via impulsive perturbation of divider motion that can generate the Richtmyer-Meshkov instability, is investigated experimentally. The measured Lagrangian history of interface motion that contains the continuum mechanics of mixing shows self-similar nearly Gaussian length stretch distribution for a wide range of control parameters encompassing an approximate Hele-Shaw cell to a three-dimensional cavity. Because of the initial configuration of the interface which is parallel to the gravitational field, we show that at critical initial potential energy mixing occurs through the stretching of the interface, which shows frontogenesis, and folding, owing to an overturning motion that results in unstable density stratification and produces an ideal condition for the growth of the single wavelength Rayleigh-Taylor instability. The initial perturbation of the interface and flow field generates the Kelvin-Helmholtz instability and causes kinks at the interface, which grow into deep fingers during overturning motion and unfold into local whorl structures that merge and self-organize into the Rayleigh-Taylor morphology (RTM) structure. For a range of parametric space that yields two-dimensional flows, the unfolding of the instability through a supercritical bifurcation yields an asymmetric pairwise structure exhibiting smooth RTM that transitions to RTM fronts with fractal structures that contain small length scales for increasing Peclet numbers. The late stage of the RTM structure unfolds into an internal breakwave that breaks down through wall and internal collision and sets up the condition for self-induced sloshing that decays exponentially as the two fluids become stably stratified with a diffusive region indicating local molecular diffusion.

Electroosmotic Flow in Mixed Polymer Brush-Grafted Nanochannels

Directory of Open Access Journals (Sweden)

Qianqian Cao

2016-12-01

Full Text Available Mixed polymer brush-grafted nanochannels—where two distinct species of polymers are alternately grafted on the inner surface of nanochannels—are an interesting class of nanostructured hybrid materials. By using a coarse-grained molecular dynamics simulation method, we are able to simulate the electrokinetic transport dynamics of the fluid in such nanochannels as well as the conformational behaviors of the mixed polymer brush. We find that (1 the brush adopts vertically-layered and longitudinally-separated structures due to the coupling of electroosmotic flow (EOF and applied electric field; (2 the solvent quality affects the brush conformations and the transport properties of the EOF; (3 the EOF flux non-monotonically depends on the grafting density, although the EOF velocity in the central region of the channel monotonically depends on the grafting density.

Experimental study of fuel bundle vibrations with rods subjected to mixed axial flow and cross-flow provided by a narrow gap (baffle jetting interaction)

International Nuclear Information System (INIS)

Boulanger, P.; Jacques, Y.; Fardeau, P.; Barbier, D.; Rigaudeau, J.

1997-01-01

The Hydraulic Core Laboratory (LHC) performs experimental studies of PWR fuel assembly mechanical behaviour submitted to representative flows in PWR core. Cross-flows prove particularly troublesome by generating on rods, in special cases, vibratory levels high enough to induce early grid to rod fretting. The fluid-structure interaction under mixed axial and cross-flow is also a major topic for analysis. The authors present a test loop devoted to the mixed axial-cross-flow fluid-structure interaction on representative half-scale mockup which is able to simulate, under ambient conditions, any complex flow (direction and flow rates) representative of PWR core flows. Despite its reduced size, the mockup retains the overall structure of a PWR fuel assembly. Rods displacement/velocity and velocity flow field are measured by laser techniques

Effects of mixing methods on phase distribution in vertical bubble flow

International Nuclear Information System (INIS)

Monji, Hideaki; Matsui, Goichi; Sugiyama, Takayuki.

1992-01-01

The mechanism of the phase distribution formation in a bubble flow is one of the most important problems in the control of two-phase flow systems. The effect of mixing methods on the phase distribution was experimentally investigated by using upward nitrogen gas-water bubble flow under the condition of fixed flow rates. The experimental results show that the diameter of the gas injection hole influences the phase distribution through the bubble size. The location of the injection hole and the direction of injection do not influence the phase distribution of fully developed bubble flow. The transitive equivalent bubble size from the coring bubble flow to the sliding bubble flow corresponds to the bubble shape transition. The analytical results show that the phase distribution may be predictable if the phase profile is judged from the bubble size. (author)

Rapidly Mixing Gibbs Sampling for a Class of Factor Graphs Using Hierarchy Width.

Science.gov (United States)

De Sa, Christopher; Zhang, Ce; Olukotun, Kunle; Ré, Christopher

2015-12-01

Gibbs sampling on factor graphs is a widely used inference technique, which often produces good empirical results. Theoretical guarantees for its performance are weak: even for tree structured graphs, the mixing time of Gibbs may be exponential in the number of variables. To help understand the behavior of Gibbs sampling, we introduce a new (hyper)graph property, called hierarchy width . We show that under suitable conditions on the weights, bounded hierarchy width ensures polynomial mixing time. Our study of hierarchy width is in part motivated by a class of factor graph templates, hierarchical templates , which have bounded hierarchy width-regardless of the data used to instantiate them. We demonstrate a rich application from natural language processing in which Gibbs sampling provably mixes rapidly and achieves accuracy that exceeds human volunteers.

The effect of mixing rates on the formation and growth of condensation aerosols in a model stagnation flow

KAUST Repository

Alshaarawi, Amjad; Bisetti, Fabrizio

2015-01-01

A steady, laminar stagnation flow configuration is adopted to investigate numerically the interaction between condensing aerosol particles and gas-phase transport across a canonical mixing layer. The mixing rates are varied by adjusting the velocity and length scales of the stagnation flow parametrically. The effect of mixing rates on particle concentration, polydispersity, and mean droplet diameter is explored and discussed. This numerical study reveals a complex response of the aerosol to varying flow times. Depending on the flow time, the variation of the particle concentration in response to varying mixing rates falls into one of the two regimes. For fast mixing rates, the number density and volume fraction of the condensing particles increase with residence time (nucleation regime). On the contrary, for low mixing rates, number density decreases with residence time and volume fraction reaches a plateau (condensation regime). It is shown that vapor scavenging by the aerosol phase is key to explaining the transition between these two regimes. The results reported here are general and illustrate genuine features of the evolution of aerosols forming by condensation of supersaturated vapor from heat and mass transport across mixing layers.

The effect of mixing rates on the formation and growth of condensation aerosols in a model stagnation flow

KAUST Repository

Alshaarawi, Amjad

2015-03-01

A steady, laminar stagnation flow configuration is adopted to investigate numerically the interaction between condensing aerosol particles and gas-phase transport across a canonical mixing layer. The mixing rates are varied by adjusting the velocity and length scales of the stagnation flow parametrically. The effect of mixing rates on particle concentration, polydispersity, and mean droplet diameter is explored and discussed. This numerical study reveals a complex response of the aerosol to varying flow times. Depending on the flow time, the variation of the particle concentration in response to varying mixing rates falls into one of the two regimes. For fast mixing rates, the number density and volume fraction of the condensing particles increase with residence time (nucleation regime). On the contrary, for low mixing rates, number density decreases with residence time and volume fraction reaches a plateau (condensation regime). It is shown that vapor scavenging by the aerosol phase is key to explaining the transition between these two regimes. The results reported here are general and illustrate genuine features of the evolution of aerosols forming by condensation of supersaturated vapor from heat and mass transport across mixing layers.

Rapid high temperature field test method for evaluation of geothermal calcite scale inhibitors

Energy Technology Data Exchange (ETDEWEB)

Asperger, R.G.

1982-08-01

A test method is described which allows the rapid field testing of calcite scale inhibitors in high- temperature geothermal brines. Five commercial formulations, chosen on the basis of laboratory screening tests, were tested in brines with low total dissolved solids at ca 500 F. Four were found to be effective; of these, 2 were found to be capable of removing recently deposited scale. One chemical was tested in the full-flow brine line for 6 wks. It was shown to stop a severe surface scaling problem at the well's control valve, thus proving the viability of the rapid test method. (12 refs.)

Effect of flow and peristaltic mixing on bacterial growth in a gut-like channel

Science.gov (United States)

Cremer, Jonas; Segota, Igor; Yang, Chih-yu; Arnoldini, Markus; Sauls, John T.; Zhang, Zhongge; Gutierrez, Edgar; Groisman, Alex; Hwa, Terence

2016-01-01

The ecology of microbes in the gut has been shown to play important roles in the health of the host. To better understand microbial growth and population dynamics in the proximal colon, the primary region of bacterial growth in the gut, we built and applied a fluidic channel that we call the “minigut.” This is a channel with an array of membrane valves along its length, which allows mimicking active contractions of the colonic wall. Repeated contraction is shown to be crucial in maintaining a steady-state bacterial population in the device despite strong flow along the channel that would otherwise cause bacterial washout. Depending on the flow rate and the frequency of contractions, the bacterial density profile exhibits varying spatial dependencies. For a synthetic cross-feeding community, the species abundance ratio is also strongly affected by mixing and flow along the length of the device. Complex mixing dynamics due to contractions is described well by an effective diffusion term. Bacterial dynamics is captured by a simple reaction–diffusion model without adjustable parameters. Our results suggest that flow and mixing play a major role in shaping the microbiota of the colon. PMID:27681630

Heat and fluid flow during rapid solidification of non-equilibrium materials

International Nuclear Information System (INIS)

Negli, S.C.; Eddingfield, D.L.; Brower, W.E. Jr.

1990-01-01

Rapid solidification technology (RST) is an advanced solidification process which is being utilized to produce non-equilibrium structures with properties not previously available with conventionally cast materials. An iron based alloy rapidly quenched to form a metallic glass is being installed on a large scale in electric power transformers where it cuts heat losses dramatically. The formation of a non-equilibrium structure usually requires a cooling rate of at least a million degrees per second. Achieving this high a cooling rate depends not only on the heat transfer conditions during the quenching process, but also on the fluid flow conditions in the molten metal before and during solidification. This paper presents a model of both heat and fluid flow during RST by the hammer and anvil method. The symmetry of two sided cooling permits analysis which is still applicable to the one sided cooling that occurs during melt spinning, the prevalent method of RST. The heat flow is modeled as one dimensional, normal to the quench surface. Previous models have shown the heat flow in the plane of the quench surface not to be significant. The fluid flow portion of the model utilizes the squeeze film solution for flow between two parallel flat plates. The model predicts the effects of superheat of the melt and of the quench hammer speed upon cooling rate during the formation of nonequilibrium phases. An unexpected result is that increased superheat results in much higher cooling rates, due to fluid flow before a potential transformation would take place; this enhanced liquid metal flow results in a thinner section casting which in turn has a dominant effect on the cooling rate. The model also predicts an expanded regime of Newtonian (interface controlled) cooling by about a factor of ten as compared to previous model of RST

Baryon stopping and charged particle production from lead-lead collisions at 158 GeV per nucleon

International Nuclear Information System (INIS)

Toy, Milton Y.

1999-01-01

Net proton (proton minus antiproton) and negative charge hadron spectra (h-) from central Pb+Pb collisions at 158 GeV per nucleon at the CERN Super Proton Synchrotron were measured and compared to spectra from central collisions of the lighter S+S system. Net baryon distributions were derived from those of net protons and net lambdas. Stopping, or rapidity shift with respect to the beam, of net protons and net baryons increase with system size. The mean transverse momentum T >60; T >62; of net protons also increase with system size. The h- rapidity density scales with the number of participant nucleons for nuclear collisions, where their T >60; T >62; is independent of system size. The T >60; T >62; dependence upon particle mass and system size is consistent with larger transverse flow velocity at midrapidity for central collisions of Pb+Pb compared to that of S+S

Reducibility of ceria-lanthana mixed oxides under temperature programmed hydrogen and inert gas flow conditions

International Nuclear Information System (INIS)

Bernal, S.; Blanco, G.; Cifredo, G.; Perez-Omil, J.A.; Pintado, J.M.; Rodriguez-Izquierdo, J.M.

1997-01-01

The present paper deals with the preparation and characterization of La/Ce mixed oxides, with La molar contents of 20, 36 and 57%. We carry out the study of the structural, textural and redox properties of the mixed oxides, comparing our results with those for pure ceria. For this aim we use temperature programmed reduction (TPR), temperature programmed desorption (TPD), nitrogen physisorption at 77 K, X-ray diffraction and high resolution electron microscopy. The mixed oxides are more easy to reduce in a flow of hydrogen than ceria. Moreover, in an inert gas flow they release oxygen in higher amounts and at lower temperatures than pure CeO 2 . The textural stability of the mixed oxides is also improved by incorporation of lanthana. All these properties make the ceria-lanthana mixed oxides interesting alternative candidates to substitute ceria in three-way catalyst formulations. (orig.)

Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

International Nuclear Information System (INIS)

Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.

2016-01-01

Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

Energy Technology Data Exchange (ETDEWEB)

Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K., E-mail: prodip.das@ncl.ac.uk [School of Mechanical and Systems Engineering Newcastle University Newcastle upon Tyne, NE1 7RU United Kingdom (United Kingdom)

2016-07-12

Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

Science.gov (United States)

Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.

2016-07-01

Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid's thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

Numerical Investigation of Mixing Characteristics in Cavity Flow at Various Aspect Ratios

Energy Technology Data Exchange (ETDEWEB)

Shin, Myung Seob [Dongyang Mirae University, Seoul (Korea, Republic of); Yang, Seung Deok; Yoon, Joon Yong [Hanyang University, Seoul (Korea, Republic of)

2015-01-15

This study numerically examined the mixing characteristics of rectangular cavity flows by using the hybrid lattice Boltzmann method (HLBM) applied to the finite difference method (FDM). Multi-relaxation time was used along with a passive scalar method which assumes that two substances have the same mass and that there is no interaction. First, we studied numerical results such as the stream function, position of vortices, and velocity profile for a square cavity and rectangular cavity with an aspect ratio of 2. The data were compared with previous numerical results that have been proven to be reliable. We also studied the mixing characteristics of a rectangular cavity flow such as the concentration profile and average Sherwood number at various Pe numbers and aspect ratios.

Heat transfer in tube bundles of heat exchangers with flow baffles induced forced mixing

International Nuclear Information System (INIS)

AbuRomia, M.M.; Chu, A.W.; Cho, S.M.

1976-01-01

Thermal analysis of shell-and-tube heat exchangers is being investigated through geometric modeling of the unit configuration in addition to considering the heat transfer processes taking place within the tube bundle. The governing equations that characterize the heat transfer from the shell side fluid to the tube side fluid across the heat transfer tubewalls are indicated. The equations account for the heat transfer due to molecular conduction, turbulent thermal diffusion, and forced fluid mixing among various shell side fluid channels. The analysis, though general in principle, is being applied to the Clinch River Breeder Reactor Plant-Intermediate Heat Exchanger, which utilizes flow baffles appropriately designed for induced forced fluid mixing in the tube bundle. The results of the analysis are presented in terms of the fluid and tube wall temperature distributions of a non-baffled and baffled tube bundle geometry. The former case yields axial flow in the main bundle region while the latter is associated with axial/cross flow in the bundle. The radial components of the axial/cross flow yield the necessary fluid mixing that results in reducing the thermal unbalance among the heat transfer to the allowable limits. The effect of flow maldistribution, present on the tube or shell sides of the heat exchangers, in altering the temperature field of tube bundles is also noted

Rapid anion exchange separation of fermium with mineral acid-methyl alcohol mixed media

International Nuclear Information System (INIS)

Usuda, S.; Shinohara, N.; Ichikawa, S.; Suzuki, T.

1987-01-01

Anion exchange separation of 250 Fm (30 m) synthesized by the 12 C+ 242 Pu and 16 O+ 238 U reactions was investigated with mineral acid-methyl alcohol mixed media at elevated temperature. Fermium was chromatographically separated from the other transplutonium elements, the target materials and an Al catcher foil by anion exchange with mixtures of nitric acid and methyl alcohol. By use of the mixed media of hydrochloric acid and methyl alcohol, Fm together with Cf was separated from Al, Am, Cm, Pu, U and from major fission products. The separation systems are suitable for rapid separation and immediate alpha-counting source preparation of Fm. (author) 22 refs.; 4 figs

Correlated stopping, proton clusters and higher order proton cumulants

Energy Technology Data Exchange (ETDEWEB)

Bzdak, Adam [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow (Poland); Koch, Volker [Lawrence Berkeley National Laboratory, Nuclear Science Division, Berkeley, CA (United States); Skokov, Vladimir [RIKEN/BNL, Brookhaven National Laboratory, Upton, NY (United States)

2017-05-15

We investigate possible effects of correlations between stopped nucleons on higher order proton cumulants at low energy heavy-ion collisions. We find that fluctuations of the number of wounded nucleons N{sub part} lead to rather nontrivial dependence of the correlations on the centrality; however, this effect is too small to explain the large and positive four-proton correlations found in the preliminary data collected by the STAR collaboration at √(s) = 7.7 GeV. We further demonstrate that, by taking into account additional proton clustering, we are able to qualitatively reproduce the preliminary experimental data. We speculate that this clustering may originate either from collective/multi-collision stopping which is expected to be effective at lower energies or from a possible first-order phase transition, or from (attractive) final state interactions. To test these ideas we propose to measure a mixed multi-particle correlation between stopped protons and a produced particle (e.g. pion, antiproton). (orig.)

Water velocity and the nature of critical flow in large rapids on the Colorado River, Utah

Science.gov (United States)

Magirl, Christopher S.; Gartner, Jeffrey W.; Smart, Graeme M.; Webb, Robert H.

2009-01-01

Rapids are an integral part of bedrock‐controlled rivers, influencing aquatic ecology, geomorphology, and recreational value. Flow measurements in rapids and high‐gradient rivers are uncommon because of technical difficulties associated with positioning and operating sufficiently robust instruments. In the current study, detailed velocity, water surface, and bathymetric data were collected within rapids on the Colorado River in eastern Utah. With the water surface survey, it was found that shoreline‐based water surface surveys may misrepresent the water surface slope along the centerline of a rapid. Flow velocities were measured with an ADCP and an electronic pitot‐static tube. Integrating multiple measurements, the ADCP returned velocity data from the entire water column, even in sections of high water velocity. The maximum mean velocity measured with the ADCP was 3.7 m/s. The pitot‐static tube, while capable of only point measurements, quantified velocity 0.39 m below the surface. The maximum mean velocity measured with the pitot tube was 5.2 m/s, with instantaneous velocities up to 6.5 m/s. Analysis of the data showed that flow was subcritical throughout all measured rapids with a maximum measured Froude number of 0.7 in the largest measured rapids. Froude numbers were highest at the entrance of a given rapid, then decreased below the first breaking waves. In the absence of detailed bathymetric and velocity data, the Froude number in the fastest‐flowing section of a rapid was estimated from near‐surface velocity and depth soundings alone.

Fluid flow and fuel-air mixing in a motored two-dimensional Wankel rotary engine

Science.gov (United States)

Shih, T. I.-P.; Nguyen, H. L.; Stegeman, J.

1986-01-01

The implicit-factored method of Beam and Warming was employed to obtain numerical solutions to the conservation equations of mass, species, momentum, and energy to study the unsteady, multidimensional flow and mixing of fuel and air inside the combustion chambers of a two-dimensional Wankel rotary engine under motored conditions. The effects of the following engine design and operating parameters on fluid flow and fuel-air mixing during the intake and compression cycles were studied: engine speed, angle of gaseous fuel injection during compression cycle, and speed of the fuel leaving fuel injector.

CFD analysis of the flow in the near wake of a generic PWR mixing grid

International Nuclear Information System (INIS)

Bieder, Ulrich; Falk, François; Fauchet, Gauthier

2015-01-01

Highlights: • The flow in a 5 × 5 rod bundle with mixing grid is analyzed experimentally and with CFD. • LES and RANS (k–ε) calculations are performed. • The parallelism of the Trio-U code was tested with a strong scaling method. • Close downstream of the grid, k–ε and LES give similar results and fit well the experiment. - Abstract: The flow in fuel assemblies of PWRs with mixing grids has been analyzed with CFD calculations by numerous authors. The comparison between calculation and experiment has often shown an insensitivity of the calculated cross flow velocity on the turbulence modeling. The study presented here was carried out to confirm this result. The comparison between measurements in the AGATE facility (5 × 5 tube bundle) and Trio-U calculations with a linear eddy viscosity turbulence model (k–ε) and Large Eddy Simulations (LES) is presented. The AGATE experiments have originally not been designed for CFD validation but to characterize different types of mixing grids. Nevertheless, the quality of the experimental data allows the quantitative comparison between measurement and calculation. The test section of the AGATE facility has been discretized for the LES calculation on 300 million control volumes by using a staggered grid approach on tetrahedral meshes. 20 days of CPU on 4600 cores of the HPC machine CURIE of the TGCC was necessary to calculate the statistics of the turbulent flow, in particular the mean velocity and the RMS of the turbulent fluctuations. The parallelism of Trio-U was tested up to 10,000 processor cores using strong scaling and has shown a good efficiency up to about 6000 cores, i.e., 40,000 control volumes per core. For various distances from the mixing grid, calculated horizontal profiles of the cross flow velocity and of the axial velocity are compared to measurements. It seems that the flow patterns directly downstream of the grid are insensitive to the used turbulence model. Inertia forces related to the

Molecular energy transfer by fluid mixing. Progress report, 1 January 1968--1 January 1971

International Nuclear Information System (INIS)

Cool, T.A.

1971-01-01

Highlights are discussed of a program on the use of rapid mixing techniques and high speed flows for laser power enhancement. Three tasks are reviewed: (1) continuous wave chemical laser development, (2) N 2 --CO 2 electrically excited fluid mixing laser techniques, and (3) gas dynamic mixing behind shock waves. Purely chemical HF and DF laser operation is also discussed

Discrete Analysis of Portfolio Selection with Optimal Stopping Time

Directory of Open Access Journals (Sweden)

Jianfeng Liang

2009-01-01

Full Text Available Most of the investments in practice are carried out without certain horizons. There are many factors to drive investment to a stop. In this paper, we consider a portfolio selection policy with market-related stopping time. Particularly, we assume that the investor exits the market once his wealth reaches a given investment target or falls below a bankruptcy threshold. Our objective is to minimize the expected time when the investment target is obtained, at the same time, we guarantee the probability that bankruptcy happens is no larger than a given level. We formulate the problem as a mix integer linear programming model and make analysis of the model by using a numerical example.

Flow mixing inside a control-rod guide tube – Experimental tests and CFD simulations

International Nuclear Information System (INIS)

Angele, Kristian; Odemark, Ylva; Cehlin, Mathias; Hemström, Bengt; Högström, Carl-Maikel; Henriksson, Mats; Tinoco, Hernan; Lindqvist, Hans

2011-01-01

This paper covers a combined experimental and computational effort carried out at Vattenfall Research and Development AB in order to study the thermal mixing in the annular region between a top tube and a control-rod stem. The low frequency thermal fluctuations in this region can result in problems with thermal fatigue and have caused cracks in the control-rod stems of several nuclear reactors (). The flow in the vertical annular region formed by the top tube and the control-rod stem is characterized by the mixing of hot bypass flow with cold crud-removal flow. The crud-removal flow is flowing upwards along the control-rod stem, and the warmer bypass flow is entering through eight horizontal holes positioned in the lower part of the guide tube and four holes in the upper part of the top tube, forming jets. Two full-scale models of a control rod, including the control-rod stem and the guide tube, were constructed. The first model, designed to work at atmospheric conditions, was made of Plexiglass, in order to be able to visualize the mixing process, whereas the second one was made of steel to allow for a higher temperature difference between the two flows, and the heating of the top tube. CFD simulations of the case at atmospheric conditions were also carried out. Both the experiments and the simulations showed that the mixing region between the cold crud-removal flow and the warm bypass flow is dominated by large flow structures coming from above. The process is characterized by low frequency, high amplitude temperature fluctuations. The process is basically hydrodynamic, caused by the downward transport of flow structures originated at the upper bypass inlets. The damping thermal effects through buoyancy is of secondary importance, as also the scaling analysis shows, however a slight damping of the temperature fluctuations can be seen due to natural convection due to a pre-heating of the cold crud-removal flow. The comparison between numerical and experimental

Measurement of turbulent mixing in a confined wake flow using combined PIV and PLIF

NARCIS (Netherlands)

Hjertager, Lene K.; Hjertager, Bjorn H.; Deen, N.G.; Solberg, Tron; Kuipers, J.A.M.

2003-01-01

Turbulent mixing in a confined wake flow was studied by using the combined PIV/PLIF technique to measure instantaneous concentration and velocity fields. Measurements were performed at two slightly overlapping areas in the initial mixing zone and at an area at the end of the channel. The

Comparison of energy flows in deep inelastic scattering events with and without a large rapidity gap

International Nuclear Information System (INIS)

Derrick, M.; Krakauer, D.; Magill, S.

1994-07-01

Energy flows in deep inelastic electron-proton scattering are investigated at a centre-of-mass energy of 296 GeV for the range Q 2 ≥10 GeV 2 using the ZEUS detector. A comparison is made between events with and without a large rapidity gap between the hadronic system and the proton direction. The energy flows, corrected for detector acceptance and resolution, are shown for these two classes of events in both the HERA laboratory frame and the Breit frame. From the differences in the shapes of these energy flows we conclude that QCD radiation is suppressed in the large-rapidity-gap events compared to the events without a large rapidity gap. (orig.)

Mid-rapidity pion cross sections: new data confront theories

International Nuclear Information System (INIS)

Frankel, K.A.; Bistirlich, J.A.; Bossingham, R.

