Theoretical And Indoor Experimental Research On Leak Detection Of Direct Buried Heating Pipes Under Abnormal Surface Temperature Response

During the 14th Five-Year Plan period,the north-south divide in China’s heating demand has gradually shifted southwards,the heating industry has developed rapidly and the area of centralized urban heating has increased,but pipeline leakage accidents caused by aging and corrosion of pipelines have occurred frequently,bringing huge economic losses to cities,and the safety of heating pipelines is of great concern.The current excavation-based pipeline leak detection technology is time-consuming and inefficient,and pipeline repair is only carried out after large-scale leaks,lacking a method to prevent serious pipeline leaks.Therefore,it is urgent to find an efficient non-excavation pipeline leak detection method to reduce the risk of leakage.In this paper,a theoretical model of wedge-shaped flowed to heat transfer of different flow rates of air is developed using a linear heat source model and the boundary layers.A sandbox test rig was built for indoor testing and a series of tests were carried out on unbroken,broken and broken pipes and insulation.Real-time monitoring of temperature,flow rate,pressure and wind speed data was carried out to verify the theoretical model and to investigate the characteristics of temperature changes in the ground and soil under different working conditions:(1)When the pipeline is not broken,the surface temperature changes more rapidly when the air temperature is higher,with the temperature rise area covering2/5 of the total area.When the soil temperature is lower,the temperature difference between the surface and the air increases,resulting in a surface temperature rise of4.5℃.The increase in the air flows rate results from a faster surface temperature rise,up to 19℃.(2)When a pipe is broken,the integrity of the insulation has a greater impact on the surface temperature.If the insulation is not broken,the difference between the theoretical and real surface temperature is small,within the range of 0-1℃.It is not possible to determine whether the pipeline is leaking through the temperature difference.(3)When both the pipe and the insulation layer are damaged,the surface temperature increases significantly.The temperature at the center of the surface rises from 14℃to 20℃,with a relatively obvious change in temperature.(4)When the leakage volume is greater than 1.4 m~3/h,if the difference between the theoretical and real surface temperature is not less than 6℃,the pipeline can be judged to have leaked.When the difference between the two is not greater than 1℃,the operating status of the pipeline can not be judged.Therefore,the initial surfaces temperature,the air temperature and flow rate,and the integrity of the insulation all have an influence on the change of the surface temperature.In this paper,the heat transfer characteristics of wedge-shaped flow are analyzed using the linear heat source model and the boundary layer principle,and a theoretical model of wedge-shaped flows to heat to transfer are established to experimentally investigate the heat transfer law of heating pipes,to provide a theoretical basis for non-excavation leak detection of heating pipes,and to provide technical support for reducing the occurrence of safety accidents.