Based on the Clustering Annular Flow Model (CA model), a scaling law for circulating fluidized beds, i.e. a set of necessary conditions to attain a geometrically similar flow structure in a scale model, is derived. To validate the theory an experiment was performed by using two geometrically similar circulating fluidized-bed cold models (CFB A: 200 mm I.D., 1600 mm high; CFB B: 50 mm I.D., 400 mm high). The longitudinal voidage distribution, the condition of choking-like transition and the radial distributions of the cluster velocity were obtained for the two CFBs where the operating conditions were adjusted to be consistent with the scaling law. Good agreement was found over a wide range of operating conditions between the performances of the two cold models, and the validity of the proposed scaling law was confirmed.
The effect of osmotic pressure gradient on the stabilities of various liquid surfactant membranes (LSMs) consisting of organic solvents was studied in terms of the change in water content of (W/O) emulsions and the breakdown ratio of the liquid membrane. No water permeation into (W/O) droplets through the membrane was observed under isotonic conditions; the entrainment of external aqueous phase was suppressed in the presence of electrolytes in the continuous phase. A greater osmotic pressure gradient brings about larger changes in the water content and membrane breakdown. A liquid membrane consisting of aliphatic hydrocarbons becomes more stable with increasing number of carbon atoms, while one consisting of toluene has very low mechanical strength. The value of the water permeation coefficient was found to be in the range from 2.9 × 10–7 to 1.5 × 10–6 m/s.
The particle entrainment rate and the size distribution of entrained particles were determined in two large-scale fluidized bed combustors and a cold model fluidized bed. A model is developed to predict the particle entrainment rate in which the vertical velocity distribution of entrained solids at the bed surface is considered. The entrainment rate increases with increase in gas velocity and coal feed rate. The effect of gas velocity on the entrainment rate is less pronounced in the combustor than in the cold model fluidized bed. However, the vertical velocity of entrained particles at the bed surface of the combustors is higher than that in the cold model fluidized bed.
A stochastic model is proposed for the kinetics of conjugative transmission of bacterial plasmids based on a Markov process with discrete states in continuous time. The kinetics of plasmid transfer in populations of Escherichia coli could be reasonably well approximated by the model. Using the stochastic model, rate constants of plasmid transfer could be estimated for three selftransmissible (R100, R100-1, RP4) plasmids and one non-selftransmissible, mobilizable (RSF2124) plasmid. The statistical significance of estimates of transfer rate constants is discussed, employing the normal distribution for the setting of significant level.
Jet mixing time of liquids tM in a rotating vessel was observed from the pulse response curve of electric conductivity. The ratio of mixing time to mean residence time, tM/tR, was well correlated with the dimensionless angular velocity Ω*, which was equal to the ratio of tangential velocity at the vessel wall to jet velocity at the nozzle hole. For the present experimental conditions, tM/tR showed a minimum value of about 0.2 regardless of jet nozzle angle, and the minimum value appeared at Ω* = 0.2–0.3. The observed response curves were classified into five types by shape. The transition of shape to shape depended only on Ω* regardless of jet flow rate, and the transition point agreed well with the Ω* value giving the minimum value of tM/tf. The ratio of mixing time to apparent circulation time, tM/tAC was 5 to 9 for the non-rotating condition (Ω* = 0), and these values were almost the same, 5 to 6, for the ratio of mixing time to circulation time in an agitated vessel with impeller. tM/tAC increases stepwise with increase of Ω* where the position of the step agrees with that of the transition of the shape of response curve.
An evolutionary method of synthesizing chemical reaction cycles effective in saving energy is developed. The stoichiometry of reactions, the thermodynamics of chemical equilibrium and the chemical reaction rates are considered in the method. By the searching procedure presented here, several novel industrial chemical processes, in which chemical reactions can be carried out at lower temperatures, and a chemical heat pump system which upgrades thermal energy to a higher temperature are synthesized on the basis of linguistic descriptions of reaction rates in the literature.
The absorption rate into slurry in a gas-sparged stirred vessel under continuous operation was investigated experimentally and theoretically. The gas–liquid specific interfacial area and volumetric mass transfer coefficient were determined experimentally. The absorption rate of CO2 into an aqueous slurry of Ca(OH)2 particles and the power required for agitation were measured simultaneously in a gas-sparged stirred vessel under continuous operation. A film theory model for the absorption rate was proposed, which was valid for the case where the concentration of the solute gas in the bulk of the slurry absorbent could not be assumed to be zero. The observed rates of absorption into the slurry agreed well with the predicted values by the present model both in the range of high solid concentration of Ca(OH)2 where the model of Sada et al. is valid and in the range of low solid concentration where the modified enhancement factor is less than unity.
The extraction rates of Er3+ and Y3+ from an aqueous phase containing diethylenetriaminepentaacetic acid (DTPA) to an organic phase containing di(2,4,4-trimethylpentyl) phosphinic acid in n-heptane were experimentally determined with both a transfer cell having a constant interface area and an agitated vessel in which organic phase was dispersed finely. The selectivity obtained was about 5.5, which was much larger than that by the usual solvent extraction: The selectivities for the various cases were studied in detail. The extraction rates and selectivity were quantitatively analyzed by taking account of the dissociation reactions of the rare earth metal DTPA complexes in the aqueous stagnant layer.
