High Mass Transfer Rates Research Articles

MASS TRANSFER CORRELATION FOR THE REMOVAL OF COPPER IONS FROM WASTEWATER

One of the biggest problems with ore processing in extractive metallurgical industries is the high toxicity of the heavy metals waste content (e.g., copper, lead, nickel and chrome). This work investigates the copper (II) íons removal from aqueous solutions in concentrations up to 1000 ppm. Therefore, a fluidized bed electrolytic reactor was used with flow-by configuration considered as a hopeful method due to the large specific surface area and the high mass transfer rate. The performance of the electrochemical reactor was investigated by using different porosities. Dimensionless Sherwood and Reynolds numbers were correlated to characterize the mass transport properties of the reactor, and they were fitted to the equation Sh = a.Reb.Sc1/3.

Propane combustion in non-adiabatic microreactors: 1. Comparison of channel and posted catalytic inserts

The reduction in size of catalytic microreactors results in high heat and mass transfer rates and a significant increase in the surface area to volume ratio. A further increase in the catalytic surface area can be achieved in a scaled-down version of fixed bed reactors. Since micro-fixed bed reactors are often deemed impractical due to their large pressure drops, one could use precisely structured inserts to increase the surface area, enhance mixing and manipulate the flow distribution. Catalytic propane combustion in microreactors with multi-channel and posted inserts, which consist of multiple static structures (walls separating various channels and pillar-like structures, respectively) in the flow channel of a microreactor, is considered in this series of two papers. In this first paper, we present numerical comparison of multi-channel and posted catalytic inserts for non-adiabatic self-sustained propane combustion. The inserts are oriented axially along the flow direction. We show that channel and post microreactors have similar performance for low thermal conductivity of the inserts. The in-line arrangement of the posted structures is preferred over a staggered arrangement because the former provides higher propane conversion and more stable combustion. The role of thermal conductivity of the microreactor wall structure and the catalytic inserts is investigated. The thermal conductivity of the microreactor structure affects the performance of the posts but not the channels; this is contrary to the effect of catalyst insert thermal conductivity where it is vice-versa. The channel microreactor is more stable towards high flow-rate blowout limit, whereas the post microreactor is significantly more stable at the lower flow-rate extinction limit. This results in stable operation of the post microreactor under more fuel-lean mixtures than the channel microreactor.

Germinated Brown Rice Drying by Hot Air Fluidization Technique

Germinated brown rice containing moisture content of 52% dry basis (db) needs to be dried in a reasonable time in order to prevent the growth of microorganisms. Fluidized bed drying is a possible method because this drying technique provides a high mass and heat transfer rate and high-temperature drying can be used. However, such a high-performance dryer may affect the quality of the finished product. The effect of fluidized bed drying temperatures (90, 110, 130, and 150°C) on the quality of germinated brown rice, that is, cooked rice textural property, γ-aminobutyric acid (GABA) level, fissured grain, and microorganisms was therefore investigated. The germinated brown rice was dried to the moisture contents of 18–20% (db), tempered for 30 min, and ventilated by ambient air until the sample moisture content reached 13–15% (db). The experimental results showed that the drying rate increased with increasing drying temperature. The high drying rate, in particular drying at 130°C or higher, caused severe fissuring on the kernel and this fissuring subsequently affected the cooked rice shape and textural property of rice; that is, hardness. The GABA contents of germinated brown rice insignificantly changed with drying temperatures and did not depend on the rice varieties. The populations of attached bacteria, yeast, and mold on the surface of the dried samples were less than 104 colony-forming units (CFU)/g, which is safe for food.

