Tien Nguyen, Muzammil Ali and Andrew E. Bayly, School of Chemical and Process Engineering, University of Leeds, Leeds, United Kingdom
Spray drying is an effective method for producing dried particulate products from liquid feedstocks. It is widely used in pharmaceutical, biochemical, food, detergent, agrochemical and ceramic industries. A good understanding of the drying process, its capabilities and limitations, is needed in order to develop and efficiently produce powders with the required attributes. Single droplet drying (SDD) is an established experimental approach in which an isolated droplet is dried under a controlled, typically isothermal, environment. Although this is a highly simplified version of the evaporating conditions that the droplet will encounter inside a dryer, it can provide valuable drying information such as drying rate and droplet/particle temperature profiles. The drying behviour observed in these experiments is often complex and significant morphology changes are often observed. Model of single droplet drying can significantly help interpret the experimental observations and potentially reduce experimentl effort.
Current models and experimental studies mainly focus on droplet drying below boiling point. However, kinetic phenomenon such as the surface ‘blowing’ effect and internal convection can be important at high temperature. Industry also demands the flexibility to tailor the formultion and process in order to transform a liquid droplet into a desirable engineered dried–product. The work reports the initial development of a drying model that can predict the development of morphology when polymeric droplets dry at high temperature and boiling is observed inside the droplet. In this system, the polymer concentration increases as the drying progresses and the outside if the droplet drys becoming more viscous layer is formed at the droplet surface with viscoelastic or elastic properties. The proposed model combines drying kinetics with mechanical deformation of this external layer which is mainly driven by the bubble growth behaviour within the droplet.
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