Experimental observation on flow patterns of thermocapillary-buoyancy convection in shallow annular pools with a heated inner cylinder

Abstract

Experimental observations on flow patterns of thermocapillary-buoyancy convection in shallow annular pools with a hot inner cylindrical wall have been carried out to understand the effect of Prandtl number on the flow pattern bifurcation. The results reveal that the flow could be weakened and the critical Marangoni number increases with the increasing aspect ratio and Prandtl number. With the increasing Marangoni number, both the transition from a stable multicellular flow to an oscillating multicellular flow and the pulsating pattern have been observed. Because the pulsating pattern is superimposed on an oscillating multicellular flow, thermocapillary convection evolves from periodic oscillatory state to quasi-periodic bifurcation state. As Prandtl number increases, both the oscillating multicellular flow and the pulsating pattern become difficult to be observed. Moreover, the pulsating pattern propagates radially from the hot inner cylindrical wall to the colder outer cylindrical wall, which is opposite to the direction of the surface-tension gradient. The underlying physical mechanism of the pulsating pattern is discussed.