New: Defense of Ph.D. thesis:

The thesis defense by Mr. Sajad Jabari Neek a Ph.D. candidate in mechanical engineering, entitled "Droplet Drying of Complex Fluids- Oleaster Extract", will be held on 2024-Dec-18 at 16:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.

Abstract
The challenge of drying droplets of complex fluids often involves unique solutions due to the diverse issues associated with different fluids. Low-fiber oleaster extract is a colloidal pharmaceutical-nutritional substance, under investigation by pharmacists as a potential replacement for the currently available commercial oleaster powder, aiming to minimize the side effects of consuming the fibrous material of the fruit in the human body. The high water-to-solids ratio in this exract—resulting from the aqueous extraction method—leads to chemical spoilage, processing issues, and interest in spray drying. Given the lack of prior studies on this emerging extract, this thesis conducts various thermophysical investigations on this fluid under different temperature and concentration conditions, providing a detailed picture of its properties. The results indicate that due to the simultaneous presence of solid, liquid, and gas phases, this extract qualifies as a complex fluid.
Experimental analysis of the drying kinetics of single droplets of the extract under various drying chamber temperatures and initial droplet concentrations reveals that, after losing water during evaporation, the extract forms an impermeable shell upon reaching a critical concentration. The formation of this shell is attributed to the presence of insoluble hydrophilic compounds and the delayed crystallization of soluble materials on the droplet surface. This shell swells and deflates continuously as water vapor escapes, eventually leading to the formation of a particle with a dry and sticky shell, approximately the same size as the initial droplet, and in some cases, with a moist center. Increasing the drying chamber temperature to 200°C resolves the issue of a moist center, though the shell remains highly sticky.
Further investigations into vacuum drying revealed that the extract does not stabilize into a solid state under vacuum conditions. After dehydration in its most concentrated form, it retains a viscous fluid structure similar to honey. Based on these findings, it was concluded that oleaster extract is not suitable for spray drying. Differential scanning calorimetry (DSC) analysis showed that the low glass transition temperature of the extract (35°C) causes its stickiness. Consequently, maltodextrin (DE5), a permitted additive with a high glass transition temperature (approximately 200°C), was employed to improve the extract, and new formulations were created with more suitable glass transition temperatures. The results showed a significant reduction in the stickiness of the dried material, with no stickiness observed in the MS2 and MS3 formulations, and the particles were properly dried.
Considering the drying kinetics of low-fiber oleaster extract observed in the experiments, it seems feasible to model its behavior using a semi-empirical model based on evaporation theory and machine learning of the drying curve data. The proposed model can predict not only the effects of independent drying variables, such as chamber temperature, concentration, and initial droplet size, on the drying kinetics of the extract but also the conditions that lead to the formation of swollen particles—larger than the initial droplet size.

Keywords
Complex fluids, Low-fibrous extract, Oleaster extract, Single droplet drying, Drying kinetic