Sharif Digital Repository

In common solar stills, a portion of the produced vapor undesirably condenses on the sidewalls and runs down to be mixed with saline water in the basin. This results in lower distillate output of the system. The aim of this study was to improve the condensation process of a solar still without complicating its structure to collect the water condensed on sidewalls. The proposed solar still was made of two containers nested one inside the other such that the smaller container, containing saline water, fitted easily into the larger container. There was a thin gap between the two in which condensed liquid on sidewalls, ran down and was collected from the bottom of the larger container. The... 

The effects of liquid density variation at the bubble surface on the dynamics of a single acoustic cavitation bubble are numerically studied. The Gilmore model together with a comprehensive hydrochemical model is used. The evaporation and condensation of water vapor are included in the hydrochemical model. The simulation results are compared to those resulting from the widely known Keller-Miksis model, which assumes a constant liquid density at the bubble surface. The numerical results for a single argon bubble in water reveal that the pressure and the temperature inside the bubble in collapse phase significantly increase, when the non-constant liquid density is used. These differences... 

Sonoluminescence (SL) radiation from an argon bubble in water and in different concentrations of sulfuric acid has numerically been studied to quantify the effects of vapor pressure and viscosity of the liquid on cavitation luminescence in a liquid with controllable vapor pressure and viscosity. For the solutions containing the noble gas with low partial pressure (about 4 Torr), it is shown that there exists an optimum acid solution in which both the temperature and the intensity of SL radiation become maximum. The calculations show that the maximum SL radiation is achieved from the solution of around 65% (wt.) H2 SO4, which is in agreement with available experimental results. © 2009 The... 

A mathematical model is developed to investigate the reduction process of hematite in the reduction zone of the Midrex shaft furnace as a moving bed reactor. It is described as a counter-current moving bed cylindrical reactor in which hematite pellets are reduced by a gaseous mixture of hydrogen, water vapour, carbon dioxide and carbon monoxide, namely Syngas. It is laterally injected into the bed at the lower part close to the bottom. Governing equations, including continuity, momentum, energy and mass equations, are derived based on the conceptual model for both gas and solid phases in the cylindrical coordinate system. A three interface unreacted shrinking core model (USCM) is applied to... 

A neural network based on the feed forward back propagation error has been developed for the design and simulation of the catalytic properties of a multi-component system based on Cu-M-Al2O3 (M=Zn,Cr,Zr) for the steam reforming of methanol. Due to the limited size of the data set, cross validation method has to be used to enhance and also evaluate the prediction ability of the network. The best structural organization has been found to include 4,3,6,3 nodes in the input, two hidden layers and the output layer respectively  

In reply to the comment of Lu and An on our publication paper [Phys. Rev. E 70, 016304 (2004)], we show that the consideration of water vapor exchange at the bubble interface is essential for obtaining our results and the adiabatic model is too simple to produce the differences. Moreover, in spite of smallness of the compressional viscosity term at the collapse, the illustrated differences are reasonable due to the strong nonlinearity of the bubble dynamics at the collapse and its sensitivity to even small perturbations. We emphasize on the correctness of our calculation results and our simulation programs are now available on the web. © 2005 The American Physical Society  

In this study, the properties of poly (vinyl alcohol)(PVA) films incorporated with Zataria multiflora essential oil (ZMO) as a potential antioxidant/antibacterial material was investigated. PVA films were prepared from PVA solutions (2% w/v) containing different concentrations of ZMO. Water solubility, moisture absorption, water swelling, and water vapor permeability for pure PVA films were 57 ± 1.1, 99 ± 3.2%, 337 ± 8%, and 0.453 ± 0.015 g mm/m2 h, respectively. Incorporation of ZMO into PVA films caused a significant decrease in water swelling and moisture absorption and increase in solubility and water vapor permeability. Tensile strength, elastic modulus, and elongation at break for pure... 

Polyvinyl alcohol (PVA) thin films were reinforced by glutaraldehyde and multiwalled carbon nanotubes (MWCNTs) and then mechanical, water solubility, water swelling, water uptake, water vapor permeability, and antibacterial properties of the films were examined. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant increase in tensile strength, decrease in elongation at break, and increase in Young's modulus of the PVA films, while MWCNTs were more effective rather than that of glutaraldehyde. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant decrease in water solubility, water swelling and water uptake, with a similar manner.... 

Chitosan films have a great potential to be used for wound dressing and food-packaging applications if their physicochemical properties including water vapor permeability, optical transparency, and hydrophilicity are tailored to practical demands. To address these points, in this study, chitosan (CS) was combined with polyvinylpyrrolidone (PVP) and graphene oxide (GO) nanosheets (with a thickness of ∼1 nm and lateral dimensions of few micrometers). Flexible and transparent films with a high antibacterial capacity were prepared by solvent casting methods. By controlling the evaporation rate of the utilized solvent (1 vol % acidic acid in deionized water), self-organization of GO in the... 

Electrospinning of biopolymers has gained significant interest for the fabrication of fibrous mats for potential applications in tissue engineering, particularly for wound dressing and skin regeneration. In this study, for the first time, we report successful electrospinning of chitosan-based biopolymers containing bacterial cellulous (33 wt %) and medical grade nanodiamonds (MND) (3 nm; up to 3 wt %). Morphological studies by scanning electron microscopy showed that long and uniform fibers with controllable diameters from 80 to 170 nm were prepared. Introducing diamond nanoparticles facilitated the electrospinning process with a decrease in the size of fibers. Fourier transform infrared... 

In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design... 

A titanium dioxide nanotube (TNT) and CuO-doped TNT (TNT-CuO) were synthesized using a hydrothermal method and incorporated into carrageenan-based films. The SEM results confirmed the formation of uniform nanocomposite films. The addition of nanoparticles imparted UV-blocking properties to the carrageenan film and increased the mechanical strength, surface hydrophobicity, and water vapor barrier properties. The modified TiO2 (TNT and TNT-CuO)-incorporated carrageenan films showed significantly higher antibacterial activity than the TiO2-added film under visible light. Bananas packaged with the neat carrageenan and TiO2-added films were degraded considerably after 12 days of storage at 20 °C.... 

The distribution of water fluxes is strongly influenced by the properties of the media adjacent to the cathode catalyst layer (CCL), viz. polymer electrolyte membrane (PEM) and gas diffusion media (GDM). We propose a model that is applied under varying humidification of the cathode feed gas, with water removal in liquid and vapor form. The model warrants the definition of a critical current density up to which water removal out of the CCL could proceed completely via vapor diffusion to the cathode side. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which drives hydraulic fluxes to PEM and GDM sides. Experimental... 

In this study operation of an optical design based on the intensity modulation for the refractive index change has been described. The reported instrument measures the transmitted output power depending up on the medium refractive index in the light path of a fiber-to-fiber design. A liquid cell is located between the fibers in the light path and power variations for different cold and hot water levels in the cell are measured. By using a reference humidity meter the calibration curve representing the relative humidity (%RH) as a function of the transmitted output power is obtained. For the hot water with the final temperature of T = 32.7°C the output power range of 255.0 -313.OnW is... 

A water balance model for a local location across a PEFC was previously developed. Below a critical current density, water removal out of the cathode catalyst layer (CCL) to cathode side proceeds by vapor diffusion. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which acts as a driving force for hydraulic fluxes to polymer electrolyte membrane (PEM) and gas diffusion media (GDM) of cathode. These fluxes are a function of local cell operating conditions such as the local relative humidity in cathode feed channel (CFC). Assuming no water condensation/evaporation in the CFC, water vapor balance along CFC under steady... 

A steady-state equilibrium-stage model based on MESH equations was proposed to simulate saline extractive distillation columns. The interaction parameters between each component of water-CaCl 2 and ethanol-water were obtained from mean ionic activity coefficients and vapor-liquid equilibrium (VLE) experimental data. Additionally, the interaction coefficients for the ethanol-CaCl 2 pair were fitted to experimental VLE data which were reported by Nishi for the ethanol-water-CaCl 2 system. It should be noted that adjustable parameters between each pair were considered to be temperature dependent. The results confirmed that the proposed model could accurately predict the experimental... 

Among major components of LiBr-H 2O absorption chillers is the absorber, which has a direct effect on the chillier size and whose characteristics have significant effects on the overall efficiency of absorption machines. In this article, heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled incline plate absorber in the Reynolds number range of 5