Multiphase Fluid Systems Research Articles

Surface tension effects on instability in viscoelastic respiratory fluids

This paper establishes the mathematical formalism for the modeling of the mucus layer in the human trachea as a viscoelastic multiphase fluid system with surface tension with a view toward study of instability properties of the air–mucus system aimed at improving the design of new bioaerosol suppressing medication. The effects of surface tension, previously only conjectured and very poorly understood, are clearly established with quantitative relationships. Several very important physiological conclusions are obtained supporting one method of potential treatment and prevention of disease transmission by alteration of the mucus layer properties over other potential methods.

Parallelizing of macro-scale pseudo-particle modeling for particle-fluid systems

A parallel algorithm suitable for simulating multi-sized particle systems and multiphase fluid systems is proposed based on macro-scale pseudo-particle modeling (MaPPM). The algorithm employs space-decomposition of the computational load among the processing elements (PEs) and multi-level cell-subdivision technique for particle indexing. In this algorithm, a 2D gas-solid system is simulated with the temporal variations of drags on solids, inter-phase slip velocities and solids concentration elaborately monitored. Analysis of the results shows that the algorithm is of good parallel efficiency and scalability, demonstrating the unique advantage of MaPPM in simulating complex flows.

Lattice Boltzmann method for modeling liquid‐vapor interface configurations in porous media

The lattice Boltzmann method (LBM) has emerged as a powerful tool for simulating the behavior of multiphase fluid systems in complex pore networks. Specifically, the single component multiphase LBM can simulate the interfacial phenomena of surface tension and adsorption and thus be used for modeling fluids such as water and its vapor in porous media. This paper provides an introduction to LBM applications to interface configurations in partially saturated porous media. Key elements of this LBM application are fluid‐fluid and fluid‐solid interactions that successfully mimic the Young‐Laplace equation and liquid film adsorption. LBM simulations of liquid behavior in simple pore geometry considering capillarity and adsorption are in good agreement with analytical solutions and serve as critical first steps toward validating this approach. We demonstrate the usefulness of LBM in constructing virtual liquid retention measurements based on porous media imagery. Results of this study provide a basis for application of LBM to understanding liquid configurations in more complex geometries and clear a path for applications involving interface migration, flow, and transport in partially saturated porous media.

Phenomenology of tremor-like signals observed over hydrocarbon reservoirs

We have observed narrow-band, low-frequency (1.5–4 Hz, amplitude 0.01–10 μm/s) tremor signals on the surface over hydrocarbon reservoirs (oil, gas and water multiphase fluid systems in porous media) at currently 15 sites worldwide. These ‘hydrocarbon tremors’ possess remarkably similar spectral and signal structure characteristics, pointing to a common source mechanism, even though the depth (some hundreds to several thousands of meters), specific fluid content (oil, gas, gas condensate of different compositions and combinations) and reservoir rock type (such as sandstone, carbonates, etc.) for each of those sites are quite different. About half of the sites are fully explored or even developed and producing fields, and hard quantitative data on the reservoirs are available (well data, reservoir monitoring data, seismic surveys, etc.). The other areas are essentially either explored prospect areas where we did not have access to hard reservoir data or (in only one case) areas where no exploration wells have been drilled at all. The tremor signal itself was observed over ALL locations investigated so far. The signals weaken at the rim of the reservoirs and are not observed outside the reservoir area. There is a strong correlation of the tremor power with the thickness of the hydrocarbon-bearing layers (‘pay zone thickness’) determined by borehole log measurements. The overall correlation between surface tremor measurements and accessible subsurface well data is higher than 90%. The phenomenological comparison of hydrocarbon tremor signals with volcanic tremor signals from Stromboli and Arenal volcanoes using both conventional spectral analysis tools and non-linear dynamics methods reveals fundamental similarities between those two phenomena as well as their close relation to bandpass filtered noise. Nevertheless, the specific signal sources are expected to be different for volcanoes and hydrocarbon reservoirs. Using the currently available data we present possible concepts (active or passive mechanisms) on the nature of the hydrocarbon tremor source. Our data lead us to conclude that we are most likely observing a characteristic filtering/mixing effect, with the energy input supplied by the natural seismo-acoustic background. The reservoir, i.e. the hydrocarbon-water-multifluid system contained in a porous medium, is expected to be the oscillatory element able to act as a filter/mixer (resembling essentially a in-reservoir path effect) for the natural seismo-acoustic background. Most intriguing seems the application aspect, i.e. the practical usability of this spectroscopic approach as a direct from-the-surface, non-invasive hydrocarbon indicator.

