Gas–liquid flow in stirred reactors: Trailing vortices and gas accumulation behind impeller blades

In a gas–liquid stirred reactor, gas tends to accumulate in low-pressure regions behind the impeller blades. Such gas accumulation significantly alters impeller performance characteristics. We have computationally investigated gas–liquid flow generated by a Rushton (disc) turbine. Rotating Rushton turbine generates trailing vortices behind the blades, which influence the gas accumulation in the impeller region. Characteristics of these trailing vortices were first investigated by considering a model problem of flow over a single impeller blade. Predicted results were compared with the published experimental data. Circulation velocity and turbulent kinetic energy of the trailing vortices were found to scale with blade tip velocity. Several numerical experiments were carried out to understand interaction of gas bubbles and trailing vortices. Gas–liquid flow in stirred vessel was then simulated by extending the computational snapshot approach of Ranade and Dometti (Chem. Engng Res. Des., 74, 476–484, 1996). The approach was able to capture the main features of gas–liquid flow in stirred vessels. The detailed analysis of predicted results with reference to experimental data and the results obtained for flow over a single impeller blade will be useful for extending the scope of computational fluid dynamics (CFD) based tools for engineering gas–liquid stirred reactors

Isolation, Identification and Screening of the Yeast Flora from Indian Cashew Apple for Sugar and Ethanol Tolerance

Cashew apple juice is rich in fermentable sugars, minerals and vitamins, which makes it a suitable substrate for production of alcoholic beverages. In the present research work, indigenous flora of cashew apple (Indian variety) was studied. Seven morphologically different strains of Candida spp. were identified and checked for their sugar and ethanol tolerance. All seven isolates were able to tolerate sugar concentrations up to 25% but varied in their ethanol tolerance. Based on the above results it can be concluded that a high sugar and ethanol tolerant Candida spp. could be used as starter culture for commercial production of alcoholic beverages from cashew apple

Flow generated by radial flow impellers: PIV measurements and CFD simulations

Particle image velocimetry (PIV) and computational fluid dynamics (CFD) have been used to investigate the single phase and gas-liquid flow generated by a Scaba SRGT turbine. The key details of the trailing vortices, the turbulent flow around the impeller blades and the accumulation of gas have been studied by using PIV measurements and CFD simulations. Both the experimental and numerical results show that the flow and the trailing vortices are not altered significantly upon gassing. The simulated results are generally in good agreement with the experimental findings. The CFD simulations also show that only small low-pressure regions exist behind the blades of the Scaba turbine compared with the very large lowpressure zones formed by the Rushton turbine. These results enable better understanding of the improved performance of the Scaba turbine for gas-liquid dispersions compared with the Rushton turbine

Model and control for cooperative energy management

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 79-80).Proto/Amorphous Cooperative Energy Management (PACEM) aims to build and deploy a highly scalable system for smart power grids that will enable efficient demand shaping for small-user networks. Two key problems are to provide distributed control algorithm for efficient demand shaping and to provide an incentive structure to encourage both users and the electric power sector to opt-in to PACEM. In this thesis, I address the first problem by designing ColoredPower, a probabilistic control algorithm. I implemented and tested ColoredPower in MIT Proto, building on previous work in spatial computing. Simulations in Proto show that ColoredPower operates within 3% error and provides a stable dynamic response time on the order of minutes. To address the second problem, I provide a model for user and power company incentives in PACEM, in the form of the Colored Procurement Mechanism, which enables further work in optimal algorithmic mechanism design.by Vinayak V. Ranade.M.Eng

Genome analysis of amaranths: determination of inter- and intra-species variations

Amaranths are an important group of plants and include grain, vegetable and ornamental types. Despite the economic importance of the amaranths, there is very little information available about the extent and nature of genetic diversity present in the genus Amaranthus at molecular level. We now report the randomly amplified polymorphic DNA (RAPD) profiles of different species of Amaranthus as well as different accessions of the species. These RAPD analyses have been carried out using 65 arbitrary sequence decamer primers. From the RAPD data, an UPGMA dendrogram illustrating the inter-as well as intra-species relationships has been computed. The putative hybrid origin of A.dubious from A. hybridus and A. spinosus is also ruled out by the RAPD data. The trends of species relationships amongst the amaranths determined by RAPDs is consistent with their cytogenetic and evolutionary relationships that have already been determined

Synthesis and interaction of thiazolo [2, 3-a] isoquinoline analog with DNA

569-573A reaction between 1-(furan-2-yl)-3,4-dihydroisoquinoline and thioglycolic acid using N,N-Dicyclohexylcarbodiimide at 0−5 °C has given 10b-(furan-2-yl)-5,6-dihydro-2H-thiazolo[2,3-a]isoquinolin-3(10bH)-one [FUIQTGA]. The interaction between FUIQTGA and DNA has been studied using UV-visible spectroscopy, fluorescence and circular dichroism techniques. Static quenching mechanism is observed from fluorescence measurements of interaction between FUIQTGA and DNA. Circular dichroism reveals the minor groove binding mode between FUIQTGA and DNA