175,708 research outputs found
Investigação experimental de escoamentos bifásicos com mudança de fase de uma mistura binária em um tubo de venturi
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2014Escoamentos bifásicos em singularidades (válvulas, orifícios ou tubos de Venturi) são encontrados em diversas aplicações de engenharia. Exemplos industriais de escoamentos bifásicos com a presença da cavitação (flashing) em dispositivos de expansão podem ser encontrados em usinas geotérmicas (bocais), sistemas emergenciais (válvulas de alívio), sistemas de refrigeração (válvulas, tubos curtos e tubos capilares) e dispositivos de medição de vazão (tubos de Venturi). Um aparato experimental foi projetado e construído a fim de estudar os escoamentos bifásicos de misturas binárias com mudança de fase por cavitação em um bocal convergente-divergente (tubo de Venturi). Discute-se a influência do fluxo mássico da mistura, da concentração mássica do componente volátil na fase líquida e do grau de sobrepressão (subsaturação) na entrada da seção de teste sobre as distribuições de pressão estática e temperatura ao longo da seção de teste. A utilização de uma seção de teste transparente permitiu a observação visual, tanto da mudança de fase líquido-vapor como do escoamento bifásico, por meio de imagens capturadas a alta velocidade. O método de Velocimetria por Imagem de Partícula (PIV) possibilitou a avaliação quantitativa dos campos de velocidades e das taxas de dissipação viscosas dos escoamentos. Resultados experimentais obtidos para as misturas de R-134a (componente volátil) e óleo lubrificante POE ISO 10 (componente não-volátil) mostraram que a viscosidade da fase líquida tem um efeito significativo sobre a queda de pressão na garganta e sobre a recuperação de pressão na seção divergente, sendo esta última inversamente proporcional à concentração de refrigerante na fase líquida. A análise visual da cavitação de bolhas no bocal convergente-divergente revelou que a ocorrência do escoamento bifásico na garganta e a jusante dela é bastante sensível a mudanças nas condições do escoamento. As bolhas de vapor presentes no escoamento atuaram, juntamente com a rodamina B, como partículas rastreadoras para o PIV. Verificou-se que à medida que a concentração mássica aumenta, os níveis de velocidade na região da garganta diminuem. Os resultados experimentais obtidos pelo método PIV permitiram concluir que a taxa de dissipação viscosa é alterada majoritariamente pela viscosidade da mistura.Abstract: Flows through singularities (e.g., valves, orifices or Venturi tubes) are encountered in several engineering applications. Industrial examples of two-phase flashing flows in expansion devices can be found in geothermal power plants (nozzles), emergency systems (safety relief valves), refrigeration systems (valves, short tubes and capillary tubes) and flow metering devices (Venturi tubes). An experimental facility was designed and constructed in order to study two-phase flashing flows of binary mixtures in a converging-diverging nozzle (Venturi tube). The effects of mass flux, concentration of the volatile component in the liquid phase and inlet sub-saturation (over pressure) on the axial distributions of static pressure and temperature is discussed. A transparent test section enabled visual observation of the two-phase flow in the Venturi by means of high-speed visualization (HSV) and quantitative assessments of the velocity field and the viscosity dissipation rates by means of a particle image velocimetry (PIV) method. Experimental results generated for mixtures of R-134a (volatile component) and POE ISO 10 lubricating oil (non-volatile component) showed that the liquid phase viscosity has a significant effect on both the throat pressure drop and pressure recovery in the diverging section, with the latter being directly proportional to the refrigerant concentration in the liquid phase. Visual analysis of bubble cavitation in the converging-diverging nozzle revealed that the occurrence of two-phase flow in the throat and downstream of it is quite sensitive to changes in the conditions of the flow. R-134a vapor bubbles and rhodamine B acted as PIV tracking particles. PIV analysis showed that as refrigerant concentration increases, Venturi throat velocity levels decreases. Viscosity dissipation rates are mainly altered by the mixture viscosity
Wet Gas Flow Metering Technique Using a Venturi With Conductance Sensors
No full textWet gas metering is becoming an increasingly important problem to the oil and gas industry. Much research has been done to measure the water and gas flow rates of two-phase flows using a Venturi meter. The Venturi meter is a favoured device for metering of unprocessed wet natural gas production flows. In this thesis, various combinations of techniques have been employed in annular gas-liquid two phase flows to measure the flow parameters (e.g. liquid film thickness, gas volume fraction and gas and water flow rates). One of the most useful techniques which was used and which has proven attractive for many previous multiphase flow applications is the electrical conductance technique used in conjunction with the Venturi.