For the purpose of selecting or developing appropriate inorganic membranes for methane fermentation membrane bioreactors, the relationship between surface charge of the inorganic membrane and filtration characteristics of methanogenic waste was examined. The zeta potential of alumina membranes with 0.5 μm pores was controlled to negative, zero and positive, respectively, in the methanogenic waste by surface treatment. Cross-flow filtration experiments showed that negatively charged alumina membranes had twice the filtration flux of positively charged membranes when waste was fed to the membrane at 3.0 m·s–1. And it was found that the influence of membrane charge on filtration flux resulted from the influence of membrane charge on the hydraulic resistance of Rp, which was attributed to the plugging of suspended particles in the feed during filtration.
The extraction of oilseed with supercritical CO2 was tested on the laboratory scale for the case of rapeseed. The influence of different rapeseed pre-treatments upon extraction time and solvent requirement was examined. The best results were obtained with flaked rapeseed press cake. Extraction at a pressure of 75 MPa appears to be more favourable than at 30 MPa, since extraction times are shorter and less water is co-extracted with oil. The energy consumption for processes with sub- or supercritical separation and pressurisation by pump or compressor was calculated. It is energetically desirable to separate the dissolved seed oil from the compressed gas at such supercritical temperature and pressure conditions that the seed oil is almost insoluble. For oilseeds, a continuous high-pressure extraction process should be employed instead of the batch process used at present for other solid natural materials.
In various electronic systems such as telephone exchange units, circuit cards are aligned on a vertical plate. The cards are usually cooled by natural convection. The local vertical velocity distribution of gas between vertical parallel heated plates was measured with a laser doppler velocimeter (L.D.V.). The local gas velocity was affected by the distance between the heated plates, the temperature of the plates and the open ratio of the distributor plate attached to the top or bottom of the plates. The average gas velocity between the plates was obtained from the measured velocity distribution. An empirical equation for the average gas velocity between the vertical parallel heated plates was obtained.
When expression is stopped before a material reaches its equilibrium compression state, the cake stress will decrease as the material relaxes. In this paper, the change of cake stress with time was measured after an interruption of a constant-pressure or constant-rate expression operation of a semisolid material. This relaxation process is analyzed by considering the elastic deformation of the material and its irreversibility and non-linearity. It is found by numerical calculation that local expansion appears near the drainage surface while local consolidation appears near the center of the cake. The calculated stress in a transient stage falls faster than the empirical stress. The theoretical values of the equilibrium cake stress, however, agree well with the empirical ones. It is found that the equilibrium cake stress does not depend on the mode of expression (constant-pressure or constant-rate expression) but is uniquely determined by the average consolidation ratio when the expression is interrupted.
Toward the application of a downcomer with gas entrainment by liquid flowing downward to a gas-liquid contactor, mass transfer characteristics in the downcomer were experimentally studied. Aqueous sodium sulfite solution was used as the liquid and it was reacted with the oxygen in entrained air. The specific gas–liquid interfacial area was larger in mixed flow than in slug flow. The maximum specific gas–liquid interfacial area appeared at a relatively high liquid flow rate in mixed flow, and increased with increasing downcomer diameter in the range of present experimental conditions. Bubble diameter decreased with liquid flow rate in slug flow and was almost unchanged in mixed flow. The liquid-phase mass transfer coefficient was higher in mixed flow than in slug flow.
A composite solar collector, in which the working fluid layer was divided into two layers by an opaque trapping surface, was considered. In the composite collector, thermal collection in the upper fluid layer is by a volume heat trap and that in lower fluid layer is by a surface heat trap. The collection characteristics of the collector were examined theoretically and experimentally. In the upper fluid layer of the composite collector natural convection was more suppressed and the temperature gradient was larger than in the volume heat trap collector. Also, in outdoor performance the mean temperature of the composite collector was higher than that of the volume heat trap collector. As solar radiation decreased, however, the difference between the two collectors became small because of thermal accumulation in the insulating layer. Under the present experimental conditions, the collection efficiency was high when the trapping surface was set near the middle of the fluid layer. As the temperature level became high or as the convective heat transfer coefficient became large, the optimum position of the trapping surface shifted to a deeper position. It was found that the optimum position of the trapping surface depended on the thermal conditions.
Uptake curves were obtained for phenol, p-chlorophenol and p-nitrophenol/XAD-2000 resin systems using a shallow-bed method for various concentration ranges at 288.2, 298.2, 308.2 and 318.2 K. Both distilled water and a 20% aqeuous solution of isopropanol were employed as solvents, to vary the molecular diffusivity of the solutes. The values of effective intraparticle diffusivity were determined by comparing experimental and theoretical uptake curves. The values obtained for both solvents, i.e., distilled water and propanol/water mixture systems, were not dependent on the amount adsorbed in the higher concentration range. Those results show that, except in the region where there is a low adsorbed amount, an adsorber packed with macroreticular resin particles can be designed using a traditional pore diffusion model.
Monosilane pyrolysis was conducted over the temperature range of a fluidized-bed reactor (823 K–973 K) by use of both packed-bed and tubular free-space reactors, with and without seed silicon particles, respectively. In the packed-bed reactor, the heterogeneous reaction was predominant and most of the silicon produced was deposited on the seed silicon surface. In the free-space reactor, the homogeneous reaction was predominant and fine powder was formed. The conversion of monosilane obtained was analyzed, based on the assumption of first-order reaction to silane concentration. The homogeneous reaction rate and heterogeneous reaction rate were separated and the rate constants of both reactions were determined. The activation energies were 231 kJ and 193 kJ respectively. The rate obtained was compared with the previously reported kinetics, obtained under different conditions from the present experimental conditions. In a reaction zone with a number of particles, such as the emulsion phase of a fluidized bed, the contribution of the homogeneous reaction was found to be less than 10% for the particles and temperature range employed in the present study.