Numerical investigation of transient natural convection in a horizontal channel heated from the upper wall

In this investigation a transient numerical analysis for laminar natural convection in air between two horizontal parallel plates, with the upper plate heated at uniform heat flux and the lower one adiabatic, is carried out by means of the finite-volume method. The model is assumed to be two-dimensional. The Navier-Stokes equations together with the continuity and energy equations are solved by a numerical scheme based on SIMPLE in an H-shaped domain. Results are presented in terms of air velocity and temperature profiles. Wall temperatures and the temporal behavior of several significant variables, such as the penetration length, are reported for different Rayleigh numbers and aspect ratio values. Correlations among penetration length, dimensionless time, Rayleigh number, and aspect ratio are evaluated for 10(2) <= Ra <= 10(4) and L/b = 5, 10, and 20. At steady state regime, correlations for average Nusselt numbers and maximum dimensionless wall temperature in terms of Rayleigh number and aspect ratio are given for 10(2) <= Ra <= 10(4) and 5 <= L/b <= 20.