Turbulent mixing and chemical reaction in baffled stirred tank reactors : a comparison between experiments and a novel micromixing-based computational fluid dynamics model

The optimization of reaction processes to maximize the yield of a desired product while minimizing the formation of undesired by-products is one of the most important steps in process development for drug manufacturing or fine chemical production. In many situations the kinetics of product formation can be quite complex and involve a number of intermediate steps as well as parallel and serial reactions. This renders the systems sensitive to the operating conditions. Often, upon scale-up, a decrease in the yield of the desired product is experienced, while more undesired by-products are produced. A large number of interrelated variables influence the outcome of a process, and furthermore, most systems of process interest take place under turbulent conditions. Present methods for process design are inadequate because they involve the use of lumped parameters which fail to capture essential flow details and the rapid changes in the local concentration of reactants. In recent years Computational Fluid Dynamics (CFD) has been successfully used to model the fluid dynamics of complex vessels (such as agitated reactors) and to predict the velocity distribution in turbulent systems such as mixers and reactors. In this work a novel approach based on the use of CFD coupled with micromixing models was used to predict the behavior of a multiple, competitive reaction system in cylindrical stirred tank reactors fitted with a variety of agitators. In particular, the following fast parallel competing reactions scheme (Bourne and Yu 1994) was modeled, and the results compared with original experimental data: NaOH (A) + HCl (B)--k1--\u3e NaCl(P) + H2O NaOH(A) + CH2ClCO2C2H5(C)-- k2--\u3e CH2ClCO2Na(Q) + C2H50H(S) The reactor was operated in semi-batch mode, with the limiting reagent (A) being slowly added to the contents of the reactor in which the other reagents (B and Q were already dissolved. The final yield of the undesired product (S) was experimentally measured. The flow field in the reactor was simulated using the Reynolds Stress (RSM) turbulence model. The full impeller geometry was incorporated in the CFD simulation using the Multiple Reference Frames (MRF) model. The reaction zone was modeled in a Lagrangian way using a multi-phase Volume of Fluid (VOF) model (Hirt and Nichols 198 1). The interaction of turbulence and reaction was accounted for by means of the engulfment-based models for micro-mixing (Baldyga and Bourne 1989a; Baldyga and Bourne 1989b; Baldyga et aL 1997). The agreement between experimental velocity distribution data and the results of the simulations was generally good. The micro-mixing models, in conjunction with CFD, predicted a final yield in close agreement with the experimental data, demonstrating that the proposed approach can be successfully used to model turbulent reactive systems without the need for experimental input

Development of a regenerable calcium-based sorbent for hot gas cleanup

Experiments were conducted to develop a regenerable calcium-based sorbent for hot coal gas desulfurization. Spherical sorbent pellets were fabricated in a novel core-in-shell configuration. All pellets were prepared using a bench-scale pelletizer. In accordance with the core-in-shell concept, a reactive calcium compound (CaO) was surrounded by a strong shell consisting of a composite material. Limestone (CaCO3) and hemihydrate (CaSO4·0.5 H2O) were used as starting materials that were eventually decomposed to produce CaO. Different types of cements and aluminas were investigated as strength enhancing shell materials.;The sorbent pellets were characterized by measuring their compressive strength, surface area, pore volume and porosity. Sectioned pellets were also viewed with an electron microscope. A thermal gravimetric analyzer was used to determine the absorption rate, absorption capacity, optimum service temperature, concentration-initial rate relationship, and the regenerability of several sorbent formulations. Sulfidation runs were performed with 0.55--3.0% H2S in nitrogen at temperatures of 840--1000°C. Regeneration of the spent sorbent was conducted at 1050°C using a cyclic oxidation/reduction scheme.;For all core-in-shell pellets tested, it was found that thicker shells provided greater strength, but reduced the absorption capacity. While Portland cement shells provided enormous strength after curing, most of this strength was lost at high temperature. Of the cement formulations, those containing high calcium aluminate concentrations provided the greatest high temperature strength. However, all cement formulations required a minimum curing time to obtain adequate calcined strength. On the other hand, a sintered alumina-based shell produced pellets that met the strength requirements without the need for the extra curing step.;For most formulations, the initial reaction rate was directly proportional to the H2S concentration, and the optimum service temperature was found to be in the neighborhood of 920°C. Unlike the limestone-based formulations, the hemihydrate-based sorbents showed no loss in sorbent capacity when subjected to repeated sulfidation and regeneration cycles. The kinetics of sulfidation were represented well by a shrinking core reaction model that accounted for the effect of chemical reaction on the surface of the unreacted core

