Theoretical Foundations of Chemical Engineering最新文献

In order to alleviate the problem of slagging caused by biomass combustion, this paper studied the slagging characteristics of peanut shell shaped granular fuel under different inorganic additives and their mixing ratios. X-ray fluorescence spectroscopy, X-ray diffraction and five evaluation indexes, such as contamination index, iron-calcium ratio, alkali-acid ratio, silicon ratio and silicon-aluminum ratio, were used to analyze the ash generated by the combustion of peanut shell shaped granular fuel. The results showed that the more acidic oxides, the less alkaline oxides, the higher the ash melting point, the less easy to slag, that is, the smaller the alkali-acid ratio, the less easy to slag. Comparing the values of the five evaluation indexes, such as contamination index, iron-calcium ratio, alkali-acid ratio, silicon ratio and silicon-aluminum ratio, it was found that the slag removal effect of kaolin additive was the best. Under the high temperature mode, the five evaluation indexes were 0.32, 0.56, 0.30, 0.79, 1.83, respectively. Under the low temperature mode, they were 0.17, 0.67, 0.25, 0.81, 1.68, respectively. It was obviously better than the slag removal effect of MgO, CaO or the proportional mixture of the three additives. This study provides a certain reference for reducing the slagging phenomenon generated by the combustion of peanut shell shaped granular fuel.

Gas discharges in the plasma atmosphere are known to consist of a collection of different particles, mainly electrons, ions, neutral atoms, and molecules. The present need is to characterize the plasmas and optimization of the designed plasma system under variable conditions. In this work, a time-dependent, one-dimensional simulation of an optimized DBD device, driven by a sinusoidal alternating high voltage, in argon gas is demonstrated. First of all, a DBD device with two electrodes, covered by the dielectric and with the variable discharge gap was assumed, and the discharge parameters were simulated versus time across the plasma gap. A comparison between the results is carried out. In the second part, with a fixed gap that was obtained from previous section, when the dielectric thickness changed, the plasma parameters were simulated. In the third case, with a fixed discharge gap and dielectric thickness, the plate diameters were varied and the best diameter was selected to deliver the best power deposition. Finally, the operating frequency and voltage were varied and the optimized values were obtained. Time-dependent and 1D profiles of the electric field, electron density, electron temperature, ion current density, electron current density, plasma, total current, and power deposition are demonstrated.

Kinetic Monte Carlo modeling was employed as a powerful tool to kinetically investigate of ibuprofen removal by direct ozonation (O₃ alone) and heterogeneous catalytic ozonation (graphene oxide and graphene oxide loaded with Fe₃O₄). The kinetic mechanisms and the values of rate constants for each step of the suggested mechanisms were found by Monte Carlo simulation. The graphene oxide loaded with Fe₃O₄ displays a significant role as a heterogeneous catalyst in the ozonation of ibuprofen by enhancing the reactivity of ibuprofen drug and O₃ on the graphene oxide surface. Optimized values of catalysts and O₃ were attained through obtaining the effect of initial O₃ and catalyst amounts on the rate of ibuprofen elimination utilizing kinetic Monte Carlo simulation. The simulation outcomes of the present investigation demonstrate satisfactory agreement with the experimental ozonation data for the systems above.

Talc, as an industrial mineral, is usually used at fine and ultrafine sizes in different applications. However, reaching the ultrafine sizes depends simultaneously on grinding conditions and the characteristics of the mineral to be ground. In this paper, the effect of talc hydrophobicity and grinding conditions in terms of grinding balls size, mill filling, grinding time, stirrer speed, and solids% on producing –45 microns in an attritor mill were studied. The change in talc particle size in dry and wet grinding modes was recorded along with monitoring the structural change by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the d₅₀ of the ground product reaches 10 µm or less at 10 mm media size, 60 min grinding time, 385 rpm stirring speed, 40% solids, and 25% mill filling. Nevertheless, under the same conditions, dry grinding not only gives a smaller product but also has higher structural changes than wet grinding. The talc hydrophobicity leads to talc particles agglomeration in aqueous media and consequently, a part of grinding energy is consumed in agglomerates breakdown resulting in delaying not only the reach to the same size as in the dry grinding but also the crystal lattice destruction. Inevitably, the intensive grinding to ≤ –5 µm changes the talc structure drastically in both grinding modes.

The efficiency of separate trapping of cesium oxide and molecular iodine formed during oxidative thermolysis of cesium iodide in the process of chemisorption on ceramic highly porous block-cellular contact elements is investigated. The dynamic sorption capacity of contact elements with an applied aluminosilicate sorption-active layer and with an active layer of silver nitrate for cesium and iodine, respectively, is determined. The developed contact elements are recommended for use in systems of local gas purification of high-temperature processing stages of recycling of spent nuclear fuel.

In general, there are many influencing factors in the cultivation of microorganisms, including yeast, among which pH control is of great importance. Since the pH characteristics of yeast fermentation processes are nonlinearity and the production of acid during yeast fermentation is typically nonlinearity, the process pH values cannot be adjusted rapidly and accurately by conventional linear control techniques. Hence, the intrinsic nonlinear characteristics of the pH control system are approximated by several nonlinear models including Hammerstein–Wiener model, and a controller is designed based on the models. To increase the yield in yeast cultures, fed-batch fermentation method should be used more than batch cultivation method. In brief, fed-batch fermentation is a method of continuous addition of the nutrient solution(glucose fluid) following the number of yeast cells present inside the yeast fermentation tank. In this paper, a mathematical model based on chemical equilibrium is proposed to control the pH of an industrial yeast fermentation tank with only inflow, no outflow, and relatively large internal volume, and a controller is designed using the input-output linearization method. The performance of the designed controller is verified by numerical simulation and field experiments.

The flow behaviors of highly viscous fluid falling film outside the vertical tube were investigated by theoretical analysis and numerical simulation. Based on gas-liquid two-phase flow methods, a new insight into flow behaviors, which mainly referred to the film thickness distribution, surface renewal frequency and residence time distribution of the highly viscous fluid falling film outside the vertical tube, were provided. Moreover, the correlation between film thickness and fluid viscosity and flow rate was established through model analysis. The numerical simulation results of film thickness were in good agreement with the experimental and theoretical values. The film surface dilated at the beginning of the falling film, and then gradually reached stable state with the largest thickness value. The distribution curve of falling film velocity from wall surface to free surface was in line with the typical Nusselt semi-parabolic profile. Normally, a large flow rate or a low fluid viscosity corresponds to a high surface renewal frequency and a narrow residence time distribution of falling film flow. The dimensionless residence time distribution of falling film flow showed little difference under different conditions, which indicates that the vertical tube falling film flow has a good application prospect in the production of high viscosity materials with uniform quality.

Boiling is an efficient mode of heat transfer and has important applications that use high heat flux systems. However, a single wettable boiling surface is not appropriate for the dual requirements of low superheat for nucleation and high critical heat flux. Here, we present a hydrophilic composite and a functional hydrophilic-hydrophobic partitioned porous structure that significantly improves boiling heat transfer performance via a double-sintering process. The superheat requirement for the onset of nucleate boiling decreased from 2°C on the single hydrophilic porous structure to 1°C on the hydrophilic-hydrophobic porous structure, the critical heat flux was reduced by 3.3% in the early stages of boiling (below 250 kW/m²), the heat transfer efficiency increased by 20%, and the heat transfer was comparable to that of the hydrophilic porous structure. Bubble dynamics were observed using a high-speed camera. The results demonstrate that the bubble nucleation sites mainly occur in the hydrophobic region and this is attributed to a decrease in the energy barrier for nucleation. The bubble dynamic statistics revealed that the product of the diameter of the bubble and the bubble escape frequency are similar for composite surfaces and hydrophilic porous surfaces, which is consistent with Zuber’s conclusion. The synergistic effect of the hydrophilic-hydrophobic partitioned porous structure can promote nucleation in the hydrophobic region and retain capillary suction for liquid reflux in the hydrophilic region to enhance boiling heat transfer. This work enables the large-scale deployment of heat exchanger surface processing technology because of its low cost, availability, and reliability.

Aircraft icing is the formation and accumulation of ice on an aircraft’s windward surface. The impingement of super-cooled water droplets floating in clouds against a solid surface is the primary cause. Because it affects the aerodynamic form and poses a rising hazard to flight safety. This research gives a technique to overcome the ice accretion problemby preparation of Superhydrophobic coatings that can be utilized in aircraft. To create superhydrophobic surfaces, scientists have used many surface-modified functional coating methods based on perfluorinated polymer mixed with biomaterials. Herein, a plant leaf extract (Senna auriculata (Avaram in Tamil) which possesses good self-cleaning properties and better water-repellant properties like a lotus leaf, and exhibits several industrial applications such as anti-corrosive, anti-fogging, and anti-icing. The dried leaf extract is blend with Nafion polymer in ethanol and the as-prepared mixture coated on the polished surface of the aluminum alloy plate by using spray coating technique. The modified aluminum alloy (AA6061) plate surface was characterized with the help of a metallurgical microscope in different magnifications, scanning electron microscope and the measured contact angle (θ → 153°) is in good agreement with the superhydrophobicity requirements. High-speed optical microscopy helped to identify steady coalescence-induced droplet jumping during atmospheric water vapor condensation. This experimental result provides a new avenue for the environmentally benign fabrication of superhydrophobic metal-modified surfaces for various automotive applications.