The lattice Boltzmann equation method in two dimensions was used to analyse natural convective flows. The method was validated with experiments in an open cavity with one of the vertical walls divided into two parts, the lower part conductive, the upper part and all the other walls adiabatic. An upward thermal boundary layer formed near the conductive wall. This layer gave way to a wall plume. The numerical results compared well with experiments in the laminar ($Ra\,{=}\,2.0\,{\times}\,10^9$) and transition ($Ra\,{=}\,4.9\,{\times}\,10^9$) regimes. The behaviour of the starting plume was numerically studied for Rayleigh numbers Ra from $10^6$ to $4.9\times 10^9$. The wall plume grows in three stages: in the first with constant acceleration, in the second with constant ascending velocity and in the third with negative acceleration due to the presence of the top boundary layer. The acceleration of the first stage and the velocity of the second both scale with the Rayleigh number.

Amplitude and phase velocity measurements on the laminar oscillatory viscous boundary layer produced by acoustic waves are presented. The measurements were carried out in acoustic standing waves in air with frequencies of 68.5 and 114.5 Hz using laser Doppler anemometry and particle image velocimetry. The results obtained by these two techniques are in good agreement with the predictions made by the Rayleigh viscous boundary layer theory and confirm the existence of a local maximum of the velocity amplitude and its expected location.

No abstract

Measurements obtained from two non-air-conditioned outdoor full-scale test cells during a year in Torreón, Coahuila, Mexico, are used to compare the thermal performance of two envelope constructive systems for walls and roofs of monolithic concrete buildings. The two constructive systems have the same thickness, one is mono-layered and other is two-layered. The two-layered constructive system has a better thermal performance due to its larger thermal resistances and thermal capacity, and the more-layers effect. The experimental data were compared with numerical simulation results obtained with EnergyPlus using the time-dependent heat transfer model. The numerical results are, in general, in good agreement with the experiments. The surface lag time is the variable with the largest differences.

The stack-driven flow between two interconnected rooms produced by a single heat source is studied. In particular, the features of the transient flow for different positions and areas of two openings in the shared vertical wall are analysed. An analytical model provides the time evolution of the stratified flows in rooms of any size. The concept of an equivalent layer representing a non-uniform density profile, which is useful in other contexts, is included in the theoretical approach and provides physical insight and aids the mathematical solution of the problem. New salt-bath experiments are performed to simulate the thermal forcing between the rooms, to validate the model and to analyse the mixing generated and the effects of a source of volume in the configuration studied.