The intrinsic fiber-optical sensor has a sensing region within the fiber and light never goes out of the fiber. In extrinsic sensors, light has to leave the fiber and reach the sensing region outside, and then comes back to the fiber [29]. Furthermore, fiber-optical sensors can also be classified under three categories Ivacaftor cystic fibrosis [25]: the sensing location, the operating principle and the application, as seen in Table 1.Table 1.Fiber-optical sensor classifications under three categories.2.4. Current ApplicationsFiber-optical sensors have been the topic of considerable amounts of research for the past 30 years and their application fields are being extended continuously in two major fields, i.e., as a direct replacement for existing sensors and the development/deployment of fiber-optical sensors in new areas.
To date, the most highlighted application fields of fiber-optical sensors are in large composite and concrete structures, electrical power industry, medicine, chemical sensing, and gas and oil industry. A wide range of environmental parameters such as position, vibration, strain, temperature, humidity, viscosity, chemicals, pressure, current, electric field and several other environmental factors have been widely monitored. More detailed information on the applications can resort to references [25] and [29].3.?Application of Fiber-Optical Probes in Multiphase ReactorsA multiphase system with gas as the dispersed phase may be a gas-liquid or gas-liquid-liquid or gas-liquid-solid system.
Due to the too small differences in refractive index between gases and Batimastat organic liquids, fiber-optical probes are rarely utilized in experimental studies on the measurement of gas-phase characteristics in a gas-liquid-liquid system. So the discussion on this system is combined with the gas-liquid one. The gas-liquid-solid system has two dispersed phases and the complicated effects between different phases make the experimental studies more difficult. So in Section 3.1, the main concern is the measurements in gas-liquid reactors, and the studies on gas-liquid-solid reactors are involved in Section 3.4. In Sections 3.2 and 3.3, the experimental studies on the measurements of the drop-phase and solid-phase characteristics are dealt with, respectively.3.1.
Measurements of Gas-Phase CharacteristicsIn gas-liquid reactors, more information selleck chem inhibitor about the local gas-phase characteristics such as bubble-size distribution, bubble velocity, local gas holdup and bubbling frequency is useful for monitoring the homogenization of aeration in the whole volume of the reactor and for predicting the mass-transfer characteristics between gas and liquid. Needle probes are always used. Single-tip probes lead to gas fraction and double-tip probes allow measurements of bubble velocity, time-averaged local interfacial area and mean bubble chord length.