MICROMIXING EFFECTS ON BARIUM SULFATE PRECIPITATION IN AN MSMPR REACTOR

The Effects of non-ideal and nonhomogeneous mixing on barium sulfate precipitation in an MSMPR reactor were observed experimentally and analyzed theoretically. To generate nonhomogeneous mixing the unmixed feed streams were fed to the reactor at the same location (joint feeding mode) or a plug flow reactor was connected to the MSMPR reactor. These nonhomogeneous mixing conditions resulted in significant reductions in particle size and increases in particle numbers. These non ideal mixing effects were dependent on the impeller speed, feed stream velocity and residence time in the connected plug flow reactor and are believed to result from elevated supersaturation levels in a premixing zone which are controlled by turbulent micromixing

To model the effect of nonhomogeneous mixing (premixing) in the MSM PR reactor a plug flow-stirred lank reactor series model was developed. The plug flow reactor represents the premixing region of the MSMPR reactor in which turbulent micromixing is important, and the stirred tank reactor describes the homogeneous mixing region of the MSMPR reactor where particle growth is important. The model predicts that the premixing effect is strongly dependent on micromixing of the feeds in the premixing region, and thus, as the turbulent mixing intensity in this region is increased, the particle size in the product suspension is reduced and the particle population is increased. These predictions of the model arc in good agreement with the experimental data. An interesting prediction of the model is that as the impeller speed increases, the precipitation of barium sulfate in an MSMPR reactor deviates increasingly from the precipitation in a perfectly mixed (ideal) reactor.     

A MODEL OF MIXING IN A MOTIONLESS MIXER

This paper deals with the modelling of a Sulzer-Koch motionless mixer. A flow model involving convection and diffusion has been solved to characterize the dispersive mixing in one node of the network and this result was then complemented by a network analysis to obtain the flow distribution. Experimental data are in general agreement with the theory. The approach of this study is shown to provide valuable conclusions about the design of the mixer and to complement the more commonly used integral or statistical treatments. In particular, it has been shown that the ratio of internal resistances controls the distributive mixing in one mixer unit and that significant convective mass transport takes place within the node even when there is no net cross-flow.     

INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETING REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

A model is proposed for interpreting micromixing experiments in a semi-batch reactor. In these experiments, a fast consecutive-competing reaction system is used A + B → R, R + B → S, B being added either dropwise or as a pulse into an excess of A. A segregation index X_s = 2n_s/n_B0 is measured after completion of the reaction for various locations of the injection point. The macroscopic flow pattern is assumed to be known, essentially characterized by the recirculation time t_c. Micromixing then takes place within the cloud via a mechanism of interaction with the mean environment (IEM model, micromixing time t_m). Experimental results published by Barthole et al. (precipitation of barium sulphate) and Bourne et al. (diazo coupling) are successfully interpreted by this model. The influence of stirring speed, injection volume, concentration of species and mode of injection (pulse or dropwise) are especially well accounted for. This model provides a simple method for predicting the influence of mixing on selectivity in semi-batch reactors.     

塑料混合机结构设计中几个问题的探讨

讨论了热混机、冷混机设计应注意的几个问题,分析了热混机浆叶倾角的设计原则,提出了一种新型冷混机结构。     

RIM混合室中对撞射流混合性能研究

以偶合反应的选择性,评价射流对撞混合器混合性能。研究了低粘流体低速条件下,结构参数(H/d、d/D)和流动参数(动量比)γ,Re)对混合质量的影响。认为 H/d 是非敏感参数,d/D 减小有利于混合,而动量比偏离l对混合稍不利,不能仅用雷诺数作为设计放大的准则。     

密炼机混炼过程的数学模型的研究

本文应用正交实验法进行密炼机的实验设计,并把数理统计、回归分析方法与混炼过程相结合,意在探讨建立一种客观的、统一的和实用的密炼机混炼过程的数学模型。从实验的选择、数据的处理、多元线性方程的求解等方面建立了一整套的建模方法。     

NUMERICAL SIMULATION OF THE TRANSPORT OF VORTEX RINGS IN AN INITIALLY STRATIFIED FLUID

A numerical study of the formation and transport of vortex rings in a cylindrical tank initially occupied by a thermally stratified fluid is presented. A control-volume based finite-difference technique (Patankar's SIMPLER method) is used. The formation of a vortex ring was simulated by injecting a quantity of a fluid through a tube centrally located near the free surface. Initially, the fluid in the tank was stably thermally stratified, with a low density in the upper half and higher density in the lower half. Buoyancy effects were considered. Modelling aspects are discussed and the formation and transport of a vortex ring in the stratified fluid as well as the resulting mixing characteristics are presented.     

