Study On Thermal-Mechanical Coupling Of New Energy Pile Based On Deep-Buried Pipe

Energy pile thermal storage technology has become an important source of clean energy by virtue of its advantages of saving energy,reducing pollutant emissions and occupying land area.The heat exchanger pipe is buried in the pile foundation.The pile foundation acts as a heat exchanger well.It is connected with the heat pump system through the water collecting pipe.The energy pile and the surrounding soil transfer heat to each other.The heat transfer capacity of conventional energy piles is greatly limited by the length of piles.Based on this,a new type of energy pile structure with deep-buried pipes is proposed,that is,the lower part of the heat transfer pipe passes through the base of the pile to the depth below 150 m,the upper part of the heat transfer pipe is encapsulated by pile foundation concrete,and the lower part is encapsulated by rock.Taking No.2 energy pile as the research object,the performance of a new type of deep-buried energy pile parallel double U-tube heat exchanger and the thermomechanical coupling effect of the energy pile are studied by numerical simulation.The heat transfer process of energy pile is analyzed theoretically,and the model of energy pile foundation parallel double U-tube heat exchanger is established,and the accuracy of the model is verified by comparing with the measured values.The performance of a new deep-buried energy pile foundation parallel double U-tube heat exchanger is studied,and the heat transfer performance of energy pile under different buried depth is analyzed.The results show that compared with conventional energy pile,the heat transfer performance of new deep-buried tube energy pile is significantly improved.When the heat transfer time is 12 hours,the outlet water temperature of the conventional energy pile with 25 m pipe depth is 28.27℃,the total heat transfer capacity of the buried pipe is 1804.5W,and the outlet water temperature of the deep energy pile with 160 m pipe depth is 22.56℃,and the total heat transfer capacity of the buried pipe is 7749.7W.Within the depth range studied,the deeper the buried pipe is,the lower the outlet water temperature is,and the greater the temperature difference between the inlet and outlet is.The model with a depth of 160 m was simulated under different soil initial temperature,flow velocity,inlet water temperature and heat transfer time.The heat transfer characteristics and rules of the new deep buried energy pile were analyzed.It is found that the heat transfer efficiency of the deep-buried tube new energy pile is better than that of the conventional energy pile under the conditions of economic benefit and practical engineering environment permitting.The thermal-mechanical coupling effect of energy pile is studied.The numerical simulation models of end-bearing energy pile and friction energy pile are established respectively.The accuracy of the model is proved by the measured values.The variation of stress and displacement under pure temperature load(ΔT),pure structure load(P)and temperature-structure load(ΔT+P)is analyzed.The results show that under the action of ΔT,the thermal expansion(cold contraction)of the pile produces additional axial compression(tension)stress and additional axial deformation;under the action of P,the settlement of the pile presents a linear distribution;the larger the structural load on the top of the pile,the larger the settlement displacement of the top of the pile;under the combined action of ΔT+P,the change of the axial stress and displacement of the pile is the superposition of the former two.Under the action of P=2000 kN,the maximum settlement displacement of pile top is about 5.40 mm at ΔT=-15℃,and the maximum uplift displacement of pile top is about 1.27 mm at ΔT=20℃,which has little effect on the stability of the structure.In this thesis,numerical simulation is used to study the heat transfer mechanism and thermodynamic performance of deep-buried tube new energy pile.The advantages and problems of deep-buried tube new energy pile as heat exchanger of new ground source heat pump system are analyzed.It provides a certain reference and scientific basis for the popularization and application of new deep-buried pipe energy pile.