Soil temperature gradient as a useful tool for small water leakage detection from district heating pipes in buried channels

A methodology for detecting small leakages from pipelines placed in buried concrete channels is presented. This methodology is based on determining soil temperature gradient using appropriate numerical and experimental processes. An equivalent thermal conductivity (λeq) was defined based on the known heat flux and temperature gradient through the insulation subjected to the leakage. Two dimensional (2D) transient–steady-state–combined simulations were conducted for evaluating the channel cross-section heat loss. To mimic the leakage, λeq values in the range 0.5–10 W/(m·K) were used. The computation exhibited a large increase in the soil temperature gradient above the channel in case of leakage, from approximately 25 °C/m for dry insulation to approximately 50 °C/m at λeq = 0.5 W/(m·K). The procedure including the evaluation of the soil thermal conductivity λs, developed in our previous work, and further soil temperature gradient monitoring through computation and measurements enabled the detection of minor leakages in a pipeline section. Applying the proposed methodology to an entire network could contribute to comprehensive leakage control in district heating systems.