Flow Splitting Research Articles

A verification problem for thermal hydraulics systems codes dealing with twin, parallel-boiling and inverted U-tubes condensing channels

In the analysis of the nuclear safety of complex nuclear systems, almost one-dimensional system thermal–hydraulics codes will be used perhaps for a couple of decades from now. Computational Fluid Dynamics (CFD) tools are accepted at present to be a support of such analyses and they are used coupled to systems codes or as separate analysis tools for isolated components with boundary conditions obtained from systems codes. The restricted acceptance of “pure” CFD codes is due to many reasons but two of them are relevant, namely (a) the apparent lack of CFD grade experimental data and (b) the need for a complete verification and validation (V&V) and the uncertainty quantification for the codes currently available. There is plenty of experimental data related to integral test facilities (ITFs) that constitute macroscopic systems behavior information and a consolidated data base for such purposes. Despite of this, additional verification cases may be added to the above mentioned consolidated data. In the present paper, flow oscillations in parallel channel configurations with system codes are studied in diverse configurations. Different models, calculation options and, in particular, in-phase or out-of-phase oscillations were studied, both in heated and cooled parallel channels. The emphasis is on the effects of concentrated irreversible pressure losses coefficients at the inlet and at the outlet of the channels. In the case of cooled steam generator channels, the results of the Semiscale Integral Test Facility operating in natural circulation conditions are revisited. The results presented in this paper, show how a validation case lead to find a not still reported (in the Authors knowledge) verification case. The problem is related to twin-parallel-boiling and condensing, inverted U-tubes channels and connected through common plena. This is, of course, a problem that deserved many tens of papers in the last four decades. Flow splitting without reversal was computationally found and to explain this behavior a theoretical model limited in scope was developed that was a posteriori verified using a particular systems code (RELAP5) commonly applied to perform safety analyses of nuclear power plants. The rationale followed, the theoretical analysis performed and the confirmatory computational results found are summarized in this paper.

On the Origin of Specimen: Load-adapted Integral Sheet Metal Products

Flexible flow splitting is a novel forming process allowing the production of a new class of semi-finished goods: nonlinear branched sheet metal parts. This advancement of the linear flow splitting process combines both, the benefits of flexibility in cross-section shape and the flexibility of the part's curvature progression in feed direction and discloses new potentials in lightweight designed sheet metal formed parts. The paper presents the implementation of this new manufacturing process, the challenges of processing bifurcated and curved band edge sheet metal parts and a strategy to enhance the part accuracy by a closed loop controlled tooling system.

Influence of a reaction mixture streamline on partial oxidation of methane in an asymmetric microchannel reactor

Partial oxidation of methane (POM) has been tested in an asymmetric microchannel reactor with different inlet configurations. One inlet of the reactor provided successive splitting of an inlet flow into parallel channels, whereas the opposite inlet allowed the inlet flow to enter the parallel channels simultaneously. It was found that concentrations of carbon monoxide and carbon dioxide changed by 20–30% and the conversion of methane changed by 5–20%, depending on the rate and direction of the inlet flow. The hydrogen production rate practically did not depend on the inlet configuration and equaled 15 l/h at the inlet flow rates from 600 to 1400 cm3/min and at the methane conversion of 80%. The data obtained demonstrated that the use of different operating modes of the asymmetric microreactor allows changing the composition of produced syngas.

Synchronized gradient elution in capillary liquid chromatography

The synchronization of injection valve operation and gradient elution in capillary liquid chromatography (cHPLC) is studied. Focus is placed on the cHPLC systems which rely on the splitting of a primary flow to provide the much smaller secondary flow required at the injection device and analytical column. Owing to the tiny secondary flow rates, synchronization is necessary to achieve proper optimization of gradient elution methods. Otherwise, there is a risk of having the analytes totally or partially eluted in the initial isocratic conditions, and there is no control on the actual gradient profile reaching the column. Synchronization is first achieved by switching back the valve to bypass after injection. This is important to save time, and to avoid the gradient slope to be reduced by mixing within the internal volume of the injector (a 47% of slope reduction, in the conditions used in this work). Valve switching to bypass should be produced immediately after the arrival of the end of the sample plug to the valve (tV). Fine system synchronization is further achieved by starting the gradient at the match time (tM), which is the time required to match the arrival of both the gradient front and the end of the sample plug to the valve, and therefore also to the column inlet. Synchronization of these two events requires starting the gradient either before or even after the injection, thus to prevent a late or an early arrival of the gradient front to the injection valve, respectively. Owing to their dependence with the backpressure, both tV and tM should be measured in the presence of the column at the initial gradient conditions. Simple experiments designed to measure tV and tM are described. With synchronization according to the techniques described in this work, control on the real gradient elution conditions at the column location is maintained, the analysis time is reduced and efficiency improves. The effects of synchronization are illustrated by injecting a mixture of alkylbenzenes. At 1μL min−1, valve switching to bypass reduced analysis time from ca. 36 to 12min (butylbenzene), and improved peak symmetry (from 2.00 to 0.94 for methylbenzene) and efficiency (the average apparent plate count increased approximately 60%). Synchronization according to the match time further improved efficiency (approximately, up to 120%).

