432 research outputs found
A preliminary study of steam and water flow in venturi tubes
No full textCER60RVS47.September 1960.Includes bibliographical references.This is a report of an exploratory study of low quality steam and water mixtures flowing in a Venturi tube. Analysis of the experimental results indicate the flow pattern may be tending to change from separated, slugging flow at the entrance to annular flow at the throat. Correlations indicate the Venturi may be calibrated for use as a quality meter if the mass flow rate is known
Study of the properties of turbulent flow through a venturi using LDA techniques
No full textVenturi flow meters are originall)' applied in single phase flows. Currently, Shell investigates their application in so-called 'wet gas' production mea,surement. Wet gas consists of a mixture of gas, condensate (light oil) and water. The liquids have been condensed from the gas, due to the pressure and temperature drop while producing. The flow rate of such a three phase mixture is not easy to measure, though necessary for e.g. allocation of the fuel and reservoir management. The determination of the gas and liquid flow rates requires understanding of the multi phase flow in a venturi, including the phenomena downstream of the throat of a venturi in order to apply such a device in wet gas metering. The project is a continuation of the worlc of Nievaart [Nievaart, 2000], who has been investigating the applied measurement technique, Laser Doppler Anemometry (LDA). This research is focussed on the effects of a venturi in turbulent flow. Therefore, measurements have been performed at eight locations, distributed upstream, in and downstream of a venturi in a single phase flow, in order to obtain more information about the velocity and turbulence intensity profiles, as well as the production and dissipation of turbulent kinetic energy. Performing LDA measurements is not that easy. First, all parameters of the LDA set-up have to be adjust carefully and the laser beams liave to be aligned very accurate, as the measuring volume has to be positioned very precisely. In order to reduce the effects of the wall, these have been replaced by thin foils in the throat and diffuser of the venturi. This has led to several adjustments to the set-up. Al the other nuiasuring locations, glass 'screws' have been applied. Furthermore, the LDA data had to be corrected for velocity bias. The time between data correction method proved to be the best out of five different methods for the performed measurements. All data sets have been tested using diagnostic techniques in order to verify their validity. The sudden contraction of the venturi influences all flow properties in and downstream of this device. It creates a 'plug'flow in the throat with a flat axial velocity profile and a turbulence intensity of almost zero, except very close to the wall. In the throat, the flow is no longer in equilibrium according to the local power spectra. Here, dissipation dominates the flow. This 'plug' flow manifests itself as a jet-like flow in the divergent section of the venturi, leading to a strong increase in the production of turbulent kinetic energy near the wall. The significant change in turbulent flow properties is persistent, as 5 diameters downstream of the venturi the turbulence intensity is three times the value of that in turbulent pipe flow. Only, production has shifted towards the centerline and the flow is in equilibrium all along the traverse. Dissipation occurs mainly close to the wall. This downstream behavior is in contrast with turbulent pipe flow, where dissipation occurs in the core region, the only region where the flow is in equilibrium.Kramers Laboratorium voor Fysische TechnologieApplied Science
LDA improvement and tailoring for near-wall turbulence measurements in a Venturi
No full textShell investigates the application of a Venturi as a flow meter in wet-gas production. Wet gas consists of gas, oil and small amounts of water and is therefore a multiphase mixture. At this moment, a reliable data-base as to turbulent flow properties in Venturi flow meters is not available, neither in single phase nor in multiphase.-However, understanding the turbulence is essential in order to describe the behaviour of a Venturi flow meter in wet-gas and therefore this project has been initiated. The project starts with a turbulent single-phase flow in the throat ofthe Venturi and is aimed to investigate the measurement technique: Laser Doppler Anemometry (LDA). It is the only technique that can provide, at relatively high Reynolds numbers and in multiphase flows, information about the turbulence and the related energy dissipation, also in the liquid layer close to the wall. LDA, however, is a comphcated measurement technique that requires knowledge of, and insight in, the entire measurement system before reliable results can be obtained. To reduce the possibility of drawing erroneous conclusions from inappropriate LDA data, some criteria, a data set has to meet, are tested. Mostly, these so-called Diagnostic Tools