摘要:

AbstractPart 1 of this contribution reported on the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced four correlations which define the respective maximum heat transfer. Part 2 of this study suggests that the heat transfer between exchanger surfaces and bubbling fluidized beds depends on superficial gas velocity, expressed as dimensionless excess gas velocity. The present paper shows that heat transfer coefficients in circulating fluidized beds can be predicted by evaluation of a state diagram, which combines three dimensionless groups: Nusselt number, Archimedes number and a dimensionless pressure gradient. A comparison of coal combustion experiments with own cold model measurements indicates that the radiative component of heat transfer coefficients is only evident at very low dimensionless pressure gradients.

ISSN:0930-7516    

DOI:10.1002/ceat.270150502

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractPure shear deformation of a bulk solid sample was performed with the True Biaxial Shear Tester. The influence of stress history on pure shearing was examined by three different consolidation procedures. Apart from the influence of the consolidation procedure, the effect of volume change, i.e. the change in the bulk solid density during consolidation, on pure shear deformation was investigated. Cohesive limestone withx50= 5 μm was used for the experiments

ISSN:0930-7516    

DOI:10.1002/ceat.270150503

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThick‐walled components subjected to pulsating internal pressure are widely applied in high‐pressure technology and in manufacturing processes such as fluid‐jet cutting and high‐pressure cleaning, mainly in conjunction with reciprocating pumps. Corrosive fluids require high‐strength and tough chrome‐nickel steels with soft martensitic or semi‐austenitic structure. This contribution reports on the fatigue of thick‐walled plain and cross‐bored pipes made from high alloy chrome‐nickel steels such as X5 CrNiMoCu 21 8 and X5 CrNiMo 16 5. The speciments, uniaxial standard form and thick‐walled pipes, were cut from forged blocks in the three axial directions. For loading with pulsating pressure, a suitable, high‐frequency piston pulsation machine has been developed. The fatigue tests on pipe specimens show typical Woehler characteristics with only slight scatter and relatively good isotropy. The surprisingly large admissible pulsating pressure can be explained for the applied steels by dynamic generation of residual stresses as a result of shake‐down effects. Presentation in a Smith digram explains the occuring dynamic shake‐down and its favourable results in comparison to the more brittle highly tensile steels. It also reveals that heat treatment to higher tensile strength does not always yield an increase in the admissible pulsating pressure. It will be shown that static autofretting and shake‐down affect the fatigue strength of thick‐walled pipe specimens in the same way. Tests with internal liners in the tube specimens provide indications on the sensitivity of material failures towards fluids. The investigation aids the understanding of the fatigue behaviour and the design of components made of modern high‐st

ISSN:0930-7516    

DOI:10.1002/ceat.270150504

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIn stirred systems, the presence of solid particles leads to a pronounced lengthening of mixing time, sometimes to over 10 times that for the single‐phase state. The mixing behaviour is strongly heterogeneous, since the slurry is mixed comparatively rapidly, while markedly slower homogenization occurs in the solid‐free zone. This is the consequence of different fluid velocities in the two regions. For particle settling velocities in excess of 5 cm/s, mixing times assume maximum values on reaching the state of complete suspension. By contrast, at lower settling velocities, maximum mixing times occur before suspension is complete. Mixing times are influenced only be the state of suspension and not by the mode of its generation. Consequently, for the fulfilment of the 90% suspended slurry height criterion, mixing times are independent of stirrer speed, solid concentration, type of agitator or diameter ratiod/D. The effects of particle diameter, viscosity and equipment dimensions on mixing time, when the 90% slurry height criterion is fulfilled, are reflected by the ratio of the vessel diameter to a representative liquid veloc

