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Analysis of coaxial borehole heat exchanger for geothermal heat and power Pokhrel, Sajjan

Abstract

Decarbonization of heat and electricity generation through geothermal energy is increasing, thanks to its universal availability and base load capacity. Although geothermal energy has several advantages compared to other renewable energy sources, more research is necessary to understand the fluid flow and heat transfer processes in diverse geological formations. These geological formations can be complex due to the variability of rock/soil properties, fluid presence, and fluid movement. Heat exchangers employed in such systems can reach thousands of meters, posing challenges for field-test experiments. In addition, mathematical modeling of such systems is a challenging task. This dissertation is based on two geothermal projects; one focused on power generation and the other on heating. Both projects employ either a coaxial borehole heat exchanger (a single coaxial borehole) or a system of coaxial borehole heat exchangers. For geothermal power, a field-test experiment is carried out in a high-temperature resource well with a thermal gradient of 0.4°C/m. Experimental results are analyzed and rock properties are measured. In addition, a numerical model is developed to replicate the 500-meter deep field-test experiment. The developed numerical model is validated with the experimental data and is used to understand the subsurface behavior of the geothermal reservoir. Additionally, the performance of the heat exchanger under the complex geological formation, accounting for the presence of subsurface fluid flow, is evaluated. For geothermal heating, a numerical model is developed to study the heat transfer characteristics of a solar-geothermal heating system. The developed numerical model solves the heat and mass transfer process in a rectangular array of 450 coaxial boreholes. It also accounts for energy generation in solar thermal collectors and thermal demand on buildings. The numerical model is used to study energy injection into boreholes, energy extraction from boreholes, thermal interactions between boreholes, thermal losses from the system, and the performance of the solar-geothermal heating system. The results showed that subsurface fluid flow has a significant impact on the energy output from geothermal systems. Solar-geothermal heating systems have good potential to decarbonize space and water heating applications in Canada.

Item Metadata

Title
Analysis of coaxial borehole heat exchanger for geothermal heat and power
Creator
Pokhrel, Sajjan
Supervisor
Ghoreishi-Madiseh, Seyed Ali
Publisher
University of British Columbia
Date Issued
2024
Description
Decarbonization of heat and electricity generation through geothermal energy is increasing, thanks to its universal availability and base load capacity. Although geothermal energy has several advantages compared to other renewable energy sources, more research is necessary to understand the fluid flow and heat transfer processes in diverse geological formations. These geological formations can be complex due to the variability of rock/soil properties, fluid presence, and fluid movement. Heat exchangers employed in such systems can reach thousands of meters, posing challenges for field-test experiments. In addition, mathematical modeling of such systems is a challenging task. This dissertation is based on two geothermal projects; one focused on power generation and the other on heating. Both projects employ either a coaxial borehole heat exchanger (a single coaxial borehole) or a system of coaxial borehole heat exchangers. For geothermal power, a field-test experiment is carried out in a high-temperature resource well with a thermal gradient of 0.4°C/m. Experimental results are analyzed and rock properties are measured. In addition, a numerical model is developed to replicate the 500-meter deep field-test experiment. The developed numerical model is validated with the experimental data and is used to understand the subsurface behavior of the geothermal reservoir. Additionally, the performance of the heat exchanger under the complex geological formation, accounting for the presence of subsurface fluid flow, is evaluated. For geothermal heating, a numerical model is developed to study the heat transfer characteristics of a solar-geothermal heating system. The developed numerical model solves the heat and mass transfer process in a rectangular array of 450 coaxial boreholes. It also accounts for energy generation in solar thermal collectors and thermal demand on buildings. The numerical model is used to study energy injection into boreholes, energy extraction from boreholes, thermal interactions between boreholes, thermal losses from the system, and the performance of the solar-geothermal heating system. The results showed that subsurface fluid flow has a significant impact on the energy output from geothermal systems. Solar-geothermal heating systems have good potential to decarbonize space and water heating applications in Canada.
Genre
Thesis/Dissertation
Type
Text
Language
eng
Date Available
2024-03-04
Provider
Vancouver : University of British Columbia Library
Rights
Attribution-NonCommercial-NoDerivatives 4.0 International
DOI
10.14288/1.0440617
URI
http://hdl.handle.net/2429/87521
Degree
Doctor of Philosophy - PhD
Program
Mining Engineering
Affiliation
Applied Science, Faculty of; Mining Engineering, Keevil Institute of
Degree Grantor
University of British Columbia
Graduation Date
2024-05
Campus
UBCV
Scholarly Level
Graduate
Rights URI
http://creativecommons.org/licenses/by-nc-nd/4.0/
Aggregated Source Repository
DSpace

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Attribution-NonCommercial-NoDerivatives 4.0 International