To prevent membrane fouling, cross-flow microfiltration with ultrasonic wave cleaning was carried out using a model suspension containing both baker’s yeast and bovine serum albumin (BSA). The effects of ultrasonic waves on the permeate flux and rejection of BSA were studied. The steady-state flux obtained in filtration with ultrasonic waves was four to six times greater than that without ultrasonic waves, and a high flux was obtained, even at a low feed flow velocity. There was an optimum membrane pore size and an optimum operating pressure. It was found that ultrasonic waves were very effective for removing the cake layer deposited on the membrane surface and preventing the plugging of the membrane pores. A filtration method in which a feed pump and an ultrasonic generator were operated alternately was very effective for enhancing the flux and solute permeation rate during cross-flow microfiltration.
Three dimensional turbulent flow was measured in the vicinity of gas-liquid interface using Laser Doppler Anemometer. The measurements were made in a 100 mm i.d. stirred cell with a flat interface. Mean and rms velocities were measured at seven radial and three axial locations. The effect of liquid viscosity on the flow pattern was investigated. These measurements form a first step in validating the published theories on mass transfer.
Liquid velocity and direction were measured by an electrochemical probe. The probe had three microelectrodes, and the two-dimensional direction and velocity were calculated from a cross-correlation function of the voltage fluctuations. Measurements were done in a rotating basin, and the most suitable values of parameters—the distance between the electrodes and the time span of calculating the cross-correlation function—were decided. This probe can be constructed cheaply, and it can be used in dilute aqueous solutions of sodium chloride (0.01 M) and also mediums for cultivation of microorganisms without employing commonly used electrolytes such as ferricyanide.
The influence of packed bed set in the riser section on the liquid-side volumetric mass transfer coefficient (KLaR) in an external-loop airlift bubble column was examined with water, 20 wt% glycerol, 10 wt% ethanol and 0.3 wt% CMC aqueous solutions. The KLaR was determined by the measurement of time-dependent oxygen concentration dissolved in the liquids. Bubble size, bubble rise velocity and gas holdup in the riser were measured to examine the effect of the packed bed using an optical fiber two-phase flow system. The presence of the packed bed in the riser increased the KLaR values for the liquids used. This was associated with the increase in the specific gas-liquid interfacial area due to bubble breakage by the packed bed. In addition, a correlation equation for KLaR was proposed for both types of airlift bubble columns with and without the packed bed.
The activity coefficients of HSO3– and H+ were determined in concentrated aqueous solutions of NaCl in order to provide a theoretical basis for using sea water as a solvent in flue gas desulfurization processes. The activity coefficient of HSO3– was determined at 313 K and 323 K by measuring the pH of mixtures of NaCl, H2O and small amounts of NaHSO3 at a known partial pressure of SO2. The activity coefficient of H+ was determined over a temperature range of 296 K–333 K by measuring the pH of mixtures of NaCl, H2O and small amounts of HCl. As the ionic strength increased, the activity coefficient of HSO3– decreased while that of H+ increased. The Pitzer Equation could correlate the activity coefficients of both species with reasonable accuracies for practical use.
This paper describes a capacitance probe measurement technique for the quantitative determination of local particle volume concentrations inside a fluidized bed combustor. The influence of temperature, water content in the fluidization gas, and burning fuel particles in the solids inventory on the measured signal is investigated in a laboratory-scale fluidized bed combustor. Application of the measurement system is demonstrated on a semi-technical scale circulating fluidized bed (CFB) sewage sludge combustor. By applying a data preprocessing step and a suitable calibration routine, the measurement system is able to quantitatively measure local average solids volume concentration as low as 0.1 vol.-%. Radial profiles of local average solid volume concentrations taken at various elevations inside the riser demonstrate the performance of the technique.
The velocity profiles, temperature distributions, average Nusselt numbers near heating wall, and maximum velocities of a circulating flow were calculated numerically by fundamental equations under different operating conditions including changing the Grashof number (at low Gr range), the location and number of heating walls, and the temperature difference between heated and cooled walls. The number of circulating flows is one or two owing to the configurations of heated and cooled walls under the present operating condition. Generally, the circulating rate was very slow and the temperature distributions were similar to those of conduction alone. In the case of a heated top wall, a domain of cold temperature extended widely as the circulating flow rate was increased, and it could be seen that heat transfer was suppressed. To check these calculated results, the velocity profiles and temperature distributions in small enclosures were measured experimentally and observed by a tracer under the same operating conditions as those of theoretical analysis. The calculated results agreed closely with the experimental ones.
