Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
25
1
2013
MODELING OF THE DROPLET ENTRAINMENT FRACTION IN ADIABATIC GAS-LIQUID ANNULAR FLOW
1-23
Abdelsalam
Al-Sarkhi
King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia
C.
Sarica
The University of Tulsa, Tulsa, OK, USA
The entrainment fraction, FE, in annular flow is defined as the fraction of the total liquid flow in the form of droplets in the gas core. Its prediction is important for estimation of the pressure drop, liquid holdup, and dry-out in annular flow. A new correlation for the entrainment fraction as a function of the Weber number based on the superficial gas velocity is developed. The proposed correlation contains only two constants that are, in essence, based only on the superficial gas and liquid velocities. The present correlation was validated against the experimental data and models available in the literature. The correlation was found to predict the experimental data available in the literature for different pipe diameters, low and high pressures, single and multi-component fluids, and horizontal to vertical flow, and does not allow negative entrainment values at low liquid flow rates or a very large value that would exceed the maximum possible value.
ONE-DIMENSIONAL MODEL FOR NUMERICAL SIMULATION OF ANNULAR FLOW IN HORIZONTAL AND VERTICAL PIPES
25-56
Mohammad
Emamzadeh
Faculty of Energy and Mechanical Engineering, Shaihd Beheshti university
Raad I.
Issa
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
The results of the application of a general mathematical model to simulate two-phase annular gas-liquid flow in both horizontal and vertical pipes are presented. The method is based on the transient one-dimensional two-fluid model wherein the two phases are considered as (i) liquid layer and (ii) a mixture of the gas and liquid droplets in which the droplet concentration in the mixture is treated as a flow variable. The model entails the introduction of a scalar transport equation for the conservation of mass of liquid droplets accounting for liquid transfer to and from the film liquid layer. The rates of the entrainment and deposition of droplets are supplied as closure relations derived from modifications of models existing in the literature. Using the new model, the droplet entrained fraction (E), which is defined as the ratio of the droplet to the total liquid mass flow rate, can be computed. The purpose of the present paper is to validate the entrainment and deposition closure models used through comparisons of the computed entrained fraction against different experimental data found in the literature for steady, fully developed flow. The present comparisons show satisfactory agreement with most of the data with discrepancies of around ±30%. What is significant is that both horizontal and vertical annular flows can be predicted to this degree of accuracy using the same model.
A MODIFIED CHISHOLM'S INTERACTION FACTOR FOR AIR-WATER TWO-PHASE FLOW THROUGH A HORIZONTAL PIPE
57-78
Mahesh J.
Vaze
Mechanical Engineering Department, S V National Institute of Technology Surat, India
Jyotirmay
Banerjee
Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, Gujarat 395007, India
Among several methods proposed by various researchers to estimate two-phase frictional pressure drop, the procedure developed by Lockhart-Martinelli is widely used in industry. The Lockhart-Martinelli correlation for the two-phase frictional multiplier, however, does not directly incorporate the influence of the flow pattern on the pressure drop. Thus, it does not provide an accurate estimation of pressure drop for all the two-phase flow regimes. Efforts have been made by various researchers to improve the Lockhart-Martinelli correlation so as to account for the influence of phase distribution. The present work is an experimental investigation to establish the influence of phase distribution on two-phase frictional multiplier for air-water two-phase flow through a horizontal pipe. The mass flow rate of air and water are varied to obtain stratified, wavy-stratified, slug, plug, and annular flow regimes. Pressure signals are recorded at different stations along the length of the pipe for 640 combinations of air and water superficial Reynolds numbers to develop the modified correlation. The modified correlation shows better accuracy for prediction of two-phase pressure drop for all the two-phase flow regimes.
A MODEL FOR PREDICTING THE TRANSITION BETWEEN STRATIFIED AND ANNULAR FLOW IN HORIZONTAL PIPES
79-100
Mohammad
Emamzadeh
Faculty of Energy and Mechanical Engineering, Shaihd Beheshti university
Raad I.
Issa
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
In this paper a mechanistic one-dimensional approach to the prediction of the transition from stratified to annular two-phase flow in horizontal pipes is presented. Such transition is deemed to occur when the liquid film wets the whole of the pipe circumference. This is determined from a consideration of the effects of the interface curvature, which is modeled here by a double circle geometric configuration incorporating a correlation for the calculation of the wetted angle. The model is cast in the framework of the two-fluid model and incorporated in a numerical procedure. The model also accounts for local droplet entrainment and deposition between the film and the gas core. With the model, it is possible to predict the growth and spread of the liquid film around the circumference along the pipe in a dynamic manner; transition to annular flow eventually occurs in a seamless manner when the film wets the whole of the circumference. The results are evaluated by comparing the numerical prediction of the transition from stratified to annular flow with an experimentally determined flow pattern map found in the literature. The comparison shows satisfactory agreement with experimental data.