Frequency response in liquid fluidized systems Part I. Effect of particle density and size

Fluid mixing in liquid fluidized beds has been characterized by a dynamic response technique using pulse inputs. Solid particles with a size range of 0.5 to 3.0 mm diameter and a density range from 1.28 to 7.02 gms/cc were fluidized with water at void fractions of 0.4 to 0.85 in a 2-inch column. A dispersed plug flow model has been applied successfully, including a frequency response comparison, and dispersion coefficients have been calculated by the moments method. The results are related to correlations previously advanced, including the use of an eddy diffusivity and of the Bodenstein number, and a more recent refined correlation allowing for density differences.     

Comparison of two-phase upflow and downflow fixed bed reactors performance: Catalytic SO2 oxidation

A time- and space-dependent model based on the piston-dispersion-exchange model for liquid flow was developed to analyze the performance of two-phase upflow and downflow fixed bed reactors and was applied to the catalytic SO₂ oxidation. The hydrodynamic parameters were determined from residence time distribution measurements, using an imperfect pulse method for time-domain analysis of nonideal pulse tracer response. A transient diffusion model of the tracer in the porous particle coupled with the PDE model was used to interpret the obtained RTD curves. Gas-liquid mass transfer parameters were determined by a stationary method based on the least square fit of the calculated concentration profiles in gas phase to the experimental values. It is shown that two-phase downflow fixed bed reactor performs better at low liquid flow rates, while two-phase downflow fixed bed reactor performs better at low liquid flow rates, while two-phase upflow performs better at high liquid flow rates.     

Performance of Fixed Bed Reactors with Two-Phase Upflow and Downflow

A time and space dependent model was developed to analyse the performance of two-phase upflow and downflow fixed bed bioreactors and was applied to biological phenol degradation. The hydrodynamic parameters were determined from residence time distribution measurements, using an imperfect pulse method for time–domain analysis of non-ideal pulse tracer response. A transient diffusion model of the tracer in the porous particle coupled with the PDE model was used to interpret the obtained RTD curves. Gas–liquid mass transfer parameters were determined by a stationary method based on the least square fit of the calculated concentration profiles in gas phase to the experimental values. The analysis of the performance of fixed bed bioreactors used for phenol biodegradation shows that for the same operating conditions two-phase upflow gives much higher conversions. Gas–liquid mass transfer is the limiting step in the rate of phenol biodegradation when the inlet phenol concentration is high. © 1997 SCI.     

高质量分数对二甲苯结晶动力学研究

利用间歇动态法研究高质量分数混合二甲苯中的对二甲苯结晶动力学,应用矩量变换法求解粒数衡算方程,通过测量结晶过程中的母液温度和对二甲苯质量分数的变化,由非线性优化法求解对二甲苯结晶动力学参数。实验结果表明,在自然降温和线性降温方式下,所得到的结晶动力学参数一致,而且能很好地模拟对二甲苯结晶过程的母液中对二甲苯质量分数的变化,相对误差大多在±0.5%以内,因而可以用来优化和模拟对二甲苯结晶过程。     

Residence time distribution in a liquid flowing cocurrently with a gas through a packed bed

Measurement of response curves to an imperfect pulse signal were carried out in a liquid flowing cocurrently with a gas at two positions in a packed bed. Three types of ceramic packing were investigated, viz. spheres, solid cylinders and Raschig rings, all of nominal size 6 mm. The liquids used were water and a corn sugar solution of viscosity 9.13 mPa·s. The curves were analyzed by means of two models: the axially dispersed plug flow model and the Markov chain model; the latter was solved for this purpose. Empirical correlations for the model parameters were obtained.     

Hydrodynamic models for the interpretation of the liquid flow in trickle-bed reactors

Two hydrodynamic models of the liquid in a trickle-bed reactor: PE and PDE model, have been considered, and the influence of the identification method on the parameter values was examined. The employed identification methods were: the moments method, supplemented by graphical determinations on the response curve, and the best fit method, where the minimum absolute and relative error between the calculated and experimental response curve was adopted as identification criteria.Except the total liquid hold-up, the values of the other parameters of both models were very sensitive to the identification method especially at low liquid flow rates. For this reason, much care must be taken in comparing literature results.The experimental runs were carried out with two tracer of rather different diffusivity; no influence of this on the parameter values was observed; this would mean, in particular, that the mass transfer between dynamic and stagnant zones is attributable to the movement of fluid streams between them.     

