Humidity-responsive jetting for flowability assessment of fine powders

The control of powder flowability under humid environments is crucial for the design and reliability of material processing operations, especially in applications involving fine powder materials such as pharmaceuticals, battery slurries, and functional powders. However, humidity-induced cohesion often degrades flowability in a complex and history-dependent manner, making in situ assessment a critical challenge. Here, we present a simple and sensitive method for evaluating flowability based on impulsive jet ejection. Upon applying a short-duration impact to a pre-formed concave powder surface, a vertical jet emerges whose height and dynamics correlate strongly with cohesion changes under varying humidity. The method requires only a few grams of sample, offers high reproducibility, and captures subtle changes in interparticle adhesion that conventional techniques fail to resolve. We demonstrate that jet height and velocity reflect the mechanical response of powder assemblies and are governed by classical impact dynamics modulated by cohesion. The method enables real-time and quantitative assessment of powder flowability with high precision, even in small-volume systems. This approach provides not only a practical tool for quality control but also offers a promising direction for developing design-oriented techniques to optimize process conditions involving humidity-sensitive powders. • A jet-based method was developed and validated for assessing powder flowability using model glass beads. • Jet velocity and maximum height were identified as sensitive, quantitative flowability metrics. • The method requires only 12-mL of material and allows direct, in-situ evaluation of cohesiveness. • Applicability to other cohesive powders is expected but remains to be systematically verified. • Flowability indices showed clear humidity dependence; further studies will test broader particle types and environmental conditions.