Drop size measurement instrumentation is being developed to provide a reliable and accurate means for obtaining drop size data with a minimum expenditure of time. The physical principles involved in the measurement concepts are relatively complicated. Thus, the instrument selection process becomes difficult without at least a general knowledge of the selection criteria, available concepts, and their inevitable limitations. At the same time, there are a broad range of applications with specific measurement goals to be met. The measurement requirements include drop size range, spatial and temporal resolution, and the determination of mass flux. Drop shape can be also an important factor when measuring large droplets that may distort under the prevailing aerodynamic forces. Measurements are further complicated by the need to obtain the results in difficult environments.
In this paper, a general review of drop size measurement applications is given with discussions of the associated conditions affecting the measurements. The descriptions of the measurement conditions and requirements are then related to the corresponding instrument capabilities. An overview of the measurement concepts most commonly used is given and the respective capabilities discussed. Techniques based upon both optical and material probe concepts are considered. The information outlined is intended to provide a guide to the evaluation and inquiries that should be made during the selection of a drop size measurement instrument.