Slug flow characteristics of gas–miscible liquids in a rectangular microchannel with cross and T-shaped junctions

The slug flow of an inert gas and two miscible liquids in microchannels has found its applications in the preparation of solid lipid nanoparticles (SLNs) by the liquid flow-focusing together with Taylor bubbles in microchannel systems, synthesis of metal nanoparticles or colloid silica in microreactors and enhancement of micro-mixing by interaction using gas bubbles in microfluidic devices. In this work, the flow characteristics of the slug flow generated by nitrogen gas and two miscible liquids (the aqueous surfactant solution and acetone or ethanol) flowing in a rectangular microchannel were investigated experimentally by using the high-speed optical imaging method. The microchannel system has a straight main channel for introducing one of the miscible liquids, a cross-junction for injecting of the other miscible liquid, and a T-junction for feeding the gas phase. The pressure drops were measured and images of Taylor bubbles and slug units at various velocities were obtained, from which other flow parameters were determined. Correlations for the velocity and length of Taylor bubbles, the bubble nose length, the bubble tail length, the liquid slug length, the maximum and minimum thicknesses of the liquid films around bubbles, as well as the pressure drop, were proposed. The calculated values of these parameters by using the correlations were compared with the experimental data. The results showed that the proposed correlations are in a good or reasonable agreement with experimental data and then expected to be available in the estimation of the slug flow parameters of the inert gas and two miscible liquids in rectangular microchannels.     

Comparison of hydrodynamic parameters for countercurrent and cocurrent flow through packed beds

Hydrodynamic parameters have been determined in common equipment, i.e., same column and liquid and gas distributors, for cocurrent and countercurrent two-phase flow through fixed beds. The piston/dispersion exchange model (PDE) with usual Danckwerts' boundary conditions (closed/closed system) has been used to describe the liquid flow. A new imperfect pulse method has been used to estimate the PDE model parameters directly from the experimentally nonideal input and output response. The transition between trickle flow and pulse flow, for two-phase downflow, and the occurrence of flooding, for countercurrent flow, has been investigated using a macroscopic model for the two-phase flow.     

Estimation of Weibull parameters for the flexural strength of PMMA‐based bone cements

The wide scatter of data observed in the strength of bone cements based on poly(methyl methacrylate) (PMMA) can be described properly by the two‐parameter Weibull function. However, the statistical character of the distribution leads to an uncertainty in the parameters evaluated from a limited number of experiments. This study is concerned with the analysis of the methods of estimation as well as sample size on the estimates of the Weibull parameters. The maximum likelihood method, moments method, and linear regression method were studied. Monte Carlo simulations were carried out in order to assess the influence of the number of specimens tested on the Weibull parameters calculated by the different methods. The number of specimens tested displayed a large influence upon the calculated Weibull modulus. By applying weighing factors to the linear regression method, the standard deviation of Weibull parameters decreased significantly. As a compromise between minimizing both the dispersion of the evaluation method and the experimental effort, the use is suggested of the linear regression method with a minimum number of 20 specimens in a nonweighted analysis and 10 in a weighted analysis.     

Size of bubbles and liquid circulation in a bubble column with a draught tube and sieve plate

The size distribution of bubbles and the liquid circulation in a bubble column with a draught tube and sieve plate were studied experimentally. The size of bubbles is well correlated with the previous result of the authors; the size distribution data are fitted reasonably well by a logarithmic normal probability distribution. Gas holdup in the draught tube and annulus and pressure drop were measured and correlations for these parameters are obtained. An energy balance is used to predict liquid circulating velocity using gas holdup and pressure drop correlations. Reasonable agreement is found between the calculated and measured circulating velocity.     

Performance Correlations for Reciprocating Plate Extraction Columns

Abstract The height equivalent to a theoretical stage (HETS) is estimated using one correlation to describe behavior for reciprocating speeds below the optimum point and a second expression to estimate HETS values for reciprocating speeds above it. These two equations are then combined to yield a generalized expression that is applicable in both regions and which can be used to predict the minimum HETS and the optimum reciprocating speed. The observed dependence on the operating parameters and the physical properties of the liquid/liquid system generally agree with those observed in HETS correlations for pulse columns.     

甲醇-乙酸-丙酸多元体系汽液平衡

用新型泵式沸点仪测定了在100kPa下甲醇-乙酸、甲醇-丙酸、乙酸-丙酸3个二元体系以及甲醇-乙酸-丙酸三元系在不同液相组成时的沸点,并用间接法T-p-x(温度、压力和液相摩尔分数)推算了3个二元体系的汽相平衡组成。3个二元体系活度系数分别用Wilson模型、NRTL模型、Margules模型和van Laar模型进行关联,用最小二乘法求出了它们的液相活度系数模型参数,同时,用这些模型参数来计算它们的汽相摩尔分数。所得的液相活度系数来计算3个二元体系的过量吉布斯自由能函数,且所研究的所有体系中各组分之间不存在共沸点。用3个二元体系Wilson模型参数对所测的三元体系数据进行关联,建立该系统汽液平衡的热力学模型并计算平衡时的汽相摩尔分数和泡点温度。由面积积分法检验这些模型参数计算的3个二元体系相平衡数据,得到很好的热力学一致性。     

Interactions of organic solvents with aromatic heterocyclic polymers. I. m-phenylene polybenzimidazole

A new method of interpreting gas-chromatographic (GC) data for determining solvents for thermally stable polymers has been developed. An equation is derived for molar Gibbs energy of sorption in terms of chromatographically measured parameters. The polymer used in this study is poly(5,5′-bibenzimidazole-2,2′-diyl-1,3-phenylene), or PBI. A battery of 40 compounds, including solvents and nonsolvents for PBI, was studied. This method involves determining molar heats of sorption and molar Gibbs energies of sorption at infinitely dilute surface coverage. Mathematical correlations between the measured thermodynamic quantities and the solvent polarizabilities and dipole moments were developed. From these correlations it was possible to explain the behavior of known solvents of PBI and predict new solvents for this polymer. The results of the interpretation of GC data were supported by quantitative solubility experiments.     

