A method to measure the heat transfer coefficient for direct-contact condensation during two-phase bubble formation is proposed. The growth behavior of a condensing vapor bubble at a single nozzle submerged in an immiscible liquid under constant-flow condition was taken by a high-speed video camera. By analyzing the recorded images of bubbles at the nozzle and calculating heat and mass balances at the bubble, the heat transfer coefficients for direct-contact condensation of a two-phase bubble of hexane or vinyl acetate are experimentally obtained. These coefficients depend on the temperature difference between vapor temperature and immiscible liquid temperature, and decrease with increasing temperature difference. The heat transfer coefficients for direct-contact condensation obtained experimentally are compared with those estimated theoretically. Under the present experimental conditions, in the range of the temperature difference less than 14 K, the experimental results correspond well to the theoretical values.
PVT data are measured for ten fractionation cuts of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) at temperatures (298–338) K and pressures up to 30 MPa. The range of number-average molecular weights for these polymer cuts is from about 210 to 4960. The Tait equation represents accurately the effect of pressure on the liquid densities. Isothermal compressibilities for each polymer cut can be calculated with the aid of this equation. The experimental results reveal that the density of PEG increases with the average molecular weight but an opposite dependence is found for PPG. Nevertheless, the densities become insensitive to molecular size when the molecular weights of PEG are greater than 420 and those of PPG are greater than 3420. These new PVT data are correlated with both the Flory-Orwoll-Vrij and the Schotte equations of state. The characteristic parameters of the models so determined appear to depend on the molecular weight of polymers.
Mutual diffusion coefficients of benzene in supercritical carbon dioxide are determined at 313.15 K from 8 to 20 MPa using the Taylor dispersion method. A 10 m diffusion tube was oriented in a horizontal position. A UV detector was used to determine solute concentration profiles. We find that the diffusion coefficients have maxima depending on injection volumes and appear to approach zero for 5.7 and 13.1 μl injection volumes near the critical pressure of carbon dioxide, although their values decrease monotonically with pressure for 0.7 and 1.0 μl injection volumes. Based on irreversible thermodynamics, calculation from an equation of state reveals qualitatively anomalous behavior. Below 8 MPa, the decay in concentration distribution due to fluctuation in the critical region is immeasurable with UV due to intense light scattering but can be measured with a flame ionization detector.
In earlier work we demonstrated numerically (Kumar and Ramamohan, 1995) that the rheological parameters of periodically forced dilute suspensions of slender bodies vary chaotically. This demonstration, if confirmed experimentally, will have important implications for both suspension rheology and chaos theory. In this paper, we develop expressions for Green’s function and the average rotation rate for a semi-dilute suspension of periodically forced slender bodies aligned along a finite set of directions. The present theory can yield physically meaningful results, either as an approximation to the evolution of an initially uniformly distributed suspension of slender rods, or as an approximation to the evolution of an initially nearly aligned suspension of slender rods when the evolution of the orientation vectors is chaotic in some parametric regimes.
Generation of larger and more stable RF plasmas at atmospheric pressure is important in order for their more widespread adoption in industrial applications. The applied frequency is strongly related to the size of the plasma torch, and also to the distributions of temperature, velocity and species concentration. In this work, the results of the investigation of the characteristics in argon-hydrogen plasmas generated at frequencies of 0.5 MHz and 4 MHz are presented by comparing the two-dimensional modeling approach and the observations of the plasma generated in a 80-mm diameter plasma tube. The fields of flow, temperature and concentration of RF thermal plasmas have been calculated by solving the two-dimensional continuity, momentum, energy, and species conservation equations using a SIMPLEC algorithm. The electromagnetic (EM) fields have been analyzed by solving Maxwell’s equations on the basis of the two-dimensional modeling approach. An Ar-H2 atmospheric pressure plasma is successfully operated at 0.5 MHz frequency and up to 75 kW RF power condition. The observations of the plasma region are performed by an air-cooled CCD camera system. Lower induction frequency generates a longer and narrower plasma region. The penetration depth of the time-varying magnetic field into plasmas, namely skin depth, increases with a decrease in frequency. At lower induction frequency, the high temperature region in the plasma exists more inside than at higher induction frequency. Numerical and experimental results show good agreement qualitatively and indicate that lower induction frequency generates a longer and narrower plasma region. The choice of induction frequency is important in determining the optimum torch diameter for the generation of larger RF plasmas.
