Showing papers on "Slug flow published in 1987"

A Mechanistic Model for Two-Phase Vertical Slug Flow in Pipes

Abstract: This paper presents the formulation of a mechanistic model for slug flow in vertical pipes. The equations required to determine holdup, the relevant velocities and pressure loss are presented. The model is fully deterministic and the pressure drop predictions of the model are compared to experimental field data for oil and gas and gas and water wells. For the 143 data points, the model shows an average percent difference of 4.83 percent, which is felt to be excellent.

Severe slug flow in offshore flowline/riser systems

Abstract: Small-scale experiments are described that simulate the unstable two-phase flow pattern of severe slugging often found in offshore flowline/riser systems. In particular, the effects of riser-base supplementary gas lift, flowline orientation, and liquid viscosity have been examined. To place the tests in perspective, the physics of severe slugging is discussed, including a method for scaling between model and prototype situations. Test results are compared with a simple hydrodynamic computer model.

Method and reaction apparatus for effecting controlled chemical reactions

Abstract: METHOD AND APPARATUS FOR CONTROLLED CHEMICAL REACTIONS ABSTRACT OF THE DISCLOSURE A method and apparatus for effecting accelerated chemical reactions at elevated temperatures and pressures including wet oxidation of materials in waste streams. An influent waste stream or first reactant is directed through a long tubular coil within a containment vessel with a second reactant being added to the influent. The now rates for the gas and liquid components of the waste stream are set to cause plug or slug flow of the waste stream through the tubular coil. The curvature of the coil tends to induce a secondary flow in the liquid such that the liquid tends to travel in a spiral thereby providing more intimate mixing with the gaseous phase. The containment vessel may be partitioned to form a series of successive compartments to permit different temperature gradients to be applied to successive sections of the tubing coil across its length. Alternatively, a tube in tube construction for the tubular coil permits counter current heat exchange between the waste stream within the inner tube and the returning stream within the outer tube. Multiple injection and extraction points are provided along the path of the tubular coil to permit gas, liquid or solid reactants to be added or extracted as desired. The tubular coil provides an excellent environmental container for the reaction stream and is extremely suitable for temperature control to permit continuous heat input, autogenic operation and continuous heat extraction. A tubular reaction coil having a plurality of generally elliptical loops is also provided with each loop having a substantially vertical upcorner portion and a substantially vertical downcorner portion. In one embodiment, the elliptical tubular reaction coil is a concentric assembly having an inner passage and an outer annulus. The preferred method includes flowing a liquid reactant stream into the elliptical reaction coil along with a gas reactant at an elevated temperature and pressure. The flow pattern of the reactants is regulated to provide slug and plug flow in the substantially vertical portions of the elliptical reaction coil loops to produce excellent mixing and mass transfer characteristics. In a modification, the reaction coil is provided within a containment vessel having a heat exchange medium. Heat can be supplied to the reaction coil or extracted by the heat exchange medium to better control the reaction.

Study of a downward bubbly flow in a vertical pipe

Abstract: This paper reports on an experimental study of downward bubble-diffused concurrent flow in a vertical pipe. Two-phase flow was induced by introducing gas into a liquid with a special mixer which made it possible to obtain a gas-liquid flow with consistent bubble size. Visualization was performed by photography and flow rate was monitored by friction transducers. Shear stress and hydraulic conductivity were determined for various flow rates and Reynolds numbers. It was found that the stabilizing effect of the gas phase is determined by the fact that the flow rate pulsations introduced into the liquid flow have a negative sign; that the flow rate of the liquid near the bubbles, in other words, is lower than the mean flow rate of the liquid. This effect is not seen in ascending flows.

Integral Equation Solution for Internal Flow Subjected to a Variable Heat Transfer Coefficient

Abstract: A solution methodology based on integral equations is presented for the problem of heat transfer to laminar duct flow subjected to an axial variation of the external heat transfer coefficient. The technique offers an efficient and accurate calculation procedure which combines standard analytical method with a simple numerical integration. In order to examine the effect of external finning, results are calculated for the cases of a stepwise periodic and a harmonic variation of the heat transfer coefficient for both fully developed laminar flow and slug flow. The general procedure is applicable to wide class of problems in heat and mass transfer involving variable boundary condition parameters.

