Showing papers on "Mixing (process engineering) published in 2000"

Passive mixing in a three-dimensional serpentine microchannel

Abstract: A three-dimensional serpentine microchannel design with a "C shaped" repeating unit is presented in this paper as a means of implementing chaotic advection to passively enhance fluid mixing. The device is fabricated in a silicon wafer using a double-sided KOH wet-etching technique to realize a three-dimensional channel geometry. Experiments using phenolphthalein and sodium hydroxide solutions demonstrate the ability of flow in this channel to mix faster and more uniformly than either pure molecular diffusion or flow in a "square-wave" channel for Reynolds numbers from 6 to 70. The mixing capability of the channel increases with increasing Reynolds number. At least 98% of the maximum intensity of reacted phenolphthalein is observed in the channel after five mixing segments for Reynolds numbers greater than 25. At a Reynolds number of 70, the serpentine channel produces 16 times more reacted phenolphthalein than a straight channel and 1.6 times more than the square-wave channel. Mixing rates in the serpentine channel at the higher Reynolds numbers are consistent with the occurrence of chaotic advection. Visualization of the interface formed in the channel between streams of water and ethyl alcohol indicates that the mixing is due to both diffusion and fluid stirring.

Generation of Solution and Surface Gradients Using Microfluidic Systems

Abstract: This paper describes a simple, versatile method of generating gradients in composition in solution or on surfaces using microfluidic systems. This method is based on controlled diffusive mixing of species in solutions that are flowing laminarly, at low Reynolds number, inside a network of microchannels. We demonstrate the use of this procedure to generate (1) gradients in the compositions of solutions, measured directly by colorimetric assays and (2) gradients in topography of the surfaces produced by generating concentration gradients of etching reagents, and then using these gradients to etch profiles into the substrate. The lateral dimensions of the gradients examined here, which went from 350 to 900 μm, are determined by the width of the microchannels. Gradients of different size, resolution, and shape have been generated using this method. The shape of the gradients can be changed continuously (dynamic gradients) by varying the relative flow velocities of the input streams of fluids. The method is ex...

Microreactors: New Technology for Modern Chemistry

Abstract: 1 State of the Art of Microreaction Technology 1.1 Definition 1.1.1 Microsystems Termed Microreactor 1.1.2 Structural Hierarchy of Microreactors 1.1.3 Functional Classification of Microreactors 1.1.4 Dividing Line Between Analysis and Reaction Systems 1.2 Fundamental Advantages of Microreactors 1.2.1 Fundamental Advantages of Miniaturized Analysis Systems 1.2.2 Fundamental Advantages of Nano-Scale Reactors 1.2.3 Advantages of Microreactors Due to Decrease of Physical Size 1.2.4 Advantages of Microreactors Due to Increase of Number of Units 1.3 Potential Benefits of Microreactors Regarding Applications 1.4 References 2 Modern Microfabrication Techniques for Microreactors 2.1 Microfabrication Techniques Suitable for Microreactor Realization 2.2 Evaluation of Suitability of a Technique 2.3 Anisotropic Wet Etching of Silicon 2.4 Dry Etching of Silicon 2.5 LIGA Process 2.6 Injection Molding 2.7 Wet Chemical Etching of Glass 2.8 Advanced Mechanical Techniques 2.8.1 Surface Cutting with Diamond Tools 2.8.2 Milling, Turning and Drilling 2.8.3 Punching 2.8.4 Embossing 2.9 Isotropic Wet Chemical Etching of Metal Foils 2.10 Electro Discharge Machining (EDM) of Conductive Materials 2.10.1 Wire-Cut Erosion and Die Sinking 2.10.2 -EDM Drilling 2.11 Laser Micromachining 2.12 Interconnection Techniques 2.12.1 Microlamination of Thin Metal Sheets 2.13 Functional Coatings 2.13.1 Functional Coatings for Corrosion Prevention 2.13.2 Functional Coatings for Fouling Prevention 2.14 References 3 Micromixers 3.1 Mixing Principles and Classes of Macroscopic Mixing Equipment 3.2 Mixing Principles and Classes of Miniaturized Mixers 3.3 Potential of Miniaturized Mixers 3.4 Contacting of Two Substreams, e.g. in a Mixing Tee Configuration 3.4.1 Mixing Tee-Type Configuration 3.4.2 Double Mixing Tee-Type Configuration 3.5 Collision of High-Energy Substreams for Spraying/Atomizing 3.5.1 Collision of Three Substreams in a Microjet Reactor 3.6 Injection of Many Small Substreams of One Component into a Main Stream of Another Component 3.6.1 Injection of Multiple Microjets 3.7 Manifold Splitting and Recombination of a Stream Consisting of Two Fluid Lamellae of Both Components 3.7.1 Multiple Flow Splitting and Recombination Combined with Channel Reshaping 3.7.2 Multiple Flow Splitting and Recombination Using Fork-Like Elements 3.7.3 Multiple Flow Splitting and Recombination Using a Separation Plate 3.7.4 Multiple Flow Splitting and Recombination Using a Ramp-Like Channel Architecture 3.8 Injection of Many Substreams of Both Components 3.8.1 Multilamination of Fluid Layers in an Interdigital Channel Configuration 3.8.2 Vertical Multilamination of Fluid Layers Using a V-type Nozzle Array 3.8.3 Multilamination Using a Stack of Platelets with Microchannels 3.8.4 Multilamination Using a Stack of Platelets with Star-Shaped Openings 3.9 Decrease of Diffusion Path Perpendicular to the Flow Direction by Increase of Flow Velocity 3.9.1 Decrease of Layer Thickness by Hydrodynamic Focusing 3.10 Externally Forced Mass Transport, e.g. by Stirring. Ultrasonic Wave, Electrical and Thermal Energy 3.10.1 Dynamic Micromixer Using Magnetic Beads 3.11 References 4 Micro Heat Exchangers 4.1 Micro Heat Exchangers with Wide and Flat Channels 4.1.1 Cross-Flow Heat Exchange in Stacked Plate Devices 4.1.2 Cross-Flow Heat Exchange Based on Cross-Mixing 4.1.3 Counter-Flow Heat Exchange in Stacked Plate Devices 4.1.4 Electrically Heated Stacked Plate Devices 4.2 Micro Heat Exchangers with Narrow and Deep Channels 4.2.1 Heat Exchanger with One-Sided Structured Channels 4.2.2 Heat Exchanger with Double-Sided Structured Channels 4.3 Micro Heat Exchangers with Breakthrough Channels 4.4 Axial Heat Conduction 4.4.1 Numerical Calculations of the Influence of Material on Heat Transfer Efficiency 4.4.2 The Use of Thermal Blocking Structures 4.5 Permanent Generation of Entrance Flow by Fins 4.6 Generation of a Periodic Flow Profile by Sine-Wave Microchannels 4.7 Microtechnology-Based Chemical Heat Pumps 4.8 Performance Characterization of Micro Heat Exchangers 4.8.1 Temperature Profiles of Micro Heat Exchangers Yielded by Thermograms of Infrared Cameras 4.9 References 