Experimental and numerical investigation of heat and mass movement in unsaturated clays

The study of heat transfer and moisture movement in liquid and vapour phase has attracted the attention of scientists from the beginning of 19th century. The study is very important to many geotechnical and geoenvironmental problems like diurnal heat mass movement in ground, performance assessment of nuclear waste disposal repositories, buried hot pipes, buried high voltage electric cables and landfill liners. Significant experimental and theoretical development has been made in this field but still there is a lack of experimental data available specially for highly swelling clays. The heat transfer and liquid moisture movement theories for clays more or less are very well established but vapour transfer theory is still based upon rigid matrix granular soils. Therefore, this thesis presents an experimental, theoretical and numerical investigation of the heat and moisture movement in unsaturated clays. A new apparatus termed a thermo-hydraulic (TH) cell has been designed, fabricated and calibrated in-house to perform thermal gradient, thermo-hydraulic gradient and isothermo-hydraulic gradient tests on two types of clays namely Speswhite kaolin and MX-80 bentonite. The TH cell is capable of measuring the transient temperature, relative humidity, volume flow rate of incoming water and swelling pressure. It also facilitates the determination of moisture content, dry density and chemical composition (anions and cations concentration) of the soil samples at the end of the tests. In the thermal test, the clay sample is subjected to fixed temperatures of 85 C at the bottom end and 25 C at the top end. In the thermo-hydraulic test, same thermal gradient is used like the thermal test and in addition to this deionised and de-aired water was supplied at the top end under a pressure of 0.6 MPa. In the isothermal test, the clay sample is supplied deionised and de-aired water from the top end under a pressure of 0.6 MPa and the temperature kept at 25 C at both ends of the clay sample. The test results show that there is a cycle of vapour and liquid moisture movement within the clay sample, vapour moves from the hot end to the cold and condense to liquid at the cold end and liquid moisture moves to the hot end. The accumulation of chloride ions near the hot end indicate that liquid moisture moved from the cold end to the hot end. An empirical method has been developed to calculate the vapour fluxes using the variation of chloride ions concentration with time. The vapour fluxes calculated empirically found to be much lower than that determined by existing vapour theories. Therefore, the existing vapour theory has been modified to more closely predict the observed vapour fluxes. The new modified vapour transfer theory has been incorporated in transient finite element code and validated against the experimental work carried out in this study. The numerically simulated results match reasonably with the experimental heat and mass results. Further research is necessary to explore the new vapour theory application to large scale tests

Neutron scattering study of strain behaviour of porous rocks subjected to heating and unconfined uniaxial compression

Peer reviewedPublisher PD

Numerical investigation of a district scale groundwater heat pump system: a case study from Colchester, UK

Nearly 40% of Europe’s total energy consumption is dedicated to buildings and heating/cooling make a significant part of this consumption. Groundwater heat pumps (GWHP) are highly efficient, and low-carbon technology that can supply heating/cooling to buildings on small or large scales. Thus, they contribute to achieving European targets of net-zero greenhouse gas emissions by 2050. In the literature, studies on the utilisation of GWHP at a district scale, particularly in chalk aquifers, are relatively rare. The implementation of district-scale geothermal heat pump (GWHP) systems poses several challenges, including dealing with the scale and complexity of the systems, addressing geological variability, managing high initial investments, balancing energy demand and supply, ensuring proper maintenance and monitoring, and mitigating potential environmental impacts. These challenges require careful consideration and strategic planning to ensure the successful deployment and sustainable operation of these systems., This study numerically investigates a district-scale GWHP system and analyses the thermal plume development created due to the heating operation, offering insights into system performance. A good match was found between field results and simulation results for water level increase and drawdown. However, there is a difference of approximately 11% in system efficiency between field tests and simulations due to the lower abstraction temperature detected in the simulation. The simulation results show that cooler water injection into the fractured chalk aquifer creates a thermal plume radially spanning out to 50 m. The thermal plume has no effect on the abstraction temperature and system performance. This result can be attributed to the large distance between injection and abstraction wells and the low hydraulic gradient

Improved quantification of CO2 storage containment risks - an overview of the SHARP Storage project

Carbon Capture and Storage (CCS) is now maturing in Europe and worldwide with several Net Zero projects emerging. Hence, the need for safe and reliable CO2 storage sites is accelerating and the accurate assessment of large-scale storage options at the gigatonne-per-year is critical. The SHARP project addresses the main priority areas required to improve current technologies to deliver CO2 storage volumes at the scale needed to meet demands for large scale storage. Research needs identified in the industry has provided the base for this well-integrated project with the ambitions to reduce the uncertainty in the geomechanical response to CO2 injection. Six case studies from sites in the North Sea and India will be matured during the projects. Ongoing work includes review of existing stress data, updating and integration of seismic catalogues and planning of new experimental data for improved constitutive models and rock failure attributes. Improved data analysis, compiling data from different sources, and new data generated in the project is expected to provide a base for updated failure risk assessment and more targeted monitoring. An initial assessment of rock failure risk in in progress and will be updated with a "Round 2" failure assessment incorporating new learnings and more mature data. The improved failure risk assessment includes the use of Bayesian statistical approach for quantification of uncertainties in geomechanical properties. Methods to quantify geological containment risk will be developed by reading across event tree techniques from other industries (e.g. nuclear). A set of generic release diagrams have been derived in a series of interdisciplinary workshops as a starting point for risk modellingImproved quantification of CO2 storage containment risks - an overview of the SHARP Storage projectpublishedVersio