Flow pattern and pressure drop in tees

Abstract: Visual observations of single and two-phase dividing flow and measurements of the gas-liquid separation behaviour, void fraction and pressure drop were performed in T-junctions having a horizontal run and vertical branch. Both tees used were geometrically similar, in scale 1:4. Plug, slug and stratified flow were observed in horizontal tubes causing mainly a total separation of the gas flow in the branch. For plug and slug flow the diverging flow pattern was stable, while for the stratified flow strong oscillations were measured. Furthermore a calculation method was developed for the prediction of the form-resistance pressure drop, based on the Gardel correlation for single-phase flow taking account of the two-phase flow pattern and the flow restriction in the tee-branch, which gives satisfactory results for all our measured data from both tees.

A microgravity boiling and convective condensation experiment

Abstract: A boiling and condensing test article consisting of two straight tube boilers, one quartz and one stainless steel, and two 1.5 m long glass-in-glass heat exchangers, on 6 mm ID and one 10 mm ID, was flown on the NASA KC-135 0-G aircraft. Using water as the working fluid, the 5 kw boiler produces two phase mixtures of varying quality for mass flow rates between 0.005 and 0.1 kg/sec. The test section is instrumented at eight locations with absolute and differential pressure transducers and thermocouples. A gamma densitometer is used to measure void fraction, and high speed photography records the flow regimes. A three axis accelerometer provides aircraft acceleration data (+ or - 0.01G). Data are collected via an analog-to-digital conversion and data acquisition system. Bubbly, annular, and slug flow regimes were observed in the test section under microgravity conditions. Flow oscillations were observed for some operating conditions and the effect of the 2-G pullout prior to the 0-G period was observed by continuously recording data throughout the parabolas. A total fo 300 parabolas was flown.

Turbulent Slug and Velocity Field in the Inlet Region for Pulsatile Pipe Flow : Fluids Engineering

Abstract: This paper describes the characteristics of a turbulent slug and the velocity field in the inlet region for pulsatile pipe flow. Experimental conditions of the present study were arranged systematically by pulsation frequency and velocity amplitude ratio A1. The experimental results regarding the onset of a turbulent slug, the propagation behavior of the slug, and the distributions of velocity and turbulence intensity inside the slug were compared with those for a turbulent patch in a pulsatile boundary layer on a flat plate. A close analogy was shown between them. When A1 was smaller than 0.608, the velocity distribution for the laminar region outside a slug was approximated by an analytical solution previously presented for pulsatile laminar flow with a smaller A1.

Separator control apparatus

Abstract: PURPOSE:To attain a constantly stabilized separation of gas and liquid by providing a detector for gas and liquid of slag flow in an inlet pipe means for the slug flow for the adjustment of the amount of slag flow into a separator according to the detected values. CONSTITUTION:The mixed flow of gas and liquid consisting of crude oil and the accompanying gas are introduced from an inlet pipe means 1 to a separator 2 for separation thereof by differences in the specific gravity. A supersonic flow meter 11 is provided in the inlet pipe means 1, adapted for detection of the flow amount of gas and liquid. The separator 2 has a manometer 7 and adjusting valves 5 and 8, and the flow is controlled to exert a constant pressure in the separator 2 based on the values detected by the supersonic flow meter 11 and the manometer 7. In addition, the separator 2 is provided with a level meter 10 which can always effect the gas and liquid separation at fixed levels by adjusting the adjusting valves 5 and 8.

Microgravity two-phase flow regime modeling

Abstract: A flow pattern or flow regime is the characteristics spatial distribution of the phases of fluid in a duct. Since heat transfer and pressure drop are dependent on the characteristic distribution of the phases, it is necessary to describe flow patterns in an appropriate manner so that a hydrodynamic or heat transfer theory applicable to that pattern can be chosen. The objective of the present analysis is to create a flow regime map based on physical modeling of vapor/liquid interaction phenomena in a microgravity environment. In the present work, four basic flow patterns are defined: dispersed flow, stratified flow, slug flow, and annular flow. Fluid properties, liquid and vapor flow rates, and pipe size were chosen as the principal parameters. It is assumed that a transition from one flow pattern to another will occur when there is a change in the dominant force which controls that flow pattern. The forces considered in this modeling are surface tension force, both force, inertial force, friction, and turbulent fluctuations.

Assessment of a modified interfacial drag correlation in two-fluid model codes

Abstract: Analysis of low flooding rate experiments and a number of boil-off experiments with the RELAP5/MOD2 computer code has shown that the code underpredicts the collapsed liquid level and, consequently, overpredicts the liquid carryover. Recent analyses using several other codes, e.g., TRAC-BD1 and the French code CATHARE, have also resulted in the underprediction of collapsed liquid level histories. The discrepancy between the measurements and code predictions is attributed to the interfacial drag between the phases. A new interfacial drag formulation in the bubbly/slug flow regimes is incorporated in the RELAP5/MOD2 code. Better agreement with the measurements is obtained.