Performance evaluation for carbonation of steel-making slags in a slurry reactor

CO2 sequestration by the aqueous carbonation of steel-making slag under various operational conditions was investigated in this study. The effects of the operational conditions, including type of steel-making slag, reaction time, reaction temperature, and CO2 flow rate, on the performance of the carbonation process were evaluated. The results indicated that the BOF slag had the highest carbonation conversion, approximately 72%, at a reaction time of 1h, an operating pressure of 101kPa and a temperature of 60°C due to its higher BET surface area of BOF slag compared to UF, FA, and BHC slags. The major factors affecting the carbonation conversion are reaction time and temperature. The reaction kinetics of the carbonation conversion can be expressed by the shrinking-core model. The measurements of the carbonated material by the SEM and XRD instruments provide evidence indicating the suitability of using the shrinking-core model in this investigation. Comparison of the results with other studies suggests that aqueous carbonation by slurry reactor is viable due to its higher mass transfer rate.

Drying of Starch Suspension in Spouted Bed with Inert Particles: Physical and Thermal Analysis of Product

Drying in a spouted bed with inert particles promotes high heat and mass transfer rates due to the gas–solid contact, which in turn is successfully achieved by particles' cyclic movements. Because of its advantages and versatility, spouted bed drying of suspensions on inert particles is a potential alternative to flash and spray drying and has received attention in research and development in recent years. In this context, this article describes the drying process of cassava starch suspension (35% initial solids content) in a laboratory-scale cone-cylindrical spouted bed dryer with polypropylene particles. The setup consists of a cone-cylindrical spouted bed dryer (internal angle of 60°, 20-cm column diameter, and 5-cm inlet orifice diameter) with top feeding of suspension, which is sprayed by a double-fluid atomizer. The study focused on the fluid dynamics of polypropylene particles at inlet air temperatures of 60, 75, and 90°C and the effects of air temperature on dried starch properties, such as gelatinization temperature, pasting temperature, particle size distribution, crystalline profile, and final moisture content. The pressure drop fluid dynamic curves did not allow a proper analysis and assessment of minimum spout air flow when air was atomized in the bed. Therefore, the minimum spout air flow was determined by the visual observation of the fountain height in this case. Inlet air temperatures did not show a significant difference in the minimum spout air flow, but the bed presented dynamic instability with increasing inlet air temperature. The results showed that the spout fluid dynamic regime during drying was stable with air flow around 1.5 times the minimum spout air flow in the range of inlet air temperature studied. Drying air temperature influenced final moisture content of samples, which was lower than 13% for all conditions. However, physical properties of dried starch were not affected by process conditions.

Photoreactors for Wastewater Treatment: A Review

Photochemical oxidation of organic and inorganic pollutants is rapidly becoming an attractive technique for water purification and wastewater treatment. Since artificial sources of light require much energy delivery, this method is recommended for toxic contaminants in a specific concentration range below the recommended levels for recovery and above the levels for conventional biological treatment. Selection of a light source and an oxidation system and determination of key-parameters play an important role in the treatment efficiency. Sufficient UV penetration into the radiated liquid is of crucial importance; especially for an opaque environment the UV radiation is only available very close to the UV lamp surface. High mass transfer rates for efficient interaction between the pollutant and the photocatalyst and for high oxygen uptake at the gas-liquid interface is another requirement for practical applications. In this regard, reactor design for efficient wastewater treatment has been a challenging problem. Many types of photoreactors have already been studied, reported and patented. This paper presents a revision of some conventional and novel photoreactors equipped with UV/vis lamps or working under solar radiation for wastewater treatment in laboratory and industrial scales. Keywords: Advanced Oxidation Processes (AOPs), catalyst immobilization, photocatalysis, photoreactor, wastewater treatment, UV/H2O2, UV/TiO2.

