Premium
Estimation of the Effective Measuring Volume of Single‐Fibre Reflection Probes for solid volume concentration measurements
Author(s) -
Rensner Detlef,
Werther Joachim
Publication year - 1993
Publication title -
particle and particle systems characterization
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.877
H-Index - 56
eISSN - 1521-4117
pISSN - 0934-0866
DOI - 10.1002/ppsc.19930100204
Subject(s) - volume (thermodynamics) , particle (ecology) , calibration , optics , materials science , particle size , range (aeronautics) , laser , optical fiber , analytical chemistry (journal) , chemistry , composite material , physics , thermodynamics , chromatography , geology , oceanography , quantum mechanics
The working principle of the single‐fibre reflection (SFR) probe is that light emitted by a laser diode is guided into the measuring volume by the same fibre which receives the proportion of light reflected by the particles in the vicinity of the probe tip and transmits it back to a photosensitive element. In contrast to other configurations of fibre optical probes, the SFR probe is characterized by an unambiguous calibration graph over the entire range of solid volume concentration values. SFR probes have been successfully applied to different kinds of multiphase flow systems, e.g. fluidized beds, pneumatic conveying lines, elutriators and thickeners. A particular question for the interpretation of measurements has always been the effective size of the measuring volume, which is mainly determined by the solid volume concentration. In this paper a simplified mathematical model of the signal generation by backscattering of the emitted light at the particle surfaces is given. The theory takes into account the average optical properties of the solids and their particle size distributions. The particle properties are determined on the basis of this model, which finally delivers the shape, size and depth of the effective measuring volume. For particle sizes between 30 and 120 μm the depth of the measuring volume of a 600‐μm fibre probe is between 0.2 mm for solid concentrations near the fixed‐bed state and approximately 4 mm for solid volume concentrations as low as 0.1 vol.‐%.