Fernando de Almeida França

The use of drift-flux techniques for the analysis of horizontal two-phase flows

Abstract New data is presented for horizontal air/water two-phase flow having various flow regimes. It is shown that drift-flux models are able to correlate these data and that the drift velocity, V g j , is normally finite.

An experimental study of three-phase flow regimes

Abstract Three-phase flow regimes for an air/water/oil system flowing in a horizontal pipe line were observed and flow regime maps were constructed. Superficial velocities, ranging from 15 to 5000 cm/s for air ( j a ) and from 0.4 to 66 cm/s for water ( j w ), were investigated. The superficial velocity of the immiscible oil “phase” ( j o ) was kept constant at three discrete values, 4.3, 9 and 24 cm/s. Water- and oil-based wavy, plug, slug and stratifying-annular flow regimes were observed. Many interesting new flow regime configurations not seen in two-phase flow were found.

Statistical method to calculate local interfacial variables in two-phase bubbly flows using intrusive crossing probes

Abstract This paper presents a statistical method to calculate local interfacial variables in two-phase gas–liquid bubbly flows from data taken with double-sensor intrusive probes. Firstly, one derives the geometrical relationship existing between the apparent and actual bubble velocity for a single spherical bubble flowing in a multidimensional flow field. The apparent variables are obtained from the experimental data when one assumes that the bubble trajectory is aligned with the probe axis. A similar relationship exists for the intersected chord length and bubble diameter. Then, the analysis is extended to a swarm of bubbles. The ratio between the apparent to the actual bubble velocity and the intersected chord length to the bubble diameter appear now as probability density functions. The experimental data were taken for air–water bubbly flow regime in a vertical round pipe with a double tip electrical probe. Processing the phase density function generated by the bubble events, one determines distribution function of the bubble velocity and intersected chord length, termed the apparent distributions. The variables of interest, actual bubble velocity and diameter, come out of the solution of a linear system of equations relating the probability function of the measured and estimated bubble velocity and bubble size ratio. The probability density function of the actual bubble velocity and bubble diameter, plus the bubble frequency, add up to various interfacial properties calculated with this technique: the void fraction, the bubble velocity, the bubble size, the interfacial area density and the interface velocity fluctuation intensity. To validate the method, the paper compares local and area averaged quantities with previously published results, volumetric measurements and extensively used correlation.

The cyclone gas–liquid separator: operation and mechanistic modeling

Abstract A research program was aimed to develop the cyclone gas–liquid separator. The program focused on testing scaled-down models and prototypes and developing mechanistic modeling for the phase separation and flow hydrodynamic processes. This paper describes the operational principles of the cyclone separator, discloses laboratory and field data and presents the modeling foundations. The laboratory tests were performed in downsized models operating with mixtures of air and water or water-based viscous liquids. The analysis of experimental data, extensive flow visualization and the identification of the operational constraints set the basis for the mechanistic modeling. The capability of the model to represent the separation processes was checked against field tests conducted with actual fluids in full dimension prototypes. Based on these results, prospective field applications are also presented.

Mechanistic Modeling of the Convective Heat Transfer Coefficient in Gas-Liquid Intermittent Flows

The development of a mechanistic procedure to estimate the convection heat transfer in horizontal gas-liquid intermittent—or slug—flow is presented. In broad terms, the mean convective heat transfer coefficient is calculated following an averaging procedure based on the unit cell model of the slug flow pattern. The flow parameters (i.e., unit cell frequency, liquid slug and elongated bubble length and velocity, and liquid hold-up) were obtained from empirical data for air/water flows in a 15 m-long, 25.4 mm ID copper pipe and for natural gas (mostly methane and ethane) and oil or water flows in an actual size, 200 m-long, 150 mm ID steel pipe. A time-averaging procedure based on the unit cell parameters was then used to calculate the mean convective heat transfer coefficient. The slug flow parameters taken on the small scale air/water loop and the actual size pipeline were used for comparisons. Heat transfer data from the small scale air/water loop were used to validate the results calculated using the averaging procedure. Finally, the approach herein proposed also showed good agreement with previously published data and well-known correlations.