indicate whether or not there is a problem with the data and assist in identifying the cause. Investigating turbulent structures close to the wall requires some special modifications. In order to prevent noticeable deformation of the measurement volume, caused by refraction and the Perspex tube, the Venturi is placed inside a rectangular box filled with water. A thin foil is replacing a part of the Perspex pipe and acts as inner wall. Scattering and detecting under an angle of 90 degrees increases the Signal to Noise Ratio significantly. By using a lens with a shorter focal length, a smaller measurement volume is created due to the spatial filter in front of the detector. This reduction in size increases the temporal and spatial resolution that are needed to study the small scales we are interested in. After optimisation of the LDA some preliminary results in the throat of the Venturi show that the turbulent fiow at that position is no longer in equilibrium, but has changed significantly. This should be investigated in greater detail in the next phase of this project.Kramers Laboratorium voor Fysische TechnologieApplied Science
Investigation of cavitation and vapor shedding mechanisms in a Venturi nozzle
No full textCavitating flow dynamics are investigated in an axisymmetric converging-diverging Venturi nozzle. Computational Fluid Dynamics (CFD) results are compared with those from previous experiments. New analysis performed on the quantitative results from both data sets reveals a coherent trend and show that the simulations and experiments agree well. The CFD results have confirmed the interpretation of the high-speed images of the Venturi flow, which indicated there are two vapor shedding mechanisms that exist under different running conditions: re-entrant jet and condensation shock. Moreover, they provide further detail of the flow mechanisms that cannot be extracted from the experiments. For the first time with this cavitating Venturi nozzle, the re-entrant jet shedding mechanism is reliably achieved in CFD simulations. The condensation shock shedding mechanism is also confirmed, and details of the process are presented. These CFD results compare well with the experimental shadowgraphs, space-time plots and time-averaged reconstructe computed tomography (CT) slices of vapor fraction
Flows from early Modernism into the Interior Streets of Venturi, Rauch and Scott Brown
No full textIn 1972 the famous diagram of the ‘Decorated Shed’ was introduced into the architectural discourse; it implied a definition of ‘architecture as shelter with decoration on it’ [1]. The diagram was part of urban research into the commercial environment of Las Vegas that was interpreted by the researchers – Robert Venturi, Denise Scott Brown and Steven Izenour – as ‘a new type of urban form’ that they meant ‘to understand’ in order ‘to begin to evolve techniques for its handling’. Yet the critique on this and other research and designs by Venturi, Rauch and Scott Brown focused essentially on questions of form and more specifically of the image of architecture.ArchitectureArchitectur
Long-term variations of FFR and iFR after transcatheter aortic valve implantation
No full textLong-term variations of fractional flow reserve (FFR) and instantaneous wave-free-ratio (iFR) after transcatheter aortic valve implantation (TAVI) have not been previously assessed. A total of 23 coronary lesions in 14 patients with aortic stenosis (AS) underwent physiology assessment at baseline, immediately after TAVI and at 14(7-29) months of follow-up. The angiographic severity of the lesions did not progress at follow-up (54[45-64] vs 54[49-63], p = .53). Overall, FFR (0.87[0.85-0.92] vs 0.88[0.82-0.92], p = .45) and iFR (0.88[0.85-0.96] vs 0.91[0.86-0.97], p = .30) did not change significantly compared with the baseline. FFR decreased in 3(13%) lesions with abnormal baseline value, whereas it remained stable in lesions with FFR > 0.80. Conversely, iFR did not show a systematic trend at long-term after TAVI. However, iFR demonstrated a higher reclassification rate at follow-up compared with FFR (p = .02). In conclusions, in this exploratory study, only minor variations of coronary physiology indices were observed at long-term after TAVI. Nevertheless, caution should be exercised in the interpretation of borderline FFR and iFR values in severe AS
De invloed van cylinders in een aanstroomgoot van een Venturi-goot
