Mechanism of natural convection of water-or aqueous solution-fine particle suspension

实验研究了水或水溶液对细颗粒（微玻璃珠）悬浮液的自然对流作用。进行了两种实验。实验(1)采用宽80mm、高120mm的矩形细胞。垂直壁面均为冷面，保持在10℃左右，对底部壁面中心部分80mm宽进行加热。在颗粒下落过程中，悬浮液形成许多层，这些层逐渐消失。随着溶液浓度的增加，在蔗糖水溶液中沉降速度变慢，而在NaCl水溶液中沉降速度变大。当NaCl水溶液孤子浓度大于lwt%时，不出现层状。在水颗粒悬浮的情况下，随着冷热壁温差的增大，水颗粒层在较短的时间内消失。在上述实验中，颗粒的平均直径为9.76mum，标准差为3.62mum。当粒径分布较窄（平均直径2.04 μ m，标准差0.52 μ m）的颗粒分散在水中时，只能观察到两层。两层的接触面逐渐下降，然后迅速上升到悬浮物的顶部并消失。在实验(2)中，将平均直径为4.75 mm的玻璃微珠分散在宽40mm、高160mm的矩形池中。相对垂直壁面之间的温差保持在10ºC。还观察到几层。界面的下降速度是恒定的，并且随着颗粒初始浓度的增加而变慢。较低的界面有较大的下降速度。

Natural convection of water-or aqueous solution-fine particle (micro glass beads) suspension was investigated experimentally. Two kinds of experiments were carried out. In the experiment (1), a rectangular cell with 80mm width and 120mm height was used. Both the vertical walls were cold surfaces maintained at 10ﾟC and a central part of the bottom wall with 80mm width was heated. During the fall of particles, the suspension forms many layrs and the layrs vanish gradually. As the concentration of the solution increases, the sedimentation velocity in the case of saccharose aqueous solution, becomes slower but it becomes larger in the case of NaCl aqueous solution. When the concentration of NaCl aqueous soliton is larger than lwt%, the layrs do not appear.In the case of water-particle suspension, as the temperature difference between the hot and cold walls increases, the layrs vanish in shorter time.In the above experiments mean diameter of particles was 9.76mum and standard deviation was 3.62mum. When particles with a narrow distribution of particle size (2.04mum mean diameter and 0.52mum standard deviation) are dispersed in water, only two layrs can be observed. The interface of the two layrs goes down gradually and after then goes up quickly to the top of the suspension and vanishes.In the experiment (2), glass beads with 4.75mum mean diameter were dispersed in water in a rectangular cell with 40mm width and 160mm height. The temperature difference between the opposing vertical walls was kept at 10ﾟC.Several layrs were also observed. The falling velocities of the interfaces are constant and become slower as the initial concentration of particle increases. The lower interfaces have the larger falling velocities.