Multistage collapse of eight western Canary Island landslides in the last 1.5 Ma: Sedimentological and geochemical evidence from subunits in submarine flow deposits

Volcaniclastic turbidites in the Madeira Abyssal Plain provide a record of major landslides from the Western Canary Islands in the last 1.5 Ma. These volcaniclastic turbidites are composed of multiple fining‐upward turbidite sands, known as subunits. The subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages. The subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different. This indicates that each subunit represents a discrete failure as part of a multistage landslide. This has significant implications for geohazard assessments, as multistage failures reduce the magnitude of the associated tsunami. The multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3. Thus although multistage failure ultimately reduce the potential landslide and tsunami threat, the landslide events may still generate significant tsunamis close to source.

Универсальный стендовый редуктор для испытаний газотурбинных двигателей мощностью 16-35 МВт

Design of gearbox for GTE tests without change in transmission ratio with speed reduction down to hydraulic dynamometer speed has been presented. The gearbox is two-stage, coaxial with the power flow splitting. The gearbox consists of housing, running gears, elements of lubrication system, parameters monitoring and protection electric system. Gearbox housing is made of steel, welded design. Running gears consists of herringbone nitride gears, sliding bearings, torsion shafts, sealing parts and disc elastic clutches of input and output shafts. Gearbox lubrication is circulation flood type from test bench electrically driven lube oil unit. Gearbox oil is drained to lubrication tank by gravity flow. Shaft cranking device is installed on gearbox for GTE-gearbox-hydraulic dynamometer transmission turning. Design feature of presented gearbox is presence of engaging/disengaging mechanisms allowing change in gearbox transmission ratio by means of torsion shafts shifting in driving and driven gearings’ inner cavities.

Multichannel rivers: their definition and classification

ABSTRACTThe etymology and historic usage of such terms as ‘anabranch’, ‘anastamose’ and ‘braided’ within river science are reviewed. Despite several decades of modern research to define river channel typologies inclusive of single channels and multiple channel networks, typologies remain ill‐conditioned and consequently ill‐defined. Conventionally employed quantitative planform characteristics of river networks possibly cannot be used alone to define channel types, yet the planform remains a central part of all modern classification schemes, supplemented by sedimentological and other qualitative channel characteristics. Planform characteristics largely have been defined using non‐standardized metrics describing individual network components, such as link lengths, braiding intensity and bifurcation angles, which often fail to separate visually‐different networks of channels. We find that existing typologies remain pragmatically utilitarian rather than fundamentally physics‐based and too often fail to discriminate between two distinctive and important processes integral to new channel initiation and flow‐splitting: (i) in‐channel bar accretion, and (ii) channel avulsion and floodplain excision. It is suggested that, first, if channel planform is to remain central to river typologies, then more rigorous quantitative approaches to the analysis of extended integral channel networks at extended reach scales (rather than network components) are required to correctly determine whether ‘visually‐different’ channel patterns can be discriminated consistently; and, second, if such visually‐different styles do in fact differ in their governing processes of formation and maintenance. A significant question is why do so many seemingly equilibrium network geometries possess a large number of anabranches in excess of predictions from theoretical considerations? The key research frontier with respect to initiating and maintaining multichannel networks remains the understanding and discrimination of accretionary‐bar flow splitting versus avulsive processes. Existing and new knowledge on flow splitting processes needs to be better integrated into channel typologies. Copyright © 2013 John Wiley & Sons, Ltd.

Parallel segmented outlet flow high performance liquid chromatography with multiplexed detection

We describe a new approach to multiplex detection for HPLC, exploiting parallel segmented outlet flow – a new column technology that provides pressure-regulated control of eluate flow through multiple outlet channels, which minimises the additional dead volume associated with conventional post-column flow splitting. Using three detectors: one UV-absorbance and two chemiluminescence systems (tris(2,2′-bipyridine)ruthenium(III) and permanganate), we examine the relative responses for six opium poppy (Papaver somniferum) alkaloids under conventional and multiplexed conditions, where approximately 30% of the eluate was distributed to each detector and the remaining solution directed to a collection vessel. The parallel segmented outlet flow mode of operation offers advantages in terms of solvent consumption, waste generation, total analysis time and solute band volume when applying multiple detectors to HPLC, but the manner in which each detection system is influenced by changes in solute concentration and solution flow rates must be carefully considered.

