Improved understanding of geothermal energy through a multiscale modelling approach

Overview

Geothermal is a carbon-free, renewable and constantly available energy source which has a huge role to play in decarbonising our economy. Geothermal heat exchangers are a technology which allow the ground to used to heat buildings in winter and cool them in winter. Central to characterising the effectiveness of geothermal heat exchangers is the thermal conductivity of the soil in which the exchangers operate [1]. This project aims to combine advanced numerical and experimental techniques to improve our understanding of how the properties of the soil affect its thermal conductivity and therefore the efficiency of heat exchangers. Thermal conductivity in soil is a fundamentally grain-scale process, i.e. heat is conducted between and around soil grains. When modelling thermal conductivity in soils two broad options are available. Firstly, one can adopt a discrete approach such as discrete element modelling (DEM), where individual grains are modelled but which is currently too computationally demanding to model field or full laboratory scale processes [2]. The second option is a continuum approach, which is computationally efficient but cannot capture the influence of individual soil grains and so is not well suited to studying the fundamental mechanisms of conductivity. In order to improve our understanding of how thermal conductivity operates at the grain-scale we require methods that can bridge this divide.
In this project we aim to build on ongoing work at the University of Glasgow and Newcastle University to create a new multiscale approach to modelling thermal conductivity which uses a discrete approach in areas of high thermal gradient and a more efficient continuum approach away from these areas. By enabling larger granular systems to be efficiently modelled we will be able to optimise heat exchangers through an improved microscale understanding. This work will be validated with advanced experimental measurements.
The key objectives of the project are:
– Develop a new method for modelling heat transfer in granular materials based on the quasi-continuum approach [3] – Validate the method using specialist laboratory apparatus for measuring the thermal conductivity of soils.
– Carry out a comprehensive study to determine how soil characteristics such as packing density, anisotropy and particle shape affect the thermal conductivity of the ground.
The successful candidate

Methodology

The majority of the work will be carried out at the University of Glasgow (UoG), with a placement at Newcastle University (NU) to carry out experimental work. Supervisors from both institutions will be involved in the work at every stage.
– Review current approaches to modelling thermal conductivity in soils at the microscale (discrete) and macroscale (continuum). [UoG] – Select the most appropriate multiphysics methods which capture both mechanical and thermal behaviour of the soil and which can be used with the quasicontinuum approach. [UoG] – Adapt an existing open-source quasicontinuum code to model thermal heat transfer and to allow the boundary conditions from the experimental device to be modelled. [UoG] – Carry out numerical validation and plan experimental validation. [UoG / NU] – Carry out laboratory testing to produce validation data with a variety of soil packing densities, grain sizes and grain shapes through a placement at Newcastle University. [NU] – Validate and improve the numerical model. [UoG] – Carry out a comprehensive parametric study to investigate the microscale mechanisms which underlie soil thermal conductivity. [UoG] – Propose a practical framework to characterise soil thermal conductivity based on the soil- microscale properties. [UoG / NU]

Project Timeline

Year 1

Review existing methods and fundamentals of the problem. Build core knowledge and skills in computer programming. Learn to use existing quasicontinuum code at UoG. Select methods to implement thermal quasicontinuum method.

Year 2

Implement new thermal quasicontinuum method and validate. Plan laboratory testing.
Present interim work at UK national conference.

Year 3

Carry out experimental validation and improve numerical model.
Parametric study of soil properties. Begin thesis write up.

Year 3.5

Complete thesis write up.

Training
& Skills

You will learn advanced coding skills which will be transferable to a range of problems in industry and research. This will be facilitated by existing staff, students and postdocs within the Glasgow Computational Engineering Centre.
Practical skills in designing and performing laboratory experiments will be learnt at Newcastle University School of Engineering.
A deep knowledge of geothermal energy will be gained. A wide range of transferable skills such as technical writing, presenting and data analysis will also be developed. The supervisory team will take an active involvement in the development of these skills, in addition to a range of taught courses provided by the University of Glasgow.

References & further reading

1. Alrtimi, A., Rouainia, M., Manning, D.A.C.: An improved steady-state apparatus for measuring thermal conductivity of soils. Int. J. Heat Mass Transf. (2014). doi:10.1016/j.ijheatmasstransfer.2014.01.034
2. Feng, Y.T., Han, K., Owen, D.R.J.: Discrete thermal element modelling of heat conduction in particle systems: Pipe-network model and transient analysis. Powder Technol. (2009). doi:10.1016/j.powtec.2009.03.001
3. Tadmor, E.B., Ortiz, M., Phillips, R.: Quasicontinuum analysis of defects in solids. Philos. Mag. A. 73, 1529–1563 (1996). doi:10.1080/01418619608243000

Further Information

Please contact Tom Shire (Thomas.shire@glasgow.ac.uk) for more information.

Application procedure: For IAPETUS2 applications to the University of Glasgow please use the dedicated application portal: www.gla.ac.uk/ScholarshipApp (you will still need to submit your administrative details to the IAPETUS2 website as well)

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