A laser diagnostic technique for the measurement of droplet and particle size distribution

Abstract

Abstract : In order to verify the various theoretical models of practical combustion systems, experimental measurements are urgently required. A number of laser instrumentation systems which do not disturb the flow are being devised to satisfy this need. This study describes a technique which has been developed for the measurement of droplet or solid particle size distribution. These measurements are required, for example, as the input to mathematical models of combustion which include evaporation. The technique is based on the Fraunhofer diffraction of a parallel beam of mono-chromatic light by the moving droplets. A Fourier transform lens is used to focus a stationary light pattern onto a multielement photo-detector to measure the diffracted light energy distribution. A mini-computer program translates the light energy distribution into the corresponding, unique, droplet size distribution. The droplets or particles are classified into 31 size groups spanning two decades of diameter, (e.g. 5 micrometers to 500 micrometers using a 300 mm focal length Fourier transform lens).