The potentials of mean force (PMFs) for the solute pairs in ambient water were reported by lots of computer simulation studies, where different simulation methods and various models were used. It turned out that the resultant PMFs are quite sensitive to both the methods and the models employed. In the present study, we selected with great care a set of molecular dynamics methods and models and then carried out the computer simulations to obtain the more reliable PMFs for methane–methane, Na+–Cl–, Na+–Na+, and Cl––Cl– pairs in water. We will thoroughly compare our results with those of other researchers to validate our set of simulation methods and models for PMF calculation.
The present work deals with the use of a torus mixer for the formation of liquid-liquid dispersion. The objective is to determine the performance of the torus reactor to form the primary emulsion of the microencapsulation process of an active product by a solvent evaporation technique. The encapsulated product is dissolved in an aqueous phase, which is emulsified into a solution of the polymer in methylene chloride to form a water/oil emulsion. The methylene chloride is gradually removed from the droplets by evaporation. Hard microcapsules are obtained when the solvent is completely removed. The formation of the water/oil primary emulsions is the key step to control the size distribution of the microcapsules. The characteristics of the dispersed phase of the water-in-oil emulsion produced in a torus mixer in batch and continuous conditions is determined by an optical method based on the use of the microscope connected to a CCD camera. The flow inside the torus mixer is directly linked to the rotation speed of the impeller. The effect of the rotation speed of the impeller and the dispersed phase volume fraction of the liquid-liquid dispersion is analyzed. The experimental data are expressed by a correlation giving the mean droplet diameter in function of the Weber number and dispersed phase concentration. The influence of the superimposed throughput, for the continuous process, on the size distribution of the dispersed phase is also taken into account.
The fundamental aspects controlling the rheology of crude oil-Alcoflood polymer emulsions are investigated. Several crude oil concentrations are covered over the range of 10–75% by volume. Three types of Alcoflood polymers of AF1235, AF1275, and AF1285 are employed over the concentration range of 0–10, 000 ppm. A cone and plate of RS100 rheometer under constant rate mode is employed for this emulsion investigation. During the shear rate sweep over the range of 0.1–1000 s–1, the measurements of shear stress, viscosity, and relative viscosity of different emulsions are extensively investigated. A Zeiss optical microscope is used to investigate the distribution and interaction of crude oil droplets within the polymer solution in order to help understanding of the rheological behavior of these emulsions.
There is fairly extensive information about mixing time under unaerated conditions in literature. However, the mixing times under aerated conditions are relatively limited, because of the insufficient measurement methods. In this work, a novel measurement technique was developed to measure mixing time under aerated conditions with an improvement on a conductivity method, by attaching a cage to the probe in order to protect the electrodes from bubbles. The effect of the cage attached to the probe and the tracer injection system on the measured mixing time was precisely investigated and it was found that the technique proposed in this work is quite effective. By using this technique, the mixing times were measured for traditional 6-bladed Rushton turbines and a modern impeller recently proposed, that is a 6-bladed hollow blade disc.
A new device of a double-pass mass exchanger is a circular tube divided by inserting a permeable barrier into two subchannels with uniform wall concentration, resulting in considerable improvement of the device performance in mass transfer compared with that in an open conduit. Efficiency improvement in mass transfer has been studied analytically by using eigenfunction expansion in power series. Analytical results show that a suitable adjustment of the permeable-barrier position can effectively enhance the mass transfer efficiency, leading to an improved performance. A numerical example in mass transfer efficiency of the two flow patterns of double-pass devices has been illustrated with the mass-transfer Graetz number as a parameter. The effects of the permeable-barrier position on the mass transfer efficiency and on the increment of power consumption have been also delineated.
Recently, the lattice gas cellular automata method has been developed to simulate the hydrodynamical phenomena by discrete lattice gas models obeying cellular automata rules. This method gives rise to macroscopic dynamics by using the simple idealized microscopic dynamics. Despite this method has made with significant contributions for complicated fluid physics, such as the flow through porous media, phase separation and interface dynamics, the application was made for several typical problems in fluid dynamics and has rarely been conducted for the equipment used in the process industries. In this work, we tried to apply the lattice gas automata method to analyze the flow field in the mixing section of a single screw extruder, which is one of the most important equipment in polymer processing. The simulated result was found to correspond to that solved by the finite difference method, giving a more accurate velocity distribution.