SIMULTANEOUS X-RAY AND ULTRAVIOLET OBSERVATIONS OF THE SW SEXTANTIS STAR DW URSAE MAJORIS

We present the first pointed X-ray observation of DW Ursae Majoris, a novalike cataclysmic variable (CV) and one of the archetype members of the SW Sextantis class, obtained with the XMM-Newton satellite. These data provide the first detailed look at an SW Sex star in the X-ray regime (with previous X-ray knowledge of the SW Sex stars limited primarily to weak or non-detections in the ROSAT All Sky Survey). It is also one of only a few XMM-Newton observations (to date) of any high mass transfer rate novalike CV, and the only one in the evolutionarily important 3–4 hr orbital period range. The observed X-ray spectrum of DW UMa is very soft, with ∼95% of the detected X-ray photons at energies <2 keV. The spectrum can be fit equally well by a one-component cooling flow model, with a temperature range of 0.2–3.5 keV, or a two-component, two-temperature thermal plasma model, containing hard (∼5–6 keV) and soft (∼0.8 keV) components. The X-ray light curve of DW UMa shows a likely partial eclipse, implying X-ray reprocessing in a vertically extended region, and an orbital modulation, implying a structural asymmetry in the X-ray reprocessing site (e.g., it cannot be a uniform corona). We also obtained a simultaneous near-ultraviolet light curve of DW UMa using the Optical Monitor on XMM-Newton. This light curve is similar in appearance to published optical–UV light curves of DW UMa and shows a prominent deep eclipse. Regardless of the exact nature of the X-ray reprocessing site in DW UMa, the lack of a prominent hard X-ray total eclipse and very low fraction of high energy X-rays point to the presence of an optically and geometrically thick accretion disk that obscures the boundary layer and modifies the X-ray spectrum emitted near the white dwarf.

The analysis of simultaneous clove/oregano and clove/thyme supercritical extraction

The goal of present work was to investigate and explain kinetics and mass transfer phenomena occurring during the SFE from the mixture of two plants with different initial composition. The extractions from pure clove, oregano and thyme as well as from clove/oregano (C/O) and clove/thyme (C/T) mixtures with various initial compositions of plant material were carried out using supercritical CO2 at 10MPa and 40°C. The results indicated that presence of light compounds in supercritical CO2 originated from the oregano leaves or thyme at the beginning of extraction process increases the extraction rate of compounds from clove bud. Only small added amounts of oregano or thyme to clove bud (C/O – 90:10%, w/w; or C/T – 84:16%, w/w) in the starting plant mixture had the same effect resulted in the similar and the highest increase of the extraction rate and had negligible influence on total extraction yield compared to extract isolated from pure clove. Different mathematical models were used for simulation of experimental data which showed that the highest increase of the solubility of extractable compounds in supercritical CO2 as well as the highest mass transfer rate in the solid phase during extractions existed during extraction from C/O (90:10, w/w) and C/T (84:16, w/w) mixtures. Decrease of SC CO2 consumption or shorter time of extraction necessary for achieving desired extract yield in the case of SFE of the clove buds could be important for industrial-scale application.

Spin-resolved spectroscopy of the intermediate polar DQ Her

We present high-speed spectroscopic observations of the intermediate polar DQ Herculis. Doppler tomography of two He I lines reveals a spiral density structure in the accretion disc around the white dwarf primary. The spirals look very similar to the spirals seen in dwarf novae during outburst. DQ Her is the first well established intermediate polar in which spirals are seen, that are in addition likely persistent because of the system's high mass transfer rate. Spiral structures give an alternative explanation for sidebands of the WD spin frequency that are found in IP light curves. The Doppler tomogram of He II 4686 indicates that a large part of the emission is not disc-like. Spin trails of spectra reveal a pulsation in the He II 4686 emission that is believed to result from reprocessing of X-rays from the white dwarf's magnetic poles in the accretion flow close to the WD. We confirm the previous finding that the pulsation is only visible in the red-shifted part of the line when the beam points to the back side of the disc. The absence of reprocessed light from the front side of the disc can be explained by obscuration by the front rim of the disc, but the absence of extra emission from the blue-shifted back side of the disc is puzzling. Reprocessing in accretion curtains can be an answer to the problem and can also explain the highly non-Keplerian velocity components that are found in the He II 4686 line. Our spin trails can form a strong test for future accretion curtain models, with the possibility of distinguishing between a spin period of 71s or 142s. Spin trails of data taken at selected orbital phases show little evidence for a significant contribution of the bright spot to the pulsations and allow us to exclude a recent suggestion that 71s is the beat period and 70.8s the spin period.

