Optimal oxygen concentration strategy through an isothermal oxidative coupling of methane plug flow reactor to obtain a high yield of C2 hydrocarbons

An optimal oxygen concentration trajectory in an isothermal OCM plug flow reactor for maximizing C₂ production was determined by the algorithm of piecewise linear continuous optimal control by iterative dynamic programming (PLCOCIDP). The best performance of the reactor was obtained at 1,085 K with a yield of 53.9%; while, at its maximum value, it only reached 12.7% in case of having no control on the oxygen concentration along the reactor. Also, the effects of different parameters such as reactor temperature, contact time, and dilution ratio (N₂/CH₄) on the yield of C₂ hydrocarbons and corresponding optimal profile of oxygen concentration were studied. The results showed an improvement of C₂ production at higher contact times or lower dilution ratios. Furthermore, in the process of oxidative coupling of methane, controlling oxygen concentration along the reactor was more important than controlling the reactor temperature. In addition, oxygen feeding strategy had almost no effect on the optimum temperature of the reactor. Finally, using the optimal oxygen strategy along the reactor has more effect on ethylene selectivity compared to ethane.     

The Development of a Robust ANFIS Model for Predicting Minimum Miscibility Pressure

Miscible gas injection has been considered one of the most important enhanced oil recovery techniques. Minimum miscibility pressure (MMP) is a key parameter in the design of an efficient miscible gas injection project. This parameter is usually determined using a slimtube apparatus in the laboratory. However, many attempts have been made to introduce MMP predicting correlations. In this study an adaptive neuro-fuzzy inference system (ANFIS)–based correlation has been developed to estimate the MMP values. In this model, the MMP of reservoir fluid is correlated with 27 variables containing concentrations of different components in reservoir oil and injecting gas, molecular weight and specific gravity of C₇ ⁺ in reservoir oil and also reservoir temperature. This correlation can be applied to predict the effect of each individual parameter on the MMP values.     

Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas

Elevated summertime temperatures in urban ‘heat islands’ increase cooling-energy use and accelerate the formation of urban smog. Except in the city’s core areas, summer heat islands are created mainly by the lack of vegetation and by the high solar radiation absorptance by urban surfaces. Analysis of temperature trends for the last 100 years in several large U.S. cities indicate that, since 1940, temperatures in urban areas have increased by about 0.5–3.0°C. Typically, electricity demand in cities increases by 2–4% for each 1°C increase in temperature. Hence, we estimate that 5–10% of the current urban electricity demand is spent to cool buildings just to compensate for the increased 0.5–3.0°C in urban temperatures. Downtown Los Angeles (L.A.), for example, is now 2.5°C warmer than in 1920, leading to an increase in electricity demand of 1500 MW. In L.A., smoggy episodes are absent below about 21°C, but smog becomes unacceptable by 32°C. Because of the heat-island effects, a rise in temperature can have significant impacts. Urban trees and high-albedo surfaces can offset or reverse the heat-island effect. Mitigation of urban heat islands can potentially reduce national energy use in air conditioning by 20% and save over $10B per year in energy use and improvement in urban air quality. The albedo of a city may be increased at minimal cost if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads. Similar incentive-based programs need to be developed for urban trees.     

Microfluidic‐Based Approaches in Targeted Cell/Particle Separation Based on Physical Properties: Fundamentals and Applications

Cell separation is a key step in many biomedical research areas including biotechnology, cancer research, regenerative medicine, and drug discovery. While conventional cell sorting approaches have led to high‐efficiency sorting by exploiting the cell's specific properties, microfluidics has shown great promise in cell separation by exploiting different physical principles and using different properties of the cells. In particular, label‐free cell separation techniques are highly recommended to minimize cell damage and avoid costly and labor‐intensive steps of labeling molecular signatures of cells. In general, microfluidic‐based cell sorting approaches can separate cells using “intrinsic” (e.g., fluid dynamic forces) versus “extrinsic” external forces (e.g., magnetic, electric field, etc.) and by using different properties of cells including size, density, deformability, shape, as well as electrical, magnetic, and compressibility/acoustic properties to select target cells from a heterogeneous cell population. In this work, principles and applications of the most commonly used label‐free microfluidic‐based cell separation methods are described. In particular, applications of microfluidic methods for the separation of circulating tumor cells, blood cells, immune cells, stem cells, and other biological cells are summarized. Computational approaches complementing such microfluidic methods are also explained. Finally, challenges and perspectives to further develop microfluidic‐based cell separation methods are discussed.     

Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant

Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100 °C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300 °C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24 μm at the surface and 19 μm internally. Sample hardness increased to in excess of 300 HV0.05 with increasing FST while samples with an FST of below 1250 °C produced an elastic–brittle stress/strain curve and samples above this displayed elastic–plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent.     

Prediction of the volumetric and thermodynamic properties of some refrigerants using GMA equation of state

The density of 11 refrigerants (hydrochlorofluorocarbon (HCFCs) and hydrofluorocarbon (HFCs)) in the extended ranges of temperature and pressure has been calculated using Goharshadi–Morsali–Abbaspour equation of state (GMA EoS) and the results have been shown as the three-dimensional surfaces of density–temperature–pressure. A wide comparison with experimental data was made. The accuracy of the equation of state in the prediction of density was determined by statistical parameters. The results show that the GMA EoS can reproduce the experimental PVT data of HCFCs and HFCs within experimental errors throughout the liquid phase. The thermodynamic properties such as isobaric expansion coefficient, isothermal compressibility, and vapor–liquid equilibrium (VLE) prediction for these HCFC and HFC refrigerants have been performed using GMA EoS. GMA EoS can predict the characteristic feature of pressure behavior of isobaric expansion and isothermal compressibility coefficients.     

Evaluation of rutting resistance of asphalt binders and asphalt mixtures modified with polyphosphoric acid

In this research, a polyphosphoric acid (PPA) additive was used to modify a performance graded binder (PG 58-22). Experimental program included use of three PPA contents (0.5%, 1%, and 1.5%) by weight of bitumen and use of antistripping limestone aggregates. High-temperature rheological properties of asphalt binders were evaluated through the frequency sweep test. Complex modulus test was also used to evaluate rutting characteristics of asphalt mixtures. Results showed that PPA significantly improved rutting resistance of both unmodified asphalt binder and unmodified asphalt mixture, especially for the asphalt binder.     

Development of 3D Scanning System for Robotic Plasma Processing of Medical Products with Complex Geometries

This paper describes the development of an intelligent automated control system of a robot manipulator for plasma treatment of medical implants with complex shapes. The two-layer coatings from the Ti wire and hydroxyapatite powders are applied on the surface of Ti medical implants by microplasma spraying to increase the biocompatibility of implants. The coating process requires precise control of a number of parameters, particularly the plasma spray distance and plasma jet traverse velocity. Thus, the development of the robotic plasma surface treatment involves automated path planning. The key idea of the proposed intelligent automatic control system is the use of data of preliminary three-dimensional (3D) scanning of the processed implant by the robot manipulator. The segmentation algorithm of the point cloud from laser scanning of the surface is developed. This methodology is suitable for robotic 3D scanning systems with both non-contact laser distance sensors and video cameras, used in additive manufacturing and medicine.     

Correlation Between Numerical Finite Element Simulation and Experiments for Explosive Cladding of Nickel Base Super Alloy on Hot Tool Steel

Abstract: Experimental tests were carried out to explosively clad solution‐annealed Inconel 718 super alloy on quench‐tempered AISI H13 hot tool steel. The tests were performed using various stand‐off distances and explosive–to‐flyer plate mass ratios. Various interface geometries were obtained from these experiments. All the experiments were simulated using ABAQUS version 6.9 finite element software. The Williamsburg equation of state and Johnson–Cook constitutive equation with its corresponding failure equation were used to model the behaviour of explosive and plates, respectively. The experimental results showed that the shape of interface fell roughly into three classes, wavy or wavy with some vortex shedding or smooth‐wavy. Various interface morphologies were achieved by changing the stand‐off distances and explosive–to‐flyer plate mass ratios because of change of impact velocity and dynamic collision angle. Numerical results showed that high localised plastic deformation was produced at the bond interface. Equivalent plastic strain and shear stress could be criteria for transition of interface morphology. Welding window of alloys was also developed.     

Ammonia sensing properties of (SnO2–ZnO)/polypyrrole coaxial nanocables

In this work, (SnO₂–ZnO)/polypyrrole (PPy) coaxial nanocables have been synthesized through simple chemical routes. The SnO₂–ZnO composite nanofibers with narrow distribution of diameter size and an average of 75 nm were synthesized via the electrospinning method. In this experiment, we were able to polymerize a shell of PPy, as a typical conducting polymer, on surface of SnO₂–ZnO nanofibers using the vapor-phase polymerization of Pyrrole monomer. The prepared nanomaterial exhibits a linear response to Ammonia (NH₃) concentrations at room temperature. The obtained results make NH₃ detection and determination of its concentration feasible. The superior features of this nanomaterial include simple synthesis method, high sensitivity, and quick response and recovery times. The aforementioned characteristics of this nanomaterial indicate the potential of industrial applications.