A plate-fin-type methanol reformer was made by preparing Cu-Zn/Al2O3/Al-plate and Pt/Al2O3/Al-plate catalysts on an aluminum plate with aluminum fins on the surfaces of both sides. Feed gas composed of methanol and steam was supplied to the Cu-Zn/Al2O3/Al-plate-catalyst side and combustion gas composed of hydrogen and air was supplied to the Pt/Al2O3/Al-plate-catalyst side. The methanol steam-reforming reaction, which is endothermic, was carried out on the Cu-Zn/Al2O3/Al-plate catalyst and the hydrogen-oxygen combustion reaction, which is exothermic, was carried out on the Pt/Al2O3/Al-plate catalyst to supply the heat needed for the methanol steam-reforming reaction to the other side. This reformer’s steam-reforming characteristics are superior to those of a fixed-bed-type methanol reformer with commercial CuO-ZnO-particle and Pt/Al2O3-particle catalysts. The gas temperature of its catalytic combustion part was similar to that of the methanol steam-reforming part at each point in the gas-flow direction. In the fixed-bed-type methanol reformer, on the other hand, it was about twenty degrees higher. The start-up time of the plate-fin-type methanol reformer was 28% of that of the fixed-bed-type methanol reformer. And its overall heat transfer coefficient was 16 times larger. Therefore, we conclude that this large overall heat transfer coefficient contributes to its higher performance and shorter start-up time as well as its large apparent heat transfer surface area. The catalyst volume in the plate-fin-type methanol reformer was only 11% of that in the fixed-bed-type one even though its methanol steam-reforming characteristics were superior. Thus, the plate-fin-type methanol reformer is an effective way to reduce the reformer size and start-up time.
The hydrophobic reactant was hydrogenated to the hydrophilic product by using two kinds of solid catalysts with different surface properties. Water was introduced to remove the product, which deposited on the surface of the catalyst. For Pd/C, catalytic deactivation was occurred in the trickle bed reactor. Since Pd/C was hydrophobic, the catalyst surface was mainly covered with organic solution. The product was deposited on the catalyst surface. On the other hand, for Pd/Al2O3, the catalytic activity was stable. Since Pd/Al2O3 was hydrophilic, the catalyst was mainly covered with water. Product was easily transferred from the catalyst to water.
An evaporator unit for use in microreactor systems was constructed. The unit consisted of a micropump driven by piezoelectricity and a microevaporator heated electrically by means of a Pt wire. The micropump was comprised of two tightly bonded plates; a silicon (100) plate having three diaphragms and a glass plate having valve and pump chambers. These flow conduits were patterned by photolithography and formed by wet-etching. The diaphragms, as well as the valve and pump chambers, were 7 mm in diameter, and were arranged triangularly. The discharge rates of the pumps were found to be dependent on the voltage and frequency applied to the piezo discs, the actuation pattern, the backpressure at the outlet, and the liquid viscosity. The pump assembled with an epoxy adhesive showed high discharge rates, while a similar one, assembled by anodic bonding, showed high discharge pressures. The flow rate of the former pump reached 60 mL/min for water. The microevaporator channel was wet-etched on a 10 mm × 40 mm silicon wafer, and a channel for a Pt wire heater was formed on the reverse side. Both sides of the silicon plate were covered with glass plates. Benzene, when pumped to the microevaporator, was evaporated to give a vapor flow rate of 6.8 cm3/min, which is sufficiently large as a feed rate for a gas-phase catalytic microreactor.
The microstructure of WC-Co/TiC-Al2O3 sintered composites has been characterized quantitatively by means of image analysis. The areal fraction, the grain size distribution and the uniformity of spatial distribution expressed by the void size distribution of each component have been correlated with the mechanical properties of samples such as Vickers hardness and transverse rupture strength under various sintering temperatures. The results revealed that the larger amount of WC dissolution and smaller grains were obtained at higher sintering temperature, while the total areal fraction of β-matrix formed increased to get higher hardness but lower strength. Further, at the higher temperature, the lower areal fraction of Al2O3 was obtained from densification of alumina aggregates due to the rearrangement of individual particles to yield lower composite strength. Void size distributions of total components were relatively uniform due to the high degree of mixing of powder achieved by means of Hybridizer™. Further, more uniform dispersions of WC and Al2O3 grains were obtained at low sintering temperature, while the TiC-WC phase was dispersed uniformly at the high temperature. Thus, the areal fraction and spatial uniformity of WC and Al2O3 components were most influential to the higher strength of composite, while the higher hardness was governed by those of the β -phase.
Vapor-liquid-equilibrium (VLE) at normal pressure for the system formed by n-heptane, benzene and N-methyl-pyrrolidone (NMP) are investigated. The results show that NMP is a good extractive solvent that reverses the volatility of the binary system of n-heptane + benzene. A UNIFAC model is selected and proved that the group interaction parameters are reliable. A modified extractive distillation (MED) process, in which a little of water is added to lower the boiling point of reboilers in aromatics recovery column, is proposed on the basis of the original extractive distillation (OED) process. The process simulation shows that the proposed process raises the yield ratio of benzene from 94.2% to 98.2%. Since the modification is not complicated, the MED process have a lasting value in industry.