Hydrodynamics of Fischer-Tropsch synthesis in slurry bubble column reactors: Final report

Abstract: This report describes studies on hydrodynamics of bubble columns for Fischer-Tropsch synthesis. These studies were carried out in columns of 0.051 m and 0.229 m in diameter and 3 m tall to determine effects of operating conditions (temperature and gas flow rate), distributor type (sintered metal plate and single and multi-hole perforated plates) and liquid media (paraffin and reactor waxes) on gas hold-up and bubble size distribution. In experiments with the Fischer-Tropsch (F-T) derived paraffin wax (FT-300) for temperatures between 230 and 280/sup 0/C there is a range of gas velocities (transition region) where two values of gas hold-up (i.e., two flow regimes) are possible. Higher hold-ups were accompanied by the presence of foam (''foamy'' regime) whereas lower values were obtained in the absence of foam (''slug flow'' in the 0.051 m column, or ''churn-turbulent'' flow regime in the 0.229 m column). This type of behavior has been observed for the first time in a system with molten paraffin wax as the liquid medium. Several factors which have significant effect on foaming characteristics of this system were identified. Reactor waxes have much smaller tendency to foam and produce lower hold-ups due to the presence of larger bubbles. Finally, new correlationsmore » for prediction of the gas hold-up and the specific gas-liquid interfacial area were developed on the basis of results obtained in the present study. 49 refs., 99 figs., 19 tabs.« less

Designing piping systems for two-phase flow

Abstract: A wide range of industrial systems, such as thermosiphon reboilers and chemical reactors, involve two-phase gas-liquid flow in conduits. Design of these systems requires information about the flow regime, pressure drop, slug velocity and length, and heat transfer coefficient. An understanding of two-phase flow is critical for the reliable and cost-effective design of such systems. The successful design of a pipeline in two-phase flow, for example, is a two-step process. The first step is the determination of the flow regime. If an undesirable flow regime, such as slug flow, is not anticipated and adequately designed for, the resulting flow pattern can upset a tower control system or cause mechanical failures of piping components. The second step is the calculation of flow parameters such as pressure drop and density to size lines and equipment. Since the mechanism of fluid flow (and heat transfer) depends on the flow pattern, separate flow models are required for different flow patterns.

Patterns of liquid lump behaviors in upward gas-liquid two-phase flow.

Abstract: The results of an experimental investigation of liquid lump behaviors are presented for vertical upward gas-liquid two-phase flow. Liquid lumps were classified into liquid slug, huge wave, disturbance wave and ephemeral large wave by analysing time-spatial signals of cross-sectional averaged liquid holdup, which were detected at twelve locations along a 25.8mm inside diameter tube. Two types of behaviors were found for liquid slug and huge wave : one shows axilly steady movement, and the other is transient as a liquid slug rapidly disappears or drastic deformation of a huge wave occurs with time. An evaluation method for the development of cap bubble flow in liquid slug coalescence is proposed. There exist various behaviors of ephemeral large waves such as forward, backward and complicatedly direction-changing movement depending on the flow conditions. It is shown how these behaviors correspond to reverse flow length of liquid film and averaged gas length.

Absorption during slug flow in a vertical pipe

Abstract: The coefficients of mass transfer accompanying absorption of carbon dioxide gas by distilled water in the slug flow regime are measured.

Thermo-hydraulic Instability Due to a Blockage of Flow by Vapor in a Boiling Two-phase Flow System (Experimental Results Concerning the Mechanism) : Heat Transfer, Combustion, Power, Thermophysical Properties

Abstract: Thermo-hydraulic instability has been investigated experimentally in a boiling two-phase flow system composed of a vertical N-shaped boiling channel and an adiabatic bypass between an inlet plenum and an outlet plenum, using Freon 113. Instability caused by the blockage of flow by vapor, which cannot be found in Boure's classification of two-phase flow instabilities, has been observed. The flow maps in each section, static characteristics, stable flow limits and characteristics of this instability have been studied under various conditions to clarify the mechanism. The inlet velocity decreases when a vapor slug combining in the inverted U-shpaed bend obstructs the flow. The vapor slug flowing into the downcomer increases the void fraction in the downcomer, resulting in increased gravitational loss. Consequently, flow instability is brought about.