The phase distribution of upward co-current bubbly flows in a vertical square channel

In this work one shows experimental data and numerical results of the void fraction distribution in vertical upward air-water bubbly flows in a square cross-section channel. To measure the void fraction distribution one used a single wire conductive probe. The averaged void fraction ranged from 3.3% to 15%; the liquid and the gas superficial velocities varied from 0.9 m/s to 3.0 m/s and 0.04 m/s to 0.5 m/s, respectively. The experimental results for the void fraction distribution were compared with numerical calculation performed by an Eulerian-Eulerian implementation of the Two-Fluid Model. In this work one performs the turbulence modeling with three approaches: using an algebraic model, the k-e two-phase model and the k-e two-phase two-layer model. Comparisons between the experimental and numerical data revealed, in general, good agreement.

Horizontal Slug Flow in a Large-Size Pipeline: Experimentation and Modeling

The knowledge of the slug flow characteristics is very important when designing pipelines and process equipment. When the intermittences typical in slug flow occurs, the fluctuations of the flow variables bring additional concern to the designer. Focusing on this subject the present work discloses the experimental data on slug flow characteristics occurring in a large-size, large-scale facility. The results were compared with data provided by mechanistic slug flow models in order to verify their reliability when modelling actual flow conditions. Experiments were done with natural gas and oil or water as the liquid phase. To compute the frequency and velocity of the slug cell and to calculate the length of the elongated bubble and liquid slug one used two pressure transducers measuring the pressure drop across the pipe diameter at different axial locations. A third pressure transducer measured the pressure drop between two axial location 200 m apart. The experimental data were compared with results of Camargos1 algorithm (1991, 1993), which uses the basics of Dukler & Hubbards (1975) slug flow model, and those calculated by the transient two-phase flow simulator OLGA.

Improved two-phase model for hydraulic jet pumps

A new model is proposed to predict the performance of hydraulic jet pumps, HJP, when pumping two-phase gas-liquid mixtures. The model performance is compared with Petrie et al. (World Oil, Nov. 83) and Jiao et al.s (SPEPE, Nov. 90) model, using as input data the set of measurements taken by Jiao (1988) when experiencing an industrial HJP The present model results from the application of the one dimensional conservation law of mass, momentum and energy to the gas-liquid flow throughout the HJP. It differs from the previous published ones because it takes into account time flow of the two-phase compressible homogeneous mixture along the different parts of the device. It is not just an adaptation of a model originally developed for single phase flows, as the existent ones. Until now, most models representing the flow of a gas-liquid mixture in a HJP were adapted from models developed for incompressible single phase flows. The gas compressibility, for instance, is fully considered, as in Cunninghams paper (J. Fluids Eng., Sep. 74), when modeling a jet pump driven by a gas. The solution of the proposed model requires the knowledge of two constant energy dissipation factors, for the flow inside the nozzle and throat. Best values for these factors were obtained performing a regression analysis over Jiaos data 3 . The results showed a consistently better agreement with the experimental data than those delivered by the existing models, over the full range of the operational variables.

Using Genetic Algorithm and Simplex Method to Stabilize an Oil Treatment Plant Inlet Flow

This paper presents a hybrid approach, composed of a genetic algorithm and a linear programming method, to achieve an efficient pipeline network operation. The pipeline network optimization consists of the determination of pump scheduling over a short-term horizon, usually one or more days ahead. The resulting mathematical problem has a dynamic and combinatorial characteristic, in which a sub-optimal solution was obtained through these two mathematical tools in a short computational time. The approach was applied in a Pipeline Network to a study case based on the Patagonia Argentina, which is comprised of 16 tanks and linked pumps, with 66 kilometers of pipelines, that transport the production of more than 100 wells to a pre-processing plant. The goal was to obtain a constant input flow rate at the plant respecting physical and chemical processes requirements.Copyright

Hydrodynamic studies on a cyclonic separator

The paper describes the operational principles, the modeling foundations and some laboratory results of the gas-liquid separation process taking place within a cyclonic gas-oil separator. The centrifugal and the gravity forces, acting on the flow of the gas-liquid mixture, are the main driving mechanism to separate the phases. A research program, conducted by PETROBRAS and UNICAMP, was aimed to the hydrodynamic processes occurring within the equipment. Laboratory data were obtained from down size scale models operating with mixture of air and liquid with different viscosities. The basis for the modeling is launched and a discussion regarding the limitations and constraints of the operation is presented in light of the experimental results. Prospective field applications, based on the extension of the laboratory results to actual fluids and full dimension prototypes, are also presented.