Five-stage sedimentation of a cold particle interacting with a hot obstacle: A criterion for thermal-plume-driven ascent

The immersed boundary-lattice Boltzmann method, coupled with a virtual heat capacity correction method, was employed to numerically simulate the sedimentation and conjugate heat transfer of a cold particle within a cavity containing a hot obstacle. The effects of the Rayleigh number (Ra) and the particle-to-fluid specific heat capacity ratio (R) on the particle’s behavior were analyzed. The computational results indicate that particle sedimentation undergoes five distinct stages: free settling, disturbance by the thermal plume, collision with the hot obstacle, ascent with the thermal plume after the first collision, and secondary sedimentation. The particle temperature was found to peak following the collision with the obstacle. In the low Ra regime, the particle did not ascend with the thermal plume after the initial collision, as the thermal plume above the obstacle was not yet fully developed. Conversely, in the high Ra regime, enhanced disturbance by the thermal plume caused the first collision to occur on the upper side of the obstacle, after which ascent with the plume was also not observed. With an increase in R, the particle’s heat absorption capacity was enhanced, and the phenomenon of ascending with the thermal plume after the first collision gradually diminished. Based on a comprehensive summary of the findings, a spatiotemporal criterion for triggering the particle’s ascent with the thermal plume following its first collision with the obstacle is proposed.