A Direct-Shadow Method for Investigating Natural Convection in Water

摘要

A direct-shadow method was used to investigate circulations caused by natural convection in distilled water layers heated uniformly from below with depths ranging from 5 mm to 2.54 cm. The top- and side-view shadow patterns indicated changes in structure which corresponded to transitions in the heat transport rate through the fluid layer. A ray-tracing technique is described in which the relative spatial intensity distribution for light that passes through a fluid layer with a known temperature field can be constructed for any path length beyond the fluid layer. This method was used to determine the ray-distribution at various screen distances for parallel light indicent on a fluid band cell having a temperature field derived by Rayleigh. The relationship between the fluid temperature variations and the shadow-pattern light-intensity variations was established by experiments with a uniformly drifting fluid layer of 5-mm depth. These experiments showed that the relative temporal temperature variations at a point in the fluid were closely correlated with the second integral of the relative temporal light-intensity variations at a corresponding point in the shadow patterns. (Author)