Feed temperature as a rheological modulator: Coupling viscosity, atomization, and drying kinetics to control particle morphology in spray drying of aqueous extracts

Spray drying of aqueous extracts is often limited by wall deposition and particle agglomeration. Using Ziziphus jujuba aqueous extracts, this study investigated how feed temperature (293.15–353.15 K) affects viscosity, atomization, drying, powder yield, and particle morphology. Apparent viscosity decreased with temperature, giving a viscous-flow activation energy of 13.9 ± 0.4 kJ·mol−1. Incorporating the measured viscosity-temperature relationship into atomization analysis predicted a 27.4% reduction in normalized initial droplet diameter, a trend qualitatively supported by the measured 56% decrease in moisture ratio and finer, more uniform particles at moderate feed temperatures. Powder yield first increased and then decreased, reaching 94.6% at 323.15 K. Lower temperatures favored wet adhesion, whereas higher temperatures increased particle adhesion and agglomeration. Further heating broadened the particle-size distribution. These results show that feed temperature regulates spray drying through coupled effects on rheology, atomization, drying, and particle formation.