Measurements on liquid holdup and interfacial area were made for cocurrent gas–liquid upflow through packed beds using four liquid systems with five different particles. Empirical correlations for the estimation of static liquid holdup, dynamic liquid holdup and the interfacial area have been developed using a data bank consisting of 49, 1337 and 129 measurements respectively. The predictive ability of the present proposed correlations was tested with the available literature data. A statistical analysis of the performance of the proposed correlations for static and dynamic liquid holdup based on the available data with a wide range of variables was also made.
Experiments were carried out in a co-current two phase upflow through a packed bed reactor using four different liquid systems and five different particles with air as the dispersed phase. An attempt has been made to predict the gas phase holdup using a slip velocity approach. The dependency of the slip velocity on the fundamental variables involved in the system are discussed in detail. Generalized correlations are proposed based on 1650 data (both 1253 experimental and 397 literature data) to represent the slip velocity and gas phase holdup in terms of basic dimensionless groups.
The influence of organic additives such as benzoic acid, iso-amyl alcohol and propanol on hydrodynamic characteristics of an internal loop airlift reactor was investigated. The effects of the draft tube to column diameter ratio, DE/D, and superficial gas velocity, Usg on the gas holdup in various sections of the reactor (riser, downcomer, overall) and liquid circulation velocity were reported. The gas holdup and the superficial liquid velocity in the riser and downcomer increased with an increase in the superficial gas velocity, Usg. In the present investigation, the DE/D ratio varied from 0.34 to 0.76 and the overall gas holdup and downcomer gas holdup increased with an increase in the DE/D ratio and the optimum was found to be 0.49. The riser gas holdup decreased with an increase in the DE/D ratio. The maximum volumetric liquid circulation rate was obtained with a DE/D ratio of 0.49 to 0.59. The addition of additives influenced the bubble coalescence reduction and increased the gas holdup. The addition of iso-amyl alcohol resulted in the maximum gas holdup. The superficial liquid velocity in the riser and downcomer decreased with the addition of additives. Correlations for the prediction of gas holdups in the different sections of the reactor and liquid circulation velocity were proposed.
To examine the separation characteristics of solid materials in the liquid-solid fluidized bed, the motion of one solid material immersed in the fluidized bed was examined. The fluidizing particles were put in the column and fluidized by the liquid flow. To reduce the effects of size and shape of a sample, the liquid velocity was set at a low value, i.e., relatively small particles were used as the fluidizing particles. The glass beads (ρp = 2500 kg/m3) whose diameters were 60, 100, 200 and 500 μm and the zirconia beads (ρp = 6000 kg/m3) whose diameters were 60 and 100 μm were used as the fluidizing particles. Tap water was used as the fluidizing liquid. One sample, whose density was adjusted, was immersed in the bed, and the existing height of the sample in the bed was examined for different liquid velocities, fluidizing particle diameters and densities, experimentally. When the liquid velocity is low and the apparent density of the particle bed is higher than that of the sample, the sample floats on the bed (floating region). As the liquid velocity increases, the apparent density of the bed decreases and the sample becomes to suspend in the bed (suspending region). Further increments of liquid velocity makes the sample settle at the bottom of the bed (settling region). As the liquid velocity increases, the apparent density of the particle bed decreases and the sample sinks in turn. The range of the non-dimensional sample existing height in the suspending region is affected by the diameter of the fluidizing particle, but is not affected by the density of the fluidizing particles.
