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Numerical Modeling of Hydrothermal Behavior of Geothermal Tunnels in Sandy Soils

Ashkbari, Mohammad Amin | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55528 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mehdi
  7. Abstract:
  8. Shallow geothermal energy is a renewable and sustainable form of energy that has the potential to help alleviate the growing climate and energy crisis. The most common system used to extract shallow geothermal energy is the ground source heat pump (GSHP) system. The concept of using underground structures in exploiting shallow geothermal energy for space heating and cooling has received increasing attention. This study focuses on the use of geothermal tunnels as a means of extracting shallow geothermal energy.This research examines the effects of different heat transfer mechanisms, and highlights the effects of this phenomenon by focusing on the effects of natural convection around the tunnel. To carry out this research, finite element numerical method and 3D modeling were used in COMSOL Multiphysics software. In order to carry out validation, three studies were used to investigate natural convection heat transfer around the heat source, tunnel modeling without water flow and tunnel modeling with flow. According to the obtained results, the thermal conduction mechanism cannot alone explain the heat transfer in saturated sandy soil, and for the proper understanding of heat distribution, natural convection and forced convection need to be considered in the modeling. Flow rate and soil permeability are important factors in investigating heat transfer in sandy soil. Parametric analysis was performed in the case of the presence of natural convection flow alone and the presence of natural and forced convection flow simultaneously. The diameter and thickness of the pipes have a great effect on the output power of the tunnel, and the increase in the flow rate entering the pipes and the temperature inside the tunnel increase the output power. If the tunnel with a higher temperature is placed next to the thermal tunnel, the output power will increase and if the adjacent tunnel extracts the same heat, the output power will decrease.Also, the effects of heat extraction with interruption and rest to the system were investigated, and these conditions make the system perform more optimally than the intermittent extraction mode, and the output power increases.

  9. Keywords:
  10. Heat Transfer ; Thermohydraulics ; Convection ; Numerical Modeling ; Finite Element Method ; Thermal Conductivity ; Energy Tunnel ; Granular Soil

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