Angela O. Nieckele

Transient Pig Motion Through Gas and Liquid Pipelines

Simulation of the transient motion of pigs through liquid and gas pipelines is presented. The differential form of the mass and linear momentum equations for compressible liquid and gas flows were solved by a finite difference numerical technique. The fluid flow equations were combined with a linear momentum equation for the pig and a model for bypass flow through the pig. The pig/wall contact forces were simulated by a stick/slip model. The contact forces developed by disk pigs and the pipe wall were predicted by a postbuckling finite element analysis of the discs. Test cases representing typical pigging operations were studied using the numerical model developed. The fluid flow and pig behavior predicted by the model presented a reasonable behavior, and contributed for a better understanding of the pig dynamics through gas and liquid pipelines.

Numerical Modeling of an Industrial Aluminum Melting Furnace

For the present work, a numerical simulation of the 100% oxy-firing combustion process inside an industrial aluminum remelting reverb furnace is presented. Three different configurations were analyzed: (i) a staged combustion process with parallel injection jets for oxygen and natural gas, (ii) a staged combustion process with a divergent jet for the oxygen, and (iii) a non-staged combustion process, with parallel jets. In all the cases, the injections were directed towards the aluminum bath, which was maintained at constant temperature. The numerical procedure was based on the finite volume formulation. The k-e model of turbulence was selected for simulating the turbulent flow field. The combustion process was calculated based on the finite rate models of Arrhenius and Magnussen, and the Discrete Transfer Radiation model was employed for predicting the radiation heat transfer The numerical predictions allowed the determination of the flame patterns, species concentration distribution, temperature and velocity fields. This kind of analysis can be a powerful tool for evaluating design options such as the type, number and positioning of the burners. The present work illustrates a preliminary comparison of three types of burners. From the results obtained, the staged combustion process with a divergent jet presented the best configuration, since the flame length was not too long as to damage the refractory wall. Further it presented the largest region with low water vapor concentration close to the aluminum surface.

Statistical characterization of two-phase slug flow in a horizontal pipe

The present paper reports the results of an ongoing project aimed at providing statistical information on slugs in two-phase flow in a horizontal pipe. To this end, the flow was examined experimentally and numerically. On the experimental side, three non-intrusive optical techniques were combined and employed to determine the velocity field and bubble shape: particle image velocimetry (PIV), Pulsed Shadow Technique (PST) and Laser-Induced Fluorescence technique (LIF). Statistical information was provided by photogate cells installed at two axial positions. The flow was numerically determined based on the one-dimensional Two-Fluid Model. The tests were conducted on a specially built transparent pipe test section, using air and water as the working fluids. The velocity fields were obtained for flow regimes where the slugs were slightly aerated to facilitate the utilization of the optical methods employed. The main parameters for characterizing the statistically steady flow regime such as slug length and velocity obtained numerically were compared with the experimental data and good agreement was obtained.

Crossflow of viscoplastic materials through tube bundles

Abstract The flow of viscoplastic materials through staggered arrays of tubes is analyzed. The mechanical behavior of the materials is assumed to obey the generalized Newtonian liquid (GNL) model, with a viscosity function given by the biviscosity law. The governing equations of this flow are solved numerically using a finite-volume method with a non-orthogonal mesh. For a representative range of the relevant parameters, results are presented in the form of velocity, pressure and viscosity fields. The pressure drop is also given as a function of rheological and geometric parameters.

ANALYSIS OF THE TRANSIENT COOLDOWN OF SUB-SEA PIPELINES

A precise analysis of the transient cooldown of subsea pipelines is crucial for offshore flow assurance, to avoid, for example, hydrate formation or wax deposition. Flow assurance in transportation lines, where column separation can occur due to large temperature drop coupled with large pressure drop, must also be addressed. Usually, pipeline thermal insulation is designed for steady state conditions. However, during shutdowns, the temperature drop experienced by the stagnant fluid is more pronounced, eventually reaching some critical temperature level, that can lead to flow line blockage and flow re-start problems. Thus, the determination of the temperature and pressure distributions along the pipeline under transient conditions is important to maintain the line operating safely. To determine the transient heat transfer in pipelines, the fluid flow conservation equations coupled with the heat conduction equation applied to the pipeline wall were numerically solved. The heat loss from the pipeline was determined by solving the transient heat conduction equation for the pipewall layers, utilizing a simple one-dimensional model in the radial direction. The coupled system was solved numerically employing the finite difference method. Transient analyses were performed for two scenarios. In the first one, the cooldown process of oil in a subsea pipeline was evaluated, with the effect of variable thermal properties on the temperature profile being investigated. The dependence of the temperature on the thermal conductivity and specific heat capacity was analyzed. In the second scenario, gas flows inside the pipeline, and the effect of temperature variation on a stagnant fluid is presented. Tests for different values of thermal diffusivity corresponding to new and old thermal insulations were performed.Copyright