An analytical study is investigated for the quasisteady sedimentation in a suspension of identical aerosol particles. The Knudsen and Reynolds numbers are assumed to be small, so that the fluid flow can be described by a continuum model with a hydrodynamic slip at the particle surfaces, with the flow field being governed by Stokes equations. A unit cell model is applied to predict the hydrodynamic behavior for a monodispersed system of spherical particles. Three different boundary conditions at the shell of a unit cell are discussed: no-slip, Happel-type cell and Kuwabara-type cell. Our analytical expressions of the average sedimentation velocity of particles are obtained in a closed form as functions of the volume fraction of particles. In general, as the volume fraction of particles increases, the effect of particle concentration on the mean translational velocity becomes significant.
Experiments were carried out to investigate bubble splitting by turbulent fluid flow from a nozzle. A liquid jet was discharged vertically upwards through a nozzle into a large volume of the same liquid. Shear layers were thus formed both around the jet and in the nozzle. A bubble rising through the nozzle and the jet splits in the shear layer both in the nozzle and around the jet. The measured bubble size spectra can be well represented by an upper limit log-normal probability function with two constant parameters and only one variable, the maximum stable bubble diameter, as found with the result obtained for orifices (Miyahara et al., 1999). The maximum stable bubble diameter of splitting bubbles by a turbulent jet from nozzle is slightly smaller than that from an orifice. On the basis of this fact, the critical Weber number, including the maximum stable bubble diameter, is correlated as a function of the Reynolds number and the Morton number.
It is investigated in the present paper how an initially nonspherical particle in a shrinking core regime changes its shape temporally, and how much the eccentricity of the particle affects the total reaction rate (i.e., conversion). The pseudo-steady state assumption may be applied because the core shrinking rate is sufficiently low. The resultant Laplace equation is solved by using the boundary element method to yield the reactant concentrations on the core, which are then used to predict the shrinking process of the core. The shape change of a spheroidal core is also analytically predicted with asymptotic analysis. It is shown that the two different approaches produce equal results. The spheroidal core becomes more and more eccentric with time, to be very slender when the core size is much reduced. The more nonspherical the particle, the faster the total reaction rate. For a highly nonspherical particle with an aspect ratio of 3.2, one may undergo about 17% error in determining the reaction constant if the spherical core is employed in the data analysis.
The influence of plate geometry (single hole plate and perforated plate) on the characteristics of fluid flow and mass transfer in an external-loop airlift bubble column was experimentally examined using an air-water system. The gas holdup can be well correlated with the drift flux correlation including liquid circulation velocity expressed by the correlation obtained by Okada et al. (1996) irrespective of plate geometry. The bubble size distribution may follow a log-normal probability distribution. The Sauter mean bubble diameter affecting the gas-liquid interfacial area decreases with increasing gas velocity for a single hole plate, whereas it increases for perforated plate. Therefore correlation equations for Sauter mean bubble diameter are proposed for both a single hole plate and a perforated plate following the result by Okada et al. (1996). The specific gas-liquid interfacial area is also correlated for a single hole plate on the basis of the result by Miyahara et al. (1997) whereas the correlation is modified for a perforated plate with respect to an effect of hole diameter of perforated plate. In addition, it is found that the correlation for the liquid-phase volumetric mass transfer coefficient is expressed by the result proposed by Okada et al. (1996) regardless of plate geometry.
Microemulsion-assisted preparation of ultra-fine particles is important. There are, however, some problems to be solved: Control of particle size and its distribution, difficulty of preparing particles in denser state, and difficulty of preparing particles in dry state. Cadmium sulfide (CdS) particles prepared with the help of the microemulsions composed of cadmium dioleylphosphate and sodium dioleylphosphate are markedly stable. We demonstrate that these problems are solved using the above mixed surfactants microemulsion: 1) The size of ultra-fine CdS particles can be controlled by changing the water-to-surfactant mole-ratio in the microemulsion. 2) A dense dispersion and a film of the CdS ultrafine particles can be prepared with the help of the surfactants system. 3) Almost all CdS ultrafine particles can be precipitated from the microemulsion by addition of dodecanethiol, pyridine, and methanol to the microemulsion containing CdS particles, and the resultant precipitates can be filtrated. The separated particles can be redispersed in hexane without change in the primary size of CdS particles.
Growth processes of gold particles prepared with the aid of microemulsions are studied focussing on the relationship between the produced particles and the structure of the microemulsion. The microemulsion was composed of sodium dioleylphosphate (SDOLP) or pentaethylene-glycol dodecylether (C12E5). It is found from the size and distribution of the produced particles that there are several retardation processes for Au-particle growth in the SDOLP system. The first retardation appears near the diameter dm of the original microemulsion droplets, followed by successive retardation in lower ranges of water-to-surfactant ratio Wo. The second retardation occurs around the diameter dnc of the natural curvature of the microemulsion droplets. Whereas, for larger Wo-values, the first and the second retardations occur around dnc and a diameter dms much larger than dnc. The size distribution of the produced particles is rather broad due to the wide gaps between dm, dnc and dms. In the C12E5-system, the size distribution was much broader than that in the SDOLP-system. This arises from the absence of the second retardation which restrains the particle growth of the maximum size. SDOLP can work as a stabilizer of the produced particles. This is caused by the peculiar nature of the microemulsion composed of SDOLP. Taking into account the above retardation mechanism, the size-distribution of Au-particles can be controlled, and Au-particles with sharper size-distribution can be prepared.
