What causes viscosity in centrifugal spray dryer and how to control it
This centrifugal spray dryer for food can be divided into two main categories namely. Non-viscous and viscous. Non-adhesive food materials are easy to centrifugal spray dryer with a simple dryer design and the final powder is free flowing. Examples of non-adhesive materials include egg powder, milk powder and solutions such as maltodextrin, gum, and protein. In the case of sticky food, drying problems occur under normal centrifugal spray dryer conditions. Sticky foods generally stick to dryer walls or they may become useless condensed in drying chambers and delivery systems, resulting in operational problems and low product yield. Examples of sticky foods include foods rich in sugar and acid. Stickiness is a phenomenon encountered during the drying process of food materials that are often sprayed with sugar and acid. Powder viscosity is a cohesive adhesive property. It can be explained in particle-particle viscosity (cohesion) and particle-wall viscosity (adhesion). The measure of strength that binds the powder particles together is due to its internal property called cohesion which leads to the formation of lumps in the powder bed. Therefore, the breakdown force of the powder aggregate should be greater than the cohesion. Adhesion is an interfacial property that powder particles adhere to the tendency of centrifugal spray dryer devices on the wall. The cohesiveness and adhesion are key parameters for designing drying and drying conditions. The surface composition of powder particles is mainly responsible for the viscosity problem. The material cohesion or adhesion tendency to the surface of powder particles cannot be the same because drying is necessary for a large amount of solute to migrate to the surface composition of the particle surface in bulk. Two viscous characteristics (cohesiveness and adhesion) can coexist in a centrifugal spray dryer on sugar-rich food materials. The cohesiveness between particles is due to the formation of fixed liquid Bridges, moving liquid Bridges, that is, mechanical interlocking between molecules and electrostatic attraction with solid Bridges. Along with the drying chamber wall powder particle adhesion is the main cause of material loss in the centrifugal spray dryer of sugar and acid rich food. The powder quality is retained longer when drying on the wall. The resulting viscosity in spray sugar acid rich food dry powder recovery in the use of centrifugal spray dryer technology due to low molecular weight sugars (glucose, fructose) and organic acids (citric acid, malic acid and tartaric acid) present a big challenge. Small molecules that are highly absorbent, thermoplastic, and have a low glass transition temperature (Tg) contribute to the viscosity problem. At temperatures above Tg 20°C in a centrifugal spray dryer, these components tend to form a sticky surface of soft particles, resulting in powder viscosity and eventually forming a paste structure rather than a powder. The molecular mobility of this molecule is high because of its lower glass transition temperature (Tg), which leads to viscosity problems at temperatures commonly popular in centrifugal spray dryers. The glass transition temperature is the main characteristic of the amorphous phase transition temperature. A glass transition event occurs when a hard solid, amorphous sugar undergoes a transformation into a soft rubber, liquid phase. On the surface energy, solid glass will have a lower surface energy and do not adhere to any low energy solid surface. As a result of the transition from a glassy state to a rubber (or liquid) state, the surface energy of the material increases and the interaction between molecules and solid surfaces begins. In food drying operations, the product is in a liquid or gelatinous state due to plasticizer removal (water) of the liquid/gelatinous food into a glassy state. If the food raw material does not pass through the transition due to the higher drying temperature than the glass transition temperature, the product will remain viscous at a high energy. If the food is made with high energy solid surfaces will stick or cling to it in contact. Controlling viscosity to reduce viscosity problems with materials and a process-based approach is in place. Material-based methods include high molecular weight liquid-material drying auxiliaries to raise the temperature outside the glass transition while process-based methods include wall scraping, bottom, etc., of the mechanical chamber.
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