Modelling of spray-freezing with compressed carbon dioxide

A spray-freezing process with compressed carbon dioxide is investigated. The objective of the study is related to production of composite powders of water-soluble bioactive molecules and stabilizing excipients with specific aim to obtain stable protein particles with a narrow size distribution for pharmaceutical purposes. A model of dispersion and solidification of aqueous droplets in turbulent flow field in the spray-freezing process based on expansion of compressed carbon dioxide is proposed and applied to interpret experimental data. The process of droplet solidification is considered by taking into account the effect of surface tension on the equilibrium temperature at the interface of two phases (Gibbs-Thomson effect). The presented method enables estimation of frozen droplets size, temperature profile and freezing time of droplets.