摘要:

AbstractNew time averaged data of two‐phase flow in bubbly and slug regimes are presented. A modified dual spherical tipped optical fiber probe is used to measure local void fractions, gas velocity and bubble sizes. Hot film anemometry was used to measure the local mean liquid velocity axially. The void fraction, gas and liquid velocities values were presented as averages over the long and short dimensions respectively. Also core values of these variables are presented along the smaller dimension of 12.7 mm, near the plane of symmetry of the longer dimension, to show the most general trend of the different bubbly and slug flow runs. Bubble sizes obtained experimentally were compared with predictive models applied to circular geometries and were found to have a reasonable agreement. It was also interesting to find that local void fractions measured using hot film anemometers were comparable to those found by optical fiber probes.Frequencies of interfacial passage of bubbles and slugs are presented which show rather flat profiles across the channel. It is hoped that these data can be further used in predictive two‐phase two‐fluid models in the future. Lastly of interest is the fact that slip values near the boundaries were shown to be less than 1.0 for some cases in bubbly flow similar to those observed in circular geome

ISSN:0008-4034    

DOI:10.1002/cjce.5450650501

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe motion of a two‐phase bubble in immiscible liquids is associated with the development of three‐phase heat exchangers applicable for heat transfer at low driving forces.An analytical expression for the instantaneous velocity of a two‐phase bubble moving through a quiescent, less viscous, immiscible liquid has been developed. This expression predicts, very well, the available experimental data over the whole operational range of temperature and initial drop dia

ISSN:0008-4034    

DOI:10.1002/cjce.5450650502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe flow in the annulus of a water spouted bed of glass particles (275 to 774 μm) was studied experimentally in a cylindrical half‐column 50.8 mm in diameter.An axisymmetric model, which assumes Darcy flow in the annulus and uses the experimental spout pressure distribution, predicts the flow and pressure fields in the annulus. The substantial differences between this flowfield and that for coarse particle beds that are observed are caused by differences in the normalized interfacial pressure profile.The model predicts that both the fluid velocity and the normalized fluid velocity at the top of the annulus decrease as the particle size and bed height are reduced. Particles are observed to enter the spout primarily near the spout inlet in agreement with predictions of the axial spout voidage distribution.The residence time distribution of the fluid in the annulus is relatively broad and the measured residence times are about 25% higher than those calculat

ISSN:0008-4034    

DOI:10.1002/cjce.5450650503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper uses a quantity of moment of momentum to combine various parameters interacting in a separation cyclone. Due to construction features and flow characteristics, the swirl flow in the cyclone is essentially frictionless and, hence, the incoming momentums of both the transporting fluid and suspended particles are conserved. Visualizing a 50%‐separation screen installed, and employing a stability‐radius theory, the momentums are expressed in terms of distributed masses in the cyclone. Further, in conjunction with the continuity equation, the collection efficiency is determined. The predicted value differs from the experimental one by about

ISSN:0008-4034    

DOI:10.1002/cjce.5450650504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractMaldistributed flow in moving‐bed reactors and heat exchangers is recognized to be a serious problem. Heat exchanger equations do not provide a clue to the cause. In this paper it is shown that maldistributed flow can occur even in perfectly homogeneous packed beds and that this arises because of inherent temperature non‐uniformities. The term thermal channelling is introduced to describe this effect.It is shown that simultaneous consideration of both the heat and the mechanical energy (the Ergun equation) balances predicts that the gas, in cooling a hot bed, divides into a multiplicity of stable channels with significantly differing mass velocities. This does not, however, occur for the inverse case of heating the bed. Further, it is shown that the system conditions where a multiplicity of states is stable can be defined in terms of an integral mean temperature and two dimensionless variables, NTU and the bed Reynolds number. In general tall beds with large temperature differences are most prone to thermal channell

ISSN:0008-4034    

DOI:10.1002/cjce.5450650505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractGas‐liquid volumetric mass transfer coefficients, (kLa), have been obtained for “dead‐end” autoclave reactors operated in two different modes: (a) gas introduced into the gas phase, and (b) gas introduced through a dip‐tube in the liquid. Three different methods ofkLadetermination have been compared. Effects of agitation speed, impeller diameter, gas to liquid volume ratio (Vg/VL), position of the impeller and reactor size onkLahave been investigated. ThekLadata were found to be correlated as:kLa= 1.48 × 10−3(N)2.18(Vg/VL)1.88(dI/dT)2.16(h1/h2)1.16The critical speed of surface breakage, at which transition from the surface convection to the surface entrainment regime occurs, was also determined for different impeller positions, impeller diameters and gas to liquid v

ISSN:0008-4034    

DOI:10.1002/cjce.5450650506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effects of interactions between the perforated and baffle plates, of pulse amplitude and of pulse frequency on axial dispersion in the continuous phase, on the dispersed phase holdup and on the flooding condition have been determined for a 10.2 cm 1D pulsed extraction column. The axial dispersion coefficient increased with both the pulse amplitude and the frequency, but it decreased with the decrease in baffle spacing in the unit module. Dispersed phase holdup increased with the number of perforated plates in the unit module at the lower pulsation velocities and increased with the pulse velocity. The baffle plate reduced the total throughputs, but baffle spacing did not have any significant effect on the total throughput.

ISSN:0008-4034    

DOI:10.1002/cjce.5450650507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe formation and growth mechanism of porous, amorphous, and fine particles were investigated. TiO2particles were produced in a tubular flow reactor by a chemical vapor deposition technique using titanium tetraisopropoxide as a starting material at low temperatures (573‐973 K) and atmospheric pressure. Prepared particles were of submicron size and had large surface area (as large as 270 × 103m2/kg). According to the proposed mechanism, reactions begin on the reactor wall and then the primary particles form in the gas phase by chemical reactions. The primary particles collide, coalesce with each other and grow. However, significant experimental deviations from the Brownian collision and coalescence theory imply that other processes, such as the surface reactions on the particle, play an important role in the growth, in addition to coalescence. Intraparticle reactions decreased the surface area by filling the por

ISSN:0008-4034    

DOI:10.1002/cjce.5450650508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractBased on plug flow of gas and catalyst particles and concentration dependent deactivation kinetics, the performance of transport reactors under a periodic (rectangular pulse) inlet concentration is analysed for improvement in conversion and extent of catalyst decay. The effects of reaction and deactivation orders, reaction and deactivation constant groups, and γ (cycle split) on the performance of the reactors are evaluated theoretically. For reaction orders greater than one, periodic operation improves conversion. Resonance behaviour is observed for certain combinations of parameters. For identical operating conditions vertical upflow, downflow and horizontal flow reactors are compared. Conversion in upflow reactors is higher than that in either horizontal flow or downflow reactors. However, catalyst decay is the least in downflow reactors

ISSN:0008-4034    

DOI:10.1002/cjce.5450650509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractIn the study of the regeneration of cracking catalyst, two approaches may be taken when determining the kinetic rate constant for the coke combustion reaction. A global coke burning rate equation may be considered, based on the observed oxygen concentration and carbon dioxide to carbon monoxide molar product ratio. This reaction may also be represented by an intrinsic coke burning equation which is a function of the oxygen concentration and the carbon dioxide to carbon monoxide molar ratio at the reaction site, combined with a carbon monoxide postcombustion equation. It is proposed in this paper that the rate constant for intrinsic coke burning,kc, is essentially equal to the global coke burning rate constant,kc, and that its value is independent of the rate equation chosen for the carbon monoxide post‐combustion reactio

ISSN:0008-4034    

DOI:10.1002/cjce.5450650510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY