Polyvinylidene fluoride (PVDF), the second most important fluoropolymer, exhibits a unique combin... more Polyvinylidene fluoride (PVDF), the second most important fluoropolymer, exhibits a unique combination of desired end-use properties including excellent chemical resistance, high thermal stability, and good mechanical as well as piezoelectric properties. Due to these unique characteristics, PVDF is widely used in wire and cable insulation, as sheet and melt-cast films in electronics, in fittings, valves and pumps, etc. PVDF is produced commercially by emulsion and suspension polymerization processes. In the present paper a comprehensive mathematical model of the vinylidene fluoride (VDF) emulsion polymerization process for a semi-batch reactor is developed. The model can predict the molecular (e.g., molecular weight distribution, etc.) and morphological (e.g., particle size distribution) properties of the particulate PVDF in agreement with experimental measurements. The mathematical model includes a comprehensive kinetic mechanism, a gel-effect model based on the generalized free-vo...
International journal of pharmaceutics, Jan 30, 2014
In this work the dynamic flow as well as the particle motion and deposition in a commercial dry p... more In this work the dynamic flow as well as the particle motion and deposition in a commercial dry powder inhaler, DPI (i.e., Turbuhaler) is described using computational fluid dynamics, CFD. The dynamic flow model presented here is an extension of a steady flow model previously described in Milenkovic et al. (2013). The model integrates CFD simulations for dynamic flow, an Eulerian-fluid/Lagrangian-particle description of particle motion as well as a particle/wall interaction model providing the sticking efficiency of particles colliding with the DPI walls. The dynamic flow is imposed by a time varying outlet pressure and the particle injections into the DPI are assumed to occur instantaneously and follow a prescribed particle size distribution, PSD. The total particle deposition and the production of fine particles in the DPI are determined for different peak inspiratory flow rates, PIFR, flow increase rates, FIR, and particle injection times. The simulation results for particle depo...
In this work the steady-state flow in a commercial dry powder inhaler device, DPI (i.e., Turbuhal... more In this work the steady-state flow in a commercial dry powder inhaler device, DPI (i.e., Turbuhaler) is described using computational fluid dynamics. The Navier-Stokes equations are solved using commercial CFD software considering different flow models, i.e., laminar, k-ε, k-ε RNG, and k-ω SST as well as large Eddy simulation. Particle motion and deposition are described using a Eulerian-fluid/Lagrangian-particle approach. Particle collisions with the DPI walls are taken to result in deposition when the normal collision velocity is less than a critical capture velocity. Flow and particle deposition, for a range of mouthpiece pressure drops (i.e., 800-8800 Pa), as well as particle sizes corresponding to single particles and aggregates (i.e., 0.5-20 μm), are examined. The total volumetric outflow rate, the overall particle deposition as well as the spatial distribution of deposition sites in the DPI are determined. The transitional k-ω SST model for turbulent flow was found to produce...
6. Conclusion In the present study, a comprehensive experimental investigation on the removal of ... more 6. Conclusion In the present study, a comprehensive experimental investigation on the removal of residual monomers and other volatile organic compounds (VOCs) from polymer latexes via post-polymerization and nitrogen stripping is reported. Both techniques are ...
ABSTRACT In the present study a comprehensive model is employed to describe the dynamic behavior ... more ABSTRACT In the present study a comprehensive model is employed to describe the dynamic behavior of an industrial scale reactor for the emulsion polymerization of vinylidene fluoride (VDF) under different initiator and chain transfer agent (CTA) addition policies. A comprehensive kinetic model combined with a thermodynamic and a particle population model were simultaneously solved to calculate the VDF addition rate, reactor pressure, molecular weight properties, and the particle size distribution of polyvinylidene fluoride produced in a semibatch emulsion polymerization reactor. The proposed emulsion polymerization model takes into account the gas–liquid equilibrium of VDF to determine the aqueous phase VDF concentration and the changes in operating pressure. The effects of particle crystallinity on radical entry and coagulation rate were also considered. The computational model results (cumulative monomer feed and feed rate, reactor pressure, molecular weights, and particle size distribution) are found to be in agreement with available experimental data.
