EVALUATION OF POLYMER ADSORPTION-GEL FORMATION AND SLIP IN POLYMER SOLUTION FLOWS

A superposition model for evaluation of the effects of polymer adsorption-gel formation and slip of polymer solutions exhibiting both phenomena has been applied to the capillary flow of aqueous solutions of two molecular weight grades of hydroxyethyl cellulose (Natrosol 250, types G and HR, supplied by Hercules Powder Company). The flow behaviour of the solutions investigated was non-Newtonian. Evaluations are presented of the effective thicknesses of polymer adsorption-gel formation and pure solvent layers, as a function of the wall shear stress, tube radius and polymer concentration, corresponding to the determinations of the effective velocity at the wall.

The results of the analysis indicate the surface characteristics undergo a dramatic change from polymer adsorption-gel formation at the tube surface to the phenomenon characterized by slip in a narrow tube radius interval which has important implications in enhanced oil recovery by polymer solution floods. It also provides an explanation for the contrasting behaviours observed in the flow of aqueous Natrosol solutions through packed beds (Sadowski, 1963) and filter cakes (Kozicki et al., 1972).     

EFFECT OF DEFORMATION SEQUENCE ON RHEOLOGICAL BEHAVIOUR AND MECHANICAL DEGRADATION OF POLYMER SOLUTIONS

The flow behaviour of polymer solutions of non-hydrolyzed polyacrylamide and Xanthan was investigated in two rectangular and similar plexiglas models containing 3 cylindrical enlargements of the same dimensions. These three enlargements were located successively at the mid point of the first model length, whereas they were equally spaced along the second one. Only non-hydrolyzed polyacrylamide polymer solutions have shown viscoelastic behaviour in these plexiglas models. However, the behaviour of these polymer solutions in the first model was different from that in the second one.

The multipass mechanical degradation of the non-hydrolyzed polyacrylamide polymer solutions was studied extensively in the two plexiglas models. It was shown that, at high flow rates, the multipass mechanical degradation was stronger in the second model than in the first one. The mechanical degradation in model 1 converges with that in model 2 as the flow rate decreases.

The difference in flow behaviour and mechanical degradation of the same polymer solutions in the used plexiglas models was ascribed to the different times allowed for polymer solutions to relax prior to extension in the tested flow fields.     

The Effects of Molecular Weight on the Single Lap Shear Creep and Constant Strain Rate Behavior of Thermoplastic Polyimidesulfone Adhesive

The bonded shear creep and constant strain rate behavior of zero, one, and three percent end capped Thermoplastic Polyimidesulfone adhesive were examined at room and elevated temperatures. End capping was accomplished by the addition of phthalic anhydrides.

The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive in the bonded form. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Crochet's relation was used to describe the experimental creep failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed.     

HYDRODYNAMICS OF LAMINAR LIQUID JETS. EXPERIMENTAL STUDY AND COMPARISON WITH TWO MODELS

Laminar jets of Newtonian liquids issuing from long vertical cylindrical nozzles and falling freely through stagnant air were studied experimentally for Reynolds numbers between 300 and 1000. Jet diameters were measured from still photographs, and radial distributions of axial velocity were obtained by laser Doppler anemometry. The effect of nozzle diameter, fluid viscosity and surface tension was investigated.

The experimental results were compared with numerical solutions of the Protean coordinate model developed by Duda and Vrentas. The boundary layer simplifications were confirmed to be valid only for the downstream region of the jet and for Reynolds numbers greater than 1000.

The experimental diameters were also compared with predictions from a form of the Bernoulli equation with a surface tension term. The asymptotic validity of the model was confirmed, provided that the dissipation term arising from fluid viscosity could be neglected.

Neither model correlated the jet formation region satisfactorily. For this region, an empirical correlation was developed which improves the diameter prediction and is complementary of either model.     

GAS MIXING IN SLUGGING AND TURBULENT FLUIDIZED BEDS

The gas phase mixing in a fluidized bed of glass beads (d_p = 0.362 mm) in the slugging and turbulent flow regimes has been studied in a 0.1 m-ID × 3.0 m high Plexiglas column.

The gas dispersion in the downstream of the bed has been described by a diffusion process with the axial and radial dispersion coefficients. The radial dispersion coefficient of the gas phase is nearly constant with the variation of gas velocity in the slugging flow regime, but it increases with an increase in gas velocity in the turbulent flow regime.

Appreciable backmixing of the gas phase is pronounced in the slugging flow regime whereas the lower gas backmixing is produced in the turbulent flow regime. The gas backmixing coefficient increases with an increase in gas velocity in the slugging flow regime, but it decreases slightly with an increase in gas velocity in the turbulent flow regime.

The radial mixing and backmixing coefficients of the gas in terms of Peclet numbers have been correlated with the relevant dimensionless parameters (U_g/U_mf, p_s/p_g, d_p/D_t).

The gas flow pattern in the bed has been well represented by a simplified model based on the two gas phases in the dilute and dense phases which are percolating through the bed in plug flow. The present model can predict the gas exchange coefficient between the phases, the fractions of the dilute phase, the interstitial gas in the dense phase, and the interstitial gas velocity in the bed.     

Peel Adhesion of Solid Films-The Surface and Bulk Effects

The peel strength of rubber and paint films has been measured over a range of peeling velocities using a dead weight method. At low peel rates the peel force is fairly constant but rises rapidly at higher peeling speeds.

Experiments show that the peel strength is a function both of the energy of interfacial bonds which must be broken as peeling proceeds and of bulk energy losses in a viscoelastic peeling material.

The interfacial effect has two components: an equilibrium surface force which accounts for the peel strength at low velocities, and a viscous peeling force which depends on the peeling rate. This viscous interfacial force explains the increase in peel strength of purely elastic films at higher peeling velocities.

The energy loss in the bulk of the peeling film introduces two additional effects: a magnification of the peel strength in steady peeling over a certain velocity range, and a slowing down or stopping of peeling as transient relaxation occurs shortly after the application of the peel force.     

APPLICATION OF UF TECHNOLOGY TO LARGE-SCALE SYNTHESIS OF GT 267-004, A SEQUESTRANT FOR C. DIFFICILE TOXIN

GT 267-004 is a nonabsorbed, nonantibiotic, high molecular weight anionic polymer that is undergoing clinical evaluation as a Clostridium difficile toxin sequestrant. The API is a mixed salt form that consists of approximately 30 to 50% potassium and 70 to 50% sodium as the counterions on the polymer.

The initial polymerization process results in an aqueous polymer solution with the polymer in the 100% sodium form. It also contains some oligomeric impurities. UF technology was applied in a novel way to convert the single-salt polymer to the mixed salt form and to simultaneously remove the oligomers below the required specification limits in a single-unit operation.

Experiments with a UF lab unit validated the concept of simultaneously performing ion exchange and purification. An appropriate amount of potassium chloride was added to the polymer solution to carry out the ion exchange considering the selectivity of the polymer for the potassium ion over the sodium ion. The resulting mixed salts in solution were removed using ultrafiltration membranes. The process produced the API in excellent purity.

The lab data were used to scale up the process to produce several hundred kg of the API. The engineering analysis of the large-scale UF operation was carried out to run the UF process in the cyclic mode and in the diafiltration mode. The UF operation was optimized with respect to time, water usage, operability, and the concentration of product solution required for the subsequent processing.

The optimized UF process was found to be a very cost-effective and time-efficient route to produce the new API.     

A GENERALIZED BUBBLE RISE VELOCITY CORRELATION

A generalized bubble rise velocity correlation is developed to cover the range of conditions:

liquid-phase density = 45.1 to 74.7 lb/ft³,

liquid-phase viscosity = 0.233 to 59 cP., and

interfacial tension = 15 to 72 dynes/cm

The gas-phase is air and the bubble size ranged from 1.2 to 15 mm. The developed correlation is based upon new dimensionless groups which contain the parameters affecting bubble rise velocity as well as their interaction, The correlation is independent of flow regimes and applicable for Reynolds numbers from 0.1 to 10⁴. It is in good agreement with work appearing in the literature.     

VISCOSITY OF GLYCEROL AND ITS AQUEOUS SOLUTIONS MEASURED BY A TANK-TUBE VISCOMETER

In this paper we demonstrate several series of experiments for the measurement of viscosity of neat glycerol and its aqueous solutions using a tank-tube viscometer. Measuring viscosity of highly viscous liquids with the tank-tube viscometer is easier than other types of viscometers. This inexpensive viscometer continuously generates numerous reproducible viscosity data of highly viscous neat glycerol and its aqueous solutions under given experimental conditions such as a desired temperature and a desired concentration of water in aqueous glycerol solutions.

Fabricating the tank-tube viscometer is inexpensive, since this viscometer does not need sophisticated accessories such as a high-pressure liquid pump, a sensitive pressure sensor, and an accurate flow meter. The tank-tube viscometer consists of a large-diameter reservoir and a long, small-diameter, vertical tube.

The viscosity equation was developed under the following assumptions. Both the quasi steady state approach and the negligible friction loss due to a sudden contraction between the reservoir tank and the tube are valid. The kinetic energy of the emerging stream from the bottom end of the vertical tube of the tank-tube viscometer also is assumed to be negligible. Very viscous glycerol and its aqueous solutions were used to test the viscometer by comparing viscosity values from the viscometer with those from literatures.

The main objective of this study is to demonstrate effects of water as well as temperature on viscosity of aqueous glycerol solutions, applying experimental data of accumulated amounts of aqueous glycerol solutions at various drain durations to the newly-developed viscosity equation for the fabricated tank-tube viscometer.     

