Akand W. Islam

Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration.

We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration.

Laminar Mixed Convection in a Lid-Driven Square Cavity with Two Isothermally Heated Square Internal Blockages

Laminar mixed convection in a lid-driven square cavity with two isothermally heated square internal blockages is numerically investigated. The top lid of the cavity is moving rightwards with a constant speed. The two blockages are maintained at an isothermal hot temperature, while the walls of the cavity are maintained at a cold temperature. The flow and heat transfer behavior is studied for various placements of the blockages through analyzing the local Nusselt number distribution around the edges of the blockages and the average Nusselt number at the blockage surfaces at various Richardson and Reynolds numbers. Investigations are performed in a range of Reynolds number (100–500), Richardson number (0.1–10), and at a fixed Prandtl number (0.71). Computations are done using the ANSYS FLUENT commercial code based on a finite volume method. It is observed that, the average Nusselt number on the blockage surfaces increases with increasing Reynolds number at any Richardson number. The average Nusselt number changes significantly due to the change of blockage placement locations. The separation distance between the two blockages has large effect on the total average Nusselt number.

A theory-based simple extension of Peng–Robinson equation of state for nanopore confined fluids

In a recent publication (Islam et al. in J Nat Gas Sci Eng 25:134–139, 2015), the van der Waals equation of state (EOS) was modified to assess phase behavior of nanopore confined fluids. Although the changes of critical properties were well captured, it was limited to only subcritical conditions. Peng–Robinson EOS showed inconsistent critical shifts. Here, we develop a simple extension of Peng–Robinson (PR) derived similarly from the Helmholtz free energy function by applying the same energy and volume parameter relations. This modified PR reproduces experimental and molecular simulation results satisfactorily. It shows that there is pore proximity effect also in supercritical condition which, however, diminishes as temperature increases. The proposed model can show heterogeneous density or layered distribution of molecules inside nanopore. We have tested common shale (natural) gas molecules and the condition of Haynesville plays where temperature and pressure can be very high. This simple model can offer alternatives to more computationally expensive molecular simulations to study the pore proximity phenomenon.

OpenMG: A New Multigrid Implementation in Python

In many large-scale computations, systems of equations arise in the form Au= b, where A is a linear operation to be performed on the unknown data u, producing the known right-hand side, b, which represents some constraint of known or assumed behavior of the system being modeled. Since such systems can be very large, solving them directly can be too slow. In contrast, a multigrid solver solves partially at full resolution, and then solves directly only at low resolution. This creates a correction vector, which is then interpolated to full resolution, where it corrects the partial solution. This project aims to create an open-source multigrid solver called OpenMG, written only in Python. The exist- ing PyAMG multigrid implementation is a highly versatile, configurable, black- box solver, but is difficult to read and modify due to its C core. Our proposed OpenMG is a pure Python experimentation environment for testing multigrid concepts, not a production solver. By making the code simple and modular, we make the algorithmic details clear. We thereby create an opportunity for education and experimentation with the partial solver (Jacobi, Gauss Seidel, SOR, etc.), the restriction mechanism, the prolongation mechanism, and the direct solver, or the use of GPGPUs, multiple CPUs, MPI, or grid computing. The resulting solver is tested on an implicit pressure reservoir simulation problem with satisfactory results.

Numerical Analysis of Laminar Mixed Convection in a Lid Driven Square Cavity With an Isothermally Heated Square Internal Blockage

Laminar mixed convection characteristics in a square cavity with an isothermally heated square blockage inside have been investigated numerically using the finite volume method of the ANSYS FLUENT commercial CFD code. Various different blockage sizes and concentric and eccentric placement of the blockage inside the cavity have been considered. The blockage is maintained at a hot temperature, Th, and four surfaces of the cavity (including the lid) are maintained at a cold temperature, Tc, under all circumstances. The physical problem is represented mathematically by sets of governing conservation equations of mass, momentum, and energy. The geometrical and flow parameters for the problem are the blockage ratio (B), the blockage placement eccentricities (ex and ey), the Reynolds number (Re), the Grashof number (Gr), and the Richardson number (Ri). The flow and heat transfer behavior in the cavity for a range of Richardson number (0.01–100) at a fixed Reynolds number (100) and Prandtl number (0.71) is examined comprehensively. The variations of the average and local Nusselt number at the blockage surface at various Richardson numbers for different blockage sizes and placement eccentricities are presented. From the analysis of the mixed convection process, it is found that for any size of the blockage placed anywhere in the cavity, the average Nusselt number does not change significantly with increasing Richardson number until it approaches the value of the order of 1 beyond which the average Nusselt number increases rapidly with the Richardson number. For the central placement of the blockage at any fixed Richardson number, the average Nusselt number decreases with increasing blockage ratio and reaches a minimum at around a blockage ratio of slightly larger than 1/2. For further increase of the blockage ratio, the average Nusselt number increases again and becomes independent of the Richardson number. The most preferable heat transfer (based on the average Nusselt number) is obtained when the blockage is placed around the top left and the bottom right corners of the cavity.Copyright