Eugênio Spanó Rosa

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.

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.

Modeling of free surface flow in a helical channel with finite pitch

The laminar fully developed free surface flow in a helical channel with finite pitch and rectangular section is modeled. The mass and momentum conservation equations are written in a local orthogonal system and solved numerically using the finite volume method. The free surface position, determined using the height of liquid method, compares favorably against the experimental data. The main and secondary velocity fields are determined as well as the friction factor for Reynolds number ranging from 352 to 856 Keywords : free surface flow, helical channel, HOL, finite volume method

The feedback effect caused by bed load on a turbulent liquid flow

Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains.Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains.

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.