Research On Heat Transfer Characteristics Of Composite Buried Pipe Based On Shallow Depression Seepag

Ground source heat pump is a new type of energy utilization system using shallow geothermal energy for heating and cooling,which has gained wide attention and rapid development in recent years at home and abroad.The heat transfer characteristics of ground source heat pump buried tube heat exchanger are related to many factors,among which the influence of seepage water,geological stratification and different tube types cannot be ignored.The karst geological structure of Guiyang is complex,and the underground rock layer is a good natural source of heat and cold,and the rainfall in Guiyang is abundant,and the infiltration of rainfall is favorable to the application of vertical buried tubes,however,there are few reports on the research of ground source heat pump based on the karst geological and climatic conditions of Guiyang.In this paper,based on theoretical analysis,experimental research and numerical simulation,the heat transfer characteristics of ground source heat pumps with composite buried pipes in shallow depressions are investigated.The specific studies are as follows:(1)Based on the theoretical basis of Darcy’s law,this paper builds a shallow depression seepage composite buried pipe ground source heat pump experimental bench according to the geological and climatic conditions of Guiyang region,and analyzes the application of depression,the stratification of geological structure and the design of composite buried pipe,and introduces the principle of the experimental bench and each component.Through the error analysis of each part of the experimental bench,the maximum relative errors of all experimental measurement instruments were obtained within 10% of the allowable errors,which satisfied the experimental accuracy requirements.(2)Through the depression seepage compound buried pipe heat transfer experiment,it was found that the inlet and outlet temperature difference,heat transfer per unit well depth,pipe wall temperature and soil temperature increased with the increase of buried pipe inlet water temperature in the non-seepage experiment.With the increase of inlet flow rate of buried pipe,the temperature difference between inlet and outlet of buried pipe gradually decreases,the temperature of pipe wall and soil temperature only increases slightly,and the heat exchange per unit well depth does not change much;in the seepage experiment,it is found that under different conditions of inlet temperature,inlet flow rate and seepage speed,the heat exchange per unit well depth of composite buried pipe in depression seepage is 2～4 times of that in no seepage,and the larger the seepage speed is,the better the heat exchange effect of buried pipe is.(3)Through the numerical simulation study of three heat transfer models,namely depression seepage composite buried pipe,depression pure thermal conductivity composite buried pipe and depression pure thermal conductivity single U pipe,it is found that the heat transfer efficiency coefficient of depression seepage composite buried pipe is 4.58 times that of depression pure thermal conductivity composite buried pipe and 7.86 times that of depression pure thermal conductivity single U pipe,and the heat transfer efficiency coefficient of depression pure thermal conductivity composite buried pipe is This shows that the composite buried pipe can significantly improve the heat transfer efficiency of the whole system compared with the single U pipe,and the heat transfer performance of the system will be changed qualitatively if the depression infiltration is added;in the intermittent operation mode,the soil temperature recovery of the composite buried pipe with depression infiltration is good,and its soil temperature recovery ability and system heat transfer ability are better than those of the composite buried pipe with depression pure thermal conductivity and the single U pipe with depression pure thermal conductivity.