Numerical Analysis of the Turbulent Flow Field Applied to Thermal Spallation Drilling

Thermal spallation is a possible drilling technique which consists of using hot supersonic jets as heat source to perforate hard rocks at high rates. This work presents a numerical analysis of a typical spallation drilling configuration, by the finite volume method. The time-averaged conservation equations of mass, momentum and energy are solved to determine the turbulent compressible gas phase flow field. Turbulence is predicted by the classical high Reynolds number κ-e model, as well as with a low Reynolds number κ-e model. The influence of the jet Reynolds number is investigated. Special attention is given to the rock surface temperature, since its accurate determination is required to predict spallation rates under field-drilling conditions.Copyright

Influence of the Type of Oxidant in the Combustion of Natural Gas Inside an Aluminum Melting Furnace

The fuel used as energy source for aluminum melting is of extreme importance for a better performance of the process. However, the type of oxidant can also lead to better performance, leading to a greater preservation of the equipments. Air is more abundant and cheaper, however due to the presence of nitrogen, there is undesirable NOx formation. An alternative is to employ pure oxygen. Although it is more expensive, it can lead to a cleaner and much more efficient combustion process, by significantly altering the combustion aspects inside the furnace, such as the shape of the flame and the distribution of temperature and heat flux. In the present work, numerical simulations were carried out using the commercial package FLUENT, analyzing different cases with pure oxygen and air as the oxidant for the combustion of natural gas. The results showed the possible damages caused by the process if long or too intense and concentrated flames are present.© 2006 ASME

Performance of the Combustion Process Inside an Aluminum Melting Furnace With Natural Gas and Liquid Fuel

The choice of the type of fuel used as energy source for the aluminum melting can be of extreme importance for a better performance as well as for a greater preservation of the equipments. The option of a liquid or gaseous fuel can significantly alter the combustion aspects inside the furnace, such as the shape of the flame and the distribution of temperature and heat flux. In the present work, numerical simulations were carried out using the commercial package FLUENT, analyzing different cases with two types of fuel: a spray of liquid oil and a natural gas jet, both reacting with pure oxygen. The results showed the possible damages caused by the process if long or too intense and concentrated flames are present, increasing very much the wall temperatures and compromising the heat flux on the aluminum surface.Copyright

Combustion performance of an aluminum melting furnace operating with liquid fuel

The characteristics associated with the delivery of the fuel to be used as the energy source in any industrial combustion equipment are of extreme importance, as for example, in improving the performance of the combustion process and in the preservation of the equipment. A clean and efficient combustion may be achieved by carefully selecting the fuel and oxidant, as well as the operational conditions of the delivery system for both. In the present work, numerical simulations were carried out using the commercial code FLUENT for analyzing some of the relevant operational conditions inside an aluminum reverb furnace employing liquid fuel and air as the oxidant. Different fuel droplets sizes as well as inlet droplet stream configurations were examined. These characteristics, associated with the burner geometry and the fuel dispersion and delivery system may affect the flame shape, and consequently the temperature and the heat flux distribution within the furnace. Among the results obtained in the simulations, it was shown the possible damages to the equipment, which may occur as a result of the combustion process, if the flame is too long or too intense and concentrated.

The Influence of Rheological Parameters in Wax Deposition in Channel Flow

Wax deposition is a critical operational problem in crude oil transportation through pipelines in cold environments. Accurate prediction of the wax deposition is crucial for the efficient design of subsea lines. Wax deposition is a complex process for which the basic mechanisms are still not fully understood. Although Fick’s molecular diffusion model is considered by several authors as the leading deposition mechanism, it is shown that it does not represent well the wax deposition thickness, measured during the transient regime, in a simple experiment, in a rectangular channel, with a laboratory oil-wax mixture. Another important wax deposition mechanism identified is associated with the rheological properties of the fluid, since oil-paraffin mixtures shows a non-Newtonian behavior at temperatures below the fluid Wax Appearance Temperature. The mixture can be modeled as a Bingham fluid, with a dependence of the yield stress on wax concentration, temperature and rate of cooling. The present paper presents a numerical model for predicting wax deposition in channel flows considering the influence of rheological properties combined with a diffusion-based deposition mechanism. To determine the amount of deposit, the conservation equations of mass, momentum, energy and wax concentration in the mixture were numerically solved with the finite volume method. A nonorthogonal moving coordinate system that adapts to the wax interface deposit geometry was employed. The results demonstrated that additional deposition is obtained as a result of the non Newtonian behavior of the fluid. This trend is in agreement with experimental observation conducted in previous studies.Copyright