Breakup of non-newtonian emulsion jets

The breakup of non-Newtonian emulsion jets into drops was experimentally studied by ejecting both O/W and W/O emulsions vertically downward into stagnant air through nozzles. Breakup lengths of non-Newtonian emulsion jets were found to be almost equivalent to those of Newtonian jets. Experimental breakup data establish that the static surface tension of the oil phase can be used as the surface tension of W/O emulsion jets, whereas the dynamic surface tension of aqueous surfactant solutions is used as that of O/W emulsion jets. Diameters of drops formed from non-Newtonian emulsion jets are in good agreement with the prediction from the stability theory previously developed by the authors. When the rheological index in a power law model is appreciably smaller than unity and the Ohnesorge number is significantly large, however, drop sizes are larger than the prediction because of the profile relaxation in jets. The critical velocity of emulsion jets, either O/W or W/O emulsion, is significantly lower than that of homogeneous Newtonian jets.     

Stability of jets in liquid-liquid systems

Experiments were carried out to study the stability of jets in immiscible liquid systems under conditions where the jet velocity relative to continuous phase was zero. The laminar breakup lengths and the diameter of drops formed from laminar jets are in good agreement with the stability analysis for stationary column while breakup data for jets injected into quiescent liquids disagree with it. An approximate solution for theoretical drop size is presented. The experiment also showed that the hydrodynamic resistance of continuous phase increases the growth rate of disturbances but does not affect the wave length.     

Breakup of relatively low-concentrated O/W emulsion jets

The breakup of emulsion jets ejected downward into air from a nozzle has been investigated experimentally, and the breakup length of jets and the drop size for kerosene-water emulsions have been measured. The concentration of the dispersed phase was less than 50 wt%, so all experimental emulsions exhibited Newtonian flow. Photographic observation indicated that the emulsion jet resembled the jet of normal homogeneous liquids. The breakup length of the jet and the drop size from the jet are in good agreement with predictions from stability analysis for normal liquids.     

Effect of pseudoplastic behaviour of liquid in co-current three-phase fluidized beds on bed expansion

Gas hold-up and bed expansion measurements were carried out for a bed of glass beads fluidized in Newtonian liquids and non-Newtonian liquids with gas. The value of gas hold-up increased and decreased with increasing particle size and liquid velocity, respectively. The effect of rheological properties on gas hold-up was insignificant and therefore the gas hold-up data for both Newtonian and non-Newtonian fluids were reasonably fitted by the available correlation which had no liquid viscosity term. The bed voidage increased with increasing superficial liquid velocities and superficial gas velocities. The increase of the viscous non-Newtonian flow behaviours resulted in an increase of the bed voidage. The correlation for the bed voidage in three-phase fluidized beds was developed for gas-Newtonian or non-Newtonian liquid–solid three-phase systems by combining the generalized wake model and the correlation for liquid–solid two-phase systems proposed previously by the authors. The predictions for bed voidage were in reasonable agreement with the present experimental data for three-phase systems with Newtonian and non-Newtonian liquids in a wide range of Reynolds numbers.     

Analysis of Liquid Jet Breakup in One‐ and Two‐Phase Flows

The phenomenon of breakup of a jet into drops has been applied mainly to separation technologies in the chemical, pharmaceutical, and metallurgical industries. The paper deals with the experimental analysis directed at the breakup of polymer solutions flowing through an orifice nozzle. The analysis of the breakup and atomization of a liquid jet by a high‐speed gas jet is presented. Additionally, non‐Newtonian effects on the breakup of the liquid jet into drops were studied using the microphotography method. In the experiments, various aqueous solutions of polyacrylamide were used. The polymer solutions studied were power‐law fluids. Analysis of the photographs of the jet breakup showed that the length of the jets depends on the liquid and gas flow rates and on the concentration of the polymer used. High‐molecular‐weight polymers added to a solvent lead to changes in the rheological properties of the liquid and the breakup length of the jet.     

Experimental measurements of the effect of viscosity on drag for liquid drops

The drag coefficients of drops of various liquids falling in air were measured experimentally. The drag coefficient was linearly related to the viscosity in the Reynolds number and viscosity range measured. Measurements also suggested there is no difference between Newtonian and non-Newtonian liquids.     

A study on polymer blending microrheology

In this paper it is shown that the formation and subsequent breakup of threadlike particles are important disperging mechanisms and largely govern the morphology resulting from a polymer blending process. Experiments on the breakup of Newtonian threads surrounded by a second Newtonian fluid have been carried out and good agreement with Tomotika's theory is achieved. Experiments on the breakup of viscoelastic fluid threads showed the influence of shear thinning and stretch thickening effects of the fluids used. To investigate the influence of non-Newtonian behavior of molten polymers on capillary instabilities, experiments were carried out on the breakup of molten polymer threads embedded in a second polymer melt. Surprisingly an absence of shear thinning and stretch thickening effects was noticed and good agreement with Tomotika's theory was obtained. Finally, the stability of threads of fluids exhibiting a yield stress was studied. A criterion predicting the stability of such threads was established and verified experimentally. On the basis of this criterion a possible explanation is given for the stability of a certain class of co-continuous morphologies.     

Development of polymer blend morphology during compounding in a twin-screw extruder. Part I: Droplet dispersion and coalescence—a review

The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ? 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, ?_d ? 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin-screw extruder. Their value is limited to serving as general guides to the process modeling.     

Shear rate dependent viscosity of suspensions in newtonian and non-newtonian liquids

Viscosity measurements in a wide shear rate range, on suspensions of six Newtonian and non-Newtonian liquids, are reported.The shear rate dependency of suspensions in non-Newtonian liquids is compared with that of suspensions in Newtonian ones and an extension to the former of the Krieger—Dougherty theory, which holds for the latter, is attempted. Although some success is obtained, an alternative explanation of the observed behavior of the suspensions of non-Newtonian liquids is discussed.     

THEORETICAL PREDICTION OF GAS HOLDUP IN BUBBLE COLUMNS WITH NEWTONIAN AND NON-NEWTONIAN LIQUIDS

A simple model based on an energy balance which takes into account the friction losses at the gas-liquid interface and the slip velocity of single bubble is used to simulate the gas holdup in bubble columns containing Newtonian and non-Newtonian liquids which circulate in both laminar and turbulent flows. Experimental data available from the literature for bubble columns up to 7 m height and 1 m diameter with water and glycerol as Newtonian liquids and different solutions of CMC in a wide range of concentrations as non-Newtonian liquids are simulated with good agreement despite the simplifications made to describe the gas liquid flow regimes. Most of the differences between experimental and calculated gas holdup are justified on the basis of the simplifying assumptions.     

Trickle bed hydrodynamics and flow regime transition at elevated temperature for a Newtonian and a non-Newtonian liquid

Despite the hydrodynamics of trickle beds experiencing high pressures has become largely documented in the recent literature, trickle bed hydrodynamic behavior at elevated temperatures, on the contrary, largely remains terra incognita. This study's aim was to demonstrate experimentally the temperature shift of trickle-to-pulse flow regime transition, pulse velocity, two-phase pressure drop, liquid holdup and liquid axial dispersion coefficient. These parameters were determined for Newtonian (air-water) and non-Newtonian (air-0.25% Carboxymethylcellulose (CMC)) liquids, and the various experimental results were compared to available literature models and correlations for confrontation and recommendations. The trickle-to-pulse flow transition boundary shifted towards higher gas and liquid superficial velocities with increasingly temperatures, aligning with the findings on pressure effects which likewise were confirmed to broaden the trickle flow domain. The Larachi-Charpentier-Favier diagram [Larachi et al., 1993, The Canadian Journal of Chemical Engineering 71, 319-321] provided good predictions of the transition locus at elevated temperature for Newtonian liquids. Conversely, everything else being kept identical, increasingly temperatures occasioned a decrease in both two-phase pressure drop and liquid holdup; whereas pulse velocity was observed to increase with temperature. The Iliuta and Larachi slit model for non-Newtonian fluids [Iliuta and Larachi, 2002, Chemical Engineering Science 46, 1233-1246] predicted with very good accuracy both the pressure drops and the liquid holdups regardless of pressure and temperature without requiring any adjustable parameter. The Burghardt et al. [2004, Industrial and Engineering Chemistry Research 43, 4511-4521] pulse velocity correlation can be recommended for preliminary engineering calculations of pulse velocity at elevated temperature, pressure, Newtonian and non-Newtonian liquids. The liquid axial dispersion coefficient (D_ax) extracted from the axial dispersion RTD model revealed that temperatures did not affect in a substantial manner this parameter. Both Newtonian and power-law non-Newtonian fluids behaved qualitatively similarly regarding the effect of temperature.     

Jet break-up in liquid-liquid systems

A study was made of the jet length, jet contraction, and size of drops resulting from the formation and break-up of liquid jets in another Newtonian, immiscible liquid. Drop size and jet contraction were correlated with system parameters, but attempts to correlate the jet length proved unsuccessful. Data were obtained from measurements of 4202 drops and 294 jet lengths and diameters on 294 photographs representing 92 runs. Variables included nozzle size, flow rate, and physical properties from six Newtonian liquid-liquid systems.     

Zur Fluiddynamik und zum Stoffübergang newtonscher und nichtnewtonscher Gemische auf Siebböden

Fluiddynamics and Mass Transfer of Newtonian and non-Newtonian Mixtures on Sieve Trays Highly viscous media are processed in a number of industries such as the chemical, pharmaceutical, petrochemical and food industries, whereby a great number of the used systems has an non-Newtonian behaviour. To improve the knowledge of mass transfer processes in Newtonian and non-Newtonian mixtures systematic experiments for fluiddynamics and mass transfer were carried out on various sieve trays. The realised results show that the separation performance of tray columns can be increased significantly by a suitable choice of operating conditions and sievetray lay-out. This paper summarizes results on the absorption of oxygene into water and in non-Newtonian liquids like carboxyl-methylcelluose/water and polyacrylamide/water. In parallel to the experimental measurements new correlations for the mass transfer of tray columns operating with average and high-viscous media were developed.     