Response of unsaturated soils to heating of geothermal energy pile

Geothermal energy piles (GEPs) are an environmentally friendly heat exchange technology that dualizes the role of structural foundation pile for load support and in meeting the building heating/cooling need. Energy loops made from high-density polyethylene which allow heat carrier fluid circulation, are fitted into the pile foundation elements to extract or inject and store heat energy in the soil surrounding the pile. This paper reports the results of a numerical study investigating the response of an energy pile embedded in unsaturated soils (sand, silt and clay) to natural thermal recovery, after heat injection process. It was found that the increase in soil saturation, duration of heating operation i.e. intermittent (8 or 16 h heating) or continuous mode, magnitude of the heat injection rates influences the temperature changes in the soil surrounding the pile, consequently impacting on the system performance. Similarly, it was observed that temperature at all location approached initial state in a duration equal to about twice that of the heating time. In addition, it was found that imposing excessive heat flux on the pile results in the drying up of the surrounding soil leading to lower thermal conductivity thus decreasing the overall GEP system performance

Long-Term Thermal Performance of Group of Energy Piles in Unsaturated Soils under Cyclic Thermal Loading

Geothermal energy piles (GEPs) are an environmentally friendly heat exchange technology that dualizes the role of the structural foundation pile for load support and in meeting the building heating/cooling need. Energy loops made from high-density polyethylene, which allow heat carrier fluid circulation, are fitted into the pile foundation elements to extract or inject and store heat energy in the soil surrounding the pile. This paper reports the results of a numerical study investigating the long-term behaviour of a group of energy piles embedded in unsaturated soils (sand and clay) under continuous cyclic heating and cooling load. Additionally, two scenarios were investigated where: (1) the whole GEPs were heated and cooled collectively; (2) alternate piles were heated and cooled. It was found that the trend of temperature magnitude at all the observed locations decreases with time as a result of the continuous heating and cooling cycles. Furthermore, subjecting alternate GEPs to the heating and cooling cycles result in lower temperature development in comparison to thermally activating all the GEPs in the group. This is attributed to the applied thermal load, which is 0.5 times that considered in the first case. However, this might not be the case where equal thermal load is applied on the GEPs in the two cases investigated

Numerical investigation of the performance of group of geothermal energy piles in unsaturated sand

The use of foundation structures (piles) coupled to a heat pump system, commonly referred to as geothermal energy pile (GEP) system, provides a renewable energy solution of achieving space heating and cooling in buildings; whilst also being utilised for the structural stability of the overlying structures. The system operates by exchanging the low-grade heat energy within the shallow earth surface with the building, via the circulation of heat carrier fluid enclosed in a high-density polyethylene plastic pipes. In summer, heat energy is extracted from the building and transferred into the ground to achieve space cooling. While in winter, the ground heat energy is harnessed and transferred to the building to achieve sustainable space heating. This paper investigates the thermal performance of group of GEP system under the effects of different initial soil pore water content. Through the five-year simulation’s period, it was found that the increase in soil pore water content decreases the possibility of thermal interaction between the GEPs in the group. Also, it was observed that the trend in maximum temperature witnessed within the soil domain decreases nonlinearly during the five years period

Evaluation of thermal conductivity estimation models with laboratory-measured thermal conductivities of sediments

Thermal conductivity is one of the key parameters for estimating low-temperature geothermal potential. In addition to field techniques, it can be determined based on physical parameters of the sediment measured in the laboratory. Following the methodology for cohesive and non-cohesive sample preparation, laboratory measurements were carried out on 30 samples of sediments. Density, porosity and water content of samples were measured and used in thermal conductivity estimation models (TCEM). The bulk thermal conductivity (λb) calculated with six TCEMs was compared with the measured λb to evaluate the predictive capacity of the analytical methods used. The results show that the empirical TCEMs are suitable to predict the λb of the analysed sediment types, with the standard deviation of the residuals (RMSE) ranging from 0.11 to 0.35 Wm−1 K−1. To improve the fit, this study provides a new modified parameterisation of two empirical TCEMs (Kersten and Côté&Konrad model) and, therefore, suggests the most suitable TCEMs for specific sample conditions. The RMSE ranges from 0.11 to 0.29 Wm−1 K−1. Mixing TCEM showed an RMSE of up to 2.00 Wm−1 K−1, meaning they are not suitable for predicting sediment λb. The study provides an insight into the analytical determination of thermal conductivity based on the physical properties of sediments. The results can help to estimate the low-temperature geothermal potential more quickly and easily and promote the sustainable use of this renewable energy source, which has applications in environmental and engineering science