Combining a capillary bundle model and the functional form of a j-function has deduced the relative hydraulic conductivity of a mesh-wick as a function only of the reduced saturation. The empirical expression of the relative hydraulic conductivity has also provided steady-state saturation profiles observed in a wick with infiltrating liquid percolating to a liquid table. The final average residual saturation can be reasonably estimated from a calculation of a newly defined capillary number, which takes into account the final equilibrium saturation profile as well as the j-function.
In order to know the fluidization characteristics in a fluidized bed of binary mixtures, soybean (FK, dP = 7.68 mm) and silica gel (SG, dP = 1.50 and 3.09 mm), the pressure fluctuations were investigated at lower bed aspect ratios (H/D = 0.56–1.56) by a statistical analysis. The results indicate that the dominant frequency in the bed changes inversely with the static bed height and decreases slightly with the increase of gas velocity provided that the mass fraction of SG is lower. The measuring position along the bed column has an insignificant influence on the dominant frequency; but there exists maximum mean amplitude at a certain position of the bed column, dependent on the fluidizing gas velocity as well as the size of the small particles (SG) added. Generally, by adding small particles into the soybean bed, both the dominant frequency and the mean amplitude of pressure fluctuations could be increased, compared to those in the soybean bed. In addition, at higher gas velocities, slug occurred in the beds of FK and SG3 (dP = 3.09 mm), but large bubble and gas-solids eddy in the beds of FK and SG2 (dP = 1.50 mm). It was observed that mixing of soybeans could be improved by adding small particles (SG) into the bed.
The objective of this paper is to find out the optimum cell size for contact detection in the algorithm of DEM (Discrete Element Method) to improve the calculation speed. The computing time of contact detection was measured by using a cubic box, which contains particles, to investigate the effect of cell size. The contact detection was inefficient when too fine grid cell or large one was introduced, the optimum cell size was given around 1.5–2.0 times of particle radius. The theoretical formula for the optimum cell size was proposed by considering the effects of the number of searched cells and contact checks. A significant correlation between the computing time of DEM work and the theoretical equation was seen in all conditions of volume fraction. Furthermore, it was found that the optimum cell size was the size, which each cell has about 0.7–0.8 particles in it, and this result was applied to a modelling of random-sized particles. Therefore, the calculation speed of DEM would be improved by using the optimum cell size for the contact detection.
The drying characteristics of a porous material immersed in a fluidized bed were examined. Some kinds of porous silica gel beads were used as the fluidizing particles. In a part of experiment, the glass bead (inert particle) was used as the fluidizing particle and the results were compared with the cases of silica gel beads. The numerical calculation of heat and mass transfers in the porous material was also performed. In this calculation, the liquid water transfer from the drying material to the fluidizing particle bed was considered in the cases of silica gel beads. The temperature and mass velocity of the drying gas were changed in experiment. In the cases of silica gel beads, the temperature decrement in drying which is observed in the case of glass bead does not appear. The phenomenon can be expressed by the numerical calculation including the liquid water transfer from the sample to the fluidizing particle bed. The drying time is shorter in the cases of silica gel beads than in the case of glass beads at the same mass velocity of the drying gas. The effects of the mass velocity of the drying gas and the heat transfer coefficient on the drying time are smaller than that of the kinds of fluidizing particles. The effects of the physical properties of the fluidizing particle on the drying time increase as the drying gas temperature becomes lower.
The drying characteristics of porous materials immersed in a superheated steam fluidized bed under reduced pressure were examined. The effect of pressure in the drying chamber on the drying characteristics was compared with that of hot air fluidized bed drying. The sample temperature in drying is almost equal to the boiling point of water in the case of superheated steam fluidized bed drying, and the temperature is higher than that in the case of hot air fluidized bed drying. The sample temperature becomes lower as the pressure in the drying chamber decreases, since the boiling point of water decreases. The effect of the mass velocity of the drying gas is not significant when the fluidization state is sufficiently vigorous. As the pressure in the drying chamber decreases, the difference of drying characteristics between superheated steam fluidized bed drying and hot air fluidized bed drying becomes small.