Vibration and Damping Characteristics of a Beam with a Partially Sandwiched Viscoelastic Layer

The purpose of this study is to verify the vibration and damping characteristics of a partially-layered elastic-viscoelastic-elastic structure both theoretically and experimentally.

The fourth-order differential equations of motion are derived for the transverse vibration of a three-layered sandwich beam with a viscoelastic (or adhesive) core layer. The transverse displacements of the constraining layer and the base beam are assumed to have different parameters. Both the transverse normal strain and the longitudinal shear strain of the viscoelastic core layer are included in the equations of motion. The solution to the resulting equations is obtained by solving a boundary value problem.

Numerical analysis of the equations and experimental measurements is illustrated by a cantilever beam in transverse vibration.

The vibration and damping effects of completely and partially covered beams are investigated and the effect of the position changes of partial coverage is intensively analyzed.     

VELOCITY PROFILES OF NEWTONIAN AND NON-NEWTONIAN TOROIDAL FLOWS MEASURED BY A LDA TECHNIQUE

Laser Doppler Anemomeiry was used to measure the primary (axial) and secondary (recirculating) velocity profiles in laminar flows of Newtonian (ethylene glycol) and non-Newtonian (aqueous solutions of CMC and PAA) liquids in curved tubes. Rheological characteristics of these liquids were measured using standard viscometric techniques (Haake and Mechanical Spectrometer). The effect of the shear-thinning viscosity is to flatten the axial velocity profile while enhancing the circulating flow close to the walls. On the other hand, the viscoelasticity reduces the extent of the secondary flow for all Dean numbers. This fact explains the reduction of laminar friction reported in the literature.

The primary and secondary velocity profiles, which appear to be the first ones ever published for the toroidal flows, are compared with the predictions of numerical simulation. The agreement is good when comparing the profiles of the axial flow but it is unsatisfactory for the secondary flows.     

PHASE HOLDUPS AND LIQUID-LIQUID EXTRACTION IN THREE PHASE FLUIDIZED BEDS

Effects of the continuous phase velocity (0.01-0.08 m/s(, the dispersed phase velocity (0.0-0.04 m/s) and particle size (1.0-3.0 mm) on the individual phase holdups and the mass transfer coefficient have been determined in two (liquid-liquid) and three (liquid-liquid-solid) phase fluidized beds.

In the beds, the dispersed phase holdup increased with dispersed phase velocity but it decreased with continuous phase velocity. Whereas the continuous phase holdup decreased with dispersed phase velocity but it increased with continuous phase velocity. The bed porosity increased with both the dispersed and continuous phase velocities in the beds of 1.7 and 3.0 mm particles. In addition, the continuous phase holdup decreased with the presence of solid particles in the bed, however, the dispersed phase holdup was not affected by the presence of the particles.

The overall mass transfer coefficients in the continuous and dispersed phases increased with increasing fluid velocities but it decreased with the bed height.

The continuous phase holdup and mass transfer coefficient data have been correlated with the operating variables and the dimensionless groups.     

EVALUATION OF PENG ROBINSON EQUATION OF STATE IN CALCULATING THERMOPHYSICAL PROPERTIES OF COMBUSTION GASES

A set of simple equations of the thermodynamic and transport properties of the combustion gases of a gas turbine have been derived based upon the critically evaluated data and two equations of state: The virial equation of state and Peng-Robinson (PR) equation of state.

The properties which have been considered were, density, specific heat at constant pressure, enthalpy, entropy, viscosity and thermal conductivity.

The temperature range was (200-2600 K) theoretically while the pressure range was (0.3-1.2 MPa).

A computer program, to evaluate the departure of thermophysical properties using virial and PR equations of state, was used.

The Peng Robinson (PR) equation of state gave better estimated accuracy than the virial equation of state especially in evaluating the departure of thermodynamic properties.     

DRAG AND MASS TRANSFER IN SLOW NON-NEWTONIAN FLOWS OVER AN ENSEMBLE OF NEWTONIAN SPHERICAL DROPS OR BUBBLES

An approximate solution for the slow motion of an ensemble of spherical drops through a power law fluid is obtained using Happel's free-surface cell model. It is shown that the drag coefficient decreases with decrease of the flow index and that this reduction is more significant at low voidage and large viscosity ratio parameter. The effect of the pseudoplastic anomaly on the mass transfer rate is more pronounced at low voidage for large values of viscosity ratio parameter, unlike the case of a single spherical drop

The present analysis covers the whole range of values of viscosity ratio parameter from infinity (an assemblage of solid spheres) to zero (a swarm of bubbles) and reduces to the solutions for those cases already known

The results for the motion of an ensemble of spherical drops also provide the basis for proposing a tentative expression for the expansion of liquid-liquid fluidized bed at low Reynolds number.     

