This project concerns a combined theoretical and experimental study of heat transfer in enclosures. The problem is of fundamental importance in building energy conservation devices and in manufacturing seminconductor crystals. The emphasis will be on the characterization of the reoutes to turbulence and the thre-dimensional fluid motion. Experiments will be conducted with low Prandtl number fluids. The theoretical study will be carried out by solving the governing equations by a pseudo-spectral method.