1981-07-01

Pion production by collisions of relativistic heavy ions has been studied recently by Wolf et al. For the reaction 1.05 GeV/A 40 Ar + Ca → π + , they discovered a peak in the invariant cross section at mid-rapidity at P/sub perpendicular/ approx. 0.5 m/sub π/c. This peak is not apparent in the 730 MeV p + p data of Cochran et al. and was attributed to possible hydrodynamic flow effects. Several authors have suggested that the π + peak is a Coulomb effect. These models predict the π - would be drawn in towards the fireball, leaving an essentially flat distribution in the mid-rapidity region. Mid-rapidity π + and π - cross sections were measured using a 1.05 GeV/A argon beam with a calcium target. The pions were measured with a magnetic spectrometer set at 15 0 to the beam and were stopped in a scintillator range telescope. Results are presented and discussed

GMSB with light stops

Energy Technology Data Exchange (ETDEWEB)

Delgado, Antonio [Department of Physics, University of Notre Dame,225 Nieuwland Science Hall, IN 46556, Notre Dame (United States); Theory Division, Physics Department CERN,CH-1211 Geneva 23 (Switzerland); Garcia-Pepin, Mateo [Institut de Física d’Altes Energies, Universitat Autònoma de Barcelona,08193 Bellaterra, Barcelona (Spain); Quiros, Mariano [ICREA at Institut de Física d’Altes Energies, Universitat Autònoma de Barcelona,08193 Bellaterra, Barcelona (Spain)

2015-08-31

Gauge mediated supersymmetry breaking (GMSB) is an elegant mechanism to transmit supersymmetry breaking from the hidden to the MSSM observable sector, which solves the supersymmetric flavor problem. However, the smallness of the generated stop mixing requires superheavy stops to reproduce the experimental value of the Higgs mass. A possible way out is to extend the MSSM Higgs sector with singlets and/or triplets providing extra tree-level corrections to the Higgs mass. Singlets will not get any soft mass from GMSB and triplets will contribute to the ρ parameter which could be an issue. In this paper we explore the second possibility by introducing extra supersymmetric triplets with hypercharges Y=(0,±1), with a tree-level custodial SU(2){sub L}⊗SU(2){sub R} global symmetry in the Higgs sector protecting the ρ parameter: a supersymmetric generalization of the Georgi-Machacek model, dubbed as supersymmetric custodial triplet model (SCTM). The renormalization group running from the messenger to the electroweak scale mildly breaks the custodial symmetry. We will present realistic low-scale scenarios (with the NLSP being a Bino-like neutralino or the right-handed stau) based on general (non-minimal) gauge mediation and consistent with all present experimental data. Their main features are: i) Light (∼1 TeV) stops; ii) Exotic couplings (H{sup ±}W{sup ∓}Z and H{sup ±±}W{sup ∓}W{sup ∓}) absent in the MSSM and proportional to the triplets VEV, v{sub Δ}; and, iii) A possible (measurable) universality breaking of the Higgs couplings λ{sub WZ}=r{sub WW}/r{sub ZZ}≠1.

Continuous precipitation of mineral products: influence of mixing conditions on the co-precipitation of cerium-zirconium mixed oxides

International Nuclear Information System (INIS)

Di Patrizio, Nicolas

2015-01-01

An automated experimental set-up with rapid mixers is used to study the influence of mixing conditions on the co-precipitation of cerium-zirconium mixed oxides. The intensity of mixing is controlled by the inlet flow rates of the reacting solutions. An engulfment model is used to estimate a mixing time from the measurement of a segregation index by the Villermaux-Dushman reaction system. Three geometries of Hartridge Roughton mixers are compared. Mixing performance is better when a separate mixing chamber upstream of a narrower outlet pipe is present. A better mixing decreases the maximal reducibility temperature of the material and increases the crystal strains of the particles calcined at 1100 C. This is probably due to a better homogenization of the particles content. The important incorporation of nitrates in the particle at the outlet of the mixers shows precipitation occurs while the mixing process is not finished. This experimental result was confirmed by numerical simulation and an estimation of sur-saturations during the mixing process. (author)

Mixed convection boundary-layer flow from a horizontal circular cylinder with a constant surface heat flux

Energy Technology Data Exchange (ETDEWEB)

Nazar, R.; Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)

2004-02-01

The laminar mixed convection boundary-layer flow of a viscous and incompressible fluid past a horizontal circular cylinder, which is maintained at a constant heat flux and is placed in a stream flowing vertically upward has been theoretically studied in this paper. The solutions for the flow and heat transfer characteristics are evaluated numerically for different values of the mixed convection parameter {lambda} with the Prandtl number Pr = 1 and 7, respectively. It is found, as for the case of a heated or cooled cylinder, considered by Merkin [5], that assisting flow delays separation of the boundary-layer and can, if the assisting flow is strong enough, suppress it completely. The opposing flow, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently strong opposing flows there will not be a boundary-layer on the cylinder. (orig.)

How granular vortices can help understanding rheological and mixing properties of dense granular flows

Directory of Open Access Journals (Sweden)

Rognon Pierre

2017-01-01

Full Text Available Dense granular flows exhibit fascinating kinematic patterns characterised by strong fluctuations in grain velocities. In this paper, we analyse these fluctuations and discuss their possible role on macroscopic properties such as effective viscosity, non-locality and shear-induced diffusion. The analysis is based on 2D experimental granular flows performed with the stadium shear device and DEM simulations. We first show that, when subjected to shear, grains self-organised into clusters rotating like rigid bodies. The average size of these so-called granular vortices is found to increase and diverge for lower inertial numbers, when flows decelerate and stop. We then discuss how such a microstructural entity and its associated internal length scale, possibly much larger than a grain, may be used to explain two important properties of dense granular flows: (i the existence of shear-induced diffusion of grains characterised by a shear-rate independent diffusivity and (ii the development of boundary layers near walls, where the viscosity is seemingly lower than the viscosity far from walls.

Continuous, size and shape-control synthesis of hollow silica nanoparticles enabled by a microreactor-assisted rapid mixing process

Science.gov (United States)

He, Yujuan; Kim, Ki-Joong; Chang, Chih-Hung

2017-06-01

Hollow silica nanoparticles (HSNPs) were synthesized using a microreactor-assisted system with a hydrodynamic focusing micromixer. Due to the fast mixing of each precursor in the system, the poly(acrylic acid) (PAA) thermodynamic-locked (TML) conformations were protected from their random aggregations by the immediately initiated growth of silica shells. When altering the mixing time through varying flow rates and flow rate ratios, the different degrees of the aggregation of PAA TML conformations were observed. The globular and necklace-like TML conformations were successfully captured by modifying the PAA concentration at the optimized mixing condition. Uniform HSNPs with an average diameter ∼30 nm were produced from this system. COMSOL numerical models was established to investigate the flow and concentration profiles, and their effects on the formation of PAA templates. Finally, the quality and utility of these uniform HSNPs were demonstrated by the fabrication of antireflective thin films on monocrystalline photovoltaic cells which showed a 3.8% increase in power conversion efficiency.

Mixing efficiency inside micro-droplets coalesced by two components in cross-structure

Science.gov (United States)

Ren, Yanlin; Liu, Zhaomiao; Pang, Yan

2017-11-01

The mixing of micro-droplets is used in analytical chemistry, medicine production and material synthesis owing to its advantages including the encapsulation and narrow time residence distribution. In this work, droplets are coalesced by two dispersed phase with different flow rates, generated in cross-structure and mixed in planar serpentine structure. The mixing efficiency of micro-droplets under control characters including the width of entrance and the flow rate of dispersed phases have been investigated by experiments and numerical simulations. The UDS (user-defined scalar) as dimensionless concentration of the solution is adopted in simulation, and is used to calculate the concentration and the mixing effect. By changing the flow rates and the entrances` width, the changing rules of the mixing characters have been obtained. The asymmetry distributions of components make rapid mixing process in half part of each droplet when travel through a straight channel. Increasing of the ratio of entrance width result into larger droplet and weaken the chaotic mixing effect. Meanwhile, the coalesced mechanism can be performed by ranging the ratio of flow rates, the ranges are also determined by the widths of entrances. The authors gratefully acknowledge the support of National Natural Science Foundation of China (Grant No. 11572013).

Second stop and sbottom searches with a stealth stop

Energy Technology Data Exchange (ETDEWEB)

Cheng, Hsin-Chia; Li, Lingfeng; Qin, Qin [Department of Physics, University of California,Davis, California 95616 (United States)

2016-11-29

The top squarks (stops) may be the most wanted particles after the Higgs boson discovery. The searches for the lightest stop have put strong constraints on its mass. However, there is still a search gap in the low mass region if the spectrum of the stop and the lightest neutralino is compressed. In that case, it may be easier to look for the second stop since naturalness requires both stops to be close to the weak scale. The current experimental searches for the second stop are based on the simplified model approach with the decay modes t̃{sub 2}→t̃{sub 1}Z and t̃{sub 2}→t̃{sub 1}h. However, in a realistic supersymmetric spectrum there is always a sbottom lighter than the second stop, hence the decay patterns are usually more complicated than the simplified model assumptions. In particular, there are often large branching ratios of the decays t̃{sub 2}→b̃{sub 1}W and b̃{sub 1}→t̃{sub 1}W as long as they are open. The decay chains can be even more complex if there are intermediate states of additional charginos and neutralinos in the decays. By studying several MSSM benchmark models at the 14 TeV LHC, we point out the importance of the multi-W final states in the second stop and the sbottom searches, such as the same-sign dilepton and multilepton signals, aside from the traditional search modes. The observed same-sign dilepton excesses at LHC Run 1 and Run 2 may be explained by some of our benchmark models. We also suggest that the vector boson tagging and a new kinematic variable may help to suppress the backgrounds and increase the signal significance for some search channels. Due to the complex decay patterns and lack of the dominant decay channels, the best reaches likely require a combination of various search channels at the LHC for the second stop and the lightest sbottom.

Studies on rapid ion-exchange separation of the transplutonium elements with mineral acid-methanol mixed media

International Nuclear Information System (INIS)

Usuda, Shigekazu

1989-03-01

In order to study properties of short-lived transplutonium nuclides synthesized by heavy-ion bombardment, three methods for rapid separation of tri-valent transplutonium elements by ion-exchange chromatography with mineral acid-methanol mixed media at elevated temperature were investigated. The first separation method was anion-exchange chromatography with nitric acid-methanol mixed media. The second method was anion-exchange choromatography with dilute hydrochloric acid-methanol mixed media. The third method was improved cation-exchange chromatography with single-column operation using the mixed media of hydrochloric acid and methanol. The separation methods developed were found applicable to studies on synthesis of the trans-plutonium nuclides, 250 Fm (T 1/2 :30 min), 244,245,246 Cf (T 1/2 :20 min, 46 min and 35.7 h, respectively) from the 16 O + 238 U and 12 C + 242 Pu reactions, and on the decay property of 245 Cf. Attempts to search for new actinide nuclides, such as 240 U and neutron deficient nuclides of Am, Cm and Bk, were made by a quick purification. The separation system was also applied to the rapid and effective separation of Nd, Am and Cm from spent nuclear fuel samples, for burn-up determination. (J.P.N.) 242 refs

Turbulent mixed buoyancy driven flow and heat transfer in lid driven enclosure

International Nuclear Information System (INIS)

Mishra, Ajay Kumar; Sharma, Anil Kumar

2015-01-01

Turbulent mixed buoyancy driven flow and heat transfer of air in lid driven rectangular enclosure has been investigated for Grashof number in the range of 10 8 to 10 11 and for Richardson number 0.1, 1 and 10. Steady two dimensional Reynolds-Averaged-Navier-Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved. The spatial derivatives in the equations are discretized using the finite-element method. The SIMPLE algorithm is used to resolve pressure-velocity coupling. Turbulence is modeled with the k-ω closure model with physical boundary conditions along with the Boussinesq approximation, for the flow and heat transfer. The predicted results are validated against benchmark solutions reported in literature. The results include stream lines and temperature fields are presented to understand flow and heat transfer characteristics. There is a marked reduction in mean Nusselt number (about 58%) as the Richardson number increases from 0.1 to 10 for the case of Ra=10 10 signifying the effect of reduction of top lid velocity resulting in reduction of turbulent mixing. (author)

Bridging Minds: A Mixed Methodology to Assess Networked Flow.

Science.gov (United States)

Galimberti, Carlo; Chirico, Alice; Brivio, Eleonora; Mazzoni, Elvis; Riva, Giuseppe; Milani, Luca; Gaggioli, Andrea

2015-01-01

The main goal of this contribution is to present a methodological framework to study Networked Flow, a bio-psycho-social theory of collective creativity applying it on creative processes occurring via a computer network. First, we draw on the definition of Networked Flow to identify the key methodological requirements of this model. Next, we present the rationale of a mixed methodology, which aims at combining qualitative, quantitative and structural analysis of group dynamics to obtain a rich longitudinal dataset. We argue that this integrated strategy holds potential for describing the complex dynamics of creative collaboration, by linking the experiential features of collaborative experience (flow, social presence), with the structural features of collaboration dynamics (network indexes) and the collaboration outcome (the creative product). Finally, we report on our experience with using this methodology in blended collaboration settings (including both face-to-face and virtual meetings), to identify open issues and provide future research directions.

Estimating preferential flow in karstic aquifers using statistical mixed models.

Science.gov (United States)

Anaya, Angel A; Padilla, Ingrid; Macchiavelli, Raul; Vesper, Dorothy J; Meeker, John D; Alshawabkeh, Akram N

2014-01-01

Karst aquifers are highly productive groundwater systems often associated with conduit flow. These systems can be highly vulnerable to contamination, resulting in a high potential for contaminant exposure to humans and ecosystems. This work develops statistical models to spatially characterize flow and transport patterns in karstified limestone and determines the effect of aquifer flow rates on these patterns. A laboratory-scale Geo-HydroBed model is used to simulate flow and transport processes in a karstic limestone unit. The model consists of stainless steel tanks containing a karstified limestone block collected from a karst aquifer formation in northern Puerto Rico. Experimental work involves making a series of flow and tracer injections, while monitoring hydraulic and tracer response spatially and temporally. Statistical mixed models (SMMs) are applied to hydraulic data to determine likely pathways of preferential flow in the limestone units. The models indicate a highly heterogeneous system with dominant, flow-dependent preferential flow regions. Results indicate that regions of preferential flow tend to expand at higher groundwater flow rates, suggesting a greater volume of the system being flushed by flowing water at higher rates. Spatial and temporal distribution of tracer concentrations indicates the presence of conduit-like and diffuse flow transport in the system, supporting the notion of both combined transport mechanisms in the limestone unit. The temporal response of tracer concentrations at different locations in the model coincide with, and confirms the preferential flow distribution generated with the SMMs used in the study. © 2013, National Ground Water Association.

Measurement of flow by-passing and turbulent mixing in a model of a fast-reactor steam generator

International Nuclear Information System (INIS)

Little, A.J.; Fallows, T.; Central Electricity Generating Board, Leatherhead

1989-01-01

A description is given of measurements of edge by-pass velocities and turbulent mixing in a model of a fast reactor steam generator. The velocity measurements were carried out using a DANTEC triple-split fibre probe which allowed both the speed and flow angle of a velocity vector to be measured in a plane normal to the axis of the probe. The measurements revealed the presence of reverse flows in the by-pass and adjacent in-bank channels downstream of a grid plate. The magnitude of the by-pass flow was reduced considerably by the insertion of a kicker grid at the mid point between grid plates. Turbulent mixing measurements revealed that circumferential mixing in channels near the by-pass channel was up to 5 times greater than the radial mixing. The level of radial mixing at the edge of the bank was similar to that measured near the centre of the bank. A method of transposing mass diffusion measurements in air to thermal diffusivities of sodium is discussed. (orig.)

Numerical Simulation on the Performance of a Mixed-Flow Pump under Various Casing Structures

Directory of Open Access Journals (Sweden)

Wu Dazhuan

2013-01-01

Full Text Available With regard to the reactor coolant pump and high flow-rate circulating pump, the requirements on the compactness of the structure, safety, and hydraulic performance are particularly important. Thus, the mixed-flow pump with cylindrical casing is adopted in some occasions. Due to the different characteristics between the special cylindrical casing and the common pump casing, the influence of the special casing on a mixed-flow pump characteristics was numerically investigated to obtain better performance and flow structure in the casing. The results show that the models with cylindrical casing have much worse head and efficiency characteristics than the experimental model, and this is caused by the flow in the pump casing. By moving the guide vanes half inside the pump casing, the efficiency gets improved while the low pressure zone at the corner of outlet pipe and pump casing disappeared. When the length of pump casing increases from the size equal to the diameter of outlet pipe to that larger than it, the efficiency drops obviously and the flow field in the outlet pipe improved without curved flow. In addition, the length of the pump casing has greater impacts on the pump performance than the radius of it.

A mathematical model for turbulent incompressible flows through mixing grids

International Nuclear Information System (INIS)

Allaire, G.

1989-01-01

A mathematical model is proposed for the computation of turbulent incompressible flows through mixing grids. This model is obtained as follows: in a three-dimentional-domain we represent a mixing grid by small identical wings of size ε 2 periodically distributed at the nodes of a plane regular mesh of size ε, and we consider incompressible Navier-Stokes equations with a no-slip condition on the wings. Using an appropriate homogenization process we pass to the limit when ε tends to zero and we obtain a Brinkman equation, i.e. a Navier-Stokes equation plus a zero-order term for the velocity, in a homogeneous domain without anymore wings. The interest of this model is that the spatial discretization is simpler in a homogeneous domain, and, moreover, the new term, which expresses the grid's mixing effect, can be evaluated with a local computation around a single wing

Intelligent Flow Control Valve

Science.gov (United States)

Kelley, Anthony R (Inventor)

2015-01-01

The present invention is an intelligent flow control valve which may be inserted into the flow coming out of a pipe and activated to provide a method to stop, measure, and meter flow coming from the open or possibly broken pipe. The intelligent flow control valve may be used to stop the flow while repairs are made. Once repairs have been made, the valve may be removed or used as a control valve to meter the amount of flow from inside the pipe. With the addition of instrumentation, the valve may also be used as a variable area flow meter and flow controller programmed based upon flowing conditions. With robotic additions, the valve may be configured to crawl into a desired pipe location, anchor itself, and activate flow control or metering remotely.

Cold and hot model investigation of flow and mixing in a multi-jet flare

Energy Technology Data Exchange (ETDEWEB)

Pagot, P.R. [Petrobras Petroleo Brasileiro S.A., Rio de Janeiro (Brazil); Sobiesiak, A. [Windsor Univ., ON (Canada); Grandmaison, E.W. [Queen' s Univ., Kingston, ON (Canada). Centre for Advanced Gas Combustion Technology

2003-07-01

The oil and gas industry commonly disposes of hydrocarbon wastes by flaring. This study simulated several features of industrial offshore flares in a multi-jet burner. Cold and hot flow experiments were performed. Twenty-four nozzles mounted on radial arms originating from a central fuel plenum were used in the burner design. In an effort to improve the mixing and radiation characteristics of this type of burner, an examination of the effect of various mixing-altering devices on the nozzle exit ports was performed. Flow visualization studies of the cold and hot flow systems were presented, along with details concerning temperature, gas composition and radiation levels from the burner models. The complex flow pattern resulting when multiple jets are injected into a cross flow stream were demonstrated with the flow visualization studies from the cold model. The trajectory followed by the leading edge jet for the reference case and the ring attachments was higher but similar to the simple round jet in a cross flow. The precessing jets and the cone attachments were more strongly deflected by the cross flow with a higher degree of mixing between the jets in the nozzle region. For different firing rates, flow visualization, gas temperature, gas composition and radiative heat flux measurements were performed in the hot model studies. Flame trajectories, projected side view areas and volumes increased with firing rates for all nozzle configurations and the ring attachment flare had the smallest flame volume. The gas temperatures reached maximum values at close to 30 per cent of the flame length and the lowest gas temperature was observed for the flare model with precessing jets. For the reference case nozzle, nitrogen oxide (NOx) concentrations were in the 30 to 45 parts per million (ppm) range. The precessing jet model yielded NOx concentrations in the 22 to 24 ppm range, the lowest obtained. There was a linear dependence between the radiative heat flux from the flames

Submillisecond mixing in a continuous-flow, microfluidic mixer utilizing mid-infrared hyperspectral imaging detection.

Science.gov (United States)

Kise, Drew P; Magana, Donny; Reddish, Michael J; Dyer, R Brian

2014-02-07

We report a continuous-flow, microfluidic mixer utilizing mid-infrared hyperspectral imaging detection, with an experimentally determined, submillisecond mixing time. The simple and robust mixer design has the microfluidic channels cut through a polymer spacer that is sandwiched between two IR transparent windows. The mixer hydrodynamically focuses the sample stream with two side flow channels, squeezing it into a thin jet and initiating mixing through diffusion and advection. The detection system generates a mid-infrared hyperspectral absorbance image of the microfluidic sample stream. Calibration of the hyperspectral image yields the mid-IR absorbance spectrum of the sample versus time. A mixing time of 269 μs was measured for a pD jump from 3.2 to above 4.5 in a D2O sample solution of adenosine monophosphate (AMP), which acts as an infrared pD indicator. The mixer was further characterized by comparing experimental results with a simulation of the mixing of an H2O sample stream with a D2O sheath flow, showing good agreement between the two. The IR microfluidic mixer eliminates the need for fluorescence labeling of proteins with bulky, interfering dyes, because it uses the intrinsic IR absorbance of the molecules of interest, and the structural specificity of IR spectroscopy to follow specific chemical changes such as the protonation state of AMP.

S-naproxen-ss-1-O-acyl glucuronide degradation kinetic studies by stopped-flow high-performance liquid chromatography-H-1 NMR and high-performance liquid chromatography-UV

DEFF Research Database (Denmark)

Mortensen, R. W.; Corcoran, O.; Cornett, Claus

2001-01-01

Acyl-migrated isomers of drug beta -1-O-acyl glucuronides have been implicated in drug toxicity because they can bind to proteins. The acyl migration and hydrolysis of S-naproxen-beta -1-O-acyl glucuronide (S-nap-g) was followed by dynamic stopped-flow HPLC-H-1 NMR and HPLC methods. Nine first or...

Microfluidic Mixing Technology for a Universal Health Sensor

Science.gov (United States)

Chan, Eugene Y.; Bae, Candice

2009-01-01

A highly efficient means of microfluidic mixing has been created for use with the rHEALTH sensor an elliptical mixer and passive curvilinear mixing patterns. The rHEALTH sensor provides rapid, handheld, complete blood count, cell differential counts, electrolyte measurements, and other lab tests based on a reusable, flow-based microfluidic platform. These geometries allow for cleaning in a reusable manner, and also allow for complete mixing of fluid streams. The microfluidic mixing is performed by flowing two streams of fluid into an elliptical or curvilinear design that allows the combination of the flows into one channel. The mixing is accomplished by either chaotic advection around micro - fluidic loops. All components of the microfluidic chip are flow-through, meaning that cleaning solution can be introduced into the chip to flush out cells, plasma proteins, and dye. Tests were performed on multiple chip geometries to show that cleaning is efficient in any flowthrough design. The conclusion from these experiments is that the chip can indeed be flushed out with microliter volumes of solution and biological samples are cleaned readily from the chip with minimal effort. The technology can be applied in real-time health monitoring at patient s bedside or in a doctor s office, and real-time clinical intervention in acute situations. It also can be used for daily measurement of hematocrit for patients on anticoagulant drugs, or to detect acute myocardial damage outside a hospital.

Rapid-mix studies on the anomalous radiosensitization of mammalian cells by 5-chloro-1-methyl-4-nitroimidazole

International Nuclear Information System (INIS)

Watts, M.E.; Hodgkiss, R.J.; Sehmi, D.S.; Woodcock, M.

1980-01-01

It has been suggested that the anomalously high radiosensitization shown by 5-chloro-1-methyl-4-nitroimidazole (CMNI) arises from dissociation of the CMNI radical-anion, yielding Cl - and an arylating free radical, and that the importance of this dehalogenation process could be investigated by irradiating hypoxic mammalian cells in vitro in the presence of CMNI, followed by the rapid addition of oxygen to prevent the dehalogenation process. 0.1 mmol dm -3 CMNI gave a sensitizer enhancement ratio (SER) of 1.7 when irradiated under steady-state conditions with 250 kVp X-rays (dose rate 3.93 Gymin -1 ) using V79 379A cells. Irradiation with 2.5 MeV electrons in the rapid-mix apparatus with 0.15 mmol dm -3 CMNI flowing through both tubes gave a slightly lower value, SER=1.5, in hypoxia. When air- or oxygen saturated 0.15 mmol dm -3 CMNI in Eagle's MEM were added to cells irradiated in hypoxic 0.15 mmol dm -3 CMNI solution 17 ms after irradiation, no change in SER was observed. Control experiments without CMNI also confirmed that the addition of oxygen at this time has no influence on radiosensitization. It was concluded that since a significant reduction in SER was not observed, the elimination of the ortho-substituted 'leaving group' is not responsible for the anomalously high radiosensitization efficiency. (U.K.)

Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico)

Science.gov (United States)

Hernández-Antonio, A.; Mahlknecht, J.; Tamez-Meléndez, C.; Ramos-Leal, J.; Ramírez-Orozco, A.; Parra, R.; Ornelas-Soto, N.; Eastoe, C. J.

