EXPERIMENTAL-TECHNIQUES IN NATURAL-CONVECTION

Experimental techniques in natural convection heat transfer employed i n the author's laboratory are introduced. The techniques are mostly re lated to visualization of flow, temperature field, and heat flux distr ibution in fluids. Three topics are presented, the first being natural convection in a horizontal rectangular liquid layer driven by surface tension and buoyancy. The patterns of flow were visualized by suspend ing fine aluminum flakes in the liquid. At the same time, the distribu tion of the temperature gradient in the liquid was visualized by an op tical method making use of the refraction of light. The second topic i s the onset of oscillatory convection in the Czochralski growth melt. In this case a forced flow due to rotation of the crystal and the vess el is superimposed on the buoyancy convection, resulting in an oscilla tory flow under certain circumstances. The flow pattern and the temper ature distribution in the liquid were visualized simultaneously by sus pending in the liquid a microencapsulated temperature-sensitive liquid crystal. Periodical oscillation of the flow and the temperature was c learly recognized. The third topic is the rollover of double liquid la yers that were stratified stably due to a density difference. A small- scale experiment was carried out to clarify the basic mechanism of rol lover. The tracer method was used to visualize boundary layer flow alo ng the vertical side wall and the shadowgraph technique to visualize t he density distribution in the liquid layers. The article emphasizes t he importance of visual observation in the investigation of natural co nvection phenomena.