Experimental Study On Heat Transfer Performance And Thermal Response Of Energy Piles

The energy pile is a building energy-saving technology that utilizes shallow geothermal energy.The traditional ground source heat pump system underground heat exchanger is embedded in the pile foundation.Due to the lack of accurate and perfect research on heat transfer performance at home and abroad,and the lack of necessary field measurement of thermodynamic characteristics in the heat transfer process of energy piles,the large-scale promotion of energy piles in practical projects is hindered.In this text,the multi-root perfusion energy piles in an experimental base are taken as the research object.Firstly,the research background of the energy piles in this experimental base is introduced in detail,and the geothermal physical parameters of the test site are obtained.The basic data are provided for the experimental study of heat transfer performance and thermal response of energy pile.The on-site thermal response test reveals the heat transfer performance of the energy pile at different flow rates,and the following conclusions are obtained: 1)When the circulating medium flow rate is 0.37 m/s,the heat exchange amount and heat exchange rate per meter of the energy pile are the largest.2)The increase of the flow rate of the circulating medium has a certain improvement on the heat exchange efficiency of the pile.It is most obvious when it reaches a certain value,and then gradually decreases.It is recommended that the flow rate of the circulating medium in the heat exchange tube should not be too large,and it is suitable to set it to about 0.4 m/s.3)By comparing the heat transfer performance of traditional drilling heat exchanger,the energy pile has obvious advantages and economy.Through the thermal response test of the energy pile under free confinement conditions,the following conclusions are obtained: 1)In the heat transfer process,the temperature distribution of the pile body is relatively uniform,and the longer the pile is,the higher the total heat transfer is.2)The lateral strain of pile is similar to that of the longitudinal strain.However,the lateral constraint of soil around the pile is stronger than that of lateral friction and the constraint effect of pile end.As a result,the lateral strain of pile is generally smaller than that of the longitudinal strain.3)As under temperature load(),,the maximum additional stress of pile in the pile in the upper position,its value could be more than 1.66 MPa,as an energy pile design personnel must consider the influence of temperature load on the pile bearing capacity.4)In the process of pile heating,temperature load causes partial lateral friction resistance to reverse.With the increase of temperature load,the change trend near the junction of positive and negative side friction resistance in the middle of pile is significantly faster than that at both ends of pile.When the temperature rises to a certain value,the growth trend of positive and negative side friction resistance of energy pile weakens.5)Through the comparison between the actual measurement and the theoretical results,the variation law of the experiment is consistent with the variation of the theoretical results when the top is unconstrained,and the test results are further verified.