The crystallization of ergosterol was performed using water-immiscible hexane as a solvent. It was found that a ppm-level of water contained in hexane plays an important role in the change in the morphology of precipitates. The morphology of the ergosterol precipitates changed from thin needle-like crystals to spherical precipitates with a decrease in the water content of hexane. The thin needle-like crystals were monohydrate crystals and obtained when a sufficient amount of water was dispersed in hexane as many small droplets. On the other hand, the spherical precipitates were obtained under less water content, for instance under 185 ppm water. The spherical precipitates had a good filtration property, compared with the thin needle-like crystals. The precipitates were a mixture of the monohydrate crystals and amorphous solid. As long as it was observed with a 10000-fold scanning electron microscope, the surface of the spherical precipitate was covered with small thin needle-like monohydrate crystals and the inside was smooth solid. We named the spherical precipitate the broccoli-like precipitate. A possible mechanism for the formation of the broccoli-like precipitate is as follows. As the first step, ergosterol precipitates as a mixture of the monohydrate micro crystals and amorphous solid from the solution containing a ppm-level of water. Then, the monohydrate crystals preferentially grow or the amorphous solid transforms to the monohydrate crystals on the surface of the precipitates by contacting with fresh solvent containing water.
Two types of molecular simulation techniques have been utilized to investigate surface modification effects on adsorption of acetone/water in mesoporous silicas with a hexagonal uniform pore structure: the NVT-ensemble Molecular Dynamics technique with the melt-quench algorithm for modeling a non-silylated mesoporous silica (an OH surface model) and a fully silylated mesoporous silica (an FS surface model), and the μVT-ensemble Orientational-Bias Monte Carlo method for calculating adsorption isotherms. A good agreement was obtained between simulations and experiments for adsorption of pure acetone and water at 298 K on non-silylated and silylated mesoporous silicas. Equilibrium adsorption densities of the equi-fugacity mixture of acetone and water are calculated for the OH and FS surface models, by specifying either the gas or the liquid phase for the mixture. A considerably large separation factor, 7300, was obtained for the adsorption from a liquid mixture in the FS surface model, though the adsorption amount was rather small, which explains why the pervaporation through highly silylated mesoporous silica membranes was effective for separation of organic/water mixtures.
A cylindrical sonochemical reactor made of an acrylic pipe was investigated under sonication at the frequency of 490 kHz. The sonochemical efficiency depended on the distance between the measuring position and the transducer. Sonochemical luminescence and oxidation of I– ions in aqueous solutions were observed at the upper part of the reactor. The liquid temperature in the reactor increased with the irradiation time, and the estimated ultrasonic power was independent of the measuring position. From these results, the sonochemical efficiency in the cylindrical reactor was estimated.
The effects of equipment dimensions and operation conditions on the liquid circulation flow rate in a rectangular airlift bubble column were investigated at relatively low gas velocities, at which few bubbles were entrained into the downcomer. The gas holdup in the downcomer was almost zero, and the gas holdup in the riser decreased with increasing length between the upper end of the partitioning plate and the liquid surface during aeration (upper clearance) and with increasing length of the partitioning plate. The liquid circulation flow rate increased with increasing upper clearance, and became constant when the clearance exceeded a certain value. The loss coefficient in the zone above the upper end of the partitioning plate was a function of the upper clearance and the riser width. By using the energy balance and experimental equations the liquid circulation flow rate was calculated, and the results agreed with the measured data within an error of +30%.
The reaction rate of the dimethyl carbonate (DMC) synthesis directly from carbon dioxide and methanol at a supercritical homogeneous state with a tin liquid catalyst is studied. Since the experimental time course for the reaction scheme has been already reported, the rate for the reverse reaction is obtained by a semi-batch reactor in this study. Together with previously reported data, the rate equations for the forward and the reverse reactions are modeled to express the dehydration effect. With the rate equation proposed, the overall reaction rate is fairly predicted. The rate equation is also applied to a flow type reactor with a simplified model. The reaction simulation shows that 90% dehydration for the reaction mixture makes the DMC yields three times larger than that for no dehydration. In addition, the pressure effect on the yield is investigated. On the contrary to linear pressure dependence of the DMC yield in the semi-batch reactor, the amount of DMC product from the flow type reactor changes slightly with the pressure. It suggests that the reaction pressure for the flow type reactor can be less than that for semi-batch reactor, showing the possibility of the industrialization of the process.
