What causes viscosity in spray dryer drying… How to control

What causes viscosity in spray dryer drying… How to control



Spray-dried food is divided into two categories: non-sticky and viscous. Non-sticky ingredients are easy to spray dry, simple dryer design and final powder flow freely. Examples of non-stick materials include egg powder, milk powder, solutions and other maltodextrin, gums and protein. In the case of sticky food, there is a drying problem under normal spray drying conditions. Sticky food usually sticks to the wall of the dryer, or becomes useless sticky food in drying chambers and transportation systems, with low operational problems and product yields. Sugar and acid foods are typical examples.


Viscos is a phenomenon encountered in the drying process of food materials rich in glycolic acid. Powder viscosity is a kind of cohesion adhesion performance. It can explain particle-particle viscosity (cohesion) and particle-wall viscosity (adhesion). The measure of binding force with powder particles is due to its internal characteristics called cohesion, forming masses in the powder bed. Therefore, the force that needs to break through the powder agglomerate should be greater than the cohesion. Adhesion is an interface performance, and the powder particles adhere to the trend of spray drying equipment. Cohesion and adhesion are the key parameters for designing drying and drying conditions. The surface composition of powder particles is mainly responsible for viscosity. The cohesion and adhesion tendency of powder particle surface materials are different. Because drying requires a large amount of solute to be transferred to the particle surface, it is in bulk. Two viscosity characteristics (cohesion and adhesion) can coexist in spray-drying sugar-rich food materials. The viscosity between particles is the formation of fixed liquid bridges, moving liquid bridges, mechanical chains between molecules, and electrostatic gravity and solid bridges. The main reason for the adhesion of wall powder particles in the drying chamber is the loss of materials in spray-drying sugar and acid-rich foods. When the powder is kept for a longer time, it will dry on the wall.


It leads to viscous

Spray-rich food drying powder recycling spray drying technology. Low molecular weight sugars are very challenging (glucose, fructose) and organic acids (citric acid, malic acid, tartaric acid). Small molecular substances such as high water absorption, thermoplasticity and low vitrification transition temperature (Tg) contribute to viscosity problems. The spray drying temperature is higher than Tg20°C. Most of these components form soft particles on the viscous surface, causing powder viscosity, and eventually forming a paste structure instead of powder. The high molecular mobility of this molecule is due to its low vitrification transition temperature (Tg), which leads to viscosity problems in spray dryers that are usually popular at temperature. The main characteristics of glass conversion temperature and amorphous phase conversion temperature. The glass transition event occurred in a hard solid, amorphous sugar, which underwent a transformation into a soft rubber liquid phase. Surface energy and solid glass have low surface energy and do not adhere to low-energy solid surfaces. Due to the state of glass to rubber ferry (or liquid), the surface of the material can be raised, and the interaction between the molecule and solid surface can begin. In food drying operations, the product is in a liquid or adhesive state, and the liquid/adhesive food that removes plastic agent (water) becomes glass. If food raw materials do not change from high drying temperature than glassy temperature, the product will maintain high energy viscosity. If this kind of food is touched with a high-energy solid surface, it will stick or adhere to it.


Controlling viscosity 

There are many materials science and process-based methods to reduce viscosity. The basic methods of materials science include materials with high molecular weight liquid drying additives to increase the temperature outside vitrification conversion, and process-based methods include the walls and bottoms of the mechanical chamber.


Post time: Feb-22-2024