SIMULATION OF MICROMIXING IN A TURBULENT TUBULAR REACTOR WITH CONCENTRIC FEED

Turbulence on the axis of a pipe is isotropic and homogeneous and the rate of turbulent energy dissipation, ε, is known as a function of the velocity, pipe diameter and viscosity. When, however, a concentric feed pipe is introduced (as in a reactor), the ε field does not seem to be known. Evidence from fast, mixing-controlled reactions indicates a disturbance near to and downstream from the feed pipe with an increase in ε. Because of the lack of experimental information, the radial and axial distribution of ε has been modeled. One parameter—ε at the outlet of the feedpipe—is undetermined in this model. It is shown how the radial dispersion and especially the micromixing and reaction of fluid emerging isokinetically from the feed pipe can then be calculated, using a one-dimensional, radially averaged formulation. An application to four coupled, mixing-controlled reactions is included. Simulated and measured product distributions compared satisfactorily at various concentration levels and two solution viscosities. Whereas the new model is plausible, more work is needed to understand how a feed pipe modifies the flow in its vicinity.     

ORIGINAL TITLE: INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETITIVE REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

Liquid-liquid equilibrium data for two ternary systems were obtained. The experimental data were measured for cyclohexane-toluene-sulfolane at 17, 25 and 50°C, and for hexane-toluene-sulfolane at 18 and 25°C. The NTRL and UNIQUAC models were used to correlate the experimental results and to calculate the phase compositions of the ternary systems. The agreement between the experimental results and the fitted values was equally good with both of the models.     

低浓度煤层气发电用发动机混合器的设计

介绍了一种新混合器的设计、特点及其工作原理,并对试验结果和原混合器进行了分析,结果表明新的混合器不仅能满足不同浓度燃气的需求,而且降低了燃料消耗,该混合器主要用于低浓度煤层气发电用发动机。     

IDENTIFICATION AND CORRELATION OF MIXING TIMES IN OPPOSED-JET MIXERS

This article deals with the theoretical investigation of the effect of suspended particles on the marginal stability of a double-diffusive ferrofluid layer with internal angular momentum heated from below subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis theory and normal mode analysis method. For the case of stationary convection, the effect of various parameters like suspended particles, solute gradient, magnetization, coupling parameter, spin diffusion parameter, and heat conduction parameter has been analyzed. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of magnetic parameter M₁ and results are depicted graphically. It is observed that the critical magnetic thermal Rayleigh number is reduced because the heat capacity of clean fluid is supplemented by that of the suspended particles. The principle of exchange of stabilities is found to hold true for the ferrofluid with internal angular momentum in the absence of suspended particles, solute gradient, coupling parameter, and microinertia. Oscillatory modes are introduced due to the presence of the suspended particles, solute gradient, coupling parameter, and microinertia, which were nonexistent in their absence. The sufficient conditions for the nonexistence of overstability are also obtained.     

BULK POLYMERIZATION OF STYRENE IN A STATIC MIXER

An experimental investigation of thermal bulk polymerization of styrene in a pilot plant will be reported. The plant is composed of a recycle tubular reactor followed by a tubular reactor. The conversion of the pre-polymerization part is in the range of 0 to 60% and at the outlet of the pilot plant up to 96%. Studies on the residence time distribution show plug-flow behaviour for a variety of different conditions with respect to viscosity and density gradient. The polymers obtained are characterized by gel permeation chromatography and compared to commercial products.     