Unspecific missing of values in real chemical and biological industries have been found. Regardless of the incompleteness of the measured sample, a monitoring system should be designed to tackle the missing data problem and be applied to on-line systems immediately. A calibration method of a factor analysis (FA) model for incomplete data sets is proposed. And a prediction method based on the calibrated model is suggested in order to estimate missing values in incomplete calibration sets and incomplete test sets. An expectation and maximization (EM) algorithm is used to calibrate the model and expectation of conditional density is used to predict the model result. The proposed method is compared with the well-known iterative singular values decomposition (iSVD) method, i.e. a principal component analysis (PCA) based method; and a simple data set is tested as an illustrative example. The proposed method gives better estimation results for the missing values than the well-known PCA based method. There are several advantages of the proposed method over the PCA based projection methods: (1) data pretreatment is not an essential step since the FA model is scale invariant whereas the PCA model is not, (2) since the proposed method utilizes probability information of all variables directly, to apply it as a statistical process monitoring technique is preferable to others, and (3) the single model can be extended to a mixture of such models by the virtue of the EM algorithm.
An integral approach for dynamic data reconciliation that combines a direct numerical integration via Simpson’s rule and data smoothing via discrete wavelet decomposition is presented. By simple numerical integration, the differential-algebraic equations governing the material balances are transformed into algebraic constraints to formulate the reconciliation problem. The frequency responses and the frequency contents of the measured variables are considered to determine the cut-off frequencies for data smoothing. Repetitious solutions for reconciliation using a moving data window are then used to generate the dynamic reconciled data for gross error detection. Compared with other methods such as the Kalman filter and another sophisticated integration approach, this proposed method is simpler and has better results.
A combined electrochemical method which added electrolysis to the electrocoagulation was proposed to overcome awaiting problems of the exiting process. In this study, the effects of operating parameters including the current density, electrolysis time, electrolyte concentration and dyestuff type were investigated. The results show that COD removal was enhanced with the electrolysis time and the current density. In the COD removal efficiency, a maximum value of 96.8% was obtained in the combination of electrocoagulation and electrolysis. Regarding the effect of electrolyte concentration, major contribution toward the increase in COD removal could be attributed due to the addition of NaCl.
The potential of an inexpensive and simple method to control the solubilities of hazardous heavy metals such as Pb and Cr from CaO rich melting furnace fly ash (MFFA) by addition of silica and alumina with preceding heat-treatment was demonstrated. The addition of SiO2 and Al2O3 to melting furnace fly ash with preceding heat-treatment at 700°C resulted in a decrease in the pHs of the leachates from 12.4 to 11.2 and in a remarkable reduction of leachabilities of heavy metals although the leachability of Cd was below the ICP-AES detection limit (0.04 mg/l) even without the addition. In the CaO-SiO2-Al2O3 system the solubilities of Pb, Cr and Cu were much lower in the area where 3CaO·Al2O3, gehlenite, CaO·Al2O3 and anorthite deposit. The solubility of Zn was also much lower in the area where pseudowollastonite, rankinite and 3CaO·SiO2 as well as the above-mentioned minerals deposit. The leachabilities were fairly well correlated with practical parameters of CaO/(CaO + SiO2 + Al2O3) (or (SiO2 + Al2O3)/CaO) and Al2O3/(CaO + SiO2 + Al2O3) (or Al2O3/CaO) for Pb and CaO/(CaO + SiO2 + Al2O3) (or (SiO2 + Al2O3)/CaO) for Cu in the range of the present study. For Cr and Zn the leachabilities were very low in the range of the present study and no particular correlations were found. The significant reduction in their solubilities was confirmed not being caused by their volatilization during heat-treatment.