5 Microseparation Systems and Specific Analytical Modules for Microreactors 5.1 Microextractors 5.1.1 Partially Overlapping Channels 5.1.2 Wedge-Shaped Flow Contactor 5.1.3 Contactor Microchannels Separated by a Micromachined Membrane 5.1.4 Contactor Microchannels Separated by Sieve-Like Walls 5.1.5 Micromixer - Settler Systems 5.2 Microfilters 5.2.1 Isoporous-Sieve Microfilters 5.2.2 Cross-Flow Microfilters 5.3 Gas Purification Microsystems 5.4 Gas Separation Microdevices 5.5 Specific Analytical Modules for Microreactors 5.5.1 Analytical Modules for In-Line IR Spectroscopy 5.5.2 Analytical Module for Fast Gas Chromatography 5.6 References 6 Microsystems for Liquid Phase Reactions 6.1 Types of Liquid Phase Microreactors 6.2 Liquid/Liquid Synthesis of a Vitamin Precursor in a Combined Mixer and Heat Exchanger Device 6.3 Acrylate Polymerization in Micromixers 6.4 Ketone Reduction Using a Grignard Reagent in Micromixers 6.5 Laboratory-Scale Organic Chemistry in Micromixer/Tube Reactors 6.6 Dushman Reaction Using Hydrodynamic Focusing Micromixers and High-Aspect Ratio Heat Exchangers 6.7 Synthesis of Microcrystallites in a Microtechnology-Based Continuous Segmented-Flow Tubular Reactor 6.8 Electrochemical Microreactors 6.8.1 Synthesis of 4-Methoxybenzaldehyde in a Plate-to-Plate Electrode Configuration 6.8.2 Scouting Potentiodynamic Operation of Closed Microcells 6.9 References 7 Microsystems for Gas Phase Reactions 7.1 Catalyst Supply for Microreactors 7.2 Types of Gas Phase Microreactors 7.3 Microchannel Catalyst Structures 7.3.1 Flow Distribution in Microchannel Catalyst Reactors 7.3.2 Partial Oxidation of Propene to Acrolein 7.3.3 Selective Partial Hydrogenation of a Cyclic Triene 7.3.4 H 2 /O 2 Reaction 7.3.5 Selective Partial Hydrogenation of Benzene 7.3.6 Selective Oxidation of 1-Butene to Maleic Anhydride 7.3.7 Selective Oxidation of Ethylene to Ethylene Oxide 7.3.8 Reactions Utilizing Periodic Operation 7.4 Microsystems with Integrated Catalyst Structures and Heat Exchanger 7.4.1 Oxidative Dehydrogenation of Alcohols 7.4.2 Synthesis of Methyl Isocyanate and Various Other Hazardous Gases 7.4.3 H 2 /O 2 Reaction in the Explosion Regime 7.5 Microsystems with Integrated Catalyst Structures and Mixer 7.5.1 Synthesis of Ethylene Oxide 7.6 Microsystems with Integrated Catalyst Structures. Heat Exchanger and Sensors 7.6.1 Oxidation of Ammonia 7.6.2 H 2 /O 2 Reaction 7.7 Microsystems with Integrated Mixer, Heat Exchanger, Catalyst Structures and Sensors 7.7.1 HCN Synthesis via the Andrussov Process 7.8 References 8 Gas/Liquid Microreactors 8.1 Gas/Liquid Contacting Principles and Classes of Miniaturized Contacting Equipment 8.2 Contacting of Two Gas and Liquid Substreams in a Mixing Tee Configuration 8.2.1 Injection of One Gas and Liquid Substream 8.2.2 Injection of Many Gas and Liquid Substreams into One Common Channel 8.2.3 Injection of Many Gas and Liquid Substreams into One Packed Channel 8.2.4 Injection of Many Gas Substreams into One Liquid Channel with Catalytic Walls 8.2.5 Injection of Many Gas and Liquid Substreams into Multiple Channels 8.3 Generation of Thin Films in a Falling Film Microreactor 8.4 References 9 Microsystems for Energy Generation 9.1 Microdevices for Vaporization of Liquid Fuels 9.2 Microdevices for Conversion of Gaseous Fuels to Syngas by Means of Partial Oxidations 9.2.1 Hydrogen Generation by Partial Oxidations 9.2.2 Partial Oxidation of Methane in a Stacked Stainless Steel Sheet System 9.2.3 Partial Oxidation of Methane in a Microchannel Reactor 9.3 Microdevices for Conversion of Gaseous Fuels to Syngas by Means of Steam Reforming 9.3.1 Steam Reforming of Methanol in Microstructured Platelets 9.4 References 10 Microsystems for Catalyst and Material Screening 10.1 Parallel Screening of Heterogeneous Catalysts in a Microchannel Reactor 10.2 Parallel Screening of Heterogeneous Catalysts in Conventional Mini-Scale Reactors 10.3 References 11 Methodology for Distributed Production 11.1 The Miniplant Concept 11.1.1 Miniplant Concept for HCN Manufacture 11.1.2 The Disposable Batch Miniplant 11.2 Paradigm Change in Large-Scale Reactor Design Towards Operability and Environmental Aspects Using Miniplants 11.3 References Index

Kinetic spray coating method and apparatus

Abstract: A method and apparatus is disclosed for kinetic spray coating of substrate surfaces by impingement of air or gas entrained powders of small particles in a range up to at least 106 microns accelerated to supersonic velocity in a spray nozzle. Preferably powders of metals, alloys, polymers and mixtures thereof or with semiconductors or ceramics are entrained in unheated air and passed through an injection tube into a larger flow of heated air for mixing and acceleration through a supersonic nozzle for coating of an article by impingement of the yieldable particles. A preferred apparatus includes a high pressure air supply carrying entrained particles exceeding 50 microns through an injection tube into heated air in a mixing chamber for mixing and acceleration in the nozzle. The mixing chamber is supplied with high pressure heated air through a main air passage having an area ratio relative to the injection tube of at least 80/1.

Investigation of combustion emissions in a homogeneous charge compression injection engine: Measurements and a new computational model

Abstract: The CO and hydrocarbon emissions of a homogeneous charge compression injection engine have been explained by inhomogeneities in temperature induced by the boundary layer and crevices according to a stochastic reactor model. The boundary layer is assumed to consist of a thin film (laminar sublayer) and a turbulent buffer layer. The heat loss through the cylinder wall leads to a significant temperature gradient in the boundary layer. The partially stirred plug flow reactor (PaSPFR) model, a stochastic reactor model (SRM), has been used to model turbulent mixing between the boundary layer, crevices, and the turbulent core and to account for the chemical reactions within the combustion chamber. The combustion of natural gas in the engine is described by a detailed chemical mechanism that is incorporated in the SRM. Molecular diffusion induced by turbulent mixing is described by the simple interaction by exchange with the mean (IEM) mixing model. The turbulent mixing intensity that describes the decay of the species and temperature fluctuations is estimated from measurements of the velocity fluctuations and the integral length scale of the turbulent flow in the engine. Pressure, CO emissions, and unburned hydrocarbons are also measured. Comparison between the mean quantities obtained from the SRM and these measurements show very good agreement. It is demonstrated that the SRM clearly outperforms a previous PFR-based one-zone model. The PaSPFR-IEM model captures the pressure rise that could not be described exactly using a simple one-zone model. The emissions of CO and hydrocarbons are also predicted well. Scatter plots of the marginal probability density function of CO 2 and temperature reveal that the emissions of hydrocarbons and CO can be explained by stochastic particles that undergo incomplete combustion because they are trapped in the colder boundary layer or in the crevices.

Particle Segregation in Granular Flows Down Chutes

Abstract: Laboratory experiments with dry particles of different sizes and different densities, and different particle-liquid mixtures flowing down rectangular chutes show the relative importance of segregation mechanisms. In uniform steady flow experiments with binary mixtures of small and large particles, the small particles fall downward and the large particles migrate upward. In slow, dry, frictional flows, the downstream segregation is so efficient that zones of 100% small and large particles separated by a concentration jump form. In rapid, dry, collisional flows, segregation is less efficient because of diffusive mixing. Diffusive mixing smoothes vertical concentration profiles so that concentration jumps blur or disappear. The presence of a viscous fluid inhibits size segregation. Little to no segregation occurs when liquid density matches particle density.

Fuel injection system of internal combustion engine

Abstract: PROBLEM TO BE SOLVED: To provide simple constitution to perform the injection of fuel with high metering precision even during the generation of vapor. SOLUTION: An ECU 6 decides the generating state of vaporized fuel in a liquid injection injector 21 to perform injection of fuel in a liquid phase based on the detecting signals of a fuel pressure sensor 72 and a cooling water temperature sensor 75. A gas injection injector 22 to decide the generation state of vaporized fuel in a liquid injection injector 21 to effect fuel injection in a liquid phase and perform liquid injection in a gaseous phase according to the degree of the generation of vaporized fuel is caused to effect assist injection. Shortage in fuel due to injection of fuel in a gas liquid mixing state by the liquid injection injector 21 is prevented from occurring.

Water heating system

Abstract: A water heating system in which the output water temperature is regulated by a mixing valve which allows the temperature of the water contained within the water heater to be maintained at a much higher temperature without compromising safety. Significantly more hot water is therefore available for use yet the maximum temperature supplied to the various points of usage are within the safe limits. The system can be additionally configured to supply unmixed hot water to points of usage where a higher temperature is needed and a user is not exposed to the water such as for example in a dishwasher.