2,2-二甲基丁烷+乙醇、+正丙醇二元体系常压汽液平衡的测定

使用自行设计的汽液平衡釜测定了常压下2,2-二甲基丁烷+乙醇和2,2-二甲基丁烷+正丙醇二元体系的汽液平衡数据,所得到的汽液平衡数据通过了Herrington面积法热力学一致性检验。实验数据用NRTL方程进行关联,采用关联得到的模型参数计算相应的汽相组成,并与实验值比较。汽相组成的平均偏差小于0.02,这说明NRTL模型适用于所研究的二元体系。     

滴流床反应器内脉冲流宏观流体力学的特性参数

引　言在石油化工工业的加氢处理中 ,滴流床反应器常操作在接近脉冲流流型区域[1] .脉冲流下气液流速都比较高 ,所以该操作方式适合催化剂活性高、反应速率快的反应[2 ] ,而且气液流量大有利于强放热反应的反应热从反应器移出。流体力学参数如脉冲速度、脉冲频率、持液量、气液分布、压力降等对于该类反应器的工业设计及操作具有很重要的意义 .Ｓａｔｏ等[3] 较早地对脉冲流的特性进行过定性的实验研究 .Ｂｌｏｋ等[4 ] 以及Ｔｓｏｃｈａｔｚｉｄｉｓ等[5] 通过电导法也对脉冲流宏观特性进行过研究 .本文用不同的实验方法对滴流床反应器内脉…     

Experimental Investigation of Gas Holdup and Slug Lengths in an Upflow Monolith Reactor

A new non‐invasive visualization technology was successfully developed to determine the hydrodynamics parameters of Taylor flow in monolith channels. With the developed method, the gas and liquid slug lengths as well as the gas holdup in channels of different radial positions were measured. Accordingly, the average gas holdup in different radial zones and the mean slug lengths over the monolith cross‐section were calculated with varying superficial gas and liquid velocities. By defining the maldistribution factor, the degree of non‐uniform distributions of these parameters over the monolith cross‐section was investigated quantitatively. The results showed that a moderate gas‐to‐liquid velocity ratio can result in uniform distribution for both gas holdup and slug lengths. In addition, the obtained mean slug lengths were well correlated with simplified Qian and Lawal correlations.     

Trickle-bed reactors: Tracer study of liquid holdup and wetting efficiency at high temperature and pressure

Liquid holdup and wetting efficiency were measured by means of stimulus-response (pulse-tracer) experiments in a trickle-bed reactor, packed with a commercial hydrodemetallization catalyst, and operated at 10 MPa and 330–370°C, with a superficial liquid velocity of 1.4 to 8.3 × 10^?4 m/s. The total liquid holdup was obtained from the first moments, and the external wetting efficiency from the second moments, of the response curves. The dynamic holdup obtained from the total holdup lies within the range described by existing correlations, but wetting efficiency is significantly lower than literature data obtained at ambient conditions.     

甲基异丙基酮制备3,4-二甲基吡唑的热力学计算与分析

采用Joback基团贡献法、Lydersen法、Riedel法、Ednister法、Rowlinson-Bondi对应状态法、Benson法估算了甲基异丙基酮制备二甲基吡唑反应体系相关物质的基本物性参数如常沸点、临界参数和偏心因子,基本热化学性质参数如气体热容、液体热容和蒸发潜热、气体标准摩尔熵、相变熵。利用键能法计算了气体的标准反应热,计算了实际反应条件下的反应热、吉布斯自由能及相关反应的化学平衡常数,并对反应体系的特点进行了分析,估算数据可为理论研究、工程设计与放大及生产提供参考。     

Residence time distributions in short tubular vessels

The results of an experimental study of the influence of vessel dimensions and fluid velocity on residence time distributions (RTD's) are presented. Length to diameter ratio (L/D) exerts the major influence on the RTD for the range of sizes and velocities studied. At L/D ≤ 2.6, the RTD resembles the response of a well stirred vessel with by-passing to a pulse signal. Both Reynolds No. (N_Re) and nozzle to vessel diameter ratio (d/D) effect the RTD. At L/D ≥ 5.2, the RTD resembles the response of stirred tanks in series to a pulse. N_Re and d/D do not effect the RTD and can be neglected for scale-up. The second and third moments of the RTD's and parameters of a finite stage model fitted to the RTD relate qualitatively to L/D, d/D and N_Re, but neither the moments or the particular finite stage model used are satisfactory for quantitative correlations.     

氯丁烷-正丁醇体系等压汽液相平衡研究

采用泵式沸点仪测定了常压下氯丁烷—正丁醇二元体系在不同液相组成下的沸点,并用间接法由TPX推算了与之平衡的汽相组成。用最小二乘法求出了该系统的液相活度系数模型参数,由模型参数推算的泡点与实验值符合良好。