Research Activities on Supercritical Fluid Science in Food Biotechnology

This article serves as an overview, introducing the currently popular area of supercritical fluids and their uses in food biotechnology. Within each application, and wherever possible, the basic principles of the technique, as well as a description of the history, instrumentation, methodology, uses, problems encountered, and advantages over the traditional, non-supercritical methods are given. Most current commercial application of the supercritical extraction involve biologically-produced materials; the technique may be particularly relevant to the extraction of biological compounds in cases where there is a requirement for low-temperature processing, high mass-transfer rates, and negligible carrying over of the solvent into the final product. Special applications to food processing include the decaffeination of green coffee beans, the production of hops extracts, the recovery of aromas and flavors from herbs and spices, the extraction and fractionation of edible oils, and the removal of contaminants, among others. New advances, in which the extraction is combined with reaction or crystallization steps, may further increase the attractiveness of supercritical fluids in the bioprocess industries. To develop and establish a novel and effective alternative to heating treatment, the lethal action of high hydrostatic pressure CO2 on microorganisms, with none or only a minimal heating process, has recently received a great deal of attention.

Carbon dioxide degassing in fresh and saline water. I: Degassing performance of a cascade column

A study was undertaken to measure carbon dioxide degassing in a cascade column operating with both fresh (0‰) and saline water (35‰ NaCl) at 15 °C. The cascade column contained bio-block type packing material, was 1.7 m long in each dimension, and was tested both with and without countercurrent air exchange. The CO 2 concentration of the influent and effluent water was measured using submersible infrared CO 2 probes over an influent range of 10–60 mg L −1 CO 2. Carbon dioxide degassing was quantified in terms of the mass transfer coefficient ( k L a, log concentration driving force divided by packing height) and the CO 2 stripping efficiency (the difference in CO 2 concentration between the influent water and the effluent water that has re-established chemical equilibria approximately 1 min after exiting the column). Mass transfer coefficients were similar between fresh and saline water. Countercurrent air flow did not improve stripping efficiency, probably because the column was already operating at a high mass transfer rate with no active ventilation and there was sufficient passive, concurrent air flow to overcome the accumulation of CO 2 inside the column. There was a positive relationship between influent CO 2 concentration and CO 2 stripping efficiency, which ranged from 67% to 89% CO 2 stripped in a single pass. The CO 2 stripping efficiency was lower in saline water compared to freshwater at equivalent influent CO 2 concentrations. The dependence of CO 2 stripping efficiency on salinity was attributed to differences in the ionization fractions of inorganic carbon species in the effluent water. The results indicate that CO 2 removal will be more problematic for saline or seawater recirculating systems compared to freshwater systems.

PIV/PLIF Study of Impinging Jet Ozone Bubble Column with Mixing Nozzles

This paper introduces the results obtained from a particle image velocimetry/planer laser-induced fluorescence (PIV/PLIF) system used in characterizing an impinging jet ozone bubble column with mixing nozzles. This research aims at evaluating the mixing effect resulting from the nozzle diffusers attached to the outlets of the impinging jets' injectors. The PIV system was used to study the flow patterns of the liquid and gas phases under different superficial gas and liquid velocities (uG and uL, respectively) values (from 0.002 to 0.017 m/s and from 0.008 to 0.024 m/s, respectively). Furthermore, a particle dynamics analyzer (PDA) system was used to characterize the bubble sizes under the same operating conditions. The PLIF system was used to determine the liquid axial dispersion coefficient (DL, m2/s) for the mentioned range of operating conditions. The column average gas hold-up (ϵG) and specific interfacial area (a) were then determined in order to evaluate the column's mass transfer efficiency. The results showed that higher mass transfer rates can be obtained by using this column, as high ϵG, and were achieved.