2015-09-01

Groundwater chemistry and isotopic data from 40 production wells in the Atemajac and Toluquilla valleys, located in and around the Guadalajara metropolitan area, were determined to develop a conceptual model of groundwater flow processes and mixing. Stable water isotopes (δ2H, δ18O) were used to trace hydrological processes and tritium (3H) to evaluate the relative contribution of modern water in samples. Multivariate analysis including cluster analysis and principal component analysis were used to elucidate distribution patterns of constituents and factors controlling groundwater chemistry. Based on this analysis, groundwater was classified into four groups: cold groundwater, hydrothermal groundwater, polluted groundwater and mixed groundwater. Cold groundwater is characterized by low temperature, salinity, and Cl and Na concentrations and is predominantly of Na-HCO3-type. It originates as recharge at "La Primavera" caldera and is found predominantly in wells in the upper Atemajac Valley. Hydrothermal groundwater is characterized by high salinity, temperature, Cl, Na and HCO3, and the presence of minor elements such as Li, Mn and F. It is a mixed-HCO3 type found in wells from Toluquilla Valley and represents regional flow circulation through basaltic and andesitic rocks. Polluted groundwater is characterized by elevated nitrate and sulfate concentrations and is usually derived from urban water cycling and subordinately from agricultural return flow. Mixed groundwaters between cold and hydrothermal components are predominantly found in the lower Atemajac Valley. Twenty-seven groundwater samples contain at least a small fraction of modern water. The application of a multivariate mixing model allowed the mixing proportions of hydrothermal fluids, polluted waters and cold groundwater in sampled water to be evaluated. This study will help local water authorities to identify and dimension groundwater contamination, and act accordingly. It may be broadly applicable to

Bedform development in mixed sand-mud: The contrasting role of cohesive forces in flow and bed

Science.gov (United States)

Baas, Jaco H.; Davies, Alan G.; Malarkey, Jonathan

2013-01-01

The majority of subaqueous sediment on Earth consists of mixtures of cohesive clay and cohesionless sand and silt, but the role of cohesion on the development and stability of sedimentary bedforms is poorly understood. The results of new laboratory flume experiments on bedform development in cohesive, mixed sand-mud beds are compared with the results of previous experiments in which cohesive forces in high concentration clay flows dominated bedform development. Even though both series of mixed sand-mud experiments were conducted at similar flow velocities, the textural and structural properties of the bedforms were sufficiently different to permit the designation of key criteria for identifying bedform generation under cohesive flows against bedform generation on cohesive substrates. These criteria are essential for improving bedform size predictions in sediment transport modelling in modern sedimentary environments and for the reconstruction of depositional processes in the geological record. The current ripples developing on the cohesive, mixed sand-mud beds, with bed mud fractions of up to 18%, were significantly smaller than equivalent bedforms in noncohesive sand. Moreover, the bedform height showed a stronger inversely proportional relationship with initial bed mud fraction than the bedform wavelength. This is in contrast with the bedforms developing under the cohesive clay flows, which tend to increase in size with increasing suspended clay concentration until the flow turbulence is fully suppressed. Selective removal of clay from the mixed beds, i.e., clay winnowing, was found to be an important process, with 82-100% clay entrained into suspension after 2 h of bedform development. This winnowing process led to the development of a sand-rich armouring layer. This armouring layer is inferred to have protected the underlying mixed sand-mud from prolonged erosion, and in conjunction with strong cohesive forces in the bed may have caused the smaller size of the

Test Facility Construction for Flow Visualization on Mixing Flow inside Subchannels of PWR Rod Bundle

Energy Technology Data Exchange (ETDEWEB)

Kim, Seok; Jeon, Byong-Guk; Youn, Young-Jung; Choi, Hae-Seob; Euh, Dong-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

Flow inside rod bundles has a similarity with flow in porous media. To ensure thermal performance of a nuclear reactor, detailed information of the heat transfer and turbulent mixing flow phenomena taking place within the subchannels is required. The subchannel analysis is one of the key thermal-hydraulic calculations in the safety analysis of the nuclear reactor core. At present, subchannel computer codes are employed to simulate fuel elements of nuclear reactor cores and predict the performance of cores under normal operating and hypothetical accident conditions. The ability of these subchannels codes to predict both the flow and enthalpy distribution in fuel assemblies is very important in the design of nuclear reactors. Recently, according to the modern tend of the safety analysis for the nuclear reactor, a new component scale analysis code, named CUPID, and has been developed in KAERI. The CUPID code is based on a two-fluid and three-field model, and both the open and porous media approaches are incorporated. The PRIUS experiment has addressed many key topics related to flow behaviour in a rod bundle. These issues are related to the flow conditions inside a nuclear fuel element during normal operation of the plant or in accident scenarios. From the second half of 2016, flow visualization will be performed by using a high speed camera and image analysis technique, from which detailed information for the two-dimensional movement of single phase flow is quantified.

Model for transversal turbulent mixing in axial flow in rod bundles

International Nuclear Information System (INIS)

Carajilescov, P.

1990-01-01

The present work consists in the development of a model for the transversal eddy diffusivity to account for the effect of turbulent thermal mixing in axial flows in rod bundles. The results were compared to existing correlations that are currently being used in reactor thermalhydraulic analysis and considered satisfactory. (author)

Effect of viscous dissipation on mixed convection flow in a vertical ...

African Journals Online (AJOL)

International Journal of Engineering, Science and Technology .... third kind for flow over a flat plate and in the thermal entrance region of a rectangular channel. ... on mixed convection in a vertical channel using Robin boundary conditions was ... Hajmohammadi and Nourazar (2014) studied the effect of a thin gas layer in ...

Impacts of a jet's exit flow pattern on mixing and combustion performance

Energy Technology Data Exchange (ETDEWEB)

Nathan, G.J.; Mi, J.; Newbold, G.J.R.; Nobes, D.S. [Turbulence, Energy and Combustion Group, School of Mechanical Engineering, The University of Adelaide, South Australia 5005 (Australia); Alwahabi, Z.T. [Turbulence, Energy and Combustion Group, Chemical Engineering, The University of Adelaide, South Australia 5005 (Australia)

2006-09-15

The influence of modifying a jet's exit flow pattern on both the near and far-field turbulent mixing processes and on the resulting combustion performance, is explored. This reveals that, in contradiction to some common assumptions, increasing the coherence of large-scale motions can decrease molecular mixing rates, and yet can still be beneficial in some applications. Even relatively minor changes to the exit flow pattern of a non-reacting round jet, through changes to the nozzle profile are found to propagate downstream into the far field, apparently through the underlying turbulent structure. Importantly, while a jet from a smoothly contracting nozzle is found to have higher rates of entrainment, mean spread and mean decay of the scalar field than does a long pipe jet, it has a lower rate of molecular mixing. That is, increased large-scale mixing does not necessarily result in increased fine-scale mixing. A range of devices are reviewed which enhance, or stimulate the large-scale, coherent motions in an emerging jet using acoustic, mechanical or fluidic methods. The available evidence suggests that those methods which induce instantaneously asymmetric flow structure are more effective at increasing the near-field spreading than are those which induce instantaneously axisymmetric flow structure. Only limited data are available of the effects of such near-field changes on the far-field properties. Nevertheless, the available data reveal a clear trend that this near-field flow undergoes a transition to a far-field state whose spread and decay is comparable with that of a steady jet, albeit being indelibly altered by the near-field excitation. It also suggests that 'self-exciting' devices (i.e. that are not externally forced), cause a net reduction in the total entrainment relative to the unexcited jet, due to the losses induced by the device itself. Nevertheless, the changes which they can impart to the flow, such as redistributing the turbulent

Storage evaporator for vehicles with start-stop technology; Speicherverdampfer fuer Fahrzeuge mit Start-Stopp-Funktion

Energy Technology Data Exchange (ETDEWEB)

Wawzyniak, Markus; Link, Joachim [Behr GmbH und Co. KG, Stuttgart (Germany)

2013-04-15

Today, the use of engine start-stop technology - a system designed to cut fuel consumption when the vehicle stops or, in future applications, when vehicles are in coasting or ''sailing'' mode - is gaining ground in more and more vehicle classes. Shutting off the internal combustion engine, though, detrimentally affects cabin air conditioning because the belt-driven A/C compressor is likewise deactivated, thus bringing the vapor compression process to a standstill. As a result, during extended stop periods and in warm weather vent temperatures and air humidity rapidly increase.

Electroweak baryogenesis and Higgs and stop searches at LEP and the Tevatron

International Nuclear Information System (INIS)

Carena, M.; Quiros, M.; Wagner, C.E.M.

1998-01-01

It has been recently shown that the observed baryon number may originate at the electroweak phase transition, provided that the Higgs boson and the lightest stop are sufficiently light. In this work, we perform a detailed analysis, including all dominant two-loop finite-temperature corrections to the Higgs effective potential, as well as the non-trivial effects proceeding from the mixing in the stop sector, to define the region of parameter space for which electroweak baryogenesis can happen. The limits on the stop and Higgs masses are obtained by taking into account the experimental bounds on these quantities, as well as those coming from the requirement of avoiding dangerous color breaking minima. We find for the Higgs mass m h < or∼105 GeV, while the stop mass may be close to the present experimental bound and must be smaller than, or of the order of, the top quark mass. These results provide a very strong motivation for further non-perturbative analysis of the electroweak phase transition, as well as for the search for Higgs and stop particles at the LEP and Tevatron colliders. (orig.)

Flow split, pressure drop, and mixing experiments in a 61-pin shaved-wire blanket assembly

International Nuclear Information System (INIS)

Wang, S.F.; Rohsenow, W.M.; Todreas, N.E.

1981-10-01

The experimental results of a series of hydraulic tests on a shaved-wire 61-pin blanket assembly are presented and compared to previously published MIT results for full-wire tests. The reduction of the wall subchannel flow area by incorporating the shaved-wire reduced the flow in edge and corner subchannels by 4.5 to 16.5% and 1.5%, respectively. The swirl velocity in the wall subchannels was reduced by 50%. The bundle average friction factor, the turbulent subchannel friction factors, and the mixing parameter and laminar/transition friction factors in the interior subchannels remained unchanged. However, the laminar/transition friction factors in the edge subchannels were significantly increased. These effects generally cannot be predicted by the current flow split, friction factor, and mixing parameter correlations

Mixing and entrainment in hydraulically driven stratified sill flows

DEFF Research Database (Denmark)

Nielsen, Morten Holtegaard; Pratt, Larry; Helfrich, Karl

2004-01-01

The investigation involves the hydraulic behaviour of a dense layer of fluid flowing over an obstacle and subject to entrainment of mass and momentum from a dynamically inactive (but possibly moving) overlying fluid. An approach based on the use of reduced gravity, shallow-water theory with a cross......-interface entrainment velocity is compared with numerical simulations based on a model with continuously varying stratification and velocity. The locations of critical flow (hydraulic control) in the continuous model are estimated by observing the direction of propagation of small-amplitude long-wave disturbances...... that the reduced gravity model systematically underestimates inertia and overestimates buoyancy. These differences are quantified by shape coefficients that measure the vertical non-uniformities of the density and horizontal velocity that arise, in part, by incomplete mixing of entrained mass and momentum over...

Flow method for rapid production of Batio3 nanoparticles in supercritical water

International Nuclear Information System (INIS)

Atashfaraz, M.; Shariati-Niassar, M.; Ohara, Satoshi; Takami, S.; Umetsu, M.; Naka, T.; Adschiri, T.

2006-01-01

Fine BaTiO 3 nanoparticles were obtained by hydrothermal synthesis under supercritical conditions with batch and flow type experimental methods. Mixture of barium hydroxide and titanium oxide starting solution was treated in the supercritical wafer at 400 d eg C and 30 MPa. The size of nanoparticles synthesized in the flow type experiment was smaller than that in the batch type. Rapid heating in a flow, reactor is effective to synthesize smaller size and narrower particle size distribution for the BaTiO 3 , nanoparticles. The mechanism for this result was discussed based on the solubility of titanium oxide

Numerical and experimental flow analysis in centifluidic systems for rapid allergy screening tests

Directory of Open Access Journals (Sweden)

Dethloff Manuel

2015-09-01

Full Text Available For the development of the automated processing of a membrane-based rapid allergy test, the flow characteristics in one part of the test, the reagents module, are analysed. This module consists of a multichannel system with several inputs and one output. A return flow from one input channel into another should be avoided. A valveless module with pointed channels at an angle of 12° is analysed with numerical and experimental methods with regard to the flow characteristics.

Models for fluid flows with heat transfer in mixed convection

International Nuclear Information System (INIS)

Mompean Munhoz da Cruz, G.

1989-06-01

Second order models were studied in order to predict turbulent flows with heat transfer. The equations used correspond to the characteristic scale of turbulent flows. The order of magnitude of the terms of the equation is analyzed by using Reynolds and Peclet numbers. The two-equation model (K-ε) is applied in the hydrodynamic study. Two models are developed for the heat transfer analysis: the Prt + teta 2 and the complete model. In the first model, the turbulent thermal diffusivity is calculated by using the Prandtl number for turbulent flow and an equation for the variance of the temperature fluctuation. The second model consists of three equations concerning: the turbulent heat flow, the variance of the temperature fluctuation and its dissipation ratio. The equations were validated by four experiments, which were characterized by the analysis of: the air flow after passing through a grid of constant average temperature and with temperature gradient, an axysymmetric air jet submitted to high and low heating temperature, the mixing (cold-hot) of two coaxial jets of sodium at high Peclet number. The complete model is shown to be the most suitable for the investigations presented [fr

Rapid dual-injection single-scan 13N-ammonia PET for quantification of rest and stress myocardial blood flows

International Nuclear Information System (INIS)

Rust, T C; DiBella, E V R; McGann, C J; Christian, P E; Hoffman, J M; Kadrmas, D J

2006-01-01

Quantification of myocardial blood flows at rest and stress using 13 N-ammonia PET is an established method; however, current techniques require a waiting period of about 1 h between scans. The objective of this study was to test a rapid dual-injection single-scan approach, where 13 N-ammonia injections are administered 10 min apart during rest and adenosine stress. Dynamic PET data were acquired in six human subjects using imaging protocols that provided separate single-injection scans as gold standards. Rest and stress data were combined to emulate rapid dual-injection data so that the underlying activity from each injection was known exactly. Regional blood flow estimates were computed from the dual-injection data using two methods: background subtraction and combined modelling. The rapid dual-injection approach provided blood flow estimates very similar to the conventional single-injection standards. Rest blood flow estimates were affected very little by the dual-injection approach, and stress estimates correlated strongly with separate single-injection values (r = 0.998, mean absolute difference = 0.06 ml min -1 g -1 ). An actual rapid dual-injection scan was successfully acquired in one subject and further demonstrates feasibility of the method. This study with a limited dataset demonstrates that blood flow quantification can be obtained in only 20 min by the rapid dual-injection approach with accuracy similar to that of conventional separate rest and stress scans. The rapid dual-injection approach merits further development and additional evaluation for potential clinical use

Rapid, high-temperature, field test method for evaluation of geothermal calcium carbonate scale inhibitors

Energy Technology Data Exchange (ETDEWEB)

Asperger, R.G.

1986-09-01

A new test method is described that allows the rapid field testing of calcium carbonate scale inhibitors at 500/sup 0/F (260/sup 0/C). The method evolved from use of a full-flow test loop on a well with a mass flow rate of about 1 x 10/sup 6/ lbm/hr (126 kg/s). It is a simple, effective way to evaluate the effectiveness of inhibitors under field conditions. Five commercial formulations were chosen for field evaluation on the basis of nonflowing, laboratory screening tests at 500/sup 0/F (260/sup 0/C). Four of these formulations from different suppliers controlled calcium carbonate scale deposition as measured by the test method. Two of these could dislodge recently deposited scale that had not age-hardened. Performance-profile diagrams, which were measured for these four effective inhibitors, show the concentration interrelationship between brine calcium and inhibitor concentrations at which the formulations will and will not stop scale formation in the test apparatus. With these diagrams, one formulation was chosen for testing on the full-flow brine line. The composition was tested for 6 weeks and showed a dramatic decrease in the scaling occurring at the flow-control valve. This scaling was about to force a shutdown of a major, long-term flow test being done for reservoir economic evaluations. The inhibitor stopped the scaling, and the test was performed without interruption.

A proposed through-flow inverse method for the design of mixed-flow pumps

Science.gov (United States)

Borges, Joao Eduardo

1991-01-01

A through-flow (hub-to-shroud) truly inverse method is proposed and described. It uses an imposition of mean swirl, i.e., radius times mean tangential velocity, given throughout the meridional section of the turbomachine as an initial design specification. In the present implementation, it is assumed that the fluid is inviscid, incompressible, and irrotational at inlet and that the blades are supposed to have zero thickness. Only blade rows that impart to the fluid a constant work along the space are considered. An application of this procedure to design the rotor of a mixed-flow pump is described in detail. The strategy used to find a suitable mean swirl distribution and the other design inputs is also described. The final blade shape and pressure distributions on the blade surface are presented, showing that it is possible to obtain feasible designs using this technique. Another advantage of this technique is the fact that it does not require large amounts of CPU time.

Turbulent Mixing of Primary and Secondary Flow Streams in a Rocket-Based Combined Cycle Engine

Science.gov (United States)

Cramer, J. M.; Greene, M. U.; Pal, S.; Santoro, R. J.; Turner, Jim (Technical Monitor)

2002-01-01

This viewgraph presentation gives an overview of the turbulent mixing of primary and secondary flow streams in a rocket-based combined cycle (RBCC) engine. A significant RBCC ejector mode database has been generated, detailing single and twin thruster configurations and global and local measurements. On-going analysis and correlation efforts include Marshall Space Flight Center computational fluid dynamics modeling and turbulent shear layer analysis. Potential follow-on activities include detailed measurements of air flow static pressure and velocity profiles, investigations into other thruster spacing configurations, performing a fundamental shear layer mixing study, and demonstrating single-shot Raman measurements.

Suppression of chaos at slow variables by rapidly mixing fast dynamics

Science.gov (United States)

Abramov, R.

2012-04-01

One of the key questions about chaotic multiscale systems is how the fast dynamics affects chaos at the slow variables, and, therefore, impacts uncertainty and predictability of the slow dynamics. Here we demonstrate that the linear slow-fast coupling with the total energy conservation property promotes the suppression of chaos at the slow variables through the rapid mixing at the fast variables, both theoretically and through numerical simulations. A suitable mathematical framework is developed, connecting the slow dynamics on the tangent subspaces to the infinite-time linear response of the mean state to a constant external forcing at the fast variables. Additionally, it is shown that the uncoupled dynamics for the slow variables may remain chaotic while the complete multiscale system loses chaos and becomes completely predictable at the slow variables through increasing chaos and turbulence at the fast variables. This result contradicts the common sense intuition, where, naturally, one would think that coupling a slow weakly chaotic system with another much faster and much stronger mixing system would result in general increase of chaos at the slow variables.

Plasma-enhanced mixing and flameholding in supersonic flow.

Science.gov (United States)

Firsov, Alexander; Savelkin, Konstantin V; Yarantsev, Dmitry A; Leonov, Sergey B

2015-08-13

The results of experimental study of plasma-based mixing, ignition and flameholding in a supersonic model combustor are presented in the paper. The model combustor has a length of 600 mm and cross section of 72 mm width and 60 mm height. The fuel is directly injected into supersonic airflow (Mach number M=2, static pressure P(st)=160-250 Torr) through wall orifices. Two series of tests are focused on flameholding and mixing correspondingly. In the first series, the near-surface quasi-DC electrical discharge is generated by flush-mounted electrodes at electrical power deposition of W(pl)=3-24 kW. The scope includes parametric study of ignition and flame front dynamics, and comparison of three schemes of plasma generation: the first and the second layouts examine the location of plasma generators upstream and downstream from the fuel injectors. The third pattern follows a novel approach of combined mixing/ignition technique, where the electrical discharge distributes along the fuel jet. The last pattern demonstrates a significant advantage in terms of flameholding limit. In the second series of tests, a long discharge of submicrosecond duration is generated across the flow and along the fuel jet. A gasdynamic instability of thermal cavity developed after a deposition of high-power density in a thin plasma filament promotes the air-fuel mixing. The technique studied in this work has weighty potential for high-speed combustion applications, including cold start/restart of scramjet engines and support of transition regime in dual-mode scramjet and at off-design operation. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Detection of flow mixing processes using transmission methods in high-duty heat exchanging apparatus

International Nuclear Information System (INIS)

Seiffert, V.

1981-01-01

The COBRA-IIIC program modified by MIT has been further improved for verifying the experimental studies described in the thesis. This work has been accompanied by a review and modification of the relevant analytical equations. A mathematical relationship has been set up for the cross-mixing phenomenon of shearing flow in narrowest cross-section between two heating rods, the relationship being taken into account in the sub-channel analysis. Despite the very complex and superposing processes of the problem studied, the results obtained by the improved sub-channel analysis program using the nearly derived cross-mixing approach are quantitatively well confirmed by comparison with experimental data. Applying the improved sub-channel analysis program to describing the author's two-phase flow experiments (air-water and water-steam) with rod bundle geometries to be found in the literature, the cross-mixing approach presented in the thesis is shown to be reliable (orig./GL) [de

The control of deliberate waiting strategies in a stop-signal task

Directory of Open Access Journals (Sweden)

R.P. Sylwan

2004-06-01

Full Text Available To inhibit an ongoing flow of thoughts or actions has been largely considered to be a crucial executive function, and the stop-signal paradigm makes inhibitory control measurable. Stop-signal tasks usually combine two concurrent tasks, i.e., manual responses to a primary task (go-task are occasionally countermanded by a stimulus which signals participants to inhibit their response in that trial (stop-task. Participants are always instructed not to wait for the stop-signal, since waiting strategies cause the response times to be unstable, invalidating the data. The aim of the present study was to experimentally control the strategies of waiting deliberately for the stop-signal in a stop-task by means of an algorithm that measured the variation in the reaction times to go-stimuli on-line, and displayed a warning legend urging participants to be faster when their reaction times were more than two standard deviations of the mean. Thirty-four university students performed a stop-task with go- and stop-stimuli, both of which were delivered in the visual modality and were lateralized within the visual field. The participants were divided into two groups (group A, without the algorithm, vs group B, with the algorithm. Group B exhibited lower variability of reaction times to go-stimuli, whereas no significant between-group differences were found in any of the measures of inhibitory control, showing that the algorithm succeeded in controlling the deliberate waiting strategies. Differences between deliberate and unintentional waiting strategies, and anxiety as a probable factor responsible for individual differences in deliberate waiting behavior, are discussed.

Electroweak Baryogenesis and Higgs and Stop Searches at LEP and the Tevatron

CERN Document Server

Carena, M S; Wagner, C E M

1998-01-01

It has been recently shown that the observed baryon number may originate at the electroweak phase transition, provided that the Higgs boson and the lightest stop are sufficiently light. In this work, we perform a detailed analysis, including all dominant two-loop finite temperature corrections to the Higgs effective potential, as well as the non-trivial effects proceeding from the mixing in the stop sector, to define the region of parameter space for which electroweak baryogenesis can happen. The limits on the stop and Higgs masses are obtained by taking into account the experimental bounds on these quantities, as well as those coming from the requirement of avoiding dangerous color breaking minima. We find for the Higgs mass $m_h \\simlt 105$ GeV, while the stop mass may be close to the present experimental bound and must be smaller than, or of order of, the top quark mass. These results provide a very strong motivation for further non-perturbative analysis of the electroweak phase transition, as well as for ...

Fluid Flow and Mixing Induced by AC Continuous Electrowetting of Liquid Metal Droplet

Directory of Open Access Journals (Sweden)

Qingming Hu

2017-04-01

Full Text Available In this work, we proposed a novel design of a microfluidic mixer utilizing the amplified Marangoni chaotic advection induced by alternating current (AC continuous electrowetting of a metal droplet situated in electrolyte solution, due to the linear and quadratic voltage-dependence of flow velocity at small or large voltages, respectively. Unlike previous researchers exploiting the unidirectional surface stress with direct current (DC bias at droplet/medium interface for pumping of electrolytes where the resulting flow rate is linearly proportional to the field intensity, dominance of another kind of dipolar flow pattern caused by local Marangoni stress at the drop surface in a sufficiently intense AC electric field is demonstrated by both theoretical analysis and experimental observation, which exhibits a quadratic growth trend as a function of the applied voltage. The dipolar shear stress merely appears at larger voltages and greatly enhances the mixing performance by inducing chaotic advection between the neighboring laminar flow. The mixer design developed herein, on the basis of amplified Marangoni chaotic advection around a liquid metal droplet at larger AC voltages, has great potential for chemical reaction and microelectromechanical systems (MEMS actuator applications because of generating high-throughput and excellent mixing performance at the same time.

Rapid-mixing studies on the time-scale of radiation damage in cells

International Nuclear Information System (INIS)

Adams, G.E.; Michael, B.D.; Asquith, J.C.; Shenoy, M.A.; Watts, M.E.; Whillans, D.W.

1975-01-01

Rapid mixing studies were performed to determine the time scale of radiation damage in cells. There is evidence that the sensitizing effects of oxygen and other chemical dose-modifying agents on the response of cells to ionizing radiation involve fast free-radical processes. Fast response technique studies in bacterial systems have shown that extremely fast processes occur when the bacteria are exposed to oxygen or other dose-modifying agents during irradiation. The time scales observed were consistent with the involvement of fast free-radical reactions in the expression of these effects

Flow-Based Systems for Rapid and High-Precision Enzyme Kinetics Studies

Directory of Open Access Journals (Sweden)

Supaporn Kradtap Hartwell

2012-01-01

Full Text Available Enzyme kinetics studies normally focus on the initial rate of enzymatic reaction. However, the manual operation of steps of the conventional enzyme kinetics method has some drawbacks. Errors can result from the imprecise time control and time necessary for manual changing the reaction cuvettes into and out of the detector. By using the automatic flow-based analytical systems, enzyme kinetics studies can be carried out at real-time initial rate avoiding the potential errors inherent in manual operation. Flow-based systems have been developed to provide rapid, low-volume, and high-precision analyses that effectively replace the many tedious and high volume requirements of conventional wet chemistry analyses. This article presents various arrangements of flow-based techniques and their potential use in future enzyme kinetics applications.

