Research On The Buried Pipes In Sandy Soil For Ground Source Heat Pump System In Cold Coastal Areas

In this paper,the methods of experiment and numerical simulation are used to study the ground source heat pump with pipe buried in sand layer in coastal area.Based on the sandy soil buried pipe ground source heat pump test bench built in the laboratory,the numerical model of sandy soil buried pipe heat transfer was established,and the correctness of the numerical model was verified under dry soil condition,wet soil condition and intermittent operation condition.Based on the verified numerical model,the related parameters of the system are optimized,and the performance of the system is analyzed according to the actual operating conditions.The main research contents are as follows:(1)Based on the ground source ground heat pump system established in Qinhuangdao,a buried pipe heat transfer model is established.The theoretical basis of turbulence model,porous medium model,solidification and melting model in numerical solution process are given.At the same time,the parameter selection method of physical properties of each material in numerical simulation and the setting of boundary conditions of the model are given.(2)The accuracy of the model in this paper is verified by comparing the simulation results with the experimental results.By analyzing the COP of the ground source heat pump system,it is found that the COP of the ground source heat pump system in the wet soil is higher than dry soil.Before the thickness of the ice reaches three centimeters,the operating efficiency of the system is relatively high.The period of returning to the natural temperature field in the sandy soil is longer,and the period for the ice to melt into water is about 1/3 of the period of the natural temperature field.(3)By comparing the effects of different flow rates on the heat transfer of the buried pipe,it is found that the smaller the flow rate,the better the heat transfer effect of the buried pipe.When the thickness of the ice reaches three centimeters,increase the flow rate can enhance the heat transfer effect.The heat transfer effect of the buried heat exchanger is best when the flow rate of the medium in the tube is in the range of 0.012m/s~0.018m/s.Comparing the influence of different moisture content in wet soil,it is concluded that the increase of water content can improve the heat exchange capacity of the buried pipe within a certain running time.For buried pipe in shallow wet soil,the temperature field of sand layer under intermittent operation is greatly affected by air temperature,so the depth of buried pipe should be increased in practical engineering.In this paper,CFD software is used to simulate the heat transfer of buried heat exchangers,and the optimization scheme of the system is obtained.The research results provide reference for similar engineering design and operation scheme.