Event-based contact angle measurements inside porous media using time-resolved micro-computed tomography

Hypothesis: Capillary-dominated multiphase flow in porous materials is strongly affected by the pore walls' wettability. Recent micro-computed tomography (mCT) studies found unexpectedly wide contact angle distributions measured on static fluid distributions inside the pores. We hypothesize that analysis on time-resolved mCT data of fluid invasion events may be more directly relevant to the fluid dynamics. Experiment: We approximated receding contact angles locally in time and space on time-resolved mCT datasets of drainage in a glass bead pack and a limestone. Whenever a meniscus suddenly entered one or more pores, geometric and thermodynamically consistent contact angles in the surrounding pores were measured in the time step just prior to the displacement event. We introduced a new force-based contact angle, defined to recover the measured capillary pressure in the invaded pore throat prior to interface movement. Findings: Unlike the classical method, the new geometric and force-based contact angles followed plausible, narrower distributions and were mutually consistent. We were unable to obtain credible results with the thermodynamically consistent method, likely because of sensitivity to common imaging artifacts and neglecting dissipation. Time-resolved mCT analysis can yield a more appropriate wettability characterization for pore scale models, despite the need to further reduce image analysis uncertainties. (C) 2020 The Authors. Published by Elsevier Inc

Algebraic approach to slice monogenic functions

In recent years, the study of slice monogenic functions has attracted more and more attention in the literature. In this paper, an extension of the well-known Dirac operator is defined which allows to establish the Lie superalgebra structure behind the theory of slice monogenic functions. Subsequently, an inner product is defined corresponding to this slice Dirac operator and its polynomial null-solutions are determined. Finally, analogues of the Hermite polynomials and Hermite functions are constructed in this context and their properties are studied

In situ assessment of the stone conservation state by its water absorbing behaviour : a hands-on methodology

This paper describes the use of the water absorbing behaviour (WAB) for assessment of the conservation state of stone in situ. A test methodology, consisting of a combination of techniques for in situ measurement of the WAB, was applied in a case study on Lede stone, a sandy limestone, used in a medieval facade in Ghent, Belgium. The methods used were the contact sponge method (CSM), the Karsten tube (KT) and the droplet method (DM). Additionally, the residual hardness of the stone was measured by Schmidt hammer (SH). After careful selection of representative measuring points, a qualitative analysis of the stone’s condition could be made, based on its WAB, residual hardness, reference data from laboratory experiments and thorough visual observations. From this analysis it could be concluded that CSM, KT and SH generated coherent and compatible results; that DM could indicate superficial alterations which were not necessarily representative for the subsuperficial WAB and that this methodology could give an insight on the conservation state, beyond visual observations, when combined with reference data