Abstract: The oil industry has sought to minimize the environmental impact from mining activities and oil transportation. Oil transportation by pipelines is subject to failures and leaks which cause financial losses and environmental damage, often irreparable. Currently, the study of leaks in pipelines has attracted the attention of many researchers. The aim of this study is to evaluate the influence of the curved curvature radius connection in pipeline leakage. We used a mathematical model of multiphase flow to describe the two-phase flow, based on the particle model. Oil is the continuous phase while water a dispersed phase. To model this effect we used the turbulence model SST. All simulations were carried out using the Ansys CFX ® commercial code. Results of the total pressure and pressure drop are presented and discussed. The results confirm the influence of the bending radius of curved connection on the behavior of the total pressure and the total pressure drop in two-phase flow in pipelines with and without leakage.
Abstract: Oil transport is used mainly by pipeline networks to transport oil from refineries and distributions points to the consumers. This is the main way to transport oils especially in areas of difficult access, ensuring efficiency, lowest cost and safety. In the chemical and petroleum industry it is possible to observe the presence of leak in the pipes, which has stimulated the development of reliable techniques for the rapid and accurate detection of leaks along the pipe in order to eliminate or minimize loss and environmental damage. In this context, this study aims to evaluate the effect of the numerical presence of leakage of two-phase flow (oil-water) pipe connections using the commercial software ANSYS CFX. The results from the fields of pressure, velocity and volume fraction are presented and assessed for illustrating the effect of the presence of the leak in the dynamic flow in the pipe with a curved connection.
Abstract: The growing global demand for energy has led researchers to seek the improvement of technology in order to maximize the generation of electricity by different ways. Among the different methods of production is the energy produced by thermal power plants, which account for more than 60% of the energy produced in the world. This energy is generated through combustion of fuels such as coal, diesel oil, natural gas and others. The main problem caused by the production of thermal energy is the emission of gaseous pollutants into the atmosphere, such as carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), and also particulate matter which causes environmental problems such as acid rain, greenhouse effect, and health problems, especially respiratory diseases. Computational fluid dynamics (CFD) is presented as an important tool in solving problems involving the dispersion of chemicals into the atmosphere. In this sense, this study aims to evaluate the thermofluid dynamics of pollutants’ dispersion emitted from the chimney of a thermal power plant, based on numerical simulations using the Ansys CFX 12.0 commercial code. Fields of velocity and mass concentration of the component involved in the process are presented and analyzed.
Abstract: The onshore and offshore production of oil and natural gas is characterized by the multiphase flow in ducts and pipes, which are interconnected by various equipments such as wellhead, pumps, compressors, processing platforms, among others. The transport of oil and oil products is essential to the viability of the sector, but is susceptible to failures, that can cause great environmental damage. Considering this necessity of the transportation sector of oil and derivatives, leakage in pipelines with curved connections, are the object of study for various researchers. In this sense, this work contributes to the study of three-phase flow (oil-water-gas) in a curved pipe (90°) using Computational Fluid Dynamics. The physical domain is constituted by two tubes of 4 meters trenched by a 90° curve, with the poring whole in the curvated accessory. The mathematical model is based on a particle model, where the oil is considered as a continuous phase and the water and gas as a particulate phase. The SST (Shear Stress Transport) turbulence model was adopted. All simulations were carried out using the Ansys CFX® 12.1 commercial code. Results of the pressure, velocity and volumetric fraction of the phases are presented and discussed.
Abstract: Two-phase pressure drop fluctuations during flow boiling in a single mini-channel were experimentally investigated. Degassed water was tested in circular cross section mini-channels with the hydraulic diameter of 1.0 mm at liquid mass fluxes range of 21.19-84.77 kg m-2 s-1 and heat fluxes of 0~155.75 kW m-2. Effects of heat flux and mass flux on pressure drop fluctuations were discussed based on the time and frequency domain analysis of the measured pressure drop. Two types of fluctuations were identified, which are the incipient boiling fluctuation (IBF) and the explosive boiling fluctuation (EBF) respectively. The IBF is a low frequency low amplitude fluctuation, which relates to the bubble dynamics when incipient boiling occurs. It is sensitive to the thermal and flow conditions. With the increase of heat flux and mass flux, the IBF is suppressed. The EBF is a low frequency high amplitude fluctuation, which occurs near the critical heat flux.
