Showing papers on "Slug flow published in 1980"

Modelling flow pattern transitions for steady upward gas-liquid flow in vertical tubes

Abstract: Models for predicting flow pattern transitions during steady gas-liquid flow in vertical tubes are developed, based on physical mechanisms suggested for each transition. These models incorporate the effect of fluid properties and pipe size and thus are largely free of the limitations of empirically based transition maps or correlations.

Theoretical Prediction of Onset of Horizontal Slug Flow

Abstract: A criterion for the onset of a slug flow in a horizontal duct is derived theoretically. A potential flow analysis is carried out by considering waves of finite amplitude. The stability criterion is obtained by introducing the wave deformation limit and the “most dangerous wave” concept in the stability analysis. The present theoretical criterion for slug formation shows very good agreement with a large number of experimental data and with some empirical correlations.

Experimental Investigation of Air-water Two Phase Upflow across Horizontal Tube Bundles : Part 1, Flow Pattern and Void Fraction

Abstract: The present paper deals with experiments of air-water mixtures flow pattern and their mean void fraction in horizontal tube bundles. The tube bundles are staggered with equilateral triangular arrangement of three different pitch/tube diameter ratios (1.4, 1.28, 1.08) and they consist of six different tube rows (7, 9, 11, 13, 15, 20) for each ratio. Experimental ranges are as follows ; Superficial air velocity (cm/s) 1.5 - 50 Superficial water velocity (cm/s) 0.032 - 0.32 Flow direction upward flow The observed mixture flows can be classified into 1. bubbly flow 2. slug flow 3. froth flow 4. spray flow with liquid forming a film around the tubes and spraying from tube to tube downstream. Besides, a simple empirical equation for void fraction is proposed.

Surface-Bed Heat Transfer in a Fluidised Bed at High Pressure

Abstract: Heat transfer experiments were carried out between a small vertical heated surface and a gas-fluidised bed. The bed diameter was 100 mm; average particle diameters ranged from 0.060 mm to 0.700 mm; pressures from 1 bar to 25 bar were employed.

Potential Improvements in the Field of Large Particle Fluidization

Abstract: This paper deals with two new techniques which seem to be very efficient for “fluidizing” large bodies. After a brief description of the mechanical and thermal gross behaviour of each of the two systems, general potential applications of the devices are discussed.

The Stability of a Cylindrical Elastic Membrane of Biological Tissue and the Effect of Internal Fluid Flow

Abstract: Some stability problems for finitely deformed elastic membranes are considered. The first part treats the stability of a stretched elastic membrane which is orthotropic in its reference state. The stability criteria for a uniformly deformed orthotropic plane sheet under conditions of dead loading are obtained. The potential energy for a uniformly extended and inflated circular cylindrical membrane (the preferred directions being axial and circumferential) with axially symmetric deformations and under constant pressure is found to have the same form as that for an isotropic material. Stability criteria for a long tube are obtained and some numerical results are given through stability diagrams using strain energy functions appropriate for biological tissues. The effect on stability of the flow of an incompressible fluid through the tube is considered next. To model the internal fluid motion, small perturbations superimposed on a state of steady flow with velocity profiles of a slug flow and a Poiseuille flow are assumed, and a one-dimensional analysis is used as a third approach. Equations for the fundamental frequencies of vibration are derived. The fluid motion is found to have a stabilizing or destabilizing influence on the membrane depending on the approach used. The results are compared to Rayleigh’s results for a circular liquid jet and they are found to agree for the slug flow and the Poiseuille flow models.

Transient Behavior of a Gas Slug : 1st Report, On an ascending gas slug with rapid growth

Abstract: The transient behavior of a gas slug with rapid growth, which is encountered in evaporators operated under the atmospheric pressure, was investigated using a simulated flow system of air-water. The growth of a gas slug is considered to be brought about in two stages: the first is caused by an instantaneously enhanced pressure due to violent evaporation in a highly superheated liquid, and the second by a rapid decrease in static head as the gas slug ascends the vertical tube connected to the water-separator kept at a vacuum. The simulation of the first stage of expansion was made by introducing a gas slug, having a greater pressure than that of the water near the gas slug, into the test tube. It was observed that the gas slug flows upwards generating a damped oscillation: i.e., the tail end of the gas slug ascends linearly, but the top fluctuates remarkably. An analysis proposed of this transient flow can predict the complex motions of the gas slug with sufficient accuracy.

Decay Heat Removal under Boiling Condition in a Pin-Bundle Geometry

Abstract: Decay heat removal capability under boiling condition was investigated using an electrically heated 37-pin bundle test section. The flow was driven by natural circulation force of the out-of-pile sodium loop SIENA in O-arai Engineering Center, PNC. As the heater power was increased, the two-phase flow regime changed from bubbly flow to slug flow and then to annular or annular mist flow. In 15 runs, dry-out was not observed in the average exit quality region of less than 0.5. The results indicated the existance of a large "boiling window" for low flow rate and low power conditions.