Thermal response to background leakages around an actively heated fiber optic sensor for leak detection in water distribution mains: modeling the effect of heating power and time

Fiber optic distributed temperature sensing (DTS) has been recently proposed as a promising technology to detect leaks in water infrastructure. However, it requires a suitable temperature difference between leaked water and the subsurface. Coupling active heating with fiber optic DTS could overcome this limitation, but very limited information is available on its application to leak detection in water pipelines. In this regard, this study addresses for the first time the use of active distributed temperature sensing (ADTS) to detect background leakages, ubiquitous and persistent leaks responsible for large losses and practically undetectable with conventional technologies. The 3D transient analysis of the thermal response to background leakages under different heating powers and times shows that there is potential to detect and locate incredibly small leaks (∼ L/d) with a detection threshold of 3 °C when actively heating a fiber optic sensor placed at distance from the pipe, in a location suitable for new and existing pipelines as well as for passive sensors. A potential to quantify background leakages also exists, since nonlinear relationships linking temperature alterations to the leak rate were predicted. The analysis further shows that it is crucial to determine for how long the detection threshold is overcome, and that increasing the heating power is not necessarily the answer. Finally, forced convection is the main heat transfer mechanism around the active sensor once reached by leaked water, and it appears that the chance of altering temperature and quality of water flowing within the nearby pipe and surrounding soil/groundwater would be very limited with ADTS.