To investigate the mechanism of heat transfer augmentation, numerical computations of turbulent flow and heat transfer in a parallel plate channel, attached transversely with turbulence promoters at regular intervals on the lower surface, have been performed by using a simple turbulence model and the Galerkin finite element method. It has been revealed that, in the optimum case, a vortex of peculiar structure is formed behind each turbulence promoter, and it plays a significant role in enhancing the heat transfer rate; and the maximum augmentation effect reaches about 13% when taking the pumping power into account, while it is 67% when neglecting the pumping power. It also turns out that the optimum interval of turbulence promoters is about 10 times the promoter diameter, and the optimum Reynolds number is about 9000.
A model is proposed to describe the distribution of distances between nearest neighbors in random-packed low-density assemblies of equal-sized spheres. The model is based on the probability of not finding any sphere center in an arbitrary volume of a given size. This probability contains a limiting packing density, φm, as a fitting parameter. The physical meaning of φm is the solids concentration above which every particle in the suspension is in contact with at least one of its neighbors. It means that at solids concentration φ = φm the fraction of particles whose motions are constrained by the presence of any other contacting particles becomes unity. The value of φm is evaluated from nearest neighbor distributions in random assemblies of spheres obtained by computer simulation. The closeness of the resulting value, φm = 0.52, to that reported by Probstein et al. (1994) from viscosity measurements leads to the possibility of interpreting the empirical viscosity correlations in terms of the local arrangement of particles in the suspension.
In order to observe the influences on microscopic behavior of water molecules caused by water treatment processes, the changes of dynamic structure of water in an ultra pure water (UPW) producing system have been studied by dielectric and 17O-NMR relaxations. The UPW system used in this study consists of typical unit processes employed in current commercial systems for semiconductor manufacturing plants, and produces UPW of the highest quality with specific resistivity of 18.2 MΩ·cm. Throughout the whole system from city water till UPW dielectric relaxation time, τd, is kept constant at about 8.7 ps, while β, a parameter describing the distribution of τd, increases with each treatment step, reaching a constant value of about 1.00 after the removal of major impurities by a reverse osmosis membrane. The spin-lattice relaxation time, T1, obtained from 17O-NMR is unchanged at about 7.3 ms through all processes in the system. Spin-spin relaxation time, T2, shows drastic changes with each treatment step. The changes of T2 are well explained by proton-exchange reactions in water and should not be related directly with rotational motions of water molecules. These results indicate that the averaged rotational motion of water molecules is unchanged from city water to UPW. The distribution around the average, however, becomes narrower during purification, and the rotational motions of water molecules are highly homogenized in UPW.
The phase equilibrium behavior of the ternary mixture, containing two completely miscible pairs and one partially miscible binary pair, of ethanol, ethyl acetate, and water was reported in this study. The phase equilibria of this mixture include vapor-liquid equilibria of ethanol-ethyl acetate and ethanol-water binary mixtures; vapor-liquid-liquid equilibrium and vapor-liquid equilibrium (in the miscible region) of water-ethyl acetate binary mixture and ethanol-ethyl acetate-water ternary mixture. All the equilibrium measurements were conducted only with a simple condensed vapor recirculating apparatus. We observed that the equilibrium was difficult to be attained by this simple apparatus in the water-rich region, x1 > 0.988, of the ethyl acetate-water binary constituent system, since the condensed vapor phase has smaller density and immiscible to the liquid phase. Thus a complete dew point curve can not be constructed. However, this difficulty was overcome by using an isobaric coexistence equation. The binary interaction parameters of the models of UNIQUAC, NRTL, and modified Wilson of Huang and Lee  were obtained based on the various correlations of VLE, LLE, and VLLE of various mixtures of the constituent components. Then those interaction parameters were used to estimate the ternary VLE and LLE of the present mixtures. Comparisons were made between the estimated results and the experimental data. Selection of the best fitted model and interaction parameters can be determined through the various correlations and analysis of the estimated results.
An equation of state (EOS) recently proposed by the present authors based on the nonrandom lattice fluid theory was applied to correlate phase equilibrium properties of polymer solutions. The EOS requires only two molecular parameters for pure r-mers and one additional interaction energy parameter for binary systems. The molecular parameters for 12 common polymers and the binary interaction energy parameters for 17 common binary polymer solutions are presented. We found that the EOS describes quantitatively well the solvent activities and heats of mixing of various polymer solutions. The results obtained with the EOS is compared with the results obtained by such models as the random lattice model (Okada and Nose, 1981a, b), Flory theory (Flory, 1970) and the EOSs proposed by Sanchez and Lacombe (1976) and Panayiotou and Vera (1982) and UNIFAC-FV model (Oishi and Prausnitz, 1978). We believe that the result obtained to date demonstrated that the EOS can be a useful tool for practical phase equilibrium calculations of polymer solutions.
Catalytic hydrocracking of sorbitol constitutes an interesting possibility of using excess production of cereals. Such reaction leads to an aqueous solution of ethylene and propylene glycol, butanediols, glycerol, alcohols, which is then to be distilled with the aim of separating the different species present. Since few equilibrium data have been published for this kind of mixtures, the first part of the present work was aimed at producing isothermal vapor-liquid equilibrium data in the range of 98°–122°C for the three binary solutions which can be obtained from water, ethylene glycol and propylene glycol. Afterwards, the equilibrium data were correlated by means of the UNIQUAC model, and the binary interaction parameters were evaluated. Eventually, the equilibrium conditions for the ternary mixture ethylene glycol-propylene glycol-water were experimentally determined, and it was shown that the UNIQUAC model is capable of estimating with very good accuracy the equilibrium conditions for such mixture.
Effects of dry grinding of a mixture composed of kaotinite and aluminum hydroxide in a tumbling ball mill on formation of mullite in a sintered body and its mechanical and thermal properties were investigated by X-ray diffraction method, TG-DTA, and measurements of bending strength and thermal expansion coefficient. Grinding of the mixture enables us to induce the structural change of the raw materials from a crystalline state into an amorphous state. About 192 h in grinding time is required to achieve an amorphous mixture, resulting in the formation of a mullite single phase at relatively low sintering temperature. When the crystalline state remains in the ground product, high temperature is needed to form a mullite single phase. The bending strength of the sintered bodies increases with an increase in not only sintering temperature but also grinding time of the mixture. Further, the thermal expansion coefficient of sintered bodies composed of mullite single phase, which is independent of grinding time, is much lower than that of different phases.
Simultaneous removal of organic carbon and nitrogen by a plunging liquid jet bioreactor with crossflow filtration was investigated under zone-limited aeration conditions in which dispersion of air bubbles was limited to the upper zone of the reactor. In the suspended growth system, TOC removal was about 95%, and nitrogen removal was about 45%. To enhance the nitrogen removal performance, biomass carrier was loaded into the reactor. In the attached growth system, nitrification proceeded successfully and the nitrogen removal was much improved. TOC and nitrogen removal efficiencies were about 98% (the effluent TOC concentration was about 2 g/m3) and 75% (the effluent T-N concentration was about 3 g/m3), respectively. Excellent organic carbon and nitrogen removal was carried out by the reactor in the attached growth system. The cake layer deposit on the membrane acted as a dynamically formed ultrafiltration membrane. The removal of organic carbon and nitrogen by the cake layer largely contributed to the overall performance. It was concluded that the bioreactor system operated under zone-limited aeration had high potentiality for the small-scale treatment of domestic wastewater.
Reactivities of two sorbents, a limestone and a half calcined dolomite, with H2S under simulated pressurized coal gasification conditions were studied by using TGA techniques. Although the activation energies for both sorbents are found to be about 180 kJ·mol–1, the initial reaction rate of the half-calcined dolomite (50 μm) is about 30 times faster than that of the limestone (50 μm). The reactions of both materials are first order with respect to H2S partial pressure. The pressure of CO2 and H2O has almost no effect on the sulfidation reaction of the half calcined dolomite, but has adverse effects on the reaction of the limestone. Although, in general, the smaller particles can react faster, it is found that the effect of particle size on the reaction rate is different, with dp–0.17 for the half calcined dolomite and dp–0.85 for the limestone.
Natural-gas hydrate fields having a large amount of methane deposits have become the object of public attention as a potential natural-gas resource. An idea of methane exploitation in linkage with CO2 isolation has been presented elsewhere. In the present study, the isothermal phase equilibrium relations of pressure and compositions in the gas, liquid, and hydrate phases for the CO2-CH4 mixed hydrate system at 280 K are obtained in company with the apparent Henry constants for the methane-water system and the three-phase coexisting lines for the methane hydrate system. The averaged distribution coefficient of methane between gas phase and hydrate phase is about 2.5, that is, methane in the hydrate phase is replaced selectively by CO2. This is the first experimental evidence for the possibility of methane exploitation combined with CO2 isolation.
In general, gas is injected into the spouted bed in the form of high velocity gas jet through a small opening such as inlet nozzle or orifice. The use of small opening causes the pressure drop of the system to increase. Furthermore, it causes large amount of gas to pass only through the spout without percolating in the annulus. In this study, gas was fed into the spouted bed with a draft-tube at a uniform velocity over the whole cross section of the vessel, without using the gas inlet nozzle or orifice. The pressure drop became lower and the flow ratio of gas which passed through the annulus considerably increased.
