@article { ISI:000260587200010, title = {Self-diffusion coefficient of ring polymers in semidilute solution}, journal = {Journal of Polymer Science Part B-Polymer Physics}, volume = {46}, number = {21}, year = {2008}, month = {NOV}, pages = {2370-2379}, publisher = {WILEY-BLACKWELL}, address = {COMMERCE PLACE, 350 MAIN ST, MALDEN 02148, MA USA}, abstract = {

In a topologically constraining environment the size of a flexible nonconcatenated ring polymer (macrocycles) and its dynamics are known to differ from that of linear polymers. Hence, the diffusion coefficient of ring polymers can be expected to be different from linear chains. We present here scaling arguments for the concentration and molecular weight dependence of self-diffusion coefficient of ring polymers in semidilute solutions, and show that contrary to expectations these scaling relations are identical to what is known for linear polymers. At higher concentrations excluded volume interactions arising from possibilities of segmental overlap can become effective for large ring polymers. In this regime the diffusion coefficient of large ring polymers shows a relatively weaker dependence on concentration and molecular weight. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2370-2379, 2008

}, keywords = {Diffusion, Macrocycles, Monte Carlo simulation}, issn = {0887-6266}, doi = {10.1002/polb.21569}, author = {Iyer, Balaj V. S. and Shanbhag, Sachin and Juvekar, Vinay A. and Lele, Ashish K.} } @article { ISI:000271103500021, title = {Self-similar dynamics of a flexible ring polymer in a fixed obstacle environment: a coarse-grained molecular model}, journal = {Industrial \& Engineering Chemistry Research}, volume = {48}, number = {21}, year = {2009}, month = {NOV}, pages = {9514-9522}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

In this contribution we concern ourselves with an interesting problem, namely, the dynamics of ideal flexible ring polymers constrained in tin array of fixed obstacles. The fundamental issue in this problem is to understand how a topologically constrained polymer chain is able to relax its conformation in the absence of chain ends. The key physics was provided in tin elegant scaling theory by Rubinstein and co-workers (Obukhov, S. P; Rubinstein, M.; Duke, T. Dynamics of a Ring Polymer in a Gel. Phys. Rev. Lett. 1994, 73, 1263-1267). In this work we develop a coarse-grained mean-field model based oil the physical arguments of the scaling theory and derive constitutive relations for rings in fixed obstacle and melt environments. The model is composed of three distinct steps. In the first step the dynamics of an arbitrary section of a ring chain is worked out based oil fractal Blob-Spring (BS) dynamics, and the center of mass diffusion and the relaxation spectrum of this section are determined. In the second step the center of mass diffusion obtained using the BS dynamics is used to model the one-dimensional diffusion of the section in a topologically constrained environment. In the final step we invoke the idea of dynamic self-similarity and argue that the dynamics described in the first and the second step, for any arbitrary section of the chain, applies to all sections of the chain. The constitutive relation is obtained consequently as the superposition of dynamic response of all sections of the ring chain.

}, issn = {0888-5885}, doi = {10.1021/ie900535v}, author = {Iyer, Balaji V. S. and Lele, Ashish K. and Juvekar, Vinay A. and Mashelkar, Raghunath Anant} } @article { ISI:000271103500038, title = {Solid suspension and liquid phase mixing in solid-liquid stirred tanks}, journal = {Industrial \& Engineering Chemistry Research}, volume = {48}, number = {21}, year = {2009}, month = {NOV}, pages = {9713-9722}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Stirred tanks are widely used in chemical process industries for catalytic reactions, dissolution of solids, crystallization, and so oil. In designing and optimizing such processes, suspension quality Of Slurry is an important parameter. Suspension quality depends upon complex interactions of impeller generated flow, turbulence, and solid loading. Most of the earlier work on solid suspension focuses Oil identifying critical impeller speed for just suspension of solids (N(js)). In this study, apart from N(js) aspects like cloud height and liquid phase mixing in solid-liquid suspensions were also studied A new way of characterizing solid-liquid suspensions and liquid phase mixing using nonintrusive wall pressure fluctuation measurements has been developed. Systematic experimental data on N(js), cloud height, power consumption, mixing time, and circulation time over a range of solid volume fraction and impeller speeds have been presented here. The results and discussion presented here will have useful implications for designing solid-liquid stirred tanks.

}, issn = {0888-5885}, doi = {10.1021/ie801858a}, author = {Sardeshpande, Madhavi V. and Sagi, Aparna R. and Juvekar, Vinay A. and Ranade, Vivek V.} } @article { ISI:000295223800016, title = {Solid suspension in stirred tanks: UVP measurements and CFD simulations}, journal = {Canadian Journal of Chemical Engineering}, volume = {89}, number = {5, SI}, year = {2011}, month = {OCT}, pages = {1112-1121}, publisher = {WILEY-BLACKWELL}, address = {COMMERCE PLACE, 350 MAIN ST, MALDEN 02148, MA USA}, abstract = {

Suspension of solids in stirred reactor is widely used for catalytic reactions, dissolution, etc. Quality of solid suspension is an important parameter required for the reliable design, optimum performance, and scale up of the system. Quality of suspension depends on local characteristics of solid velocity and hold up profiles. The present work was focused on investigating quality of solid suspension using ultrasound velocity profiler (UVP) measurements and CFD simulations. The slip velocity measurements carried out with UVP were used to evaluate different drag correlations used in CFD simulations. Results discussed in this work would be useful for extending the applications of CFD models for simulating large stirred slurry reactors.

}, keywords = {CFD, drag coefficient, solid suspension, solid-liquid velocities, UVP}, issn = {0008-4034}, doi = {10.1002/cjce.20548}, author = {Sardeshpande, Madhavi V. and Juvekar, Vinay A. and Ranade, Vivek V.} }