Tortuosity of porous media: Image analysis and physical simulation

Tortuosity is widely used as a critical parameter to predict transport properties of porous media, such as rocks and soils. But unlike other standard microstructural properties, the concept of tortuosity is vague with multiple definitions and various evaluation methods introduced in different contexts. Hydraulic, electrical, diffusional, and thermal tortuosities are defined to describe different transport processes in porous media, while geometrical tortuosity is introduced to characterize the morphological property of porous microstructures. In particular, the rapid development of microscopy imaging techniques has made digital microstructures of porous media increasingly accessible, from which geometrical and physical tortuosities can be evaluated using various image analysis and numerical simulation methods. These tortuosities are defined differently and can differ greatly in value, but in many works of literature, they are used interchangeably. To address this situation, we systematically examine geometrical, hydraulic, electrical, diffusional, and thermal tortuosities from the viewpoints of the definition and evaluation method. For the same porous medium, visible discrepancies are found in the evaluated geometrical and physical tortuosities, depending on the specific definition and the evaluation method adopted. This observation makes it questionable to directly use the geometrical tortuosity as a substitute for physical tortuosities, a common practice in the literature. Thus, the correlations between geometrical and physical tortuosities are further analyzed, which also takes into account the influence of both image size and resolution. From the correlation analysis, phenomenological relations between geometrical and physical tortuosities are established, so that the latter can be accurately predicted by using the former which is much cheaper to evaluate from digital microstructures

A review on performance of energy piles and effects on surrounding ground

Thermo-active ground structures represent low-energy and sustainable technology which is a clear priority for many countries. Heat transfer between such structures and the surrounding soil is understood to play an important role both in the overall thermal performance of buildings and in the evolution of stresses in structural elements and the surrounding soil. This paper presents an overview of recent research efforts and developments in relation to energy piles. General aspects on the performance of energy piles and their impact on the surrounding ground are presented based on previous field, laboratory and numerical investigations as well as existing case studies. Based on the current knowledge, further research opportunities are identified and highlighted

High-pressure CO2 excess sorption measurements on powdered and core samples of high-rank coals from different depths and locations of the South Wales Coalfield

The experimental analysis aimed at investigating the high-pressure (sub- and super-critical) CO2 sorption behaviour on two high-rank coals of different sizes is presented in this paper. Coals from the same seam (9ft seam), but from depths of 150 m (BD coal) and 550 m (AB coal) and different locations of the South Wales (UK) coalfield, known to be strongly affected by tectonically developed fracture systems, are employed for that purpose. Hence, the sorption behaviour of powdered (0.25-0.85 mm, 2.36-4.0 mm) and core samples obtained from locations associated with the deformation related changes is analysed in this paper to assess the CO2 storage potential of such coals. The results show that the coals exhibit maximum adsorption capacities up to 1.93 mol/kg (BD coal) and 1.82 mol/kg (AB coal). No dependence of the CO2 maximum sorption capacity with respect to the sample size for the BD coal is observed, while for the AB coal the maximum sorption capacity is reduced by more than half between the powdered and core samples. The CO2 sorption rates on BD coal decrease by a factor of more than 9 from 0.25-0.85 mm to 2.36-4.0 mm and then remain relatively constant with further increase in sample size. The opposite is observed for the AB coal where sorption rates decrease with increasing sample size, i.e. reducing by a factor of more than 100 between the 0.25-0.85 mm and core samples. The differences in behaviour are interpreted through the structure each coal exhibits associated with the burial depths and sampling locations as well as through the minor variations in ash contents. This study demonstrates that anthracite coals, having experienced sufficient deformation resulting in changes in fracture frequency, can adsorb significant amounts of CO2 offering great prospect to be considered as a CO2 sequestration option

Pregled načina rada energetskih pilota i utjecaja na okolno tlo

Thermo-active ground structures represent low-energy and sustainable technology which is a clear priority for many countries. Heat transfer between such structures and the surrounding soil is understood to play an important role both in the overall thermal performance of buildings and in the evolution of stresses in structural elements and the surrounding soil. This paper presents an overview of recent research efforts and developments in relation to energy piles. General aspects on the performance of energy piles and their impact on the surrounding ground are presented based on previous field, laboratory and numerical investigations as well as existing case studies. Based on the current knowledge, further research opportunities are identified and highlighted.Termički aktivne podzemne konstrukcije predstavljaju nisko-energetsku i održivu tehnologiju čija je primjena prioritet za mnoge države. Izmjena topline između podzemnih konstrukcija i okolnog tla ima važnu ulogu u ukupnoj energetskoj učinkovitosti zgrada te doprinosi naprezanjima u konstruktivnim elementima i okolnom tlu. U ovom je radu prikazan pregled nedavnih terenskih, laboratorijskih i numeričkih znanstvenih istraživanja te izvedenih projekata i dobivenih saznanja na području energetskih pilota gdje su prikazani glavni aspekti energetskih pilota i utjecaji njihova rada na okolno tlo. Na temelju navedenih spoznaja, u ovom se radu navode smjernice za buduća istraživanja u ovom području

Investigation of strain-sensitive properties of porous media through micro-CT imaging and numerical modelling

