摘要:

AbstractDue to induced turbulent interactions between particles to be separated and the scrubbing liquid present as droplets, very good collection efficiency down to submicron particle size can be achieved as shown by detailed studies [1]. Assumed are suitable flow conditions, a long residence time and a certain droplet size distribution or a special liquid dispersion system. As the name implies, the cyclone scrubber basically consists of a cyclone. This cyclone serves as a contact space in which the interaction between dust particles and scrubbing liquid droplets takes place, and as a droplet separator. Thus, under normal conditions, a water saturated but dust‐ and droplet‐free gas stream leaves the cyclone. The droplets are generated by a pneumatic atomization nozzle, arranged at the cyclone inlet in the direction of flow. A complete theoretical description of the three‐dimensional, three‐phase, non‐steady turbulent flow in the cyclone scrubber has not been possible up to now. The detailed experimental investigations presented in this work, and covering multiple parameters, led to physically based conclusions about the dominant interactions and separation mechanisms involved. Grade efficiencies which did not fall below 0.75, down to a particle size of 0.5 μm, could be measured by an optical particle counter. Collection efficiency of 99.2% was determined by gravimetric analysis of the dust load, according to VDI‐guideline 2066, in the raw and clean gas sections of the dust load, according to VDI‐guideline 2066, in the raw and clean gas sections of the cy

ISSN:0930-7516    

DOI:10.1002/ceat.270170202

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractPlasma arc welding processes are used in the off‐shore industry for construction and maintenance of underwater structures and pipelines in a wet environment. At greater water depths the density of the plasma gas increases because of the greater hydrostatic pressure. This causes conductive heat losses to the wet environment to increase. To maintain the energy flux to the workpiece to be welded, the plasma arc has to burn in a local dry area with an inside pressure of 1 bar. This requirement can be fulfilled by a rotating cylinder with a liquid film flowing down the inner wall. The flow around the rotating cylinder is experimentally investigated. The rotating cylinder is placed above the work surface which is simulated by a flat plate. Because of the centrifugal forces of the rotating flow inside the gap between the lower end of the cylinder and the flat plate the water is forced out of the cylinder. The velocity distribution in the flow is measured by laser Doppler anemometry. The phase distribution in the two‐phase flow in the gap is measured by local electrical probes. The static pressure inside the gaseous atmosphere is reduced in comparison to the hydrostatic pressure of the surrounding water. The pressure reduction is given by the void fraction, the phase distribution and the volume flow rates of both phases in the gap as well as by the speed of revolution and the design of the cylinder and the work surface. The influence of these parameters on heat transfer from the workpiece to the two‐phase flow regime is also investi

ISSN:0930-7516    

DOI:10.1002/ceat.270170203

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractInertial deposition of aerosol droplets (diameter: 1–14 μm) on steel spheres (diameter: 3–9 mm) was investigated. Air velocity was varied between 7 and 28 m/s (corresponding sphere Reynolds numbers: 1400–17000). The impaction on single spheres as well as that on linear arrays of eight spheres was measured. Theoretical results, based on potential flow investigations were verified by single sphere experiments. Of special interest was the range of lower Stokes numbers, where the theoretically predicted limit of deposition cannot be verified. The experiments on sphere arrays were for the first time performed in the low Stokes number range. Deposition on the leading sphere, relative to that on the shielded spheres, exhibits a maximum in the high Stokes number range, but this changes drastically in the low Stokes number range. Here, maximum deposition can be found on the shielded spheres while the leading sphere shows a markedly lower depo

ISSN:0930-7516    

DOI:10.1002/ceat.270170204

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe process of homogenization of liquids in a tall vessel equipped with a multiple impeller was studied. Up to four standard Rushton turbines and/or six pitched‐blade turbines were used. The mixing time in the system was measured by the conductivity method. A continuous time history of the tracer concentration at several points in the system was recorded. The data were interpreted by means of an adapted cell model of the flow within the stirred vessel with several impellers based on the assumption of well mixed cells and intercellular flow of liquid. The liquid transfer flow rate between the cells, as a parameter of the model, was calculated from experimental data. A good agreement between the time dependence of concentration obtained experimentally and that calculated from theory was obtained. A direct relationship between the flow numbers between cells and those of impellers was establishe

