Hierarchically Structured Microsieves Produced via Float-Casting.

This article shows a new way to produce hierarchical microsieves by layering three types of float-cast microsieves, differing from each other in their pore diameters (approximately 68 µm, 7 µm, and 0.24 µm) on top of each other. The unsupported microsieves with 7 and 0.24 µm pore sizes are mechanically fragile. The complete hierarchical sieve composed of all three layers, however, can be handled manually without special precaution. This article further investigates the flow through the hierarchical sieve and filtration via experiment, theory (Hagen-Poiseuille's and Sampson-Roscoe's law), and simulation (numerically solving the Navier-Stokes equations for a predefined set of discrete volumetric elements). The experimental, theoretical, and simulated permeances of the microsieves and the hierarchical sieves are in reasonable agreement with each other and are significantly higher than the permeances of conventional filtration media. In filtration experiments, the hierarchical sieves show the expected sharp size cut-off, retaining particles of diameters exceeding the pore diameter.

Experimental and CFD analysis of fluid flow through nanofiber filter media.

This work presents a novel approach to investigating the slip effect in nanofiber filter media. Electrospun nanofiber media with high efficiency and low pressure drop were produced at different concentrations and durations. The surface and cross-sectional morphology of nanofiber media were studied using FE-SEM. Fiber orientation and diameter distributions were also examined. The 3D virtual nanofiber media was modeled using this information along with the experimentally measured porosity and thickness of the media. The effect of the slip phenomenon in nanofiber media was studied numerically, and the results were compared to experimental data. Excellent agreements were found between the measured and simulation results. Additionally, filtration simulations considering aerosols injected with airflow through the nanofibrous filter media were conducted by considering the slip effect, and the effect of filter structure on filtration performance (removal efficiency and pressure drop) was investigated.

Confinement Effect on Porosity and Permeability of Shales.

Porosity and permeability are the key factors in assessing the hydrocarbon productivity of unconventional (shale) reservoirs, which are complex in nature due to their heterogeneous mineralogy and poorly connected nano- and micro-pore systems. Experimental efforts to measure these petrophysical properties posse many limitations, because they often take weeks to complete and are difficult to reproduce. Alternatively, numerical simulations can be conducted in digital rock 3D models reconstructed from image datasets acquired via e.g., nanoscale-resolution focused ion beam-scanning electron microscopy (FIB-SEM) nano-tomography. In this study, impact of reservoir confinement (stress) on porosity and permeability of shales was investigated using two digital rock 3D models, which represented nanoporous organic/mineral microstructure of the Marcellus Shale. Five stress scenarios were simulated for different depths (2,000-6,000 feet) within the production interval of a typical oil/gas reservoir within the Marcellus Shale play. Porosity and permeability of the pre- and post-compression digital rock 3D models were calculated and compared. A minimal effect of stress on porosity and permeability was observed in both 3D models. These results have direct implications in determining the oil-/gas-in-place and assessing the production potential of a shale reservoir under various stress conditions.