arXiv subjects

Loris Grossi

Publications and source records attributed to Loris Grossi.

4 recordsLinked to original sources

arXiv2016

Simulation of capillary infiltration into packing structures by the Lattice-Boltzmann method for the optimization of ceramic materials

In this work we want to simulate with the Lattice-Boltzmann method in 2D the capillary infiltration into porous structures obtained from the packing of particles. The experimental problem motivating our work is the densification of carbon preforms by reactive melt infiltration. The aim is to determine optimization principles for the manufacturing of high-performance ceramics. Simulations are performed for packings with varying structural properties. Our analysis suggests that the observed slow infiltrations can be ascribed to interface dynamics. Pinning represents the primary factor retarding fluid penetration. The mechanism responsible for this phenomenon is analyzed in detail. When surface growth is allowed, it is found that the phenomenon of pinning becomes stronger. Systems trying to reproduce typical experimental conditions are also investigated. It turns out that the standard for accurate simulations is challenging. The primary obstacle to overcome for enhanced accuracy seems to be the over-occurrence of pinning.

cond-mat.mtrl-sci↗

arXiv2015

Lattice Boltzmann simulations on the role of channel structure for reactive capillary infiltration

It is widely recognized that the structure of porous media is of relevance for a variety of mechanical and physical phenomena. The focus of the present work is on capillarity, a pore-scale process occurring at the micron scale. We attempt to characterize the influence of pore shape for capillary infiltration by means of Lattice Boltzmann simulations in 2D with reactive boundaries leading to surface growth and ultimately to pore closure. The systems under investigation consist of single channels with different simplified morphologies: namely, periodic profiles with sinusoidal, step-shaped and zig-zag walls, as well as constrictions and expansions with rectangular, convex and concave steps. This is a useful way to decompose the complexity of typical porous media into basic structures. The simulations show that the minimum radius alone fails to characterize properly the infiltration dynamics. The structure of the channels emerge as the dominant property controlling the process. A factor responsible for this behavior is identified as being the occurrence of pinning of the contact line. It turns out that the optimal configuration for the pore structure arises from the packing of large particles with round shapes. In this case, the probability to have flow paths wide and straight is higher. Faceted surfaces presenting sharp edges should be avoided because of the phenomenon of pinning near narrow-to-wide parts. This study is motivated by the infiltration of molten metals into carbon preforms. This is a manufacturing technique for ceramic components devised to advanced applications. Guidelines for experimental work are discussed.

cond-mat.soft↗

arXiv2014

Surface growth effects on reactive capillary-driven flow: Lattice Boltzmann investigation

The Washburn law has always played a critical role for ceramics. In the microscale, surface forces take over volume forces and the phenomenon of spontaneous infiltration in narrow interstices becomes of particular relevance. The Lattice Boltzmann method is applied in order to ascertain the role of surface reaction and subsequent deformation of a single capillary in 2D for the linear Washburn behavior. The proposed investigation is motivated by the problem of reactive infiltration of molten silicon into carbon preforms. This is a complex phenomenon arising from the interplay between fluid flow, the transition to wetting, surface growth and heat transfer. Furthermore, it is characterized by slow infiltration velocities in narrow interstices resulting in small Reynolds numbers that are difficult to reproduce with a single capillary. In our simulations, several geometric characteristics for the capillaries are considered, as well as different infiltration and reaction conditions. The main result of our work is that the phenomenon of pore closure can be regarded as independent of the infiltration velocity, and in turn a number of other parameters. The instrumental conclusion drawn from our simulations is that short pores with wide openings and a round-shaped morphology near the throats represent the optimal configuration for the underlying structure of the porous preform in order to achieve faster infiltration. The role of the approximations is discussed in detail and the robustness of our findings is assessed.

cond-mat.soft↗

arXiv2013

Lattice Boltzmann simulation of the surface growth effects for the infiltration of molten Si in carbon preforms

The infiltration of molten silicon into carbon preforms is a widespread technique employed in the industry in order to enhance the thermal and mechanical properties of the final ceramic products. A proper understanding of this phenomenon is quite challenging since it stems from the reciprocal action and reaction between fluid flow, the transition to wetting, mass transport, precipitation, surface growth as well as heat transfer. As a result, the exhaustive modeling of such problem is an involved task. Lattice Boltzmann simulations in 2D for capillary infiltration are carried out in the isothermal regime taking into account surface reaction and subsequent surface growth. Precisely, for a single capillary in the linear Washburn regime, special attention is paid to the retardation for the infiltration process induced by the thickening of the surface behind the contact line of the invading front. Interestingly, it turns out that the process of surface growth leading to pore closure marginally depends on the infiltration velocity. We conclude that porous matrices with straight and wide pathways represent the optimal case for impregnation. Our analysis includes also a comparison between the radii characterizing the infiltration process (i.e., minimum, hydraulic, average and effective radii).

cond-mat.soft↗