A concentration depletion is developed nearby a capillary wall from the result of flow-induced radial migration to the axis region of capillary incorporating with the chain extension. The velocity enhancement factor can be defined quantifying the migration of polymers. For the experimental observation of the radial migration, the capillary hydrodynamic fractionation (CHDF) system has been adopted as a probe on the microcapillary flow of water-soluble flexible polymers. As a practical implication, the migration phenomena may lead to apply this system due to the possible alteration of the elution characteristics. In order to verify the experimental results more accurately, a model has been provided based on the diffusion equation and the conformation-dependent friction involving a radial dependence of hydrodynamic force on the dumbbell extension. For the nonionic polyacrylamide, the experimental behavior of velocity enhancement was shown to be in accordance with the present model within the somewhat increased We. In case of the anionic polyelectrolyte with 30% hydrolyzed polyacrylamide, the increasing slopes of velocity enhancement are different with the eluant ionic strength. Note that the experimental data allow us to consider an enhanced migration due to the long-ranged repulsive force between capillary wall and polymer.
The effects of urea molar ratio (1.0–2.0), reaction temperature and additives on NO reduction in flue gas have been determined in a pilot-scale flow reactor. A kinetic model is proposed for NO reduction rate with -NH and -CN in selective reducing agents (urea, cyanuric acid, ammonia). Two primary reactions can be expressed kinetically in the DeNOx process as:
N.S. (nitrogenous species) + Ox (oxidants) → NO + … (kf; rate constant for NO formation)
N.S. + NO → N2 + … (kr; rate constant for NO reduction)
in which the rate constants of kf and kr in the model are determined from the experimental data in the temperature range 1173 K–1373 K as:
kf = 4.01 × 1011 exp(–267/RT)
kr = 7.24 × 1011 exp(–230/RT)
The proposed model can predict the lowered activation energies caused by the addition of different species and molar ratio to NO.
In order to elucidate the antibacterial mechanisms of magnesium oxide (MgO), calcium oxide (CaO) and zinc oxide (ZnO), the generation of active oxygen from these ceramic powder slurries was examined by oxygen electrode analysis and chemiluminescence analysis. Hydrogen peroxide (H2O2) generated from the ZnO powder slurry was detected using the oxygen electrode. Active oxygen from the MgO and CaO powder slurries was not detected by the oxygen electrode analysis. Chemiluminescence analysis could detect the generation of active oxygen from three kinds of powders. The luminescence response of the CaO powder slurry was markedly strong. The chemiluminescence responses of the CaO and MgO powder slurries are due to the superoxide anion (O2–). The order of the strength of luminescence response was CaO, MgO, and ZnO, which agreed with that of the antibacterial activity of these powders. These results suggested that active oxygen species generated from the ceramic powders were associated with their antibacterial activities.
The surface tension relaxation at interfaces between surfactant solutions and immiscible fluids is calculated by the rate that surfactant adsorbs in a two-step process: surfactant in the sublayer adsorbs, which, in turn, establishes a diffusive flux from the bulk. Therefore, both the adsorption and diffusion rates determine the behavior. These rates are commonly determined by minimizing the difference between experimental surface tension vs. time profiles and mass transfer model predictions. Usually, only a limited range of bulk concentrations Co is studied, and the profiles are found to be in agreement with a diffusion-control model. It is argued here that such apparent agreement is insufficient evidence to disregard the role of the adsorption/desorption kinetics in the adsorption process. In this paper, the concept of a shift in controlling mechanism from diffusion control at dilute concentration to mixed diffusion-kinetic control at more elevated bulk concentration is explored. This idea is illustrated theoretically for clean interface adsorption on a pendant bubble or drop using the Langmuir adsorption model in dimensionless form. It is further developed using the model constants for C12E8.
Growth rates of potassium hydrogen phthalate (KAP) crystals were measured at 28°C in a flow cell under a microscope in the presence of chromium(III) added in the form of CrCl3·6H2O. Chromium(III) concentration was changed up to 5.7×102 ppm (mg Cr(III)/dm3 solution). Measurements were done at three levels of supersaturation of KAP solution (relative supersaturation σ: 0.0204, 0.0417 and 0.0878). The growth rate decreased with increasing impurity concentration and it eventually stopped. The impurity effect was stronger at lower supersaturations. The concentration effect of the impurity (chromium(III)) on the crystal growth rate and the supersaturation effect on the impurity action was explained by the model proposed previously by Kubota and Mullin (Journal of Crystal Growth,152, 203–208 (1995)). The impurity effects are shown theoretically to be divided into three parts: effect of growth environments (chemical potential difference of the crystallizing species between in the solution and in the crystal, or, in other words, temperature and supersaturation), effect of characteristic properties of the crystal (edge free energy and size of the crystal growth unit) and effect of mutual interaction between the impurity and the crystal (average distance between the active sites and coverage of the active sites by adsorbed impurities). The effect of the impurity concentration is related to the coverage of the active sites through the Langmuir adsorption isotherm. Anomalous dissolution of KAP crystals was observed even under superaturated conditions in the presence of chromium(III) at higher concentrations.