Enzyme Catalysis in an Aqueous/Organic Segment Flow Microreactor: Ways to Stabilize Enzyme Activity

Multiphase flow microreactors benefit from rapid mixing and high mass transfer rates, yet their application in enzymatic catalysis is limited due to the fast inactivation of enzymes used as biocatalysts. Enzyme inactivation during segment flow is due to the large interfacial area between aqueous and organic phases. The Peclet number of the system points to strong convective forces within the segments, and this results in rapid deactivation of the enzyme depending on segment length and flow rate. Addition of surfactant to the aqueous phase or enzyme immobilization prevents the biocatalyst from direct contact with the interface and thus stabilizes the enzyme activity. Almost 100% enzyme activity can be recovered compared to 45% without any enzyme or medium modification. Drop tensiometry measurements point to a mixed enzyme-surfactant interfacial adsorption, and above a certain concentration, the surfactant forms a protective layer between the interface and the biocatalyst in the aqueous compartments. Theoretical models were used to compare adsorption kinetics of the protein to the interface in the segment flow microreactor and in the drop tensiometry measurements. This study is the basis for the development of segment flow microreactors as a tool to perform productive enzymatic catalysis.

Supersoft X-ray sources: Confronting the van den Heuvel paradigm

The origin of the extremely soft (low temperature) X-rays produced in the supersoft X-ray sources (or SSS) has been a subject of debate for much of the 25 years since their discovery. The currently accepted paradigm is that they are Eddington-limited accreting white dwarfs in which the accreted material is undergoing steady nuclear burning, thereby achieving the high luminosities recorded from the brightest SSS in the Magellanic Clouds. Such a model requires an extremely high mass transfer rate from the donor, only achievable via thermally unstable mass transfer from a massive (>1 M ⊙) donor. An ideal SSS to probe this model in detail is the (only) recurrent, transient SSS, RX J0513.9-6951 which outbursts in X-rays every 100–150 days for a month or so, but is accompanied by a substantial (∼1 mag) optical decline. Using XMM we have obtained simultaneous soft X-ray, UV and optical observations through such an event, showing that as the X-ray flux declines the temperature declines as well (moving the peak emission into the UV) whereas the optical flux and (implied) white dwarf radius increase. Such an expansion of the white dwarf is evidenced by highly ionised outflowing gas in the high resolution X-ray spectra.

Development of a slurry continuous flow reactor for photocatalytic treatment of industrial waste water

The water treatment capability of a novel photocatalytic slurry reactor was investigated using methylene blue (MB) as a model pollutant in an aqueous suspension. A pellet TiO 2 catalyst was employed and this freed the system from the need of filtration of catalyst following photocatalysis. This configuration combines the high surface area contact of catalyst with pollutant of the slurry reactor and also offers a high illumination of catalyst by its unique array of weir-like baffles. In this work, the batch adsorption of MB from aqueous solution (10 μM) onto the TiO 2 catalyst was studied, adsorption isotherms and kinetics were determined from the experimental data. Complete degradation of MB was achieved within 60 min illumination with various loadings of catalyst (30–200 g L −1). A modest catalyst loading (30 g L −1) achieved 98% degradation within 60 min of irradiation. Experimental results indicate that this novel reactor configuration has a high effective mass transfer rate and UV light penetration characteristics.

Plasma spouted/fluidized bed for materials processing

Plasma when coupled with spout/fluidized bed reactor for gas-solid reaction brings in several advantages such as high rate of heat and mass transfer, generation of high bulk temperature using a thin jet of plasma itself as a heat source. The science and technology of plasma and fluidization or spouted bed are well established except of these two put together for high temperature application. Plasma heating of fluid/ spouted bed can bring down the size of the equipment and increase the productivity. However the theory and practice of the hybrid technology has not been tested in a variety of applications that involves high temperature synthesis of materials, TRISO particle coating for nuclear fuel particle, thermal decomposition of refractory type ore, halogenations of minerals, particulate processes and synthesis of advanced materials. This paper gives an account of the use and exploitation of plasma coupled with spouted/ fluidized bed especially for material processing and also addresses the issues for adapting the same in the era of developing advanced high temperature materials.

