Generation and Size Distribution of Droplet in Annular Two-Phase Flow

1983 ◽  
Vol 105 (2) ◽  
pp. 230-238 ◽  
Author(s):  
Isao Kataoka ◽  
Mamoru Ishii ◽  
Kaichiro Mishima
Keyword(s):  
Experimental Data ◽  
Size Distribution ◽  
Droplet Size ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Mechanistic Modeling ◽  
Dominant Factor ◽  
Phase Flow ◽  
Two Phase ◽  
Detailed Model

The mean droplet size and size distribution are important for detailed mechanistic modeling of annular two-phase flow. A large number of experimental data indicate that the standard Weber number criterion based on the relative velocity between droplets and gas flow predicts far too large droplet sizes. Therefore, it was postulated that the majority of the droplets were generated at the time of entrainment and the size distribution was the direct reflection of the droplet entrainment mechanism based on roll-wave shearing off. A detailed model of the droplet size in annular flow was then developed based on the above assumption. The correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data. A comparison with experimental data indicated that indeed the postulated mechanism has been the dominant factor in determining the drop size. Furthermore, a large number of data can be successfully correlated by the present model. These correlations can supply accurate information on droplet size in annular flow which has not been available previously.

Progress on Prediction of Bubbly Flows Around Ships

2016 ◽  
Author(s):  
J. Li ◽  
A. M. Castro ◽  
P. M. Carrica
Keyword(s):  
Experimental Data ◽  
Size Distribution ◽  
Two Phase Flow ◽  
Fluid Model ◽  
Bubbly Flows ◽  
Phase Flow ◽  
Flat Bottom ◽  
Two Phase ◽  
Practical Applications ◽  
Bubble Entrainment

This paper presents recent progress on prediction of bubbly flows around ships, including bubble entrainment modeling, bubble transport and numerical issues. The bubbly flow is described by a polydisperse two-fluid model that can predict the bubble entrainment locations and rates, bubble dissolution, breakup and coalescence rates, bubble velocities, turbulence quantities and bubble size distribution. To test the performance of the two phase flow model, several simulations are conducted on canonical bubbly flows with wave breaking. These well experimentally studied flows provide important information for the design of the bubble entrainment model, which is the weakest link in the model chain but crucial for prediction of the bubbly wake. The results are compared with experimental data to study the model’s accuracy and to calibrate the entrainment model constants. Full scale simulations for the flat bottom Kann boat and the Athena R/V are performed to evaluate the model under more complex flows of naval relevance that have considerable data available. It is found that the model calibrated with canonical problems predicts good results for Athena R/V, but the current turbulent entrainment model significantly underestimates the entrainment at the bow of Kann boat due to other entrainment mechanisms involved (entrainment due to impact, droplets, etc.). The breakup model, which currently considers turbulent mechanisms, underestimates the population of small bubbles in the boundary layer where strong shear is present. Finally, a grid study is carried on Athena R/V to test grid convergence. Void fraction and size distribution are compared against available experimental data and discussed in detail. Overall, the simulations show encouraging results considering the complexity of two phase flow involved in ship applications, and the model is proven to be grid independent, a very important property for practical applications.

scholarly journals MODELLING AIR AND WATER TWO-PHASE ANNULAR FLOW IN A SMALL HORIZONTAL PIPE

2016 ◽  
Vol 42 ◽  
pp. 1660158 ◽  
Author(s):  
JUN YAO ◽  
YUFENG YAO ◽  
ANTONINO ARINI ◽  
STUART MCIIWAIN ◽  
TIMOTHY GORDON
Keyword(s):  
Experimental Data ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Cfd Simulation ◽  
Two Phase Flow ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Two Phase ◽  
Horizontal Pipe