SOLIDS DISTRIBUTION IN STIRRED SLURRY REACTORS: INFLUENCE OF SOME MIXER CONFIGURATIONS AND LIMITS TO THE APPLICABILITY OF A SIMPLE MODEL FOR PREDICTIONS

The features of solids concentration distribution were investigated in baffled and unbaffled tanks of high aspect ratio, stirred with multiple radial, mixed-flow or axial impellers. In the baffled tanks the average profiles can be predicted with the sedimentation-dispersion model regardless of impeller type - in spite of slight systematic departures from the average trend at the impeller plane and/or midway between the impellers. This is hardly possible for the unbaffled tanks due to lack of physical foundation of this simple model. When the unbaffled tank is stirred with hydrofoil impellers, an inverted profile is even obtained. The mentioned departures and this last anomalous behaviour are qualitatively discussed with reference to particle-turbulence interaction.     

SOLIDS DISTRIBUTION IN STIRRED SLURRY REACTORS: INFLUENCE OF SOME MIXER CONFIGURATIONS AND LIMITS TO THE APPLICABILITY OF A SIMPLE MODEL FOR PREDICTIONS

The features of solids concentration distribution were investigated in baffled and unbaffled tanks of high aspect ratio, stirred with multiple radial, mixed-flow or axial impellers. In the baffled tanks the average profiles can be predicted with the sedimentation-dispersion model regardless of impeller type - in spite of slight systematic departures from the average trend at the impeller plane and/or midway between the impellers. This is hardly possible for the unbaffled tanks due to lack of physical foundation of this simple model. When the unbaffled tank is stirred with hydrofoil impellers, an inverted profile is even obtained. The mentioned departures and this last anomalous behaviour are qualitatively discussed with reference to particle-turbulence interaction.     

氧气转炉吹炼前期的最佳化脱磷工艺基础

通过对上钢五厂15t氧气顶吹转炉试验数据的多元逐步回归分析，进行了脱磷最佳化工艺探讨，提出了分阶段的（MgO），（ZFeO）最佳控制值及Lp，np和（TFe）控制模型，以求“一倒”或终点时Lp接近最大值和np≈1．0强化前期脱磷的技术关键是：采用大氧压、高枪位和添加适量助熔剂，以造好R＝1．6～2．0的初渣和达到［P］t＝7min＝0．05～0．07wt％的目标值．并籍助LP.b控制模型计论了达此［P］值的措施．     

混炼机转子自蒸发循环冷却技术的研究

提出一种新型高效自蒸发循环旋转热管冷却技术来冷却连续混炼机的转子，并进行了模拟试验研究。研究结果表明：采用自蒸发循环旋转热管冷却技术冷却连续混炼机的转子，具有高效的导热性，良好的表面均温性，无泄露，节水等优点。同时试验也表明：充液比（V^ )、工作温度（tv)、转速（n)对自蒸发循环旋转热管冷却技术的传热性能有影响。     

AGGREGATION AND BREAKAGE OF SOLID PARTICLES IN SUSPENSIONS AGITATED IN A VIBRATING MIXER: A NON-FRACTAL APPROACH

Aggregation and breakage of solid particles or aggregates suspended in liquid can be found in numerous industrial processes. It is crucially important to predict the evolution of aggregates at any moment during the process. This aim can be achieved by modeling based on solid phase population balances. A lumped discrete population balance model has been selected for the verification of the experimental data. The experiments have been carried out in a laboratory-scale vibrating mixer equipped with a disc-type reciprocating impeller. A reasonably good agreement between the computational and experimental results of PSD data has been obtained. Dependencies between aggregation and breakage rate coefficients and the average energy dissipation rate in the mixer have been shown.     

MIXING WITH DIFFUSION AND FAST CHEMICAL REACTION IN SIMPLE SHEAR FLOW: A COMPARISON OF STRETCH MODEL TO TWO-DIMENSIONAL DIFFUSION WITH PERIODIC BOUNDARY CONDITIONS

The lamellar stretch model for describing mixing with simultaneous diffusion and fast chemical reaction is evaluated for simple shear flow between two parallel plates by comparing the predicted concentration profiles to those computed from the governing partial differential equation. A direct algorithm is devised to solve the sparse matrix originating from the discretization of the PDE. Under conditions where initial striation thickness equals the characteristic dimension of the flow geometry, the lamellar stretch model turns out to be quite accurate for k ≥ 10⁶ or k ≤ 1, where k is the product of the Reynolds number and the Schmidt number. In the intermediate range of k values, where mechanical and diffusional mixing are of comparable importance, the model is less accurate