Spray drying is used for the manufacture of many consumer and industrial products such as instant dairy and food products, laundry detergents, pharmaceuticals, ceramics, and agrochemicals. During spray drying, agglomerates of powder particles are formed which determine the instant properties of the powder. Agglomeration during spray drying is considered to be a difficult process to control. The main cause of this is the complex interaction of the process variables: the atomization process, the mixing of spray and hot air, the drying of suspension droplets and the collision of particles which might lead to coalescence or agglomeration. As a consequence, agglomeration during spray drying is operated by trial-anderror. In an EC-sponsored project, named the EDECAD projects, an industrially validated computer model, using CFD technology, to predict agglomeration processes in spray drying machines is developed. An Euler-Lagrange approach with appropriate elementary models for drying, collision, coalescence and agglomeration of the dispersed phase is used. The main result of the EDECAD project is a so-called ''Design Tool,'' which establishes relations between the configuration of the drying installation (geometry, nozzle selection), process conditions, product composition and final powder properties. The Design Tool is being validated on pilot-plant scale and industrial scale. It will provide an advanced tool for improved design and optimization of spray drying and agglomeration equipment, to improve the quality of products and to increase the productivity of such equipment. This article introduces the background and approach of the project and some preliminary results.

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The outcome of collision dynamics of suspension drops (process fluids) is an interesting and challenging problem in industrial spray applications as e.g. spray drying. As a result of the liquid fragmentation process as well as a result of a binary droplet collision in the spray, fine droplets may be formed at the very low end of the overall droplet size distribution in the spray. The fine particles (dust) during spray drying are considered to be a difficult process to control. One of the main causes is the complex interaction of suspension droplets in the hot air flow and the collision of droplets. An experimental study of binary collisions of suspension droplets in off center collisions (impact parameter of B > 0) is discussed. The aim is to study the collision phenomena and derive dominant physical mechanisms of binary droplet collision of suspensions. Two suspension droplet streams of equal size have been generated by means of piezoelectric droplet generators. The drop velocities of the two streams of suspension drops have been varied systematically to change the Weber number of the collision. A collision map for suspension droplet collisions will be derived. The formation of satellite droplets by suspension droplets collisions is correlated by a function based on the basic parameters and dimensionless numbers of the process. The results support the understanding of the phenomena of binary droplet collision dynamics between droplets from pure fluids and suspensions.

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