No full textDit laboratoriumonderzoek is één van de opdrachten in het laatste jaar van het ingenieursexamen aan de afdeling Weg- en Waterbouwkunde. Het omvat enerzijds een onderzoek naar de invloed van cylinders op een waterstroom in een goot. Anderzijds is een onderzoek gedaan naar de invloed van cylinders op de stuwhoogtemeting, cq. afvoer voor een Venturi-goot als deze cyclinders van verschillende diameters in de aanvoergoot staan. Sinds het in werking treden van de Wet op de Verontreiniging van Oppervlaktewateren, worden aan veel afvalwaterstromen hoeveelheidsmetingen gedaan om in verband met de heffingen op het lozen van afvalwater de totale hoeveelheid per jaar te bepalen. Om de graad van verontreiniging te weten te komen worden er van deze afvalwaterstromen monsters genomen, die verder geanalyseerd worden. Dit onderzoek beperkt zich ten aan van het meten van afvalwaterstromen tot de meetputten met meetschaften en open meetgoten en ten aanzien van de bemonstering tot het bemonsteringsapparaat van het type "Fleebalt". Uit de discussiegroep "Meet- en bemonsteringsapparatuur" is de vraag naar voren gekomen: wat is de plaats voor dit bemonsteringsapparaat in meetputten of meetgoten zodat, ten aanzien van de hoeveelheidsmeting en de proportionaliteit van de grootte van het monster t.o.v. de afvoer op het moment van monstername, de afwijkingen minimaal zijn met betrekking tot de werkelijkheid. Om hier een antwoord op te krijgen is het bemonsteringsapparaat vervangen door een serie cylinders met verschillende diameters om langs deze weg de invloed te bepalen van de verhouding tussen de diameter van het apparaat en de breedte van de goot, waarin deze geplaatst zal worden, op de stuwhoogtemeting van de Venturi. Uit de proeven is gebleken dat het verval, uitgedrukt in procenten van de waterhoogte voor de cylinder, tussen de twee plaatsen, die respectievelijk voor en achter de cylinders genomen zijn, groter wordt naarmate de verhouding tussen de diameter van de cylinder en de breedte van de goot groter wordt evenals bij een toename van het Froude-getal. Vervolgens zijn op diverse afstanden voor de versmalling in de aanvoergoot van een Venturi-goot de vijf cyclinders geplaatst om bij een aantal stuwhoogten de invloed van de cylinders op deze stuwhoogten na te gaan. Dit om een indruk te krijgen hoe groot de afwijking in de afvoer, behorende volgens de Q-h kromme van de Venturi-goot bij de gemeten stuwhoogte, ten opzichte van de werkelijkheid is. Hieruit is gebleken dat de fout in de afvoer, afgeleid van de gemeten stuwhoogte t.o.v. de werkelijke afvoer, minimaal is als aan de eis voor Venturi-goten voldaan wordt, namelijk dat tot op een afstand van 10 maal de breedte van de goot vanaf de versmalling in de aanvoergoot geen verstoringen aanwezig zijn. Tevens is gebleken dat het verschil in waterhoogten tussen die aan het begin van de aanvoergoot voor het bemonsteringsapparaat en die voor de versmalling van de Venturi-goot minimaal is als het bemonsteringapparaat eveneens op een afstand van 10 x de breedte van de goot voor de versmalling geplaatst wordt.Hydraulic EngineeringCivil Engineering and Geoscience
Utopia and Reform in the Enlightenment
No full textIn this detailed study of the republican tradition in the development of the Enlightenment, the central problem of utopia and reform is crystallized in a discussion of the right to punish. Describing the political situation in Europe in the seventeenth and eighteenth centuries, the author shows how the old republics in Italy, Poland and Holland stagnated and were unable to survive in the age of absolutism. The Philosophes discussed the ideal of republicanism against this background. They were particularly influenced by the political and religious radicalism of John Toland, which had survived the English Restoration and was then reaching Europe. Professor Venturi traces the debate on the penal laws and the attempt to relate utopian ideas of society to the practical problem of dealing with man in society, which culminated in the assertion by many Philosophes that an unjust social system necessitated harsh penal laws, thereby rejecting the possibility of reform.</jats:p
Real World Performance Evaluation of Transcatheter Aortic Valve Implantation
No full textBackground: The aim of this research is to describe the performance over time of transcatheter aortic valve implantations (TAVIs) in a high-volume center with a contemporary, real-world population. Methods: Patients referred for TAVIs at the University Hospital of Verona were prospectively enrolled. By cumulative sum failures analysis (CUSUM), procedural-control curves for standardized combined endpoints-as defined by the Valve Academic Research Consortium-2 (VARC-2)-were calculated and analyzed over time. Acceptable and unacceptable limits were derived from recent studies on TAVI in intermediate and low-risk patients to fit the higher required standards for current indications. Results: A total of 910 patients were included. Baseline risk scores significantly reduced over time. Complete procedural control was obtained after approximately 125 and 190 cases for device success and early safety standardized combined endpoints, respectively. High risk patients (STS >= 8) had poorer outcomes, especially in terms of VARC-2 clinical efficacy, and required a higher case load to maintain in-control and proficient procedures. Clinically relevant single endpoints were all influenced by operator's experience as well. Conclusions: Quality-control analysis for contemporary TAVI interventions based on standardized endpoints suggests the need for relevant operator's experience to achieve and maintain optimal clinical results, especially in higher-risk subjects
- …
