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In the present research work, we introduce a new method for estimating the slip length on superhydrophobic surfaces. Hence, a dynamic force is added to momentum equations and velocity boundary condition is rewritten in a new form. Laminar and turbulent channel flows are considered and two force functions are used with different profiles to investigate their effects on results. The turbulent channel flow is considered at Reτ=180 and the Large Eddy Simulation (LES) method has been applied to analyze this flow. All results indicate that this method can predict the streamwise slip length with a good accuracy, which is comparable with the Navier's method. So, using this numerical solution and also measuring pressure drop and mass flow rate in the channel, slip length can be calculated. Consequently, the errors and difficulties of slip length measurements in typical methods such as AFM and £gPIV would be eliminated. [ABSTRACT FROM AUTHOR]

To measure the aerodynamic and hydrodynamic forces and moments acting on scaled models in water and wind tunnel tests, multi-component strain gauge force and moment balance are usually used. Their performance and accuracy largely depends on the rig and calibration method, including the load table (design matrix) and analysis of experimental data. In this article, for the calibration of a six-component balance, a calibration procedure using the BoxBehnken design (BBD) of experiments was developed. In the suggested design matrix, in addition to all possible combinations of the two-component load of the six component load (Test vectors with two active factors), the pure loads (test vectors with one active factor) are also used. The implementation of the design matrixwas done using a calibration rig, which has the ability to perform formal experimental design techniques completely. The obtained experimental data were fitted with second-order equations using regression analysis. The statistical significance of independent variables and interactions was tested using the analysis of variance (ANOVA) with 95% confidence (α = 0.05). The results of residuals indicate that the suggested model sufficiently predicts the responses as a function of input factors. The comparison between the Modified Box-Behnken design (MBBD) and BBD calibrations indicates that the MBBD method estimates the data more accurate. The results show that the MBBD method is the most appropriate method compared to the existing methods for calibrating balance in this paper. [ABSTRACT FROM AUTHOR]

Conservation of mass, momentum, energy and state equations are recognized as basic mathematical models in analysis of the acoustic behavior of cavitation, as well as supercavitation. Also, it is known that the order of acoustic effects is not as high as that of hydrodynamics. Therefore, in this paper, initially, for comparing different terms of equations, using scale analysis, conservation equations are converted into dimensionless ones. Then, by comparing all conditions, coupled with weighting terms available in those equations, groups of parameters most appropriate with the hydrodynamics and hydroacoustics of the cavitating flow, are selected. By regarding acoustics as lower order phenomena, compared to the hydrodynamics of flow, and simultaneously using the perturbation method, two equations containing leading and first orders and different terms can be attained. Obtained results indicate that leading order equations represent the hydrodynamics of the cavitating flow, and first order equations indicate the acoustics of cavitation or supercavitation. Acoustic equations of the present study contain terms related to uid viscosity, density and pressure changes, and background flow velocity. As acoustic equations are coupled with leading order equations, in order to find the noise of cavitation, equations of fluid flow for compressible flow should be resolved. [ABSTRACT FROM AUTHOR]

The present work examines the role of chaotic mixing as a means of heat transfer enhancement in plate heat exchangers. In order to demonstrate the chaotic behavior, sensitivity to initial conditions and horseshoe maps are visualized. The Nusselt number and the friction factor were computed in the range of reynolds number, 1 < Re < 10. The Nusselt number increases considerably in chaotic models whereas the friction factor increases only marginally. [ABSTRACT FROM AUTHOR]

Considering the point that the existence of heavy metals in the wastewater are so dangerous for the environment and it would have many bad consequences for all the creatures including human beings, we must try out the ways that make us capable of adsorbing these heavy metals. In order to accomplish this goal we should use a method called adsorbing. In this study the adsorption of copper ions in hydrated copper nitrate (Cu (NO3)2, 3H2O) aqueous solution on natural zeolite (Clinoptilolite) and vermiculite was studied in batch reactors. The effect of temperature (25, 50, 75°C), solution pH (1.00-5.5) and concentration effect on the traditionally defined adsorption isotherm in the adsorbate range 100-325 mg/L for clinoptilolite and 100- 650 mg/L for vermiculite on the removal of copper was studied. The results showed that an increase in pH increases the adsorptivity of vermiculite. Pseudo second order model best described the reaction rate. Batch adsorption experiments conducted at room temperature (25±1 °C) showed that the adsorption pattern followed the Langmuir and Freundlich isotherm models. Optimum conditions for adsorption were determined at pH 5.5, and vermiculite and clinoptilolite at a dose of 3g. The concentration of metal ions was measured by Atomic Absorption Spectrometer (AAS). The results indicated that vermiculite and clinoptilolite are appropriate for adsorbing copper ions. [ABSTRACT FROM AUTHOR]

In this paper, an approach is identified using concepts in molecular dynamics (MD) and discrete element method (DEM) to generate the microstructure of polycrystalline materials. Using the proposed methods, different types of particles with different grain size and volume fraction in the real material, can be easily generated. It is assumed that the particles can be randomly packed together into a simulation region, by defining artificial interaction forces among them. Such forces may be either adopted from Van der Waals potential energy, or Hooke pair and gravity forces. The proposed method has proved to be fast due to the fact that the algorithm has been implemented on graphical processing units (GPU). Utilizing the Voronoi tessellation method, the set of the generated discrete grains have been altered to space-filling, adjoining polyhedrons with respect to the real geometry. Moreover, as an advantage, the boundary and the interface region of the microstructures were modeled. [ABSTRACT FROM AUTHOR]