Enhanced fracture toughness in carbon-nanotube-reinforced amorphous silicon nitride nanocomposite coatings

Multiwalled-carbon-nanotube (MWCNT)-reinforced silicon nitride coatings were grown to evaluate the toughness contribution of nanotubes in a ceramic coating. An MWCNT array was first grown using catalytic chemical vapor deposition of acetylene on a silicon substrate. This aligned MWCNT preform was then infiltrated with an amorphous silicon nitride matrix by low-pressure chemical vapor deposition of dichlorosilane (DCS) and ammonia (NH₃). The fracture toughness of this material was determined by generating cracks using nanoindentation and then employing finite-element analysis to estimate the bridging toughness contribution of the MWCNTs. The MWCNT bridging toughness of the composites is determined to be ～5.6 MPa m^1/2, which is seven times higher than that of the matrix. The interfacial frictional stress is also estimated and ranges from 7 to 20 MPa.     

Analysis of Bejan’s heatlines on visualization of heat flow and thermal mixing in tilted square cavities

This article analyzes the detailed heat transfer phenomena during natural convection within tilted square cavities with isothermally cooled walls (BC and DA) and hot wall AB is parallel to the insulated wall CD. A penalty finite element analysis with bi-quadratic elements has been used to investigate the results in terms of streamlines, isotherms and heatlines. The present numerical procedure is performed over a wide range of parameters (10³ ? Ra ? 10⁵,0.015 ? Pr ? 1000,0° ? φ ? 90°). Secondary circulations cells are observed near corner regions of cavity for all φ’s at Pr = 0.015 with Ra = 10⁵. Two asymmetric flow circulation cells are found to occupy the entire cavity for φ = 15° at Pr = 0.7 and Pr = 1000 with Ra = 10⁵. Heatlines indicate that the cavity with inclination angle φ = 15° corresponds to large convective heat transfer from the wall AB to wall DA whereas the heat transfer to wall BC is maximum for φ = 75°. Heat transfer rates along the walls are obtained in terms of local and average Nusselt numbers and they are explained based on gradients of heatfunctions. Average Nusselt number distributions show that heat transfer rate along wall DA is larger for lower inclination angle (φ = 15°) whereas maximum heat transfer rate along wall BC occur for higher inclination angle (φ = 75°).     

Image-Based Machine Learning for Reduction of User Fatigue in an Interactive Model Calibration System

The interactive multiobjective genetic algorithm (IMOGA) is a promising new approach to calibrate models. The IMOGA combines traditional optimization with an interactive framework, thus allowing both quantitative calibration criteria as well as the subjective knowledge of experts to drive the search for model parameters. One of the major challenges in using such interactive systems is the burden they impose on the experts that interact with the system. This paper proposes the use of a novel image-based machine-learning (IBML) approach to reduce the number of user interactions required to identify promising calibration solutions involving spatially distributed parameter fields (e.g., hydraulic conductivity parameters in a groundwater model). The first step in the IBML approach involves selecting a few highly representative solutions for expert ranking. The selection is performed using unsupervised clustering approaches from the field of image processing, which group potential parameter fields based on their spatial similarities. The expert then ranks these representative solutions, after which a machine-learning model (augmented with the spatial information of the selected fields) is trained to learn user preferences and predict rankings for solutions not ranked by the expert. To better mimic the “visual” information processing of human experts, algorithms from the field of image processing are used to mine information about the spatial characteristics of parameter fields, thus improving the performance of the clustering and machine-learning algorithms. The IBML approach is tested and demonstrated on a groundwater calibration problem and is shown to lead to significant improvements, reducing the amount of user interaction by as much as half without compromising the solution quality of the IMOGA.     

Assessment of Soil and Water Contamination at the Tab-Simco Coal Mine: A Case Study

In 1996, the Tab-Simco site, an abandoned coal mine 10 km southeast of Carbondale, Illinois, was listed as one of the most highly contaminated AMD sites in the mid-continent region. A suite of impacted soil and water samples were collected from various locations to characterize the current extent of AMD pollution, following standard U.S. EPA protocols. The mean pH of soil and water samples were found to be 2.69 and 2.07, respectively. The mean sulfur content of the soil samples was 0.5 %. The AMD-impacted soils contained high concentrations of Fe, Zn, Ni, Cr, Cu, Pb, and As. The AMD also contained high concentrations of Fe, As, Zn, Pb, Cr, Al, Cd, Cu, and Ni, as well as \({\text{SO}}_{4}^{2 - }\), all of which were significantly above their U.S. EPA permissible limits for surface water.     

