Showing papers on "Slug flow published in 1997"

Two-phase flow structure of sheet cavitation

Abstract: An experimental study of flow within sheet cavities is performed in a cavitation tunnel equipped with a Venturi-type test section. The flow is investigated by means of a double optical probe allowing void fraction, velocity, and chord length of the vapor structures to be measured. Laser velocimetery, wall pressure measurements, and visualization techniques are also used to characterize the liquid flow around the cavity. The consistency of the experimental results was checked though mass and momentum balances. The effects of Reynolds and cavitation numbers are analyzed. Special attention is given to the dynamic behavior of the flow, and to the vapor flow rate within the cavities. The measurements show a complex two-phase flow characterized by the presence of an extended reversed flow occurring along the solid surface and a regular decrease in void fraction along the cavity. The phase transitions seem to be mainly restricted by the dynamic of the bubbles and thermodynamic effects.

Comparison Of Ecn And Eis Measurement For Corrosion Monitoring Under Multiphase Flow Conditions

Abstract: Electrochemical Noise (ECN) and Electrochemical Impedance Spectroscope (EIS) measurements were made simultaneously in a 75 mm I.D., 10 m long acrylic pipeline using salt-water/carbon dioxide mixtures. Full pipe flow was studied for liquid velocities of 0.5, 0.75, 1.1, 1.5 m/s and slug flow for Froude numbers 4, 6 and 9. Experiments were carried out at a constant pressure of 136 kPa and temperature of 40 C. ECN data were measured with a fast auto zero resistance ammeter. The ECN technique is able to detect changes in flow regime, showing distinct differences between full pipe flow and slug flow. The choice of sampling rate when using ECN is very important. For slug flows, sampling rates as high as 100 Hz are necessary to include most of the transients in the flow. Distinct differences can be seen in the Fast Fourier Transforms where dominant frequencies exist which correspond to possible bubble action in the slug body. EIS can be used to measure corrosion rate in multiphase flows. It does show an increase in the corrosion rate with liquid flow rates for full pipe flow and Froude numbers for stationary slug flow. A simple statistical analysis of ECN response gives a correlation withmore » corrosion rate. These show ECN could be a very powerful tool for determining corrosion rate and corrosion mechanism in multiphase flow.« less

Flux enhancement by a continuous tangential gas flow in ultrafiltration hollow fibres for drinking water production: Effects of slug flow on cake structure

Abstract: A new process is proposed to reduce particulate membrane fouling by injecting air into the feed stream, creating a gas/liquid two-phase flow on the membrane surface. The injected air is supposed to form air slugs inside the hollow fibres; these slugs create high wall shear stresses and flow instabilities. These phenomena may prevent filtered particles from settling on the membrane surface, and so enhance the ultrafiltration flux. Experiments were carried out with clay suspensions in hollow fibre membranes. A range of air velocities and particle concentrations was examined. The air injection process led to an increase in the permeate flux, depending on the liquid velocity and transmembrane pressure, for all the various concentrations studied. For specific conditions, the flux can be increased by 155% using a critical gas velocity. Above this critical value, the flux is no longer enhanced. The air injection clearly modifies the cake structure, and seems to expand the cake. Evolutions of cake thickness, porosity and specific resistance with gas velocity are given and analysed.

Film profiles behind liquid slugs in gas-liquid pipe flow

Abstract: A comprehensive one-dimensional fully coupled hydrodynamic treatment of the film profiles behind liquid slugs in horizontal and inclined gas - liquid slug flow is presented. Experiments were performed in horizontal air - water pipes 32 and 50 mm in diameter, the smaller also being inclined to an angle of 5 degrees. Time traces of film thickness were produced with the use of a wire-probe technique. The experimental results are compared against the theory presented here, as well as previously reported hydrodynamic models. It is concluded that the film profiles calculated by the use of one-dimensional models are highly sensitive to the choice of input variables, for example, the slug translational velocity; however good agreement is achievable provided that consistent hydrodynamic equations and correct input variables are used. It is hoped that the work presented here will influence future mechanistic models of slug flow.

Continuous Synthesis of Titanium Dioxide Fine Particles Using a Slug Flow Ageing Tube Reactor

Abstract: A continuous reactor system for titanium dioxide fine particle synthesis has been proposed, in which a packed bed for the nucleation of fine particles was connected in series with a slug flow ageing tube for growth of the particles. By injection of nitrogen gas into the inlet of the ageing tube, the continuous liquid feed was separated into small portions so that slug flow was formed. Spherical unagglomerated fine particles of titanium dioxide were obtained using this reactor system, and the effectiveness of using slug flow was elucidated. The effects of some operation variables such as liquid flow rate in the ageing tube and tube diameter were also examined. The particles obtained under the slug flow condition had narrower particle size distribution than those under a laminar flow condition at any flow rate. Particle geometric standard derivation (GSD) was found to be as small as that obtained in a batch process. No quality difference in particle GSD exists between ageing tubes of 2 mm i.d. and 3 mm i.d. for the slug flow. Chronomal analysis assuming diffusion-controlled growth was applied and was found to be effective for simulating a continuous particle synthesis process of titanium dioxide.

Prediction of the flow regime transitions in high pressure, large diameter, inclined multiphase pipelines

Abstract: WILKENS~ ROBERT, JOSEPH. Ph.D. June 1997 Chemical Engineering Prediction of the Flow Regime Transitions in High Pressure, Large Diameter, Inclined Multiphase Pipelines Director of Dissertation: W. Paul Jepson In multiphase flows, flow regime determination has many design applications such as boiler tubes and oil and gas pipelines. This study focuses on the oil production from older wells in which brine and carbon dioxide gas are commonly present in the pipelines. Often these oil~ water, and gas mixtures create a highly corrosive environment for typical carbon steel pipelines. Since the highest corrosion rate occurs in slug flow, the ability to predict this flow regime becomes of great importance. The transitions from stratified to slug and from slug to annular flow are not well understood. Further, little data is available for flows in large diameter, multiphase pipes which include the effects of pressure and inclination. For this purpose, oil/water/gas tests were conducted in a 9.72-cm diameter, 18-m long pipe at inclinations of 0, ±2, and ±5° and pressures of 0.27, 0.45, and 0.79 MPa. The ratio of the translational velocity to the superficial mixture velocity was found to be about 2.0 for plug flow, 1.2 for slug flow, and 0.5 1.2 for pseudo-slug flow. The film Froude number in slug flow was found to increase with increasing gas flow rate to a value of about 18. The value then dropped as pseudo-slug flow was achieved. It again increased with gas flow rate until it reached a value of about 16, then annular flow ensued.