ISSN:0930-7516    

DOI:10.1002/ceat.270150505

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractFor water saturated tri‐n‐butyl phosphate (TBP) and for solutions of nitric or nitrous acid therein, the density, viscosity, physical solubility of nitric oxide (NO) and phase equilibria with aqueous phase, as distribution coefficients and water content of the TPB‐phase, were determined. The diffusion coefficient of nitric oxide was calculated, considering the solvent mixture to consist of one, two or, in the presence of nitric acid, three compo

ISSN:0930-7516    

DOI:10.1002/ceat.270150506

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo ways of enhancing liquid to solid mass transfer in regular packings are proposed and investigated: the introduction of a fluidized bed of inert particles and of turbulence promoters by constructing the packing from expanded metal. It is shown that both systems can be of considerable benefit in improving the mass transfer performance: up to 200% in the first case and up to 130% in the second case. However, the energy dissipated by fluidized particles is excessive in comparison to that consumed by turbulence promoters.

ISSN:0930-7516    

DOI:10.1002/ceat.270150507

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to evaluate the exergetic efficiency of the sulphuric acid decomposition process, which occurs in hydrogen producing thermochemical cycles and chemical energy storage systems. It is a process in which sulphuric acid is decomposed to a gaseous mixture consisting of water, sulphur dioxide and oxygen, using high temperature thermal energy, oxygen as a vector and mostly adiabatic equipment. Parts of the basic process with excessive exergy losses have been identified and a modified flow sheet has been developed and analyzed from thermodynamic and engineering points of view. Thermodynamic analysis of the modified flow sheet indicates that the overall exergetic efficiency of the decomposition process is 79.86%, which represents an improvement of 14.17% over the basic process. Engineering analysis of a plant producing 106mol of SO2per hour shows that the typical levelized cost of chemical exergy production was $ 2.25/GJ exergy from the basic process and $ 1.79/GJ exergy from the modified process.

ISSN:0930-7516    

DOI:10.1002/ceat.270150508

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractChemical transesterification is of major importance to the edible oil industry. While alkali catalysts randomize all the fatty acids in a triglyceride mixture, the use of a1,3specific lipase causes a more selective exchange of fatty acid residues. Basic process parameters for the development of a continuous solvent‐free process in a fixed bed reactor have been determined. The kinetics of the transesterfication reaction and the influence of particle diameter, substrate and water concentration on the effective reaction rate were examined in batchwise experiments. Residence time distribution and parameters of inter‐ and intraparticle mass transfer were determined by modelling of experiments carried out in a fixed bed reactor under transient conditions. Fixed bed reactors with side stream analysis were used for continuous transesterification. A kinetic model was developed for the enzyme catalyzed reaction, thereby showing the analogy between heterogeneous catalytic and enzyme catalyzed reactions. A one‐dimensional heterogeneous reactor model was formulated on the basis of the kinetic equation and different process parameters. For numerical calculations, an exponential enzyme distribution inside the carrier was assumed. The simulation of experimental results indicates that they are well described by the developed model. Water concentration and presence of other substances strongly influence the stability of the immobilized e

ISSN:0930-7516    

DOI:10.1002/ceat.270150509

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper presents a new approach to the modelling of solid catalyzed Ziegler‐Natta polymerization of propylene, using orthogonal collocation technique. It is shown that this model can predict the width of the molar mass distribution (MWD) of the product polymer. Its computation time is much shorter compared to other models. An interesting feature of the model is that it considers the discrete nature of the microcatalyst particles and takes advantage of solving a smaller number of stiff differential equations by choosing the number of internal collocation points judiciously. In addition, pseudo‐steady state approximation (QSSA) is applied to some of the moment generating equati

ISSN:0930-7516    

DOI:10.1002/ceat.270150510

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractFor pure tri‐n‐butyl phosphate (TBP) as well as solutions of cupric chloride in TBP and for mixtures of TBP withn‐decane or solutions of cupric chloride therein, the density, viscosity, physical solubility of nitric oxide (NO) and its diffusion coefficient have been determined and a discussion is pre

ISSN:0930-7516    

DOI:10.1002/ceat.270150511

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY