Showing papers on "Slug flow published in 1992"

Modeling of two-phase slug flow

Abstract: Slug flow belongs to a class of intermittent flows that has very distinctive features Even if the inlet conditions are stationary, the flow as seen by an observer, is an unsteady phenomenon, dispersed flow appearing alternately with separated flow These two states follow in a random-like manner, inducing pressure and velocity fluctuations In vertical flow, the large bUbbles-typically longer than, say, one pipe diameter-rise with a round shaped front followed by a cylindrical main body surrounded by an annu­ lar liquid film In the literature, these long bubbles are frequently referred to as Taylor bubbles or Dumitrescu bubbles In the film, gravity forces the

Upward Vertical Two-Phase Flow Through an Annulus—Part II: Modeling Bubble, Slug, and Annular Flow

Abstract: This paper reports that mechanistic models have been developed for each of the existing two-phase flow patterns in an annulus, namely bubble flow, dispersed bubble flow, slug flow, and annular flow. These models are based on two-phase flow physical phenomena and incorporate annulus characteristics such as casing and tubing diameters and degree of eccentricity. The models also apply to the new predictive means for friction factor and Taylor bubble rise velocity. Given a set of flow conditions, the existing flow pattern in the system can be predicted. The developed models are applied next for predicting the flow behavior, including the average volumetric liquid holdup and the average total pressure gradient for the existing flow pattern. In general, good aggrement was observed between the experimental data and model predictions.

The Current Status of Theoretically Based Approaches to the Prediction of the Critical Heat Flux in Flow Boiling

Abstract: The phenomena governing the critical heat flux (CHF) in flow boiling in ducts and rod bundles vary with the flow pattern. Separate models are needed for dryout in annular flow, wall overheating in ...

Slug flow mitigtion for production well fluid gathering system

Abstract: Oil and gas well production flow is gathered in field common line manifolds and conducted through a separator to make a coarse separation of gas from liquid and minimize slug flow in the conduits leading from the manifolds to further separation, treatment and pumping facilities. A liquid level signal transmitter provides a signal to a valve controller which controls separate liquid and gas discharge flow control valves or a variable speed pump to maintain a set point level of liquid in the separator. Liquid level control is accomplished automatically by varying the flow from the fluid discharge conduit which is connected to the lower pressure flow line, which is usually the gas flow line. Manifold pressures may be sensed to prevent exceeding a predetermined pressure in the manifolds and the well flow lines.

Slug Flow Characteristics and Their Effect on Corrosion Rates in Horizontal Oil and Gas Pipelines

Abstract: The flow characteristics of slug flow and their effect on the corrosion rates are examined experimentally in a 100 mm diameter, horizontal, Plexiglass pipeline. The system was maintained at a pressure of 2 bars and temperature of approximately 35 0C. Mter initial tests with oil only and water only, 80% water and 20% oil, and 60% water and 40% oil mixtures were examined. Carbon dioxide was used as the gas. Using the stationary slugs described by Jepson1,2, the mean wall shear stress and turbulent intensity at 7 different axial and three circumferential locations were measured using flush mounted TSI hot f1lm anemometer probes. The regions included the f1lm region ahead of the slug, the mixing zone at the slug front, and a short distance into the slug body. The oil, water, and carbon dioxide fractions were measured across a vertical diameter using. a sampling probe. Corrosion rates at the top and bottom of the pIpe were measured using electrical resistance probes. Pressure gradients across the slug front were also taken. The results clearly show that the slug front is a highly turbulent region that has large wall shear stresses at the bottom of the pipe. The wall shear stress decreases with circumferential position but increases with increasing oil fraction in the fluids. For a Froude number of 12, the shear stress for water only is 26 N/m2. For the mixture of 60% water and 40% oil a value of 97 N/m2 is attained. These are much greater than anticipated. Instantaneous values are much larger than this. The corrosion rates are much greater than those predicted by usual laboratory methods such as rotating cylinde~s or disks. The rates are shown to be grea;est at the bottom of the pIpe and correspond to the regions of high wall shear. Corrosion rates increase with an increase in oil concentration at the same Froude number. It is concluded that the wall shear stress associ~ted with the slug front is sufficient to continuously remove corrOSIonproducts from the pipe wall.

Slug flow eliminator and separator

Abstract: A method and apparatus for substantially eliminating slug flow and for separating the liquid phase of a liquid/gas mixture from the gas phase thereof is provided. A deceleration table contained within a housing decelerates liquid slugs and causes entrained gas to separate therefrom. The decelerated liquid passes through orifices in the deceleration table and is subsequently discharged from the housing while the separated gas rises above the deceleration table and is separately discharged from the housing. The liquid and gas phases can be recombined or permanently separated.

A study of terrain-induced slugging in two-phase flow pipelines

Abstract: The presence of gas and liquid flowing simultaneously in pipelines made of several uphill and downhill sections can lead to the formation of long liquid slugs which are blown from one pipeline section to the next due to gas pressure. This terrain-induced slugging gives rise to undersirable unsteady flow conditions. In this paper, a transient two-fluid model is validated for conditions of terrain-induced slugging. This model contains new correlations, for the drag coefficient and the virtual mass force for the slug flow regime, that were presented in previous papers. An experimental study of terrain-induced slugging in a laboratory scale pipeline, made of two uphill and two downhill sections, is also reported. This provides data for the model validation. The model predicts all the major features of the data, and is in good quantitative agreement as well.

Flow of viscoplastic fluids in a rotating concentric annulus

Abstract: A difficulty in any flow calculation with viscoplastic fluids such as Bingham fluids is the determination of possible plug zones in which no deformation occurs. This paper investigates the flow in a concentric annulus when there is both an axial and tangential flow, the tangent flow arising from rotation of the inner cylinder of the annulus. The flow is analyzed by considering flow in a slot, for which an analytical solution is given, and by solving the full problem numerically. It is shown that when the boundary is set in motion an applied pressure gradient will always cause flow. If the applied pressure gradient is small compared to the yield stress of the fluid then the full solution predicts the existence of plugs attached to the outer wall of the annulus. The slot approximation fails to predict this feature. For larger pressure gradients the two solutions are in good agreement. The analytical calculation gives a simple expression for the critical rate at which the wall has to move to reduce the plug size to zero.

Effects of gas density on the structure of liquid jets in still gases

Abstract: A theoretical and experimental study of the near jet-exit region of nonevaporatin g round liquid jets in still gases is described, emphasizing effects of ambient gas density in the atomization breakup regime where liquid breakup begins right at the jet exit. Mean liquid volume fraction distributions were measured for 9.5-mm-diam water jets in still air at pressures of 1-8 atm. Mixing was strongly affected by the gas/liquid density ratio and the degree of flow development at the jet exit, with the largest gas/liquid density ratio and fully developed turbulent pipe flow yielding the fastest mixing rates. Flow properties were predicted using the locally homogeneous flow approximation, where relative velocities between the phases are assumed to be small in comparison to mean flow velocities. Predictions were in good agreement with measurements, including representation of effects of gas/liquid density ratio and flow development at the jet exit, but only at relatively high mixture fractions. In contrast, separated flow effects caused predictions to overestimate rates of flow development at low mixture fractions.

Holdup for two-phase flow of gas-non-newtonian liquid mixtures in horizontal and vertical pipes

Abstract: The paper deals with the experimental investigations carried out to evaluate holdup for gas-non-Newtonian (pseudoplastic) liquid mixtures in vertical and horizontal flow in pipes. Correlations developed predict holdup in slug flow regime with acceptable statistical accuracy. Des travaux experimentaux ont ete effectues dans le but d'evaluer la retention de melanges gaz-liquides non newtoniens (pseudoplastiques) en ecoulement dans des tubes horizontaux et verticaux. Les correlations proposees predisent la retention en regime piston avec une precision statistique acceptable.

