Particle Dynamics in Heterogeneous Suspension: Size-dependent Behaviour, Natural Convection Effects and Long-term Stability

Particle suspensions exhibit complex homogeneity issues governed by size-dependent sedimentation, surface-driven floatation, and interfacial forces, with critical implications for product performance or safety across food, pharmaceutical and consumer applications. Meanwhile, preparing these suspensions is often accompanied by heating and cooling processes, where natural convection occurs. The spontaneous fluid flows significantly alter the movement of the particles inside, resulting in unpredictable particle size distribution in the suspension.
This work firstly focusses on size characterization of the floating, sticking (on the wall), suspended and settling particles. Three types of sizing techniques are involved and evaluated. It shows that the smallest fraction of particles tends to stick on the wall and stay in the liquid. While, the larger particles tend to settle down or float on the water surface due to its hydrophobicity. Based on the results, the target size range that could be stably suspended in CaCO3-water system is successfully established.
Furthermore, the particle size and velocity are measured under the natural convection conditions. It is found that the small particles (2-7 μm) follow the movement of the fluid. Besides, the results show the effects of particles on the liquid temperature distribution. The addition of particles accelerates the formation of temperature gradient. After the large particles settling down, the small particles show negative effects on the heat transfer process. Lastly, the different viscosities of the liquid are considered to mimic the milk suspension. The suspension coefficient is introduced in this part to model the critical particle size using the liquid and particle properties. The essential understandings of particle suspension could potentially guide the food manufactures to improve their existing products and develop new products.