| Guizhou is rich in geothermal resources,but due to its unique karst landform,it is difficult and costly to drill buried pipes.At the same time,after the long-term operation of the ground source heat pump system,it will lead to heat accumulation in the rock and soil,thereby reducing the heat exchange effect of the buried pipe.Groundwater seepage can enhance the heat exchange performance of buried pipe heat exchanger,alleviate the thermal accumulation phenomenon of rock and soil,and if the seepage effect is quantified in the design stage,it can improve the heat exchange performance of buried pipe and reduce the design length of buried pipe,so as to ensure the economy and efficiency of the system.In this paper,it is proposed to enhance the heat transfer performance of buried tube heat exchanger by forced seepage,and the heat transfer characteristics of buried tube heat exchanger under different seepage modes are studied and analyzed by the experimental sand box platform built,and the results are as follows:Firstly,based on the geological conditions of Guiyang karst,this paper builds a sand box experimental bench based on the principle of heat transfer in porous media.Through the experimental system,the heat release process of buried pipe without seepage was simulated,and the influence of water temperature and flow rate of buried pipe inlet on the heat transfer characteristics of buried pipe and the temperature response of rock and soil was explored,which provided a basic control for subsequent experiments.Secondly,the heat transfer characteristics and temperature response of underground pipes in the process of forced seepage and natural infiltration are studied based on the experimental platform,and compared with those without seepage.The results show that forced seepage and natural seepage can significantly improve the heat transfer performance of buried pipes and accelerate the temperature response of rock and soil under different working conditions.Taking the experimental working conditions with a flow rate of 0.2 m/s and an inlet water temperature of 45 °C as an example,the average meter-long heat exchange of buried pipes under natural infiltration and forced seepage increased by 99.08% and 114.82%,respectively,compared with no seepage,while forced seepage increased by 7.91% compared with natural infiltration.At the same time,forced seepage has a greater impact on the middle and lower dolomite layer and limestone layer,while natural seepage has a greater impact on the upper yellow clay layer.Finally,based on the aforementioned experimental process,the difference between the heat transfer characteristics of buried pipes and the temperature response of rock and soil under different operation modes and different seepage modes of the experimental bench system is studied and analyzed by designing different operation modes.The results show that the intermittent operation mode can stabilize the heat exchange performance of buried pipes,delay the rise of rock and soil temperature,and alleviate the thermal accumulation phenomenon of rock and soil during continuous operation.Moreover,under different operating modes,forced seepage and natural infiltration can improve the heat exchange performance of buried pipes,and can better alleviate the phenomenon of geothermal accumulation and accelerate the recovery of geotechnical temperature. |