Numbering-up and mass transfer studies of liquid–liquid two-phase microstructured reactors

Microstructured reactors are known to provide high heat and mass transfer rates for liquid–liquid two-phase systems when used as a single channel. For industrial scale production, scale-up of microstructured reactors is essential to achieve throughput in the required range which is done by numbering-up of a single channel. The important issues are uniform flow distribution and identical slug size in all channels. In the present work, a capillary microstructured reactor is numbered up for six capillaries and the mass transfer performance is investigated for various operating conditions. A cationic surfactant was used to study the effect of interfacial tension on the mass transfer performance. If compared to conventional contactors, the mass transfer coefficients were approximately one order of magnitude higher allowing the process intensification. The results obtained demonstrate the benefits of microstructured reactors and confirm that the throughput of conventional reactors can be achieved.

Intensification of the rate of heavy metal removal from wastewater by cementation in a jet reactor

Removal of copper by cementation on zinc disc from dilute copper sulfate solution in a recirculating batch reactor which consisted of a horizontal zinc disc impinged by an axial turbulent submerged jet was studied. The effect of different parameters such as, initial copper ion concentration, solution flow rate and the axial distance between the zinc disk and submerged jet on the rate of copper ion removal were investigated. The rate of cementation was found to increase with increasing solution flow rate, decreasing the axial distance between jet and zinc disc, and by increasing copper ion concentration. The rate of diffusion controlled cementation of copper ion was expressed in terms of the mass transfer coefficient, the data were correlated with the following dimensionless correlation: Sh = 0.306 S c 0.33 Re 0.997 ( d n / l ) 0.0337 . The high rate of mass transfer of the jet reactor, qualifies the reactor for diffusion controlled heavy metals removal from wastewater.

二酸化炭素気泡の溶解過程のダイナミクス(&lt;特集&gt;第14回動力・エネルギー技術シンポジウム)

Mass transfer and flow structure of gas-liquid two-phase flows are essential in a chemical reactor, bio reactor and so on. In this research, a mass transfer process of a single rising bubble is investigated by using LIF (Laser Induced Fluorescence) measurement. We examined single ascending bubbles of 2-3mm in equivalent diameter, which have the highest mass transfer rate. However their flow structure and mass transportation process are complicated because they show zigzagging or spiraling motion in rest water. We visualized both the mass transfer from bubble to water, and wake of the single zigzag ascending bubble via LIF. Next, the relation between mass transfer and shape oscillations of the bubble interface is discussed. We compared the process of mass transportation 2.3mm and 2.9mm bubbles. From these results, we conclude that the shape oscilations are considered to play an important role in mass transportation of CO_2 bubbles.

Biotreatment of waste gas containing pyridine in a novel rotating rope biofilter

A novel Rotating Rope Biofilter (RRB) has been developed especially for the treatment of Volatile Organic Compounds (VOCs) at higher loadings and characterised by high volatility along with high water solubility. The RRB provides a higher interfacial area (per unit reactor liquid volume) along with high oxygen mass transfer rate, greater microbial culture stability, and consequently higher substrate loadings and removal rates in comparison with other conventional reactors (e.g. biofilters) widely used for the treatment of VOCs. Pyridine was used as a model compound to demonstrate the enhanced performance of the RRB. The experimental results indicate that the novel RRB system is able to degrade pyridine with removal efficiency of more than 90%, up to a loading of 250 g/m³/h. The reactor has been in operation for the past 15 months and no loss of activity has been observed.