Hybrid Capillary/Microfluidic System for Comprehensive Online Liquid Chromatography-Capillary Electrophoresis-Electrospray Ionization-Mass Spectrometry

A hybrid multidimensional separation system was made by coupling capillary liquid chromatography (LC) to a microfluidic device. The microfluidic device integrated flow splitting, capillary electrophoresis (CE), electroosmotic pumping, and electrospray ionization (ESI) emitter functional elements. The system was used with a time-of-flight mass spectrometer for comprehensive online LC-CE-MS of proteolytic digests. Analysis of a complex mixture of peptides yielded a peak capacity of approximately 1400 in 50 min. Three replicate runs demonstrated mean reproducibility for LC retention and CE migration times of 0.32% and 0.75% relative standard deviation (RSD), respectively. The same LC-CE-MS method was also used to characterize the N-linked glycosylation of a monoclonal antibody. Glycopeptides from two different N-linked glycosylation sites were separated from all other tryptic peptides and identified using MS data. The relative amounts of each glycoform and total site occupancy were quantified using LC-CE-MS data.

Electrospray ion source with a dynamic liquid flow splitter

Although the electrospray method is widely used in biomedical mass spectrometry and ion-drift spectrometry, the electrospray system can generate large drops that are the cause of electrical breakdowns, and of the fast clogging of the inlet diaphragm of the differential pumping first stage and system of ion transportation to the analyzer. Thus, a system free of such problems would be of benefit. To drain the condensate away from the electrospraying zone and to maintain stability of spraying, a source was designed where the excessive non-sprayed solution flowing down over the metal capillary outer wall is pumped away by an air micropump. An anti-electrode is mounted opposite the metal capillary and is slightly tilted with respect to the horizon to make the condensed liquid flow down. An electrospray ion source allowing work with chromatographic flows of the solution under normal conditions was tested. The applicability of the operating modes of the electrospray ion source with dynamic liquid flow splitting for both ion-drift and mass spectrometers was demonstrated. The flow rate range of liquid fed to the electrospray ion source with dynamic liquid flow splitting is such that it can be used in high performance liquid chromatography/Ion Mobility Spectrometry (HPLC/IMS) and HPLC/MS in the online mode. An electrospray ion source with a dynamic liquid flow splitter was developed and tested. Optimal operating modes of the electrospray ion source with dynamic liquid flow splitting were determined.

Changes in the Metastability of the Midlatitude Southern Hemisphere Circulation and the Utility of Nonstationary Cluster Analysis and Split-Flow Blocking Indices as Diagnostic Tools

Abstract Changes in the metastability of the Southern Hemisphere 500-hPa circulation are examined using both cluster analysis techniques and split-flow blocking indices. The cluster methodology is a purely data-driven approach for parameterization whereby a multiscale approximation to nonstationary dynamical processes is achieved through optimal sequences of locally stationary fast vector autoregressive factor (VARX) processes and some slow (or persistent) hidden process switching between them. Comparison is made with blocking indices commonly used in weather forecasting and climate analysis to identify dynamically relevant metastable regimes in the 500-hPa circulation in both reanalysis and Atmospheric Model Intercomparison Project (AMIP) datasets. The analysis characterizes the metastable regime in both reanalysis and model datasets prior to 1978 as positive and negative phases of a hemispheric midlatitude blocking state with the southern annular mode (SAM) associated with a transition state. Post-1978, the SAM emerges as a true metastable state replacing the negative phase of the hemispheric blocking pattern. The hidden state frequency of occurrences exhibits strong trends. The blocking pattern dominates in the early 1980s, and then gradually decreases. There is a corresponding increase in the SAM frequency of occurrence. This trend is largely evident in the reanalysis summer and spring but was not evident in the AMIP dataset. Further comparison with the split-flow blocking indices reveals a superficial correspondence between the cluster hidden state frequency of occurrences and split-flow indices. Examination of composite states shows that the blocking indices capture splitting of the zonal flow whereas the cluster composites reflect coherent block formation. Differences in blocking climatologies from the respective methods are discussed.

