Modification of Langmuir isotherm for the adsorption of asphaltene or resin onto calcite mineral surface: Comparison of linear and non-linear methods

In this paper, the Langmuir isotherm, originally derived for the adsorption of three samples of asphaltenes and one sample of resin onto calcite, was modified to fit the adsorption isotherm. The modified Langmuir isotherm parameters obtained from the four linear equations using the different linear method. The aim of this modification is based on the fact that direct application of the Langmuir isotherm often leads to poor data fitting. In the present communication, it is shown that the level of data fitting to the Langmuir isotherm can be improved by a simple modification introducing a concentration dependent factor, X. Four Modified Langmuir linearized isotherm models and one non-linear isotherm model was discussed in this paper, and their coefficients were estimated. In the present study, to study non-linear isotherm model, genetic algorithm was used. A genetic algorithm procedure was utilized to optimize the modified Langmuir constants for a more accurate estimation of the set of model parameters. The obtained results demonstrate that the best fit is obtained using genetic algorithm. Furthermore, it is found that among the mentioned different samples of oil, filtered shale oil follows a multilayer adsorption isotherm.     

The Effect of Post Weld Heat Treatment (PWHT) on the Microstructure,Microhardness and Sulphide Stress Corrosion Cracking (SSCC) of Ni-Base Superalloy IN625 Hot Wire TIG Cladding on AISI 4130 Steel

Protection of Metals and Physical Chemistry of Surfaces - This study aims to investigate the effect of post-weld heat treatment (PWHT) on the microstructure, microhardness, and sulfide stress...     

Uniform Cooling of a Flat Surface by an Optimized Array of Turbulent Impinging Air Jets

Abstract

The aim of this study is to investigate the uniform cooling of a hot isothermal heated target surface, using four turbulent impinging air jets. Eight parameters including the width of jets, the space between the inner jets, the space between inner and outer jets, the distance of jets from the plate, the impingement angle of jets, and the overall volumetric flow rate of the cooling air per unit depth of the nozzle are considered as design variables. The normalized standard deviation of the local Nusselt number from the desired Nusselt number is considered as the objective function. An optimization algorithm based on pattern search method is utilized to obtain the optimum array of the jets. Two different scenarios of the problem are considered, one with fixed normal impingement angles and the other with the optimized angles. Results show an almost uniform distribution of the local Nusselt number. Increasing the amount of desired Nusselt number for the case with fixed impinging angles results in a higher Reynolds number, a wider opening for outer jets and a reduction in jet to jet and jet to surface distances. However, changes in design parameters for the case with optimum impinging angles are erratic.     

Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

Experimental and Numerical Investigation of a Cu–Al Bimetallic Tube Produced by ECAP

In this paper, a new application of equal channel angular pressing (ECAP) for fabrication of Cu–Al bimetallic tubes is presented. For the evaluation of ECAP effects, the microstructure and micro-hardness of samples are considered. To investigate of bonding properties of Cu–Al tubes, optical microscopy and shear strength testing were used. In addition, the effect of friction coefficient and thickness on applied force was evaluated by numerical analysis. The results from the experiments indicated that the hardness of Cu and Al increased by 156.8 and 129%, respectively. Also, the average Cu grain size after three passes fell from 62.5 to 11.2 µm. Finally, Cu and Al tubes were well interconnected as a bimetallic tube at higher passes.     

The Prediction of Asphaltene Adsorption Isotherm Constants on Mineral Surfaces

In this study, a novel model for adsorption of asphaltene, extracted from shale oil and dissolved in toluene on Kaolin, Smectite, Fluorite, and Hematite, was proposed using genetic algorithms (GAs). A GA procedure was utilized to optimize the Langmuir constants for a more accurate estimation of the set of model parameters. The GA outputs show that all three except latter mineral follow the Langmuir-type isotherms, which have good agreement with experimental results. However, Hematite mineral follows a multilayer adsorption isotherm.     

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.     

Lattice Boltzmann simulation of mixed convection heat transfer in a corrugated wall cavity utilizing water‐based nanofluids

In the present study, the effects of Cu and CuO nanoparticles' presence on mixed convection heat transfer in a lid‐driven cavity with a corrugated wall are investigated using the lattice Boltzmann method. The boundary fitting method with second‐order accuracy at both velocity and temperature fields is used to simulate the curved boundaries in the LBM. The problem is investigated for different Richardson numbers (0.1–10), volume fractions of nanoparticles (0–0.05), curve amplitudes (0.05–0.25), and phase shifts of corrugated wall (0–270) when the Reynolds number is equal to 25. The volume fraction of added nanoparticles to the water‐based fluid is less than 0.05 to make dilute suspensions. Results show that adding nanoparticles enhances the rate of heat transfer. It is found that nanoparticles have significant effects on both fluid flow and heat transfer of the mixed convection, especially for low Richardson numbers. A comparison between Cu and CuO nanoparticles shows the Cu nanoparticles have a better effect on heat transfer enhancement for all tested conditions. The results also represent the effective role of a corrugated wall on the rate of nanofluid heat transfer. It is observed that increasing the wavy wall's amplitude leads to a decrease of the average Nusselt numberfor a high Richardson number. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21024