Showing papers on "Mixing (process engineering) published in 2003"

Formation of droplets and mixing in multiphase microfluidics at low values of the Reynolds and the capillary numbers

Abstract: This paper reports an experimental characterization of a simple method for rapid formation of droplets, or plugs, of multiple aqueous reagents without bringing reagents into contact prior to mixing. Droplet-based microfluidics offers a simple method of achieving rapid mixing and transport with no dispersion. In addition, this paper shows that organic dyes at high concentrations should not be used for the visualization of flow patterns and mixing of aqueous plugs in multiphase flows in this system (fluorinated carrier fluid and PDMS microchannels). It reports an inorganic dye that can be used instead. This work focuses on mixing in plugs moving through straight channels. It demonstrates that, when traveling through straight microchannels, mixing within plugs by steady recirculating flow is highly sensitive to the initial distribution of the aqueous reagents established by the eddy flow at the tip of the forming plug (twirling). The results also show how plugs with proper distribution of the aqueous reagents could be formed in order to achieve optimal mixing of the reagents in this system.

Chemical processing and micromixing in confined impinging jets

Abstract: Rapid processes such as certain organic reactions or precipitations at high supersaturation require the rapid mixing provided by jet mixers. Micromixing in a confined impinging jets (CIJ) mixer was characterized employing the Damkohler number to correlate processing. A scaling theory for the characteristic micromixing time, proportional to momentum diffusion starting at the Kolmogorov microscale, is shown as sufficient to express the micromixing performance of the CIJ mixer. A recently characterized second-order competitive reaction set is used as a “chemical ruler” to assign an absolute value to the mixing time in the CIJ mixer. A wide range of characteristic time (320 to 5 ms) is evaluated with hydrochloric acid competing for sodium hydroxide neutralization or 2,2-dimethoxypropane acid catalyzed hydrolysis. This reaction set was sensitive enough to detect the onset of a turbulent-like flow at a Re of 90 and was able to demonstrate a decrease in undesired products up to the highest Re tested, 3,800 or a jet velocity of 19 m/s. It represents a significant advancement to the reaction sets and techniques used for previous mixing studies, which are reviewed. Experiments verify the characteristic mixing time in a CIJ mixer scales as the inverse of the jet velocity to the three halves power, and the “mesomixing volume” (the volume over which the majority of flow energy was dissipated) is best approximated as proportional to the internozzle separation cubed. For each of the different jet diameters, chamber diameters and outlet configurations tested, the selectivity of the reaction scaled linearly with the Damkohler number, as determined from the known reaction kinetics and the calculated Kolmogorov diffusion time. The first full characterization is provided of micromixing in impinging jets that allows the prediction of mixing performance, reaction selectivity, and scale-up criteria.

Liquid Droplet Dispersions Formed by Homogeneous Liquid−Liquid Nucleation: “The Ouzo Effect”

Abstract: The “ouzo effect” enables one to create a dispersion of small droplets in a surrounding liquid phase without the use of surfactants, dispersing agents, or mechanical agitation: a phenomenon which can be of value in many disciplines. In the quantitative studies presented here, dispersions of oil droplets in water are formed by the addition of water to a solution of the oil dissolved in a solvent. This causes the oil to supersaturate and then nucleate into small droplets. The mean droplet diameter is a function only of the oil-to-solvent ratio at a given temperature. The number density of droplets formed can be controlled independently from the droplet diameter by changing the amount of water added. Smaller droplets are formed by using more hydrophilic cosolvents. The droplet size distribution is typically log−normal. The width of the distribution can be narrowed by mixing the components at an elevated temperature and then allowing the dispersion to cool.

