On the importance of droplet shrinkage in CFD-modeling of spray drying

Shrinkage behavior or the change of droplet diameter in the course of drying is quite diverse and has been the focus of many studies due to its crucial importance in accurate modeling of spray drying. However, the specific impacts of capturing it while performing computational fluid dynamics simulations have not yet been investigated comprehensively. Therefore, this work aimed to directly compare predictions obtained by the perfect shrinkage and linear shrinkage models. As compared to linear shrinkage, the assumption of perfect shrinkage led to a decrease in the surface area as well as an increase in the transport coefficients, resulting in an overall decrease in drying rate. Furthermore, the predicted particle size distribution was significantly affected by the implemented shrinkage model, while contrary to the expectation commonly expressed in the literature, the residence time of the particles was similar for the investigated pilot-scale dryer. Considerable difference ascertained in predicted drying histories, particularly for larger droplets, led to the conclusion that the assumption of perfect shrinkage leads to overprediction of particle stickiness and underestimation of drying rates. This difference is particularly important in modeling phenomena like agglomeration and particle–wall deposition.