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- Coating; pneumatic conveying; two-fluid nozzles; rapid prototyping; additive manufacturing nozzles; in-line particle coating (1)
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Institute
Coating is an important step for the protection of drugs and flavors in the pharmaceutical and food industry. This paper presents a method for the experimental investigation of the coating process of a single freestream-fluidized particle by an infrared camera. The coating is dispersed by a nozzle with ultrasonic fluid atomization, allowing constant droplet size at different spray rates. The temperature of the fluidized particle was measured online by an infrared camera. The application of the coating on the particle in a spray cycle and the subsequent solvent vaporization is linked to the temperature and hence monitored during the whole coating process. The cyclic coating process of a Wurster coater is hence reproduced. The temperature evolution for different coating amounts in a single spray cycle, for different particle sizes, materials and temperature levels is monitored. A micro-computed tomography image shows the result of the levitator coating, giving a homogeneous layer.
The effectiveness of hot-melt coating depends on its uniformity and the extent to which the surface is completely covered. Compared with solvent-based coating, spreading is more limited in hot-melt coating; thus, the coating uniformity is more affected by the process parameters. This study presents a new method for identifying and quantifying factors influencing coating uniformity. The proposed method facilitates the determination of coating-thickness distribution and non-covered surface proportion based on micro-computed tomography measurements. The proposed method is based on particles that have undergone hot-melt coating in a fluidized bed, and it is compared to common methods for layer-thickness determination. The influencing factors are quantified in terms of the dependency of coating uniformity on the coating amount and material. Material properties have a significant impact because stearin and palm fat create different coating layers. The proposed method is confirmed to be well suited for analyzing coating qualities.
Stirring is used for mass and heat transfer, particle suspending or similar processes. It is commonly conducted in a steady operation mode. This paper targets on performing the stirring process dynamically by reversing the rotation direction to introduce additional turbulences and hence accelerating the dispersing processes. The power introduced into the fluid as well as mixing kinetics performing dynamic mixing were studied based on the rotational acceleration, blade pitch angle, liquid volume and duration of the rotational speed direction interval for a vessel equipped with a turbine agitator with and without baffles. Experiments show that baffles are not necessary if reverse mixing is performed at a specific frequency.