Energy Performance and Radial Force of a Mixed-Flow Pump with Symmetrical and Unsymmetrical Tip Clearances

Directory of Open Access Journals (Sweden)

Yue Hao

2017-01-01

Full Text Available The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal axis is located at the coordinate origin when the tip clearance is symmetrical, and moves to the third quadrant when the tip clearance is unsymmetrical. Analysis results show that the total radial force on the principal axis is closely related to the fluctuation of mass flow rate in each single flow channel. Unsteady simulations show that the dominant frequencies of radial force on the hub and blade correspond to the blade number, vane number, or double blade number because of the rotor stator interaction. The radial force on the blade pressure side decreases with the tip clearance increase because of leakage flow. The unsymmetrical tip clearances in an impeller induce uneven leakage flow rate and then result in unsymmetrical work ability of each blade and flow pattern in each channel. Thus, the energy performance decreases and the total radial force increases for a mixed flow pump with unsymmetrical tip clearance.

Numerical prediction of flow and mixing characteristics in CVCS chemical addition system

International Nuclear Information System (INIS)

Chang, K.S.

1999-01-01

A numerical result of the flow and mixing characteristics is presented for the flow field created by water injected into a cylindrical tank with an initially stationary fluid. The flow is relevant to the operation of the chemical addition system in the chemical and volume control system (CVCS) of nuclear power plants. This study was undertaken to provide a basis for modification of the previous design which gave a number of difficulties in installation and operation of the chemical addition system because it needs a special reciprocating pump with a high actual head. For the tank of length-to-diameter ratios (L/D) of 1, 2 and 3, each with and without a baffle inside, calculation results were obtained by solving the unsteady laminar two-dimensional elliptic forms of governing equations for the mass, momentum and species concentration. Finite-difference method was used to obtain discretization equations, and the SIMPLER solution algorithm was employed for the calculation procedure. Results showed that the baffle was very effective in enhancing the mixing in the tank, and that a baffle should be installed near the tank entrance in order to inject chemicals into the reactor coolant system (RCS) within the operating time required. (orig.)

Flow injection analysis: Emerging tool for laboratory automation in radiochemistry

International Nuclear Information System (INIS)

Egorov, O.; Ruzicka, J.; Grate, J.W.; Janata, J.

1996-01-01

Automation of routine and serial assays is a common practice of modern analytical laboratory, while it is virtually nonexistent in the field of radiochemistry. Flow injection analysis (FIA) is a general solution handling methodology that has been extensively used for automation of routine assays in many areas of analytical chemistry. Reproducible automated solution handling and on-line separation capabilities are among several distinctive features that make FI a very promising, yet under utilized tool for automation in analytical radiochemistry. The potential of the technique is demonstrated through the development of an automated 90 Sr analyzer and its application in the analysis of tank waste samples from the Hanford site. Sequential injection (SI), the latest generation of FIA, is used to rapidly separate 90 Sr from interfering radionuclides and deliver separated Sr zone to a flow-through liquid scintillation detector. The separation is performed on a mini column containing Sr-specific sorbent extraction material, which selectively retains Sr under acidic conditions. The 90 Sr is eluted with water, mixed with scintillation cocktail, and sent through the flow cell of a flow through counter, where 90 Sr radioactivity is detected as a transient signal. Both peak area and peak height can be used for quantification of sample radioactivity. Alternatively, stopped flow detection can be performed to improve detection precision for low activity samples. The authors current research activities are focused on expansion of radiochemical applications of FIA methodology, with an ultimate goal of creating a set of automated methods that will cover the basic needs of radiochemical analysis at the Hanford site. The results of preliminary experiments indicate that FIA is a highly suitable technique for the automation of chemically more challenging separations, such as separation of actinide elements

Effect of adaptive cruise control systems on mixed traffic flow near an on-ramp

Science.gov (United States)

Davis, L. C.

2007-06-01

Mixed traffic flow consisting of vehicles equipped with adaptive cruise control (ACC) and manually driven vehicles is analyzed using car-following simulations. Simulations of merging from an on-ramp onto a freeway reported in the literature have not thus far demonstrated a substantial positive impact of ACC. In this paper cooperative merging for ACC vehicles is proposed to improve throughput and increase distance traveled in a fixed time. In such a system an ACC vehicle senses not only the preceding vehicle in the same lane but also the vehicle immediately in front in the other lane. Prior to reaching the merge region, the ACC vehicle adjusts its velocity to ensure that a safe gap for merging is obtained. If on-ramp demand is moderate, cooperative merging produces significant improvement in throughput (20%) and increases up to 3.6 km in distance traveled in 600 s for 50% ACC mixed flow relative to the flow of all-manual vehicles. For large demand, it is shown that autonomous merging with cooperation in the flow of all ACC vehicles leads to throughput limited only by the downstream capacity, which is determined by speed limit and headway time.

Precession of a rapidly rotating cylinder flow: traverse through resonance

Science.gov (United States)

Lopez, Juan; Marques, Francisco

2014-11-01

The flow in a rapidly rotating cylinder that is titled and also rotating around another axis can undergo sudden transitions to turbulence. Experimental observations of this have been associated with triadic resonances. The experimental and theoretical results are well-established in the literature, but there remains a lack of understanding of the physical mechanisms at play in the sudden transition from laminar to turbulent flow with very small variations in the governing parameters. Here, we present direct numerical simulations of a traverse in parameter space through an isolated resonance, and describe in detail the bifurcations involved in the sudden transition. U.S. National Science Foundation Grant CBET-1336410 and Spanish Ministry of Education and Science Grant (with FEDER funds) FIS2013-40880.

Scalar mixing and strain dynamics methodologies for PIV/LIF measurements of vortex ring flows

OpenAIRE

Bouremel, Y.; Ducci, A.

2017-01-01

Fluid mixing operations are central to possibly all chemical, petrochemical, and pharmaceutical industries either being related to biphasic blending in polymerisation processes, cell suspension for biopharmaceuticals production, and fractionation of complex oil mixtures. This work aims at providing a fundamental understanding of the mixing and stretching dynamics occurring in a reactor in the presence of a vortical structure, and the vortex ring was selected as a flow paradigm of vortices com...

Appendix to the thesis an experimental and numerical study of a jetfire stop material and a new helical flow heat exchanger

Energy Technology Data Exchange (ETDEWEB)

Austegard, Anders

1997-12-31

This thesis consists of two parts. Part 1: Experimental and numerical study of jetfire stop, and Part 2: Experimental and numerical study of a new kind of shell and tube heat exchanger with helical flow on shell side. Part 1 describes the development of the model for simulation of the temperature development through Viking jetfirestop. A simulation program is developed that calculates the temperature development through Viking jetfirestop. In the development of the model, measurements of reaction energy, pyrolysis and heat conductivity at low temperatures are made. The conductivity at higher temperatures and when pyrolysis reactions are going on is estimated experimentally and by numerical calculations. Full-scale jet fire test and small-scale xenon lamp experiments are made to test the simulation model. Part 2 contains the development of a model that simulate the fluid flow and heat transfer in a helical flow shell and tube heat exchanger. It consists of the development of a porosity model and a model for pressure drop and heat transfer as well as experiments in non-standard tube layouts. Results from the simulation program are compared with experiments on a helical flow shell and tube heat exchanger. This is a separate appendix volume, including computer codes and simulated results. 316 figs., 11 tabs.

Mixed Hitting-Time Models

NARCIS (Netherlands)

Abbring, J.H.

2009-01-01

We study mixed hitting-time models, which specify durations as the first time a Levy process (a continuous-time process with stationary and independent increments) crosses a heterogeneous threshold. Such models of substantial interest because they can be reduced from optimal-stopping models with

Oxidation mode of pyranose 2-oxidase is controlled by pH.

Science.gov (United States)

Prongjit, Methinee; Sucharitakul, Jeerus; Palfey, Bruce A; Chaiyen, Pimchai

2013-02-26

Pyranose 2-oxidase (P2O) from Trametes multicolor is a flavoenzyme that catalyzes the oxidation of d-glucose and other aldopyranose sugars at the C2 position by using O₂ as an electron acceptor to form the corresponding 2-keto-sugars and H₂O₂. In this study, the effects of pH on the oxidative half-reaction of P2O were investigated using stopped-flow spectrophotometry. The results showed that flavin oxidation occurred via different pathways depending on the pH of the environment. At pH values lower than 8.0, reduced P2O reacts with O₂ to form a C4a-hydroperoxyflavin intermediate, leading to elimination of H₂O₂. At pH 8.0 and higher, the majority of the reduced P2O reacts with O₂ via a pathway that does not allow detection of the C4a-hydroperoxyflavin, and flavin oxidation occurs with decreased rate constants upon the rise in pH. The switching between the two modes of P2O oxidation is controlled by protonation of a group which has a pK(a) of 7.6 ± 0.1. Oxidation reactions of reduced P2O under rapid pH change as performed by stopped-flow mixing were different from the same reactions performed with enzyme pre-equilibrated at the same specified pH values, implying that the protonation of the group which controls the mode of flavin oxidation cannot be rapidly equilibrated with outside solvent. Using a double-mixing stopped-flow experiment, a rate constant for proton dissociation from the reaction site was determined to be 21.0 ± 0.4 s⁻¹.

Inseparability of Go and Stop in Inhibitory Control: Go Stimulus Discriminability Affects Stopping Behavior.

Science.gov (United States)

Ma, Ning; Yu, Angela J

2016-01-01

Inhibitory control, the ability to stop or modify preplanned actions under changing task conditions, is an important component of cognitive functions. Two lines of models of inhibitory control have previously been proposed for human response in the classical stop-signal task, in which subjects must inhibit a default go response upon presentation of an infrequent stop signal: (1) the race model, which posits two independent go and stop processes that race to determine the behavioral outcome, go or stop; and (2) an optimal decision-making model, which posits that observers decides whether and when to go based on continually (Bayesian) updated information about both the go and stop stimuli. In this work, we probe the relationship between go and stop processing by explicitly manipulating the discrimination difficulty of the go stimulus. While the race model assumes the go and stop processes are independent, and therefore go stimulus discriminability should not affect the stop stimulus processing, we simulate the optimal model to show that it predicts harder go discrimination should result in longer go reaction time (RT), lower stop error rate, as well as faster stop-signal RT. We then present novel behavioral data that validate these model predictions. The results thus favor a fundamentally inseparable account of go and stop processing, in a manner consistent with the optimal model, and contradicting the independence assumption of the race model. More broadly, our findings contribute to the growing evidence that the computations underlying inhibitory control are systematically modulated by cognitive influences in a Bayes-optimal manner, thus opening new avenues for interpreting neural responses underlying inhibitory control.

Inseparability of Go and Stop in Inhibitory Control: Go Stimulus Discriminability Affects Stopping Behavior

Directory of Open Access Journals (Sweden)

Ning eMa

2016-03-01

Full Text Available Inhibitory control, the ability to stop or modify preplanned actions under changing task conditions, is an important component of cognitive functions. Two lines of models of inhibitory control have previously been proposed for human response in the classical stop-signal task, in which subjects must inhibit a default go response upon presentation of an infrequent stop signal: (1 the race model, which posits two independent go and stop processes that race to determine the behavioral outcome, go or stop; and (2 an optimal decision-making model, which posits that observers decides whether and when to go based on continually (Bayesian updated information about both the go and stop stimuli. In this work, we probe the relationship between go and stop processing by explicitly manipulating the discrimination difficulty of the go stimulus. While the race model assumes the go and stop processes are independent, and therefore go stimulus discriminability should not affect the stop stimulus processing, we simulate the optimal model to show that it predicts harder go discrimination results in a longer go reaction time (RT, a lower stop error rate, as well as a faster stop-signal RT. We then present novel behavioral data that validate these model predictions. The results thus favor a fundamentally inseparable account of go and stop processing, in a manner consistent with the optimal model, and contradicting the independence assumption of the race model. More broadly, our findings contribute to the growing evidence that the computations underlying inhibitory control are systematically modulated by cognitive influences in a Bayes-optimal manner, thus opening new avenues for interpreting neural responses underlying inhibitory control.

Multilevel Monte Carlo methods using ensemble level mixed MsFEM for two-phase flow and transport simulations

KAUST Repository

Efendiev, Yalchin R.; Iliev, Oleg; Kronsbein, C.

2013-01-01

In this paper, we propose multilevel Monte Carlo (MLMC) methods that use ensemble level mixed multiscale methods in the simulations of multiphase flow and transport. The contribution of this paper is twofold: (1) a design of ensemble level mixed

Experimental study on the rheological behaviour of debris flow

Directory of Open Access Journals (Sweden)

A. Scotto di Santolo

2010-12-01

Full Text Available A model able to describe all the processes involved in a debris flow can be very complex owing to the sudden changing of the material that turns from solid into liquid state. The two phases of the phenomenon are analysed separately referring to soil mechanics procedures with regard to the trigger phase, and to an equivalent fluid for the post-failure phase. The present paper is devoted to show the experimental results carried out to evaluate the behaviour assumed by a pyroclastic-derived soil during the flow. A traditional fluid tool has been utilized: a standard rotational rheometer equipped with two different geometries. The soils tested belong to deposits that cover the slopes of the Campania region, Italy, often affected by debris flows. The influence of solid concentration C_v and grain size distribution was tested: the soils were destructurated, sieved and mixed with water starting from the in situ porosity. All material mixtures showed a non-Newtonian fluid behaviour with a yield stress τ_y that increases with a solid volumetric concentration and decreases for an increase of sand fraction. The experimental data were fitted with standard model for fluids. A simple relation between C_v and τ_y was obtained. The yield stress seems to be a key parameter for describing and predicting the post-failure behaviour of debris flows. These results suggest that in the field a small change in solid fraction, due to rainfall, will cause a slight decrease of the static yield stress, readily inducing a rapid flow which will stop only when the dynamic yield stress is reached, namely on a much smoother slope. This can explain the in situ observed post-failure behaviour of debris flows, which are able to flow over very long distances even on smooth slopes.

Gluon saturation and baryon stopping in the SPS, RHIC, and LHC energy regions

International Nuclear Information System (INIS)

Li Shuang; Feng Shengqin

2012-01-01

A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb + Pb collisions at the LHC are made in this paper. (authors)

Using 3D Printing for Rapid Prototyping of Characterization Tools for Investigating Powder Blend Behavior

DEFF Research Database (Denmark)

Hirschberg, Cosima; Boetker, Johan P; Rantanen, Jukka

2018-01-01

of complex powder behavior, such as mixing process and segregation phenomenon. An approach based on the fast prototyping of new powder handling geometries and interfacing solutions for process analytical tools is reported. This study utilized 3D printing for rapid prototyping of customized geometries...... the percolation thresholds. Blends with a paracetamol wt% above the percolation threshold were subsequently investigated in relation to their segregation behavior. Rapid prototyping using 3D printing allowed designing two funnels with tailored flow behavior (funnel flow) of model formulations, which could...... blend were monitored during blending. Rapid prototyping allowed for fast modification of powder testing geometries and easy interfacing with process analytical tools, opening new possibilities for more detailed powder characterization....

Mixed hybrid finite elements and streamline computation for the potential flow problem

NARCIS (Netherlands)

Kaasschieter, E.F.; Huijben, A.J.M.

1992-01-01

An important class of problems in mathematical physics involves equations of the form -¿ · (A¿¿) = f. In a variety of problems it is desirable to obtain an accurate approximation of the flow quantity u = -A¿¿. Such an accurate approximation can be determined by the mixed finite element method. In

Enhanced stopping of macro-particles in particle-in-cell simulations

International Nuclear Information System (INIS)

May, J.; Tonge, J.; Ellis, I.; Mori, W. B.; Fiuza, F.; Fonseca, R. A.; Silva, L. O.; Ren, C.

2014-01-01

We derive an equation for energy transfer from relativistic charged particles to a cold background plasma appropriate for finite-size particles that are used in particle-in-cell simulation codes. Expressions for one-, two-, and three-dimensional particles are presented, with special attention given to the two-dimensional case. This energy transfer is due to the electric field of the wake set up in the background plasma by the relativistic particle. The enhanced stopping is dependent on the q 2 /m, where q is the charge and m is the mass of the relativistic particle, and therefore simulation macro-particles with large charge but identical q/m will stop more rapidly. The stopping power also depends on the effective particle shape of the macro-particle. These conclusions are verified in particle-in-cell simulations. We present 2D simulations of test particles, relaxation of high-energy tails, and integrated fast ignition simulations showing that the enhanced drag on macro-particles may adversely affect the results of these simulations in a wide range of high-energy density plasma scenarios. We also describe a particle splitting algorithm which can potentially overcome this problem and show its effect in controlling the stopping of macro-particles

Study of void fraction and mixing of immiscible liquids in a pool configuration by an upward gas flow

International Nuclear Information System (INIS)

Casas, J.C.; Corradini, M.L.

1992-01-01

In this paper, investigations are performed to study the mixing between immiscible liquids in a pool configuration due to an upward gas flow. A water-R113 system is sued in the bubbly/churn-turbulent regimes to determine the effects of the unagitated pool depth on layer mixing. The superficial gas velocity at which full mixing is attained is observed to increase with the pool depth, although it is concluded that this is a weak dependency. Mixing in the churn-turbulent regime is studied with Wood's metal-water and Wood's metal-silicone fluid (100 cS) as pairs of fluids. Additional past mixing data from six other fluids are also included in the data base. A criterion is proposed to determine if two liquids will entrain in bubbly or churn-turbulent flow. Correlations are derived that, for a set of given conditions, allow prediction of the mixing state (mixed or segregated) of a system. Because of the indirect method of measuring the mixed layer thickness, pool void fraction experiments are also performed. For the case of water and R113, the effect of unagitated pool depth on the void fraction is studied

Development of a Reduced-Order Three-Dimensional Flow Model for Thermal Mixing and Stratification Simulation during Reactor Transients

Energy Technology Data Exchange (ETDEWEB)

Hu, Rui

2017-09-03

Mixing, thermal-stratification, and mass transport phenomena in large pools or enclosures play major roles for the safety of reactor systems. Depending on the fidelity requirement and computational resources, various modeling methods, from the 0-D perfect mixing model to 3-D Computational Fluid Dynamics (CFD) models, are available. Each is associated with its own advantages and shortcomings. It is very desirable to develop an advanced and efficient thermal mixing and stratification modeling capability embedded in a modern system analysis code to improve the accuracy of reactor safety analyses and to reduce modeling uncertainties. An advanced system analysis tool, SAM, is being developed at Argonne National Laboratory for advanced non-LWR reactor safety analysis. While SAM is being developed as a system-level modeling and simulation tool, a reduced-order three-dimensional module is under development to model the multi-dimensional flow and thermal mixing and stratification in large enclosures of reactor systems. This paper provides an overview of the three-dimensional finite element flow model in SAM, including the governing equations, stabilization scheme, and solution methods. Additionally, several verification and validation tests are presented, including lid-driven cavity flow, natural convection inside a cavity, laminar flow in a channel of parallel plates. Based on the comparisons with the analytical solutions and experimental results, it is demonstrated that the developed 3-D fluid model can perform very well for a wide range of flow problems.

Influence of convective conditions on three dimensional mixed convective hydromagnetic boundary layer flow of Casson nanofluid

Energy Technology Data Exchange (ETDEWEB)

Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Siddiq, M.K. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Abbasi, F.M. [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Meraj, M.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Ashraf, M. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan)

2016-10-15

The present work deals with the steady laminar three-dimensional mixed convective magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluid over a bidirectional stretching surface. A uniform magnetic field is applied normal to the flow direction. Similarity variables are implemented to convert the non-linear partial differential equations into ordinary ones. Convective boundary conditions are utilized at surface of the sheet. A numerical technique of Runge–Kutta–Fehlberg (RFK45) is used to obtain the results of velocity, temperature and concentration fields. The physical dimensionless parameters are discussed through tables and graphs. - Highlights: • Mixed convective boundary layer flow of Casson nanofluid is taken into account. • Impact of magnetic field is examined. • Convective heat and mass conditions are imposed. • Numerical solutions are presented and discussed.

Stopping, goal-conflict, trait anxiety and frontal rhythmic power in the stop-signal task.

Science.gov (United States)

Neo, Phoebe S-H; Thurlow, Jane K; McNaughton, Neil

2011-12-01

The medial right frontal cortex is implicated in fast stopping of an initiated motor action in the stop-signal task (SST). To assess whether this region is also involved in the slower behavioural inhibition induced by goal conflict, we tested for effects of goal conflict (when stop and go tendencies are balanced) on low-frequency rhythms in the SST. Stop trials were divided, according to the delays at which the stop signal occurred, into short-, intermediate-, and long-delay trials. Consistent with goal-conflict processing, intermediate-delay trials were associated with greater 7-8 Hz EEG power than short- or long-delay trials at medial right frontal sites (Fz, F4, and F8). At F8, 7-8 Hz power was linked to high trait anxiety and neuroticism. A separate 4-7 Hz power increase was also seen in stop, relative to go, trials, but this was independent of delay, was maximal at the central midline site Cz, and predicted faster stopping. Together with previous data on the SST, these results suggest that the right frontal region could be involved in multiple inhibition mechanisms. We propose a hierarchical model of the control of stopping that integrates the literature on the neural control of fast motor stopping with that on slower, motive-directed behavioural inhibition.

Rapid and sustained cost management

International Nuclear Information System (INIS)

Hanson, D.

2009-01-01

Accenture helps clients develop comprehensive, process-driven strategies for rapid and sustained cost management that leverage deep insights and analytics. This approach enables companies to gain operating cost advantages by rationalizing, simplifying and automating current operating capabilities. It drives structural cost advantages by optimizing business mix, capital structure, organizational structure and geographic presence. This paper discussed how successful companies achieve high performance during times of economic turmoil. It also discussed the value of the winner's strategy in terms of rapid and sustained cost management (RSCM). It discussed how Accenture operates and its leveraged capabilities, improved efficiency, margins and cash flow while maintaining customer service levels. Building structural advantage and the Accenture difference were also discussed. It was concluded that RSCM is one vital way that Accenture can help companies achieve success. 4 figs

Development and application of ZM-2 drilling fluid density adjustment mixing device

Directory of Open Access Journals (Sweden)

Zongming Lei

2015-01-01

Full Text Available High-pressure shallow (gas/water flow is often hidden in the deepwater seabed, so penetrating shallow flow in drilling without BOP will be highly risky. In this case, the conventional well killing method to balance the formation pressure with back pressure generated by well head equipment is no longer suitable. Based on the analysis of structural characteristics of domestic and foreign multi-phase mixing systems, a ZM-2 drilling fluid density adjustment mixing device with independent intellectual property right was developed according to the principles of dynamic well killing. The device is mainly composed of a throttle valve, a high-precision electromagnetic flowmeter, a mixer, dumbbell-shaped nozzles, connecting pipes and other components. Fixed on the mixer are three inlets to fill heavy mud, seawater and additives. Opposed jetting is adopted to realize rapid and uniform mixing of fluids with different densities. A laboratory test was conducted to work out the relationship between throttle opening and injection flow rate and establish a linear relationship between killing fluid density and heavy mud flow. The results of field test conducted in the Nanhai No.8 drill ship showed that the mixing device was stable in operation and excellent in mixing performance. The density difference of ingredient mixture could be controlled within 0.05 g/cm3 after the mixture flowed out of the mixing chamber of the mixer of about 0.3 m long, so such high precision can meet the requirement of dynamic well killing.

Double stratification effects in chemically reactive squeezed Sutterby fluid flow with thermal radiation and mixed convection

Directory of Open Access Journals (Sweden)

S. Ahmad

2018-03-01

Full Text Available A current analysis is carried out to study theoretically the mixed convection characteristics in squeezing flow of Sutterby fluid in squeezed channel. The constitutive equation of Sutterby model is utilized to characterize the rheology of squeezing phenomenon. Flow characteristics are explored with dual stratification. In flowing fluid which contains heat and mass transport, the first order chemical reaction and radiative heat flux affect the transport phenomenon. The systems of non-linear governing equations have been modulating which then solved by mean of convergent approach (Homotopy Analysis Method. The graphs are reported and illustrated for emerging parameters. Through graphical explanations, drag force, rate of heat and mass transport are conversed for different pertinent parameters. It is found that heat and mass transport rate decays with dominant double stratified parameters and chemical reaction parameter. The present two-dimensional examination is applicable in some of the engineering processes and industrial fluid mechanics. Keywords: Squeezing flow, Sutterby fluid model, Mixed convection, Double stratification, Thermal radiation, Chemical reaction

Impact of chemical reaction in fully developed radiated mixed convective flow between two rotating disk

Science.gov (United States)

Hayat, T.; Khan, M. Waleed Ahmed; Khan, M. Ijaz; Waqas, M.; Alsaedi, A.