When liquid CO2 is disposed into the deep sea or stored on the sea floor in order to prevent anthropogenic CO2 from entering the atmosphere, the CO2 reacts immediately with the seawater and forms solid CO2 hydrate. In this study, a growth model is proposed for CO2 hydrate layers. In addition, an estimation is shown for the CO2 concentration profile, the growth rate of the layer, and its thickness in the quasi-steady state. The simulation results indicate that the hydrate layer diminishes CO2 dissolution from the storage pool into the upper sea. This growth process is extremely sensitive to the density difference between the CO2 hydrate particles and its environmental liquid.
An ideal heat integrated distillation column (HIDiC), which has neither a reboiler nor a condenser, was studied based on its non-linear and linearized dynamic models. It was found that heat integration between rectifying and stripping sections does not lead to an unstable plant. Moreover, the thermal interaction appears to be relatively stronger at low pressure difference than that at high pressure difference. Strong gain directionality has been found in the ideal HIDiC, where the pressure difference and feed thermal condition correspond to low and high gain direction respectively. With proper design of the process, thermal interaction, affects the system time constant only to a limited extent, and intensifies the interaction within a dual point composition control scheme. In fact, the degree of coupling between top and bottom control loops is governed by feed thermal condition since it is in line with high gain direction and can simultaneously introduce changes of both internal and external flows.
This paper demonstrates a three-dimensional graphical representation of energy losses in a distillation column by applying an Energy-Utilization Diagram (EUD). The concepts of both premixing model and individual energy level are applied to classify the energy loss in a column into six kinds; losses due to heating, and mixing in liquid phase, losses due to cooling and mixing in vapor phase, and losses due to evaporation of light components and condensation of heavy components through phase changes. The diagram displays transformed energy, its energy level, and unit height of the column in three-dimensional space. This diagram is useful for qualifying and quantifying the energy loss in a distillation column, and the target to minimize the energy and exergy consumption can be identified. The characteristics of close-to-equilibrium points (CEP) are also demonstrated.
Carbon fiber-reinforced carbon matrix (C/C) composites are useful engineering materials because they have a high strength to weight ratio and good creep resistance at high temperature. They are stable up to very high temperatures in inert or vacuum environments, but have a serious drawback of reaction with oxidizing atmospheres at temperatures as low as 773 K. In this study, the effects of double coating of SiC and glass materials on the oxidation resistance of C/C composites were investigated. The first coating of SiC was made by pack cementation in a graphite crucible with metallic silicon, and the second coating of glass materials was applied with ceramics mixtures in order to seal cracks in the SiC layer. The components of the mixtures were m-Si (metallic Si), Al2O3, B4C, SiC and ZrSi2. SiC/Si-B4C-SiC-ZrSi2 coatings were found to provide very effective oxidation resistance at 1773 K in air for 10 hrs. Furthermore, the effects of seven kinds of silicide additive on oxidation resistance of C/C composites were also studied. It was found that ZrSi2 and HfSi2 were very effective on the resistance compared with other silicides.
The instantaneous fluctuating velocities of particles acquired in three different flow regions of three-phase systems were measured by direct visualization. The local dynamics of particles were characterized by the deterministic chaos analysis of particle velocity fluctuations in terms of the correlation dimension obtained based on the time-delay embedding theorem. The results show that particles in the stable wake region exhibit highly chaotic velocity fluctuations with large correlation dimensions in spite of the apparently smooth trajectories with low fractal dimensions determined based on the box-counting method. In large particle systems the self-induced particle motion due to eddy shedding was found to be significant, resulting in an increase in correlation dimension with particle size. A sudden change in the correlation dimension was found to occur at the superficial gas velocity corresponding to the transition from the homogeneous bubbly flow to churn-turbulent flow regime.
Chromatographic techniques were used for measuring the adsorption of toluene and naphthalene on silica gel packed beds under the supercritical and subcritical conditions at 301–318 K, 54–150 atm, and 0.3 < NRe < 7. The moment method was used to determine the equilibrium constants and rate parameters. The results showed a significant reduction of the adsorption equilibrium constant as the pressure changed from subcritical to supercritical; the axial dispersion coefficients at supercritical conditions were intermediate to those of what would be obtained in gases and liquids; in the pressure range where density fluctuations with concentration were large, axial dispersion was influenced by both natural convection and molecular diffusion; diffusion within the pores of the adsorbent was found to be the major resistance to adsorption. In addition to these parameters, partial molar volumes were determined from the chromatographic experiment and were found to agree well with the values reported in earlier work.