Abstract: The growing demand for oil brings the need for discovery of deeper reservoirs, especially of ultra-deepwater reservoirs. Thus, production in marine systems using components such as risers (flexible or rigid pipes) has been the focus of many studies in different areas. These ducts are used in the transportation of multiphase fluids (oil, water and gas) produced from the oil well located on the seabed to the platform surface. Due to the extreme conditions present in the offshore fields of production, the equipments that transport produced fluids operate close to their limits. So eventually, the flexible pipes may have structural integrity faults like leaks, which can cause production losses, accidents with victims and environmental disasters. The leak depends of a number of properties or parameters measured at the site of the leak, for example, integrity of the pipe material, release of fluids and noise emission characteristics or manifestation of some other type of signal behavior, variation of pressure drops close to the leak, among others. There are a variety of techniques available for detecting leaks, among which there is the mathematical modeling approach using computational techniques. In this context, this paper aims to study the fluid dynamics of a transient multiphase flow in a catenary riser in the presence of leakage. Herein a 3D Eulerian-Eulerian model was applied, including the turbulent model (RNG k-ε), using the commercial package ANSYS CFX® 15 to perform all simulations. The numerical results of velocity, volume fraction and pressure of the involved phases are presented and discussed.
Abstract: The present work exhibits a numerical study comparing the fluid dynamic and thermal fields of turbulent, three-dimensional forced convective cylindrical cavity flows obtained with Large Eddy Simulation (LES) and Reynolds-Averaged Navier Stokes (RANS). In the latter approach, three different closure models are employed: Reynolds Stress Model (RSM), standard k – ε and standard k - ω. It is considered a three-dimensional, incompressible, turbulent fluid flow at the steady state with ReD = 22,000 and Pr = 0.71. The main purpose is to investigate whether discrepancies are noticed in time-averaged and statistics of turbulent flows between LES and RANS predictions. Differences in time-averaged and statistical fields can be important for evaluation of convective fluxes in turbulent flows and combined convective and radiative transfer in participant media, i.e., for study of Turbulence-Radiation Interactions (TRI). The spatially-filtered and time-averaged conservation equations of mass, momentum and energy are solved with the Finite Volume Method (FVM). Results showed that time-averaged and RMS thermal fields obtained with LES and RANS presented reasonable discrepancies in regions near the cavity surfaces, which affects the convective fluxes in this region. For the highest temperature region of the cavity (near its inlet) the predictions obtained with LES and RANS are similar, which can led to similar predictions in heat exchange when thermal radiation is taken into account in optically thin participant media. For optically thick media, where local differences increase their importance, the employment of RANS is not recommended.
Abstract: This study is focused on the optimization of a sensible thermal storage system subjected to a cyclic energy source. The objective is to minimize the system heat storage mass and its geometry to guarantee its operation within an admissible temperature range. The storage medium is modeled as a Lumped system and the working fluid by a non-capacitive energy balance. The storage medium is composed of an array of parallel flat plates submitted to an air stream. The optimization is based on an exhaustive search method. It is observed that the minimum heat storage mass is proportional to the mass airflow rate. An optimal relationship between the superficial heat transfer rate and the fluid flow inertia, given by the dimensionless parameter NTU, is found to be constant (4.03) and independent in respect to the mass flow rate. The system time constant was invariable (3,230 s) for the optimal relationship between the interface heat transfer rate and the system inertia.
Abstract: Drying is an important way to improve the quality of lignite with high moisture. In this paper, a single-shaft paddle dryer experimental system was built to investigate the drying characteristics of fine-particle lignite with diameter 0-5mm. The experimental results show that with the increasing in shaft rotation speed the flow rate of lignite increases linearly approximately and the residence time decreases correspondingly. Increasing the inclination angle of dryer frame helps increase the flow rate. Both shaft rotation speed and heating source (heat transfer oil) temperature have significant effects on outlet moisture content of lignite. Shaft rotation speed affects the average heat transfer coefficient greatly and heating source temperature affects it weakly for specified conditions. It is found that for 5-12mm coarse-particle lignite, flow is not smooth and the average heat transfer coefficient is much less than that of fine-particle lignite. This research shows that it is feasible technically to dry fine-particle lignite by using paddle dryers, but not suitable to dry coarse-particle lignite.