2018-06-01

Flow of magnetohydrodynamic (MHD) viscous fluid between two rotating disks is modeled. Angular velocities of two disks are different. Flow is investigated for nonlinear mixed convection. Heat transfer is analyzed for nonlinear thermal radiation and heat generation/absorption. Chemical reaction is also implemented. Convective conditions of heat and mass transfer are studied. Transformations used lead to reduction of PDEs into the ODEs. The impacts of important physical variables like Prandtl number, Reynold number, Hartman number, mixed convection parameter, chemical reaction and Schmidt number on velocities, temperature and concentration are elaborated. In addition velocity and temperature gradients are physically interpreted. Our obtained results indicate that radial, axial and tangential velocities decrease for higher estimation of Hartman number.

Simulation of turbulent flows with and without combustion with emphasis on the impact of coherent structures on the turbulent mixing

Energy Technology Data Exchange (ETDEWEB)

Cunha Galeazzo, Flavio Cesar

2016-07-01

The analysis of turbulent mixing in complex turbulent flows is a challenging task. The effective mixing of entrained fluids to a molecular level is a vital part of the dynamics of turbulent flows, especially when combustion is involved. The work has shown the limitations of the steady-state simulations and acknowledged the need of applying high-fidelity unsteady methods for the calculation of flows with pronounced unsteadiness promoted by large-scale coherent structures or other sources.

Preferential Flow Paths In A Karstified Spring Catchment: A Study Of Fault Zones As Conduits To Rapid Groundwater Flow

Science.gov (United States)

Kordilla, J.; Terrell, A. N.; Veltri, M.; Sauter, M.; Schmidt, S.

2017-12-01

In this study we model saturated and unsaturated flow in the karstified Weendespring catchment, located within the Leinetal graben in Goettingen, Germany. We employ the finite element COMSOL Multiphysics modeling software to model variably saturated flow using the Richards equation with a van Genuchten type parameterization. As part of the graben structure, the Weende spring catchment is intersected by seven fault zones along the main flow path of the 7400 m cross section of the catchment. As the Weende spring is part of the drinking water supply in Goettingen, it is particularly important to understand the vulnerability of the catchment and effect of fault zones on rapid transport of contaminants. Nitrate signals have been observed at the spring only a few days after the application of fertilizers within the catchment at a distance of approximately 2km. As the underlying layers are known to be highly impermeable, fault zones within the area are likely to create rapid flow paths to the water table and the spring. The model conceptualizes the catchment as containing three hydrogeological limestone units with varying degrees of karstification: the lower Muschelkalk limestone as a highly conductive layer, the middle Muschelkalk as an aquitard, and the upper Muschelkalk as another conductive layer. The fault zones are parameterized based on a combination of field data from quarries, remote sensing and literary data. The fault zone is modeled considering the fracture core as well as the surrounding damage zone with separate, specific hydraulic properties. The 2D conceptual model was implemented in COMSOL to study unsaturated flow at the catchment scale using van Genuchten parameters. The study demonstrates the importance of fault zones for preferential flow within the catchment and its effect on the spatial distribution of vulnerability.

Hydraulic performance numerical simulation of high specific speed mixed-flow pump based on quasi three-dimensional hydraulic design method

International Nuclear Information System (INIS)

Zhang, Y X; Su, M; Hou, H C; Song, P F

2013-01-01

This research adopts the quasi three-dimensional hydraulic design method for the impeller of high specific speed mixed-flow pump to achieve the purpose of verifying the hydraulic design method and improving hydraulic performance. Based on the two families of stream surface theory, the direct problem is completed when the meridional flow field of impeller is obtained by employing iterative calculation to settle the continuity and momentum equation of fluid. The inverse problem is completed by using the meridional flow field calculated in the direct problem. After several iterations of the direct and inverse problem, the shape of impeller and flow field information can be obtained finally when the result of iteration satisfies the convergent criteria. Subsequently the internal flow field of the designed pump are simulated by using RANS equations with RNG k-ε two-equation turbulence model. The static pressure and streamline distributions at the symmetrical cross-section, the vector velocity distribution around blades and the reflux phenomenon are analyzed. The numerical results show that the quasi three-dimensional hydraulic design method for high specific speed mixed-flow pump improves the hydraulic performance and reveal main characteristics of the internal flow of mixed-flow pump as well as provide basis for judging the rationality of the hydraulic design, improvement and optimization of hydraulic model

MCMsf -- Mixing-cell model for a steady flow MIG -- Mixing-cell input generator: A short manual for installation and operation of MCMsf using the MIG -- mixing-cell input generator

International Nuclear Information System (INIS)

Adar, E.M.; Kuells, C.

2002-01-01

The following MIG computer code is restricted to a steady flow and steady hydrochemical system. The code for a non-steady hydrological system is still heavily dependant on external optimization libraries, such as the NAG Library. Therefore, a stand-alone 'friendly' code or solver for the non-steady system has yet to be compiled. Readers looking to implement the mixing-cell approach in a non-steady hydrological flow system are encouraged to contact the authors. In order to simplify the procedure of preparing the data and running the Mixing-Cell Model for steady flow system (MCMsf), a special Mixing Input Generator (MIG) has been programmed. MIG is a Visual Basic Microsoft application that runs within Excel 5.0 (and with more advanced versions such as Office 2000) via Windows 95 or newer environment. The program has been tested and used successfully in Windows NT, Windows 95 and Windows 98 together with Excel 5.0, 7.0 and 2000. The development of the standalone Version MIGSA that will run on a Windows system without Microsoft Excel is under development. Section 1 provides some clarifications of terms that are used both in MCMsf and MIG, whereas Section 2 briefly reviews the mathematical algorithm. For elaboration of the basic assumptions and for further mathematical description, the user is referred to the explanations provided in the Model Simplification and to the references provided in this publication

Rapid detection of microbial contamination in grape juice by flow cytometry

Directory of Open Access Journals (Sweden)

Marielle Bouix

1999-03-01

Full Text Available This study presents an application of flow cytometry to evaluate rapidly the viable micro-organisms in grape juice. In this method, viable cells are firstly specitically labelled with a fluorescent reagent. The sample is then injected into the flow cytometer where the labelled micro-organisms are individually illuminated by a laser beam. The emission of fluorescence is measured. The system counts the number of fluorescent events and prints out a histogram of the fluorescence intensity which is characteristic of the micro-organism being analysed. In laboratory conditions, preliminary trials have been undertaken with an artificially inoculated grape juice with pure yeast and bacteria cultures. This method succeeded in counting simultaneously yeasts and bacteria within 15 minutes, with a high degree of sensitivity, 5.103 yeasts perml and 5.104 bacteria per ml. This technique can also be applied to the detection of mould contamination and the test has been done with Botrytis spores. The method makes direct cell counts possible and is capable of analysing 30 samples per hour. It can be automatised and easily used in industrial laboratory. During the last harvest, more than a thousand of must samples were controled using this technique. The results let to determine the yeast contamination level of a grape juice tank even before unloading. The results obtained by flow cytometry were compared to the plate count reference method. The correlation between cytometry and count by plate culture was 99 p. cent for the threshold of 5.1 04 yeasts/ml which seemed to point out a high contamination. By using this flow cytometry method during the harvest period, the results were supplied in real time. This allowed a rapid selection of the musts, depending upon the scale of their contamination and improved the quality of the wine by corrective actions.

Effect of the mixing fields on the stability and structure of turbulent partially premixed flames in a concentric flow conical nozzle burner

KAUST Repository

Mansour, Mohy S.; Elbaz, Ayman M.; Roberts, William L.; Senosy, Mohamed S.; Zayed, Mohamed F.; Juddoo, Mrinal; Masri, Assaad R.

2016-01-01

of partially premixed methane flames. The mixing field in a concentric flow conical nozzle (CFCN) burner with well-controlled mechanism of the mixing is investigated using Rayleigh scattering technique. The flame stability, structure and flow field of some

pH control and rapid mixing in spinning NMR samples

Science.gov (United States)

Yesinowski, James P.; Sunberg, Richard J.; Benedict, James J.

An apparatus is described which permits the acquisition of NMR spectra from spinning 20-mm sample tubes while: (1) constantly monitoring the pH; (2) adding reagents to maintain constant pH (pH-statting); (3) efficiently mixing the added reagent. The apparatus was built to study the spontaneous precipitation of calcium phosphates from supersaturated solutions using 31P NMR. Other applications include the rapid determination of NMR titration curves, and the minimization of temperature gradients in large sample tubes. The apparatus was used to measure the 31P chemical shift titration of dilute phosphoric acid, which yielded accurate shifts for the three species of protonated orthophosphate ion. The bulk magnetic susceptibility of 85% H 3PO 4 relative to a dilute aqueous sample was also measured, and is shown to contribute significantly to chemical shift measurements.

A numerical model for the design of a mixed flow cryogenic turbine ...

African Journals Online (AJOL)

Present day cryogenic gas turbines are in more popular as they meet the growing need for low pressure cycles. This calls for improved methods of turbine wheel design. The present study is aimed at the design of the turbine wheel of mixed flow impellers with radial entry and axial discharge. In this paper, a computer code ...

Investigations on mixing phenomena in single-phase flow in a T-junction geometry

International Nuclear Information System (INIS)

Walker, C.; Simiano, M.; Zboray, R.; Prasser, H.-M.

2009-01-01

The paper deals with T-junction mixing experiments carried out with wire-mesh sensors. The mixing of coolant streams of different temperature in pipe junctions leads to temperature fluctuations that may cause thermal fatigue in the pipe wall. This is practical background for an increased interest in measuring and predicting the transient flow field and the turbulent mixing pattern downstream of a T-junction. Experiments were carried out at a perpendicular connection of two pipes of 51 mm inner diameter. The straight and the side branches were supplied by water of different electrical conductivity, which replaced the temperature in the thermal mixing process. A set of three wire-mesh sensors with a grid of 16 x 16 measuring points each was used to record conductivity distributions downstream of the T-junction. Besides the measurement of profiles of the time averaged mixing scalar over extended measuring domains, the high resolution in time and space of the mesh sensors allow a statistic characterization of the stochastic fluctuations of the mixing scalar in a wide range of frequencies. Information on the scale of turbulent mixing patterns is obtained by cross-correlating the signal fluctuations recorded at different locations within the measuring plane of a sensor

Effect of particle diameter of porous media on flow and heat transfer in a mixing tee

International Nuclear Information System (INIS)

Wang, Yongwei; Lu, Tao; Wang, Kuisheng

2012-01-01

Highlights: ► Three particle diameter cases of 28 mm, 14 mm and 7 mm were simulated by LES. ► With the diameter decreasing, mixing scale tends to decrease in the mixing tee. ► With the diameter decreasing, thermal mixing is weakened. ► With the diameter decreasing, the thermal stratification is obvious. ► When the particle diameter ratio is 4:2:1, pressure drop ratio is 1:2:4. -- Abstract: Numerical simulations have been carried out to investigate flow and heat transfer in a mixing tee filled with periodic sintered copper spheres. Three particle diameter cases of 28 mm, 14 mm and 7 mm with the array of 4 × 4, 8 × 8 and 16 × 16 at the same porosity of 0.3 have been calculated using large-eddy simulations and the Smagorinsky–Lilly sub-grid scale model. With the particle diameter decreasing, the mixture scale of hot and cold fluid tends to decrease in the mixing tee; the pressure drop of fluid flow through porous media increases. When the particle diameter ratios are 4:2:1 and the specific surface ratios are 1:2:4, the pressure drop ratios are 1:2:4; the thermal mixing in porous media is weakened because the temperature fluctuation decreases and the stratification of hot and cold fluids is observed.

Has Human Evolution Stopped?

Directory of Open Access Journals (Sweden)

Alan R. Templeton

2010-07-01

Full Text Available It has been argued that human evolution has stopped because humans now adapt to their environment via cultural evolution and not biological evolution. However, all organisms adapt to their environment, and humans are no exception. Culture defines much of the human environment, so cultural evolution has actually led to adaptive evolution in humans. Examples are given to illustrate the rapid pace of adaptive evolution in response to cultural innovations. These adaptive responses have important implications for infectious diseases, Mendelian genetic diseases, and systemic diseases in current human populations. Moreover, evolution proceeds by mechanisms other than natural selection. The recent growth in human population size has greatly increased the reservoir of mutational variants in the human gene pool, thereby enhancing the potential for human evolution. The increase in human population size coupled with our increased capacity to move across the globe has induced a rapid and ongoing evolutionary shift in how genetic variation is distributed within and among local human populations. In particular, genetic differences between human populations are rapidly diminishing and individual heterozygosity is increasing, with beneficial health effects. Finally, even when cultural evolution eliminates selection on a trait, the trait can still evolve due to natural selection on other traits. Our traits are not isolated, independent units, but rather are integrated into a functional whole, so selection on one trait can cause evolution to occur on another trait, sometimes with mildly maladaptive consequences.

Mixing of immiscible fluids in chaotic flows and related issues

International Nuclear Information System (INIS)

Ottino, J.M.

1993-01-01

The basis goal of this work was to obtain a basic understanding of mixing of immiscible fluids leading to the determination of flow conditions which result in efficient breakup and dispersion of one mass of fluid in the bulk of another. Related issues were the prediction of the morphological structures and drop size distribution for a given set of operating conditions. The primary motivation for these investigations was to produce basic knowledge leading to increased understanding of industrial processes involving blending, agitation, emulsification, and dissolution

Effects of turbulent hyporheic mixing on reach-scale solute transport

Science.gov (United States)

Roche, K. R.; Li, A.; Packman, A. I.

2017-12-01

Turbulence rapidly mixes solutes and fine particles into coarse-grained streambeds. Both hyporheic exchange rates and spatial variability of hyporheic mixing are known to be controlled by turbulence, but it is unclear how turbulent mixing influences mass transport at the scale of stream reaches. We used a process-based particle-tracking model to simulate local- and reach-scale solute transport for a coarse-bed stream. Two vertical mixing profiles, one with a smooth transition from in-stream to hyporheic transport conditions and a second with enhanced turbulent transport at the sediment-water interface, were fit to steady-state subsurface concentration profiles observed in laboratory experiments. The mixing profile with enhanced interfacial transport better matched the observed concentration profiles and overall mass retention in the streambed. The best-fit mixing profiles were then used to simulate upscaled solute transport in a stream. Enhanced mixing coupled in-stream and hyporheic solute transport, causing solutes exchanged into the shallow subsurface to have travel times similar to the water column. This extended the exponential region of the in-stream solute breakthrough curve, and delayed the onset of the heavy power-law tailing induced by deeper and slower hyporheic porewater velocities. Slopes of observed power-law tails were greater than those predicted from stochastic transport theory, and also changed in time. In addition, rapid hyporheic transport velocities truncated the hyporheic residence time distribution by causing mass to exit the stream reach via subsurface advection, yielding strong exponential tempering in the in-stream breakthrough curves at the timescale of advective hyporheic transport through the reach. These results show that strong turbulent mixing across the sediment-water interface violates the conventional separation of surface and subsurface flows used in current models for solute transport in rivers. Instead, the full distribution of

Mixed convective magnetohydrodynamic flow in a vertical channel filled with nanofluids

Directory of Open Access Journals (Sweden)

S. Das

2015-06-01

Full Text Available The fully developed mixed convection flow in a vertical channel filled with nanofluids in the presence of a uniform transverse magnetic field has been studied. Closed form solutions for the fluid temperature, velocity and induced magnetic field are obtained for both the buoyancy-aided and -opposed flows. Three different water-based nanofluids containing copper, aluminium oxide and titanium dioxide are taken into consideration. Effects of the pertinent parameters on the nanofluid temperature, velocity, and induced magnetic field as well as the shear stress and the rate of heat transfer at the channel wall are shown in figures and tables followed by a quantitative discussion. It is found that the magnetic field tends to enhance the nanofluid velocity in the channel. The induced magnetic field vanishes in the cental region of the channel. The critical Rayleigh number at onset of instability of flow is strongly dependent on the volume fraction of nanoparticles and the magnetic field.

A Simple Parameterization of Mixing of Passive Scalars in Turbulent Flows

Science.gov (United States)

Nithianantham, Ajithshanthar; Venayagamoorthy, Karan

2015-11-01

A practical model for quantifying the turbulent diascalar diffusivity is proposed as Ks = 1 . 1γ'LTk 1 / 2 , where LT is defined as the Thorpe length scale, k is the turbulent kinetic energy and γ' is one-half of the mechanical to scalar time scale ratio, which was shown by previous researchers to be approximately 0 . 7 . The novelty of the proposed model lies in the use of LT, which is a widely used length scale in stably stratified flows (almost exclusively used in oceanography), for quantifying turbulent mixing in unstratified flows. LT can be readily obtained in the field using a Conductivity, Temperature and Depth (CTD) profiler. The turbulent kinetic energy is mostly contained in the large scales of the flow field and hence can be measured in the field or modeled in numerical simulations. Comparisons using DNS data show remarkably good agreement between the predicted and exact diffusivities. Office of Naval Research and National Science Foundation.

An analytical solution for the Marangoni mixed convection boundary layer flow

DEFF Research Database (Denmark)

Moghimi, M. A.; Kimiaeifar, Amin; Rahimpour, M.

2010-01-01

In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is presented. A similarity transform reduces the Navier-Stokes equations to a set of nonlinear ordinary differential equations, which are solved analytically by means of the homotopy analysis method (HAM...... the convergence of the solution. The numerical solution of the similarity equations is developed and the results are in good agreement with the analytical results based on the HAM....

Role of medium heterogeneity and viscosity contrast in miscible flow regimes and mixing zone growth: A computational pore-scale approach

Science.gov (United States)

Afshari, Saied; Hejazi, S. Hossein; Kantzas, Apostolos

2018-05-01

Miscible displacement of fluids in porous media is often characterized by the scaling of the mixing zone length with displacement time. Depending on the viscosity contrast of fluids, the scaling law varies between the square root relationship, a sign for dispersive transport regime during stable displacement, and the linear relationship, which represents the viscous fingering regime during an unstable displacement. The presence of heterogeneities in a porous medium significantly affects the scaling behavior of the mixing length as it interacts with the viscosity contrast to control the mixing of fluids in the pore space. In this study, the dynamics of the flow and transport during both unit and adverse viscosity ratio miscible displacements are investigated in heterogeneous packings of circular grains using pore-scale numerical simulations. The pore-scale heterogeneity level is characterized by the variations of the grain diameter and velocity field. The growth of mixing length is employed to identify the nature of the miscible transport regime at different viscosity ratios and heterogeneity levels. It is shown that as the viscosity ratio increases to higher adverse values, the scaling law of mixing length gradually shifts from dispersive to fingering nature up to a certain viscosity ratio and remains almost the same afterwards. In heterogeneous media, the mixing length scaling law is observed to be generally governed by the variations of the velocity field rather than the grain size. Furthermore, the normalization of mixing length temporal plots with respect to the governing parameters of viscosity ratio, heterogeneity, medium length, and medium aspect ratio is performed. The results indicate that mixing length scales exponentially with log-viscosity ratio and grain size standard deviation while the impact of aspect ratio is insignificant. For stable flows, mixing length scales with the square root of medium length, whereas it changes linearly with length during

Prediction of flow in mix-proof valve by use of CFD - Validation by LDA

DEFF Research Database (Denmark)

Jensen, Bo Boye Busk; Friis, Alan

2004-01-01

was done on a spherical shaped mix-proof valve (MPV). Flow were predicted by Computational Fluid Dynamics (CFD) and validated by data obtained from experiments using laser sheet visualization and laser Doppler anemometry. Correction of the measured velocities and probe location was required as refraction......-wall region is shown. Fully 3D flow patterns were identified and valuable information was obtained for further investigations concerning prediction of cleanability in the MPV based on knowledge of the hydrodynamics herein....

Numerical study of internal flow in twin screw extruder and its mixing performance analysis

International Nuclear Information System (INIS)

Kim, Nak Soo; Kim, Hong Bum; Lee, Jae Wook

2006-01-01

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder

Calculated viscosity-distance dependence for some actively flowing lavas

International Nuclear Information System (INIS)

Pieri, D.

1987-01-01

The importance of viscosity as a gauge of the various energy and momentum dissipation regimes of lava flows has been realized for a long time. Nevertheless, despite its central role in lava dynamics and kinematics, it remains among the most difficult of flow physical properties to measure in situ during an eruption. Attempts at reconstructing the actual emplacement viscosities of lava flows from their solidified topographic form are difficult. Where data are available on the position of an advancing flow front as a function of time, it is possible to calculate the effective viscosity of the front as a function of distance from the vent, under the assumptions of a steady state regime. As an application and test of an equation given, relevant parameters from five recent flows on Mauna Loa and Kilauea were utilized to infer the dynamic structure of their aggregate flow front viscosity as they advanced, up to cessation. The observed form of the viscosity-distance relation for the five active Hawaiian flows examined appears to be exponential, with a rapid increase just before the flows stopped as one would expect

Air Distribution in a Room and Design Considerations of Mixing Ventilation by Flow Elements

DEFF Research Database (Denmark)

Nielsen, Peter V.; Jensen, Rasmus Lund; Pedersen, D. N.

2001-01-01

The paper shows detailed measurements of the air distribution in a room ventilated by mixing ventilation according to the specifications given by the International Energy Agency work. (Energy Conservation in Buildings and Community Systems Programme, Annex 20). It describes a number of flow...

Rapid MR measurements of contrast medium dilution kinetics (gadolinium-DTPA) in a flow phantom

International Nuclear Information System (INIS)

Boeck, J.C.; Sander, B.; Frank, J.; Schoerner, W.

1991-01-01

We studied first-pass MRI-contrast dilution to compute flow and volume of distribution in a realistic flow phantom. Pulsatile flow was provided by a one-chamber artificial heart. Physiological stroke volume, rate, pressure, and flow were adjustable. An elastic tube with dimensions similar to that of the human aorta was imaged at a rate of 2.4 Hz. After contrast injection, an initial increase in signal intensity was followed by a decrease. Signal-intensity-time plots demonstrated slightly skewed curves as expected from dispersion theory. After calibration at different gadolinium-DTPA concentrations, signal intensities were converted into true gadolinium concentrations, and flow was calculated from the concentration-time curves. Flow was varied between 2.5 and 10.0 l/min and a significant correlation was found between the MRI-estimate and true flow. Volume of distribution between injection and detection site was reliably estimated. This study demonstrates rapid 2-D imaging of a paramagnetic contrast bolus in a realistic flow phantom. Reliable estimates of flow and volume are obtained. (orig.) [de

Rapid dual-tracer PTSM+ATSM PET imaging of tumour blood flow and hypoxia: a simulation study

International Nuclear Information System (INIS)

Rust, T C; Kadrmas, D J

2006-01-01

Blood flow and hypoxia are interrelated aspects of physiology that affect cancer treatment and response. Cu-PTSM and Cu-ATSM are related PET tracers for blood flow and hypoxia, and the ability to rapidly image both tracers in a single scan would bring several advantages over conventional single-tracer techniques. Using dynamic imaging with staggered injections, overlapping signals for multiple PET tracers may be recovered utilizing information from kinetics and radioactive decay. In this work, rapid dual-tracer PTSM+ATSM PET was simulated and tested as a function of injection delay, order and relative dose for several copper isotopes, and the results were compared relative to separate single-tracer data. Time-activity curves representing a broad range of tumour blood flow and hypoxia levels were simulated, and parallel dual-tracer compartment modelling was used to recover the signals for each tracer. The main results were tested further using a torso phantom simulation of PET tumour imaging. Using scans as short as 30 minutes, the dual-tracer method provided measures of blood flow and hypoxia similar to single-tracer imaging. The best performance was obtained by injecting PTSM first and using a somewhat higher dose for ATSM. Comparable results for different copper isotopes suggest that tracer kinetics with staggered injections play a more important role than radioactive decay in the signal separation process. Rapid PTSM+ATSM PET has excellent potential for characterizing both tumour blood flow and hypoxia in a single, fast scan, provided that technological hurdles related to algorithm development and routine use can be overcome

Lateral Flow Field Behavior Downstream of Mixing Vanes In a Simulated Nuclear Fuel Rod Bundle

International Nuclear Information System (INIS)

Conner, Michael E.; Smith, L. David III; Holloway, Mary V.; Beasley, Donald E.

2004-01-01

To assess the fuel assembly performance of PWR nuclear fuel assemblies, average subchannel flow values are used in design analyses. However, for this highly complex flow, it is known that local conditions around fuel rods vary dependent upon the location of the fuel rod in the fuel assembly and upon the support grid design that maintains the fuel rod pitch. To investigate the local flow in a simulated nuclear fuel rod bundle, a testing technique has been employed to measure the lateral flow field in a 5 x 5 rod bundle. Particle Image Velocimetry was used to measure the lateral flow field downstream of a support grid with mixing vanes for four unique subchannels in the 5 x 5 bundle. The dominant lateral flow structures for each subchannel are compared in this paper including the decay of these flow structures. (authors)

Quantum dots as chemiluminescence enhancers tested by sequential injection technique: Comparison of flow and flow-batch conditions

Energy Technology Data Exchange (ETDEWEB)

Sklenářová, Hana, E-mail: sklenarova@faf.cuni.cz [Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Department of Analytical Chemistry, Hradec Králové (Czech Republic); Voráčová, Ivona [Institute of Analytical Chemistry of the CAS, v. v. i., Brno (Czech Republic); Chocholouš, Petr; Polášek, Miroslav [Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Department of Analytical Chemistry, Hradec Králové (Czech Republic)

2017-04-15

The effect of 0.01–100 µmol L{sup −1} Quantum Dots (QDs) with different emission wavelengths (520–640 nm) and different surface modifications (mercaptopropionic, mercaptoundecanoic, thioglycolic acids and mercaptoethylamine) on permanganate-induced and luminol–hydrogen peroxide chemiluminescence (CL) was studied in detail by a sequential injection technique using a spiral detection flow cell and a flow-batch detection cell operated in flow and stop-flow modes. In permanganate CL system no significant enhancement of the CL signal was observed while for the luminol–hydrogen peroxide CL substantial increase (>100% and >90% with the spiral detection cell in flow and stop-flow modes, respectively) was attained for CdTe QDs. Enhancement exceeding 120% was observed for QDs with emissions at 520, 575 and 603 nm (sizes of 2.8 nm, 3.3 nm and 3.6 nm) using the flow-batch detection cell in the stop-flow mode. Pronounced effect was noted for surface modifications while mercaptoethylamine was the most efficient in CL enhancement compared to mercaptopropionic acid the most commonly applied coating. Significant difference between results obtained in flow and flow-batch conditions based on the entire kinetics of the extremely fast CL reaction was discussed. The increase of the CL signal was always accompanied by reduced lifetime of the CL emission thus application of QDs in flow techniques should be always coupled with the study of the CL lifetime.

