Measurement of particle/droplet size distributions by a laser diffraction technique.

The measurement of the size distribution of droplets and particles is a common problem in current technology. Many processes involve the production or use of particulate matter, e.g. crystallization, pigment manufacture, cement, combustion of pulverized coal and liquid fuel, aerosols, insecticide sprays etc. In such processes measurement and control of particle size is of great importance but on-line measurement of particle size distribution has not been possible until recently. An optical technique initially developed in this department and later in conjunction with Malvern Instruments Ltd., makes this possible. The technique uses the diffraction pattern formed when particles are illuminated by a parallel beam of monochromatic, coherent light to determine the particle size distribution. Special problems are encountered with monosized distributions, bimodal distributions and rapidly changing time dependent particle fields and techniques to deal with these are described.