Theoretical study of superheated vapor effect on liquid film condensation in a saturated porous medium using Forchheimer's model

In this work, the superheated vapor effect on liquid film condensation in a saturated porous medium using Forchheimer's model has been investigated analytically and numerically. The applied governing equations, the continuity equation, the Forchheimer equation, and the energy equation were transformed using the similarity transformation technique into a dimensionless form using a set of suitable variables and then solved numerically using the Runge–Kutta method. Results obtained were graphically drawn to illustrate the effects of superheated vapor and subcooled liquid on the liquid film condensation, temperature, and heat transfer rate through the porous medium. It was found that the film thickness is a function of dimensionless parameters related to the degree of subcooling and Grashof number without a superheating effect. Consequently, the Nusselt number depends on the square root of the Rayleigh number, the Grashof number, and the dimensionless film thickness. It was also found that if superheating exists, the liquid film thickness then depends on four dimensionless parameters related to the Grashof number, the degree of subcooling of the liquid, the extent of the superheating of the surrounding vapor, and a property ratio of the liquid and the vapor phase.     

Characterization of Mechanical and Thermal Properties of Vinyl-ester/TiO2 Nanocomposites Exposured to Electron Beam

The effect of electron beam irradiation (EBI) on the properties of vinyl-ester/TiO₂ nanocomposites has been studied in the present paper. The nanoparticles (1, 3 and 5 wt%) in the matrix are dispersed by high shear matrix characterized by transition electron microscopy. Neat polymer and nanocomposites were exposed to EBI in 100, 500 and 1,000 kGy doses. The mechanical, thermal behaviors of nanocomposites were studied by tensile and flexural tests and thermo-gravimetric analysis. The results showed that irradiation improved the properties of neat resin and nanocomposies. Fourier transform spectroscopy spectra showed that VE and nanocomposite are stable against of irradiation of EBI up to 1,000 kGy.     

Aging resistance of asphalt binders through the use of zinc diethyldithiocarbamate

Abstract

Aging can significantly reduce the durability of binders used in asphalt pavements and can consequently impose long-term maintenance cost to the owners. Antioxidants are additives that can be used to hinder oxidation and hardening of petroleum asphalt binders. In this study, the effect of zinc diethyldithiocarbamate (ZnDEC) as an antioxidant on chemical and rheological features of the binder were evaluated and monitored during laboratory aging process. The results indicated that not only ZnDEC can retard the aging process, but it also improves the low- and mid-temperatures cracking resistance without negatively affecting the rutting performance of the binder.     

Full-scale mechanically stabilized earth (MSE) walls under strip footing load

This study analyses two full-scale model tests on mechanically stabilized earth (MSE) walls. One test was conducted with a rigid and one with a flexible wall face. Other parameters were the same in these two tests, like the number and type of geogrid layers, the vertical distance between the layers and the soil type. The loads and strains on the reinforcement are measured as function of the horizontal and vertical earth pressure and compared with analytical models. Specifics regarding the behavior of the geogrids under the compaction load during the construction of the model and under strip footing load are included in the study. Results are compared with AASHTO and the empirical K-stiffness method. In this study, an analytical method is developed for the MSE walls taking into account the facing panel rigidity both after backfill construction and after strip footing load. There is good agreement between the proposed analytical method and the experimental results considering the facing panel rigidity. The results indicate that the tensile force on reinforcement layers for rigid facing is less than the flexible facing. The maximum strains in the reinforcement layers occurred in the upper layers right below the strip footing load. The maximum wall deflection for the flexible facing is more than for the rigid facing. The maximum deflection was at the top of the wall for the rigid facing and occurred at z/H?=?0.81 from top of the wall for the flexible facing.     

Sustainability assessment in the presence of undesirable factors over time: A case on gas companies

Sustainability is an essential ingredient for long-term success of firms, and its assessment has a significant impact on decision making and sustainability management. In the current paper, a data envelopment analysis-based approach is proposed to assess the sustainability of systems over several periods when undesirable outputs are present in the process. Indeed, sustainability is assessed in each period and, as a whole, simultaneously. Furthermore, social, economic, and environmental efficiency scores of multiperiod systems are evaluated in each period. The weak disposability assumption is used to handle undesirable outputs. Also, the current study concerns socio-economic, socioenvironmental, and eco-environmental factors in addition to economic, social, and environmental aspects. A real-world application on Iranian gas companies is used to illustrate the applicability of the proposed approach.     

An experimental study on plunging depth of density currents

Mass density of the current flows is the one of the important problem in the hydraulics of the dam reservoir. Plunge point occurs when the mass density current penetrates in the stagnant fluid. Recognition the place of this point is very important because of clearing the boundary of the density current flow and ambient fluid. In this study the influences of bed slope and hydraulic parameters on plunging depth were experimentally investigated. The results show that the slope has a minor effect on the plunging depth. The height of plunging depth is increased by increasing the density of the current flow. Also increasing the densimetric Froude number caused of decreasing the plunging depth. Finally an equation was proposed to estimate the plunging depth using as function of flow characteristics.     

Thermal and flow analysis of a magneto-hydrodynamic micropump

A study of transient fully developed laminar flow and temperature distribution in a magnetohydrodynamic (MHD) micropump is presented. The micropump is driven using the Lorentz force which is induced as a result of interaction between an applied electric field and a perpendicular magnetic field. The governing equations are solved analytically by an eigenfunction expansion method, and numerically by a finite-difference (ADI) method. The numerical and analytical results are found to be in good agreement with each other. The effect of different parameters on the transient velocity and temperature, such as aspect ratio, Hartman number, Prandtl number, and Eckert number is studied. The results obtained showed that controlling the flow and the temperature can be achieved by controlling the potential difference, the magnetic flux, and by a good choice of the electrical conductivity.