Plastic Deformation and the Fracture Surface Energy of Sodium Chloride

A correlation between plastic deformation at crack tips in sodium chloride and the measured value of the fracture surface energy is presented. Plastic deformation can either aid or hinder crack growth, depending on the mode of deformation at the crack tip. If plane-stress deformation occurs, crack motion is hindered by step formation, dislocation generation, and plastic blunting of the crack tip. If plane-strain deformation occurs, crack motion is aided by stress fields that arise from the deformation. The specific surface free energy of sodium chloride, {100} plane, is estimated to be less than 0.37 J/m².     

URBAN POLICY,PRESS, AND PLACE: CITY‐MAKING IN FLORIDA'S MIAMI‐DADE COUNTY

This article enhances the notion of city‐making by explicating its communicative processes and functions within the press. Through a quantitative content analysis and qualitative textual analysis of Miami Herald news coverage related to incorporation and annexation policies and practices over a period of 3 years, we argue for a stronger implication of the press in coverage of local policy‐ and place‐making. Through a quantitative content analysis of 437 articles from the Miami Herald about communities affected by incorporation and annexation and a qualitative textual analysis of 51 articles related to general coverage of geographic policy‐making in Miami‐Dade County over a 3‐year period, we argue that this coverage reveals the press as being a central feature and function of policy‐making through the lens of city‐making.     

Synthesis of ZSM‐5 by hydrothermal method with pre‐mixing in a stirred‐tank reactor

This work proposed a synthesis route of ZSM‐5 via the hydrothermal method with premixing in a stirred tank reactor (STR). Effects of various operating conditions, including pre‐mixing time, molar ratio of SiO₂/Al₂O₃, TPAOH (organic template agents) concentration, NaCl (alkali metal cations) concentration, crystallization temperature, and crystallization reaction time, on the average particle size (PS) and particle size distribution (PSD) were investigated. It was found that the pre‐mixing time in the STR significantly affect the formation of proto‐nuclei in premixing process and crystal growth in hydrothermal reaction process, and consequently influence the PS and PSD of the prepared ZSM‐5. ZSM‐5 with good thermal stability, a PS of 380 nm, PSD of 0.17–0.9 µm, pore diameter of 2.31 nm, pore volume of 0.19 cm³ · g^?1 and specific surface area of 337.25 m² · g^?1 were obtained under the optimal conditions of a crystallization reaction time of 24 h, a crystallization temperature of 130 °C, a molar ratio of SiO₂/Al₂O₃ of 200, a TPAOH concentration of 3.5 mol · L^?1, NaCl concentration of 0.3 mol · L^?1, and a pre‐mixing time of 5 h. This work indicated that the operating conditions including premixing time have a significant effect on its PS and PSD.     

旋转泡沫填料反应器的研究进展

旋转泡沫填料反应器是一种新型多相搅拌釜式反应器,其将传统的搅拌桨替换成圆环型泡沫填料,可有效强化反应器内多相间传质混合过程,且多孔填料可作为催化剂载体,能减小多相催化反应中固体催化剂的使用量,具有替换传统多相搅拌釜式反应器和浆态反应器的潜力,将有较好的应用前景。本文详细阐述了旋转泡沫填料反应器的结构和反应器内多相流动形式,着重介绍了反应器内多相流动特性的研究进展及反应器内传质性能的研究现状,并与传统的多相反应器传质性能进行比较;从应用方面分析了反应器用于葡萄糖催化氧化、苯乙烯催化加氢等多相过程的强化方式及优势,通过对比得出旋转泡沫填料反应器能有效降低化工过程中物耗、提高物料的利用率;介绍了与旋转泡沫填料反应器类似的其他多孔式搅拌桨反应器的研究进展,分析了这类反应器的优势,并对其性能进行对比;最后,对旋转泡沫填料反应器研究的不足及未来的发展进行了阐述和展望。     

CO2 absorption into K2CO3/KHCO3 solution enhanced by organic phase in a rotor–stator reactor

ABSTRACT

This work studied the gas–liquid–liquid (G–L–L) reaction system of CO₂ absorption into K₂CO₃/KHCO₃ buffer solution enhanced by organic phase in a rotor–stator reactor (RSR). The effects of volume fraction of organic phase, type of organic phase, rotational speed of RSR, gas and liquid volumetric flow rate, and temperature on CO₂ absorption percentage were investigated. Results indicate that the addition of the organic phase with a volume fraction of 1.3–1.6% had significant promoting effect on CO₂ absorption. CO₂ absorption percentage increased with increase in the rotational speed of the RSR but decreased with rise in liquid temperature and gas–liquid ratio. This work demonstrates that RSR can significantly enhance liquid–liquid mixing and gas–liquid mass transfer processes in the G–L–L system.     

Mass Transfer Characteristics in a Rotor‐Stator Reactor

Mass transfer characteristics in a rotor‐stator reactor in terms of the overall volumetric mass‐transfer coefficient (K_xa) using the N₂‐H₂O‐O₂ system were investigated. The effects of various operating parameters including rotation speed, liquid volumetric flow rate, and gas volumetric flow rate on K_xa were systematically examined, and a gas‐liquid mass transfer model was established to predict K_xa. Results reveal that K_xa increased with higher rotation speed, liquid volumetric flow rate, and gas volumetric flow rate. The results also confirm that the predicted values of K_xa were in agreement with the experimental values with deviation within 15 %. The results contribute to a better understanding of mass transfer characteristics in rotor‐stator reactors.     

Regulating the micromixing efficiency of a novel helical tube reactor by premixing behavior optimization

In this work, a novel helical tube reactor (HTR) was constructed, including a pre‐mixer for adjusting the premixing behavior of reactants and a helical tube as a further mixing unit. The pre‐mixer was modified to optimize the premixing behavior by using two methods, named as tangential‐feeding and insertion of a helical baffle. The premixing behaviors were investigated via computational fluid dynamics (CFD) simulation. Simulation results indicated that both methods can change the fluid flow, enhance the turbulence kinetic energy, and improve the premixing performance in the pre‐mixers. Based on the results of CFD simulation, it could be predicted that the micromixing efficiency of the HTR can be regulated by these methods accordingly. Then the predicated results were confirmed experimentally by a parallel competing reaction. Furthermore, the relationship between the premixing performance increasing and the corresponding micromixing efficiency increasing of the HTR was quantitatively analyzed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2876–2887, 2017     

A review on computational fluid dynamic simulation for rotating packed beds

A rotating packed bed (RPB) is one of the cutting-edge process intensification technologies due to its high mass transfer and mixing efficiency. Nevertheless, owing to the complex structure and hydrodynamic characteristics of RPBs, valuable data inside the reactor is hard to obtain by conventional experimental methods. Computational fluid dynamics (CFD) owing to its unique advantages of low cost, completeness of data and ability to simulate real and ideal conditions, has been adopted by many researchers to carry out fundamental research and practical application of RPBs in recent years. This paper therefore elaborates on the research progress on CFD simulation of RPBs. The building of a physical model of these reactors as well as selection of mathematical models are described, then applicability and accuracy of these models are compared and discussed. Simulation results for gas and multiphase flow in reactors are also presented. Additionally, the application of CFD to mixing and mass transfer between phases and processes in rotating packed beds is introduced. Optimum designs of reactors by the CFD method are also described. Finally, problems remaining with CFD simulation of rotating packed beds and future development directions are discussed. © 2018 Society of Chemical Industry