Extracellular production of pigment was conducted in a culture of red beet hairy roots accompanied by pigment release under oxygen starvation. The phenomenon of pigment release into medium by oxygen starvation was found that a part of hairy root cells associated with a declination of cell viability decayed and the pigment release arose from the cells. The kinetics of pigment release was expressed by the declination of cell viability during oxygen starvation as the time response of first-order lag plus dead time. Moreover, the variation in cell viability affected the growth rate after oxygen starvation and the growth rate was evaluated by the extent of the decay of growing points in hairy roots. According to the kinetics, the culture accompanied by repeated pigment release was performed under oxygen starvation to achieve maximum extracellular production. From experimental data, the extracellular production rate was found to attain to 2.70 × 10–4 kg/(m3·h) when oxygen starvation of 16 h duration was repeated three times.
Previous theoretical studies have demonstrated that chlorine-containing materials significantly affected heavy metals behavior during incineration. In this study, we examine the effects of operating temperature in both primary and second combustion chambers along with those of various chlorine-containing materials (organic or inorganic) on metal partitioning in sand-bed sorbents, fly ash, waste water, and flue gas. A bubbling fluidized bed made from 310 stainless steel (100 cm bed height; 10 cm ID; and 100 cm freeboard; 25 cm. ID) was used, in addition to two cyclones and a wet scrubber. The synthetic solid wastes used were plastics, sawdust and water. These results indicated that the fluidized medium (silica sands) can absorb a high proportion of metals in the incineration process; in addition, the extent of absorption ability follows the sequence: Pb > Cr > Cd. The effect of organic and inorganic chlorine on metal partitioning were very different; organic chlorine (P.V.C.) caused a more serious metal emission than inorganic chlorine (NaCl). The operating temperature and chemical reaction influenced absorption by the fluidized media. Within the operating temperature ranges, 500–600°C for the main combustion chamber, 600–800°C for the second combustion chamber), the effect of freeboard temperature on the metal partitioning is insignificant.
The mechanism of formation of silver halide ultrafine particles in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane reverse micellar systems has been studied. The particle formation process was followed by a change in the UV-visible absorption spectra. The effects of the concentrations of reactants and water content of reverse micellar solution on the size of formed particles were investigated. The size of AgCl particles decreased with increasing water content or reactant concentration, whereas the size of AgBr and AgI particles increased. A possible interpretation is the dissolution of AgCl, which is caused by some impurities in the AOT. Particle coagulation processes of AgBr and AgI particles are found to be dominated by the concentration of micellar droplets containing two or more particles.
A mathematical model was developed for predicting the flow characteristics and temperature distribution of a transferred arc plasma enclosed in a cylindrical chamber. The simulation incorporated the k–ε turbulence model to account for turbulent flow of the introduced gas. The model was adopted to a supplied current of 200 A, an arc length of 0.01 m, and Argon gas inflow rates of 3.33 × 10–4 and 6.67 × 10–4 m3/s. Goodagreement of the calculated isotherms in the arc with measured temperatures available from the literature was obtained, thus validating the model. The gas introduced through the nozzle was observed to pass along the edge of the arc region and creep close to the wall, result in a recirculating flow that covers most of the chamber. A high temperature region concentrated only at the vicinity of the electrodes, while substantially lower temperatures were predicted in most sections of the chamber away from the arc.
The distribution coefficients of benzene between slit pores and supercritical carbon dioxide at infinite dilution are calculated by the Monte Carlo simulation method over a wide temperature range. The Lennard-Jones potential function is used for describing interactions between benzene, CO2, and graphitic carbon. The distribution coefficient, K2, which is defined as the ratio of the concentration of benzene in a pore to that in the fluid phase, is calculated from the residual chemical potentials of benzene, μ2res, for both phases by applying Widom’s test particle insertion method. Under the condition of the constant fluid density, the logarithm of K2 increases linearly with increasing reciprocal temperature, while it shows a maximum in the constant pressure condition. We observed a remarkable difference between the influence of density on μ2res: that is, μ2res in the fluid phase gets stabilized with an increase in fluid density due to the increase of number of CO2 molecules interacting with the benzene molecule, while μ2res in the pore becomes unstable with an increase in pore-phase density after the first monolayer near the wall has been occupied by CO2 molecules. The radial distribution functions of CO2 surrounding a benzene molecule in several pores of different slitwidths are displayed in three-dimensional graphics and they indicate how the benzene molecule and the surface walls influence the microstructure of CO2 in pores.
Experimental work has been undertaken using a radiation method to ignite single coal particles and to study their ignition behaviour. Particle sizes used were in the range of 600 μm–1800 μm. Effect of particle size on ignition temperature and ignition time was investigated for three types of coal under conditions of constant heating rates. Results show that under these conditions, ignition temperature increases with particle size contrary to the widely reported trend of decreasing ignition temperature with increasing particle size. It was also found that ignition temperature increases with heating rate. When particles of different sizes are heated by the same power, smaller particles experience higher heating rates than larger ones. The effect of particle size on ignition time was found to be the same as reported by other researchers where ignition time increases with particle size.