Effects of Prandtl number on the formation and evolution of single laminar plume.

In this work, the formation and evolution processes of single laminar plume is studied over the Prandtl (Pr) number range of 50\textasciitilde 1000 by using shadow visualization technology. The heating power input is shut down immediately once a single plume is formed. It is found that the plume formation time increases with Pr number increasing, and the exponent of Pr-dependent power law decreases as the flux Rayleigh number Ra$_{\mathrm{F}}$ (i.e. the heating power) increases. After its formation, the plume first undergoes an accelerated ascending process, and then decelerates after reaching a maximum velocity, without a uniform ascending region as observed in previous studies. Both the maximum velocity and acceleration are decreased as Pr number increases, and their Pr number dependencies become weaker for larger Ra$_{\mathrm{F}}$ numbers. We also examine how the spanwise width of single laminar plume changes during its rising process, and the results are compared with previous studies.