Optical fiber probe local solids concentration

In measurement and visualization of gas-solid flow in fast fluidization, various techniques have been developed and used, such as pressure gradient, pressure fluctuation, capacitance probe, optical fiber probe, momentum probe, laser Doppler velocimeter, night-television, and video camera. The resulting data on local gas and solid velocity, solids concentration and its... 

The application of optic fiber probes to the measurement of local concentration of solids and particle velocity, will be described below separately. 

The application of the reflection-type optic fiber probes to measurement of local concentration of solids was developed on the basis of the optic fiber displacement sensor. Salins (1975) and Krohn (1986) summarized the arrangement of different optic fiber probes and their response curves, as illustrated in Figure 4-6. It shows that when the displacement sensor detects... 

Both the transmission-type probe and the reflection-type probe, need be calibrated for their measuring range in local solids concentration. The calibration of optic fiber probes is known to be a difficult problem. Calibration methods fall into two categories the first is to calibrate a probe against agitated or fluidized liquid—solid systems the second is to use particle free-fall in gas—solid systems or the traditional pressure drop method for fluidized solids the third is in a flow system with particle density deduced from mass flux of particles and measurement where phase velocities were nearly equal. 

The major methods for local solids concentration measurement with fiber optic probes are summarized in Table 4-1. 

Backscattering optical fiber probes are not without disadvantages either [238]. For instance, the measuring volume at the probe tip apparently decreases as the solids concentration increases. That is, for higher solids concentrations, the probe has a smaller measuring volume and thus provides a more local measurement because particles which could have been in the measuring volume would be blocked by particles in front of them. Also, for multi-fiber probes consisting of separate emission and... 

Herbert, P.M., Gauthier, T.A., Briens, C.L., and Bergougnou, M.A., "Application of Fiber Optic Reflection Probes to the Measurement of Local Particle Velocity and Concentration in Gas—Solid Flow", Powder Tech., 80, 243 (1994). 

Herbert PM, Gauthier TA, Briens CL, Bergougnou MA. Application of fiber optic reflection probes to the measurement of local particle velocity and concentration in gas solid flow. Powder Technol 80 243-252, 1994. 

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