The Chemical Engineering Journal and the Biochemical Engineering Journal, 1995
membranes can be used for the dead-end filtration of suspensions of fine particles, with a period... more membranes can be used for the dead-end filtration of suspensions of fine particles, with a periodic backwash to remove the cake and restore filtrate flux. The optimum operation of such a two-stage discontinuous operation is determined by using cake filtration theory and assuming that the backwash period depends on the geometry of the fil$er module. This allows identification of the conditions where such a process can be used. The case where flux restoration by backwashing is imperfect due to progressive internal fouling of the membrane is also treated and allows the periodicity of chemical cleaning to be determined as a function of the degree of fouling. Finally, mention is made of the possible extension 'of the theory to the case of cross-flow filtration.
This paper describes a technique for investigating the fouling of microfiltration membranes by me... more This paper describes a technique for investigating the fouling of microfiltration membranes by measuring the pressure drops across two membranes fed in series by a constant rate pump, which enables a distinction to be made between surface fouling and internal fouling of the membrane. In the case of the microfiltration of BSA solutions, the technique shows how the type of pump and the operating temperature influence membrane fouling and how protein denaturation and adsorption give rise to different types of fouling. The technique is also used to investigate the microfiltration of beer and shows how this is affected by membrane properties and the aging of beer.
EXPERIMENTAL investigation of the characteristics of multi-component packings of particles would ... more EXPERIMENTAL investigation of the characteristics of multi-component packings of particles would involve a large number of manipulations for even very few components in the mixture, and each additional component would increase this number enormously. A method of calculating the properties of such mixtures would be of interest if only as a framework within which to design experiments. One difficulty is that for this very reason a theoretical approach cannot be subjected to a thorough experimental verification. We therefore think it useful to take the problem further by comparing two previously published theoretical approaches, by a statistical geometric model1 and a computer simulation2, for calculating the contacts between disks in two-dimensional multicomponent random mixtures.
Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid... more Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid flows in packed-bed reactors, capillary pressure gradients can have a significant influence on liquid distribution and, consequently, on the overall reactor performance. In particular, capillary pressure is important for non-uniform liquid distribution, causing liquid spreading as it flows down the packing. An analytical model for capillary pressure–saturation relation is developed for the pendular and funicular regions and the factors affecting capillary pressure in the capillary region are discussed. The present model is compared to the capillary pressure models of Grosser et al. (AIChE J., 34:1850–1860, 1988) and Attou and Ferschneider (Chem. Eng. Sci., 55:491–511, 2000) and to the experiments of Dodds and Srivastava (Part Part Syst. Charact., 23:29–39, 2006) and Dullien et al. (J. Colloid Interface Sci., 127:362–372, 1989). The non-homogeneity of real packings is considered through particle size and porosity distributions. The model is based on the assumption that the particles are covered with a liquid film, which provides hydrodynamic continuity. This makes the model more suitable for porous or rough particles than for non-porous smooth particles. The main improvements of the present model are found in the pendular region, where the liquid dispersion due to capillary pressure gradients is most significant. The model can be used to improve the hydrodynamic models (e.g., CFD and cellular automata models) for packed-bed reactors, such as trickle-bed reactors, where gas, liquid, and solid phases are present. Models for such reactors have become quite common lately (Sáez and Carbonell, AIChE J., 31:52–62, 1985; Holub et al., Chem. Eng. Sci, 47, 2343–2348, 1992; Attou et al., Chem. Eng. Sci., 54:785–802, 1999; Iliuta and Larachi, Chem. Eng. Sci., 54:5039–5045, 1999, IJCRE 3:R4, 2005; Narasimhan et al., AIChE J., 48:2459–2474, 2002), but they still lack proper terms causing liquid dispersion.
The method presented in Part I, for studying a simplified ion-exchange cycle, is extended to cove... more The method presented in Part I, for studying a simplified ion-exchange cycle, is extended to cover the usual case of the regenerant having a total concentration different from that of the saturant. This change in total concentration, as it propagates in the column, gives rise to interference phenomena with the exchange fronts. The study of these interferences allows, as in Part I, the detailed effluent history to be predicted.
Particle & Particle Systems Characterization, 2007
This paper discusses the effects of ultrasound on the production of particles by precipitation an... more This paper discusses the effects of ultrasound on the production of particles by precipitation and crystallization. Examples are given from the formation of crystals of BaSO 4 , K 2 SO 4 , TiO 2 and sucrose. It is shown that ultrasound reduces the induction time, narrows the width of the metastable zone and leads to the production of more, finer, and more uniform crystals in some cases. The reasons for these effects of ultrasound on the nucleation of crystals are discussed and a possible mechanism is presented.
Flow field-flow fractionation (F.FFF) is a technique for measuring the size of species in the col... more Flow field-flow fractionation (F.FFF) is a technique for measuring the size of species in the colloidal range (1 nm to 1 μm) which makes the use of the formation of a molecular or colloidal polarization layer at the surface of a filtering membrane. The species to be analyzed are introduced into a flow of liquid passing through a channel with porous walls (of pore size less than that of the colloids to be analyzed) which allow a certain controlled flow to pass through. The remaining fraction of the flow passes through the system, carrying the colloids to a nonspecific detector. The transit time of the colloids through the channel is found to be a function of their size and the permeation rate through the porous membrane. This chromatographic system can be calibrated by using known colloids, such as standard latex particles or fractionated polymer samples, and then used to determine the size of unknown colloids. Here we present results obtained in two different systems, an asymmetric ...
Colloids and Surfaces A Physicochemical and Engineering Aspects
We present an experimental investigation of the transport and capture of model colloids in a well... more We present an experimental investigation of the transport and capture of model colloids in a well-defined porous medium. The experiments were performed using standard liquid chromatography equipment and involve detecting the passage of small impulses of monodisperse latex particles passing through a bed of monosize glass beads. Experiments were performed with three samples of monodisperse latex particles of diameters 226, 550 and 790 nm in carrier solutions with ionic strengths ranging from pure water up to 0.1 M at a pH of either 5.2 or 8 at flow velocities varying from 0.01 to 0.1 cm s−1. The results are presented as capture efficiency as a function of the various parameters and also in the form of Sherwood number vs Reynolds number for comparison with existing correlations of mass transfer. It is shown that capture is strongly influenced by hydrodynamics and the repulsive potential energy barrier.
An analytical solution for the axial and transverse flow fields in laminar flow in porous channel... more An analytical solution for the axial and transverse flow fields in laminar flow in porous channels for both a rectangular channel with one porous wall and a porous tubular channel is presented. The solution is obtained from the Navier-Stokes equations without the simplifying assumption of constant permeation rate along the length of the duct. A dimensionless criterion for the validity of previous simplified solutions is developed which shows that the validity of the assumption of a constant permeation rate depends on the permeability of the membrane and the dimensions of the channel. Long channels with high permeability membranes can have significant departures from the constant permeation rate. The importance of these effects for the design of ultrafiltration and microfiltration modules is discussed.
ABSTRACT We present a study of talc grinding in an Alpine 100 AFG opposed air jet mill with an in... more ABSTRACT We present a study of talc grinding in an Alpine 100 AFG opposed air jet mill with an inline laser granulometer. The conditions for steady state operation have been determined from continuous grinding experiments and show that overloading occurs above a critical value of feed rate classifier resulting in unstable product size distribution. For each rotation speed of the classifier, there is an optimum feed rate, which gives the finest product, thus fixing a maximum reduction ratio. A linear relation exists between this ratio and the rotation speed of the classifier. The use of liquid grinding aids have been studied and showed they can result in an increase in the production rate but can also lead to a coarser product.
Particle & Particle Systems Characterization, 2007
This paper discusses the effects of ultrasound on the production of particles by precipitation an... more This paper discusses the effects of ultrasound on the production of particles by precipitation and crystallization. Examples are given from the formation of crystals of BaSO 4 , K 2 SO 4 , TiO 2 and sucrose. It is shown that ultrasound reduces the induction time, narrows the width of the metastable zone and leads to the production of more, finer, and more uniform crystals in some cases. The reasons for these effects of ultrasound on the nucleation of crystals are discussed and a possible mechanism is presented.
... In order to study the influence of static electricity on the minimum fluidisation velocity (u... more ... In order to study the influence of static electricity on the minimum fluidisation velocity (u mf ... Theelectrostatic behaviour of the two products was studied in order to set the ... As low-density polyethylene has an extremely high resistivity, ohmic dissipation during contact time with the ...
This special edition of Powder Technology presents a selection of papers from the symposium STP-P... more This special edition of Powder Technology presents a selection of papers from the symposium STP-PMF 2007, Science et Technologie des Poudres-Poudres et Matériaux Frittés, (Powder Science and Technology-Powders and Sintered Material) which was held at the Ecole des Mines d'Albi from 23 to 25 May 2007. This event brought together three scientific communities interested in research in particle technology, which usually hold separate meetings. These were:
A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has bee... more A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle.
The Chemical Engineering Journal and the Biochemical Engineering Journal, 1995
membranes can be used for the dead-end filtration of suspensions of fine particles, with a period... more membranes can be used for the dead-end filtration of suspensions of fine particles, with a periodic backwash to remove the cake and restore filtrate flux. The optimum operation of such a two-stage discontinuous operation is determined by using cake filtration theory and assuming that the backwash period depends on the geometry of the fil$er module. This allows identification of the conditions where such a process can be used. The case where flux restoration by backwashing is imperfect due to progressive internal fouling of the membrane is also treated and allows the periodicity of chemical cleaning to be determined as a function of the degree of fouling. Finally, mention is made of the possible extension 'of the theory to the case of cross-flow filtration.
This paper describes a technique for investigating the fouling of microfiltration membranes by me... more This paper describes a technique for investigating the fouling of microfiltration membranes by measuring the pressure drops across two membranes fed in series by a constant rate pump, which enables a distinction to be made between surface fouling and internal fouling of the membrane. In the case of the microfiltration of BSA solutions, the technique shows how the type of pump and the operating temperature influence membrane fouling and how protein denaturation and adsorption give rise to different types of fouling. The technique is also used to investigate the microfiltration of beer and shows how this is affected by membrane properties and the aging of beer.
EXPERIMENTAL investigation of the characteristics of multi-component packings of particles would ... more EXPERIMENTAL investigation of the characteristics of multi-component packings of particles would involve a large number of manipulations for even very few components in the mixture, and each additional component would increase this number enormously. A method of calculating the properties of such mixtures would be of interest if only as a framework within which to design experiments. One difficulty is that for this very reason a theoretical approach cannot be subjected to a thorough experimental verification. We therefore think it useful to take the problem further by comparing two previously published theoretical approaches, by a statistical geometric model1 and a computer simulation2, for calculating the contacts between disks in two-dimensional multicomponent random mixtures.
Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid... more Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid flows in packed-bed reactors, capillary pressure gradients can have a significant influence on liquid distribution and, consequently, on the overall reactor performance. In particular, capillary pressure is important for non-uniform liquid distribution, causing liquid spreading as it flows down the packing. An analytical model for capillary pressure–saturation relation is developed for the pendular and funicular regions and the factors affecting capillary pressure in the capillary region are discussed. The present model is compared to the capillary pressure models of Grosser et al. (AIChE J., 34:1850–1860, 1988) and Attou and Ferschneider (Chem. Eng. Sci., 55:491–511, 2000) and to the experiments of Dodds and Srivastava (Part Part Syst. Charact., 23:29–39, 2006) and Dullien et al. (J. Colloid Interface Sci., 127:362–372, 1989). The non-homogeneity of real packings is considered through particle size and porosity distributions. The model is based on the assumption that the particles are covered with a liquid film, which provides hydrodynamic continuity. This makes the model more suitable for porous or rough particles than for non-porous smooth particles. The main improvements of the present model are found in the pendular region, where the liquid dispersion due to capillary pressure gradients is most significant. The model can be used to improve the hydrodynamic models (e.g., CFD and cellular automata models) for packed-bed reactors, such as trickle-bed reactors, where gas, liquid, and solid phases are present. Models for such reactors have become quite common lately (Sáez and Carbonell, AIChE J., 31:52–62, 1985; Holub et al., Chem. Eng. Sci, 47, 2343–2348, 1992; Attou et al., Chem. Eng. Sci., 54:785–802, 1999; Iliuta and Larachi, Chem. Eng. Sci., 54:5039–5045, 1999, IJCRE 3:R4, 2005; Narasimhan et al., AIChE J., 48:2459–2474, 2002), but they still lack proper terms causing liquid dispersion.
The method presented in Part I, for studying a simplified ion-exchange cycle, is extended to cove... more The method presented in Part I, for studying a simplified ion-exchange cycle, is extended to cover the usual case of the regenerant having a total concentration different from that of the saturant. This change in total concentration, as it propagates in the column, gives rise to interference phenomena with the exchange fronts. The study of these interferences allows, as in Part I, the detailed effluent history to be predicted.
Particle & Particle Systems Characterization, 2007
This paper discusses the effects of ultrasound on the production of particles by precipitation an... more This paper discusses the effects of ultrasound on the production of particles by precipitation and crystallization. Examples are given from the formation of crystals of BaSO 4 , K 2 SO 4 , TiO 2 and sucrose. It is shown that ultrasound reduces the induction time, narrows the width of the metastable zone and leads to the production of more, finer, and more uniform crystals in some cases. The reasons for these effects of ultrasound on the nucleation of crystals are discussed and a possible mechanism is presented.
Flow field-flow fractionation (F.FFF) is a technique for measuring the size of species in the col... more Flow field-flow fractionation (F.FFF) is a technique for measuring the size of species in the colloidal range (1 nm to 1 μm) which makes the use of the formation of a molecular or colloidal polarization layer at the surface of a filtering membrane. The species to be analyzed are introduced into a flow of liquid passing through a channel with porous walls (of pore size less than that of the colloids to be analyzed) which allow a certain controlled flow to pass through. The remaining fraction of the flow passes through the system, carrying the colloids to a nonspecific detector. The transit time of the colloids through the channel is found to be a function of their size and the permeation rate through the porous membrane. This chromatographic system can be calibrated by using known colloids, such as standard latex particles or fractionated polymer samples, and then used to determine the size of unknown colloids. Here we present results obtained in two different systems, an asymmetric ...
Colloids and Surfaces A Physicochemical and Engineering Aspects
We present an experimental investigation of the transport and capture of model colloids in a well... more We present an experimental investigation of the transport and capture of model colloids in a well-defined porous medium. The experiments were performed using standard liquid chromatography equipment and involve detecting the passage of small impulses of monodisperse latex particles passing through a bed of monosize glass beads. Experiments were performed with three samples of monodisperse latex particles of diameters 226, 550 and 790 nm in carrier solutions with ionic strengths ranging from pure water up to 0.1 M at a pH of either 5.2 or 8 at flow velocities varying from 0.01 to 0.1 cm s−1. The results are presented as capture efficiency as a function of the various parameters and also in the form of Sherwood number vs Reynolds number for comparison with existing correlations of mass transfer. It is shown that capture is strongly influenced by hydrodynamics and the repulsive potential energy barrier.
An analytical solution for the axial and transverse flow fields in laminar flow in porous channel... more An analytical solution for the axial and transverse flow fields in laminar flow in porous channels for both a rectangular channel with one porous wall and a porous tubular channel is presented. The solution is obtained from the Navier-Stokes equations without the simplifying assumption of constant permeation rate along the length of the duct. A dimensionless criterion for the validity of previous simplified solutions is developed which shows that the validity of the assumption of a constant permeation rate depends on the permeability of the membrane and the dimensions of the channel. Long channels with high permeability membranes can have significant departures from the constant permeation rate. The importance of these effects for the design of ultrafiltration and microfiltration modules is discussed.
ABSTRACT We present a study of talc grinding in an Alpine 100 AFG opposed air jet mill with an in... more ABSTRACT We present a study of talc grinding in an Alpine 100 AFG opposed air jet mill with an inline laser granulometer. The conditions for steady state operation have been determined from continuous grinding experiments and show that overloading occurs above a critical value of feed rate classifier resulting in unstable product size distribution. For each rotation speed of the classifier, there is an optimum feed rate, which gives the finest product, thus fixing a maximum reduction ratio. A linear relation exists between this ratio and the rotation speed of the classifier. The use of liquid grinding aids have been studied and showed they can result in an increase in the production rate but can also lead to a coarser product.
Particle & Particle Systems Characterization, 2007
This paper discusses the effects of ultrasound on the production of particles by precipitation an... more This paper discusses the effects of ultrasound on the production of particles by precipitation and crystallization. Examples are given from the formation of crystals of BaSO 4 , K 2 SO 4 , TiO 2 and sucrose. It is shown that ultrasound reduces the induction time, narrows the width of the metastable zone and leads to the production of more, finer, and more uniform crystals in some cases. The reasons for these effects of ultrasound on the nucleation of crystals are discussed and a possible mechanism is presented.
... In order to study the influence of static electricity on the minimum fluidisation velocity (u... more ... In order to study the influence of static electricity on the minimum fluidisation velocity (u mf ... Theelectrostatic behaviour of the two products was studied in order to set the ... As low-density polyethylene has an extremely high resistivity, ohmic dissipation during contact time with the ...
This special edition of Powder Technology presents a selection of papers from the symposium STP-P... more This special edition of Powder Technology presents a selection of papers from the symposium STP-PMF 2007, Science et Technologie des Poudres-Poudres et Matériaux Frittés, (Powder Science and Technology-Powders and Sintered Material) which was held at the Ecole des Mines d'Albi from 23 to 25 May 2007. This event brought together three scientific communities interested in research in particle technology, which usually hold separate meetings. These were:
A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has bee... more A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle.
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Papers by John Dodds