Transient free convection in passive buildings using 2D air-filled parallelogram-shaped enclosures with discrete isothermal heat sources

This work evaluates the transient convective exchanges taking place in a building wall made up of air-filled inclined cells. Each cell is formed by two vertical active walls connected by a channel of insulating material. The active hot wall is composed by alternated isothermal and adiabatic bands and is opposite to the active cold wall. Both walls are vertical and separated by a distance equal to their height. The channel connecting these walls is inclined at an angle α with respect to the horizontal, being the values considered in the present work 0° (square cell), ±15°, ±30°, ±45° and ±60°. Two-dimensional temperature fields and streamlines are presented at some representative instants. The temporal evolution of the average Nusselt number at each band of the hot wall is determined for all the treated configurations. Numerical results are validated by comparison with other experimental and numerical studies for cavities with isothermal hot wall in steady state. The maximum deviation found is about 9% for the Nusselt number. This can be considered as very satisfactory for this type of studies characterized by high Rayleigh numbers varying between 1 × 105 and 3 × 108, representative of real building installations.