Papers by Keyword: Evaporation

Abstract: Retracted paper: Evaporation of a saline solution from a porous medium often leads to the formation of salt efflorescence at the surface of the medium. We look at the special case where the medium is formed by the assembly of fine and coarse medium vertical columns perpendicular to the evaporation surface and where there is a continuous wicking of the solution into the medium in combination with evaporation. Experiments lead to distinguish two main cases depending on the development or not of the efflorescence at the surface of the coarse medium. On the contrary, the presented analysis suggests that the coarse medium surface colonization occurs when the evaporation flux is sufficiently high no matter what the type of efflorescence is on the fine medium surface. In addition, the analysis suggests that the colonization will always occur when the supersaturation is close to the solubility.

Abstract: Retracted paper: Crystallization of a salt in a porous medium can lead to the generation of stresses on the pore wall. This stress generation mechanism causes the phenomenon of surface heave, i.e. the upward displacement of the porous material surface.This surface heave phenomenon is studied from experiments with random packings of particles (glass beads) confined in a quasi-2D cell when the crystallization of sodium chloride is induced by evaporation. It is shown that the grain size has a significant impact on the surface heave. In addition, it show the existence of an optimal grain size maximizing the heave. This suggest that the bead size dependence is not related to the mechanical aspect of the problem but is rather linked to the impact of the bead size on the morphology and internal properties of the growing subflorescence.

Abstract: A vacuum-assisted thermal evaporation method for the preparation of undoped and Zn-doped erbium sesquiselenide Er₂Se₃ thin films on various substrates using independent elementary sources is developed. The electrophysical parameters, such as electrical resistivity and thermo-electromotive force of the films, are measured from 77 up to 650 K.

Abstract: Pollution problems caused by industrial production of leather tanneries are an important environmental issue. In the present paper we propose to study effects of tannery sludge (TS) addition in manufactured clay bricks applying a mixture design formed by different proportions of four components: Clay, two types of sand and TS. The analysis leads to an optimal practical mixture of around 10% of TS, 20% of sand and 70% of clay and this to remain with an acceptable aspect, an admissible water absorption below 15%, an admissible total shrinkage (drying and after fire) lower than 8%, a tensile strength higher than 5MPa and a thermal conductivity of 0.93 Wm^-1K^-1, 15% lower than the reference mixture with 0% of TS. Experimental results indicate that a temperature cycle firing up to 950°C can lead to higher tensile strength and lower water absorption compared to a cycle that reaches only 850°C. Furthermore, incorporating (TS) in the fired brick manufacturing process can lead to significant energy saving. Additionally, it was observed that a moderate inclusion of TS can enhance evaporation process. Keywords : Mixture design, Tannery Sludge (TS); Clay bricks ; Evaporation ; Strength; Water absorption; Shrinkage; Leaching; Energy.

Abstract: The contributions balance of isolation and cooling effects relative to the liquids surface to slow down their evaporation and to achieve safe vapor concentrations is determined. The influence of liquids characteristic temperatures and their water solubility on this process is considered. It is proven that the long-term effect of such means is provided by systems based on closed-pore floating solid materials (for example, foam glass). It is proposed to increase the foam glass low isolation and cooling capacity either by coating it with an inorganic gel or by wetting it with water. Smaller evaporation retardation coefficients by gel were obtained for liquids with the higher water solubility. A 5–6 times greater cooling capacity of the wet foam glass than dry foam glass was obtained for both polar and non-polar liquids. A smaller cooling effect is observed for liquids with a higher vaporization heat and is similar for both the use of the dry and wet foam glass. It was found that for low-boiling non-polar liquids, the evaporation slowing down is more effectively achieved by using isolation effects, and for high-boiling polar and non-polar liquids - by using cooling effects. It is proved that the fire extinguishing effect by applying the foam glass layer on the flammable liquid surface occurs in a similar way for liquids with close equivalent cluster lengths and not flash temperatures.

