Approximate design and performance of the robust control charts for monitoring dispersion in Phase I

This article designs and studies the approximate performance of robust dispersion charts, namely, MAD chart, S_n chart, and Q_n chart, in Phase I analysis (recently developed in the literature). The proposed limits are based on false alarm probability for monitoring the dispersion of a process in Phase I analysis. The charting constants are determined to achieve the required nominal FAP (FAP₀). The performance of these structures is evaluated in (i) the attained false alarm rate and (ii) the probability of signals for out‐of‐control situations. The analysis shows that the proposed design of Phase I robust dispersion charts correctly controls the FAP and shows a good performance in detecting the shifts in the process variation. An illustrative example is used to explain the practical implementation of these limits.     

Synthesis, Structural, and Magnetic Characterization of Mn1?x Ni x Fe2O4 Spinel Nanoferrites

Nanoferrites of composition Mn_1−x Ni _x Fe₂O₄ with x=0.00, 0.25, 0.50, 0.75, 1.00 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological and magnetic changes taking place with varying Ni concentration in the composition of the prepared nanoferrites. IR reveals the presence of both high-frequency and low-frequency bands due to tetrahedral and octahedral sites, respectively. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 14–26 nm. The lattice parameters (a) decrease with the increase of the Ni concentration x in the lattice. Further information about the morphology of the nanoferrites was obtained from the AFM and SEM results. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic properties such as saturation magnetization (M _s ) and remanence (M _r ) are calculated from the hysteresis loops and observed to be dependent on the composition.     

Effects of moisture content and heating condition on pyrolysis and combustion properties of structural fuels

The objective of this research was to measure the pyrolysis and combustion properties of selected structural fuels as a function of fuel moisture content (MC) levels under various external heating conditions. The pyrolysis properties were measured by using the thermogravimetric analysis technique at 3 MC levels (5%, 10%, and 15%) and 3 heating rates (5, 15, and 25K/min.). The combustion properties were measured by using a cone calorimeter at the same MC levels and 3 heat flux levels (20, 30, and 50 kW/m²). In addition, density and thermal conductivity as a function of MC levels were also measured. Statistical analysis was performed over the experimental data by using a 95% confidence interval. Most materials had significant increase in density when the MC levels increased, while the increase was more significant for natural woods than engineered woods. No statistically significant changes in thermal conductivity were observed for most materials. The pyrolysis properties were affected by both the MC and heating rate levels. Both MC and heat flux levels affected the combustion properties.     

Transport of two metal oxide nanoparticles in saturated granular porous media: role of water chemistry and particle coating

The growing use of nanosized titanium dioxide (nTiO₂) and zinc oxide (nZnO) in a large number of commercial products raises concerns regarding their release and subsequent mobility in natural aquatic environments. Laboratory-scale sand-packed column experiments were conducted with bare and polymer-coated nTiO₂ and nZnO to improve our understanding of the mobility of these nanoparticles in natural or engineered water saturated granular systems. The nanoparticles are characterized over a range of environmentally relevant water chemistries using multiple complimentary techniques: dynamic light scattering, nanoparticle tracking analysis, transmission electron microscopy, and scanning electron microscopy. Overall, bare (uncoated) nanoparticles exhibit high retention within the water saturated granular matrix at solution ionic strengths (IS) as low as 0.1 mM NaNO₃ for bare nTiO₂ and 0.01 mM NaNO₃ for bare nZnO. Bare nTiO₂ and nZnO also display dynamic (time-dependent) deposition behaviors under selected conditions. In contrast, the polymer-coated nanoparticles are much less likely to aggregate and exhibit significant transport potential at IS as high as 100 mM NaNO₃ or 3 mM CaCl₂. These findings illustrate the importance of considering the extent and type of surface modification when evaluating metal oxide contamination potential in granular aquatic environments.     

A simulation study on selection of optimized process for azeotropic separation of methanol and benzene: Internal heat integration and economic analysis

This work provides an insight into the separation of azeotropic mixtures by using two different techniques: pressure swing distillation and extractive distillation. Both methods are used to separate an azeotropic mixture of methanol and benzene. This mixture exhibits a minimum boiling azeotrope at temperature 57.97 °C and pressure 1 bar with mole fractions of 0.61 and 0.39 for methanol and benzene, respectively. However, the azeotropic point in methanol and benzene mixture is pressure sensitive, which can be shifted by changing pressure with a process called pressure swing distillation. Extractive distillation with suitable solvent is another method to separate such kind of mixture. Both methods are rigorously simulated and optimized for minimum heat duties. Internal heat integration is applied too for increasing energy efficiency. New optimization techniques are carried out with process simulator Aspen HYSYS V8.4 and results reveal the best method for separation of methanol and benzene azeotropic mixture.     

Multiobjective Genetic Algorithm Approach to the Economic Statistical Design of Control Charts with an Application to bar and S2 Charts

Control charts are the primary tools of statistical process control. These charts may be designed by using a simple rule suggested by Shewhart, a statistical criterion, an economic criterion, or a joint economic statistical criterion. Each method has its strengths and weaknesses. One weakness of the methods of design listed is their lack of flexibility and adaptability, a primary objective of practical mathematical models. In this article, we explore multiobjective models as an alternative for the methods listed. These provide a set of optimal solutions rather than a single optimal solution and thus allow the user to tailor their solution to the temporal imperative of a specific industrial situation. We present a solution to a well‐known industrial problem and compare optimal multiobjective designs with economic designs, statistical designs, economic statistical designs, and heuristic designs. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of variable viscosity and thermal conductivity on a thin film flow over a shrinking/stretching sheet

The effects of variable viscosity and thermal conductivity on the flow and heat transfer in a laminar liquid film on a horizontal shrinking/stretching sheet are analyzed. The similarity transformation reduces the time independent boundary layer equations for momentum and thermal energy into a set of coupled ordinary differential equations. The resulting five-parameter problem is solved by the homotopy perturbation method. The results are presented graphically to interpret various physical parameters appearing in the problem.