Prospects for the modelling and design of spray dryers in the 21st century

It is becoming increasingly clear that the flow patterns in spray dryers are inherently transient and three-dimensional and that these flow patterns are closely linked to the key problem of wall deposition of particles in this equipment. We are also developing the confidence that current Computational Fluid Dynamics simulations, with standard approaches to modelling turbulence, can predict the frequencies of the transient flows and the three-dimensional nature of the flow patterns with adequate accuracy for both laboratory and industrial conditions. This situation demonstrates the potential for incorporating other important physical processes, such as those involved in wall deposition, into such models, leading to simulations that predict all the key physical processes quantitatively and accurately. Further research into the adhesion and cohesion of particles due to stickiness is important for addressing the challenges of predicting wall adhesion and agglomeration, as is the need to measure thermal degradation under conditions that reflect those inside the dryers. It will then be possible to design new dryer systems from first principles for specific product engineering outcomes, rather than relying on trial and error as in the past.