Abstract: This work is devoted to finding of a solution of the actual problem of modern solar power engineering that consists in incomplete conversion of the Planck spectrum of solar radiation using photoelectric conversion. Concentrated solar power being an alternative faces other limiting features such as high cost of building and maintenance, large areas occupied by these plants, the need of precise adjustment of mirrors-lenses systems and also its detrimental effect on nature, birds in particular. An intensification of vaporization from the surface of water can become a solution. In this work a thin layer made of graphene nanoflakes was used as an absorbing media for solar radiation that intensifies evaporation. Also it acts as a catalyst for transmission of water through porous substrate that was made of wood. Results for these experiments were compared with evaporation from free surface. The possibility of using of these porous substrates for the purpose of desalting and purifying water was also experimentally studied.

Abstract: A modelling system was utilised to simulate the movement and behaviour of oil slicks for two types of hydrocarbons, a diesel and another residual, considering hydrodynamic variations. Susceptible areas to oil touching were found in adjacent regions of two vessel manoeuvring zones, in two types of zones, one in a marine coastal and another in an estuarine environment. The evaporation rates were calculated for an estimate of the mass losses. For the maritime zone, the oil particles reached the vicinity of the beaches in approximately 4 to 8 hours after the beginning of the spill simulations, while for the estuary in approximately 1 hour. For the scenarios with diesel oil, mass losses oscillated between 13 to 16% in the estuarine region, and between 23 and 29% in the marine coastal zones. The evaporation rates for scenarios with residual oil, between 2 and 5%, were considerably lower than for diesel (15 and 22%), especially for spills simulated in the estuarine region, where the oil particles reached the lagoon banks after 1 hour. Mass losses by evaporation were more intense in marine coastal areas than for oil spills simulated in estuarine regions, possibly due to the more intense hydrodynamic conditions and the longer time that the oil needs to reach the coast. The fluctuations of observed environmental conditions justify the need for a robust number of simulations for reducing the uncertainties related to the oceanographic and meteorological variability that affect oil spill movement.

Abstract: The article describes the development of a mathematical model for a condenser-evaporator, which occupies a central position in chlorine liquefaction process. The model describes the key processes in the equipment unit: freon evaporation, chlorine condensation, change in freon level and in equipment pressure. The model is based on the equations characterizing the processes mentioned above, which makes it possible to use the model for design and calculations of non-contact heat transfer equipment with phase transitions of heat carriers of various characteristics. The simulation was carried out with the aim of further development of a condenser-evaporator control system.

Abstract: Population density and automation is the main reason for the demand of drinking water. Water purification without affecting an ecosystem is the important need for daily life. Desalination is the best and effective way to satisfy the demand of fresh water. It is the most effective application of the solar energy. There are many conventional and non-conventional techniques available to make drinking water from the saline water. Among these solar desalination proves to be both economical and eco-friendly system particularly for rural areas. Solar stills are simple device which is used to provide pure water from the saline water by the principle of evaporation and condensation. This article reviews on the several research done on the solar stills to enhance productivity. Different designs of solar still and energy storage materials have been used to increase the yield and also this study proved the fact that efficiency of the solar still is majorly influenced by design and operating parameters.

Abstract: Evaporation and boiling from porous media has drawn a broad attention in many applications ranging from industrial, environmental to engineering and technologies. However, prediction of evaporation rates from porous media remains a challenge due to complex interactions between ambient conditions and the porous media properties such as complex geometry, material of the matrices composing porous medium, many length scales, surface phenomena, and effective transport coefficients. In this study, the evaporation rates of distilled water from porous media of different matrices were studied experimentally. Porous media were made up from spherical brass balls of different diameters of 2 mm, 3 mm, 4 mm and 5 mm. The temperature profiles across porous media, air temperature, humidity, and amount of water evaporated were measured in experiments. The effects of the porosity, the thickness of a porous layer, and particle size on the evaporation from porous media were investigated. Different materials of the porous matrices have allowed bringing to light the influence of the material properties. The experimental data show that the rate of evaporation of distilled water with brass balls is higher than that of only distilled water without a porous medium embedded into the water layer and does not change significantly after a steady state condition is achieved.