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Physical Modeling of a Heat Exchanger Pile under Thermo-mechanical Loading in Sand

Hashemi Senejani, Hossein | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51673 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Heat exchanger piles are innovative technologies used to harvest heat from shallow ground. Heat exchanger pile, also known as energy pile, transfers mechanical (structural) loads to the ground while acting as a heat exchanger. Heat extraction in winter and heat rejection during summer changes the pile, pile-soil interaction and the surrounding soil temperature. Therefore, pile temperature increments have been recognized as a new factor of controlling the behavior of energy piles in recent decades. Besides, thermal cyclic loadings may affect the serviceability and geotechnical performance of heat exchanger piles. Physical models provide an affordable experimental medium through which new designs and elements can be more deeply understood. A physical model of a heat exchanger pile is developed and instrumented to study the thermo-mechanical performance of an energy pile. A sand raining device was used to achieve a homogeneous relative density of dry sand throughout the model. A closed-end aluminum tube of 2 cm diameter is used as the model geothermal pile. Four strain-gauges are placed at four locations on the length of pile to monitor the changes in the mechanical and thermal strain of the pile. An LVDT is used to measure the heave or settlement of the pile cap. To monitor the soil temperature variations surrounding the model pile, 10 thermocouples were buried in the soil tank. To provide the cyclic thermal loading, a heater and a thermostat is embedded inside the pile model and it is filled with water to reach a homogenous temperature. The model pile is embedded in dry Babolsar Sand in the rigid box and it simulates non-displacement piles (drilled-shafts). The model is assembled in a temperature controlled room. The pile is tested under sustained mechanical loads and thermal cyclic loadings. The thermo-mechanical behaviour of the pile is investigated and compared with previously built models of similar type. The effects of the thermal load cycles on the geotechnical performance of the heat exchanger pile will be discussed. The initial results showed temperature increments are more dominant in the vicinity of the pile. Also for loads less than 20% of the ultimate load capacity of the pile, the pile would act in an elastic manner after undergoing thermal cycles. The initial results showed temperature increments slightly change the shaft and base capacity (up to 10%). The increase in pile capacity is more dominant under the serviceability condition. However cyclic thermal loading does not show any irreversible thermal stress and strain. Further studies are being performed. Further studies are required and being performed for a reliable framework of the behaviour of geothermal piles to be developed. The model can be easily modified and augmented to perform more advanced tests in the future
  9. Keywords:
  10. Physical Model ; Heat Exchanger Pile ; Geothermal Pile ; Babolsar Sand ; Thermomechanical Loading

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