In this thesis, research has been done on designing a novel wet gas flow metering technique, which combines a Venturi with conductance sensors at the inlet and throat to measure the gas and the water flow rates and gas mass flow rate in vertical annular (wet gas) flows. Two ring conductance sensors at the inlet of the Venturi were used to measure the film velocity by cross correlation, one of the inlet ring conductance sensors was used to measure the film thickness and the inlet gas volume fraction. A ring conductance sensor at the throat was used to measure the gas volume fraction at the Venturi throat. A digital level sensor was also used to measure the film thickness (and the gas volume fraction) at the inlet of the Venturi. The reason for measuring the film thickness, the film velocity, the gas volume fraction at the inlet and the throat of the Venturi was to determine the gas and water flow rate and the gas mass flow rate in annular wet gas two phase flow using a variety of mathematical models of Venturis.
This work included both static ‘bench’ and flow loop experiments. In the flow loop experiments, which were limited to air-water two-phase flow, the test section included a Venturi meter with a 50mm inlet diameter with conductance sensors at inlet and the throat. Reference measurements of the water and air were made with a turbine flow meter and a variable area flow meter respectively. A Honeywell DP cell sensor was used to measure the differential pressure between the inlet and the throat of the Venturi.
A NI USB 6009 data acquisition device was used to integrate the system measurements and to control the operation of the overall Venturi system. A program was created using Labview software to read the input signals from the throat conductance ring sensor; the inlet conductance ring sensors; the digital level sensor; the DP cell sensor; the variable area flow meter and the turbine meter. From these measurements the gas volume fraction at the Venturi inlet and the throat, the differential pressure between the inlet and the throat of the Venturi, the film thickness and the film velocity at the Venturi inlet were calculated and were used with appropriate mathematical models to calculate the gas volumetric rate; gas mass flow rate; and the water mass and volumetric flow rates. Reference values of the gas a water flow rates were also calculated from the turbine meter and variable area flow meter outputs
Modeling of a homogenous gas-water two phase flow through a Venturi and vertical pipe (A prediction of pressure drop sign change in two phase flow)
No full textIn two phase flow, differential pressures technique can be used to measure the volume fraction of the gas phase. In the
case where no restriction is available in the pipeline, the differential pressure technique can be used only in vertical or
inclined pipelines. Two phase air-water pressure drop across a Venturi meter may change its sign from positive to negative
due to change in the compressibility of the gas phase. In other words, the inlet of the venturi (upstream section) is not
always positive as in a single phase flow. A new model to predict the sign change of the two phase pressure drop across a
Venturi was developed and checked against data recently obtained from an air-water flow rig at the University of
Huddersfield. The predication of a two phase pressure drop through a vertical pipe was also investigated and compared with
experimental data. Four sets of data were investigated. In each set the water volumetric flow rate was fixed while the gas
volumetric flow rate was varied (see table-1). It was inferred from the model proposed in this paper and the experimental
data that the sign of the differential pressure drop across Venturi meter and parallel pipe for homogenous air-water flow
depends mainly on the parameters C1, C2, Uh and K. Therefore, if C1 > C2 then, the differential pressure drop across Venturi
tends to be negative and if Uh
2 > K then the differential pressure drop across a 1m long Perspex pipe will be negative
Medição de vazão de escoamentos bifásicos utilizando tubo de Venturi ou placa de orifício associados a um sensor de fração de vazio com campo elétrico girante