Mean-field effects on matter and antimatter elliptic flow

We report our recent work on mean-field potential effects on the elliptic flows of matters and antimatters in heavy ion collisions leading to the production of a baryon-rich matter. Within the framework of a multiphase transport (AMPT) model that includes both initial partonic and final hadronic interactions, we have found that including mean-field potentials in the hadronic phase leads to a splitting of the elliptic flows of particles and their antiparticles, providing thus a plausible explanation of the different elliptic flows between p and anti-p, K+ and K-, and pi(+) and pi(-) observed by the STAR Collaboration in the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Using a partonic transport model based on the Nambu-Jona-Lasinio (NJL) model, we have also studied the effect of scalar and vector mean fields on the elliptic flows of quarks and antiquarks in these collisions. Converting quarks and antiquarks at hadronization to hadrons via the quark coalescence model, we have found that the elliptic flow differences between particles and antiparticles also depend on the strength of the quark vector coupling in baryon-rich quark-gluon plasma, providing thus the possibility of extracting information on the latter's properties from the BES program at RHIC.

Comparison of different methods aiming to account for/overcome matrix effects in LC/ESI/MS on the example of pesticide analyses

In this paper some of the most common methods for overcoming matrix effects in LC/ESI/MS (matrix-matched calibration, standard addition, post-column standard infusion, extrapolative dilution, and post-column flow splitting) are compared according to their ability to give both true and accurate results for pesticide determination in complicated matrices such as onion and garlic. In order to provide a quantitative comparison we use a measure of accuracy that would account for both average trueness and scatter of the results. Extrapolative dilution and standard addition were found to give results statistically insignificantly different from the correct values. In addition extrapolative dilution – a hybrid approach for both reducing and correcting for matrix effects – was found to result in the highest accuracy of the measurements.

Geometry Optimization of Branched Sheet Metal Products

AbstractWe consider the geometry optimization of branched sheet metal products, which can be produced continuously and in integral style using the new technologies of linear flow splitting and linear bend splitting. These are explored within the framework of the Collaborative Research Centre (CRC) 666. The geometry of such products can be parameterized by means of free form surfaces whereas their mechanical behaviour is described by the three dimensional linear elasticity equations. The associated PDE‐constrained problem for optimizing the stiffness of the structure is formulated and an algorithm for solving this problem using exact constraints and a globalization strategy based on adaptive cubic regularization is presented. Numerical results for an example are given. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fluid dynamics of horizontal air–water slug flows through a dividing T-junction

Experimental data from horizontal air–water slug flows were obtained in a test facility which was a 34mm internal diameter, 10m long Plexiglas pipe connected to the 90° branch arms from a T-junction. The test points were located on the flow pattern map in the proximity of the transition lines which separates different flow patterns. Capacitive probes with helical and concave plate sensors were used to quantify the dynamic liquid holdup in each branch. They were combined with Venturi nozzles+differential pressure transmitters in each outlet branch for measuring the two-phase mass flow rates. The dynamic characteristics of the slug flow splitting in a T-junction were studied from the acquired signals. Diaphragm straight-through type valves were used in the run and in the lateral branch arms to imitate equipments consuming the two-phase flow after the T-junction. This assembly can also be used as a gas–liquid separation system. The results showed different mechanisms acting on the slug flow division phenomenon. Liquid accumulation into the run branch, between the TJ and the control valve, caused more gas to come to the lateral branch.

Application of the local strain approach on a rolling point contact model

A newly developed cold forming process, the linear flow splitting process, allows the bifurcation of thin metal sheets by severe plastic deformation (SPD). This process produces flanges with an ultra-fine grained (UFG) microstructure, which is characterized by an increased hardness and lower surface roughness in comparison to the material in as-received state. The technology is researched within the Collaborative Research Centre 666 (CRC 666) “Integral Sheet Metal Design with Higher Order Bifurcations”. The increased hardness and reduced surface roughness of the flanges make this technology suitable for manufacturing linear guide rails. In order to achieve the required reliability and fatigue strength, the assessment of the performance of the linear flow-split profiles with gradient microstructure is of great importance. When considering rolling contact fatigue, the examination of the mechanical behavior of the side of the flange with higher hardness due to the UFG microstructure is required. In order to reduce time and costs, a numerical method to determine the rolling contact fatigue behavior would be useful minimizing the normally applied experimental effort. The present work aims to check the applicability of the local strain approach for the evaluation of the rolling contact fatigue behavior of linear flow split components by a Finite Element (FE) analysis. The Hertzian theory is only valid for homogeneous materials and cannot be directly applied to the flanges with gradient microstructure. Therefore an accurate modeling of the material in order to take into account the gradient in the mechanical properties is required. In this paper the characterization of the material behavior under axial cyclic loading will be presented. These results will be used for the Bergmann damage parameter to analyze the rolling contact fatigue behavior. Some parameters required for the application of the Bergmann approach are determined by a numerical simulation of the rolling contact. Results are compared to rolling contact fatigue tests performed on a recently developed test rig under the assumption of rolling without sliding and neglecting the effect of surface roughness and residual stresses.

