Fiber Bragg gratings sensor for thermal conductivity measurements in liquids

This paper presents the development of a thermal conductivity sensor for oils and other liquids. Considering the toxic and explosive environments of oil industry, usual methods such as hot wire lead to unsafe measurements due to electric current on the sensor head. Thus, we propose a fiber Bragg grating (FBG) based sensor, which is chemically stable, intrinsically safe and has passive operation. In the experiments, it was chosen a range temperature between 25 and 45°C to guarantee the liquid state of three different elements analyzed: water, glycerin and mineral oil. As thermal conductivity depends on liquid temperature, the results obtained show that the device built is able to simultaneously measure temperature and thermal conductivity. Results show the feasibility of the proposed approach, where the temperature estimation using the FBGs resulted in a sensor with 0.9999 linearity and the thermal conductivity estimation of each liquid is in accordance with the results obtained in the literature for each of the tested liquids.