A numerical simulation of droplet dynamics in shear layers.

A numerical simulation of droplet dynamics in shear layers

Activity of Catalyst for Liquid Phase Methanol Synthesis

The effects of reduction procedure, reaction temperature and composition of feed gas on the activity of a CuO-ZnO-Al2O3 catalyst for liquid phase methanol synthesis were studied. An optimized procedure different from conventional ones was developed to obtain higher activity and better stability of-the catalyst. Both CO and CO2 in the feed gas were found to be necessary to maintain the activity of catalyst in the synthesis process. Reaction temperature was limited up to 523K, otherwise the catalyst will be deactivated rapidly. Experimental results show that the catalyst deactivation is caused by sintering and fouling, and the effects of CO and CO2 on the catalyst activity are also investigated. The experimental results indicate that the formation of water in the methanol synthesis is negligible when the feed gas contains both CO and CO2. The mechanism for liquid-phase methanol synthesis was discussed and it differed slightly from that for gas-phase synthesis

Construction of 2‑Pyrone Skeleton via Domino Sequence between 2‑Acyl-1-Chlorocyclopropanecarboxylate and Amines

A base-promoted domino reaction of 2-acyl-1-chlorocyclopropaneformic esters with amines is described. In the presence of inorganic bases like Cs₂CO₃ or Mg­(OEt)₂, the reaction proceeded smoothly in acetonitrile to afford 2-pyrone derivatives in modest to excellent yields (up to 97%). This reaction provides a straightforward and transition metal-free protocol to efficiently construct 2-pyrone skeleton. A possible mechanistic process involving 1,2-elimination of hydrogen chloride, aza-Michael addition, ring-opening, and intramolecular lactonization was suggested to rationalize the formation of the target 2-pyrone derivatives

Chem. Eng. Sci.

The cell model approach was extended to the catalytic reaction over a spherical catalyst pellet and the effects of several parameters on the effectiveness factor were investigated via numerical simulation. The proposed mathematical model consisted of the partial differential equations for gas reactant flow in the external gas phase around a catalyst sphere, mass transport in the gas phase, and two-dimensional diffusion-reaction in the catalytic sphere. Numerical simulation in the orthogonal boundary fitted reference frame demonstrated the decrease in effectiveness factor of a catalyst sphere due to the external mass transfer resistance and inter-particle hydrodynamic interaction. It was observed that the voidage of the particle assemblage shows more recognized influence than the Peclet and Reynolds numbers of particles and the azimuthal diffusion of reactant inside the particle was negligible. On this basis, a simplified set of cell model equations for catalytic reaction in particle assemblages were proposed. An example of optimizing search indicated the present model may be used to detect the most strong influence on catalytic reaction in particle assemblage over the practical ranges of operating and designing parameters to avoid excessive loss in the effectiveness factor. (c) 2007 Elsevier Ltd. All rights reserved.The cell model approach was extended to the catalytic reaction over a spherical catalyst pellet and the effects of several parameters on the effectiveness factor were investigated via numerical simulation. The proposed mathematical model consisted of the partial differential equations for gas reactant flow in the external gas phase around a catalyst sphere, mass transport in the gas phase, and two-dimensional diffusion-reaction in the catalytic sphere. Numerical simulation in the orthogonal boundary fitted reference frame demonstrated the decrease in effectiveness factor of a catalyst sphere due to the external mass transfer resistance and inter-particle hydrodynamic interaction. It was observed that the voidage of the particle assemblage shows more recognized influence than the Peclet and Reynolds numbers of particles and the azimuthal diffusion of reactant inside the particle was negligible. On this basis, a simplified set of cell model equations for catalytic reaction in particle assemblages were proposed. An example of optimizing search indicated the present model may be used to detect the most strong influence on catalytic reaction in particle assemblage over the practical ranges of operating and designing parameters to avoid excessive loss in the effectiveness factor. (c) 2007 Elsevier Ltd. All rights reserved

Kinematics and workspace analysis of a novel 3-DOF parallel manipulator with virtual symmetric plane

This article presents a novel 3-DOF parallel manipulator extracted from an origami fold in the context of mechanisms. The parallel manipulator consists of a base, a platform and four chain-legs that connect the platform to base through revolute joints. Each chain-leg contains a closed-loop sub-chain, which is spherical 6R linkage with symmetrical angle lengths. The geometry of the parallel manipulator is revealed according to the configuration design and specifics of the origami fold. This leads to unravelling of the symmetric plane which is determined by the common points of spherical 6R linkages in the four chain-legs. Based on geometric approach, the solutions for both inverse and forward kinematics are derived and the reachable workspace is then analyzed. </jats:p