Settlement of a swelling plastic particle in the hydrothermal environment

The knowledge of particle motion is vital for improving the conversion efficiency of hydrothermal reactors. Compared with evaporating or burning particles at gas ambient, the distinct thermophysical properties of the liquid fluid are expected to affect the motion of reactive particles. This work conducts an experimental study on the settlement of a plastic particle in hydrothermal conditions. A static hydrothermal process of particles is first performed to clarify particle morphology changes. Subsequently, in the dynamic settlement, all experimental particles are determined to be at a swelling stage, where the particle size increases by absorbing the fluid. The falling trajectory of particles shows an irregular spatial curve, and the eccentric position of the particle during the settlement also affects its size. Finally, the thermophysical properties of fluid and particle are also estimated based on the static experiment to predict the drag coefficient of falling particles. The results show that the drag coefficient of swelling particles in the tube is significantly larger than that of rigid particles, and the drag coefficient gradually decreases with the Reynolds number, especially in the case of small particles.