Experimental and numerical analyses on the effect of increasing inflow temperatures on the flow mixing behavior in a T-junction

International Nuclear Information System (INIS)

Selvam, P. Karthick; Kulenovic, Rudi; Laurien, Eckart

2016-01-01

Highlights: • Experimental and numerical analyses of three T-junction mixing cases. • Temperature difference (ΔT) between fluids are 51.5 K, 76 K and 97 K. • Thermally stratified flow behavior is observed in all cases in the mixing zone. • Temperature fluctuations have maximum amplitudes of about 6.3–9.9% of ΔT. • High amplitude fluctuations occur near stratification layer in the mixing region. • Power spectral density (PSD) of fluctuations contains energy in 0.1–2 Hz range. - Abstract: Thermal degradation of piping induced by high cycle thermal fatigue (HCTF) is of significant importance as operating Nuclear Power Plants (NPP) become older and lifetime extension activities are initiated. In particular, HCTF incidents related to turbulent thermal mixing of fluids in a T-junction piping system are not well understood and could not be adequately monitored using common thermocouple instrumentation. To investigate this phenomenon, an experimental T-junction test facility was commissioned at the University of Stuttgart, known as the Fluid Structure Interaction (FSI) test facility. The paper presents the experimental investigation and the corresponding numerical validation using the large eddy simulation (LES) method to study T-junction flow mixing. Three experimental test cases are investigated with temperature differences (∆T) of 51.5 K (Case 1), 76 K (Case 2) and 97 K (Case 3) between the mixing fluids. A constant mass flow rate ratio (main/branch) of 4:1 is maintained in all the investigated cases. Flow mixing is observed to be incomplete in all the cases, resulting in a thermally stratified flow with an oscillating stratification layer downstream of the T-junction. Mean temperature and root mean square (RMS) temperature fluctuations predicted by LES in the mixing region are found to be in good agreement with measurement data, with the exception of few positions. Amplitudes of temperature fluctuations are observed to be higher near the

The oxidation mode of pyranose 2-oxidase is controlled by pH

Science.gov (United States)

Prongjit, Methinee; Sucharitakul, Jeerus; Palfey, Bruce A.; Chaiyen, Pimchai

2013-01-01

Pyranose 2-oxidase (P2O) from Trametes multicolor is a flavoenzyme that catalyzes the oxidation of D-glucose and other aldopyranose sugars at the C2 position by using O2 as an electron acceptor to form the corresponding 2-keto-sugars and H2O2. In this study, the effects of pH on the oxidative half-reaction of P2O were investigated using stopped-flow spectrophotometry. The results showed that flavin oxidation occurred via different pathways depending on the pH of the environment. At pH values lower than 8.0, reduced P2O reacts with O2 to form a C4a-hydroperoxy-flavin intermediate, leading to elimination of H2O2. At pH 8.0 and higher, the majority of the reduced P2O reacts with O2 via a pathway which does not allow detection of the C4a-hydroperoxy-flavin, and flavin oxidation occurs with decreased rate constants upon the rise in pH. The switching between the two modes of P2O oxidation is controlled by protonation of a group which has a pKa of 7.6 ± 0.1. Oxidation reactions of reduced P2O under rapid pH change as performed by stopped-flow mixing were different from the same reactions performed with enzyme pre-equilibrated at the same specified pH values, implying that the protonation of the group which controls the mode of flavin oxidation cannot be rapidly equilibrated with outside solvent. Using a double-mixing stopped-flow experiment, a rate constant for proton dissociation from the reaction site was determined to be 21.0 ± 0.4 s-1. PMID:23356577

Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.

Science.gov (United States)

Sekhar, Y Raja; Sharma, K V; Kamal, Subhash

2016-05-01

The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.

Progress in understanding heavy-ion stopping

Energy Technology Data Exchange (ETDEWEB)

Sigmund, P., E-mail: sigmund@sdu.dk [Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M (Denmark); Schinner, A. [Institut für Experimentalphysik, Johannes Kepler Universität, A-4040 Linz (Austria)

2016-09-01

We report some highlights of our work with heavy-ion stopping in the energy range where Bethe stopping theory breaks down. Main tools are our binary stopping theory (PASS code), the reciprocity principle, and Paul’s data base. Comparisons are made between PASS and three alternative theoretical schemes (CasP, HISTOP and SLPA). In addition to equilibrium stopping we discuss frozen-charge stopping, deviations from linear velocity dependence below the Bragg peak, application of the reciprocity principle in low-velocity stopping, modeling of equilibrium charges, and the significance of the so-called effective charge.

Progress in understanding heavy-ion stopping

International Nuclear Information System (INIS)

Sigmund, P.; Schinner, A.

2016-01-01

We report some highlights of our work with heavy-ion stopping in the energy range where Bethe stopping theory breaks down. Main tools are our binary stopping theory (PASS code), the reciprocity principle, and Paul’s data base. Comparisons are made between PASS and three alternative theoretical schemes (CasP, HISTOP and SLPA). In addition to equilibrium stopping we discuss frozen-charge stopping, deviations from linear velocity dependence below the Bragg peak, application of the reciprocity principle in low-velocity stopping, modeling of equilibrium charges, and the significance of the so-called effective charge.

Impact of Flight Enthalpy, Fuel Simulant, and Chemical Reactions on the Mixing Characteristics of Several Injectors at Hypervelocity Flow Conditions

Science.gov (United States)

Drozda, Tomasz G.; Baurle, Robert A.; Drummond, J. Philip

2016-01-01

The high total temperatures or total enthalpies required to duplicate the high-speed flight conditions in ground experiments often place stringent requirements on the material selection and cooling needs for the test articles and intrusive flow diagnostic equipment. Furthermore, for internal flows, these conditions often complicate the use of nonintrusive diagnostics that need optical access to the test section and interior portions of the flowpath. Because of the technical challenges and increased costs associated with experimentation at high values of total enthalpy, an attempt is often made to reduce it. This is the case for the Enhanced Injection and Mixing Project (EIMP) currently underway in the Arc-Heated Scramjet Test Facility at the NASA Langley Research Center. The EIMP aims to investigate supersonic combustion ramjet (scramjet) fuel injection and mixing physics, improve the understanding of underlying physical processes, and develop enhancement strategies and functional relationships between mixing performance and losses relevant to flight Mach numbers greater than 8. The experiments will consider a "direct-connect" approach and utilize a Mach 6 nozzle to simulate the combustor entrance flow of a scramjet engine. However, while the value of the Mach number is matched to that expected at the combustor entrance in flight, the maximum value of the total enthalpy for these experiments is limited by the thermal-structural limits of the uncooled experimental hardware. Furthermore, the fuel simulant is helium, not hydrogen. The use of "cold" flows and non-reacting mixtures of fuel simulants for mixing experiments is not new and has been extensively utilized as a screening technique for scramjet fuel injectors. In this study, Reynolds-averaged simulations are utilized (RAS) to systematically verify the implicit assumptions used by the EIMP. This is accomplished by first performing RAS of mixing for two injector configurations at planned nominal experimental

Rapid runoff via shallow throughflow and deeper preferential flow in a boreal catchment underlain by frozen silt (Alaska, USA)

Science.gov (United States)

Koch, Joshua C.; Ewing, Stephanie A.; Striegl, Robert G.; McKnight, Diane M.

2013-01-01

In high-latitude catchments where permafrost is present, runoff dynamics are complicated by seasonal active-layer thaw, which may cause a change in the dominant flowpaths as water increasingly contacts mineral soils of low hydraulic conductivity. A 2-year study, conducted in an upland catchment in Alaska (USA) underlain by frozen, well-sorted eolian silt, examined changes in infiltration and runoff with thaw. It was hypothesized that rapid runoff would be maintained by flow through shallow soils during the early summer and deeper preferential flow later in the summer. Seasonal changes in soil moisture, infiltration, and runoff magnitude, location, and chemistry suggest that transport is rapid, even when soils are thawed to their maximum extent. Between June and September, a shift occurred in the location of runoff, consistent with subsurface preferential flow in steep and wet areas. Uranium isotopes suggest that late summer runoff erodes permafrost, indicating that substantial rapid flow may occur along the frozen boundary. Together, throughflow and deep preferential flow may limit upland boreal catchment water and solute storage, and subsequently biogeochemical cycling on seasonal to annual timescales. Deep preferential flow may be important for stream incision, network drainage development, and the release of ancient carbon to ecosystems

Agutaynen Glottal Stop.

Science.gov (United States)

Quakenbush, J. Stephen

A study investigated the phonemic and morphophonemic patterning of the glottal stop in Agutaynen, a Meso-Philippine language, and some comparison with two northern Philippine languages. Agutaynen glottal stop has as its sole origin a neutralization of contrast rule, the operation of which can be noted in three different linguistic environments.…

Impacts of Bus-stops on the Speed of Motorized Vehicles under Heterogeneous Traffic Conditions: A Case-Study of Delhi, India

Directory of Open Access Journals (Sweden)

Prateek Bansal

2014-06-01

Full Text Available The presence of friction generators1 such as bus-stops, intersections, petrol pumps and pedestrian crossings, etc. significantly influences the speed of traffic stream. Among all the friction generators, understanding the impact of bus-stops is particularly important from planning and modeling perspective in the Indian context. Therefore, this study presents a methodology to quantify the impact of bus-stops on the speed of other motorized vehicles (the total motorized vehicle fleet minus the buses under heterogeneous traffic conditions. The methodology was validated on the typical urban arterials in Delhi, India. Two types of data, location of bus-stops and speed profiles of motorized vehicles, were collected by GPS and V-box respectively. These two data sets were mapped and merged using ArcGIS. To understand the nature of traffic stream near bus-stops, ‘influence regions’ of bus-stops were extracted. Later, characteristic parameters such as lengths of the influence regions and average speeds in the influence regions were computed. Finally, 95% confidence intervals of these characteristic parameters were obtained and regression analysis was performed to quantify the impact of bus-stops on the speed of motorized vehicles. The results of study suggest that the influence region of bus-stops on the corridors investigated varies from 140–170 meters and average speed of motorized vehicles in the influence region is reduced by 26–38% of the free flow speed. These findings can better inform planners about the speeds used in traffic flow and travel demand modeling under heterogeneous conditions by helping them in accounting for the speed-reducing impacts of bus-stops. Moreover, transit planners may also consider the magnitudes and characteristics of the influence regions of bus-stops while determining their locations along the corridor to minimize their adverse impacts on the speed of other motorized vehicles.

Suppression of turbulent resistivity in turbulent Couette flow

Science.gov (United States)

Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe

2015-07-01

Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.

Suppression of turbulent resistivity in turbulent Couette flow

Energy Technology Data Exchange (ETDEWEB)

Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2015-07-15

Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.

Suppression of turbulent resistivity in turbulent Couette flow

International Nuclear Information System (INIS)

Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.

2015-01-01

Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations

Collaborative Optimization of Stop Schedule Plan and Ticket Allotment for the Intercity Train

Directory of Open Access Journals (Sweden)

Xichun Chen

2016-01-01

Full Text Available As regards the ticket allotment issue of the intercity passenger corridor designed for different train grades, the matching relationship between the ticket allotment and the passenger flow demand is studied. The passenger flow conversion equation which is based on the collaborative optimization of the intercity train stop schedule plan and ticket allotment is established. Then the mathematical model aiming at the maximum revenue of intercity train system and the highest satisfaction from the passengers is established. The particle swarm harmony search algorithm is designed to solve the model. The example verifies the effectiveness of the model and algorithm, which indicates that, through the collaborative optimization of the stop schedule plan and ticket allotment for different grades intercity trains, the sectional utilization rate of the train can be improved; meanwhile, the optimum matching between the intercity train revenue and the passenger satisfaction can be realized.

Mixed Convection Flow along a Stretching Cylinder in a Thermally Stratified Medium

Directory of Open Access Journals (Sweden)

Swati Mukhopadhyay

2012-01-01

Full Text Available An analysis for the axisymmetric laminar boundary layer mixed convection flow of a viscous and incompressible fluid towards a stretching cylinder immersed in a thermally stratified medium is presented in this paper. Similarity transformation is employed to convert the governing partial differential equations into highly nonlinear ordinary differential equations. Numerical solutions of these equations are obtained by a shooting method. It is found that the heat transfer rate at the surface is lower for flow in a thermally stratified medium compared to that of an unstratified medium. Moreover, both the skin friction coefficient and the heat transfer rate at the surface are larger for a cylinder compared to that for a flat plate.

All in One Stop? The Accessibility of Work Support Programs at One-Stop Centers.

Science.gov (United States)

Richer, Elise; Kubo, Hitomi; Frank, Abbey

The accessibility of work support programs at one-stop centers was examined in a study during which 33 telephone directors or managers of one-stop centers in 22 states were interviewed by telephone. The interviews established the existence of extensive differences between one-stop centers from the standpoint of all aspects of their operation,…

LHC Availability 2017: Technical Stop 1 to Technical Stop 2

CERN Document Server

Todd, Benjamin; Apollonio, Andrea; Walsh, David John; CERN. Geneva. ATS Department

2017-01-01

This document summarises the LHC machine availability for the period of Technical Stop 1 (TS1) to Technical Stop 2 (TS2) in 2017. This period was dedicated to proton physics with a bunch spacing of 25ns. This note has been produced and ratified by the Availability Working Group which has complied fault information for the period in question using the Accelerator Fault Tracker.

The golden-mean surface pattern to enhance flow mixing in micro-channel.

Science.gov (United States)

Wang, J F; Liu, Y; Xu, Y S

2009-04-01

Mixing of analytes and reagents in microfluidic devices is often crucial to the effective functioning of lab-on-a-chip. It is possible to affect the mixing in microfluidics by intelligently controlling the thermodynamic and chemical properties of the substrate surface. Numerous studies have shown that the phase behavior of mixtures is significantly affected by surface properties of microfluidics. For example, the phase separation between the fluids can be affected by heterogeneous patterns on the substrate. The patterned substrate can offer an effective means to control fluid behavior and in turn to enhance mixing. The golden mean is a ratio that is present in the growth patterns of many biological systems--the spiral formed by a shell or the curve of a fern, for example. The golden mean or golden section was derived by the ancient Greeks. Like "pi" the golden mean ratio is an irrational number 1.618, or (square root{5} + 1) / 2. It was found that the golden mean was an optimum ratio in natural convection heat transfer problem (Liu and Phan-Thien, Numer Heat Transf 37:613-630, 2000). In this study, we numerically studied the effect of optimum surface pattern on mixing in a micro channel and found that the flow oscillation and chaotic mixing were enhanced apparently when the ratio of hydrophobic and hydrophilic boundary follows the golden mean.

Luminescent beam stop

Energy Technology Data Exchange (ETDEWEB)

Bryant, Diane; Morton, Simon A.

2017-10-25

This disclosure provides systems, methods, and apparatus related to beam stops. In one aspect, a device comprises a luminescent material, a beam stop plate, and an optical fiber. The luminescent material is a parallelepiped having a first side and a second side that are squares and having a third side that is a rectangle or a square. The first side and the second side are perpendicular to the third side. The beam stop plate is attached to the first side of the luminescent material. The optical fiber has a first end and a second end, with the first end of the optical fiber attached to the third side of the luminescent material.

Modelling rapid subsurface flow at the hillslope scale with explicit representation of preferential flow paths

Science.gov (United States)

Wienhöfer, J.; Zehe, E.

2012-04-01

Rapid lateral flow processes via preferential flow paths are widely accepted to play a key role for rainfall-runoff response in temperate humid headwater catchments. A quantitative description of these processes, however, is still a major challenge in hydrological research, not least because detailed information about the architecture of subsurface flow paths are often impossible to obtain at a natural site without disturbing the system. Our study combines physically based modelling and field observations with the objective to better understand how flow network configurations influence the hydrological response of hillslopes. The system under investigation is a forested hillslope with a small perennial spring at the study area Heumöser, a headwater catchment of the Dornbirnerach in Vorarlberg, Austria. In-situ points measurements of field-saturated hydraulic conductivity and dye staining experiments at the plot scale revealed that shrinkage cracks and biogenic macropores function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of artificial tracers at the hillslope scale. For modelling of water and solute transport, we followed the approach of implementing preferential flow paths as spatially explicit structures of high hydraulic conductivity and low retention within the 2D process-based model CATFLOW. Many potential configurations of the flow path network were generated as realisations of a stochastic process informed by macropore characteristics derived from the plot scale observations. Together with different realisations of soil hydraulic parameters, this approach results in a Monte Carlo study. The model setups were used for short-term simulation of a sprinkling and tracer experiment, and the results were evaluated against measured discharges and tracer breakthrough curves. Although both criteria were taken for model evaluation, still several model setups

Multi-condition optimization and experimental study of impeller blades in a mixed-flow pump

Directory of Open Access Journals (Sweden)

Houlin Liu

2016-05-01

Full Text Available On the basis of design of experiment and numerical simulation, a reliable optimization method for blades of a mixed-flow pump is proposed with the maximum weighted average efficiency at multi-conditions as optimum objective. First, the performance of the model pump was measured and the test results were used to validate the simulation method. To improve the simulation accuracy, the check of the grid independence and the comparison of different turbulence models were done in detail. Then, the method of design of experiment for key geometrical parameters was used to obtain the optimization scheme. The maximum weighted average efficiency of pump at three operation conditions was chosen as optimum objective. The optimum solution was gotten and confirmed by the experiment. The results demonstrate that efficiency of the mixed-flow pump with optimized impeller increases by 3.9%, and the high-efficiency zone is increased from 0.021 to 0.040.

Diffusion and mixing in gravity-driven dense granular flows.

Science.gov (United States)

Choi, Jaehyuk; Kudrolli, Arshad; Rosales, Rodolfo R; Bazant, Martin Z

2004-04-30

We study the transport properties of particles draining from a silo using imaging and direct particle tracking. The particle displacements show a universal transition from superdiffusion to normal diffusion, as a function of the distance fallen, independent of the flow speed. In the superdiffusive (but sub-ballistic) regime, which occurs before a particle falls through its diameter, the displacements have fat-tailed and anisotropic distributions. In the diffusive regime, we observe very slow cage breaking and Péclet numbers of order 100, contrary to the only previous microscopic model (based on diffusing voids). Overall, our experiments show that diffusion and mixing are dominated by geometry, consistent with long-lasting contacts but not thermal collisions, as in normal fluids.

Mixing by rotary jet heads: Indications of the benefits of head rotation under turbulent and transitional flow conditions

DEFF Research Database (Denmark)

Nordkvist, Mikkel; Vognsen, Marie; Nienow, Alfred W.

2008-01-01

Mixing times were obtained by the iodine-thiosulphate decolorization technique using rotary jet heads (RJH) for mixing in a Perspex tank with an inner diameter of 0.75 m and an aspect ratio of 2.5 using both water (turbulent flow) and shear-thinning, carboxymethyl cellulose (CMC) solutions...

Water Quality and Environmental Flow Management in Rapidly Urbanizing Shenzhen Estuary Area, China

Science.gov (United States)

Qin, H.; Su, Q.

2011-12-01

Shenzhen estuary is located in a rapidly urbanizing coastal region of Southeast China, and forms the administrative border between mainland China and Hong Kong. It receives the waters of the Shenzhen River, where it enters the Deep Bay. The estuary has great ecological importance with the internationally recognized mangrove wetlands, which provides a habitat for some rare and endangered waterfowl and migratory birds.Water quality in the esturay has deteriorated not only due to increasing wastewater discharges from domestic and industrial sources, but also as a consequence of decreasing base environmental flow during rapid urbanization in the Shenzhen River catchment since 1980s. Measures to improve water quality of the estuary include not only reducing pollutant inputs by intercepting wastewater, but also increasing environmental flow by reusing reclaimed wastewater or withdrawing nearshore seawater into the river. However, salinity alternation due to flow increase is deemed to have impacts on the mangrove wetland ecosystem. In this paper, Environmental Fluid Dynamics Code (EFDC) is used to simulate hydrodynamics, salinity, and water quality condition in the Shenzhen estuary. After calibration and validation, the model is used to evaluate effects of various control measures on water quality improvement and salinity alteration in the estuary. The results indicate that implementing different measures independently does not reach the goals of water quality improvement; furthermore, increasing environmental flow by importing nearshore seawater may greatly increase the salinity in the Shenzhen River, destroy the fresh ecosystem of the river and have non-negligible impacts on the mangrove wetland ecosystem. Based on the effectiveness and impacts of the measures, an integrated measure, which combine pollutant loads reduction and environmental flow increase by reusing reclaimed wastewater, is proposed to achieve water environmental sustainability in the study area.

Elucidation of thermal hydraulic mixing mechanism in a mixing tee area with a 90-degree bend upstream and development of thermal-striping relaxation and control methods

International Nuclear Information System (INIS)

Sugawara, Yoshimasa; Yuki, Kazuhisa; Hashizume, Hidetoshi; Tanaka, Masa-aki; Muramatsu, Toshiharu

2004-10-01

In the region where two fluids with different temperatures mix, unstable fluid mixing like thermal striping occurs accompanying with unsteady temperature fluctuation of fluid. This temperature fluctuation is transported toward the surrounding area and becomes an important factor that induces thermal fatigue of structural materials, which sometimes results in crack generation of them. In fast breeder reactors that utilize liquid sodium as a coolant, the fluid temperature fluctuation could be easier to conduct toward the structural materials due to its high thermal conductivity, so that careful consideration for the thermal fatigue is required. In particular, since the low frequency band of temperature fluctuation strongly affects the thermal fatigue, evaluation and development of the relaxation and control methods for it become important issues. In this study, non-isothermal fluid mixing experiments in a T-junction area with a 90-degree bend upstream were carried out to estimate the fluid-temperature fluctuation in the vicinity of wall. The temperature fluctuations for various flow mixing conditions were measured, changing a velocity ratio and a pipe diameter ratio of a main pipe to a branch pipe to quantitatively evaluate the effect of a secondary flow on the temperature fluctuation. In addition, by analyzing both the visualization data taken by a PIV system and the temperature fluctuation data, it was attempted to construct a prediction formula for the temperature fluctuation. Our findings are summarized below. (1) Classifying the flow mixing pattern of jet flow running out from the branch pipe makes it possible to predict the maximum temperature fluctuation in the mixing area with higher accuracy by using the flow velocity ratio (0.2 -0.06 (d/D) 0.22 . Re-attachment Flow - deflecting Flow: Max(ΔTrms*)=0.64(v/V) -0.92 (d/D) 1.11 . (2) Prediction formulas for the maximum temperature fluctuation in the case of the curvature ratio of 1.0 are also constructed as

Numerical simulation of a plane turbulent mixing layer, with applications to isothermal, rapid reactions

Science.gov (United States)

Lin, P.; Pratt, D. T.

1987-01-01

A hybrid method has been developed for the numerical prediction of turbulent mixing in a spatially-developing, free shear layer. Most significantly, the computation incorporates the effects of large-scale structures, Schmidt number and Reynolds number on mixing, which have been overlooked in the past. In flow field prediction, large-eddy simulation was conducted by a modified 2-D vortex method with subgrid-scale modeling. The predicted mean velocities, shear layer growth rates, Reynolds stresses, and the RMS of longitudinal velocity fluctuations were found to be in good agreement with experiments, although the lateral velocity fluctuations were overpredicted. In scalar transport, the Monte Carlo method was extended to the simulation of the time-dependent pdf transport equation. For the first time, the mixing frequency in Curl's coalescence/dispersion model was estimated by using Broadwell and Breidenthal's theory of micromixing, which involves Schmidt number, Reynolds number and the local vorticity. Numerical tests were performed for a gaseous case and an aqueous case. Evidence that pure freestream fluids are entrained into the layer by large-scale motions was found in the predicted pdf. Mean concentration profiles were found to be insensitive to Schmidt number, while the unmixedness was higher for higher Schmidt number. Applications were made to mixing layers with isothermal, fast reactions. The predicted difference in product thickness of the two cases was in reasonable quantitative agreement with experimental measurements.

Flow and mixing characteristics in a stirred tank with dual wide paddles; 2 dan waido padoruyoku tsuki kakuhan sonai no ryudo{center{underscore}dot}kongo tokusei

Energy Technology Data Exchange (ETDEWEB)

Takata, Kazutaka; Ito, Hisayoshi; Kikuchi, Masahiko; Okamoto, Yukimichi [Shinko Pantec Corp., Hyogo (Japan)

1999-03-10

Flow structure and mixing characteristics in a stirred tank with dual wide paddle impeller were examined using computational fluid dynamics (CFD). CFD was conducted using analysis code for fluid flow, and velocity measured by laser doppler velocimeter, power consumption and mixing time were used for evaluating computed results. The computed flow field and power consumption agreed well with themeasured values within 5 % mixing process well agreed with the observations. Since the computed flow pattern and mixing process agreed well with the measured values, computed results are useful for evaluating complex flow field in a stirred tank. A detailed investigation using computed results are useful for evaluating complex flow field in a stirred tank A detaile investigation using computed results shows that dual cross-installed wide paddle impellers lead to superior mixing performance in the stirred tank, and pressure gradient between upper and lower paddles is found to be the factor that promotes fluid transport in the tank, which is never the case when the dual wide paddles are installed in the same plane. (author)

Stopping atoms with diode lasers

International Nuclear Information System (INIS)

Watts, R.N.; Wieman, C.E.