ABSTRACT The present study describes the development of a nonhomogeneous two-compartment model fo... more ABSTRACT The present study describes the development of a nonhomogeneous two-compartment model for the prediction of particle size distribution in a semibatch emulsion ter-polymerization reactor. The multicompartment model accounts for spatial variations of particle size distribution (PSD) in the reactor due to nonideal mixing conditions. A comprehensive emulsion polymerization model is applied to each compartment, which allows the calculation of the various species concentrations in the aqueous and particle phases in each compartment. Moreover, a particle population balance equation is solved for each compartment to determine the individual PSDs as well as the overall PSD in the reactor. The effects of the two-compartment nonhomogeneous model parameters, that is, the volume ratio of the two compartments, the compartment exchange flow rates, and the partitioning of the monomer and initiator feed streams into the two compartments, on the overall polymerization rate and PSD are analyzed in detail. It is shown that depending on the selected values of the two-compartment model parameters, the overall PSD in the reactor can significantly vary (i.e., from a narrow and/or broad unimodal distribution to a bi- and/or multimodal PSD). Small compartment exchange flow rates, uneven monomer and initiator feed partitioning, or unequal compartment volumes can result in very different PSDs in the two compartments. Moreover, it is shown that for a range of parameter values in the two-compartment model (i.e., reflecting the degree of reactor nonhomogeneity), the calculated overall PSD in the industrial-scale reactor can be unimodal but significantly broader than the respective PSD calculated by the homogeneous one-compartment model.
Computer Methods in Biomechanics and Biomedical Engineering, 2013
A computational model for flow and particle deposition in a three-dimensional representation of t... more A computational model for flow and particle deposition in a three-dimensional representation of the human nasal cavity is developed. Simulations of steady state and dynamic airflow during inhalation are performed at flow rates of 9-60 l/min. Depositions for particles of size 0.5-20 μm are determined and compared with experimental and simulation results from the literature in terms of deposition efficiencies. The nasal model is validated by comparison with experimental and simulation results from the literature for particle deposition under steady-state flow. The distribution of deposited particles in the nasal cavity is presented in terms of an axial deposition distribution as well as a bivariate axial deposition and particle size distribution. Simulations of dynamic airflow and particle deposition during an inhalation cycle are performed for different nasal cavity outlet pressure variations and different particle injections. The total particle deposition efficiency under dynamic flow is found to depend strongly on the dynamics of airflow as well as the type of particle injection.
... Liq. Cryst., 27 (1974) 23. 16 S. Krishnaswamy and R. Shashidhar, Mol. Cryst. ... 27 (1974), p... more ... Liq. Cryst., 27 (1974) 23. 16 S. Krishnaswamy and R. Shashidhar, Mol. Cryst. ... 27 (1974), p. 23. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (5). 16S. Krishnaswamy and R. Shashidhar, Mol. Cryst. Liq. Cryst. 35 (1976), p. 253. Full Text via CrossRef. 17S. ...
The present paper presents a study on the application of the Galerkin finite element method (FEM)... more The present paper presents a study on the application of the Galerkin finite element method (FEM) for the solution of the dynamic multivariate population balance equation (PBE) in batch particulate systems undergoing aggregation as well as combined aggregation and growth. The performance of the Galerkin FEM in terms of accuracy and stability was assessed by a direct comparison of the calculated particle size distributions and/or their corresponding moments to available analytical solutions as well as by comparison to univariate numerical solutions. Numerical simulations were carried out for a variety of particle aggregation and growth mechanisms including constant, Brownian, and modified Brownian aggregation as well as constant and linear growth rate functions and for a wide range of values for the aggregation and growth rate coefficients. The simulation results revealed that the proposed Galerkin FEM produces very accurate numerical solutions but at significant computational cost.
Polyvinylidene fluoride (PVDF), the second most important fluoropolymer, exhibits a unique combin... more Polyvinylidene fluoride (PVDF), the second most important fluoropolymer, exhibits a unique combination of desired end-use properties including excellent chemical resistance, high thermal stability, and good mechanical as well as piezoelectric properties. Due to these unique characteristics, PVDF is widely used in wire and cable insulation, as sheet and melt-cast films in electronics, in fittings, valves and pumps, etc. PVDF is produced commercially by emulsion and suspension polymerization processes. In the present paper a comprehensive mathematical model of the vinylidene fluoride (VDF) emulsion polymerization process for a semi-batch reactor is developed. The model can predict the molecular (e.g., molecular weight distribution, etc.) and morphological (e.g., particle size distribution) properties of the particulate PVDF in agreement with experimental measurements. The mathematical model includes a comprehensive kinetic mechanism, a gel-effect model based on the generalized free-vo...
International journal of pharmaceutics, Jan 30, 2014
In this work the dynamic flow as well as the particle motion and deposition in a commercial dry p... more In this work the dynamic flow as well as the particle motion and deposition in a commercial dry powder inhaler, DPI (i.e., Turbuhaler) is described using computational fluid dynamics, CFD. The dynamic flow model presented here is an extension of a steady flow model previously described in Milenkovic et al. (2013). The model integrates CFD simulations for dynamic flow, an Eulerian-fluid/Lagrangian-particle description of particle motion as well as a particle/wall interaction model providing the sticking efficiency of particles colliding with the DPI walls. The dynamic flow is imposed by a time varying outlet pressure and the particle injections into the DPI are assumed to occur instantaneously and follow a prescribed particle size distribution, PSD. The total particle deposition and the production of fine particles in the DPI are determined for different peak inspiratory flow rates, PIFR, flow increase rates, FIR, and particle injection times. The simulation results for particle depo...
In this work the steady-state flow in a commercial dry powder inhaler device, DPI (i.e., Turbuhal... more In this work the steady-state flow in a commercial dry powder inhaler device, DPI (i.e., Turbuhaler) is described using computational fluid dynamics. The Navier-Stokes equations are solved using commercial CFD software considering different flow models, i.e., laminar, k-ε, k-ε RNG, and k-ω SST as well as large Eddy simulation. Particle motion and deposition are described using a Eulerian-fluid/Lagrangian-particle approach. Particle collisions with the DPI walls are taken to result in deposition when the normal collision velocity is less than a critical capture velocity. Flow and particle deposition, for a range of mouthpiece pressure drops (i.e., 800-8800 Pa), as well as particle sizes corresponding to single particles and aggregates (i.e., 0.5-20 μm), are examined. The total volumetric outflow rate, the overall particle deposition as well as the spatial distribution of deposition sites in the DPI are determined. The transitional k-ω SST model for turbulent flow was found to produce...
6. Conclusion In the present study, a comprehensive experimental investigation on the removal of ... more 6. Conclusion In the present study, a comprehensive experimental investigation on the removal of residual monomers and other volatile organic compounds (VOCs) from polymer latexes via post-polymerization and nitrogen stripping is reported. Both techniques are ...
ABSTRACT In the present study a comprehensive model is employed to describe the dynamic behavior ... more ABSTRACT In the present study a comprehensive model is employed to describe the dynamic behavior of an industrial scale reactor for the emulsion polymerization of vinylidene fluoride (VDF) under different initiator and chain transfer agent (CTA) addition policies. A comprehensive kinetic model combined with a thermodynamic and a particle population model were simultaneously solved to calculate the VDF addition rate, reactor pressure, molecular weight properties, and the particle size distribution of polyvinylidene fluoride produced in a semibatch emulsion polymerization reactor. The proposed emulsion polymerization model takes into account the gas–liquid equilibrium of VDF to determine the aqueous phase VDF concentration and the changes in operating pressure. The effects of particle crystallinity on radical entry and coagulation rate were also considered. The computational model results (cumulative monomer feed and feed rate, reactor pressure, molecular weights, and particle size distribution) are found to be in agreement with available experimental data.