Strain-sensitive characteristics of porous media are studied through micro-CT imaging and numerical simulations. First, high-fidelity Discrete Element Method (DEM) models are constructed for practical porous media based on micro-CT images. These DEM models prioritize the overall system morphology over individual grain/particle shapes, ensuring robustness and flexibility controlled by easily adjustable algorithm parameters. Subsequently, we validate the accuracy of our proposed DEM models by comparing them with the Finite Element Method (FEM), achieving consistent agreement across all test cases. Finally, the CT-image based DEM approach is employed to investigate strain-sensitive properties of porous media, such as permeability, porosity, tortuosity, specific surface area, and fractal dimension. With a primary focus on transport and morphology properties, our approach is versatile and applicable to exploring various other properties of porous media. This study introduces a generic methodology for examining practical porous media under in-situ conditions, providing valuable insights into their response to stress and deformation

Virtue in medical practice:an exploratory study

Virtue ethics has long provided fruitful resources for the study of issues in medical ethics. In particular, study of the moral virtues of the good doctor—like kindness, fairness and good judgement—have provided insights into the nature of medical professionalism and the ethical demands on the medical practitioner as a moral person. Today, a substantial literature exists exploring the virtues in medical practice and many commentators advocate an emphasis on the inculcation of the virtues of good medical practice in medical education and throughout the medical career. However, until very recently, no empirical studies have attempted to investigate which virtues, in particular, medical doctors and medical students tend to have or not to have, nor how these virtues influence how they think about or practise medicine. The question of what virtuous medical practice is, is vast and, as we have written elsewhere, the question of how to study doctors’ moral character is fraught with difficulty. In this paper, we report the results of a first-of-a-kind study that attempted to explore these issues at three medical schools (and associated practice regions) in the United Kingdom. We identify which character traits are important in the good doctor in the opinion of medical students and doctors and identify which virtues they say of themselves they possess and do not possess. Moreover, we identify how thinking about the virtues contributes to doctors’ and medical students’ thinking about common moral dilemmas in medicine. In ending, we remark on the implications for medical education

Response of compacted bentonites to thermal and thermo-hydraulic loadings at high temperatures

The final disposal of high-level nuclear waste in many countries is preferred to be in deep geological repositories. Compacted bentonites are proposed for use as the buffer surrounding the waste canisters which may be subjected to both thermal and hydraulic loadings. A significant increase in the temperature is anticipated within the buffer, particularly during the early phase of the repository lifetime. In this study, several non-isothermal and non-isothermal hydraulic tests were carried on compacted MX80 bentonite. Compacted bentonite specimens (water content = 15.2%, dry density = 1.65 Mg/m3) were subjected to a temperature of either 85 or 150 °C at one end, whereas the temperature at the opposite end was maintained at 25 °C. During the non-isothermal hydraulic tests, water was supplied from the opposite end of the heat source. The temperature and relative humidity were monitored along predetermined depths of the specimens. The profiles of water content, dry density, and degree of saturation were established after termination of the tests. The test results showed that thermal gradients caused redistribution of the water content, whereas thermo-hydraulic gradients caused both redistribution and an increase in the water content within compacted bentonites, both leading to development of axial stress of various magnitudes. The applied water injection pressures (5 and 600 kPa) and temperature gradients appeared to have very minimal impact on the magnitude of axial stress developed. The thickness of thermal insulation layer surrounding the testing devices was found to influence the temperature and relative humidity profiles thereby impacting the redistribution of water content within compacted bentonites. Under the influence of both the applied thermal and thermo-hydraulic gradients, the dry density of the bentonite specimens increased near the heat source, whereas it decreased at the opposite end. The test results emphasized the influence of elevated temperatures (up to 150 °C) on the thermo-hydro-mechanical response of compacted bentonites in the nuclear waste repository setting

Effects of thermo-osmosis on hydraulic behaviour of saturated clays

Despite a body of research carried out on thermally coupled processes in soils, understanding of thermo-osmosis phenomenon in clays and its effects on hydromechanical behavior is incomplete. This paper presents an investigation on the effects of thermo-osmosis on hydraulic behavior of saturated clays. A theoretical formulation for hydraulic behavior was developed, incorporating an explicit description of thermo-osmosis effects on coupled hydromechanical behavior. The extended formulation was implemented within a coupled numerical model for thermal, hydraulic, chemical, and mechanical behavior of soils. The model was tested and applied to simulate a soil heating experiment. It is shown that the inclusion of thermo-osmosis in the coupled thermohydraulic simulation of the case study provides a better agreement with the experimental data compared with the case in which only thermal expansion of the soil constituents was considered. A series of numerical simulations are also presented, studying the pore-water pressure development in saturated clay induced by a heating source. It is shown that pore-water pressure evolution can be considerably affected by thermo-osmosis. Under the conditions of the problem considered, it was found that thermo-osmosis changed the pore-water pressure regime in the vicinity of the heater when the value of thermo-osmotic conductivity was larger than 10−12 m2·K−1·s−1. New insights into the hydraulic response of the ground and the pore-pressure evolution due to thermo-osmosis are provided in this paper