1986-01-01

The use of light pressure to cool and stop neutral atoms has been an area of considerable interest recently. Cooled neutral atoms are needed for a variety of interesting experiments involving neutral atom traps and ultrahigh-resolution spectroscopy. Laser cooling of sodium has previously been demonstrated using elegant but quite elaborate apparatus. These techniques employed stabilized dye lasers and a variety of additional sophisticated hardware. The authors have demonstrated that a frequency chirp technique can be implemented using inexpensive diode lasers and simple electronics. In this technique the atoms in an atomic beam scatter resonant photons from a counterpropagating laser beam. The momentum transfer from the photons slows the atoms. The primary difficulty is that as the atoms slow their Doppler shift changes, and so they are no longer in resonance with the incident photons. In the frequency chirp technique this is solved by rapidly changing the laser frequency so that the atoms remain in resonance. To achieve the necessary frequency sweep with a dye laser one must use an extremely sophisticated high-speed electrooptic modulator. With a diode laser, however, the frequency can be smoothly and rapidly varied over many gigahertz simply by changing the injection current

Expanded Mixed Multiscale Finite Element Methods and Their Applications for Flows in Porous Media

KAUST Repository

Jiang, L.

2012-01-01

We develop a family of expanded mixed multiscale finite element methods (MsFEMs) and their hybridizations for second-order elliptic equations. This formulation expands the standard mixed multiscale finite element formulation in the sense that four unknowns (hybrid formulation) are solved simultaneously: pressure, gradient of pressure, velocity, and Lagrange multipliers. We use multiscale basis functions for both the velocity and the gradient of pressure. In the expanded mixed MsFEM framework, we consider both separable and nonseparable spatial scales. Specifically, we analyze the methods in three categories: periodic separable scales, G-convergent separable scales, and a continuum of scales. When there is no scale separation, using some global information can significantly improve the accuracy of the expanded mixed MsFEMs. We present a rigorous convergence analysis of these methods that includes both conforming and nonconforming formulations. Numerical results are presented for various multiscale models of flow in porous media with shale barriers that illustrate the efficacy of the proposed family of expanded mixed MsFEMs. © 2012 Society for Industrial and Applied Mathematics.

Stop smoking support programs

Science.gov (United States)

Smokeless tobacco - stop smoking programs; Stop smoking techniques; Smoking cessation programs; Smoking cessation techniques ... You can find out about smoking cessation programs from: Your ... Your employer Your local health department The National Cancer ...

The Impact of Volute Aspect Ratio on the Performance of a Mixed Flow Turbine

Directory of Open Access Journals (Sweden)

Samuel P. Lee

2017-11-01

Full Text Available Current trends in the automotive industry towards engine downsizing mean turbocharging now plays a vital role in engine performance. A turbocharger increases charge air density using a turbine to extract waste energy from the exhaust gas to drive a compressor. Most turbocharger applications employ a radial inflow turbine. However, mixed flow turbines can offer non-zero blade angles, reducing leading edge (LE separation at low velocity ratios. The current paper investigates the performance of a mixed flow turbine with three different volute aspect ratio (AR designs (AR = 0.5, 1 and 2. With constant A/r (ratio of volute area to centroid radius, the AR = 0.5 volute design produced a 4.3% increase in cycle averaged mass flow parameter (MFP compared to the AR = 2 design. For the purpose of performance comparison, it was necessary to manipulate the volute A/r’s to ensure constant MFP for aerodynamic similarity. With the volute A/r’s manipulated to ensure constant MFP for aerodynamic similarity, the maximum variation of cycle averaged normalized efficiency measured between the designs was 1.47%. Purely in the rotor region, the variation in normalized cycle averaged efficiency was 1%. The smallest tested volute aspect ratio showed a significant increase in volute loss while the ARs of 1 and 2 showed similar levels of loss. The smallest AR volute showed significant secondary flow development in the volute. The resulting variation in LE incidence was found to vary as a result.

Retroactive Stop Loss Special Pay

Science.gov (United States)

Pay (RSLSP), providing $500 for each month/partial month served in stop loss status. Service members served under stop loss must submit a claim for the special pay. Throughout the year, the services have or extension of service, became ineligible to receive retroactive stop loss special pay. There may be

Effect of the mixing fields on the stability and structure of turbulent partially premixed flames in a concentric flow conical nozzle burner

KAUST Repository

Mansour, Mohy S.

2016-10-22

The mixing field is known to be one of the key parameters that affect the stability and structure of partially premixed flames. Data in these flames are now available covering the effects of turbulence, combustion system geometry, level of partially premixing and fuel type. However, quantitative analyses of the flame structure based on the mixing field are not yet available. The aim of this work is to present a comprehensive study of the effects of the mixing fields on the structure and stability of partially premixed methane flames. The mixing field in a concentric flow conical nozzle (CFCN) burner with well-controlled mechanism of the mixing is investigated using Rayleigh scattering technique. The flame stability, structure and flow field of some selected cases are presented using LIF of OH and PIV. The experimental data of the mixing field cover wide ranges of Reynolds number, equivalence ratio and mixing length. The data show that the mixing field is significantly affected by the mixing length and the ratio of the air-to-fuel velocities. The Reynolds number has a minimum effect on the mixing field in high turbulent flow regime and the stability is significantly affected by the turbulence level. The temporal fluctuations of the range of mixture fraction within the mixing field correlate with the flame stability. The highest point of stability occurs at recess distances where fluid mixtures near the jet exit plane are mostly within the flammability limits. This paper provides some correlations between the stability range in mixture fraction space and the turbulence level for different equivalence ratios.

Stop feeling: inhibition of emotional interference following stop-signal trials.

Science.gov (United States)

Kalanthroff, Eyal; Cohen, Noga; Henik, Avishai

2013-01-01

Although a great deal of literature has been dedicated to the mutual links between emotion and the selective attention component of executive control, there is very little data regarding the links between emotion and the inhibitory component of executive control. In the current study we employed an emotional stop-signal task in order to examine whether emotion modulates and is modulated by inhibitory control. Results replicated previous findings showing reduced inhibitory control [longer stop-signal reaction time (SSRT)] following negative, compared to neutral pictures. Most importantly, results show decreased emotional interference following stop-signal trials. These results show that the inhibitory control component of executive control can serve to decrease emotional effects. We suggest that inhibitory control and emotion have a two-way connection in which emotion disrupts inhibitory control and activation of inhibitory control disrupts emotion.

Stop feeling: Inhibition of emotional interference following stop-signal trials

Directory of Open Access Journals (Sweden)

Eyal eKalanthroff

2013-03-01

Full Text Available Although a great deal of literature has been dedicated to the mutual links between emotion and the selective attention component of executive control, there is very little data regarding the links between emotion and the inhibitory component of executive control. In the current study we employed an emotional stop-signal task in order to examine whether emotion modulates and is modulated by inhibitory control. Results replicated previous findings showing reduced inhibitory control (longer stop-signal reaction time following negative, compared to neutral pictures. Most importantly, results show decreased emotional interference following stop-signal trials. These results show that the inhibitory control component of executive control can serve to decrease emotional effects. We suggest that inhibitory control and emotion have a two-way connection in which emotion disrupts inhibitory control and activation of inhibitory control disrupts emotion.

A new oxidation flow reactor for measuring secondary aerosol formation of rapidly changing emission sources

Science.gov (United States)

Simonen, Pauli; Saukko, Erkka; Karjalainen, Panu; Timonen, Hilkka; Bloss, Matthew; Aakko-Saksa, Päivi; Rönkkö, Topi; Keskinen, Jorma; Dal Maso, Miikka

2017-04-01

Oxidation flow reactors (OFRs) or environmental chambers can be used to estimate secondary aerosol formation potential of different emission sources. Emissions from anthropogenic sources, such as vehicles, often vary on short timescales. For example, to identify the vehicle driving conditions that lead to high potential secondary aerosol emissions, rapid oxidation of exhaust is needed. However, the residence times in environmental chambers and in most oxidation flow reactors are too long to study these transient effects ( ˜ 100 s in flow reactors and several hours in environmental chambers). Here, we present a new oxidation flow reactor, TSAR (TUT Secondary Aerosol Reactor), which has a short residence time ( ˜ 40 s) and near-laminar flow conditions. These improvements are achieved by reducing the reactor radius and volume. This allows studying, for example, the effect of vehicle driving conditions on the secondary aerosol formation potential of the exhaust. We show that the flow pattern in TSAR is nearly laminar and particle losses are negligible. The secondary organic aerosol (SOA) produced in TSAR has a similar mass spectrum to the SOA produced in the state-of-the-art reactor, PAM (potential aerosol mass). Both reactors produce the same amount of mass, but TSAR has a higher time resolution. We also show that TSAR is capable of measuring the secondary aerosol formation potential of a vehicle during a transient driving cycle and that the fast response of TSAR reveals how different driving conditions affect the amount of formed secondary aerosol. Thus, TSAR can be used to study rapidly changing emission sources, especially the vehicular emissions during transient driving.

Continuous Flow Controlled Synthesis of Gold Nanoparticles Using Pulsed Mixing Microfluidic System

Directory of Open Access Journals (Sweden)

Guojun Liu

2015-01-01

Full Text Available To prepare the gold nanoparticles (AuNPs with uniform sizes, fine morphology, and good monodispersity, a pulsed mixing microfluidic system based on PZT actuation was presented. The system includes PZT micropump and Y type micromixer. By adjusting voltage (entrance flow rate, pulsed frequency, phase, and other parameters, a variety of mixing modes can be achieved, so as to realize the controllable synthesis of nanoparticles in a certain range. By numerical simulation and analysis, the channel section size, entrance angle, and pulse frequency were optimized. Based on the optimized structure and working parameters, the test prototype has been manufactured in lab, and the related synthesis tests of AuNPs were carried out. The test results indicate that AuNPs with uniform morphology and good monodispersity can be synthesized using the system with the section size (0.4 mm × 0.4 mm, the entrance channel angle (60° under condition of the pulsed frequency (300 Hz, and the entrance flow rate (4 mL/min. The average diameter and its standard deviation of AuNPs synthesized were 21.6 nm, 4.83 nm, respectively. The research work above can be applied to the fields such as the controlled synthesis of noble metal nanoparticles, biomedicine, and microchemical system.

Validating the Galerkin least-squares finite element methods in predicting mixing flows in stirred tank reactors

International Nuclear Information System (INIS)

Johnson, K.; Bittorf, K.J.

2002-01-01

A novel approach for computer aided modeling and optimizing mixing process has been developed using Galerkin least-squares finite element technology. Computer aided mixing modeling and analysis involves Lagrangian and Eulerian analysis for relative fluid stretching, and energy dissipation concepts for laminar and turbulent flows. High quality, conservative, accurate, fluid velocity, and continuity solutions are required for determining mixing quality. The ORCA Computational Fluid Dynamics (CFD) package, based on a finite element formulation, solves the incompressible Reynolds Averaged Navier Stokes (RANS) equations. Although finite element technology has been well used in areas of heat transfer, solid mechanics, and aerodynamics for years, it has only recently been applied to the area of fluid mixing. ORCA, developed using the Galerkin Least-Squares (GLS) finite element technology, provides another formulation for numerically solving the RANS based and LES based fluid mechanics equations. The ORCA CFD package is validated against two case studies. The first, a free round jet, demonstrates that the CFD code predicts the theoretical velocity decay rate, linear expansion rate, and similarity profile. From proper prediction of fundamental free jet characteristics, confidence can be derived when predicting flows in a stirred tank, as a stirred tank reactor can be considered a series of free jets and wall jets. (author)

Higgs mass from neutrino-messenger mixing

International Nuclear Information System (INIS)

Byakti, Pritibhajan; Khosa, Charanjit K.; Mummidi, V.S.; Vempati, Sudhir K.

2017-01-01

The discovery of the Higgs particle at 125 GeV has put strong constraints on minimal messenger models of gauge mediation, pushing the stop masses into the multi-TeV regime. Extensions of these models with matter-messenger mixing terms have been proposed to generate a large trilinear parameter, A t , relaxing these constraints. The detailed survey of these models (DOI: 10.1007/JHEP05(2013)055; 10.1007/JHEP08(2013)093 ) so far considered messenger mixings with only MSSM superfields. In the present work, we extend the survey to MSSM with inverse-seesaw mechanism. The neutrino-sneutrino corrections to the Higgs mass in the inverse seesaw model are not significant in the minimal gauge mediation model, unless one considers messenger-matter interaction terms. We classify all possible models with messenger-matter interactions and perform thorough numerical analysis to find out the promising models. We found that out of the 17 possible models 9 of them can lead to Higgs mass within the observed value without raising the sfermion masses significantly. The successful models have stop masses ∼1.5 TeV with small or negligible mixing and yet a light CP even Higgs at 125 GeV.

Stop feeling: Inhibition of emotional interference following stop-signal trials

OpenAIRE

Eyal eKalanthroff; Noga eCohen; Avishai eHenik

2013-01-01

Although a great deal of literature has been dedicated to the mutual links between emotion and the selective attention component of executive control, there is very little data regarding the links between emotion and the inhibitory component of executive control. In the current study we employed an emotional stop-signal task in order to examine whether emotion modulates and is modulated by inhibitory control. Results replicated previous findings showing reduced inhibitory control [longer stop...

14C age reassessment of groundwater from the discharge zone due to cross-flow mixing in the deep confined aquifer

Science.gov (United States)

Mao, Xumei; Wang, Hua; Feng, Liang

2018-05-01

In a groundwater flow system, the age of groundwater should gradually increase from the recharge zone to the discharge zone within the same streamline. However, it is occasionally observed that the groundwater age becomes younger in the discharge zone in the piedmont alluvial plain, and the oldest age often appears in the middle of the plain. A new set of groundwater chemistry and isotopes was employed to reassess the groundwater 14C ages from the discharge zone in the North China Plain (NCP). Carbonate precipitation, organic matter oxidation and cross-flow mixing in the groundwater from the recharge zone to the discharge zone are recognized according to the corresponding changes of HCO3- (or DIC) and δ13C in the same streamline of the third aquifer of the NCP. The effects of carbonate precipitation and organic matter oxidation are calibrated with a 13C mixing model and DIC correction, but these corrected 14C ages seem unreasonable because they grow younger from the middle plain to the discharge zone in the NCP. The relationship of Cl- content and the recharge distance is used to estimate the expected Cl- content in the discharge zone, and ln(a14C)/Cl is proposed to correct the a14C in groundwater for the effect of cross-flow mixing. The 14C ages were reassessed with the corrected a14C due to the cross-flow mixing varying from 1.25 to 30.58 ka, and the groundwater becomes older gradually from the recharge zone to the discharge zone. The results suggest that the reassessed 14C ages are more reasonable for the groundwater from the discharge zone due to cross-flow mixing.

Study of Dynamic Flow and Mixing Performances of Tri-Screw Extruders with Finite Element Method

OpenAIRE

X. Z. Zhu; G. Wang; Y. D. He; Z. F. Cheng

2013-01-01

There is a special circumfluence in the center region of cross-section for a tri-screw extruder. To study the effect of the dynamic center region on the flow and mixing mechanism of the tri-screw extruder, 2D finite element modeling was used to reduce the axial effects. Based on the particle tracking technology, the nonlinear dynamics of a typical particle motions in the center region was carried out and the mixing process in the tri-screw extruder was analyzed with Poincaré maps. Moreover, m...

Microreactortechnology: Real-Time Flow Measurements in Organic Synthesis

Directory of Open Access Journals (Sweden)

Pieter J. Nieuwland

2012-03-01

Full Text Available With the commercial availability of integrated microreactor systems, the numbers of chemical processes that are performed nowadays in a continuous flow is growing rapidly. The control over mixing efficiency and homogeneous heating in these reactors allows industrial scale production that was often hampered by the use of large amounts of hazardous chemicals. Accurate actuation and in line measurements of the flows, to have a better control over the chemical reaction, is of added value for increasing reproducibility and a safe production.

Numerical simulation of double-diffusive mixed convective flow in rectangular enclosure with insulated moving lid

Energy Technology Data Exchange (ETDEWEB)

Teamah, M.A. [Faculty of Engineering, Alexandria University, Mech. Eng. Dept, Alexandria (Egypt); El-Maghlany, W.M. [Faculty of Engineering, Suez Canal University, Ismailia (Egypt)

2010-09-15

The present study is concerned with the mixed convection in a rectangular lid-driven cavity under the combined buoyancy effects of thermal and mass diffusion. Double-diffusive convective flow in a rectangular enclosure with moving upper surface is studied numerically. Both upper and lower surfaces are being insulated and impermeable. Constant different temperatures and concentration are imposed along the vertical walls of the enclosure, steady state laminar regime is considered. The transport equations for continuity, momentum, energy and spices transfer are solved. The numerical results are reported for the effect of Richardson number, Lewis number, and buoyancy ratio on the iso-contours of stream line, temperature, and concentration. In addition, the predicted results for both local and average Nusselt and Sherwood numbers are presented and discussed for various parametric conditions. This study was done for 0.1 <= Le <= 50 and Prandtl number Pr = 0.7. Through out the study the Grashof number and aspect ratio are kept constant at 10{sup 4} and 2 respectively and -10 <= N <= 10, while Richardson number has been varied from 0.01 to 10 to simulate forced convection dominated flow, mixed convection and natural convection dominated flow. (authors)

Rapid Vortex Fluidics: Continuous Flow Synthesis of Amides and Local Anesthetic Lidocaine.

Science.gov (United States)

Britton, Joshua; Chalker, Justin M; Raston, Colin L

2015-07-20

Thin film flow chemistry using a vortex fluidic device (VFD) is effective in the scalable acylation of amines under shear, with the yields of the amides dramatically enhanced relative to traditional batch techniques. The optimized monophasic flow conditions are effective in ≤80 seconds at room temperature, enabling access to structurally diverse amides, functionalized amino acids and substituted ureas on multigram scales. Amide synthesis under flow was also extended to a total synthesis of local anesthetic lidocaine, with sequential reactions carried out in two serially linked VFD units. The synthesis could also be executed in a single VFD, in which the tandem reactions involve reagent delivery at different positions along the rapidly rotating tube with in situ solvent replacement, as a molecular assembly line process. This further highlights the versatility of the VFD in organic synthesis, as does the finding of a remarkably efficient debenzylation of p-methoxybenzyl amines. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational model for turbulent flow around a grid spacer with mixing vane

International Nuclear Information System (INIS)

Tsutomu Ikeno; Takeo Kajishima

2005-01-01

Turbulent mixing coefficient and pressure drop are important factors in subchannel analysis to predict onset of DNB. However, universal correlations are difficult since these factors are significantly affected by the geometry of subchannel and a grid spacer with mixing vane. Therefore, we propose a computational model to estimate these factors. Computational model: To represent the effect of geometry of grid spacer in computational model, we applied a large eddy simulation (LES) technique in couple with an improved immersed-boundary method. In our previous work (Ikeno, et al., NURETH-10), detailed properties of turbulence in subchannel were successfully investigated by developing the immersed boundary method in LES. In this study, additional improvements are given: new one-equation dynamic sub-grid scale (SGS) model is introduced to account for the complex geometry without any artificial modification; the higher order accuracy is maintained by consistent treatment for boundary conditions for velocity and pressure. NUMERICAL TEST AND DISCUSSION: Turbulent mixing coefficient and pressure drop are affected strongly by the arrangement and inclination of mixing vane. Therefore, computations are carried out for each of convolute and periodic arrangements, and for each of 30 degree and 20 degree inclinations. The difference in turbulent mixing coefficient due to these factors is reasonably predicted by our method. (An example of this numerical test is shown in Fig. 1.) Turbulent flow of the problem includes unsteady separation behind the mixing vane and vortex shedding in downstream. Anisotropic distribution of turbulent stress is also appeared in rod gap. Therefore, our computational model has advantage for assessing the influence of arrangement and inclination of mixing vane. By coarser computational mesh, one can screen several candidates for spacer design. Then, by finer mesh, more quantitative analysis is possible. By such a scheme, we believe this method is useful

Non-flood season neap tides in the Yangtze estuary offshore: Flow mixing processes and its potential impacts on adjacent wetlands

Science.gov (United States)

Wei, Taoyuan; Wang, Zhanghua; Chen, Jing; Li, Maotian

2018-02-01

How flow mixing process influences the wetlands of the Yangtze Estuary is still poorly understood. Hydrological fieldwork was conducted on five vessel-anchored sites (S1-S2; M1-M2-M3) near the major wetlands of the Yangtze Estuary offshore (121°57‧-122°30‧E, 30°50‧-31°23‧N) on May 8-11 2004, to examine the dynamics of neap tides in the non-flood season of the Yangtze (∼24, 700 m3s-1 at Datong) and their impacts on adjacent wetlands. Based on the measurement of the acoustic Doppler current profiler (aDcp), direct-reading current meter and optical backscattering sensor (OBS-3A), two flow patterns were revealed: 1) well mixing flow pattern caused by the turbulent tidal currents, and 2) weak mixing flow pattern resulted by the estuarine circulation in the North Port of the estuary. The characteristics of such different flow patterns were analyzed and resultant sediment dispersals were discussed in relation to the adjacent wetlands. It is suggested that the estuarine circulation might be the important process to nourish the eastern wetland of the Yangtze Estuary which has been neglected before.

MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid

Science.gov (United States)

Armaghani, T.; Esmaeili, H.; Mohammadpoor, Y. A.; Pop, I.

2018-01-01

In this paper, the steady mixed convection flow and heat transfer of water-copper oxide nanofluid in an open C-shaped enclosure is investigated numerically. The enclosure is under constant magnetic field. Effects of Richardson number, magnetic and nanofluid volume fraction parameters are studied and discussed. The nanofluid with a cold temperature of T C and a velocity of u c enters the enclosure from the top right corner and exits from the bottom right corner. The vertical wall of the left side is subjected to a hot and constant temperature T h . Also, other walls are insulated. It is found that the heat transfer is increased via increasing the Hartmann and Reynolds numbers. For low Reynolds numbers, the enhances of the Hartman number leads to a slightly increases of the average Nusselt number, but for high Reynolds numbers, the average Nusselt number gets an ascending trend and the increase in the Hartmann number shows its effect more pronounced. Also, with increase in Ri, the effect of nanofluid on the heat transfer increases. Due to practical impotence, the study of mixed convection heat transfer in enclosures and various shaped of cavities has attracted remarkable attentions in the past few decades. Significant applications of the mixed convection flow can be found in atmospheric flows, solar energy storage, heat exchangers, lubrication technology, drying technologies, cooling of the electronic devices, etc. The present results are original and new for the problem of MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid. Comparison of the obtained results with those from the open literature (Mahmoodi et al. [24]) is acceptable.

A whistle-stop tour of statistics

National Research Council Canada - National Science Library

Everitt, Brian

2012-01-01

"Preface according to my Penguin English dictionary, whistle-stop, used before a noun means 'consisting of brief stops in several places' and this whistle-stop tour of statistics does just that, with...

Characterising the structure of quasi-periodic mixing events in stratified turbulent Taylor-Couette flow

Science.gov (United States)

Singh, Kanwar Nain; Partridge, Jamie; Dalziel, Stuart; Caulfield, C. P.; Mathematical Underpinnings of Stratified Turbulence (MUST) Team

2017-11-01

We present results from experiments conducted to study mixing in a two-layer stably-stratified turbulent Taylor-Couette flow. It has previously been observed that there is a quasi-periodic mixing event located at the interface separating the layers. We observe, through conductivity probe measurements, that the power of the mixing event in the frequency spectrum of the density data at the interface is higher when measured near the inner cylinder than in the middle of the annular gap. This is consistent with Oglethorpe's (2014) hypothesis that the mixing structure is triggered near the inner cylinder, and then advects and decays or disperses radially. We also observe that at Ri =g/'Ro (RiΩi)2 7 , where Ri, Ro are the inner and outer cylinder radius, respectively, g ' the reduced gravity characterising the density jump between the layers and Ωi is the rotation rate of the inner cylinder, the power drops significantly at all radial locations, which is reminiscent of the onset of the enhanced flux regime as observed by Oglethorpe et al. (2013). We perform experiments to characterise the spatial extent and dynamics of this mixing structure using particle image velocimetry (PIV) giving further insights into this important mixing process. EPSRC programme Grant EP/K034529/1 & SGPC-CCT Scholarship.

Mixed-flow vertical tubular hydraulic turbine. Determination of proper design duty point

Energy Technology Data Exchange (ETDEWEB)

Sirok, B. [Ljubljana Univ. (Slovenia). Faculty of Mechanical Engineering; Bergant, A. [Litostroj Power, d.o.o., Ljubljana (Slovenia); Hoefler, E.