Microfiltration experiments were conducted using TiO2 particles suspended in aqueous methanol, ethanol, t-butanol, and acetone solvents of various concentrations. Filtration behaviors were examined in terms of the average specific filtration resistance and the average porosity of the filter cake formed on the membrane surface. Such properties of the filter cake were strongly dependent on the sort of organic solvent used, and the concentration and pH of the aqueous organic solvent. The results indicate that the electric nature of particles controlled via changes in the solution environment plays a significant role in determining the structure of the filter cake which, in turn, influenced the filtration rate in microfiltration of colloidal particles suspended in aqueous organic solvents. The experimental results were analyzed based upon a DLVO theory which considered the balance between the electrostatic repulsion and the attraction. The concept of the coagulation parameter derived based upon the DLVO theory has been introduced to evaluate the degree of the coagulation and the dispersion of the systems, and to elucidate the filtration behaviors of the colloidal particles suspended in the aqueous organic solvents. In addition, it was shown that in the dispersion range the coagulation parameter was closely related to the stability ratio.
A Boundary-Driven type Non-Equilibrium MD (BD-NEMD) technique combined with the μVT-MC and NpT-Gibbs MC methods has been developed to simulate membrane permeation of gas mixtures. By using the new technique, simulations were carried out on permeation of binary mixtures, which consist of two kinds of LJ fluids differing in the LJ energy parameter and the molar mass. Two important results were obtained; (1) the permselectivity is affected by two factors, the adsorption equilibrium selectivity and the difference in molecular diffusivity, and (2) it increases as the weakly adsorptive molecules diffuse more slowly.
Gold nanoparticles were prepared sonochemically in an aqueous solution containing alcohol as an additive. The effects of the type of alcohol and hydrogen ion concentration on the formation rate of gold nanoparticles were examined. The ultrasound field was provided with a 200 kHz ultrasonic cleaning bath. It was found that the formation rate was controllable by varying the type of alcohol and the hydrogen ion concentration. When lower alcohol such as methanol or ethanol was used, the formation rate of gold nanoparticles at the neutral pH was rapid compared to that in the acidic or alkaline range. At pHs below 8, the formation rate in the presence of higher alcohol such as pentanol or hexanol was faster than that with lower alcohol. When the formation rate was higher, the particle size became smaller under this pH condition. The formation rate at pHs higher than 9.5 using butanol, pentanol or hexanol as an additive, however, was extremely low and the size of gold nanoparticles prepared was very small.
Database modeling has been proposed as a nonlinear modeling technique in which historical data during normal operations are accumulated in the database and used directly for the predictions of normal states of a dynamical system. In the previous paper, the scope of this database modeling technique was demonstrated by experiments using a tank-pipeline system and the results of the predictions were almost very good but there was one bad case. This reason is considered that the database model in the previous paper was a first order model. In this paper, a database model is extended to a multiple-order model and compared with the results in the previous paper.
A novel flow reactor adopted for the adiabatic expansion cooling method, a rapid quenching method, was designed to synthesize oligopeptides from amino acids under hydrothermal conditions. We studied the hydrothermal reaction under the two experimental conditions, whose raw materials were glycine and diglycine aqueous solution. The temperature, the pressure and the residence time of the reaction were 270°C, 10 MPa and 27 seconds, respectively. Then we could obtain long oligoglycines like octa-, nona- and decaglycine. The concentration profiles of each product in the two experimental conditions were similar. It suggests that the equilibrium relations would be established between condensation reactions and hydrolysis reactions of oligoglycines, which might light up a new pathway to the study of the origin of life.
The magnetically photocatalytic particles prepared have a core-shell structure of three layers coating magnetite core particles with silica and titania by the hydrolysis of tetraethoxysilane and titanium tetraisopropoxide, respectively. The thicknesses of silica and titania layers were controlled by changing the concentrations of two alkoixides used. The coated photocatalytic particles were heated at 773 K under the nitrogen or hydrogen atmosphere in the tube furnace. By the heating process, the surface titania layer of photocatalytic particles varied to titanium dioxide, of an anatase type, and the magnetism of particles increased. It was found that, from the decomposition experiments of the rhodamine B, the prepared photocatalytic particles had good photocatalytic activities and that they can be easily separated by magnetism. Furthermore, the result of the decomposition experiments revealed that the thicknesses of silica and titanium layers are mainly influenced by the photocatalytic activity.