A mixing model for diagnosing reacting tracers and tracing reactants in chemical and biochemical processes

It has previously been shown (Tanner et al., 1985) that biochemical and chemical reaction processes of the Type A → B → C can lead not only to kinetic hysteresis between the rate of formation of C and the concentration of species B in batch processes, but also hysteresis between those variables in a closed, imperfectly mixed (two zone) batch reactor. Furthermore, crossplotting the intermediate reactant, B, in one region of the poorly mixed reactor against B from the other major region leads to a clockwise hysteresis curve which is defined by both its area and the coordinate phase angle. This paper shows that the earlier analysis (Tanner et al., 1985) can be extended to the more general system A → B, where A in one region of the vessel is crossplotted against A measured in the other region. With an initial concentration of A* in one zone equal to its highest concentration, the inscribed area double-valued crossplot of A, uniquely defines the system in terms of the inter-vessel flowrate to reaction rate constant ratio, D/k.     

Design of the spherical agglomerate size in crystallization by developing a two-step bridging mechanism and the model

Spherical agglomeration technology can produce high-performance spherical particles in a single crystallization unit, although it is still challenging to control the particle size and shape. To solve this issue, a two-step bridging (TSB) mechanism containing a preconditioning period, size period, and shape period is proposed. The dynamic balance among the forces of adhesion, dispersion, and capillary action in the multi-liquid phases plays a key role. This is fully considered to establish the TSB-based thermodynamic size model and particle design framework by weighting the force action regions in multi-liquid phases with dynamic composition. The spherical agglomerates of benzoic acid, celecoxib, and salicylic acid with narrow particle size distributions and tunable particle size ranges of 2000–5000, 800–3500, and 1500–4500 μm, respectively, were designed and prepared successfully, showing good correlation with the calculation, which is superior to the reported methods and indicates that the mechanism has certain universality and guiding significance.     

Stability analysis of the Euler-Bernoulli beam with multi-delay controller

In this paper, we investigate the stabilization of an Euler-Bernoulli beam with time delays in the boundary controller. Theboundary velocity feedback law is applied to obtain the closed-loop system. It is shown that this system generates a C0-semigroup of linear operators. Moreover, the stability of the closed-loop system is discussed for different values of thecontroller constants and time delays via using spectral analysis and a suitable Lyapunov function.     

Band gap reduction of (Mo+N) co-doped TiO2 nanotube arrays with a significant enhancement in visible light photo-conversion: A combination of experimental and theoretical study

The present research aimed to evaluate the effects of co-doping TiO₂ nanotube aligned arrays (TNAs) with molybdenum and nitrogen on photocatalytic activity/performance under visible light irradiation. The surface morphology, electronic and optical properties of the pure and modified TNAs based on experimental characterization and theoretical calculations are reported. Both, pure and doped/modified TNAs were synthesized using a single step/low cost anodization method. Titanium sheets were immersed in ethylene glycol-based electrolytes containing NH₄F and NH₄F + K₂MoO₄ to fabricate highly ordered TNAs and Mo-doped TNAs, respectively. Mo–N-doped TNAs were fabricated by a thermal annealing process of Mo-doped samples in nitrogen environment (N₂-gas flow rate of 400 cc/min) for 2hr at 520 °C. Physical/chemical characteristics, structural and photo-electrochemical/electronic properties of the photo-electrodes were observed using several techniques including, field emission scanning electron microscopy (FESEM), Energy Dispersive X-Ray Spectroscopy (EDX), XRD, X-ray photoelectron spectroscopy (XPS), Raman and UV–Vis spectroscopy. We further used a full potential density functional theory (DFT) method to estimate the morphological and electronic structure of the synthesized photo-anodes and also observed a good agreement between theoretical calculations and characterization results. The characterization techniques confirm that Mo and N atoms have been incorporated into the lattice of anodized TNAs and molybdenum atoms partially substituted titanium atoms in the structure of TNAs. UV–Vis DRS spectroscopy experiments and theoretical results reveal that (Mo + N) co-doping creates a positive synergic effect on the band structure of TNAs which can enhance photo-conversion activity, compared to the single Mo/N-doped TNAs samples. In presence of sacrificial agent/electrolyte (aqueous solution of Na₂S/Na₂SO₃) and visible light irradiation, average photocurrent density of the co-doped TNAs photo-anode is 14 times greater than that of the undoped TNAs.     

STUDY ON THE ACETYLENE HYDROGENATION PROCESS FOR ETHYLENE PRODUCTION: SIMULATION,MODIFICATION, AND OPTIMIZATION

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen flow rate, and H-1/H-2 ratio were regulated as adjustable parameters for the process optimization. The simulation shows that ethylene selectivity increases by 12%, while acetylene concentration and hydrogenation reactor temperature remains within acceptable ranges. Such selectivity could be achieved at the hydrogen flow rate of 50 kg/h with H-1/H-2 ratio of 0.1/0.9.     

Estimation of air concentration in dissolved air flotation (DAF) systems using a simple predictive tool

Dissolved air flotation (DAF) has been used for several decades in water treatment systems. It is a unit operation for the separation of solid and semisolid (floc) particles from a liquid phase that has been used for the clarification of potable water. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The increased dissolved air concentration in water at elevated pressure is the fundamental principle that allows the formation of microbubbles. In this article a simple predictive tool is developed to estimate air saturated concentration in dissolved air flotation (DAF) systems. Estimations are found to be in excellent agreement with reported data in the literature with average absolute deviation being around 0.5%. The tool developed in this study can be of immense practical value for process engineers to have a quick check of air concentration in dissolved air flotation systems (DAF) at various conditions without opting for any experimental trials. In particular, water practitioners and process engineers would find the proposed approach to be user-friendly with transparent calculations involving no complex expressions.     

Experimental analysis of lipid extraction and biodiesel production from wastewater sludge

The most promising renewable alternative fuel, biodiesel, is produced from various lipid sources. Primary and secondary sludge of municipal wastewater treatment facilities are potential sources of lipids. In this study, factorial experimental analyses were used to study the influence of different variables on the lipid extraction and biodiesel production from dried municipal primary and secondary sludge (Adelaide Pollution Control Plant, London, ON, Canada). The empirical models were developed for each factorial analysis. The temperature turned out to be the most significant variable for lipid extraction by using methanol and hexane as solvents. Extraction using methanol resulted in a maximum of 14.46 (wt/wt) % and 10.04 (wt/wt) % lipid (on the basis of dry sludge), from the primary and secondary sludge sources respectively. A maximum of 11.16 (wt/wt) % and 3.04 wt/wt% lipid (on the basis of dry sludge) were extracted from the primary and secondary sludge sources, respectively, using hexane as a solvent. The FAME (fatty acid methyl ester) yield of the H₂SO₄ catalyzed esterification–transesterification of the hexane and methanol extracted lipids were 41.25 (wt/wt) % and 38.94(wt/wt) % (on the basis of lipid) for the primary sludge, and 26.89 (wt/wt) % and 30.28 (wt/wt) % (on the basis of lipid) for the secondary sludge. The use of natural zeolite as a dehydrating agent was increased the biodiesel yield by approximately 18 (wt/wt) % (on the basis of lipid). The effect of temperature and time was also investigated for biodiesel production from the lipid of wastewater sludge. The yield and quality of the FAME were determined by gas chromatography.     

Feasibility analysis of specialized PEEC solvers in comparison to SPICE-like solvers

The Partial Element Equivalent Circuit (PEEC) method provides an electric equivalent circuit for a physical geometry. This circuit can be combined with external passive/active lumped elements, enabling the simulation and co-design of combined circuit and electromagnetic (EM) structures. The resulted circuit can be solved in a dedicated solver, or equivalently can be exported to a SPICE-like solver. In this paper, the inclusion of passive and active lumped circuit elements in PEEC method has been studied and a combined solver has been developed. To demonstrate the capability of the solver, three structures are examined. All examples include a transmission line-PEEC model and active components. Results are compared with those from OrCAD, where an analytical model for the transmission line is used. Good agreement between the results shows the feasibility of using PEEC to solve this type of mixed problems. Also, comparison has been made in terms of implementation and feasibility for the aim of developing the optimal EM solver with active elements support. It is shown that SPICE is not a suitable choice to solve the PEEC models and, a specialized solver can solve the system in a much faster way. On the other hand, all the definitions and models of circuit devices e.g. transistors, MOSFETs, etc. should be implemented in the specialized solver, which raises a trade-off between the solution time and the implementation time.     

Power and energy consumption of skid-steer rovers turning on loose soil

This study highlights two key phenomena affecting power and energy consumption of skid-steer rovers on loose soil that is not present on the hard ground: soil excavation due to wheel counterrotation and impeded turning when dragging a braked wheel. Experiments in the field and in a controlled laboratory sandbox show that, on sand, power peaks by 15%–20% in a newly identified range of turns with radii between half the rover width, $B∕2$, to $R^{\prime }$, the radius at which the inner wheel does not turn. In this range of turns, the inner wheels rotate backwards but are being dragged forward through piles of sand they excavate by counterrotation. At $R\prime$, turns are shown to take much longer, leading to higher total energy consumption over time. Experiments in a controlled laboratory sandbox isolate the high motor torque and the resistance force experienced when a skid-steer rover drags a counterrotating or braked wheel, respectively, through loose soil. Other field experiments also demonstrate that paths combining circular arcs and lines can lead to energy savings of up to 15% relative to common ones consisting of point turns and lines; the experimental results suggest the circular arcs should have radii of approximately $2R\prime$. The quantitative values presented in this paper are specific to the rover and soils tested, but there are reasons to support the overall conclusions generalizing to all skid-steer rovers in loose soil.