Uday Agarwal - Academia.edu (original) (raw)
Papers by Uday Agarwal
The Journal of Supercritical Fluids, 2003
We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and... more We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and (carbon dioxide–diphenyl carbonate (DPC)). The bubble points are measured using a Cailletet apparatus in the temperature range 70–180°C and pressures up to 130 bar. The experimental data are adequately represented by the Peng–Robinson equation of state (PR EOS) with quadratic mixing rules. The two binary interaction parameters kij and lij are obtained by fitting, and were found to have a linear dependency with temperature. The data available from literature for the CO2–phenol system could also be predicted very well by the same model and parameter values.
Journal of Non-Newtonian Fluid Mechanics, 1994
ABSTRACT
The Journal of Chemical Physics, 1993
Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly pl... more Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly placed circular reactive sites are considered. The diffusing species adsorbs onto the surface following Langmuir–Hinshelwood kinetics and reacts instantaneously on contact with a reactive site. Approximate theories are formulated to describe the process for high concentrations of the reactive sites, when competition between the sites is significant, following three different approaches: (i) modification of the single sink theory; (ii) using a cell model; and (iii) using an effective medium theory. The predictions of the theories are compared with the results of multiparticle Brownian dynamics simulations for the overall reaction rate, the bulk concentration of the reactive species, and the ensemble averaged concentration profile around a reactive site. The effective medium theory is found to give the best results among the theories considered, and the predictions are in good agreement with...
The Journal of Chemical Physics, 1994
Enhanced shear stability of associating polymers during drag reduction observed recently has been... more Enhanced shear stability of associating polymers during drag reduction observed recently has been attributed to the breakage of reversible associations (e.g., hydrogen bonds) in preference to covalent bonds in the polymer backbone. A simple mechanistic analysis of a perfectly ‘‘zipped’’ assembly of fully extended bead rod chain model of two macromolecules in steady elongational flow is presented. It explains the enhanced stability as a result of (i) distribution (near the vulnerable chain center) of the drag tension into the two parallel ‘‘zipped’’ chains, and (ii) reduction of the drag force due to the enhanced hydrodynamic shielding. Some guidelines for optimum design of shear stable and effective drag reducing macromolecules have been deduced.
The Journal of Chemical Physics, 1998
We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solutio... more We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solution. Into a simple elongational flow field, we introduce freely jointed bead-rod chain model molecules in their coiled and stretched states, and follow the conformational changes. We find good agreement of our simulation results with the available theoretical predictions for low and high strain rates (ε̇). At the intermediate elongation rates (near the onset of coil–stretch transition) of the flow field, we find that the residence time required for stretching of an initially coiled chain can be extremely large as compared to predicted (1+ln(√N))ε̇−1, especially for the non-free-draining case. Hence, the chain conformation is dependent on the initial state of the chain molecule for residence time as long as 100ε̇−1. Thus, hysteresis is predicted when chain residence time in such an elongational flow field is limited, as in practical situations. Further, at such intermediate ε̇, the chain mo...
The Journal of Chemical Physics, 1992
A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike mo... more A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike molecules in dilute solutions is presented, incorporating both translational and rotational diffusion of the molecules. Simplified criteria for reaction are proposed according to which molecules must approach within a specified reaction radius, and have a relative orientation angle in a specified range to react. The translational diffusion of the molecules is assumed to be isotropic. The results of the exact analytical solution, finite element computations, as well as approximate solutions for low rotational diffusivity, are presented. The match between the solutions is satisfactory in the appropriate limits, although the exact solution is found to be computationally intensive for low rotational diffusivities and rapid intrinsic kinetics. The reaction rate is found to decrease to a limiting value with decreasing rotational diffusivity, and the magnitude of the decrease in rate increases wi...
Journal of Applied Polymer Science, 2006
... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006... more ... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006), Extraction of CdS pigment from waste polyethylene. Journal of Applied Polymer Science, 100: 10241031. ... Copyright © 1999-2010 John Wiley & Sons, Inc. All Rights Reserved.
Journal of Applied Polymer Science, 2007
Chemical Engineering Science, 1994
... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecule... more ... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecules during ... shearing flow stretches the spnngs, caus ing a component F of the stretching tension F0 to ... migration in such flows, the polymer molecular weight must be higher than 106. ...
