流化床二组分混合物的适宜分离气速

在等密度与非等密度二组分混合物分离体系中，考察操作气速对分离度的影响，提出物料的静床高对高效分离气速没有影响，而操作气速取其混合物最小流化速度的１．２倍左右时，二组分混合物产生高效分离，并且此操作气速随着二组分混合物分离状态的判定值（等密度混合物指Ｒｍｆ值，非等密度混合物主要指Ｒｐ值）的增加而拓宽。     

含CO2气体混合物在60℃时的混合性质

测定了６０℃和２－６００ｂａｒ时由ＣＯ２和Ｈｅ、Ａｒ、ＳＦ６以及ＣＨＦ３组成的等分子二元混合物的压缩因子，根据纯物质和混合物的压缩因子计算了压力混合效应和过剩体积。对于真实气体混合性质的描述，本文采用五参数的ＢＡＣＫ方程，方程计算值与实验值符合较好。     

Size segregation in gas-solid fluidized beds with continuous size distributions

Discrete-particle simulations of a gas-solid fluidized bed are used to investigate the species segregation (de-mixing) behavior of systems with continuous particle size distributions. Both Gaussian and lognormal distributions are investigated over a range of distribution widths, restitution and friction coefficients, and gas velocities. The results indicate that: (i) the average particle diameter decreases as the height within the bed increases, (ii) the level of segregation increases with an increase in the width of the particle size distribution, and (iii) segregation is attenuated as bubbling becomes more vigorous. Furthermore, the shape of the local size distribution (i.e., Gaussian or lognormal) is found to mimic that of the overall size distribution in most regions of the fluidized bed.     

Hydrodynamic characteristics of a FCC regenerator

The hydrodynamic and gas mixing characteristics have been determined in a FCC regenerator (0.48 m I.D.x3.4 m high) with FCC particles. Solids holdup in the dense bed decreases with increasing gas velocity, but it increases in the freeboard region. The bubble/void fraction increases with an increase along the bed height at a given gas velocity and increases with increasing gas velocity at a constant bed height. Backmixed tracer gas at the wall region is higher than that at the center region of the bed. The gas backmixing coefficient decreases with increasing gas velocity.     

EVALUATION OF A METHOD FOR MEASURING MIXING TIME USING NUMERICAL SIMULATION AND EXPERIMENTAL DATA

A method for measuring mixing performance in large-scale vessels is investigated. The method is evaluated experimentally in a pilotscale reactor and by using a model based on the three-dimensional calculation of the flow field. The method is based on injection of a tracer and measuring the concentration with several detectors at different locations. The mixing performance is measured as the decay rate of the difference between the concentration at the detectors and the final concentration.

The model predicts a strong dependence on injection point. The assumption of a first-order decay rate of the concentration deviation is more appropriate for some injection points.     

Gas hold-up, mixing time and gas-liquid volumetric mass transfer coefficient of various multiple-impeller configurations: Rushton turbine, pitched blade and techmix impeller and their combinations

Gas hold-up, mixing intensity of dispersion characterised by exchange flows between adjacent impellers and a volumetric mass transfer coefficient are presented for 18 impeller configurations in triple-impeller vessel of inner diameter . Rushton Turbines, six Pitched Blade impellers pumping down and hydrofoil impellers Techmix 335 (Techmix co., Czech republic) pumping up or down and their combinations were used. aqueous solution was used as a liquid phase, which represents non-coalescent batches. Gas hold-ups and volumetric mass transfer coefficients are presented for individual configurations as functions of specific power dissipated and superficial gas velocity. The regression of the mass transfer coefficients shows large standard deviation (30%). The power number included to the regression to express the impeller configuration effect did not improve the standard deviation significantly (23%). The impeller configurations with low power number (less than unity) provide higher dispersion mixing intensities, while the impeller configurations with high power number provide better mass transfer performance.     

Numerical study on the turbulent reacting flow in the vicinity of the injector of an LDPE tubular reactor

Three-dimensional (3-D), transient numerical simulations of the turbulent reacting flow in the vicinity of the initiator injection point of a low-density polyethylene (LDPE) tubular reactor using a large eddy simulation (LES) approach combined with a filtered density function (FDF) technique are presented. The numerical approach allows for detailed predictions of the turbulent flow field and the associated (passive and reactive) scalar mixing. The aim is to study the influence of the injector geometry and initiator injection temperature on the LDPE process in terms of product quality (average polymer chain length, and polydispersity) and process efficiency (such as initiator consumption).     

Shape optimization of a micromixer with staggered herringbone groove

Shape optimization of a staggered herringbone groove micromixer using three-dimensional Navier-Stokes analysis has been carried out. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique is applied to optimize the shape of the grooves on a single wall of the channel. Two design variables, namely, the ratio of the groove depth to channel height ratio and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling the mixing in microdevices. The mixing is affected by the depth of the groove much more than the angle of the groove.     

Enhancement of combustion efficiency with mixing ratio during fluidized bed combustion of anthracite and bituminous blended coal

In order to investigate the effect of mixing ratio of bituminous coal to blended coal on the enhancement of combustion efficiency, combustion experiments of blended coal with anthracite and bituminous are done in a laboratory scale fluidized bed combustor (10.8 cm ID and 170 cm height). The gross heating values of anthracite and bituminous coal used in this study are 2,810 cal/g and 6,572 cal/g, respectively. Experimental parameters are fuel feed rate, superficial gas velocity and mixing ratio of bituminous coal to blended coal. The combustion efficiency increases with the mixing ratio of bituminous coal due to the lower unburned carbon losses and higher burning velocity of bituminous coal. The rate of combustion in the combustor was increased with mixing ratio resulted from a higher burning velocity of bituminous coal. The measured combustion efficiency experimentally is about 3.5-12.4% higher than that of the calculated value based on the individual combustion of anthracite and bituminous coal under the same operating conditions. The optimum mixing ratio (MR) of bituminous coal determined is around 0.75 in this study. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.