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica.A medição em tempo real das vazões mássicas em escoamentos bifásicos líquido-gás, sem a separação das fases, é a solução mais adequada para a redução dos custos e dos desperdícios, aumento da produtividade e melhora da qualidade da produção da tradicional indústria do petróleo e gás natural, justificando a substituição dos custosos e tradicionais separadores de fases. Nesse contexto, é proposto um sistema de medição de vazão composto de um tubo de venturi ou placa de orifício associados a um sensor de fração de vazio média, por impedância elétrica. O sensor opera no modo resistivo e é alimentado por um campo elétrico girante em quatro pares de eletrodos. Os resultados obtidos são comparados com as vazões medidas por rotâmetros instalados antes da seção em que é feita a mistura de ar e água. Apesar de não ser o objetivo principal do trabalho, foi demonstrada a capacidade de se utilizar o sensor de fração de vazio para fazer a identificação dos regimes de escoamento bifásico. Os testes foram realizados em uma bancada experimental de escoamentos bifásicos adiabáticos ar-água a pressões máximas de 3 bar e títulos inferiores a 0,011, na direção vertical ascendente e na horizontal. As vazões mássicas máximas para a água e o ar foram de 4000 kg/h e 50 kg/h, respectivamente, e os padrões de escoamento testados foram o borbulhado, o pistonado e o anular. O trabalho é dividido em duas partes: na primeira, é apresentada a calibração do sistema de medição de fração de vazio através de vávulas de fechamento rápido, sendo analisados os sinais provenientes do sistema transdutor, e, na segunda parte, é apresentado um estudo comparativo entre o venturi e a placa de orifício em sistemas bifásicos ar-água. Na última, são analisados os parâmetros bifásicos como o título, o fator de escorregamento e a vazão mássica total a partir de correlações e modelos da literatura. A comparação entre as vazões previstas por correlações e os resultados experimentais para os padrões borbulhado e pistonado indicam valores de RMS dos desvios de 6,8 % para a correlação de Chisholm (1967), com tubo de venturi na direção vertical ascendente, e de 5,5 % para a correlação de Zhang et al. (2005), com placa de orifício na mesma direção. When it comes to gas-liquid flow in the oil and gas conventional industry, the two-phase mass flow rate measurement on real time without separating them is the desirable solution in order to achieve cost reduction, avoid waste, increase production and reach excellence in the oil and gas transport. The fiscal requirement for precise measurements is the greater motivator to support research. With this purpose, a measurement system consisting of impedance void meter, a nonintrusive conductance type, applied to determine the mean void fraction and forecast method for identifying flow patterns coupled to venturi or orifice plate flow meter is employed to predict the phases flow rates. Results are compared with the flow rates measured by single-phase meters installed previously to the air-water mixture point. The measurement system was evaluated by an air-water experimental facility. Experiments included vertical upward and horizontal flow; annular, bubbly, churn and slug patterns; void fraction ranging from 2% to 95%; water flow rate ranging up to 4000 kg/h; air flow rate ranging up to 50 kg/h; and quality ranging nearly up to 1%. The work is divided into two major parts. The first one is devoted to the calibration of the void fraction measurement system by means of quick closing valves. The second one is devoted to the comparisons between venturi and orifice plate meters in air-water two-phase flow. Quality, slip ratio and overall mass flow rate analysis are performed in this second stage. The frictional root-mean-square errors (RMS) of mixture mass flow rate in vertical upward flow through venturi were 6,8 % for Chisholm (1967). In the orifice plate, the RMS errors of vertical flow were 5,5 % for Zhang et al. (2005)
"Intelligencija" e "intellectuels": un punto di vista russo sul caso Dreyfus
No full textDiscutendo la nota tesi di Michael Confino secondo cui la specificità del concetto di intelligencija, affermatosi nella cultura russa negli anni ’60 dell’Ottocento, già da fine secolo si identificava invece totalmente con il valore europeo-occidentale del termine “intellettuale” (un valore più sociale che etico-politico), questo testo analizza invece l’uso della parola nelle corrispondenze di Nikolaj Rusanov inviate da Parigi alla “Russkoe bogatstvo”, la principale rivista legale del neo-populismo russo, negli anni del caso Dreyfus e della nascita in Francia del termine intellectuels. Da esse risulta, ancora negli anni a cavallo tra Otto e Novecento, non solo una forte coscienza russa della specificità dell’intelligencija, ma anche un’identificazione di quella specificità con la scoperta francese del ruolo sociale dell’intellettuale eticamente e politicamente impegnato, per altro considerata un tardivo adeguamento al modello russo
Stapled anopexy versus transanal haemorrhoidal dearterialization for haemorrhoidal disease: a three-year follow-up from a randomized study
No full textBACKGROUND: This randomized study compared the medium-term results of stapled anopexy (SA) and transanal hemorrhoidal dearterialization with anopexy (THD) in 4 homogeneous groups of patients, 2 with third- and 2 with fourth-degree hemorrhoids.