Chemical Engineering Science, 2001
As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposit... more As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposited on the catalyst fragment. This presents diffusional resistance to further monomer transport to the catalyst fragment. In the recent past, we considered that this deposited polymer brings in additional viscous deformational resistance to the otherwise Fickian diffusion, thereby limiting the polymerization rate. In the present work we account for the rheological behavior of polymers being not just viscous, but viscoelastic. We find that the elastic deformation may largely facilitate the overall polymer deformation in situations where monomer transport would have been predicted to suffer severe limitations if only viscous deformation were considered.
The Journal of Chemical Physics, 1993
Multimolecule Brownian dynamics simulation results for diffusion controlled polymerization of bea... more Multimolecule Brownian dynamics simulation results for diffusion controlled polymerization of bead–rod chain molecules in 2D solution are presented. Reaction between any two molecules undergoing Brownian diffusion takes place if the reactive chain ends approach each other to within a certain reaction radius, and if the chain end carrying segments are collinear within certain specified limits. The second order reaction rate constant is found to decrease with time as the molecular lengths increase and the diffusivities decrease. Application of a shear flow is seen to result in alignment of the molecules along the flow direction, thereby enhancing the concentration of molecular pairs with parallel orientation of reactive-end carrying chain segments, and hence the overall reaction rate. This effect is found to be more pronounced in the case of long rigid molecules as compared to flexible molecules because of the slow rotation and high level of orientation under flow of the former. Even ...
The present disclosure relates to a tablet comprising at least one property modifying agent adapt... more The present disclosure relates to a tablet comprising at least one property modifying agent adapted to modify at least one property of a melt processable polymer and at least one processing aid having softening temperature lower than or equal to the melt processing temperature of the melt processable polymer.
The Journal of Supercritical Fluids, 2003
We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and... more We report the vapor–liquid equilibria (VLE) of the two binary systems (carbon dioxide–phenol) and (carbon dioxide–diphenyl carbonate (DPC)). The bubble points are measured using a Cailletet apparatus in the temperature range 70–180°C and pressures up to 130 bar. The experimental data are adequately represented by the Peng–Robinson equation of state (PR EOS) with quadratic mixing rules. The two binary interaction parameters kij and lij are obtained by fitting, and were found to have a linear dependency with temperature. The data available from literature for the CO2–phenol system could also be predicted very well by the same model and parameter values.
Journal of Non-Newtonian Fluid Mechanics, 1994
ABSTRACT
The Journal of Chemical Physics, 1993
Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly pl... more Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly placed circular reactive sites are considered. The diffusing species adsorbs onto the surface following Langmuir–Hinshelwood kinetics and reacts instantaneously on contact with a reactive site. Approximate theories are formulated to describe the process for high concentrations of the reactive sites, when competition between the sites is significant, following three different approaches: (i) modification of the single sink theory; (ii) using a cell model; and (iii) using an effective medium theory. The predictions of the theories are compared with the results of multiparticle Brownian dynamics simulations for the overall reaction rate, the bulk concentration of the reactive species, and the ensemble averaged concentration profile around a reactive site. The effective medium theory is found to give the best results among the theories considered, and the predictions are in good agreement with...
The Journal of Chemical Physics, 1994
Enhanced shear stability of associating polymers during drag reduction observed recently has been... more Enhanced shear stability of associating polymers during drag reduction observed recently has been attributed to the breakage of reversible associations (e.g., hydrogen bonds) in preference to covalent bonds in the polymer backbone. A simple mechanistic analysis of a perfectly ‘‘zipped’’ assembly of fully extended bead rod chain model of two macromolecules in steady elongational flow is presented. It explains the enhanced stability as a result of (i) distribution (near the vulnerable chain center) of the drag tension into the two parallel ‘‘zipped’’ chains, and (ii) reduction of the drag force due to the enhanced hydrodynamic shielding. Some guidelines for optimum design of shear stable and effective drag reducing macromolecules have been deduced.
