CALCULATION OF OPTIC FIBERS CALIBRATION CURVES FOR THE MEASUREMENT OFSOLIDS VOLUME FRACTIONS IN MULTIPHASE FLOWS

A model that calculates calibration curves (probe response functions) of reflection type optical probes for the measurement of solids volume fractions is presented. The reflection from a single surface is calcu lated from a relaxed inverse square law to allow the introduction of t he effects of multiple reflections that occur in the cavities of rough surfaces, represented as an assembly of spherical particles. The prob e response function is then calculated as the summation of the reflect ions of several successive surfaces with corrections for obscuration. The probe response function obtained agrees reasonably well with exper iments using aqueous suspensions of aluminium hydroxide particles, wit h a surface volume mean diameters of 75 and 20 mu m. For 200 mu m diam eter sand particles good agreement was found for solids volume fractio ns greater than 5%. The difference between the predictions and experim ents for low solids volume fraction suspensions of large particles was shown to be related to the large interparticle distances in compariso n to the fibre diameter. When applied to a suspension of the same soli ds in air, the method gives a probe response function that is differen t from that obtained in water, especially at low solids volume fractio ns. The departure of the probe response function from the power law ru le at low solids volume fraction, observed experimentally, is replicat ed by the model.