摘要:

AbstractThe combustion of single bituminous char particles (4‐12 mm diameter) was studied in a turbulent fluidized bed operated at 1098 K using air as the fluidising medium. Results indicated that particles burn with constant density following a shrinking sphere model. Burning rates are much higher than those observed in a bubbling fluidized bed. The rate of transfer of oxygen to the particle surface is also higher than that observed in bubbling beds. A model is proposed to calculate the Sherwood numbers of the burning carbon particles. Experimental values of the Sherwood numbers agree well with those predicted from the mode

ISSN:0008-4034    

DOI:10.1002/cjce.5450710102

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

年代:1993

数据来源: WILEY

摘要:

AbstractDevolatilization and char burning were studied in an electrically heated bench‐scale fluidized‐bed reactor at 750 to 900°C bed temperature, gas oxygen mole fractions ranging from zero to 0.21, superficial gas velocities from 0.3 to 0.7 m/s and coal particle diameters 5 to 35 mm. The coals investigated include lignite, bituminous and anthracite. The coal devolatilization and char burning times, H/C ratio histories, and particle fragmentation were measured. Statistical correlations with the operating variables were developed for the devolatilization time. A mathematical model is given for the combustion of char. Most predictions of the model agree quite well with the experimental res

ISSN:0008-4034    

DOI:10.1002/cjce.5450710103

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe grade collection efficiencies and particle size distributions from Stairmand‐type cyclones are compared with predictions from four theories, viz. the models of Leith and Licht (1972), Dietz (1981) Mothes and Loffler (1988) and Li and Wang (1989). It is shown that the theory of Mothes and Loffler, which recogizes different flow regions within a cyclone, coupled with a realistic estimate of the particles turbulent diffusivity, is capable of providing good estimates of both the grade‐efficiency curves and particle size distributions of the cyclone catch and/or outlet dusts. The lack of adequate theories or empirical formulae to estimate the effective turbulent diffusivity under cyclone flow seems the major factor hindering the use of the Mothes and Loffler theory for predictive purposes. High loadings and agglomeration of fines, if present, are responsible for strong departures from theoretical predicti

ISSN:0008-4034    

DOI:10.1002/cjce.5450710104

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

年代:1993

数据来源: WILEY

摘要:

AbstractA recent laser doppler anemometer study, by other researchers, of turbulent flow through a sudden expansion has been simulated using a kinetic energy of turbulence‐dissipation rate of turbulence (k‐ ϵ) model. The near wall region was modelled in two different ways; using wall functions (WF), and a low‐Reynolds number (LRN) formulation.The reattachment length under particular flow conditions was obtained. Radial profiles for the mean axial and radial velocity, turbulence kinetic energy and Reynolds shear stress were determined for six locations downstream of the sudden expansion. Both models performed reasonably well in predicting the flow with the LRN approach performing slightly better than the WF approach near to the wall.The application of the LRN approach to the calculation of local mass transfer rates in wall bounded complex turbulent flows is demons

ISSN:0008-4034    

DOI:10.1002/cjce.5450710105

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

年代:1993

数据来源: WILEY

摘要:

AbstractFlow regime data of condensing steam inside an inclined 13.4 mm ID tube are presented. The effect of upward and downward inclinations within ± 10° on the different transition lines is discussed. In all test runs, complete condensation has been achieved inside the condenser, with or without full tube at exit depending on the total mass flow rate and inclination angle. It is shown that the zones occupied by the wavy and slug regimes experience significant shifts, whereas the effect on the annular flow boundary appears to be insignificant at the present small inclination angles. The present data sets are compared with adiabatic gas‐liquid flow regime maps developed analytically and experimentally for horizontal and inclined tubes. Deviations due to the condensation process are observed; however, consistent trends are identified among the two types of f

ISSN:0008-4034    

DOI:10.1002/cjce.5450710106

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe impeller discharge stream and bulk circulation flow produced by a pitched blade turbine (PBT) in a fully baffled stirred tank have been defined, using a combination of flow visualization and laser Doppler anemometry measurement techniques. Two distinct bulk circulation patterns have been identified, one for higher off bottom clearances, and one for lower clearances. The circulation patterns are shown to have a substantial impact on the discharge stream, even very close to the edge of the impeller blades. These findings indicate that the action of the impeller is not independent of the tank geometry, but contains a substantial feedback component from the bulk flow. This conclusion has substantial implications for the modelling and prediction of stirred tank flow fields.

ISSN:0008-4034    

DOI:10.1002/cjce.5450710107

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

年代:1993

数据来源: WILEY

摘要:

AbstractNumerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel widthb= 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air‐water and air‐ethanol systems with gas Reynolds numberReg= 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporat

ISSN:0008-4034    

DOI:10.1002/cjce.5450710108

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe fluid dynamic behaviour and the liquid‐solid mass transfer to horizontal cylinders, under bubble induced convection, was investigated. The gas void fraction was measured and overall mass transfer coefficients were determined for single cylinders as well as for banks of tubes with various characteristic

ISSN:0008-4034    

DOI:10.1002/cjce.5450710109

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

年代:1993

数据来源: WILEY

摘要:

AbstractExperimental data on the kinetics of methane hydrate formation in aqueous electrolyte solutions are reported. The experiments were carried out in a semi‐batch stirred tank reactor in three NaCl and two KCl solutions as well as in a solution containing a mixture of NaCl and KCl at three different nominal temperatures from 270 to 274 K and at pressures ranging from 3.78 to 7.08 MPa. The kinetic model developed by Englezos et al. (1987a) was adapted to predict the growth of hydrates. The model is based on the crystallisation theory coupled with the two‐film theory for gas absorption in the liquid phase. The kinetic rate constant which appears in the model was that obtained earlier for methane hydrate formation in pure water. The effect of the electrolytes was taken into account through the computation of the three‐phase equilibrium conditions and the corresponding fugacities. Overall, the model predictions match the experimental data very well with the largest prediction error being less tha

ISSN:0008-4034    

DOI:10.1002/cjce.5450710110

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe influence of pressure up to 5600 kPa and temperature up to 175 °C on the oxidation of low concentrations of H2S in natural gas was studied in a fixed bed reactor over an activated carbon catalyst. Operation of this system at 5600 kPa provides higher catalyst activity (virtually 100% H2S conversion) over a longer period of time and with lower selectivity to SO2than when operated at atmospheric pressure. The desorption of sulfur from a loaded catalyst occurs first from the macropores (>100 nm) of the catalyst which contain a substantial portion of the sulfur load and then from the micropores (<100 nm). This study also indicated that the sulfur recovery process is both rapid and effective at 327°

ISSN:0008-4034    

DOI:10.1002/cjce.5450710111

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

年代:1993

数据来源: WILEY