Analysis of heat transfer capacity of double-pipe heat exchangers of medium-shallow layers

With the implementation of China's "double carbon" strategic goal geothermal energy as a sustainable development and utilization of clean energy is also highly respected.At present, the researches on geothermal energy development and utilization mainly focus on shallow and middle-deep geothermal energy, few studies on middle-shallow geothermal energy (200-500 m).There is also a lack of engineering cases and theoretical research support for heating and cooling using middle-shallow geothermal energy.This paper based on a 300 m geothermal well constructed in a building air conditioning cold and heat source project in Handan City, Hebei Province, carrying out the heat transfer experiment and theoretical analysis of middle-shallow double-pipe heat exchanger.Firstly, the structure, construction technology and heat transfer characteristics of heat exchanger are studied, based on the established heat exchanger, carrying out the field heat transfer tests under five different conditions, obtaining the related thermal physical parameters.Secondly, analyzing the characteristics of middle-shallow geothermal energy, studying the heat transfer law and circulation direction of heat exchanger, based on the existing heat transfer models of shallow buried pipe and middle deep coaxial pipe, the heat transfer model for middle and shallow casing heat exchanger in winter and summer is innovatively established, simulation analysis of the heat transfer model is performed by the corresponding control equations, verifying the accuracy of the heat transfer model by comparing the simulated data with the experimental data.The last, based on the established heat transfer model, the geothermal well is simulated for the whole year, obtaining the parameters of inlet and outlet temperature difference and heat transfer at different flow rates in winter and summer, as well as the transverse and longitudinal changes of rock mass temperature, providing theoretical basis and technical guidance for further improving the structure of middle-shallow layers double-pipe heat exchanger and the design and optimization of outdoor buried tube system.