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Energy consumption in the building sector has become a global concern. Among the most energy-intensive equipment: air conditioning units, especially in hot countries. This paper investigates this rise of energy consumption for a case study of a laboratory located at the National Engineering School of Tunis, Tunisia. The key idea of this paper is to look for an optimal solution to reduce the energy consumption of the air conditioner while ensuring occupant’s comfort. For this purpose, firstly a laboratory dynamic thermal model is designed. Then, a Hysteresis control is adopted to ensure thermal comfort and to maintain the ambient temperature within a range predefined by the user. To achieve an outcome compatible with expectations, the thermal transfer through laboratory wall’s envelope constituents, considering loads effects on air conditioner functioning and, meanwhile, the energy balance of the system are analyzed. Then, a comparative study of different solutions to improve the energy consumption of the laboratory was also carried out. The results indicate that the use of double-glazed windows is the most suitable. The window model used guarantees an energy gain of 27% if it is used only for the windows of the east wall and an additive gain of 30% if it is used for all the openings. Otherwise, if an external insulation is adopted, the energy gain is negligible. The proposed model is implemented in Matlab / Simscape and results are validated by the experimental measurements provided by a network of temperature sensors and transmitted to cloud service.

The present work presents a numerical study of the evaporation of a sessile liquid droplet deposited on a substrate and subjected to different heating configurations. The physical formulation accounts for evaporation, the Marangoni effect, conductive transfer in the support, radiative heating, and diffusion–convection in the droplet itself. The moving interface is solved using the Arbitrary Lagrangian–Eulerian (ALE) method. Simulations were performed using COMSOL Multiphysics. Different configurations were performed to investigate the effect of the heating conditions on the shape and intensity of the Marangoni circulations. A droplet can be heated by the substrate (different natures and thicknesses were tested) and/or by a heat flux supplied at the top of the droplet. The results show that the Marangoni flow can be controlled by the heating configuration. An upward Marangoni flow was obtained for a heated substrate and a downward Marangoni flow for a flux imposed at the top of the droplet. Using both heat sources generated two vortices with an upward flow from the bottom and a downward flow from the top. The position of the stagnation zone depended on the respective intensities of the heating fluxes. Controlling the circulation in the droplet might have interesting applications, such as the control of the deposition of microparticles in suspension in the liquid, the deposition of the solved constituent, and the enhancement of the evaporation rate.

International audience; In this work, we present an experimental study of the evaporation of oil drops deposited on both textured and smooth silicon substrates at two different temperatures (20 °C and 270 °C). We show that the sessile drops take a hexagonal form and are linked by an oil film (a droplet sitting on a mixture of solid and liquid). This wetting regime represents the Wenzel-like regime. We are particularly interested in the propagation of the oil film on the textured surface over time. The effect of the surface fraction of the micro-textures ∅ and the temperature of the substrate Th on the film propagation were also studied. We reveal that the spreading length of the oil drops increases as ∅ decreases and Th increases. We also demonstrate that the textured surface favors oil drop evaporation.

Water spraying in exchanger systems is widely used to allow cooling and improving their performance. However, transfers within the spray mixture are difficult to express because the combined mass and heat are transferred between phases, which complicates the design of the spray systems. This article presents a numerical study of the influence of water volume fraction on the distribution of the temperature in a canal. A 2D numerical model of a horizontal channel was generated and the equations governing the continuous phases (air) and the dispersed phase (water) were developed. These equations were solved using Comsol multiphysics. A comparison of the simulation results and those of the experiment reveals an acceptable concordance.

The present work represents a numerical study of a solar desalination system that operates on the humidification-dehumidification (HDH) principle. This system consists essentially of a humidifier integrated into a solar collector and a tubular condenser. A mathematical model governing evaporation and condensation in the desalination unit has been elaborated. This model is based on energy and mass balances at the humidifier and the condenser. The work consists essentially of a parametric study to improve the desalination unit production installed at the faculty of sciences of Bizerte, Tunisia.

International audience; The objective of this work was to analyze the influence of compaction pressure on the intrinsic acoustic parameters (porosity, tortuosity, airflow resistivity, viscous and thermal characteristic lengths) of compressed earth blocks through their identification by solving an inverse acoustic wave transmission problem. A low frequency acoustic pipe (60-6000 Hz of length 22 m, internal diameter 3.4 cm) was used for the experimental characterization of the samples. The parameters were identified by the minimization of the difference between the transmission coefficients data obtained in the pipe with that from an analytical interaction model in which the compressed earth blocks were considered as having rigid frames. The viscous and thermal effects in the pores were accounted for by employing the Johnson-Champoux-Allard-Lafarge model. The results obtained by inversion for high-density compressed earth blocks showed some discordance between the model and experiment especially for the high frequency limit of the acoustic characteristics studied. This was as a consequence of applying high compaction pressure rendering them very highly resistive therefore degrading the signal to noise ratios of the transmitted waves. The results showed that the airflow resistivity was very sensitive to the degree of the applied compaction pressure used to form the blocks.

One of the challenges to reduce energy consumption in the construction sector around the world is the development of appropriate construction materials. Due to its thermal properties, gypsum plaster is one of these materials. Tunisia ranks second worldwide for the production of gypsum. It used almost exclusively for decorative purposes although it has interesting thermal properties. This study deals with the thermal characterization of Tunisian gypsum plaster from Meknassi region. Particular attention is paid to the effect of temperature and water content on the thermal conductivity. The plaster thermal conductivity vs. temperature exhibits an interesting behavior for buildings walls. Thermal analysis by DSC was conducted to explain this behavior.