摘要:

AbstractWhen a supercritical solution is rapidly expanded, large solute supersaturations can be attained, and small particles are formed. The evolution of the homogeneous nucleation rate, work of nucleus formation, and critical nucleus size along different expansion paths is investigated here for the model system phenanthrene‐carbon dioxide. Nucleation rates are the result of the competition among solvent expansion, cooling due to depressurization, and high supersaturation. Although supersaturations can reach very high values (>106), relatively flat nucleation rate profiles result due to cooling and expansion. For an interfacial tension of 0.02 N/m, computed nucleation rates never exceed 104s−1· cm−3. A substantial fraction of the maximum nucleation rate is attained with partial decompression to pressures above

ISSN:0001-1541    

DOI:10.1002/aic.690360902

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractScaling rules have been developed which are able to change the dimension of a pressure swing adsorption plant keeping its main performance constant. Such scaling rules result from a system of algebraic equations which arises by constraining the solution of a fairly general dimensionless mathematical model to be the same in the old and new plant configuration. Different heat and mass transfer mechanisms, purification, and multicomponent bulk separation processes, both isothermal and nonisothermal, have been considered. Furthermore, the influence of different equilibrium isotherms and the main practical limitations have been discussed. The application of these rules shows that column size can be reduced significantly by using smaller particles in shorter beds with rapid cycles.

ISSN:0001-1541    

DOI:10.1002/aic.690360903

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractScanning electron microscopy (SEM) was used to study the mechanism of falling‐strand devolatilization of polymer melts. Polystyrene and low‐density polyethylene were enriched with styrene and hexane, respectively, and were subsequently extruded as thin strands at various conditions. The polymer strands were exposed to superheat conditions for preset periods of time ranging from tenths to tens of seconds. The strands were then frozen, fractured, and studied by SEM. Devolatilization was found to proceed through a blistering mechanism, both on the surface of the strands and on the surfaces of volatile bubbles formed within the core of the melt. At all volatile concentrations surface blistering and foaming preceded bubble growth in the core, and occurred before the strands foamed. A mechanism for the observed polymer melt devolatilization is propo

ISSN:0001-1541    

DOI:10.1002/aic.690360904

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe principles of static balancing, also called measurement error reconciliation (MER), have been generalized to transient conditions. An exactly linear dynamic balance model has been stated where flow variables are assumed to be stochastic processes with independent increments. With this model the residual error of static MER due to dynamic effects can be estimated. Dynamic balancing is proposed as the estimation of flow and inventory variables by Kalman filtering applied to the balance model. The error of estimates obtained in this way is significantly less than that for the static MER estimates, even if the process is nearly in steady state. The main problem of dynamic balancing is that it requires not only the redundant observation of flow variables but also the observation of inventory variables. Compatibility of MER and dynamic balancing has been shown.

ISSN:0001-1541    

DOI:10.1002/aic.690360905

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractAbsorption experiments of H2S into aqueous Fe2(SO4)3solutions, concerned with a unique process capable of regenerating by biological oxidation the reactant from the products, were performed at 20–40°C in an agitated vessel with a flat interface. The absorbents were aqueous solutions of Fe2(SO4)3with and without the addition of K2SO4, KOH or H2SO4of various concentrations, which was added to change the ionic strength or pH of the solutions. The experimental results revealed that the species which reacts with H2S is FeOH2+. While comparing the observed absorption rates with the theoretical predictions, it was found that the reaction is irreversible and first order with respect to H2S and FeOH2+. The reaction rate constants were measured and correlat

ISSN:0001-1541    

DOI:10.1002/aic.690360906

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA new theory to predict liquid circulation was derived and compared with applicable literature data. A single dimensionless group,ε(gRd2/v2c), is shown to control mixing intensity under low‐viscosity conditions, but two separate groups (εandgRd2/v2c) are necessary for viscous systems. Closure was accomplished using the Prandtl model for Reynolds stress. Locally varying mixing length was taken to be proportional to bubble size and bubble concentration. The model was constructed based on the premise that two distinct zones exist: a mainly turbulent core joined to a thin viscous wall la

ISSN:0001-1541    

DOI:10.1002/aic.690360907

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractBatch distillation processes are very attractive for the recent development of the chemical industry: multipurpose, flexible plants and fine chemistry. For many separations of high‐added value products, even a modest change in operating conditions has a significant economic impact—there is an important challenge for optimizing such processes.Short‐cut and dynamic models are the two classical approaches to the simulation of batch distillation columns. For problems without holdup, an intermediate procedure based on a decoupling method is validated.For a multifraction separation problem with fixed final time, the reflux policies for each period and the period switching times constitute the set of decision variables. For predefined reflux policies, we apply an engineering approach to the solution of a such constrained variational problem, based on its transformation into a nonlinear programming problem. In this computer‐implementable algorithm, the gain in distillate for the optimal linear or exponential reflux policies is significant (about 10%) compared with the optimal constant reflux

ISSN:0001-1541    

DOI:10.1002/aic.690360908

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractDistribution data of local values of specific kinetic energy of medium flow in the bioreactor volume made it possible to determine some integral criteria. The relationship of these criteria, microorganism growth and biosynthesis characteristics was studied in 5–5,000‐L bioreactors. Energy‐efficient stirring systems that ensure a minimum damage of cells have been also st

ISSN:0001-1541    

DOI:10.1002/aic.690360909

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractLocal and average heat transfer were measured for a system of multiple jets impinging on a moving permeable surface at which there may be throughflow. Multiple jets were confined by a hood, as is required industrially for thermal efficiency. Exhaust ports located symmetrically between the jet nozzles eliminated crossflow, otherwise a strongly detrimental effect. Impingement surface motion decreases average heat transfer, by 17% at industrially relevant values of the surface motion parameter,Mvs. Enhancement of impingement heat flux by throughflow is linearly additive. Expressed as ΔSt, this enhancement depends only on the throughflow parameter,Mus, with ΔSt/Mus= 0.17. For typical operating conditions, withdrawal as throughflow of only 10% of the jet flow increases mean Nusselt number by over 50%. Industrial design modeling for the potential process of combined impingement and throughflow drying of wet webs such as paper is demonstrate

ISSN:0001-1541    

DOI:10.1002/aic.690360910

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractNumerical simulations of mass transfer into falling liquid films, both through the wavy interface and from the wall, have been performed for experimentally measured large waves within which the flow fields have been computed. Experiments have shown that the occurrence of waves on free falling films causes dramatic increases in mass transfer into the film, even under laminar flow conditions. Wave effects have been modeled in several ways, none of which predicts the observed rate of enhancement. The present numerical procedure includes solving the convective‐diffusion equation for wavy films by extending a technique developed for hydrodynamic simulation. The presence of waves is shown to cause significant velocities normal to each interface. In conjunction with recirculation within the large waves, these flow patterns produce transfer rates for large waves that are several times larger than predicted for quasiparallel velocity fields. Experimental wave structure data were used to define the dimensions and frequency of an average large wave and surrounding substrate. Computed transfer rates at both the gas‐liquid interface and the wall for a film composed of a periodic sequence of average waves agree well with published data. These simulations confirm the inadequacy of parabolic, or Kapitza‐type velocity profiles in formulating transport m

ISSN:0001-1541    

DOI:10.1002/aic.690360911

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY