Volume 20, Issue 2

In this paper, the transient MRF approach coupled with the standard k - ε and SST k - ω turbulence models was employed to study the effect of bottom shape, impeller diameter ( D J ) and bottom height ( H 2 ) on critical impeller off-bottom clearance ( C ). It was found the bottom shape and bottom height ( H 2 ) have obvious influence on the flow pattern transition from double-loop to single-loop of RT impeller. The flow pattern transition mechanism was inferred to relate to the relationship between the space required by the lower circulation zone and the actual space. The boundary conditions of critical C were further concluded to help distinguish the flow pattern and receive the expected one in the stirred vessel design.

By CFD-DEM simulations, the present work is aimed to investigate the transient gas-solid bubbling mechanisms along a whole bubble lifecycle in a 2D fluidized bed from a micro perspective. Systemic comparisons with CCD measurements confirm the validity of current simulations. Afterward, the manner of particle motion and its driving mechanisms at various stages are investigated. In order to do that, external forces are analyzed at an individual particle level, including the drag, pressure gradient force, and their resultant acceleration together with gravity. Many interesting findings have been achieved. For example, a switch in directions of drag and pressure gradient forces at the root of an initial bubble enables its detachment. And, regarding their contributions to the burst of a bubble, the drag force is several times of the pressure gradient forces. Present efforts help to offer a novel view of particle dynamics during the bubbling fluidization.

An effective procedure of response surface methodology (RSM) has been successfully developed for a coiled agitated vessel by finding the optimal values of working parameters to achieve the high heat transfer performance. Studies have been performed for two types of agitators, propeller and disk turbine respectively. TiO 2 /water nanofluid has been used as agitated medium. Various operating parameters, such as impeller speed (100–700 rpm for propeller and 100–300 rpm for disk turbine), TiO 2 /water nanofluid concentration (0–0.3 vol%), heat input (400–2200 W) to the agitated medium were explored by experiment. Experiments were performed at desired set of working conditions suggested by a standard RSM design called a Box-Behnken Design. Nusselt number was considered as performance parameter. The results identify the significant influence factors to achieve high coefficient of heat transfer. A set of 690 rpm, 0.28 vol%, 1480 W for propeller and 220 rpm, 0.15 vol%, 1330 W for disk turbine have been suggested by the model for achieving improved heat transfer performances. The obtained optimal working parameters have been predicted and verified by conducting validation experiments. A good agreement of discrepancy ±4% have been obtained between experimental and predicted values.

Photocatalysis is an extraordinary and vastly researched topic; there is a need to find new ways to support producing composite materials that are cost-effective, efficient and have a low environmental impact. The investigation was undertaken on syn TiO 2 by depositing it on silica. The results elucidate the positive effect on photocatalysis activity and the macroscopic structure on which the TiO 2 is formed. For the analysis of photocatalyst, various characterisation measurements were undertaken, such as XRD, FTIR, DRS, FESEM, TEM, RS, and BET. The accumulated TiO 2 onto the surface of SiO 2 stabilised its transformation of the phase from anatase to rutile, resulting in decreased particle size and enhancing its photocatalytic activity under UV irradiation. The concentration of OH• radicals was determined using terephthalic acid as a probe molecule to determine its role in the photocatalytic degradation of antihistamine. The results of BET analysis showed that the syn TiO 2 -SiO 2 sample has a large specific surface area of 192.6 m 2  g −1 . Maximum degradation of cetirizine (about 97%) was achieved with 80% TiO 2 -20% SiO 2 (TS-4). Recyclability test confirmed that 80% TiO 2 -20% SiO 2 sample was stable up to six cycles.

Effect of the length of cylindrical particle on repose angle and porosity of a pile was numerically studied using discrete element method. The variation of repose angle and porosity with coefficient of sliding and rolling friction were also discussed. The results shown that compared with sphere particle, the bottom size of cylindrical pile is smaller, while the height of cylinder pile is larger and the heap is steeper. With the increase of the length of cylinder, the contour line of the pile becomes steep, and the angle of repose increases. The repose angle shows a positive correlation with coefficient of sliding and rolling friction. The porosity increases with the increase of the length of cylinders. The trends of porosity are basically consist with that of repose angle, and with increase of friction coefficient, the average porosity increases.

Based on two cases of the double impellers on different shafts in the co-rotating and counter-rotating, the distribution of the velocity, streamline, turbulent kinetic energy, and turbulent energy dissipation rate are obtained through three-dimensional unsteady numerical simulation. Very good agreements between experimental and numerical results have been obtained. The hydrometallurgy purification experimental platform was built with the size of one third of the simulated. The results show that the mechanical string mixing system with double impellers on different shafts can form a more obvious convection effect in the central area of the double impellers, which can effectively break the mixing isolation region and improve the mixing effect. In the co-rotating case, the two impellers can generate strong convection in the central area and form an interactive vortex and a high-speed flow channel between the two impellers. while the convection formed by counter-rotating case is weaker and the vortex structures are independent of each other. The counter-rotating system performs better in the macro momentum transfer and the co-rotating system performs better in the micro-mixing level. In the experiments of hydrometallurgy purification, 7.93% more energy is used in the co-rotating system than that of the counter-rotating system. The average energy consumed by co-rotating in the process of purifying every one percent of Cd 2+ ions are 8.65% lower than that of counter-rotating. The co-rotating system can improve microscopic mass transfer effect and finally save energy and time compared to the counter-rotating system.

As an industry with high energy consumption and high emission, the iron and steel industry not only drives the economic development, but also brings serious environmental pollution problems. In order to achieve green and low-carbon steel manufacturing, reducing CO 2 emissions in the blast furnace ironmaking process has become the current mainstream, of which the accurate judgment of the blast furnace status is a key to achieve it. Firstly, combining theory with production experience, this research established 6 evaluation systems of the blast furnace and extracted 22 evaluation parameters from them through mathematical statistics. After completing the data preprocessing with the help of Python, the potential elements in the initial variables were excavated and a comprehensive evaluation model of the blast furnace status was developed by Factor Analysis. Based on this, the status of the blast furnace were divided into four degrees, i.e. good, normal, poor and warning and the rationality was verified by comparison to the production logs. By means of comparing the law of data distribution under different furnace status, the optimal range of operation parameters was summarized. This study is expected to provide guidance for realizing energy conservation and consumption reduction of the blast furnace.

The present work emphasizes the development of a generic methodology that addresses the core issue of any running chemical plant, i.e., how to maintain a delicate balance between profit and environmental impact. Here, an ethylene oxide (EO) production plant has been taken as a case study. The production of EO takes place in a multiphase catalytic reactor, the reliable first principle-based model of which is still not available in the literature. Artificial neural network (ANN) was therefore applied to develop a data-driven model of the complex reactor with the help of actual industrial data. The model successfully built up a correlation between the catalyst selectivity and temperature with other operational parameters. A hybrid multi-objective metaheuristic optimization technique, namely ANN-multi-objective genetic algorithm (MOGA) algorithm was used to develop a Pareto diagram of selectivity versus reactor temperature. The Pareto diagram will help the plant engineers to make a strategy on what operating conditions to be maintained to make a delicate balance between profit and environmental impact. It was also found that by applying this hybrid ANN-MOGA modeling and optimization technique, for a 720 KTA ethylene glycol plant, approximately 32,345 ton/year of carbon-di-oxide emission into the atmosphere can be reduced. Along with the reduction of environmental impact, this hybrid approach enables the plant to reduce raw material cost of nine million USD per annum simultaneously.

Pd/CeO 2 catalysts with different metallic Pd loading were synthesized by impregnation method. The physicochemical properties of prepared Pd/CeO 2 catalysts and corresponding precursors were studied by XRD, XPS, H 2 -TPD and H 2 -TPR. Moreover, the catalytic performance of the Pd/CeO 2 catalysts was investigated via gas phase benzene hydrogenation reaction at the temperature of 100–200 °C under atmosphere pressure. Results show that the catalytic performance of prepared Pd/CeO 2 catalysts is directly related to the metallic Pd content. The amounts of active metallic Pd and adsorbed-desorbed hydrogen species on Pd/CeO 2 catalysts increase with the increasing metallic Pd loading from 1.0 to 3.0%, while the numbers of them are slightly reduced on Pd/CeO 2 (3.5) catalyst. Furthermore, metallic Pd is highly dispersed on the nano-CeO 2 supports, therefore, the prepared Pd/CeO 2 catalysts present good gas phase benzene catalytic hydrogenation performance. At 200 °C, the benzene conversion over the Pd/CeO 2 catalysts with different metallic Pd loading follows the rule: Pd/CeO 2 (3.0) > Pd/CeO 2 (3.5) > Pd/CeO 2 (2.5) > Pd/CeO 2 (2.0) > Pd/CeO 2 (1.5) > Pd/CeO 2 (1.0), corresponding values are 94.3, 96.4, 89.9, 82.8, 72.7, 42.6 and 94.3%. And the cyclohexane selectivity is 100% on all prepared Pd/CeO 2 catalysts.

Microchannel parallel flow gas cooler is commonly used in transcritical carbon dioxide automotive air conditioning system. To investigate the influence of the flat tube protrusion depth on fluid distribution, a numerical calculation model of microchannel parallel flow gas cooler with D-shaped header is established. With the object of even flow distribution, a novel stepped protrusion depth header is proposed. The effects of new header on the flow distribution of gas cooler were studied by numerical simulation. The results show that the flow distribution performance of gas cooler can be improved by changing the flat tube protrusion depth. Changing the protrusion depth of three groups of flat tubes simultaneously can achieve a better flow distribution performance of gas cooler than changing the protrusion depth of only one or two groups of flat tubes. When compared with the protrusion depth of all flat tubes is 0, the novel stepped protrusion depth header reduces the total flow distribution nonuniformity of gas cooler by 34–51%. The research in this paper provides a method for improving the flow distribution performance of gas coolers.