M. Gopal

Bio: M. Gopal is an academic researcher from Ohio University. The author has contributed to research in topics: Slug flow & Two-phase flow. The author has an hindex of 4, co-authored 4 publications receiving 40 citations.

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part I: Flow Visualization

Abstract: This paper reports the application of novel, digital image analysis techniques in the study of slug flow characteristics, under dynamic conditions in two-phase gas-liquid mixtures. Water and an oil of viscosity 18 cP were used for the liquid phase and carbon dioxide was used for the gas phase. Flow in a 75-mm i.d., 10-m long acrylic pipeline system was studied. Images of slugs were recorded on video by S-VHS cameras, using an audio-visual mixer. Each image was then digitized frame -by-frame and analyzed on a SGI workstation. Detailed slug characteristics, including liquid film heights, slug translational velocity, mixing length, and, slug length, were obtained.

Multiphase Flow-Enhanced Corrosion Mechanisms in Horizontal Pipelines

Abstract: Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of gas bubbles (Gopal et al, 1997) Corrosion rate measurements have been made at pressures up to 079 MPa and temperatures up to 90°C, and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude number This paper describes mass transfer measurements under multiphase slug and annular flows using the limiting current density technique The experiments are carried out in a 10-cm-dia pipe using a 001-M potassium ferro/ferricyanide solution in 13 N sodium hydroxide for the liquid phase and nitrogen in the gas phase Froude numbers of 4, 6, and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows The results show instantaneous peaks in the mass transfer rates corresponding to the pulses of bubbles in slug flow Instantaneous increases of 10–100 times the average values in multiphase flow are seen Peaks are also seen in instantaneous mass transfer rates in some annular flows

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part II: Modeling Results

Abstract: A definition is given for a Froude number in the liquid film ahead of the slug and it is seen that slug characteristics are strongly influenced by the Froude number. The mechanisms in the mixing zone of the slug are described in detail and are shown to be a function of the film Froude number. It is shown that the Hubbard and Dukler model for mixing length is inadequate. A new expression is proposed for the slug mixing length as a function of the film Froude number.

Investigation of Flow Regime Transitions in Large-Diameter Inclined Pipes

Abstract: Multiphase oil/water/gas flow regime transition studies are carried out in a lO-cm i.d., I8-m long pipe at inclinations of ::t2 deg at system pressures between 0 to 0.79 MPa. The results are compared to those of other researchers, and the effects of pressure, inclination, and liquid viscosity are shown. The water cut of the liquid has some effects on the transition from stratified to slug flow. Increasing the water ~ut results in the transition occurring at higher liquid velocity at the same gas velocIty. Water cut has little effect on the slug/annular transition for low viscosity oil used. The system pressure has a moderate effect on the transition from stratified to slug and slug to annular. For the transition from stratified to slug, increasing the system pressure requires higher liquid velocity. The transition from slug to 'annular occurs at lower liquid velocity with increasing the system pressures. The inclination of the pipe has little effect on the transition from slug to annular flow. Increasing the inclination causes the transition to occur at approximately the same gas velocity at the same liquid velocity. The experimental results show a good agreement with Wilkens' model.

Continuous-Flow Tubular Crystallization in Slugs Spontaneously Induced by Hydrodynamics

Abstract: A novel continuous crystallizer design is described with the potential to provide improved control of crystal properties, improved process reproducibility, and reduced scale-up risk. Liquid and gas are introduced into one end of the tube at flow rates selected to spontaneously generate alternating slugs of liquid and gas that remain stable while cooling crystallization occurs in each liquid slug. Mixing within each stable self-circulating slug is maximized by controlling the slug aspect ratio through specification of liquid and gas flow rates. The crystallizer is designed so that nucleation and growth processes are decoupled to enhance the individual control of each phenomenon. Coaxial or radial mixers combine liquid streams to generate seed crystals immediately upstream of the growth zone where nucleation is minimized, and crystal growth is controlled by the varying temperature profile along the length of the tube. The slug-flow crystallizer design is experimentally demonstrated to generate large uniform...

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