ISSN:0930-7516    

DOI:10.1002/ceat.270170205

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe objective of this study was to determine the influence of viscosity on micromixing in turbulent flow. It was first necessary to find a suitable viscosity‐raising additive. HEC (hydroxyethyl cellulose) proved to be better than previously studied additives [sorbitol and carboxymethylcellulose (CMC)]. In concentrations up to 1 wt‐%, HEC solutions are almost Newtonian with viscosities independent of pH over the range 2 to 10. HEC had no effect on the reaction rate constants and the spectrophotometric analysis of the fast, competing reactions used – the diazo coupling between 1‐naphthol and diazotized sulphanilic acid. The viscosity can then be raised by around an order of magnitude by adding less than 1 wt‐% HEC to this reaction system.Diazo couplings were conducted in a 20 1 semi‐batch tank reactor stirred by a Rushton turbine at two viscosity levels (0.9 and 6.2 mPa s). Long feed times ensured that micromixing was controlling. More bisazo dye was formed in the more viscous solution, all other conditions being unchanged, indicating more intense segregation and slower micromixing.This was also shown by visualizing the extent of neutralisation zones, with more spreading and slower micromixing being observed in viscous solution. Higher turbine speeds reduced this spreading. One feed point near and one far from the turbine were employed: the strong inhomogeneity of the turbulence led to smaller amounts of bisazo dye when the feed was added to the turbine suction, irrespective of the viscosity. All results agreed with the trends predicted by the engulfment model of micromixing. Its simplest form assigns an average energy dissipation rate to the reaction zone: the values obtained are of similar magnitude to those measured by physical techniques and were related to the spreading of the re

ISSN:0930-7516    

DOI:10.1002/ceat.270170206

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been shown that, after a partial deactivation, γ‐alumina (γ‐Al2O3) is a good catalyst for selective methylation of 1,2‐benzenediol in the temperature range of 260–310°C. The main products are the desired 3‐methyl‐1,2‐benzenediol and 2‐methoxyphenol, which may be converted in another step into 3‐methyl‐1,2‐benzenediol, giving an overall selectivity for the desired products of 80 to 90%. The catechol forms a strongly chemisorbed surface species on γ‐alumina and its steric adsorption model corre

ISSN:0930-7516    

DOI:10.1002/ceat.270170207

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractKinetic studies as well as morphological and physico‐chemical surface studies have been carried out on the deactivation of a palladium carrier catalyst for vinyl acetate synthesis in the ethylene gas phase process. The experiments cover concentration and temperature ranges of technical interest at a total pressure of 900 kPa. The deactivation rate depends on the temperature and the oxygen and acetic acid concentrations. The decline in activity is best described by a rate law of second order relative to the activity number. This behaviour is attributed to the observed aggregation of finely dispersed palladium. It can be concluded that palladium(II) acetate acts as a transport species in a chemically assisted sintering mechanism. At temperaturesT≤ 438 K the more advantageous final texture of the catalyst will only be formed on react

ISSN:0930-7516    

DOI:10.1002/ceat.270170208

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractUsing methods of statistical thermodynamics, adsorption isotherms for the description of multicomponent chemisorption of different‐sized molecular species are derived by assuming the adsorbing surface to be energetically homogeneous and by neglecting lateral interactions between the adsorbed particles. In the first part of this contribution, the adsorption equilibria for a mixture of different‐sized chain molecules adsorbed on a lattice of coordination numberzare discussed supposing each unit of a given chain to bind to one adsorption site only. In the second part, the coadsorption of molecular species consisting of a different number of segments on a continuous surface is treated. A comparison of the predicted to the measured isotherms for the coadsorption of two freon species on activated carbon shows that the proposed equations describe the results of the coadsorption measurements sufficiently well, provided the adsorption data for the pure components have been determined experimenta

ISSN:0930-7516    

DOI:10.1002/ceat.270170209

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractA novel reactor arrangement for the anionic polymerization of styrene described in this paper comprises alternating adiabatically operated plug‐flow reactors and heat exchangers. A novel tube‐bundle recycle reactor is presented for the bulk polymerization of styrene and acrylonitr

ISSN:0930-7516    

DOI:10.1002/ceat.270170210

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractA continuous production process has been developed up to pilot scale (300 l) for FDH production with the methylotrophic yeastCandida boidinii. A high cell mass specific FDH activity (50 U/g) is achieved by process computer controlled supply of pure methanol to operate the reactor at an optimum methanol concentration of 10 g/l. The maximum FDH spacetime yield achievable with this process control involves a residence time of 7 h. The FDH space‐time yield (STY) and FDH concentration are a function of the oxygen transfer rate (OTR) of the fermenter (maximumSTY= 255 U/(l h) atkLa= 870 l/h). For a reasonable compromise between high FDH space‐time yield and high FDH concentration, an optimum residence time is adjustable by regulating the supply of nutrient salt solution in relation to theOTRof the fermenter. On a pilot scale (200 l continuously stirred tank reactor) roughly 4 million U of FDH were produced within 10 days at a residence time of 14.3 h. Isolation of intracellular FDH enzyme was performed using extraction with an aqueous two‐phase system (PEG/K2HPO4). A technical product quality of 1.2 U/mg FDH was achieved without any chromatographic purification

ISSN:0930-7516    

DOI:10.1002/ceat.270170211

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY