Characterization of the spray droplets and spray pattern by means of innovative optical microscopy measurement method with the high-speed camera
Nejc Koračin, Matevž Zupančič, Franc Vrečer, Grega Hudovornik, Iztok Golobič
Abstract
Liquid atomization plays an important role in the manufacturing of the pharmaceutical products. It is used in all production steps where liquid is applied. In some productions steps precise control over spraying parameters is essential. These steps include fluid bed granulation, film coating of tablets and pellet coating. Precise atomization of liquids enables control over the granule formation in granulation steps and film formation in coating steps. Atomization process includes breakup of liquid and formation of droplets, which is a complex and important phenomenon that should be carefully evaluated for each particular use. This study focuses on characterization of atomization process by the means of combining high-speed imaging, optical microscopy and continuous backlight illumination together with robust image processing algorithm. With pure water and three different hypromellose (HPMC) polymer dispersions that are frequently used for film coating of solid dosage forms, we successfully measured mean droplet size (Sauter mean diameter between 49 and 413 μm), droplet size distribution and droplet speed (in average 10-46 m/s). It was shown that the shape of cumulative volumetric droplet size distribution can be used to evaluate the successfulness of ligament breakup (i.e., formation of droplets) and by that the spray quality. Moreover, the obtained trends and empirical correlations between droplet size and other process parameters are useful in practice in order to select appropriate settings for optimal coating process parameters. Due to the simplicity of proposed method and data processing, the entire system is potentially suitable for near real-time coating monitoring and for rapid optimization of the atomization process.