Transient natural convection in a rectangular enclosure is analyzed using a finite difference scheme. The enclosure is adiabatic and filled with water. The buoyancy induced flow is generated by a flat vertical uniform flux surface that has a finite thermal capacity. The full two-dimensional equations representing conservation of mass, momentum, and energy are solved in their time-dependent form. The solution technique used is a modified finite difference procedure very similar to Simple Arbitrary Lagrangian Eulerian (SALE) technique. Two values of surface thermal capacity are investigated, each resulting in a different flow regime during the transient. At short times a simple one-dimensional conduction regime is found to occur. As the leading edge effects arrive at any downstream location the conduction regime is terminated and true convection effects set in. At intermediate times a different flow regime is detected, namely a steady two-dimensional regime that approaches the steady state similarity solution for a similarly heated surface immersed in an infinite fluid medium. Excellent agreement is found with previous analyses and measurements during the early and intermediate transients.

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