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• Investigations of free convection condensation of steam in air. • Comprehensive investigation of transient condensation characteristics. • Condensation rate expression based on water vapour partial pressure discrepancies. • Simulated total condensation amounts were average 8.9% higher than the measured. In this paper, experimental and numerical investigations have been conducted to evaluate the steam condensation in the presence of air over a vertical plate for a small temperature difference between the air and a cold wall. In the paper, we describe the experimental set-up, emphasizing the conditioning and measuring equipment introduced for this research. A numerical model is also described in detail. The estimated condensation quantities agreed well with the experimental data. According to the data, simulated total condensation quantities were higher than measured total condensation amounts in all cases, ranging from 6.8 to 13.4% (average 8.9%). The condensation rate increases by 28% as the sub-cooling temperature rises from 2.1 °C to 4.4 °C. The mass fraction of water vapor in the air also induces condensation. Average condensation flux decreases 41.7% when relative humidity decreases from 74.9 to 65.4% at the same surface temperature. In the last part, an empirical correlation, which is characterized by the partial pressure difference of water vapor at the surface and out of the boundary layer conditions, was proposed to estimate the condensation flux over the vertical plate. This practical correlation is novel and can be used for various engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, a vertical gypsum plate with thermal capacity placed in an open cavity under dynamic temperature decrease is numerically investigated in order to assess the evolution of the thermal and kinetic structure of the boundary layer and the convective heat transfer coefficient h over time. The particularity of this work resides in the fact that the system was made to simulate the case of a plate with thermal capacity under nocturnal conditions where the temperature is constantly decreasing. Thus, a two-dimensional CFD model is developed under the Ansys Fluent 14.5 environment and is validated using experimental data obtained for a plasterboard studied under dynamic temperature changes. This study contributes to give precise results about temperature, flux, convective heat transfer coefficient and velocity in the vicinity of a vertical wall with a thermal conductivity at the building scale. All the phenomena that occur in the vicinity of the heat capacitive vertical plate (gypsum) are analyzed and explicitly discussed. The main results of this study show that after simulating 1 h real time we observe that turbulent flow begins to appear at the top level of the plate and after this moment the three flows (laminar, transitional and turbulent) coexist. Finally, mean convective heat transfer coefficient depends on the thermal storage capacity of the adjacent material. The average value of convective heat transfer coefficient increases over time by obtaining for a plasterboard ( C p = 1100 J/kg K) value of 1.8 W/m 2 K and for a phase change material in a solid state ( C p = 4350 J/kg K) value of 2.4 W/m 2 K at steady state. [ABSTRACT FROM AUTHOR]