Thermo-mechanical modelling of rock-like materials at very high temperature : application to ceramic refractories

Rock-like materials like ceramic refractories, in working conditions may be subject to large temperature variations. To simulate practical applications, bespoke constitutive modelling is required. In this work a general, thermodynamically consistent framework, able to incorporate key micromechanical features of the material behaviour, and applicable to a wide range of geomaterials, is formulated and validated. Different thermodynamic potentials are proposed to deal with both reversibility and irreversibility. A key advantage of this approach is the ability to freely choose the thermal dependency interpolation functions. Extensive model validation is provided by correctly reproducing both reversible and irreversible experimental trends of different materials under different loading conditions. It is found that even for simple materials, if a sample is subject to a large stress level, its thermal and mechanical responses become unexpectedly coupled. The proposed modelling framework is not limited to refractories and can be easily adapted to different types of rock-like materials

A computational framework for immiscible three-phase flow in deformable porous media

Several soil decontamination processes and enhanced oil recovery techniques involve the co-existence of three immiscible fluids, such as water, a nonaqueous phase liquid and a gas. In this work, a computational framework based on the individual mass balance of each phase is developed, aimed at simulating three-phase flow in a deformable rock through the finite element method, without resorting to specific simplifications that are usually required by standard numerical schemes. Key ingredients of the model are: expression of the residual in terms of mass contents, consistent lumping of the storage terms in the residual and algorithmic (tangent) matrix, consistent integration rules, the use of a minimum relative permeability and a time marching scheme based on trapezoidal integration. Special convective boundary conditions are adopted for pressures to be consistent with the assumed rock wettability properties during co-current imbibition. The resulting numerical scheme can deal with arbitrary saturation and/or pressure boundary conditions. The model is tested by simulating gas injection tests, and both co- and counter-current water imbibition tests, in a deformable core. To assess the performance and robustness of the whole framework, sensitivity analyses are performed upon varying key constitutive, loading and numerical parameters

A new modelling approach for piled and other ground heat exchanger applications

Pile heat exchangers have an increasing role to play in the delivery of renewable heating and cooling energy. Traditionally the thermal design of ground heat exchangers has relied upon analytical approaches which take a relatively simple approach to the inside of the heat exchanger. This approach is justified while the heat exchanger diameter remains small. However, as larger diameter piled foundations are used as heat exchangers, the transient heat transfer processes operating within the pile become more important. To increase our understanding of these processes and ultimately lead to improved thermal design approaches for pile heat exchangers it is important to examine the heat transfer within the pile in detail. To accomplish this, a new numerical approach has been implemented within the finite element software ABAQUS. Coupling of the convective heat transfer due to fluid flow within the heat transfer pipes and the heat transfer by conduction within the pile concrete is the most important facet of the model. The resulting modelling approach, which is ready to generalise to other geothermal applications and to assess thermo-mechanical couplings, has been validated against a multi-stage thermal response test carried out on a test pile in London Clay

Dynamical effects during compaction band formation affecting their spatial periodicity

Compaction bands (CBs) are responsible for significant anisotropy alterations of permeability in geological materials; hence, understanding their formation conditions appears of key importance to all applications involving fluid extraction/injection from/into the ground. While most of the available models to understand CB formation are focused on interpreting the onset of a single CB, little effort has been so far dedicated to understand the documented periodicity of CBs. In this paper, the role of dynamical effects in inducing the post onset evolution of CBs is analyzed by means of a dedicated model for porous media with compressible constituents, with reference to a horizontal layer of sandy, water-saturated material. Elastic waves are generated as a first CB occurs due to sudden, localized volumetric collapse. If the waves are reflected at the interface with a softer material or with a previously formed CB, they produce significant local effective stress concentrations, which can promote the formation of further CBs in a cascade fashion, according to a regular geometric pattern. The spatial distribution of dynamically generated CBs, as well as the extent of the phenomenon, depends on the geometry of the domain and on the material's permeability. Sensitivity analysis is also performed to assess the key properties that promote dynamical CB in situ formation, identifying as the most influential conditions large stratum stiffness (increasing with depth) and the presence of softer layers. In contrast, the presence of less permeable and/or stiffer layers is not believed to play a major role in the proposed mechanism

Influences on the thermal efficiency of energy piles

Energy piles have recently emerged as a viable alternative to borehole heat exchangers, but their energy efficiency has so far seen little research. In this work, a finite element numerical model is developed for the accurate 3D analysis of transient diffusive and convective heat exchange phenomena taking place in geothermal structures. The model is validated by reproducing both the outcome of a thermal response test carried out on a test pile, and the average response of the linear heat source analytical solution. Then, the model is employed to carry out a parametric analysis to identify the key factors in maximising the pile energy efficiency. It is shown that the most influential design parameter is the number of pipes, which can be more conveniently increased, within a reasonable range, compared to increasing the pile dimensions. The influence of changing pile length, concrete conductivity, pile diameter and concrete cover are also discussed in light of their energetic implications. Counter to engineering intuition, the fluid flowrate does not emerge as important in energy efficiency, provided it is sufficient to ensure turbulent flow. The model presented in this paper can be easily adapted to the detailed study of other types of geothermal structures

Air monitoring for synthetic cannabinoids in a UK prison: Application of personal air sampling and fixed sequential sampling with TD-GC×GC-TOF MS analysis

In recent years there have been increasing complaints from staff working in UK prisons of secondary exposure to psychoactive drug fumes, often believed to be synthetic cannabinoids. Our pilot study aimed to provide an initial evidence base for this issue and reveal compounds of interest within indoor prison air. Here we present a new method for the detection of synthetic cannabinoids in air, and demonstrate its application in a UK prison. Air sampling was conducted using a fixed sequential sampler, alongside personal air sampling units worn by prison officers within an English prison. Air samples were collected onto thermal desorption (TD) tubes and analysed via comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF MS). This study is the first of its kind in a prison setting and the approach is of importance to analytical scientists, policy makers and public health employees tasked with the health and safety of prison staff. GC×GC-TOF MS analysis was able to separate and identify a range of compounds present in the prison air samples. Analysis of the TD tubes did not reveal any synthetic cannabinoids from the fixed pump air samples or the personal pump samples worn by prison officers. Air monitoring in prisons presents a challenge of logistics as well as science. Fixed sequential air sampling combined with personal air monitoring devices allowed air from multiple locations within a prison to be collected, providing a comprehensive approach to evaluating the air that prison staff are exposed to during a fixed time period

Energy performance of diaphragm walls used as heat exchangers

The possibility of equipping diaphragm walls as ground heat exchangers to meet the full or partial heating and cooling demands of overlying or adjacent buildings has been explored in recent years. In this paper, the factors affecting the energy performance of diaphragm walls equipped as heat exchangers are investigated through finite element modelling. The numerical approach employed is first validated using available experimental data and then applied to perform parametric analyses. Parameters considered in the analysis include panel width, the ratio between the wall and excavation depths, heat transfer pipe spacing, concrete cover, heat-carrier fluid velocity, concrete thermal properties and the temperature difference between the air within the excavation and the soil behind the wall. The results indicate that increasing the number of pipes by reducing their spacing is the primary route to increasing energy efficiency in the short term. However, the thermal properties of the wall concrete and the temperature excess within the excavation space are also important, with the latter becoming the most significant in the medium to long term. This confirms the benefits of exploiting the retaining walls installed for railway tunnels and metro stations where additional sources of heat are available

High Doses of Ursodeoxycholic Acid Up-Regulate the Expression of Placental Breast Cancer Resistance Protein in Patients Affected by Intrahepatic Cholestasis of Pregnancy

BACKGROUND: Ursodeoxycholic acid (UDCA) administration in intrahepatic cholestasis of pregnancy (ICP) induces bile acids (BA) efflux from the foetal compartment, but the molecular basis of this transplacental transport is only partially defined. AIM: To determine if placental breast cancer resistance protein (BCRP), able to transport BA, is regulated by UDCA in ICP. METHODS: 32 pregnant women with ICP (14 untreated, 34.9\ub15.17 years; 18 treated with UDCA--25 mg/Kg/day, 32.7\ub14.62 years,) and 12 healthy controls (33.4\ub13.32 years) agreed to participate in the study. Placentas were obtained at delivery and processed for membrane extraction. BCRP protein expression was evaluated by immunoblotting techniques and chemiluminescence quantified with a luminograph measuring emitted photons; mRNA expression with real time PCR. Statistical differences between groups were evaluated by ANOVA with Dunn's Multiple Comparison test. RESULTS: BCRP was expressed only on the apical membrane of the syncytiotrophoblast. A significant difference was observed among the three groups both for mRNA (ANOVA, p\u200a=\u200a0.0074) and protein (ANOVA, p<0.0001) expression. BCRP expression was similar in controls and in the untreated ICP group. UDCA induced a significant increase in placental BCRP mRNA and protein expression compared to controls (350.7\ub1106.3 vs 100\ub118.68% of controls, p<0.05 and 397.8\ub156.02 vs 100\ub111.44% of controls, p<0.001, respectively) and untreated ICP (90.29\ub117.59% of controls, p<0.05 and 155.0\ub113.87%, p<0.01). CONCLUSION: Our results confirm that BCRP is expressed only on the apical membrane of the syncytiotrophoblast and show that ICP treatment with high dose UDCA significantly upregulates placental BCRP expression favouring BA efflux from the foetal compartment