摘要:

A new model for turbulent heat and mass transfer in the wall region is developed. It is based on the energy dissipation rate concept. The energy dissipation rate, which is a parameter characterizing turbulent heat and mass transfer, is evaluated using the hydrodynamic properties of the flow in the wall region. Applicability of the proposed model is examined using the experimental data and correlations for flows on a flat plate, wall jets and flows on a rotating disk. Satisfactory agreement is found between the proposed model and the available experimental data and correlations.

ISSN:0098-6445    

DOI:10.1080/00986449308936206

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this paper, the competitive permeation of cobalt and nickel from nitrate solutions through supported liquid membranes was studied, in which contained 2-ethylhexyIphosphonic acid mono-2-cthylhexyl ester (HEHEHP) dissolved in kerosene as a mobile carrier. The permeation rate equations were derived taking into account the aqueous film diffusion of metal ions towards and out of the membrane and the membrane diffusion of HEHEHP and its metal complexes. The mass transfer coefficients of metal ions and metal-HEHEHP complexes were also determined using the permeation cell. It was found that the calculated permeation rates were in good agreement with the measured ones.

ISSN:0098-6445    

DOI:10.1080/00986449308936207

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The nature of chlorine dioxide substitution for chlorine in the chlorination reaction sequence of pulp bleaching in not well understood. Multiple results may be obtained by simply altering the order of chlorine-chlorine dioxide addition and the amount of chlorine dioxide substitution. Kinetic curves for chlorine, chlorine dioxide, and various levels of chlorine dioxide substitution were generated. The effects of these various processes on delignification (kappa number reduction) and Adsorbable Organic Halogen (AOX) generation were investigated. More than half of the AOX was found to be generated within the first one minute of any reaction sequence. Similar portions of the delignification were also found to occur within the first one minute of chlorination. The work examines the assumption that chlorine and chlorine dioxide react with different portions of the lignin. Thus chlorine and chlorine dioxide compete for only a part of the lignin molecule. The order of chemical addition dictates which chemical most rapidly attacks the competitive region. The hypothesis that chlorine dioxide substitution is simply a competing/parallel reaction sequence was studied.

ISSN:0098-6445    

DOI:10.1080/00986449308936208

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The chemical reaction of trioctylamine (TOA) and sulfuric acid in organic solvent/aqueous solution was carried out. TOA salt products of various kinds were obtained based on different conditions of operation and organic solvents. An equilibrium model, based on the chemical reaction of sulfuric acid and trioctylamine, is proposed. The equilibrium constants of various reactions of trioctylamine and sulfuric acid were searched by means of the modified LETAGROP-DISTR computer program, from which the sum of the least-square error of the extraction of sulfuric acid per unit concentration of TOA salts was minimized. The corresponding concentration profiles of the various main products as a function of the activity of sulfuric acid in the aqueous solution were also obtained. The activity coefficient of the sulfuric acid in the aqueous phase and the density of the aqueous solution of sulfuric acid were considered in order to evaluate the activity of the sulfuric acid in the aqueous solution more accurately. The results obtained from the proposed model are consistent with that of Wilson's published model.

ISSN:0098-6445    

DOI:10.1080/00986449308936209

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The hydrodesulfurization (HDS) of thiophene was carried out over mildly deactivated NiMo/ahimina catalysts used for the hydrotreatment of coal-derived liquids. Arrhenius plots were obtained covering a wide temperature range, 180-54O°C. The observed rate constant is found to level off at the highest temperatures. This phenomenon cannot be explained by further catalyst deactivation, catalyst desulfiding, external mass transfer control, formation of an inert external shell or thermodynamic equilibrium for the HDS of thiophene. A modified two-step reaction mechanism is suggested to explain these results. Step 2 has a higher activation energy and controls the reaction rate at lower temperatures. Step 1 has a low activation energy and controls the rate at the highest temperatures. The proposed mechanism successfully predicts the experimental observations. Increasing deactivation affects the effective diffusivity to a greater extent than it does the intrinsic reaction rate constants.