Effects of the Stirred Tank's Design on Power Consumption and Mixing Time in Liquid Phase

Abstract: The influence of the stirrer type and of the geometrical parameters of both tank and agitator (clearance of an impeller from tank bottom, impeller diameter, draft tube and geometry of the tank bottom) on power consumption and mixing time in liquid phase under turbulent regime conditions (Re > 104) have been studied. Different types of agitators have been used, namely Rushton turbine, 45° pitched-blade turbine, MIXEL TT and TTP propellers and 1-stage or 2-stage EKATO-INTERMIG propellers. All these stirrers were tested with the same power consumption per unit mass of liquid. On the basis of measured power consumption per unit mass, which is required to achieve the same degree of mixing, the results obtained in the present work show that the TTP propeller is the most efficient in liquid phase. Recommendations on the optimum geometric configuration have been made for each type of stirrer.

Centralized bicarbonate mixing system

Abstract: A centralized bicarbonate mixing system is provided for a plurality of dialysis machines of a dialysis clinic. The system includes a source of purified water, a mix tank, an eductor having a hopper for receiving dry bicarbonate material, a mixing pump and a mixing conduit loop connecting the mixing pump, the eductor and the mix tank so that as water is circulated by the mixing pump through the mixing conduit loop, the dry bicarbonate material is drawn into the eductor and mixed with the water. The system further includes a circulation tank, and a transfer conduit connecting the mixing conduit loop to the circulation tank, so that a mixed bicarbonate solution can be transferred from the mixing conduit loop to the circulation tank. The system further includes a circulation pump, and a circulation supply conduit connecting the circulation tank and the circulation pump so that mixed bicarbonate solution can be pumped from the circulation tank to the dialysis machines. The system is preferably constructed of cross-linked polyethylene and/or polypropylene plastic pipe and fittings, and is provided with heat exchangers so that the same can be heat disinfected. Furthermore, the use of the eductor and closed hopper allows for easy loading of dry bicarbonate material into the system, and for sanitary mixing of a batch of bicarbonate solution in the closed system.

Efficient mixing of polymer blends of extreme viscosity ratio : Elimination of phase inversion via solid-state shear pulverization

Abstract: A novel, continuous process, solid-state shear pulverization (S 3 P), efficiently mixes blends with different component viscosities. Melt mixing immiscible polymers or like polymers of different molecular weight often requires long processing times. With a batch, intensive melt mixer, a polyethylene (PE)/polystyrene (PS) blend with a viscosity ratio (low to high) of 0.019 required up to 35 min to undergo phase inversion. Phase inversion is associated with a morphological change in which the majority component, the high-viscosity material in these blends, transforms from the dispersed to the matrix phase, and may be quantified by a change from low to high mixing torque. In contrast, such blends subjected to short-residence-time (∼3 min) S 3 P yielded a morphology with a PS matrix and a PE dispersed phase with phase diameters ≤ 1 μm. Thus, S 3 P directly produces matrix and dispersed phases like those obtained after phase inversion during a melt-mixing process. This assertion is supported by the similarity in the near-plateaus in torque obtained in the melt mixer at short times with the pulverized blend and at long times with the non-pulverized blend. The utility of S 3 P to overcome problems associated with melt mixing like polymers of extreme viscosity ratio is also shown.

Suspension of High Concentration Slurry

Abstract: This paper presents experimental research carried out in a model mixing vessel on suspending solid particles at high concentrations. It was found that the maximum solid concentration at which slurry suspension can be maintained is approximately 0.90 when normalised by the bed packing coefficient. A higher exponent a-value was found for the dependency of just-off-bottom impeller speed on solids loading in the high solids loading range. At high solids loadings, radial impellers require relatively less power than axial flow impellers to suspend solids, the opposite to that observed in the low solids loading range. When operating in high solid concentration, there is an increase in power number for pitch-bladed turbines and a reduction in power number for Rushton turbines, in comparison with operating in water.