STUDY OF THE PARAMETERS CONTROLLING THE ALTERNATING COPOLYMERIZATION OF METHYL METHACRYLATE AND STYRENE

The copolymerization of methyl methacrylate and styrene, in the presence of zinc chloride, was conducted in the aqueous phase. The zinc chloride acting as a complexing agent

Among the factors affecting the polymerization yield, we have; the level of complexing agents, the monomer ratio and the temperature

The polymers were characterized for their molecular weight (G.P.C.) and analyzed by N.MR, and D.T.A

A model taking into account the various parameters is proposed.     

Welding Mechanisms of Plastics: A Review

Strength of welded joints is a function of technological parameters of the production process. The type of function is dependent on the welding mechanism. Different mechanisms were found under various welding conditions. The processes included in the plastic welding mechanism are divided into two groups:

1) Processes which realize the joining of the parts.

2) Processes which create conditions for the first group to proceed. The first series of processes includes:

a) diffusion of macroradicals, molecular segments or molecules of the polymer which can be either in a solid, melted or dissolved state.

b) convective mass transfer.

c) recombination of macroradicals across the contact surface.

d) physical (surface) interaction.

e) any combination of processes described above.

The second group contains:

a) formation of the real contact surface.

b) formation of the macroradicals.

c) destruction and removal of inert layers which prevent real contact of active material.

Each process and the conditions of its proceeding are discussed individually.     

Structural Effects on the Adhesive Properties of Butadiene/Styrene Radial Teleblock Copolymers

The effects of butadiene/styrene ratio, monomer distribution, and molecular weight distribution and branching on the pressure sensitive adhesive properties of butadiene/ styrene radial teleblock copolymers are reported. Styrene content of polymers with varying structures shows a close relation with tack response, and styrene content and structure affect solution viscosity and shear adhesion. When part of the styrene is incorporated into the polybutadiene segment to yield a block progressively enriched in styrene (tapered block), solution viscosity and shear adhesion are reduced. When the butadiene segment is replaced by a block of randomly copolymerized butadiene and styrene, the polymers provide lower solution viscosities and shear adhesion but unchanged tack.

The molecular weight distribution of the radial teleblock polymers can vary from broad, highly branched compositions to narrow molecular weight distributions of almost Iinear polymers. The latter have relatively high solution viscosity and low shear adhesion, whereas the former polymers produce moderate solution viscosity but high shear adhesion. Tack is generally unaffected.     

UNSTEADY, TWO-DIMENSIONAL HEAT AND MASS TRANSFER IN A PACKED BED OF FINE PARTICLES WITH AN ENDOTHERMIC PROCESS

The basic differential equations controlling the temperature and concentration field in a single packed bed of fine particles were derived and solved for the general case in which unsteady, two-dimensional heat and mass transfer lakes place with an endothermic process.

The time-change of particle- and fluid-temperature and concentration of water vapor (humidity) were calculated by a numerical method which assumed that the rate of the endothermic process can be expressed by a first-order rate equation and that the fluid flowing through the bed is of the piston flow type.

The experiments were conducted for the drying of silica-gel and the two-stage dehydration reaction of natural gypsum to demonstrate the applicability of the present theoretical analysis.

It has been found that the calculated results show satisfactory agreement with the measured data within the range of the experimental conditions employed.     

TAYLOR DISPERSION OF MULTICOMPONENT SOLUTES

Coupled transport of multicomponent solutes in globally continuous systems is considered in the framework of the Generalized Taylor dispersion theory. Coupling between transports of n different species at the local (or micro-) scale, is considered to result from first-order irreversible surface reactions occurring on the local space boundaries, or from the off-diagonal terms of the solute diffusivity matrices.

General expressions are obtained for the global effective (long-time) solute dispersion matrix cofficients: mean global scalar reactivity, velocity vector and dispersivity dyadic.

The effect of surface chemical reactions is to partition the matter between different solute constituents. This is manifested in a coupling of the global transport coefficients, which may be mathematically removed by a linear (canonic) transformation applied to the effective global transport equation. This type of coupling does not exist for inert solutes.

The second type of the global coupling is represented by the off-diagonal terms of the global velocity and dispersivity matrices. It exists for both reactive and inert solutes. This coupling stems from the convective dispersion process (dependence or the global velocity vector on the local space coordinate). Is shown to be irremovable from the global transport equation by any linear transformation via the solute partition matrix. In the canonic form of the global equation the irremovable coupling is manifested by the traceless parts of the global solute velocity matrix and the global solute dispersivity.

The solution scheme is illustrated by calculating the mean global diffusivity of a solute consisting of two components, transport of which is coupled at the microscale via the molecular diffusivity matrix. At the macroscale the coupling is shown to be represented by negative off-diagonal terms of the global diffusivity matrix,