A Study of Cooling Initially Uniform and Thermally Stratified Layers of Water.

摘要

A laboratory study is described of the cooling of initially uniform and thermally stratified layers of water by convection,evaporation,and radiation. Temperature measurements were made with a Mach-Zehnder interferometer and the flow field was visualized by electro-chemical dye. A lake was simulated in a 40 x 25 x 10cm cell. Thermal stratification was induced by tungsten lamps in parabolic reflectors which produced collimated incident radiation flux. For the uniform temperature cell,water descended by free convection to a depth of 10-25cm. The cooling rate had a decisive influence on the frequency of the descending parcels of cooler water. Mixing motion occurred near the surface in the thermally stratified cell. The motion had an initial regular roll pattern,but as cooling continued,the roll pattern in the convective layer deteriorated into motion similar to that observed during cooling of an initially uniform temperature layer of water. A model was developed to predict the dynamics of the convective layer. The numerical solution to the model equation was found to agree better with the experimental data than alternatives based on the closed form analytical solution using a constant average surface heat flux.