Nowadays, powder agglomeration technologies are increasingly employed in the food industry, in particular in the dairy processing industry, in order to control powder functionalities, such as rehydration behaviour, flowability, sensitivity to storage conditions, etc. Granulated powders are produced from agricultural raw materials and used both in the form of end products (e.g. milk powders in instant hot chocolate, or aggregated semolina in couscous dishes) and ingredient for food products manufacture (e.g. dairy protein powders for baby food formulation). However, the design and control of food powder granulation processes are still based on empirical knowledge, owing to the complexity of the involved physicochemical mechanisms. It would greatly benefit from the development of a multiscale model for food powder agglomeration that would integrate the intricate influences of powder reactivity and process parameters. In this work, a dimensional analysis approach was performed to identify the adimensional ratios governing agglomeration and their impact on granulated powder characteristics, whatever the considered food powder (milk, semolina, etc.) and agglomeration process (fluidised bed or drying chamber coupled with fine recycling). This dimensional analysis approach was validated through milk powder agglomeration experiments in a drying pilot. To achieve this, a liquid nozzle was modified to inject fine powder particles in the spraying cone of milk concentrate. The feasibility of fine powder agglomeration was demonstrated and the role of the main process parameters (liquid and powder flow-rates, atomisation air pressure) was investigated. Moreover, the granulometric characteristics of the spray produced by the modified nozzle were measured in order to link granulated powder and sprayed droplets sizes, as suggested by dimensional analysis.
