Film formation in two‐phase annular flow

Abstract

The liquid film in annular two-phase flow is maintoined by droplet movement to and from the gas core and by wave action. This work examines droplet movement and its effect on the liquid film. Film formation and movement both axially and circumferentially were investigated by using transient techniques.The simultaneous flow of a gas and a liquid in a closed conduit occurs frequently in engineering practice. If the conduit is a horizontal pipeline and the phases are flowing concurrently, there are seven visually classified flow patterns that can exist ( 2 ) , depending on the mass flow rates of each phase, the physical properties of each phase, and the pipeline geometry. For high mass flow rates of gas (for example, 10,000 lb./hr. x sq.ft. for air) and a ratio of the liquid mass flow rate to the gas mass flow rate of 100 or less ( 4 ) , the flow pattern that will exist is called annularIn fully developed annular flow, the gas flows as a high speed core down the center of the pipeline. The liquid flows in two ways: in an annular film around the pipe wall and as droplets entrained by the gas core. For a given liquid rate, the fraction of the liquid flowing as entrained droplets increases as the gas rate is increased. There is a dynamic equilibrium between the droplets in the gas core and the film. New droplets are continually being formed at the gas-liquid interface, and droplets in the core continually impinge on the film. This phenomenon is known as interchange.The effect of these entrained droplets on heat and mass transfer in annular flow is of obvious importance, since the droplets greatly increase the interfacial area between the two phases. Moreover, because of interchange, new droplets are continually being generated at the gas-liquid interface, while droplets which have been in the gas core return to the film. This convected transport will greatly affect the overall rates of mass, momentum, and heat transfer.In order to quantitatively predict the effect of interchange, it would be necessary to have the following information:1. The rate of droplet generation and its circumferential 2. Information on the movement of droplets while they 3. The rate of droplet deposition and its circumferential This paper presents experimental results from a 1 in. I.D. horizontal pipeline on the rate of droplet deposition and its circumferential variation. Two kinds of interchange from the gas core to the liquid film were measured. One is a value of interchange which is an average value for the entire pipe circumference. In fully developed annular flow, this will also be the circumferential averaged value of interchange from the film to the core because of the dynamic equilibrium which exists. In the paper, this kind of interchange is denoted by I and has units of pounds per second per foot of pipe. The second kind of interchange measured is a value for a specified circumferential position; it is denoted by G and has units of pounds per second per square foot of inside pipe surface. pow.variation.are in the gas core. variation. ...

Extended Analytical Turbulent Diffusion Model for Particle Dispersion and Deposition in a Horizontal Pipe: Comparison with CFD Simulation

“…Except for very large particles (>100 μm), for which the motion is totally dominated by gravity and the particle's initial entrainment velocity [1,2,11], there is no theoretical analysis of this deposition flux in a two-dimensional geometry. Anderson and Russell [1] developed a semiempirical expression to correlate deposition and entrainment fluxes, but only for the top half in the tube.…”

Erosion Analysis for the Misaligned U2 Nozzle and its Connector Block

“…Droplets of liquid are torn from the film and carried suspended in the gas. Under any given conditions within this range, a dynamic equilibrium may be established between the rate of droplet formation and the rate of droplet condensation by impingement on the existing film [9]. This phenomenon of droplet interchange is of considerable importance in transient multiphase heat and mass transfer studies.…”

Analytical and CFD Investigation of Turbulent Diffusion Model for Particle Dispersion and Deposition

“…Except for very large particles (>100 m), for which the motion is totally dominated by gravity and the particle's initial entrainment velocity [6][7][8] , there is at present no theoretical analysis of this deposition flux in a twodimensional geometry. Anderson and Russell 6 developed a semi-empirical expression to correlate deposition and entrainment fluxes, but only for the top half in the tube.…”

“…The model used to derive this expression assumes that droplet deposition is caused by deterministic drop trajectories intersecting the liquid film. The work of 8 is an extension of the work of 7 . In both approaches no effect of turbulence was taken into account because only very large particles were considered.…”

“…The motion of the particles is then statistically similar to Brownian motion. [7] Particle free fall velocity, v g , is considered stationary. The assumptions of homogeneous turbulence and uniform, axial fluid velocity are more or less justified by assumption (viii).…”