METHODS: Forty patients with third-degree and 30 with fourth-degree hemorrhoids were randomly submitted to SA (N.=20+15) and THD (N.=20+15), respectively. Clinical controls were done every 6 months from 1 to 42 months after the operation, with incidence of recurrent hemorrhoids as primary outcome measure. Operative time, complications, pain, time to return to normal activity, costs, Short Form-36, and overall patient satisfaction were also evaluated.
RESULTS: Frequencies of preoperative obstructed defecation symptoms and prolapse recurrence were higher in patients with fourth-degree hemorrhoids, and SA was more effective than THD in reducing the risk of recurrence at 36±6 months follow-up (P=0.049). Operative time, complications, pain, and time of return to normal activity were similar in the 4 groups. Costs were significantly higher for SA in patients with fourth-degree hemorrhoids (P>0.01). A significant improvement of quality of life was observed in all groups, and no significant difference was found in overall patient satisfaction.
CONCLUSIONS: Both techniques are safe and effective in the mid-term period. SA is more effective in reducing prolapse and obstructed defecation symptoms in fourth-degree hemorrhoids, with the disadvantage of higher costs. Prolapse size and presence of obstructed defecation symptoms could be predictive criteria for choice of the best surgical technique
(Cite this article as: Venturi M, Salamina G, Vergani C. Stapled anopexy versus transanal hemorrhoidal dearterialization for hemorrhoidal disease: a three-year follow-up from a randomized study. Minerva Chir 2016;71:365-71
Chaotic Solutions in the Lucas model
No full textCHAOTIC SOLUTIONS IN THE LUCAS MODEL
In this paper we show that the investigation of limit set regular or chaotic is of central importance to economists who care about the long run impact of policies and institutions (see inter al. Lorenz H.W.,1989, Benhabib J. 1992, Medio A. 1992, Jarsulic M., 1993, Boldrin Michele, Nishimura Kazuo, Shigoka Tadashi, Yano Makoto 2000, Nishimura K., Shigoga T., Yano M, 2006). We use global bifurcation theory as understand complicated stability phenomena of a three-dimensional, economic financial models as a the well known simplified version of Lucas’s model. ( see also Benhabib J., and Nishimura K., 1979; Benhabib J., 1992; .Mattana P. and Venturi B. 1999; Fiaschi and Sordi, 2002; De Cesare L. and Sportelli M., 2004; Cai J., 2005, Neri and Venturi 2007).
We analyze the trajectories of this endogenous growth two sector model for some parameters values.
With the help of a numerical investigation we found a region in the parameter space that gives rise to a homoclinic orbit.
We point out that, on the basis of the Shil’nikov theorem assumptions, the presence of chaos is ensured in a parameter set where the homoclinic orbit occur
The economic implications of this analysis are discussed
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
An approach to the Venturi effect by historical instruments
No full textStudent understanding of the laws that describe the flow of a fluid is often hampered by a defective knowledge of basic classical mechanics (kinematics, statics, dynamics, and conservation laws) and by wrong common-sense ideas about quantities related to fluids, such as velocity and pressure. A pedagogical discussion about the Venturi effect, based on experiments inspired by historical instruments, may be an effective way to introduce students to these laws. In this paper, we discuss an approach to the understanding of the Venturi effect based on the study of historical instruments and on simple experiments. In particular, after a presentation of the Venturi effect, also from a historical point of view, we illustrate some interesting applications, the Venturi meter, the Bunsen burner, the Venturi vacuum pump, and propose some simple experiments
Antonio Venturi - verso
No full textBotanico: Venturi, Antonio (1805-1864).
Botanico e musicista valente.
Titolo ed estremi cronologici riportati manoscritti sul recto, dove compaiono anche le note: da un ritratto ad olio nell’Ist. music. "A. Venturi" in Brescia; procurò prof. U. Ugolini 1898.
Nota manoscritta sul verso: Da un ritratto ad olio esistente nell’Istituto musicale. "Ant. Venturi" in Brescia. A cura del prof. Ugolini VII.98.
Montata su cartone 162 x 110 mm.
1 fotografia : aristotipo ; 136 x 102 mm.
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