| The heat transfer performance of the buried tube heat exchanger is the key to the efficient operation of the ground source heat pump system.The heat transfer process in the buried pipe is closely related to the physical and thermal properties of the surrounding rock layers.The thermal conductivity of different geotechnical lithologies varies greatly.If there is groundwater seepage in the stratum,the heat transfer process of the surrounding rock and soil will be affected.At present,the method of treating the rock and soil around the buried pipe as a homogeneous body is not accurate,because the physical inhomogeneity of the formation will greatly affect the heat transfer process inside the pipe,thus affecting the heat exchange efficiency of the buried pipe heat exchanger.The study on the heat transfer performance of the buried pipe in the stratification of underground rock and soil structure can more accurately describe the difference of heat transfer performance between different lithological structures and different hydrogeological environments to the buried heat exchanger,which can effectively guide the ground.The depth of the borehole is buried,and the advantageous heat transfer layer is found,so that the length of the buried pipe is reasonably designed,the initial investment cost is reduced,and the safe and effective operation of the system is ensured,which plays an important role in the design and operation of the ground source heat pump system.Based on the actual engineering of Xuzhou and Nantong,this paper develops multiple sets of distributed thermal properties for different geological compositions of geotechnical bodies in the two regions,and different strata with or without groundwater seepage.The test experiment,using field measurement and theoretical analysis methods,studied the heat transfer performance of buried pipes in different geological structures.Firstly,the paper compares the differences in heat transfer performance of buried pipes in different stratigraphic geological structures,and solves the distributed thermal properties of each layer.According to the test results,the heat transfer performance of the buried pipe is dynamically changed with depth.The heat transfer capacity of the pipe is affected by the lithology and groundwater seepage factors of the rock and soil around the layer.The underground rock and soil is conventionally considered as homogeneous.The way to guide the depth of the hole and the length of the buried pipe is not accurate enough.Secondly,the effects of different flow velocity,depth,inlet water temperature,intermittent operation mode and buried pipe form on the buried pipe heat exchanger are analyzed.The test results show that the variation range of different stratum structures for different operating parameters is different.Explain that the stratification of the stratum structure will not only affect the heat transfer capacity of the buried heat exchanger during the initial investment and design of the ground source heat pump system,but also affect the reasonable selection of operating parameters during the operation of the ground source heat pump..Finally,different geotechnical properties,groundwater seepage formation,and heat transfer investment costs are different.The heat transfer performance of the buried pipe in the 100m inner area of Xuzhou Gulou area is weakened and strong from top to bottom.The heat transfer performance of the buried pipe in Tongzhou District of Nantong City is characterized by "two small,medium large" with the increase of depth within 100m.The better stratum and the groundwater seepage are more conducive to the improvement of the heat transfer performance of the buried pipe,and the economy is better,which is the advantageous heat exchange layer which is beneficial to the development and utilization.The better stratum and the stratum with groundwater seepage are more conducive to the improvement of the heat transfer performance of the buried pipe,and the economy is better,which is the advantageous heat exchange layer which is beneficial to the development and utilization. |