In freezing water which contains solutes, the solutes are removed from the frozen phase and concentrated in the unfrozen liquid phase, and strong agitation of the freezing interface is very effective. We used a supersonic radiation method instead of propeller agitation. The experiments of freeze concentration with/without supersonic radiation were carried out under a constant freezing rate (40 mm/h), using two concentrations (0.5, 5.0 kg/m3) of three aqueous solutions (sodium chloride, L-phenyl alanine and saccharose). Under this freezing rate, freezing without supersonic radiation could not concentrate solutes, but freezing with supersonic radiation could greatly do, and decreased the average distribution factor under 0.4. The distribution factors at a late stage of freezing are much smaller than those at an early stage, because the turbulence of solution by supersonic cavitation and the agitating intensity per unit unfrozen volume increases. Therefore the solutes are not easily caught on the freezing interface as the freezing interface approaches the supersonic radiation horn. The low mass concentration solution is concentrated more than high concentration solution. For a constant mass concentration solution, the solutes of large molecular weight are more easily separated and concentrated than those of small molecular weight.
The surface zeta-potential of a cross-linked polyamide thin film composite reverse osmosis membrane was measured using an electrophoresis method. It was confirmed that this method could be effectively applied to analyze the fouling of such membranes. It is known that the water flux of membranes drastically decreases as a result of fouling by surfactants. Although the surfactants adsorbed on reverse osmosis membranes could not be detected by conventional methods such as SEM, EDX and FT-IR, their presence could be clarified by the profile measurements of the surface zeta-potential. The profiles of the membrane surface zeta-potentials changed to more positive values in the measured pH range as a result of fouling by cationic or amphoteric surfactants. This measuring method of surface zeta-potentials allowed us to analyze a very small amount of fouling of a thin film composite reverse osmosis membrane. This method could be used to analyze the fouled surface of the thin film composite reverse osmosis membrane which is used for production of ultrapure water and shows a remarkable decrease in flux. It also became clear that this method is easy and effective for the reverse osmosis membrane surface analysis of adsorbed materials such as surfactants.
An experimental study is made on mass transfer in a packed distillation column with the structured packing covering homogeneous and heterogeneous liquid regions for an ethanol-benzene-water system under total reflux conditions. The vapor phase diffusion fluxes obtained in the homogeneous liquid region agree well with the correlation derived from an acetone-ethanol system by Olaño et al. (1995). On the other hand, the observed diffusion fluxes in the heterogeneous liquid region exhibit wide scattering, which may be due to the neglect of the liquid phase resistance and the assumption of three-phase equilibrium at the vapor-liquid interface in this experimental analysis. In order to examine the effect of liquid phase resistance on the separation performance in the packed distillation column, its simulation is also carried out by considering or neglecting the liquid phase resistance. The liquid phase resistance has much influence on the vapor phase concentration driving force, and then the diffusion and convective mass flux in the heterogeneous liquid region. The top concentrations and reflux flow rates predicted by considering the liquid phase resistance agree reasonably well with the experimental data in the heterogeneous liquid region. On the contrary, the effect of the liquid phase resistance on the separation performance in the homogeneous liquid region is very small as generally accepted.
A method is proposed for estimation of the binding constants B of solutes to a counter-ion of cation-exchange resins from their apparent distribution coefficients onto resins with different divinylbenzene contents. The method can be modified when the B value of a solute is zero. The methods were applied for estimation of the B values of glucose, mannose, fructose, galactose, and sorbose to the sodium ion at 25°C. Assuming that the B value of glucose is zero and using the modified method, the B values of mannose, fructose, galactose and sorbose are evaluated.
Compression and expansion processes of cross-linked sodium polyacrylate hydrogels under mechanical pressure were investigated. A packed spherical gel bed shows irreversible deformation when the applied pressure is decreased; the expansion behavior depends on the maximum pressure applied to the gel bed. The time required to attain a certain degree of deformation is directly proportional to the square of the total solid volume of the gel bed; this relation is very similar to that observed in expression or expansion processes of ordinary solid-liquid mixtures. The driving force of the deformation is an effective osmotic pressure gradient in the gel bed, where the effective osmotic pressure of the gel is the difference between the swelling pressure of the gel and the pressure applied to the gel. The flow rate of liquid through any gel layer can be expressed by Darcy’s equation. The deformation ceases when the swelling pressure of each gel particle is equal to the applied pressure. Thus, the deformation of a packed gel bed can be recognized as a process of equalizing the swelling pressure distribution in the bed.