The Journal of Chemical Physics, 1998
We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solutio... more We use Brownian dynamics simulation to study coil–stretch transition of macromolecules in solution. Into a simple elongational flow field, we introduce freely jointed bead-rod chain model molecules in their coiled and stretched states, and follow the conformational changes. We find good agreement of our simulation results with the available theoretical predictions for low and high strain rates (ε̇). At the intermediate elongation rates (near the onset of coil–stretch transition) of the flow field, we find that the residence time required for stretching of an initially coiled chain can be extremely large as compared to predicted (1+ln(√N))ε̇−1, especially for the non-free-draining case. Hence, the chain conformation is dependent on the initial state of the chain molecule for residence time as long as 100ε̇−1. Thus, hysteresis is predicted when chain residence time in such an elongational flow field is limited, as in practical situations. Further, at such intermediate ε̇, the chain mo...
The Journal of Chemical Physics, 1992
A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike mo... more A theoretical investigation of rates of diffusion-limited polymerization between rigid rodlike molecules in dilute solutions is presented, incorporating both translational and rotational diffusion of the molecules. Simplified criteria for reaction are proposed according to which molecules must approach within a specified reaction radius, and have a relative orientation angle in a specified range to react. The translational diffusion of the molecules is assumed to be isotropic. The results of the exact analytical solution, finite element computations, as well as approximate solutions for low rotational diffusivity, are presented. The match between the solutions is satisfactory in the appropriate limits, although the exact solution is found to be computationally intensive for low rotational diffusivities and rapid intrinsic kinetics. The reaction rate is found to decrease to a limiting value with decreasing rotational diffusivity, and the magnitude of the decrease in rate increases wi...
Journal of Applied Polymer Science, 2006
... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006... more ... How to Cite. Wanrooij, PHP, Agarwal, US, Meuldijk, J., Kasteren, JMN v. and Lemstra, PJ (2006), Extraction of CdS pigment from waste polyethylene. Journal of Applied Polymer Science, 100: 10241031. ... Copyright © 1999-2010 John Wiley & Sons, Inc. All Rights Reserved.
Journal of Applied Polymer Science, 2007
Chemical Engineering Science, 1994
... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecule... more ... Dill (1979) and Dill and Zimm (1979), who observed radially inwards migration of DNA molecules during ... shearing flow stretches the spnngs, caus ing a component F of the stretching tension F0 to ... migration in such flows, the polymer molecular weight must be higher than 106. ...
Chemical Engineering Science, 2001
As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposit... more As olefin polymerization proceeds on a heterogeneous catalyst, the polymer so formed gets deposited on the catalyst fragment. This presents diffusional resistance to further monomer transport to the catalyst fragment. In the recent past, we considered that this deposited polymer brings in additional viscous deformational resistance to the otherwise Fickian diffusion, thereby limiting the polymerization rate. In the present work we account for the rheological behavior of polymers being not just viscous, but viscoelastic. We find that the elastic deformation may largely facilitate the overall polymer deformation in situations where monomer transport would have been predicted to suffer severe limitations if only viscous deformation were considered.
The Journal of Chemical Physics, 1993
Multimolecule Brownian dynamics simulation results for diffusion controlled polymerization of bea... more Multimolecule Brownian dynamics simulation results for diffusion controlled polymerization of bead–rod chain molecules in 2D solution are presented. Reaction between any two molecules undergoing Brownian diffusion takes place if the reactive chain ends approach each other to within a certain reaction radius, and if the chain end carrying segments are collinear within certain specified limits. The second order reaction rate constant is found to decrease with time as the molecular lengths increase and the diffusivities decrease. Application of a shear flow is seen to result in alignment of the molecules along the flow direction, thereby enhancing the concentration of molecular pairs with parallel orientation of reactive-end carrying chain segments, and hence the overall reaction rate. This effect is found to be more pronounced in the case of long rigid molecules as compared to flexible molecules because of the slow rotation and high level of orientation under flow of the former. Even ...
The present disclosure relates to a tablet comprising at least one property modifying agent adapt... more The present disclosure relates to a tablet comprising at least one property modifying agent adapted to modify at least one property of a melt processable polymer and at least one processing aid having softening temperature lower than or equal to the melt processing temperature of the melt processable polymer.