Development And Application Of In-situ Thermal Response Tester For Rock And Soil

The position of clean energy in the energy structure has become the vane of the international energy transition.The ground-source heat pump has attracted more and more attention because of its characteristics such as not occupying the surface area,clean and pollution-free.However,in the engineering practice of ground source heat pumps,there are often serious mismatches between the actual operating load and the heat dissipation capacity of the underground heat exchanger,which affects the energy-saving performance and effective service life of the ground source heat pump system.This is mainly because the ground source heat pump system did not accurately obtain the equivalent thermal physical properties of the rock and soil during the design.This problem needs to be completely solved by accurately and efficiently obtaining the in-situ thermal physical properties of the rock and soil.In this context,this paper designs,optimizes and develops a geotechnical in-situ thermal response tester,proposes a data processing method based on parameter fitting,and applies it to engineering practice.The tester’s performance is verified by comparison and analysis.Correctness and reliability.The main work completed in this paper and the main conclusions obtained are as follows:(1)Based on the line heat source theory,this paper independently designed,developed and produced a geotechnical in-situ thermal response tester,which mainly includes the carrier fluid circulation system,heating system,data acquisition system and electrical control system.During the development process,this paper completed the selection design of the key components of the thermal response tester,and constructed a three-dimensional digital model of the tester according to the 1:1 size of the components.After multiple rounds of optimization,the digital prototype of the thermal response tester was obtained.Finally,an in-situ thermal response tester for rock and soil was built according to the optimized model.(2)Apply the developed thermal response tester to the test hole of underground heat exchanger in Chongqing University,and respectively test single U underground heat exchangers with diameters of Φ25 and Φ32 at different depths(150m and 100m).Carry out TRT thermal response test to obtain the in-situ thermal response test data of rock and soil under different heating power and different carrier fluid circulation flow;based on the online heat source model,use Matlab’s lsqcurvefit nonlinear parameter estimation method to obtain the buried pipe test hole The internal thermal resistance of the borehole,the equivalent thermal conductivity of the soil,the original soil temperature and other parameters;the influence of factors such as different heating power and different test durations on the TRT thermal response test results was systematically studied.(3)Designed and built a ground temperature monitoring system,studied the changing laws and characteristics of soil temperature within 150 meters below the surface,and determined the depth of the variable temperature layer and constant temperature layer and the warming layer in the rock and soil area where the buried pipe test hole is located.The geothermal gradient in the middle;the Baggs formula is used to predict the geothermal distribution at different depths,and compared with the measured data to verify the correctness of the formula.(4)In the in-situ thermal response test data processing method of rock and soil proposed in this paper,the innovative integration of initial ground temperature into the output variable of parameter estimation is a new attempt to process the in-situ thermal response test data of rock and soil.The application of the method and related research results will help the further popularization and application of geotechnical thermal response testing in engineering practice.