Mixing and Compaction Temperatures for Hot Mix Asphalt Concrete

Abstract: According to Superpave mixture design, gyratory specimens are mixed and compacted at equiviscous binder temperatures corresponding to viscosities of 0.17 and 0.28 Pa*s, respectively. These were the values previously used in the Marshal mix design method to determine the mixing and compaction temperatures. In order to estimate the appropriate mixing and compaction temperatures for Superpave mixture design, a temperature-viscosity relationship for the binder should be developed (ASTM D 2493, Calculation of Mixing and Compaction Temperatures). This approach is simple and provides reasonable temperatures for unmodified binders. However, some modified binders have exhibited unreasonably high temperatures for mixing and compaction using this technique. These high temperatures could result in construction problems, asphalt damage, and fume production. ASTM D 2493 was established for unmodified asphalt binders, which are Newtonian fluids at high temperatures. For these materials, viscosity does not depend on shear rate. However, most of the modified asphalt binders exhibit a phenomenon known as pseudoplasticity, in which viscosity depends on shear rate. Thus, at the high shear rates that occur during mixing and compaction, it is not necessary to use very high temperatures. A research study was undertaken to determine the shear rate during compaction so that the effect of this parameter could be included during viscosity measurements. The use of practical shear rate results in reasonable mixing and compaction temperatures for hot mix asphalt design and construction with modified asphalt binders. It was found that application of the shear rate concept rather than the traditional approach used for unmodified binders can reduce the mixing and compaction temperatures between roughly 14 to 38 degrees C for the former and 10 to 27 degrees C for the latter, depending on the type and the amount of modifier.

Continuous flow liquids/solids slurry cleaning, recycling and mixing system

Abstract: A continuous flow slurry cleaning method, apparatus and system including a filter portion and a mud re-circulation manifold for receiving partially filtered slurry, containing the slurry and mixing the slurry with liquid ready for use and thereby enabling a continuous, re-circulating flow through the filter portion The continuous flow slurry cleaning apparatus and system further include a tank for storing and delivering liquid ready to be used by a drilling machine The continuous flow slurry cleaning method, apparatus and system further includes a mud circulation/agitation system for keeping solids in suspension and for mixing additives along with the liquid ready for use and thereby modifying the makeup of the liquid ready for use

Pumping or mixing system using a levitating magnetic element, related system components, and related methods

Abstract: A system for pumping or mixing a fluid using a levitating, rotating magnetic bearing and various other components for use in a pumping or mixing system are disclosed. The magnetic bearing is placed in a fluid-containing vessel in close proximity to a superconducting element. A separate cooling source thermally linked to the superconducting element provides the necessary cooling to induce levitation in the magnetic bearing. The superconducting element may be thermally isolated, such that the bearing, the vessel, and any fluid contained therein are not exposed to the cold temperatures required to produce the desired superconductive effects and the resulting levitation. By using means external to the vessel to rotate and/or stabilize the magnetic bearing levitating in the fluid, including possibly rotating the superconducting element itself or moving it relative to the vessel, the desired effective pumping or mixing action may be provided.

Apparatus and method for preparing microparticles

Abstract: Apparatus and method for preparing microparticles. An emulsion is formed by combining two phases in a static mixing assembly. The static mixing assembly preferably includes a preblending static mixer and a manifold. The emulsion flows out of the static mixing assembly into a quench liquid whereby droplets of the emulsion form microparticles. The residence time of the emulsion in the static mixing assembly is controlled to obtain a predetermined particle size distribution of the resulting microparticles.

Mixing and pumping vehicle

Abstract: A vehicle, such as a truck, includes mixing and pumping equipment for mixing a liquid and a particulate material (e.g., cement) and for pumping the mixture. One application is to pump the mixture into a wellbore for cementing a casing or liner to the wellbore inner wall. The vehicle includes a cab, with the mixing and pumping equipment positioned behind the cab. The equipment includes one or more reservoirs, with at least one used as both a mixing and displacement tank. A hose assembly is also positioned on the vehicle. To reduce the weight load placed on the rear axle(s) of the vehicle, relatively heavy components, such as the pump, are placed further forward on the truck. In one arrangement, the pump may be placed between the cab and the one or more reservoirs.