ABSTRACT The present study describes the development of a nonhomogeneous two-compartment model fo... more ABSTRACT The present study describes the development of a nonhomogeneous two-compartment model for the prediction of particle size distribution in a semibatch emulsion ter-polymerization reactor. The multicompartment model accounts for spatial variations of particle size distribution (PSD) in the reactor due to nonideal mixing conditions. A comprehensive emulsion polymerization model is applied to each compartment, which allows the calculation of the various species concentrations in the aqueous and particle phases in each compartment. Moreover, a particle population balance equation is solved for each compartment to determine the individual PSDs as well as the overall PSD in the reactor. The effects of the two-compartment nonhomogeneous model parameters, that is, the volume ratio of the two compartments, the compartment exchange flow rates, and the partitioning of the monomer and initiator feed streams into the two compartments, on the overall polymerization rate and PSD are analyzed in detail. It is shown that depending on the selected values of the two-compartment model parameters, the overall PSD in the reactor can significantly vary (i.e., from a narrow and/or broad unimodal distribution to a bi- and/or multimodal PSD). Small compartment exchange flow rates, uneven monomer and initiator feed partitioning, or unequal compartment volumes can result in very different PSDs in the two compartments. Moreover, it is shown that for a range of parameter values in the two-compartment model (i.e., reflecting the degree of reactor nonhomogeneity), the calculated overall PSD in the industrial-scale reactor can be unimodal but significantly broader than the respective PSD calculated by the homogeneous one-compartment model.
Computer Methods in Biomechanics and Biomedical Engineering, 2013
A computational model for flow and particle deposition in a three-dimensional representation of t... more A computational model for flow and particle deposition in a three-dimensional representation of the human nasal cavity is developed. Simulations of steady state and dynamic airflow during inhalation are performed at flow rates of 9-60 l/min. Depositions for particles of size 0.5-20 μm are determined and compared with experimental and simulation results from the literature in terms of deposition efficiencies. The nasal model is validated by comparison with experimental and simulation results from the literature for particle deposition under steady-state flow. The distribution of deposited particles in the nasal cavity is presented in terms of an axial deposition distribution as well as a bivariate axial deposition and particle size distribution. Simulations of dynamic airflow and particle deposition during an inhalation cycle are performed for different nasal cavity outlet pressure variations and different particle injections. The total particle deposition efficiency under dynamic flow is found to depend strongly on the dynamics of airflow as well as the type of particle injection.
... Liq. Cryst., 27 (1974) 23. 16 S. Krishnaswamy and R. Shashidhar, Mol. Cryst. ... 27 (1974), p... more ... Liq. Cryst., 27 (1974) 23. 16 S. Krishnaswamy and R. Shashidhar, Mol. Cryst. ... 27 (1974), p. 23. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (5). 16S. Krishnaswamy and R. Shashidhar, Mol. Cryst. Liq. Cryst. 35 (1976), p. 253. Full Text via CrossRef. 17S. ...
The present paper presents a study on the application of the Galerkin finite element method (FEM)... more The present paper presents a study on the application of the Galerkin finite element method (FEM) for the solution of the dynamic multivariate population balance equation (PBE) in batch particulate systems undergoing aggregation as well as combined aggregation and growth. The performance of the Galerkin FEM in terms of accuracy and stability was assessed by a direct comparison of the calculated particle size distributions and/or their corresponding moments to available analytical solutions as well as by comparison to univariate numerical solutions. Numerical simulations were carried out for a variety of particle aggregation and growth mechanisms including constant, Brownian, and modified Brownian aggregation as well as constant and linear growth rate functions and for a wide range of values for the aggregation and growth rate coefficients. The simulation results revealed that the proposed Galerkin FEM produces very accurate numerical solutions but at significant computational cost.
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