Spray drying refined using CFD
GEA Niro has been working with the Technical University of Denmark (DTU) to simulate the fluid dynamics that take place within a full-sized spray dryer. The data gathered helps GEA Niro refine the development of its spray drying equipment and ensures that its technology keeps pace with, and sometimes drives, its customers' production needs.
The tests are done using a scaled down model with water instead of air. The process allows experiments to be performed at a laboratory level that would otherwise require full-scale equipment of several metres in all dimensions.
Microscopic particles within a scaled-down clear polycarbonate spray dryer are activated by a laser. 'We let the water run through the container and then create vertically aligned laser light,' explained associate professor Knud Erik Meyer, DTU Mechanics. 'We shoot twice in a row and record each laser pulse. As the particles in the water move from the first to the second picture we can see how fast and in which direction the particles move.'
Thorvald Ullum, fluid mechanics manager at GEA Niro, has been working on the development of spray dryers primarily used for powder production in food, chemical and pharmaceutical products for many years. 'This research collaboration makes it possible for GEA Niro to optimise our systems to be as compact and energy efficient as possible. At the same time, it makes it possible to improve the drying process, allowing the systems to produce better products by controlling the temperature of the particles during the drying process,' he said.
'We can now make computer simulations of the spray drying process very accurately,' he continued. 'By using CFD (Computational Fluid Dynamics) we can predict how the air moves and thereby how the particles dry. It is essential to know how close the simulations are to reality. How much can we trust our computer simulations? In truth the simulations are only part of the evaluation process. Although the simulation results are very accurate, every assumption has to be tested and validated on production equipment.'
Turbulence is a known problem in fluid dynamics and has to be taken into account when performing CFD calculations. It makes the flow pattern complicated and it would take too much computing power to predict the flow accurately without some simplifications. Therefore the system uses commercially available turbulence models, and different models are used depending on the flow conditions.
The results from DTU's experiments will help Thorvald Ullum and his colleagues to choose the right turbulence model for their CFD simulations to further refine the drying processes in newly developed spray dryers.