A cryogenic sensor based on fiber Bragg grating for storage monitoring of liquefied natural gas

Abstract

Condition monitoring is critical for the safe usage of Liquefied Natural Gas (LNG). Temperature distribution is an important index of LNG storage and it can reflect the tendency of heat leakage and the situation of evaporation. However, traditional electric sensor may cause explosion due to spark. In this paper, a cryogenic sensor based on fiber Bragg grating (FBG) is developed in which the fiber with pre-tensile force is adhered onto temperature-sensitive metal. The liquefied nitrogen (LN2) is used to test the designed sensor instead of LNG for safety consideration. By setting every 10 K as a testing point from 83 K to 193 K, the experimental investigation reveals that there is a positive linear relation between the reflected wavelength and the testing temperature. By using multiple linear functions to fit experimental data, the maximum measuring error of FBG sensor is less than ±0.35 K, which indicates the usability of this sensor in LNG storage. Finally, an experiment of temperature stratification is performed to validate usability of FBG sensor for LNG monitoring. The results indicate that the designed FBG sensor has enough accuracy to reveal LNG rollover and it has similar dynamic performance with RTD sensor.