An experimental study on the pressure drop has been carried out for a counter-current multistage fluidized bed having a downspout as well as on the particle holdup relating to a pressure drop. Three kinds of fluidized beds were used; a 3-stage column with 48.6 mm i.d., a 2-stage column with 99.6 mm i.d. and a batch-wise single stage column without downspout. The holdups for three kinds of ion exchange resins in the multistage fluidized bed are expressed by the correlation obtained for a batch-wise single stage fluidized bed. The pressure drop of the 48.6 mm column, however, varied little with the superficial liquid velocity, while that of the single stage column with the same diameter decreased with an increase in liquid velocity as expected from the theoretical consideration. A 99.6-mm column, where diameter of the downspout is small in comparison with the column diameter, shows that the pressure drop in the multistage column was the same as in the single stage column. By covering a part of stage-partitioning screen of the 99.6-mm column with a plate producing a non-uniform liquid flow, the pressure drop behavior approached the one that is observed for a 48.6-mm column. Discrepancy of the observed and the estimated pressure drops for the multistage fluidized bed is ascribed to the non-uniform flow generated by the downspout which is indispensable to the multistage operation.
The solution of realistic simulation and optimization problems is computationally very intense. Along with the development of parallel computing environment, it is necessary to construct an effective parallel strategy in order to exploit supercomputing power. A parallel solution strategy was developed for the optimization of the whole periodic operation of the cracking coils. The most time-consuming computation step for the gradients is deserialized, an approximate linear speed-up is acquired and the optimization calculation is well accelerated. The optimization work was carried out successfully on a cluster of workstations and the properties of the coarse-grained parallel computation technique were analyzed. The results suggest that the execution time of the steam cracking process optimization can be reduced significantly by distributing the heavy simulation duties onto several computing nodes, which communicate via communication networks.
In recent years robust control theory has met wide acceptance and made significant advances especially in terms of development of tools for analysis and design. However, the application of those tools, like the H∞ optimal theory and μ-synthesis in MATLAB, to real-time control of chemical processes has not been very successful. Among the factors hindering widespread application is lack of systematic way to model uncertainty that occurs at different locations in the feedback structure. In this work, time series data is used to model additive plant uncertainty through power spectral methods by performing least-squares regression in frequency domain. The concept is illustrated for real-time control of axial temperature distribution in a packed-bed column, which is modelled by partial differential equations and Fourier transforms to obtain an eigen-mode plant for controller design and robust analysis. Spectral uncertainty description is obtained from error analysis of smooth signals from the nominal and the perturbed plant and robustness is evaluated using the structured singular value (SSV). It is shown that through a proper choice of parameters, the spectral method gives better uncertainty description for robustness analysis than parametric methods.
In medical treatment, a constant plasma concentration for an extended period of time is preferable for some diseases, while pulsatile delivery or delayed delivery is also required to avoid the tolerance and set a delayed time for medication. The dissolution-type TTS is expected to achieve pulsatile delivery. In this work, a mathematical model was proposed for the prediction of the plasma concentration–time profile following the application of the dissolution-type TTS. In vivo animal data was compared with the simulated profile together with the model parameters determined independently. The calculated concentration–time profile well agreed with the in vivo animal data.
A lipophilic drug, 17-β-estradiol (E2), and two enhancers, Isopropyl Myristate (IPM) and Glycerol Monooleate (GO), were dissolved in an acrylic pressure sensitive adhesive (DUROTAK® 87-2516, DTM) to manufacture a supersaturated dissolution matrix transdermal delivery system. The analysis of variance (α = 0.05) on the in vitro experimental data showed that the cumulative amount of E2 penetrated from 2–6% E2 (w/w) DTM with 20%(w/w) IPM was not statistically different. When 16% (w/w) crystal inhibitor, polyvinylpyrrolidone (PVP, average M.W. ca. 10, 000), was mixed in DTM, the in vitro cumulative penetration amount of E2 increased proportionally to the concentration of E2 up to 6% (w/w). The cumulative penetration amount of E2 obtained from 4% E2 (w/w) DTM with 20% IPM (w/w) and 16% PVP (w/w) reached 70.0 μg/cm2 at 24 h, and was about 12-fold higher than that from 1% E2 (w/w) DTM. CCD micrograph and X-ray diffraction analysis demonstrated that the enhancers accelerated the crystallization process, but PVP delayed or inhibited this process and maintained the degree of saturation (DS) of E2 in an extended period. The synergistic enhancement can be attributed to the E2 supersaturated dissolution maintained by crystallization inhibitor and alter the solubility and/or diffusion coefficient of E2 in stratum corneum by the chemical enhancers.