Axisymmetry-Breaking in a Cool-Down Process of Water in Vertical Cylinder through Maximum-Density Temperature

摘要

Thermal convection in a vertical cylinder in the transient coo-down process of water is investigated experimentally with three different types of bottom: (a) a conical bottom, (b) a flat one, (c) a semispherical one. The water is kept to be quiescent and isothermal at a temperature about 10 ℃ initially, and cooled down through its maximum-density temperature. We visualize a natural convection in the cylinder by Indian ink. During the early stage of cooling, the thermal boundary layer with downward flow is formed along the wall of the cylinder. After the water temperature near the bottom falls below 4 ℃, a tiny convection with upward flow along the wall appears and grows up in time. It is observed that a bicellular convection is not uniform but wavy in the circumferential direction independently of the bottom shapes.