Process intensification of biodiesel production using a continuous oscillatory flow reactor

Abstract: Oscillatory flow reactors (OFRs) are a novel type of continuous reactor, consisting of tubes containing equally spaced orifice plate baffles. An oscillatory motion is superimposed upon the net flow of the process fluid, creating flow patterns conducive to efficient heat and mass transfer, whilst maintaining plug flow. Unlike conventional plug flow reactors, where a minimum Reynolds number must be maintained, the degree of mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio. Many long residence time processes are currently performed in batch, as conventional designs of plug flow reactor prove to be impractical due to their high length-to-diameter ratios, which lead to problems such as high capital cost, large 'footprint', high pumping costs and, also control is difficult. The OFR allows these processes to be converted to continuous, thereby intensifying the process. The transesterification of various natural oils to form 'biodiesel' is a 'long' reaction, usually performed in batch. Conversion to continuous processing should improve the economics of the process, as the improved mixing should generate a better product (rendering the downstream separation processes easier), at lower residence time (reduction in reactor volume). These improvements can decrease the price of 'biodiesel', making it a more realistic competitor to 'petrodiesel'. This paper shows that it is feasible to perform this reaction in an OFR at a lower residence time. The reaction was performed in a pilot-scale plant, using rapeseed oil and methanol as the feedstocks, and NaOH as the catalyst. # 2003 Society of Chemical Industry

Ultrafast microfluidic mixer and freeze-quenching device.

Abstract: The freeze-quenching technique is extremely useful for trapping meta-stable intermediates populated during fast chemical or biochemical reactions. The application of this technique, however, is limited by the long mixing time of conventional solution mixers and the slow freezing time of cryogenic fluids. To overcome these problems, we have designed and tested a novel microfluidic silicon mixer equipped with a new freeze-quenching device, with which reactions can be followed down to 50 μs. In the microfluidic silicon mixer, seven 10-μm-diameter vertical pillars are arranged perpendicular to the flow direction and in a staggered fashion in the 450-pL mixing chamber to enhance turbulent mixing. The mixed-solution jet, with a cross section of 10 μm × 100 μm, exits from the microfluidic silicon mixer with a linear flow velocity of 20 m/s. It instantaneously freezes on one of two rotating copper wheels maintained at 77 K and is subsequently ground into an ultrafine powder. The ultrafine frozen powder exhibits e...

Thermoplastic processing of protein-based bioplastics: Chemical engineering aspects of mixing, extrusion and hot molding

Abstract: Proteins, as heteropolymers, offer a large range of possible interactions and chemical reactions. The thermoplastic behavior of proteins has been studied in order to produce bioplastics by thermal or thermomechanical processes such as mixing, extrusion or hot molding. The extrusion trials were performed by using a corotating twin-screw extruder, recording torque, temperature and die pressure. Batch mixing was done in a two blade counter-rotating mixer, with continuous recording of torque and product temperature. Proteins were alternatively extruded, mixed or hot molded under a large range of processing conditions. Protein aggregation during each process was estimated from the accumulation of SDS-insoluble protein fraction. Protein aggregation evidences a cross-linking reaction the activation energy of which was dependent on the thermoplastic process used. The increase in network density appears to be induced by the severity of the treatment: temperature and shear strongly affect the structural characteristics of the protein-based bioplastics.

Particle concentration and mixing characteristics of moderate-to-dense solid-liquid suspensions

Abstract: Mixing time, power consumption, and solids concentration were measured in solid−liquid flow in a T = 290 mm vessel stirred by a Rushton turbine (D = T/3). The influence of particle size, density, and concentration, as well as impeller off-bottom clearance, on the mixing characteristics of two-phase flow was studied in the Reynolds number range 10 000 < Re < 200 000 for concentrations up to 15.5 vol %. The mixing time measurements revealed the presence of a peak in the number of revolutions necessary to achieve full “mixedness”, in comparison to the single-phase results. Power consumption was determined with a strain gauge technique, and the power number variation with impeller speed showed a similar trend for all slurries tested. The local solids concentration was measured at different heights and radii in the vessel using a conductivity probe to study the quality of solids distribution and the amount of solids suspended with speed.