A numerical method for two-phase flows with an interface

One of the challenges in modelling multiphase fluid systems is to capture accurately the discontinuous-interface phenomenon. In this paper a numerical model for two-phase flows with a varying density is presented, in which a modified volume of fluid (VOF) method is combined with a semi-implicit algorithm ( simple) and a higher-order advection scheme in a collocated grid. The improved volume tracking method allows interfaces to be captured and maintained compactly in one cell, without imposing restrictions on the topological complexity or the number of interfaces that can be represented. The surface tension force is modelled by a continuum surface force approximation. An efficient solver is used for the resulting system of the linear equations. Example problems simulated in this paper are the buoyancy-driven motion of multiple bubbles in a viscous liquid, and bubble-rise towards an interface. The complex topological changes that occur during bubble rise are well predicted. The result is verified by experimental data in the literature.

Electro-Rheological-Fluid-Based Articulating Robotic Systems

The limitations of the current generation of robotic systems has triggered a new research thrust for predicting the elastodynamic response of assemblages of articulating flexible-bodied systems. This research thrust is extended herein by proposing the fabrication of robotic systems in either monolithic or ultra-advanced composite laminated high-strength, high-stiffness materials in which are incorporated electro-rheological fluids. These multiphase fluid systems, which change their rheological behavior instantaneously when subjected to an externally applied electrical field, provide a potential for tailoring the vibrational characteristics of these hybrid materials from which the structural members of the proposed robotic systems are fabricated. This paper is focused on developing the necessary design tools for predicting the vibrational response of flexible multibodied articulating systems fabricated with this new class of advanced materials. A variational theorem is developed herein as a basis for finite element formulations which can be employed to predict the elastodynamic response of these systems. A coherent combination of experimental and theoretical work on cantilevered beams is presented to demonstrate the viability of the proposed design methodology. In addition, computer simulation results are presented to demonstrate the potential payoffs in terms of superior performance characteristics of a new generation of robotic systems capitalizing on this innovative and revolutionary design philosophy.

Simulation of gas and oil flow in hydrocarbon reservoirs

Summary The non-specialist is introduced to the uses made of numerical simulation in modelling the behaviour and performance of hydrocarbon reservoirs. Hydrocarbon reservoir modelling can be compared with groundwater modelling, but is generally more complex, commonly dealing with multiphase fluid systems in two or three dimensions. Both finite difference and finite element techniques are used to solve numerically the equations of motion. The application of two powerful models, PORES and PROGRESS, illustrates the use of simulation during the various stages of development of the Morecambe and Rough gas fields by British Gas.

Surface tension variation in multiphase fluid systems

Surface tension variation in multiphase fluid systems

The characteristic functions of multiphase fluid systems and the thermodynamic interpretation of vapour bubble collapse

The effects of phase interface and surface tension in multiphase fluid systems are investigated. The modification of the entropy, free energy, internal energy, enthalpy, free enthalpy, and their differentials are deduced for both droplet and vapour bubbles of uniform and nonuniform temperature and size distribution. The investigation yields also the latent heat, the Clausius-Clapeyron equation, and the polytropic exponent, adapted for disperse state. The relationships deduced for one-component systems are generalized for two-and more-component systems. It is presented that in the course of bubble size reduction both the vapour temperature and pressure arise much over the critical values taken in the usual sense, since the saturation state, the coexistence curve, and the critical state are significantly modified because of the bubble size in submicroscopic order of magnitude. Also the interdependence of bubble annihilation and cavitation damage is explained.