Threshold wavelength on filaments of complex fluids

The breakup into drops of complex-fluid filaments – usually jets of polymeric and surfactant solutions – plays a central role in many engineering applications ranging from crop spraying to food processing and propulsion systems. To assess the influence of interfacial perturbations in the breakup process, we followed the dynamics of the initial wavelength of surface instability on complex-fluid filaments using direct numerical simulation. We found a threshold wavelength at low Reynolds numbers corresponding to a change on the filament's configuration near breakup from large primary drops connected by slender liquid threads for wavelengths below the threshold to clearly defined satellite drops in between the primary drops for wavelengths larger than the threshold. We also found that shear-thinning effects, by reducing the viscous resistance to the Marangoni stress responsible for the formation of the satellites, cause the threshold to appear at shorter wavelengths.     

Behavior of Elongated Liquid Jets in Viscous Liquid‐Liquid‐Systems

The stability of jets in elongational flow is exploited to obtain thin threads before breakup. Fine drops can be generated in suitable geometries with comparably large ducts. The examination deals with the stability of liquid threads simultaneously extended with the continuous phase in convergent flow. Breakup limits and regimes are discussed.     

PRESSURE DROPS OF NON-NEWTONIAN PURELY VISCOUS FLUID FLOW THROUGH SYNTHETIC FOAMS

This work aims at giving a first insight of non-Newtonian fluid flow through synthetic foams.

At first, a review of experimental pressure drops measured with Newtonian fluids through various foams is proposed as well as a recall of a capillary-type flow model used to determine structural parameters. In this particular case of Newtonian fluid flow, a single equation is shown to correlate experimental data whatever the grade of the foam. Results of an image analysis study are also given; they allow to give a physical sense to the value of the equivalent diameter of pore given by the flow model.

In a second part, results of pressure drops measured with a non-Newtonian fluid are reported. A model allowing the determination of the pressure drops for non-Newtonian purely viscous fluid flow through packed beds of particles, based on the same capillary representation of porous media, is tested in the case of fluid flow through synthetic foams. The model predictions are acceptable for foams of high grades, but a discrepancy is observed for foams of low grades. An attempt is made to explain the underevaluation of pressure drops with the aid of results of image analysis.     

Gas/Flüssig-Reaktoren

Gas-liquid reactors . The gas hold-up in bubble columns increases in proportion to the gas flux density in the homogeneous flow regime and rises less than proportionally in the heterogeneous flow regime. Both the gas and the liquid axial dispersion coefficient increase with gas flow. Gas phase dispersion becomes more intensive with increasing liquid viscosity, while liquid dispersion drops slightly. Experimental results for mass transfer in low viscosity liquids show that the two-range turbulence model best fits experimental data. When aerating highly viscous Newtonian and non-Newtonian liquids, mass transfer in the liquid phase is well described by known relations valid for very low bubble-Reynolds number and very high Schmidt number.     

Two-dimensional modeling of the effects of insoluble surfactant on the breakup of a liquid filament

Breakup of surfactant-laden liquid jets has received increasing consideration during the last few years because of its diverse applications, but theoretical studies have been largely restricted to evolution equations based on one-dimensional flow assumptions. Here, a fully two-dimensional finite element algorithm was used to solve the set of equations describing the dynamics of a Newtonian liquid filament covered with an insoluble surfactant in order to provide a better understanding of the underlying physical principles governing the formation of satellite drops. Results indicate that for a viscous liquid jet, formation of satellite drops between main drops is favored by the addition of surfactants. This effect is lessened, and even eliminated, by either decreasing the surfactant strength or increasing the surfactant diffusivity. On the other hand, low-viscosity liquid jets form satellite drops regardless of the presence of surfactant, but the addition of surfactant can either reduce or increase the size of the satellite formed. Reduction of the size of the satellite drop is favored by the addition of weak surfactants, a result that is in agreement with previous one-dimensional flow analyses. Conversely, addition of strong surfactants of low surface diffusivity increases the size of the satellite drop formed due to Marangoni stress-induced reversal of the capillary flow. The detailed information provided by the two-dimensional model has enabled a better understanding of the competition between viscous, inertia and capillary forces during jet breakup, and of how the competition between them changes due to the presence of the surfactant. This understanding can help in the rational design of systems such as spray, atomization, and jet printing to prevent the formation of satellite drops.     

Drop size in power law non-newtonian systems

Drop volume studies were made by forming non-Newtonian pseudoplastic drops in a continuous toluene phase and chlorobenzene drops in non-Newtonian continuous phases. Combination of results for these cases enabled development of a correlation for the prediction of non-Newtonian drop volume in a non-Newtonian continuous phase. The development is confined to power law fluids and provides expressions for both long and short nozzles in terms of a two-stage drop formation process. Variables included nozzle size, formation time, and rheological properties from eight non-Newtonian systems in a program of 144 runs.