Water temperature measurements with a Rayleigh backscatter distributed sensor

•Successful implementation of fully-distributed temperature sensing in a liquid water environment.•Full temperature profile of a component revealed with a fiber distributed sensor.•Excellent agreement with compared reference temperatures. A Rayleigh scattering-based optical fiber distributed temperature sensor (DTS) was used to perform fully-distributed temperature measurements of a vertical water column in a natural circulation heat transfer facility. Five thermocouples were collocated along the length of the DTS in the centerline of the water column. In-situ calibration was performed on the DTS recordings, which revealed the complete temperature profile of the water column during two different steady flow conditions. The uncertainty of these measurements was estimated to be ±4.2 °C. This study proves the feasibility and integrity of fiber DTS in heated liquid water applications. The results obtained with this DTS can also be used towards validation efforts of high-resolution prediction techniques such as computational fluid dynamics (CFD).