Storage water heater

Abstract: PROBLEM TO BE SOLVED: To provide a storage water heater having little temperature fluctuation even if there is rapid flow rate change. SOLUTION: The storage water heater includes a hot water storage tank 9, a tapping pipe 12 delivering high temperature water from the hot water storage tank 9, a first water supply pipe 13 supplying water to the hot water storage tank 9, a mixing means 15 for connecting the tapping pipe 12 and a second water supply pipe 14 branched from the first water supply pipe 13 and mixing the water and the hot water, a hot water supply pipe 44 supplying the water and hot water mixed by the mixing means 15 to a hot water supply terminal 11, a flow rate detecting means 17 for detecting a flow rate of hot water flowing through the hot water supply pipe 44, a temperature detecting means 16 for detecting a temperature of the hot water and water mixed in a downstream side of the mixing means 15, and a controller controlling the mixing means 15 on the basis of detected values of the flow rate detecting means 17 and/or the temperature detecting means 16. When the flow rate detecting means 17 is detecting delivery of the hot water and water, if a flow rate difference of a predetermined flow rate or more is detected within a certain period, a mixing ratio of the hot water and water of the mixing means 15 is set at a predetermined mixing ratio. COPYRIGHT: (C)2010,JPO&INPIT

Gravity-driven flow of liquid films and droplets in horizontal tube banks

Abstract: Liquid films falling over banks of internally cooled horizontal tubes are often used to absorb mass from a surrounding vapor This arrangement is particularly suitable for absorption processes where the vapor has a high heat of absorption and where high transfer rates and low pressure drops are required, as is the case of absorption heat pumps and other chemical processes When the liquid film presents a significant resistance to heat and mass transfer, understanding the motion of the film is critical However, mathematical models of these types of systems in the literature have generally made use of many simplifying assumptions about the behavior of the falling liquid The formation, detachment, and impact of droplets and the associated waves and film disturbances can all affect the mixing of the liquid and can enhance transfer rates accordingly The objective of this paper is to identify and visually document these deviations from idealized film behavior and discuss their implications on the heat and mass transfer processes, which are important to consider in the development of mechanistic models of the absorption process

Method and apparatus for mixing fluids

Abstract: The invention relates in general to methods of controlled mixing one fluid with another. In particular it relates to a distributed direct fluid contactor including arrays of streamlined perforated tubes distributed across a flow to efficiently contact and mix one or more fluids flowing through one or more tubes with a second fluid flowing across those tubes. These distributed contactors thereby mix the fluids in a fairly uniform fashion causing a prescribed uniformity or variation in the ratio of the first to second fluid across the space. This thereby to generally creates and controls the physical and/or chemical changes in those fluids, including evaporation, condensation, forming powders and conducting chemical reactions including combustion.

Prediction of Cloud Height for Solid Suspensions in Stirred Tanks

Abstract: For solids loadings greater than 10 weight percent in a stirred tank, a clear interface may form towards the top of the vessel at what is known as the cloud height. Under these conditions, mixing between the lower solids rich volume (the cloud) and the upper clear volume is very limited. This is of critical importance in slurry catalyst reactor design, as the poor mixing in the clear layer will lead to large amounts of unreacted fluid. This investigation concentrates on developing a model for the prediction of the solids cloud height. The model is based upon two essential features of the flow: the velocity decay in the three-dimensional wall jets which form along the baffles, and the impeller speed required to fully suspend the solids off the bottom of the tank ( N js ).

Foamed cleaning liquid dispensing system

Abstract: A foamed cleaning liquid dispensing system (100) for use in a washing machine (102) includes a cleaning liquid dispenser (120) and a foaming device (122). The cleaning liquid dispenser includes an output flow of cleaning liquid (124), which is received by the foaming device. The foaming device includes an input flow of air (126) and a mixing member (128), in which the flows of air and the cleaning liquid are combined to form an output flow of foamed cleaning liquid (116) that is directed to a washing chamber (108) of the washing machine.

Axial liquid mixing in high‐pressure bubble columns

Abstract: Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn-turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid-phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid-phase turbulence. The scale-up effect on liquid mixing reduces as the pressure increases.

Burner with oxygen and fuel mixing apparatus

Abstract: An oxygen-fuel combustion system combines oxygen and fuel to produce a flame. The system distributes oxygen to a stream of fluidized, pulverized, solid fuel at various sites before and after ignition. The system is operable to vary the concentration of oxygen in an oxygen-fuel mixture extant at those sites.

Mixing and condensation in a wet granular medium.

