Defect and Diffusion Forum Vol. 348

Abstract: Multiphase flows commonly occur in the production and transportation of oil, natural gas and water. In this type of flow, the phases can flow in different spatial configurations disposed inside the pipe, so called multiphase flow patterns. The identification of flow patterns and the determination of the pressure drop along the pipe lines for different volumetric flows are important parameters for management and control of production. In this sense, this work proposes to numerically investigate the non-isothermal multiphase flow of a stream of ultraviscous heavy oils containing water and natural gas in submerged risers (catenary) via numerical simulation (ANSYS CFX 11.0). Results of the pressure, volumetric fractions and temperature distributions are presented and analyzed. Numerical results show that the heat transfer was more pronounced when using the largest volume fraction of gas phases.

Abstract: Accurate multi-phase flow solvers at low Reynolds number are of particular interest for the simulation of interface instabilities in the co-processing of multilayered material. We present a two-phase flow solver for incompressible viscous fluids which uses the streamfunction as the primary variable of the flow. Contrary to fractional step methods, the streamfunction formulation eliminates the pressure unknowns, and automatically fulfills the incompressibility constraint by construction. As a result, the method circumvents the loss of temporal accuracy at low Reynolds numbers. The interface is tracked by the Volume-of-Fluid technique and the interaction with the streamfunction formulation is investigated by examining the Rayleigh-Taylor instability and broken dam problem. The results of the solver are in good agreement with previously published theoretical and experimental results of the first and latter mentioned problem, respectively.

Abstract: This paper presents an experimental study of flow boiling heat transfer from carbon nanotube (CNT) structures in a two-phase cooling facility. Multi-walled CNT (MWCNT) structures of dimensions 80 mm × 60 mm were applied to a horizontal flow boiling channel. Two CNT structures with different properties viz. NC-3100 and MERCSD were tested with a dielectric liquid FC-72. The height of the CNT structures was fixed at 37.5 μm and tests were conducted at coolant mass fluxes of 35, 50, and 65 kg/m²·s under saturated flow boiling conditions. The experimental results show that the CNT structures enhance the boiling heat transfer coefficients by up to 1.6 times compared to the smooth aluminum surface. The results also show that the CNT structures increase significantly the Critical Heat Flux (CHF) of the smooth aluminum surface from 66.7 W/cm² to 100 W/cm².

Abstract: The present work aims to study convection and heat transfer and mass in a porous cubic cavity. The configuration considered is a cavity cube with vertical walls left and right are subjected to temperatures required while others are impermeable and adiabatic. We realized that the results depend on several characteristic parameters, and general correlations are established for the calculation of heat and mass transfer, according to various studied parameters. The study focuses on the influence of the control parameters on the structure of the flow, heat and mass transfer.

Abstract: The present study deals with the numerical analysis of heat transfer inside a lithium bromide solution flowing down between finely meshed plastic wire screens. These screens confine the flow through capillary action while allowing the water vapor transfer inside an innovative absorber technology. The complex menisci shape formed on the confinement grid level, where the surface tension forces are of first importance, are reconstructed by a volume of fluid (VOF) model. A continuum surface force model is used to account for the surface tension force. A static contact angle is used to define the wall adhesion. A new algorithm, consisting to set an unique constant temperature at the liquid/vapour interface and to determine the evolution of heat transfer characteristics over the simulation domain, has been implemented and validated by analytical solutions. A parametric study has been conducted to determine the effect of the inlet velocity and the geometrical parameters (wire diameter and the number of divisions).

Abstract: In recent years, attention has been given to the processes controlling the emission of oily effluents and their environmental impact. Many industrial processes generate large volumes of water contaminated with oil, called oily waters. The oily water must be treated before its discard in order to meet the criteria established by environmental agencies (for example in Brazil, 20 mg/L). In present days, the process of separating oil/water with ceramic membranes has attracted the attention of many researchers [1,2]. In this sense, the aim of this study is to evaluate the influence of the tangential inlet shape in the oil/water separation via ceramic membranes. We use a mathematical multiphase flow model to describe the oil-water separation, based on the particle model. Here oil is the dispersed phase while water the continuous phase. To model the turbulence effect we use the RNG k-ε model. All simulations were carried out using the Ansys CFX ® commercial code. Results of streamlines and velocity, pressure and volume fraction of phase fields are present and analyzed. The numerical results indicate that no significant difference when using a circular or rectangular pipe with the same cross-sectional area.

Abstract: The oil industry has sought to minimize the environmental impact from mining activities and oil transportation. The oil transportation by pipeline is subject to failures and leaks that cause financial losses and environmental damage, often irreparable. In this sense, the aim of this study is to evaluate the influence of the leak diameter in the behavior of the two-phase flow (oil and water) in a pipe. A transient and incompressible multiphase flow mathematical model based on the particle model was used here. Oil is the dispersed phase while water is the continuous phase. To model the turbulence effect it was used the standard k-ε model. All simulations were carried out using the Ansys CFX^® commercial code. Results of the pressure, velocity and volumetric fraction of the phases are presented and discussed. The results confirm the difficulty to detect leakage with small diameters.

Abstract: The transport of oil and its derivates is mainly done through pipelines linking the oil fields, refineries and distribution networks to consumers. They are considered the best, safe and economical way to fluids transportation over long distances. Despite significant advances in the development of lighter and stronger materials for the construction of pipelines and the growing number of gas and oil pipelines, many problems of leaks have been observed, which has encouraged the development of reliable techniques to inspect and detect quickly and accurately possible leaks along these pipelines. The goal is to eliminate or minimize damage to the oil industry and mainly to the environment. In this context, this paper aims to study the thermo-fluid dynamics of a transient three-phase flow (oil, water and gas) in a horizontal pipe in the presence of a leakage at different positions. Herein it was applied a 3D Eulerian-Eulerian model, including the transient turbulent model (RNG k-ε), using the ANSYS CFX^® 12.1 commercial package to perform all simulations. Numerical results of velocity, pressure and volume fraction fields of the involved phases are presented and discussed.

Abstract: We address the problem of estimating the particle distribution in the suspension flow near solid walls which is of considerable interested in science and technology. The present paper focuses on the methodology that can be used to study the dynamics of moving particles. A statistical-mechanics based analytical model is developed for the particle concentration distributions (Eulerian approach). The performance of this approach is compared with a standard force balance model on moving particles that treats particles as a discrete phase (Lagrangian approach). The attractive properties of these approaches are demonstrated in the simulation of a gas-solid suspension flow above solid surfaces with a rebound effect. Results shows that our model can effectively predict particle concentration distributions and both approaches are complementary descriptions for simulating aerosol flows.