Wormhole formation in dissolving fractures

We investigate the dissolution of artificial fractures with three-dimensional, pore-scale numerical simulations. The fluid velocity in the fracture space was determined from a lattice-Boltzmann method, and a stochastic solver was used for the transport of dissolved species. Numerical simulations were used to study conditions under which long conduits (wormholes) form in an initially rough but spatially homogeneous fracture. The effects of flow rate, mineral dissolution rate and geometrical properties of the fracture were investigated, and the optimal conditions for wormhole formation determined.Comment: to be published in J. Geophys Re

Simulations of Dissolution of Structured Particles

This thesis presents a new modelling framework for the simulation of detergent powder dissolution. Focusing on population of particles containing multi ingredients with porous structure, the general model framework links mixing system power and particle dissolution behaviour by combining convective dissolution equations and computational fluid dynamics simulation. Particle dissolves in a variety way due to many factors for example particle shape and size, pore structure, agitation speed, solvent material and temperature. It is difficult to quantitatively conclude these factors on dissolution. As a result, detailed simulations based on Lattice-Boltzmann method are carried out to investigate factors for instance particle shape, surface area to volume ratio and pore structure separately. Later on, both experiment and simulation methods have been studied to explore the effects of agitation and particle wetting process. Results show that surface area to volume ratio plays a more important role in terms of particle related properties. Results also indicate that agitation affects dissolution significantly comparing to the other studied factors. The new dissolution model, expressed as a coupled system of numerical and computational issues, is used to predict particle dissolution behaviour in a well mixed system. Simple case study of single ingredient non porous particle sodium carbonate (provided by Proctor and Gamble) successfully shows the capability of the model by validating modelling results with experimental results. Later on, more complicated case study of multi ingredients porous detergent powder (PANDORA, one of the semi product in Proctor and Gamble) suggests that this model can predict porous particle dissolution while the particles are treated as spheres with envelope density. Based on the good agreements between modelling and experiment data, this model can be applied for predicting bulk particle dissolution behaviour in different mixing systems, or the same mixing system but different bulk particle

Microscale modeling of fluid flow in porous medium systems

Proper mathematical description of macroscopic porous medium flows is essential for the study of a wide range of subsurface contamination scenarios. Existing mathematical formulations, however, demonstrate inadequacies that preclude the accurate description of many systems. Multi-scale models developed using thermodynamically constrained averaging theory (TCAT) rigorously define macroscopic variables in terms of more well-understood microscopic counterparts, permitting detailed analysis of macroscopic model forms based on microscale simulation and experiment. Within this framework, the primary objectives of microscale modeling are to elucidate important physical mechanisms and to inform both the form of macroscale closure relations as well as associated parameter values. In order to meet these goals, numerical tools must include: (1) simulations that provide accurate microscopic solutions for physical phenomena in large, complex domains; (2) morphological analysis tools that can be used to upscale simulation results to larger scales as dictated by the associated theoretical framework. Development of a numerical toolbox for microscale porous medium studies is considered in line with these objectives, including both implementation and optimization strategies. High-performance implementations of the lattice Boltzmann method are developed to simulate one- and two-phase flows using several computing platforms. A modified marching cubes algorithm is developed to explicitly construct all entities in a two-phase system, including all interfaces between the fluid and solid phases in addition to the three phase contact curve. These entities serve as a numerical skeleton for upscaling multiphase porous medium simulation results to the macroscale. Based on these tools, development of macroscopic constitutive laws is illustrated for a special case of anisotropic flow in porous media. In this example, microscale simulation is used to demonstrate a limitation of existing macroscopic forms for cases in which the momentum resistance depends on the flow direction in addition to the orientation. A modified macroscopic form is proposed in order to properly account for this phenomenon

Lattice Boltzmann model for diffusion-controlled indirect dissolution

Indirect dissolution is modelled using a two-component lattice Boltzmann model. A boundary condition is developed to impose equilibrium concentrations on the interfaces. The interfaces are captured using a volume-tracking scheme. The model is applied to a one-dimensional diffusion couple and the expected behaviour is observed. A two-dimensional situation with and without convection is also simulated, and the behaviour under grid refinement is studied. © 2007 Elsevier Ltd. All rights reserved.status: publishe