When d / λ θ ≈ 0.5 , three isotherms of 0.1, 0.2, and 0.3 are selected (a) and d / λ θ ≈ 1 , three isotherms of −0.1, 0, and 0.1 are selected (b) at Ra=10⁷ (dots), Ra=10⁸ (dash Dot), and Ra=10⁹ (solid). The gray area in the figure is the area where the partition is located.