Numerical simulation using computational fluid dynamics (CFD) has been carried out to study air and water two-phase flow in a small horizontal pipe of an inner diameter of 8.8mm, in order to investigate unsteady flow pattern transition behaviours and underlying physical mechanisms. The surface liquid film thickness distributions, determined by either wavy or full annular flow regime, are shown in reasonable good agreement with available experimental data. It was demonstrated that CFD simulation was able to predict wavy flow structures accurately using two-phase flow sub-models embedded in ANSYS-Fluent solver of Eulerian–Eulerian framework, together with a user defined function subroutine ANWAVER-UDF. The flow transient behaviours from bubbly to annular flow patterns and the liquid film distributions revealed the presence of gas/liquid interferences between air and water film interface. An increase of upper wall liquid film thickness along the pipe was observed for both wavy annular and full annular scenarios. It was found that the liquid wavy front can be further broken down to form the water moisture with liquid droplets penetrating upwards. There are discrepancies between CFD predictions and experimental data on the liquid film thickness determined at the bottom and the upper wall surfaces, and the obtained modelling information can be used to assist further 3D user defined function subroutine development, especially when CFD simulation becomes much more expense to model full 3D two-phase flow transient performance from a wavy annular to a fully developed annular type.

Thermal-Hydraulics of OC-OTEC Spout Flash Evaporators

1992 ◽  
Vol 114 (3) ◽  
pp. 187-196 ◽  
Author(s):  
S. M. Ghiaasiaan
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Two Phase Flow ◽  
Mechanistic Model ◽  
Droplet Size Distribution ◽  
Momentum Conservation ◽  
Phase Flow ◽  
Two Phase ◽  
Conservation Equations ◽  
Size Groups

A mechanistic model was developed for the thermal-hydraulic processes in the spout flash evaporator of an OC-OTEC plant. Nonequilibrium, two-fluid, conservation equations were solved for the two-phase flow in the spout, accounting for evaporation at the gas-liquid interface, and using a two-phase flow regime map consisting of bubbly, churn-turbulent and dispersed droplet flow patterns. Solution of the two-phase conservation equations provided the flow conditions at the spout exit, which were used in modeling the fluid mechanics and heat transfer in the evaporator, where the liquid was assumed to shatter into a spray with a log-normal size distribution. Droplet size distribution was approximated by using 30 discrete droplet size groups. Droplet momentum conservation equations were numerically solved to obtain the residence time of various droplet size groups in the evaporator. Evaporative cooling of droplets was modeled by solving the 1-D heat conduction equation in spheres, and accounting for droplet internal circulation by an empirical thermal diffusivity multiplier. The model was shown to favorably predict the available single-spout experimental data.

On Instabilities in Horizontal Two-Phase Flow

1994 ◽  
Vol 59 (12) ◽  
pp. 2595-2603
Author(s):  
Lothar Ebner ◽  
Marie Fialová
Keyword(s):  
Differential Equation ◽  
Flow Regime ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Annular Flows ◽  
Flow Regime Maps

Two regions of instabilities in horizontal two-phase flow were detected. The first was found in the transition from slug to annular flow, the second between stratified and slug flow. The existence of oscillations between the slug and annular flows can explain the differences in the limitation of the slug flow in flow regime maps proposed by different authors. Coexistence of these two regimes is similar to bistable behaviour of some differential equation solutions.

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

1992 ◽  
Vol 114 (1) ◽  
pp. 14-30 ◽  
Author(s):  
E. F. Caetano ◽  
O. Shoham ◽  
J. P. Brill
Keyword(s):  
Flow Pattern ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubble Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Through ◽  
Physical Phenomena ◽  
Good Agreement

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 the new predictive means for friction factor and Taylor bubble rise velocity presented in Part I. 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 agreement was observed between the experimental data and model predictions.

scholarly journals Experimental data for the slug two-phase flow characteristics in horizontal pipeline

Data in Brief ◽  
2018 ◽  
Vol 16 ◽  
pp. 527-530 ◽  
Author(s):  
Abdalellah O. Mohmmed ◽  
Mohammad S. Nasif ◽  
Hussain H. Al-Kayiem
Keyword(s):  
Experimental Data ◽  
Two Phase Flow ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Two Phase

scholarly journals Investigation of representing hysteresis in macroscopic models of two-phase flow in porous media using intermediate scale experimental data

2017 ◽  
Vol 53 (1) ◽  
pp. 199-221 ◽  
Author(s):  
Abdullah Cihan ◽  
Jens Birkholzer ◽  
Luca Trevisan ◽  
Ana Gonzalez-Nicolas ◽  
Tissa Illangasekare
Keyword(s):  
Experimental Data ◽  
Porous Media ◽  
Two Phase Flow ◽  
Flow In Porous Media ◽  
Phase Flow ◽  
Two Phase ◽  
Intermediate Scale ◽  
Macroscopic Models
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