Use of Heating Configuration to Control Marangoni Circulation during Droplet Evaporation

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

Numerical Simulation of Fog Transport in a Horizontal Channel

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

Influence of compaction pressure on the mechanical and acoustic properties of compacted earth blocks: An inverse multi-parameter acoustic problem

International audienceIn this work we focus on the study of the acoustic and mechanical behavior of compressed earth blocks (CEBs). The aim was to study the influence of compaction pressure on the compressive strength and intrinsic acoustic parameters influencing sound absorption of these materials (porosity, tortuosity, airflow resistivity, viscous characteristic length). Specimens made by varying the applied compaction pressure and therefore having various bulk densities were studied. Low bulk density CEBs where stabilized by adding 15% cement. The acoustic absorption coefficients of the different specimens were determined experimentally employing data obtained using the Kundt tube. The intrinsic acoustic parameters were identified by minimizing the discrepancies between the experimentally measured absorption coefficient (α) and the theoretical one modeling the CEBs using the equivalent fluid model. The results showed that the acoustic and mechanical behavior of CEBs were strongly influenced by the applied compaction pressure including, inter alia, the bulk density of the specimen and the added cement used as stabilizer

Numerical study of a solar desalination system by humidification-dehumidification

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

Numerical study of a solar desalination system by humidification-dehumidification

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

Characterization of compressed earth blocks using low frequency guided acoustic waves

International audienceThe 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