Validation of a heat transfer model for noninvasive leak detection in heating pipes

Heat leaks from underground heating pipes can increase the temperature of the ground surface boundary layer. Therefore, this study proposes a heat transfer model for noninvasively detecting leaks from underground heating pipes by analyzing the ground surface boundary layer temperature using the unsteady heat transfer theory, a laminar boundary layer model of an outward-swept flat plate, and the recovery coefficient equation. On-site experiments were conducted on newly installed heating pipes under 12 cases with varying air temperatures, pipe wall temperatures, and wind speeds to examine the soil thermal conductivity and validate the model. The actual and model-calculated temperatures of the ground surface boundary layer were analyzed. During the no-water-supply period, the relative error ranged from 0.65 % to 4.71 % under windless conditions and from 0.20 % to 3.29 % under windy conditions. During the water-supply period, the relative error ranged from 0.62 % to 0.77 % under windless conditions and from 2.40 % to 2.93 % under windy conditions. These relative errors are defined as warning values. When the monitored actual relative error exceeds the warning value, the heating pipe is judged to be leaking. This study demonstrates the applicability and potential of the proposed model for noninvasive leak detection in new heating pipes.