Role of Entropy Generation On Thermal Management During Natural Convection in a Tilted Square Cavity with Isothermal and Non-Isothermal Hot Walls

Entropy generation during natural convection within tilted square cavity inclined with different angles (? = 30°and 75°) for various thermal boundary conditions (case 1: isothermal heating and case 2: non-isothermal heating) has been studied. Simulations are carried out over a range of parameters: Rayleigh number (10³ ≤ Ra ≤ 10⁵) and Prandtl numbers (Pr = 0.025 and 998.24). The numerical results are presented in terms of isotherms (θ), streamlines (ψ), entropy generation due to heat transfer (S _θ ) and fluid friction (S _ψ ). Heating strategy is energy efficient for case 2 (non-isothermal heating) due to its less total entropy generation with reasonable heat transfer rate, irrespective of Pr.     

LIQUID/SOLID FLUIDIZATION ITS ROLE AND LIMITATION IN FINE BENEFICIATION – A REVIEW

Among many emerging fine beneficiation methods, the liquid/solid fluidization technique has become the operator's choice owing to its superior performance. In this article, the subject is revisited with the aim to enhance process efficiency through basic understanding of the process. Bulk density difference between ore and gangue particles during fluidization leads to segregation when fluidized together and is the preferred condition for mineral beneficiation. Size ratio, density ratio, and shape difference between particle components control difference in bulk density. Based on this knowledge, a feed for liquid/solid fluidization is presumed as a mixture of three different types of binary systems; (a) easily separable, (b) difficult to separate, and (c) nonseparable. This classification suggests that feed rich with easily separable–type particles is the ideal choice for this technique. The feed is very sensitive to operating parameters that contains large proportion of difficult-to-separate-type particles.     

Thermal performance analysis of small-sized solar parabolic trough collector using secondary reflectors

ABSTRACT

In this paper, theoretical analysis of receiver tube misalignment, the design of secondary reflector and experimental analysis of a small-sized solar parabolic trough collector (PTC) with and without secondary reflectors are represented. Experimental analysis of PTC has been done using a parabolic secondary reflector (PSR) and triangular secondary reflector (TSR) and compared with PTC without secondary reflector (WSR). The maximum outlet temperature of heat transfer fluid is observed as 49.2°C, 47.3°C and 44.2°C in the case of PSR, TSR and WSR conditions, respectively. The maximum thermal efficiency of 24.3%, 22.5% and 17.8% is observed in the case of PSR, TSR and WSR conditions, respectively. The circumferential temperature difference on the outer surface of the receiver tube is obtained more uniform in the case of PSR and TSR than WSR condition. This indicates that the use of a secondary reflector can improve the performance of a solar PTC system.     

Synthesis and crosslinking of partially disulfonated poly(arylene ether sulfone) random copolymers as candidates for chlorine resistant reverse osmosis membranes

Biphenol-based, partially disulfonated poly(arylene ether sulfone)s synthesized by direct copolymerization show promise as potential reverse osmosis membranes. They have excellent chlorine resistance over a wide range of pHs and good anti-protein and anti-oily water fouling behavior. Crosslinking of these copolymers that have high degrees of disulfonation may improve salt rejection of the membranes for reverse osmosis performance. A series of controlled molecular weight, phenoxide-endcapped, 50% disulfonated poly(arylene ether sulfone)s were synthesized. The copolymers were reacted with a multifunctional epoxy resin and crosslinked thermally. The effects on network properties of various factors such as crosslinking time, copolymer molecular weight and epoxy concentration were investigated. The crosslinked membranes were characterized in terms of gel fraction, water uptake, swelling and self-diffusion coefficients of water. The salt rejection of the cured membranes was significantly higher than that for the uncrosslinked copolymer precursors.     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over SnO2–ZrO2 mixed oxide nanocomposite catalysts

SnO₂–ZrO₂ nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO₂ were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO₂–ZrO₂ nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH₃ and CO₂. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO₂ or ZrO₂). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO₂ was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity.