Simultaneous particle size and concentration measurements using a back-lighted particle imaging system

Abstract

A back-lighted particle imaging system (BLPIS) is developed to simultaneously measure particle size distribution and volume concentration of suspended particles in water. Based upon optical principles, a modified in-focus parameter, incorporating optical conditions, particle shape, overlapping, and depth-of-field variations due to particle size, is developed to identify particles. BLPIS is calibrated with a precise graticule with an accuracy of particle sizes within the measurement uncertainty of image pixel size resolution. For volume concentration, BLPIS employs an adaptive sampling volume methodology that varies with each particle size based upon a critical in-focus parameter value. Experiments show that under lower volume concentration, measured and actual particle size distributions are in good agreement. For higher volume concentration, measured particle concentration is corrected using a Poisson-based distribution to account for overlapping. Overall the volumetric concentration measurement is reliable and accurate with a relative error of approximate 10%. Finally BLPIS is applied to accurately measure both size and concentration of flowing particles near the bottom boundary with resuspension and sedimentation processes.