Experimental study of the characteristics of an upward two-phase slug flow in a vertical pipe

Characteristics of the slug flow, mean void fraction, liquid slug and Taylor bubble lengths; and structure frequency were all extracted from the void fraction time series. Average void fractions at nine axial positions have been measured on a 6 m long (and 34 mm diameter) pipe test section by using conductance probes.For the flow conditions used, bubbly (with spherical cap bubble), slug/plug and churn/semi-annular flow patterns were observed. These observations were also confirmed by using statistical numbers.Time series analysis of the mean void fraction and its corresponding PDFs show that the effect of the mixer on the flow becomes, practically, negligible from a distance of 95 pipe diameter.It was found that, generally, the structure velocity can be well predicted from other available correlations in the literature.The theoretical model of Brauner and Ullmann was used to estimate the liquid in slug void fraction. It was inferred that this model is able to predict well the liquid slug void fraction; thus, it can be considered as one of the useful methods for predicting such parameter and to ascertain slug flow regime.The total pressure gradient was found to decrease with increasing gas superficial velocity

Experimental investigation of the vertical upward single and two-phase flow pressure drops through gate and ball valves

This paper presents an experimental investigation of the pressure drop through valves in vertical upward flows. Experiments were carried out using a 1¼" (DN 32) ball and a gate valve. Five opening areas have been investigated from fully open to the nearly fully closed valve, using air with a superficial velocity of (0-3.5 m/s) and water (0.05-0.91 m/s). These ranges cover single-phase and the bubbly, slug and churn two-phase flow regimes. It was found that for the single-phase flow experiments, the valve coefficient increases with the valve opening and is the same, in both valves, for the openings smaller than 40%. The single-phase pressure drop increases with the liquid flowrate and decreases with the opening area. The two-phase flow pressure drop was found considerably increased by reducing the opening area for both valves. It reaches its maximum values at 20% opening for the ball valve and 19% opening for the gate valve. It was also inferred that at fully opening condition, the two-phase flow multiplier, for both valves, has been found close to unity for most of the tested flow conditions. For the 40 and 20 % valve openings the two-phase multiplier decreases in the power-law with liquid holdup for the studied flow conditions. Models proposed originally for evaluating the pressure drop through an orifice in single-phase and two-phase flows were also applied and assessed in the present experimental data

Experimental investigation of a vertically downward two-phase air-water slug flow

The present experimental work investigates the vertical downward two-phase slug flow in a transparent vertical pipe of 34 mm internal diameter. The gas and liquid superficial velocities are in the range of 0–3.27 m/s and 0.015–1.4 m/s respectively. The cross-sectional averaged void fraction has been measured at seven positions along the test section by the intermediary of the conductance probe technique.The results of the development of the void fraction time-series and Probability Density Function along the tube are presented. A good accordance was found between the experimental data and the line transitions of the flow pattern map proposed by (Usui, 1989). We also present results of the structure velocity of the slug flow, where the distribution parameter is found to be lower than unity. A new correlation for the prediction of slug frequencies is also proposed. It agrees well with the data collected in this study with +_10% error

Vertical upward and downward churn flow: Similarities and differences

Investigation of downward two-phase flows received less attention compared to the vertical upward flows. Downward flows are found in many industries and facilities including; oil/gas production, nuclear industry and petroleum refinery/production facilities such as evaporators, chemical reactors and distillation towers. A thorough understanding of the flow dynamic characteristics occur in such transportation lines, process plants and units is very crucial in terms of design, operation, production and safety.In the current work, air-water two-phase churn flow in a 34 mm I.D. pipe was investigated for two configurations of vertical upward (51 cases) and downward (48 cases). Several conductance probes and pressure transducers were used to measure cross-sectional averaged void fraction time series, and pressure drop along the pipe, respectively.The main objectives of the work were to investigate the similarities and dissimilarities between vertically upward and downward churn flow and specifically understand how gravity could affect the behavior of liquid structures present within the flow. To quantify this, different parameters such as Probability Density Function, distribution coefficient in the drift-flux model, structural velocity, slippage number, dimensionless pressure gradient etc. were used.It was noticed that in both configurations, dimensionless pressure gradient and slippage number demonstrated a strong correlation with the mixture Froude number. There were, however, discrepancies in Probability Density Functions (PDFs) and structural velocities of flow in the two orientations