2011-12-15

A new vertical single-regulated mixed-flow turbine with conical guide apparatus and without spiral casing is presented in this paper. Runner blades are fixed to the hub and runner band and resemble to the Francis type runner of extremely high specific speed. Due to lack of information and guidelines for the design of a new turbine, a theoretical model was developed in order to determinate the design duty point, i.e. to determine the optimum narrow operation range of the turbine. It is not necessary to know the kinematic conditions at the runner inlet, but only general information on the geometry of turbine flow-passage, meridional contour of the runner and blading, the number of blades and the turbine speed of rotation. The model is based on the integral tangential lift coefficient, which is the average value over the entire runner blading. The results are calculated for the lift coefficient 0.5 and 0.6, for the flow coefficient range from 0.2 to 0.36, for the number of the blades between 5 and 13, and are finally presented in the Cordier diagram (specific speed vs. specific diameter). Calculated results of the turbine optimum operation in Cordier diagram correspond very well to the adequate area of Kaplan turbines with medium and low specific speed and extends into the area of Francis turbines with high specific speed. Presented model clearly highlights the parameters that affect specific load of the runner blade row and therefore the optimum turbine operation (discharge - turbine head). The presented method is not limited to a specific reaction type of the hydraulic turbine. The method can therefore be applied to a wide range from mixed-flow (radial-axial) turbines to the axial turbines. Applicability of the method may be considered as a tool in the first stage of the turbine design i.e. when designing the meridional geometry and selecting the number of blades according to calculated operating point. Geometric and energy parameters are generally defined to an

Fluid mixing III

International Nuclear Information System (INIS)

Harnby, N.

1988-01-01

Covering all aspects of mixing, this work presents research and developments in industrial applications, flow patterns and mixture analysis, mixing of solids into liquids, and mixing of gases into liquids

Flowing holographic anyonic superfluid

Science.gov (United States)

Jokela, Niko; Lifschytz, Gilad; Lippert, Matthew

2014-10-01

We investigate the flow of a strongly coupled anyonic superfluid based on the holographic D3-D7' probe brane model. By analyzing the spectrum of fluctuations, we find the critical superfluid velocity, as a function of the temperature, at which the flow stops being dissipationless when flowing past a barrier. We find that at a larger velocity the flow becomes unstable even in the absence of a barrier.

Rapid detection of fungal alpha-amylase in the work environment with a lateral flow immunoassay

NARCIS (Netherlands)

Bogdanovic, J.; Koets, M.; Sander, I.; Wouters, I.; Meijster, T.; Heederik, D.J.J.; Amerongen, van A.; Doekes, G.

2006-01-01

Background Occupational allergen exposure assessment usually requires airborne dust sampling at the worksite followed by dust extraction and enzyme immunoassay (EIA) analysis at the laboratory. Use of semiquantitative lateral flow immunoassays (LFIAs) may allow a more rapid detection procedure with

Fast optical measurements and imaging of flow mixing

DEFF Research Database (Denmark)

Clausen, Sønnik; Fateev, Alexander; Nielsen, Karsten Lindorff

Project is focused on fast time-resolved infrared measurements of gas temperature and fast IR-imagining of flames in various combustion environments. The infrared spectrometer system was developed in the project for fast infrared spectral measurements on industrial scale using IR-fibre- optics. F...... engine and visualisation of gas flow behaviour in cylinder.......Project is focused on fast time-resolved infrared measurements of gas temperature and fast IR-imagining of flames in various combustion environments. The infrared spectrometer system was developed in the project for fast infrared spectral measurements on industrial scale using IR-fibre- optics....... Fast time-and spectral-resolved measurements in 1.5-5.1 μm spectral range give information about flame characteristics like gas and particle temperatures, eddies and turbulent gas mixing. Time-resolved gas composition in that spectral range (H2O, CH4, CO2, CO) which is one of the key parameters...

Mixing vane grid spacer

International Nuclear Information System (INIS)

Patterson, J.F.; Galbraith, K.P.

1978-01-01

An improved mixing vane grid spacer having enhanced flow mixing capability by virtue of mixing vanes being positioned at welded intersecting joints of the spacer wherein each mixing vane has an opening or window formed therein substantially directly over the welded joint to provide improved flow mixing capability is described. Some of the vanes are slotted, depending on their particular location in the spacers. The intersecting joints are welded by initially providing consumable tabs at and within each window, which are consumed during the welding of the spacer joints

Large eddy simulations of flow and mixing in jets and swirl flows: application to a gas turbine

Energy Technology Data Exchange (ETDEWEB)

Schluter, J.U.

2000-07-01

a last step all parts of the burner investigated as detached objects are assembled and a computation of a 20 deg.segment of the burner is made. Flow features, like vane flow separations and mixing quality are examined. Finally, burner modifications are proposed and their effect discussed. Emphasis is put on the suppression of large scale structures in the combustion chamber, which are suspected to be one source of combustion instabilities. (author)

Foam flow in a model porous medium: I. The effect of foam coarsening.

Science.gov (United States)

Jones, S A; Getrouw, N; Vincent-Bonnieu, S

2018-05-09

Foam structure evolves with time due to gas diffusion between bubbles (coarsening). In a bulk foam, coarsening behaviour is well defined, but there is less understanding of coarsening in confined geometries such as porous media. Previous predictions suggest that coarsening will cause foam lamellae to move to low energy configurations in the pore throats, resulting in greater capillary resistance when restarting flow. Foam coarsening experiments were conducted in both a model-porous-media micromodel and in a sandstone core. In both cases, foam was generated by coinjecting surfactant solution and nitrogen. Once steady state flow had been achieved, the injection was stopped and the system sealed off. In the micromodel, the foam coarsening was recorded using time-lapse photography. In the core flood, the additional driving pressure required to reinitiate flow after coarsening was measured. In the micromodel the bubbles coarsened rapidly to the pore size. At the completion of coarsening the lamellae were located in minimum energy configurations in the pore throats. The wall effect meant that the coarsening did not conform to the unconstricted growth laws. The coreflood tests also showed coarsening to be a rapid process. The additional driving pressure to restart flow reached a maximum after just 2 minutes.

Measurement of stopping power of heavy ions

International Nuclear Information System (INIS)

Kitahara, Tetsuo

1981-01-01

The stopping power of heavy ions is discussed. In the low energy region, heavy ions keep some of their orbital electrons, and have equilibrium electron charge. The stopping power of penetrating particles depends on this effective charge. At present, it is hard to estimate this effective charge theoretically, accordingly, the estimation is made experimentally. Another difficulty in this estimation is that the Born approximation is not effective for heavy ions. In the low energy region, electronic stopping and nuclear stopping contribute to the stopping power. For the electronic stopping, a formula for the stopping power was given by Lindhard et al. The experimental values were obtained at GSI, and are inconsistent with the estimation by the Lindhard's formula. In the high energy region, where the Born approximation can be used, the Bethe's formula is applied, but the experimental data are scarce. Oscillations are seen in the Z dependence graph of the experimental stopping cross sections. Experimental works on the stopping power have been done. The differential and the integral methods were carried out. (Kato, T.)

Rapid screening of mixed edible oils and gutter oils by matrix-assisted laser desorption/ionization mass spectrometry

Energy Technology Data Exchange (ETDEWEB)

Ng, Tsz-Tsun; So, Pui-Kin; Zheng, Bo [Food Safety and Technology Research Centre, State Key Laboratory of Chirosciences and Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom Kowloon, Hong Kong Special Administrative Region (China); Shenzhen Key Laboratory of Food Biological Safety Control and State Key Laboratory of Chinese Medicine and Molecular Pharmacology (Incubation), Shenzhen Research Institute of The Hong Kong Polytechnic University, Shenzhen (China); Yao, Zhong-Ping, E-mail: zhongping.yao@polyu.edu.hk [Food Safety and Technology Research Centre, State Key Laboratory of Chirosciences and Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom Kowloon, Hong Kong Special Administrative Region (China); Shenzhen Key Laboratory of Food Biological Safety Control and State Key Laboratory of Chinese Medicine and Molecular Pharmacology (Incubation), Shenzhen Research Institute of The Hong Kong Polytechnic University, Shenzhen (China)

2015-07-16

Highlights: • Simplified sample preparation method for direct analysis of edible oils by MALDI-MS. • Establishment of a preliminary MALDI-MS spectral database of edible oils. • Rapid screening of mixed edible oils and gutter oils. - Abstract: Authentication of edible oils is a long-term issue in food safety, and becomes particularly important with the emergence and wide spread of gutter oils in recent years. Due to the very high analytical demand and diversity of gutter oils, a high throughput analytical method and a versatile strategy for authentication of mixed edible oils and gutter oils are highly desirable. In this study, an improved matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) method has been developed for direct analysis of edible oils. This method involved on-target sample loading, automatic data acquisition and simple data processing. MALDI-MS spectra with high quality and high reproducibility have been obtained using this method, and a preliminary spectral database of edible oils has been set up. The authenticity of an edible oil sample can be determined by comparing its MALDI-MS spectrum and principal component analysis (PCA) results with those of its labeled oil in the database. This method is simple and the whole process only takes several minutes for analysis of one oil sample. We demonstrated that the method was sensitive to change in oil compositions and can be used for measuring compositions of mixed oils. The capability of the method for determining mislabeling enables it for rapid screening of gutter oils since fraudulent mislabeling is a common feature of gutter oils.

Rapid screening of mixed edible oils and gutter oils by matrix-assisted laser desorption/ionization mass spectrometry

International Nuclear Information System (INIS)

Ng, Tsz-Tsun; So, Pui-Kin; Zheng, Bo; Yao, Zhong-Ping

2015-01-01

Highlights: • Simplified sample preparation method for direct analysis of edible oils by MALDI-MS. • Establishment of a preliminary MALDI-MS spectral database of edible oils. • Rapid screening of mixed edible oils and gutter oils. - Abstract: Authentication of edible oils is a long-term issue in food safety, and becomes particularly important with the emergence and wide spread of gutter oils in recent years. Due to the very high analytical demand and diversity of gutter oils, a high throughput analytical method and a versatile strategy for authentication of mixed edible oils and gutter oils are highly desirable. In this study, an improved matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) method has been developed for direct analysis of edible oils. This method involved on-target sample loading, automatic data acquisition and simple data processing. MALDI-MS spectra with high quality and high reproducibility have been obtained using this method, and a preliminary spectral database of edible oils has been set up. The authenticity of an edible oil sample can be determined by comparing its MALDI-MS spectrum and principal component analysis (PCA) results with those of its labeled oil in the database. This method is simple and the whole process only takes several minutes for analysis of one oil sample. We demonstrated that the method was sensitive to change in oil compositions and can be used for measuring compositions of mixed oils. The capability of the method for determining mislabeling enables it for rapid screening of gutter oils since fraudulent mislabeling is a common feature of gutter oils

Multicomponent mixed dopant optimization for rapid screening of polycyclic aromatic hydrocarbons using ultra high performance liquid chromatography coupled to atmospheric pressure photoionization high-resolution mass spectrometry

KAUST Repository

Sioud, Salim; Amad, Maan H.; Al-Talla, Zeyad

2012-01-01

with water-soluble organic solvents. In order to achieve a more efficient and less toxic dopant, a multicomponent mixed dopant was explored. METHODS A multicomponent mixed dopant for non-targeted rapid screening of polycyclic aromatic hydrocarbons (PAHs

On Electromagnetic Modulation of Flow Instabilities, Mixing and Heat Transfer in Conducting and Magnetized Fluids

NARCIS (Netherlands)

Kenjeres, S.

2016-01-01

In the present paper we give a concise review of some recent highlights of our research dealing with electromagnetic control of flow, mixing and heat transfer of electrically conductive or magnetized fluids. We apply a combination of state-of-art numerical (DNS and LES) and experimental (PIV and

Gas and particle motions in a rapidly decompressed flow

Science.gov (United States)

Johnson, Blair; Zunino, Heather; Adrian, Ronald; Clarke, Amanda

2017-11-01

To understand the behavior of a rapidly decompressed particle bed in response to a shock, an experimental study is performed in a cylindrical (D = 4.1 cm) glass vertical shock tube of a densely packed (ρ = 61%) particle bed. The bed is comprised of spherical glass particles, ranging from D50 = 44-297 μm between experiments. High-speed pressure sensors are incorporated to capture shock speeds and strengths. High-speed video and particle image velocimetry (PIV) measurements are collected to examine vertical and radial velocities of both the particles and gas to elucidate features of the shock wave and resultant expansion wave in the lateral center of the tube, away from boundaries. In addition to optically analyzing the front velocity of the rising particle bed, interaction between the particle and gas phases are investigated as the flow accelerates and the particle front becomes more dilute. Particle and gas interactions are also considered in exploring mechanisms through which turbulence develops in the flow. This work is supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science and Academic Alliance Program, under Contract No. DE-NA0002378.

The effects of curvature on the flow field in rapidly rotating gas centrifuges

International Nuclear Information System (INIS)

Wood, H.G.; Jordan, J.A.

1984-01-01

The effects of curvature on the fluid dynamics of rapidly rotating gas centrifuges are studied. A governing system of a linear partial differential equation and boundary conditions is derived based on a linearization of the equations for viscous compressible flow. This system reduces to the Onsager pancake model if the effects of curvature are neglected. Approximations to the solutions of the governing equations with and without curvature terms are obtained via a finite-element method. Two examples are considered: first where the flow is driven by a thermal gradient at the wall of the centrifuge, and then for the flow being driven by the introduction and removal of mass through the ends of the centrifuge. Comparisons of the results obtained show that, especially for the second example, the inclusion of the terms due to curvature in the model can have an appreciable effect on the solution. (author)

Mixed convection between horizontal plates and consequences for chemical vapor deposition flows

International Nuclear Information System (INIS)

Chiu, K.C.

1986-01-01

To simulate the fluid dynamics of VD systems, mixed convection between horizontal plates (AR = width/height = 10) heated from below was studied by laser Doppler anemometry in a range 1368 < Ra < 8300 and 15 < R3 < 170. The entrance effects were characterized by two lengths: one for the onset of bouyancy-driven instability, and one for the full development of longitudinal convection rolls. Explicit expressions for both entrance lengths are given in terms of Ra and Re. In addition, unsteady longitudinal convection rolls were observed. These are discussed in terms of the admixture of transverse convection rolls and/or contributions from upstream turbulence. For the fully developed region it is shown analytically that the transverse velocities of the longitudinal convection rolls, v and w, are independent of the forced flow and are identical to those of the two-dimensional Rayleigh-Benard convection rolls. These fundamental results serve as a base for the discussion of horizontal CVD flows. The entrance and sidewall effects are found to have pronounced influences on the flow patterns observed in CVD (AR = 2) reactors

Experimental study of mixed convection flow through a horizontal orifice or vent linking two compartments

International Nuclear Information System (INIS)

Varrall, Kevin

2016-01-01

To answer building issues and fire safety challenges, this thesis deals with the mixed convection flow through a horizontal orifice or vent linking two compartments. The aim is to improve the understanding and the modeling of the exchange of gas through the opening. A small scale experimental study and a theoretical approach are proposed. The study focuses first on the influence of the geometrical ratio L/D of the opening on the flow rate at the vent for free convection regime. Non-intrusive measurements, via the tracking of the interface between two non miscible liquids in an isothermal approach, and thanks to the SPIV in a thermal approach, permit to describe the bidirectional exchange process and to consolidate existing correlations. Experiments for mixed convection regime aim to study the impact of mechanical ventilation (in blowing and extracting modes) on the exchanged flow rates. The comparison between existing correlations and experimental data shows large differences. A modification of the correlation of Cooper is proposed. A theoretical approach from the simplified Navier Stokes equations and with the Boussinesq approximation permits to discuss the construction of existing correlations. From this theory, a more accurate model than those available in the literature is proposed thanks to an adjustment of discharge coefficients from experimental data. (author)

Numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area, South Dakota

Science.gov (United States)

Putnam, Larry D.; Long, Andrew J.

2009-01-01

The city of Rapid City and other water users in the Rapid City area obtain water supplies from the Minnelusa and Madison aquifers, which are contained in the Minnelusa and Madison hydrogeologic units. A numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area was developed to synthesize estimates of water-budget components and hydraulic properties, and to provide a tool to analyze the effect of additional stress on water-level altitudes within the aquifers and on discharge to springs. This report, prepared in cooperation with the city of Rapid City, documents a numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units for the 1,000-square-mile study area that includes Rapid City and the surrounding area. Water-table conditions generally exist in outcrop areas of the Minnelusa and Madison hydrogeologic units, which form generally concentric rings that surround the Precambrian core of the uplifted Black Hills. Confined conditions exist east of the water-table areas in the study area. The Minnelusa hydrogeologic unit is 375 to 800 feet (ft) thick in the study area with the more permeable upper part containing predominantly sandstone and the less permeable lower part containing more shale and limestone than the upper part. Shale units in the lower part generally impede flow between the Minnelusa hydrogeologic unit and the underlying Madison hydrogeologic unit; however, fracturing and weathering may result in hydraulic connections in some areas. The Madison hydrogeologic unit is composed of limestone and dolomite that is about 250 to 610 ft thick in the study area, and the upper part contains substantial secondary permeability from solution openings and fractures. Recharge to the Minnelusa and Madison hydrogeologic units is from streamflow loss where streams cross the outcrop and from infiltration of precipitation on the outcrops (areal recharge). MODFLOW-2000, a finite-difference groundwater-flow

Using nitrate to quantify quick flow in a karst aquifer

Science.gov (United States)

Mahler, B.J.; Garner, B.D.

2009-01-01

In karst aquifers, contaminated recharge can degrade spring water quality, but quantifying the rapid recharge (quick flow) component of spring flow is challenging because of its temporal variability. Here, we investigate the use of nitrate in a two-endmember mixing model to quantify quick flow in Barton Springs, Austin, Texas. Historical nitrate data from recharging creeks and Barton Springs were evaluated to determine a representative nitrate concentration for the aquifer water endmember (1.5 mg/L) and the quick flow endmember (0.17 mg/L for nonstormflow conditions and 0.25 mg/L for stormflow conditions). Under nonstormflow conditions for 1990 to 2005, model results indicated that quick flow contributed from 0% to 55% of spring flow. The nitrate-based two-endmember model was applied to the response of Barton Springs to a storm and results compared to those produced using the same model with ??18O and specific conductance (SC) as tracers. Additionally, the mixing model was modified to allow endmember quick flow values to vary over time. Of the three tracers, nitrate appears to be the most advantageous because it is conservative and because the difference between the concentrations in the two endmembers is large relative to their variance. The ??18O- based model was very sensitive to variability within the quick flow endmember, and SC was not conservative over the timescale of the storm response. We conclude that a nitrate-based two-endmember mixing model might provide a useful approach for quantifying the temporally variable quick flow component of spring flow in some karst systems. ?? 2008 National Ground Water Association.

GEOCHEMICAL AND ISOTOPIC CONSTRAINTS ON GROUND-WATER FLOW DIRECTIONS, MIXING AND RECHARGE AT YUCCA MOUNTAIN, NEVADA

International Nuclear Information System (INIS)

A. Meijer; E. Kwicklis

2000-01-01

This analysis is governed by the Office of Civilian Radioactive Waste Management (OCRWM) Analysis and Modeling Report Development Plan entitled ''Geochemical and Isotopic Constraints on Groundwater Flow Directions, Mixing and Recharge at Yucca Mountain'' (CRWMS M and O 1999a). As stated in this Development Plan, the purpose of the work is to provide an analysis of groundwater recharge rates, flow directions and velocities, and mixing proportions of water from different source areas based on groundwater geochemical and isotopic data. The analysis of hydrochemical and isotopic data is intended to provide a basis for evaluating the hydrologic system at Yucca Mountain independently of analyses based purely on hydraulic arguments. Where more than one conceptual model for flow is possible, based on existing hydraulic data, hydrochemical and isotopic data may be useful in eliminating some of these conceptual models. This report documents the use of geochemical and isotopic data to constrain rates and directions of groundwater flow near Yucca Mountain and the timing and magnitude of recharge in the Yucca Mountain vicinity. The geochemical and isotopic data are also examined with regard to the possible dilution of groundwater recharge from Yucca Mountain by mixing with groundwater downgradient from the potential repository site. Specifically, the primary tasks of this report, as listed in the AMR Development Plan (CRWMS M and O 1999a), consist of the following: (1) Compare geochemical and isotopic data for perched and pore water in the unsaturated zone with similar data from the saturated zone to determine if local recharge is present in the regional groundwater system; (2) Determine the timing of the recharge from stable isotopes such as deuterium ( 2 H) and oxygen-18 ( 18 O), which are known to vary over time as a function of climate, and from radioisotopes such as carbon-14 ( 14 C) and chlorine-36 ( 36 Cl); (3) Determine the magnitude of recharge from relatively

Mixing in a Microfluid Device

DEFF Research Database (Denmark)

Hjorth, Poul G.; Deryabin, Mikhail

Mixing of fluids in microchannels cannot rely on turbulence since the flow takes place at extremly low Reynolds numbers. Various active and passive devices have been developed to induce mixing in microfluid flow devices. We describe here a model of an active mixer where a transverse periodic flow...

Visualizing the flow of evidence in network meta-analysis and characterizing mixed treatment comparisons.

Science.gov (United States)

König, Jochem; Krahn, Ulrike; Binder, Harald

2013-12-30

Network meta-analysis techniques allow for pooling evidence from different studies with only partially overlapping designs for getting a broader basis for decision support. The results are network-based effect estimates that take indirect evidence into account for all pairs of treatments. The results critically depend on homogeneity and consistency assumptions, which are sometimes difficult to investigate. To support such evaluation, we propose a display of the flow of evidence and introduce new measures that characterize the structure of a mixed treatment comparison. Specifically, a linear fixed effects model for network meta-analysis is considered, where the network estimates for two treatments are linear combinations of direct effect estimates comparing these or other treatments. The linear coefficients can be seen as the generalization of weights known from classical meta-analysis. We summarize properties of these coefficients and display them as a weighted directed acyclic graph, representing the flow of evidence. Furthermore, measures are introduced that quantify the direct evidence proportion, the mean path length, and the minimal parallelism of mixed treatment comparisons. The graphical display and the measures are illustrated for two published network meta-analyses. In these applications, the proposed methods are seen to render transparent the process of data pooling in mixed treatment comparisons. They can be expected to be more generally useful for guiding and facilitating the validity assessment in network meta-analysis. Copyright © 2013 John Wiley & Sons, Ltd.

Higgs mass from neutrino-messenger mixing

Energy Technology Data Exchange (ETDEWEB)

Byakti, Pritibhajan [Center for High Energy Physics, Indian Institute of Science,C.V. Raman Ave, Bangalore 560012 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science,2A & 2B Raja S.C. Mullick Road, Kolkata 700 032 (India); Khosa, Charanjit K. [Center for High Energy Physics, Indian Institute of Science,C.V. Raman Ave, Bangalore 560012 (India); Mummidi, V.S. [Harish-Chandra Research Institute,Chhatnag Road, Jhusi, Allahabad 211019 (India); Vempati, Sudhir K. [Center for High Energy Physics, Indian Institute of Science,C.V. Raman Ave, Bangalore 560012 (India)

2017-03-06

The discovery of the Higgs particle at 125 GeV has put strong constraints on minimal messenger models of gauge mediation, pushing the stop masses into the multi-TeV regime. Extensions of these models with matter-messenger mixing terms have been proposed to generate a large trilinear parameter, A{sub t}, relaxing these constraints. The detailed survey of these models (DOI: 10.1007/JHEP05(2013)055; 10.1007/JHEP08(2013)093 ) so far considered messenger mixings with only MSSM superfields. In the present work, we extend the survey to MSSM with inverse-seesaw mechanism. The neutrino-sneutrino corrections to the Higgs mass in the inverse seesaw model are not significant in the minimal gauge mediation model, unless one considers messenger-matter interaction terms. We classify all possible models with messenger-matter interactions and perform thorough numerical analysis to find out the promising models. We found that out of the 17 possible models 9 of them can lead to Higgs mass within the observed value without raising the sfermion masses significantly. The successful models have stop masses ∼1.5 TeV with small or negligible mixing and yet a light CP even Higgs at 125 GeV.

Rapid non-destructive quantitative estimation of urania/ thoria in mixed thorium uranium di-oxide pellets by high-resolution gamma-ray spectrometry

Energy Technology Data Exchange (ETDEWEB)

Shriwastwa, B.B.; Kumar, Anil; Raghunath, B.; Nair, M.R.; Abani, M.C.; Ramachandran, R.; Majumdar, S.; Ghosh, J.K

2001-06-01

A non-destructive technique using high-resolution gamma-ray spectrometry has been standardised for quantitative estimation of uranium/thorium in mixed (ThO{sub 2}-UO{sub 2}) fuel pellets of varying composition. Four gamma energies were selected; two each from the uranium and thorium series and the time of counting has been optimised. This technique can be used for rapid estimation of U/Th percentage in a large number of mixed fuel pellets from a production campaign.

Rapid non-destructive quantitative estimation of urania/ thoria in mixed thorium uranium di-oxide pellets by high-resolution gamma-ray spectrometry

International Nuclear Information System (INIS)

Shriwastwa, B.B.; Kumar, Anil; Raghunath, B.; Nair, M.R.; Abani, M.C.; Ramachandran, R.; Majumdar, S.; Ghosh, J.K.

2001-01-01

A non-destructive technique using high-resolution gamma-ray spectrometry has been standardised for quantitative estimation of uranium/thorium in mixed (ThO 2 -UO 2 ) fuel pellets of varying composition. Four gamma energies were selected; two each from the uranium and thorium series and the time of counting has been optimised. This technique can be used for rapid estimation of U/Th percentage in a large number of mixed fuel pellets from a production campaign