Cut-First Branch-and-Price-Second for the Capacitated Arc-Routing Problem

This paper presents the first full-fledged branch-and-price (bap) algorithm for the capacitated arc-routing problem (CARP). Prior exact solution techniques either rely on cutting planes or the transformation of the CARP into a node-routing problem. The drawbacks are either models with inherent symmetry, dense underlying networks, or a formulation where edge flows in a potential solution do not allow the reconstruction of unique CARP tours. The proposed algorithm circumvents all these drawbacks by taking the beneficial ingredients from existing CARP methods and combining them in a new way. The first step is the solution of the one-index formulation of the CARP in order to produce strong cuts and an excellent lower bound. It is known that this bound is typically stronger than relaxations of a pure set-partitioning CARP model. Such a set-partitioning master program results from a Dantzig-Wolfe decomposition. In the second phase, the master program is initialized with the strong cuts, CARP tours are iteratively generated by a pricing procedure, and branching is required to produce integer solutions. This is a cut-first bap-second algorithm and its main function is, in fact, the splitting of edge flows into unique CARP tours.

Quantification of local and global elastic anisotropy in ultrafine grained gradient microstructures, produced by linear flow splitting

Severely deformed materials often show strong plastic strain gradients, which can lead to a variety of gradients in microstructure and texture. Since the elastic behavior of a material is in most cases linked to its crystallographic texture, gradients in the elastic properties are also possible. Consequently, the macroscopic elastic behavior results from the local elastic properties within the gradient. In the present investigation profiles produced by the linear flow splitting process were examined with respect to local and global elastic anisotropy, which develops during the complex forming process. The local grain orientations determined by EBSD measurements were used to calculate the elastic tensors at several positions along the strain gradient. Based on the geometric mean, the calculated local elastic constants were transferred into global ones by appropriate weighting. Ultrasonic measurements were carried out to determine the macroscopic stiffness tensor of the severely deformed parts, showing a good agreement with the global stiffness tensor calculated from orientation data.

The effect of deformation texture on the thermal stability of UFG HSLA steel

The microstructures of ultrafine grained (UFG) metals processed by severe plastic deformation are far from the thermodynamic equilibrium thus being prone to undergo coarsening processes. Theoretical and experimental investigations revealed that the stability against discontinuous grain growth in UFG metals with high stacking fault energy strongly depends on the fraction of high angle grain boundaries (HAGBs). This means that discontinuous grain growth does not occur if the fraction of HAGBs exceeds a certain level. The present work focuses on the impact of strong deformation textures on the thermal stability of UFG microstructures in a ferritic steel processed by linear flow splitting. It shows that the expected correlation between thermal stability and fraction of HAGBs is valid up to moderate texture intensities, whereas a strong deformation texture promotes discontinuous grain growth in spite of a high fraction of HAGBs. EBSD measurements reveal that this behavior is attributed to a strain-induced grain boundary migration causing a progressive orientation pinning effect with ongoing grain growth. Thereby, a large fraction of HAGBs is transformed into low angle grain boundaries (LAGBs) with low mobility. Consequently, a microstructure with a majority of LAGBs evolves being unstable against discontinuous grain growth.

Performance Analysis of Probabilistic Multipath Transmission of Video Streaming Traffic over Multi-Radio Wireless Devices

Popular smart wireless devices become equipped with multiple radio interfaces. Multihoming support can be enabled to allow for multiple simultaneous associations with heterogeneous networks. In this study, we focus on video streaming traffic and propose analytical approaches to evaluate the packet-level and call-level performance of a multipath transmission scheme, which sends video traffic bursts over multiple available channels in a probabilistic manner. A probability generation function (PGF) and z-transform method is applied to derive the PGF of packet delay and any arbitrary moment in general. Particularly, we can obtain the average delay, delay jitter, and delay outage probability. The essential characteristics of video traffic are taken into account, such as deterministic burst intervals, highly dynamic burst length, and batch arrivals of transmission packets. The video substream traffic resulting from the probabilistic flow splitting is characterized by means of zero-inflated models. Further, the call-level performance, in terms of flow blocking probability and system throughput, is evaluated with a three-dimensional Markov process and compared with that of an always-best access selection. The numerical and simulations results demonstrate the effectiveness of our analysis framework and the performance gain of multipath transmission.