An Appraisal of Religion and Nigerian Public Policy

Nigerian public sees religiosity mostly as a “Nigercentric†affair which influences policy making and decision taking. This nigercentrism describes the public and political dominance of religion in Nigeria. In other words, the geography of religion influences the geography of politics in all national decisions, including elective and appointive offices even in the admission to public schools and institutions. In fact, Nigerian society since independence till date is strongly connected to religion. The consistency in the use of religion is attributable to the essentials and fundamentals of virtually all the successive regimes in the country in recognizing the pride of place it has always assumed in the policy and style of government. Thus, public policy describes the notion of decisions and actions of government in relation to issues and questions affecting the society. The affinity of religion and public policy in essence gives the indication that the two institutions are inter-changeably important, instrumental and enforceable through governmental processes which is universally applicable to society as a whole

Democratization and Corruption in Religious Environment: The Nigerian Experience

The late 20th century till date has greatly witnessed paradigm shift in democratization crusade around African continents where Nigeria belongs. This becomes significant and crucial in order to perpetually keep the military cabals in the barrack. Thus, stable democracy becomes the only solution to the perennial problems of corruption, insecurity, religious violence and political angst in Nigeria. This paper adopts historio-political and ethico-religious methods leading to the fact that religious and corrupt-free society can be the only hallmark of sustaining democratization process in Nigeria. As a matter of fact, this paper seeks to postulate that democracy should be allowed to grow and build domestic consensus, reassert and readdress corporate participation and as well assume new roles indispensable for keeping and extending the life span of democracy and to immune it against military regime since Nigerians are religious in all things. To this end, democratization as an institution is aimed at furthering political conscientization processes propelled by political regimes and continuously assume new roles in keeping with the exigencies of times and the political developments around them. This would make democratization the only game in town. Keywords: Corruption, Democratization, Democracy, Religious Society, Nigeri

Fosco Maraini (1912-2004) and Japan

【学術論文

Automatic Mosquito Control Device Using Infrared Motion Sensor

Malaria is a disease transmitted by female Anopheles mosquitoes to humans. Mosquitoes are a carrier of malaria. There are many types of vector control strategies, including physical, chemical, and biological methods. Individuals, local communities, and more organized public health vector management programs often need to work together to effectively identify and control mosquito farms. Efforts should be made to destroy mosquito eggs and reduce the density of larvae and adults. The World Health Organization recommends integrated vector management (IVM) as a strategy to improve vector control. IVM combines good practices that maximize an effective, safe, environmentally friendly, and cost-effective approach to disease vector control. Effective and well-tested vector control strategies include: Biological control: larvae and biolarvicidal fish, such as mosquitoes in ditches and ponds or other predators to control mosquito larvae. Chemical control: larvae and adults (indoor spray residues, insecticide-treated bed nets, etc.). Adult mosquitoes are small vulnerable insects with slender bodies, a pair of slender wings and three pairs of thin long legs. Mosquito control can be improved by using an automatic mosquito control device with an infrared motion sensor. Suppression of malaria vectors is an important means of preventing and reducing malaria transmission. To reduce malaria, mosquitoes in and around our environment must be controlled. The introduction of an infrared motion sensor in an automatic mosquito control device would eliminate the reduction in the number of mosquitoes in our environment. Add an infrared motion sensor to the automatic mosquito control device for easier mosquito control in our homes and environments. To customize automatic mosquito control by adding an infrared motion sensor. DOI: 10.7176/ISDE/12-3-01 Publication date:September 30th 202