Single-mode sapphire fiber optic distributed sensing for extreme environments

The authors have developed a single-mode sapphire sensor for distributed temperature and flow measurement to address the extreme environments encountered in energy applications. The sensor is designed to also detect and localize fouling and deposits that accumulate on its surface over time. Optical frequency-domain reflectometry (OFDR) and spectral back scatter analysis are employed with the single mode sapphire fiber to yield these distributed measurements. Temperature accuracy was on the order of 5°C for measurements ranging from room temperature to over 1000°C. Spatial resolution of 11 mm was attained and enabled visualization of the temperature gradients along a fiber passing through a furnace. The effects of cooling flow were characterized for steady operation, with the intent to leverage this data in future work to infer velocity profiles of high temperature flows. Dynamic cooling flow tests showed that the presence of simulated deposits on the outside of the sensor resulted in slower time response in the vicinity of the deposit. This technique could be used to determine the presence and location of deposits along the length of the sensor assembly. The newly developed sensor will be applicable to fossil energy production, nuclear energy production, and gas turbine engines or generators.