Optical Fiber-Based Level Sensor for High Temperature Applications

The novel optical fiber-based level sensing probe previously developed by Weathered was optimized to operate at higher temperatures and modified to measure local flow rates. The probe was submerged into a molten salt pool and a heating element run along the length of the probe was used to create a distinct temperature profile at the fluid-gas interface. An optical fiber was run in parallel which utilized optical frequency domain reflectometry to measure the temperature along the length of the probe at fine increments providing a quasi-continuous temperature profile. A numeric model was created in ANSYS to determine the optimal level sensor design. Three unique designs were then created and compared against one another to verify performance. A new level determining algorithm was generated in an attempt to increase the robustness of the sensor. With the optimal design and newly developed algorithm, the new level sensor was successfully tested up to 750 degrees C with an accuracy of +/- 1.5 mm and a response time of 3.0 +/- 1.2 s and 7.5 +/- 3.5 s for increasing and decreasing fluid levels, respectively. Additionally, the optimized level sensor was also tested under dynamic fluid level conditions to analyze the level sensors capability to measure fluid velocity. The velocity measurement capabilities were successfully tested in temperatures up to 750 degrees C with fluid velocities of 0.2 cm/s and 0.1 cm/s for increasing and decreasing fluid levels, respectively.