Speaker
Description
The gentle yet cost-efficient drying of sensitive products in the food and pharmaceutical industries is becoming increasingly important. However, the freeze-drying process is very time-consuming and costly, which is due to poor mass and heat transfer. Therefore, a microwave freeze-drying process was developed, in which the bulk material is continuously mixed in a rotating drum.
To determine the influence of the drum's rotational speed and the particle size on the drying process without interference, the drying process characteristics and spatial homogeneity were studied using in-operando imaging at the Centre for Energy Research in Budapest. Using this technique allows monitoring non-invasively not only the drying characteristics but also the changes in particle bulk during drying. For this purpose, a dryer suitable for the requirements of microwave freeze-drying and neutron imaging was developed first, and then the drying process was imaged in-operando for two drum rotational speeds and two different particle sizes for maltodextrin model particles. This approach enabled real-time quantification of local water content through step-wedge calibration and determination of initial outer porosity. High-resolution imaging provided accurate moisture mapping and showed that rotational speed primarily affects drying homogeneity, while particle size had a smaller influence on drying kinetics under the tested conditions. Furthermore, changes in porosity during drying and decrease in total bulk volume during the drying process were also observed and analyzed.