ISSN:0098-6445    

DOI:10.1080/00986449308936210

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The kinetics of the reaction of goethite (a-FeOOH(s)) and barium hydroxide (Ba(OH)2) in an alkaline solution to produce BaO-6Fe2O3by the hydrothermal method was investigated in the present study. The reaction was carried out in a batch closed reactor under high temperature and high pressure. The effects of α-FeOOH(s), Ba(OH)2and NaOH concentrations in the feed and the temperature on the reaction rate were examined. It was found that the reaction rate was highly dependent upon the concentration of Fe(OH)4(aq) (i.e., the dissolved a-FeOOH(s)) and Ba(OH)2. A kinetic model, based on the homogeneous phase reaction, was built to describe the dissolution of a-FeOOH(s) and the precipitation of the dissolved α-FeOOH(s) (or Fe(OH)4(aq)) and Ba(OH)2in sequence to produce the desired product, BaO.6Fe2O3. The reaction rate at 280°C is expressed as function of Fe(OH)4(aq) and Ba2+concentration.

ISSN:0098-6445    

DOI:10.1080/00986449308936211

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Oxidative reactions of phenol and chlorobenzene with electrogenerated Fenton's reagent, Fe2++ H2O2, were investigated. The electrogeneration of H2O2and the regeneration of Fe2+were performed at a graphite cathode. Results are compared for conventional vs. electrogenerated Fenton's reagent. It was found that the conversion of chlorobenzene was substantially greater by the electrochemical method than the conventional system. The rates of H2O2generation were dependent on solution pH; electrogeneration was favored at low pH, while the opposite was the case for the hydroxylation of the organics. The hydroxylation products of phenol with electrogenerated Fenton's reagent included hydroquinone, catechol and resorcinol. For chlorobenzene, a hydroxylated product (p-chlorophenol) and a dehalogenated product (phenol) were obtained. The rates of phenol and chlorobenzene hydroxylation were dependent on pH, and concentrations of F2+and H2O2. Results indicated that the electrochemical system provided an efficient way to regenerate Fe2+

ISSN:0098-6445    

DOI:10.1080/00986449308936212

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

During dead-end filtration, spatial non-uniformities in the velocity profile upstream of the membrane (for example, Poiseuille flow) can potentially lead to non-uniform retentate accumulation on the rejecting membrane. To investigate this effect, we model the filter plus accumulated retentate as a thin porous layer with spatially variable Darcian permeability. By replacing the thin porous layer with an appropriate distribution of stokeslets, expressions for the transmembrane velocity profile for a variety of retentate accumulation profiles and permeabilities are obtained. The time evolution of the retentate accumulation is then considered. Our results indicate that for physically realistic parameter values the retentate will almost always accumulate uniformly on the rejecting membrane. Thus spatial non-uniformities in the upstream velocity can be ignored in the analysis of dead-end ultrafiltration.

ISSN:0098-6445    

DOI:10.1080/00986449308936213

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A numerical scheme based on the Galerkin's finite element method is used to analyze nonisothermal flows of Bingham plastics. These fluids exhibit yield stresses, below which the material does not flow. This condition is enforced by introducing the bi-viscosity model in which the plug behaviour is approximated by a highly viscous fluid. The bi-viscosity model approaches the ideal Bingham plastic model if the pre-yield viscosity becomes large. This numerical method is applied to solve three problems namely the Graetz-Nusselt, recirculating flow, and sinusoidal channel flow problems for various values of the yield stress. The size of the plug as well as the velocity and temperature fields correspond closely with values available in literature.

ISSN:0098-6445    

DOI:10.1080/00986449308936214

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Traditional evolutionary methods for the synthesis of heat exchanger networks normally produce an initial network containing excess units when compared to the minimum units target. Subsequently, this network is simplified by energy relaxation. However, current methods fail to guarantee that the evolution follows a pathway ensuring that the minimum energy penalty is incurred. A new method to guide this evolution is presented. It is based on the application of Kirchhoff's Law to the network. This enables easy prediction of the actual energy penalties incurred by instituting different loop-breaking strategies. The minimum energy penalty may be discovered and the units to be removed to constitute an optimal solution readily identified. The precedence order for loop breaking in networks containing multiple loops can also be determined according to their respective energy penalties. The proposed algorithm enables the designer to undertake the loop-breaking phase of network design with confidence. The minimum energy path may be followed until a final network is discovered.

ISSN:0098-6445    

DOI:10.1080/00986449308936215

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor