| The energy problem is relevant to the human survival and social development,along with the development of industry and modernization,our country energy consumption increased year by year,the traditional heating system to environmental pollution is more serious,so it is urgent to solve the problem of energy consumption and environmental problems caused by greenhouse gas pollution emission.The medium-deep closed ground source heat pump heating system is a low-carbon,clean,green and renewable heating and heating system.Compared with the shallow traditional buried tube heat exchanger system,the system has the advantages of small floor area,high energy efficiency,"take heat without water",and can be used for large-scale urban buildings or low temperature cold area heating.Compared with the middle-deep hydrothermal system,it also has the advantages of protecting groundwater resources and preventing casing from scaling and corrosion.As the key part of the medium and deep depth heat extraction system,the buried tube heat exchanger is the foundation of the efficient operation of the whole system.The buried pipe heat exchanger usually adopts the butt well to form an approximate Ushaped structure to ensure the stable and efficient operation of the underground heat extraction system.In this thesis,a numerical heat transfer model is established for the buried pipe heat exchanger of the butt well of middle and deep geothermal underground.Considering the large span of the middle and deep heat exchange area and the large variation of the rock and soil physical parameters,stratified treatment is carried out for the rock and soil in the heat exchange area.After verifying the model based on the actual operating data,the heat extraction characteristics of the buried pipe heat exchanger of the butt well for middle and deep geothermal are studied by using this model.In this thesis,the deep geothermal heating project of the new campus of Hebei University of Engineering is taken as the object.Based on the geological information of the rock strata around the geothermal well obtained from the previous investigation and sampling of the geological conditions around the geothermal well,the initial values of various thermal physical parameters of the surrounding rock of the buried tube heat exchanger are sorted out.Then in the heating season,the field operation experiment of the middle-deep buried pipe heat exchange system was carried out,and the parameters such as rock and soil temperature distribution after the operation of the butt well heat exchanger heat extraction system,heat extraction from the geothermal well,and water outlet temperature of the geothermal well were obtained.Secondly,for the medium and deep thermal reservoir porous rock and soil,a model for predicting the effective thermal conductivity of unsaturated rock and soil in the medium and deep layers is established based on fractal theory,taking into account the microscopic parameters such as saturation and porosity of soil and soil in each layer of buried pipes.After comparing the published experimental data with the model simulation data to verify its accuracy,This model is used to discuss the influence of microcosmic parameters on the thermal conductivity of medium and deep porous media.Based on the model and previous geological survey results,the effective thermal conductivity of each layer of rock and soil is calculated.Finally,the heat transfer process of U-type buried tube heat exchanger and rock and soil heat storage is analyzed.MATLAB software is used to establish the numerical heat transfer model of mid-deep butt U-type buried tube heat exchanger in layered rock and soil mass.The equation is solved by catch-up method,and the numerical simulation results are compared with the field experimental data.Combined with the model of effective thermal conductivity of unsaturated porous medium,the influence of different factors on heat extraction performance of buried tube heat exchanger was analyzed and evaluated. |
PDF Full Text Request