Abstract: We have studied the effect of small amounts of added liquid on the dynamic behavior of a granular system consisting of a mixture of glass beads of two different sizes. Segregation of the large beads to the top of the sample is found to depend in a nontrivial way on the liquid content. A transition to viscoplastic behavior occurs at a critical liquid content, which depends upon the bead size. We show that this transition can be interpreted as a condensation due to the hysteretic liquid bridge forces connecting the beads, and we provide the corresponding phase diagram.

Interphase drag coefficients in gas–solid flows

Abstract: Gassolid fluidized-bed reactors are commonly used in the process industries due to their high operational efficiency regarding, for instance, solids mixing and heat and mass transŽ.

Mixing in tanks agitated by jets

Abstract: Experiments have been carried out to study the effects of various parameters such as nozzle diameter, angle of inclination and jet velocity, on mixing time. The dependence of mixing time on the nozzle angle has been explained based on the flow patterns and concentration profiles. It has been observed that an increase in the nozzle diameter reduces the mixing time at a given level of power consumption. The energy efficiency of the jet mixers has been compared with impeller stirred tanks. Attempts have been made to identify the correlation (from previous literature) that could satisfactorily predict the experimental results obtained.

Natural gas vapor recondenser system

Abstract: An apparatus for re-liquefying boil-off gas produced by liquid natural gas is described. The apparatus is made up of a collector, wherein the collector contains liquid natural gas, at least one first pump, wherein the first pump is in or adjacent to the liquid natural gas collector, a compressor, wherein the compressor communicates with the liquid natural gas (LNG) collector by a first conduit, at least one mixing device, wherein the mixing device communicates with the compressor by a second conduit, and wherein the mixing device communicates with the first pump by a third conduit, at least one separating device, wherein the separating device communicates with the mixing device by a fourth conduit, and wherein the separating device also communicates with the liquid natural gas (LNG) collector by a fifth conduit.

Cementing materials for filling, slurry and preparing and filling processes

Abstract: A gelatining material similar to cream for filling underground working surface is preapred from the Ca-contained non-crystal and microcrystal material, alkali and/or sulfur contained exciting material, active material, aggregate and regulator A filling slurry is prepared from said gelatining material, filling aggregate, fine particles, regulator and water through heating to at least 18 degC andproportional mixing

Preparation of metal nanoparticles and nanocomposites therefrom

Abstract: Disclosed are nanocomposites made of guest metal nanoparticles and metal oxide sols made by mixing at least one metal alkoxide, at least one organosilane, at least one boron oxide compound, and a liquid. Also disclosed are dielectric composites containing a dielectric material such as a polymer and the nanocomposites.

Mixture comprising sulphonic acid containing vinyl, polymer electrolyte membrane comprising polyvinylsulphonic acid and the use thereof in fuel cells

Abstract: The present invention relates to a proton-conducting polymer membrane which is based on polyvinylsulphonic acid and is obtainable by a process comprising the steps A) mixing of a polymer with vinyl-containing sulphonic acid, B) formation of a flat structure using the mixture from step A) on a support, C) polymerization of the vinylsulphonic acid present in the flat structure from step B). Owing to its excellent chemical and thermal properties, a membrane according to the invention can be used in a wide variety of applications and is particularly useful as polymer electrolyte membrane (PEM) in PEM fuel cells.

Method for manufacturing toner

Abstract: PROBLEM TO BE SOLVED: To provide a method for manufacturing toners which have high specific resistance and excellent electrostatic chargeability, are uniformly fixed with particulates on their surfaces and make it possible to obtain high-quality images with lessened deterioration of the toners for a long period of time SOLUTION: This method for manufacturing the toners have a stage for making a core particle dispersion by dispersing core particles into an aqueous solution; a stage for making a particulate dispersion by dispersing particulates by a nonionic surfactant and a cationic surfactant; a stage for mixing the particulate dispersion into the core particle dispersion, making the pH of the resultant solution mixture smaller than 7 and uniformly adhering the particulates to the core particle surfaces, a stage for fixing the particulates to the core particle surfaces by controlling the temperature of the solution mixture to a temperature range from above the glass transition temperature (Tg) of the core particles to the glass transition temperature (Tg) +50 degC or below and applying impact force thereto by a media dispersing machine; a stage for adding an anionic surfactant to the solution mixture and washing the same and a stage for executing drying and taking out the toner particles of powder