Coffee aroma recovered from the extraction process of roasted coffee beans is used to improve the quality of soluble coffee products. Coffee aroma often has an irritating sulfurous odor. In the present work, it is experimentally elucidated that methyl mercaptan could be selectively removed from the coffee aroma-containing gas by the oxidized microporous carbon. Breakthrough curves of coffee aroma-containing gas on zeolite 5A, microporous carbon (MSC 5A), and MSC 5A oxidized with 13.2M HNO3 aqueous solution revealed that the adsorption capacity of methyl mercaptan on the oxidized carbon was 4.2 times of that on the zeolite. The loss of desired coffee aroma was decreased using the oxidized carbon in the removal of methyl mercaptan.
An efficient scheduling algorithm using the Simulated Annealing (SA) method is proposed. In an actual large scheduling problem, the number of schedules searched within a reasonable time is restricted, because calculation of the starting times of jobs requires a long computation time when the problem has various types of constraints. In the proposed algorithm, two types of improvements are proposed to reduce the computation time of a scheduling algorithm: One is to reject, at an early stage of the starting time calculation, those schedules that have little possibility of being accepted in the simulated annealing method. The other is to reject unpromising schedules stochastically using the data related to the production sequence of jobs—not after the calculation of the starting times of jobs but at the step of generating a new production sequence of jobs. Thus, compared with the algorithm which selects a new production sequence randomly, better schedules can be derived in shorter computation time. The developed algorithm has been applied to a practical scheduling problem at a resin production plant, and it has become clear that this algorithm can generate significantly better schedules with a much shorter computation time.
Environmental pollution with toxic metals has become a global phenomenon. Research on fundamental and applied aspects of wastes with heavy metals in the environment has mushroomed to the trace metal contamination emitted during various high-temperature processes. Research leading to better understanding of their behavior and better controlling of their emissions is urgently needed. An experimental scale fixed bed incinerator with a treatment capacity of 5 kg/hr was used to study the effect of incineration temperature on lead (Pb) emission from waste incineration without chlorine effect. A series of incineration experiments have been carried out. Drawn from the experimental results, the conclusion is that incineration temperature affects significantly the emission rate of lead. It is also found that the weight partition fraction of lead after incinerated is about 65–85% in bottom ash, 13–30% in flyash, and 2–5% in flue gas. Obtained by regression, a practical formula is proposed to estimate the emission of lead from a small scale fixed bed incinerator with overfire combustion as following:
lnE (wt.%) = –3, 083/T1.257 + c (T: K)
where c is an experimental constant dependent on combustion air distribution, typically 3.659 for the general operation with stoichiometric air as primary combustion air, and 20–50% excess air as secondary combustion air.
Off gases produced in the reprocessing of spent nuclear fuel contain various radioactive components and emission of these components to the environment must be prevented as low as possible. Carbon-14 with a long half-life, which is mainly released as the form of carbon dioxide, is one of such gaseous radioactive materials. One of the measures to capture radioactive gases from the off-gas is the utilization of adsorption technique. In this work, the adsorption behavior of carbon dioxide on synthetic zeolites and natural mordenites was studied at lower partial pressure ranges. Moreover, the authors quantitatively investigated the influence of coexistent water vapor, which is also contained in the off-gas, on the adsorption behavior of carbon dioxide.
In a study on prevention of silica scale formation in geothermal applications, two silica removal methods were examined using actual geothermal brine in the Sumikawa and Onuma geothermal areas: one was the addition of silica gel seeds. The other was the addition of aluminum ions. The results for silica gel seed show that the material precipitates on the seeds withdrawn from Sumikawa and model geothermal brine is only silica. On the other hand, the seeds withdrawn from Onuma brine contain not only silica but a small amount of aluminum. In the case of aluminum ion addition, the deposits withdrawn from Sumikawa geothermal brine contain not only silicon and aluminum, but also sodium, potassium and calcium. The composition of the deposits is similar to that of common silica scale. Also, the distribution ratios of these elements between the deposits and the brine are consistent with their common distribution ratios between silica scale and brine. In each case of silica gel seed and aluminum ion addition, the silica removal performance in the actual geothermal brines is found to agree with that in the model ones. Therefore results obtained in model geothermal brine can be applied to actual geothermal brine.