Spraying is the production of defined droplets of fluids in a surrounding gas phase. The product produced from atomisation is referred to as the spray. Ideally, a spray is desired in which all droplets have an identical diameter. This ideal spray has a monodispersed droplet-size distribution, in which case the specification of an individual droplet diameter suffices in order to describe the characteristics of this type of spray. In reality sprays produce a spectrum of droplet sizes.Sprays and nozzles produce a polydispersed droplet-size spectrum, so that the droplet-size distribution must be determined by measurement (e.g., by means of our Droplet Analyser). The calculation of thermal and mass-transfer processes is possible only following the sufficient characterization of spray properties.