Modelling of the Interaction between Gas and Liquid in Stirred Vessels

Abstract: Publisher Summary Although existing literature demonstrates substantial progress in developing computational fluid dynamics (CFD) methods for stirred tanks, most studies are limited to single-phase liquid flow. In modeling of multiphase mixtures, there are a range of additional complexities. Further development of CFD modeling is being investigated for gas–liquid contacting in a mixing vessel. This chapter highlights the general method of simulation, and discusses modeling of the gas–liquid interaction. It is shown that predictions of gas distribution and holdup are sensitive to the specification of the drag force. This force is usually determined according to the drag force correlation. There is evidence however that in a forced turbulent flow the drag coefficient on particles or bubbles is increased. Using the correlation, it is found that gas holdup is substantially underpredicted. Alternative methods of calculating drag coefficient in turbulent flow are found to increase the predicted holdup but give an incorrect pattern of gas distribution. A modified correlation based on that of Brucato et al. is found to give improved results, but the generality of the method is uncertain. To improve the accuracy of the CFD model, better knowledge of bubble drag coefficients is needed.

Mixing method and apparatus

Abstract: According to a new partial stream method, different reagents (I, II) may be mixed quickly and intensively, especially for the production of emulsions, in a dispersing apparatus (10) which has a rotor/stator system (40, 50) at a container (B) near the bottom. A hot initial product, e.g. containing wax, may be dispersed with a dosed partial stream (R I') of a cold carrier in a premixing chamber (60) via a feeding device (30, 38) below the rotor (50). The resulting mixture is then remixed with a cold main stream (R I) or a part hereof (R I'') fed from above. Contrary to the dispersing systems known, wherein mixing and shearing of the components is performed simultaneously in the region of maximum shearing gradient, the method of the invention separates both time and location of mixing and shearing by feeding said components into the premixing chamber (60). The basic principle is that an optimum emulsion be obtained by preparing a homogeneous phase mixture first.

Macro-Mixing and Streptomyces fradiae: Modelling Oxygen and Nutrient Segregation in an Industrial Bioreactor

Abstract: Some illustrative results are presented for a 3 m3 triple-impeller stirred reactor producing tylosin (using Streptomyces fradiae) being fed with air and a concentrated aqueous ammonium nitrate solution. The analysis is performed for a 3 × 2 (10 × 10) configuration of a networks-of-zones model comprising 600 zones. The gas-liquid flows, giving rise to circulation and bubble dispersion, are calculated assuming that bubbles move independently at their rise velocity without distorting the liquid flows being generated by the impellers. In this way the gas hold-up distribution in 3-D is obtained from simple continuity principles. Mass transfer and a 2nd order bioreaction may then be combined with gas-liquid flow to predict the spatial distribution of the (pseudo-stationary) concentration fields. The observed overall gas voidage, overall oxygen mass transfer and a locally measured dissolved oxygen level are all exactly matched by the simulations. The predicted segregated concentration fields show remarkably complicated patterns. Micro-organisms following stochastic paths around the vessel will experience wide variations in chemical environments.

Controlled Laboratory Investigations of Wellbore Concentration Response to Pumping

Abstract: The relationship between the ground water sample and the surrounding ground water environment is controlled by wellborn flow and mixing that carry ground water to the sampling device. Controlled laboratory conditions and uniform inflow and inflowing concentration allowed detailed investigations of wellbore concentration responses to pump-induced flow and mixing independent of external complicating influences. During pumping from the top of the screen, the results agreed with wellbore flow theory except for high-frequency, high-amplitude concentration fluctuations and mixing with the blank casing due to slight density contrasts (∼0.005%). Concentration fluctuations indicated partial mixing of ground water with well water and declining concentrations in the blank casing indicated that convection due to the slight density contrast overcame pump-induced velocities. During pumping from the bottom of the well, opposing forces of buoyancy and pumping produced small-scale cumulative mixing as the ground water from different portions of the screen approached the pump. Even during low-flow pumping (i.e., 220 mL/min), 5% of the water was prepurge well water after five well volumes were pumped. In the field the density contrasts that resulted in these mixing processes might be caused by a slight cooling of the wellhead or a slight increase in temperature with depth (>0.2°C/m). If the temperature gradient was more pronounced, the convective mixing of screen water with the potentially altered casing water would be more thorough and sampling without mixing would not be possible. If the temperature gradient is stable or if the water in the blank casing is not significantly altered, casing water mixing will not present a problem.