Dispersed-phase structure of pressure-atomized sprays at various gas densities

Abstract: The dispersed-phase structure of the dense-spray region of pressure-atom ized sprays was studied for atomization breakup conditions, considering large-scale (9.5 mm initial diameter) water jets in still-air at ambient pressures of 1, 2, and 4 atm, with both fully developed turbulent pipe flow and nonturbulent slug flow at the jet exit. Drop sizes and velocities and liquid-volume fractions and fluxes were measured using holography. Measurements were compared with predictions based on the locally homogeneous flow (LHF) approximation as well as recent correlations of drop sizes after primary breakup of turbulent and nonturbulent liquids. The dispersed-flow region beyond the liquid surface was relatively dilute (liquid-volume fractions less than 0.1%), with significant separated-flow effects throughout, and evidence of near-limit secondary breakup and drop deformation near the liquid surface. Turbulent primary breakup predictions were satisfactory at atmospheric pressure, where the correlation was developed, but failed to predict observed trends of decreasing drop sizes with increasing gas density due to aerodynamic effects; in contrast, the laminar primary breakup predictions successfully treated the relatively small effects of gas density for this breakup mechanism. Effects of liquid turbulence at the jet exit were qualitatively similar to single-phase flows, yielding faster mixing rates with increased turbulence levels even though drop sizes tended to increase as well. LHF predictions within the dispersed-flow region were only qualitatively correct due to significant separated-flow effects, but tended to improve as the ambient pressure and the distance from the jet exit increased.

Gas absorber and refrigeration system using same

Abstract: An absorption refrigeration system with ammonia as refrigerant and a salt solution as absorbent operates with an improved margin of safety to crystallization of the salt solution by incorporating an absorber having a precooler and narrow nozzles. The precooler serves to additionally lower the temperature of the salt solution before it is caused to absorb ammonia exothermically, and the nozzles are for injecting the salt solution into ammonia gas flows, while maintaining the solution on the upstream side at relatively high pressure. The flow characteristics of the gas-liquid mixture through absorber tubes change from churn flow to slug flow and finally to bubble flow. A blower is provided for recycling a portion of the ammonia gas back to the absorber for optimizing absorption efficiency. The precooler and the absorber tubes are cooled evaporatively to reduce operating temperatures and system operating costs.

Study on the Vibrational Characteristics of a Tube Array Caused by Two-Phase Flow—Part 1: Random Vibration

Abstract: This paper presents the experimental results on turbulent buffeting forces generated both by air-water flow and by steam-water two-phase flow for the extreme pressure conditions up to 5.8 MPa and temperatures reaching 272oC, the explanation of the mechanism producing these forces, and a method for evaluating tube response caused by two-phase flow. The main source of the buffeting forces in slug or froth two-phase flow is recognized to be the impact forces caused by the intermittently rising water slugs. The slug speed and the fluid forces acting on a tube are estimated, together with an estimation of the period of the occurrence of the rising water slug. The accuracy of this estimation method is proved by comparing the theoretical response with the measured one.

The relationship between void waves and flow regime transition

Abstract: The results of an extensive experimental and analytical study on the relationship between void waves and flow regime transition are presented, in particular, the bubbly/slug flow regime transition. It is shown that void wave instability signals a flow regime transition.

Transition to slug flow in horizontal pipes

Abstract: The transition to slug flow in horizontal pipelines is reviewed. Experimental observations of the interface prior to slugging and of the effect of physical properties and pipe diameter on the transition are described. Theoretical progress in understanding the initiation of slugging through a stability analysis is summarized. Theories are classified by whether they invoke a long-wave assumption and whether they include viscous and nonlinear effects. Despite considerable progress, a general theory for predicting the initiation of slugging for arbitrary fluids in pipelines of varying size and pressure is far from being realized.