喷射泵式气、液反应器的流型及其转变规律

本文研究了喷射泵式气、液反应器的四种流型及其转变规律.基于动量原理及能量、质量守恒定律,导得了判定反应器正常工作流型的判别式.实验验证了这种判别式.     

A new design concept of structured packing column auxiliaries

This paper discusses the criteria for obtaining an improved performance of structured packing columns in gas-liquid contacting, by improving the liquid and gas distributors. A new liquid distributor design, specific for structured packing columns is presented. Experimental measurements which quantify the improvements attained by the new distributor are also presented. Furthermore, gas flow distribution requirements for structured packing columns are discussed. Three “case studies” indicative of the implementation of the proposed distributor concept in industrial columns are included. Case (a) CO₂/MEA removal column, case (b) ammonia splitter and case (c) acid gas neutralization column.     

旋流动力稳定性对传热影响的研究

旋流动力稳定性是影响旋流传热和流动性能的重要因素, 今提出了基于旋流稳定性基本判据的瑞利判据和失稳指标b,分析旋流动力稳定性的影响因素及其对传热效果的影响作用。结果表明旋流强度、轴向分量速度和旋转流道的几何尺寸均会对旋流稳定性产生重要影响。随着旋流失稳指标b 的提高传热系数明显增加,对于Vz=2.14ms-1的旋流, b 由0增至500时传热系数提高100%以上。旋流动力稳定性的研究结果为旋流强化传热研究的深入提供重要的手段。     

受限微细通道内的流动沸腾流型转化准则

理论分析了微细尺度条件下通道尺寸对气泡运动特性的影响,指出当通道尺寸小于气泡脱离直径时一种特殊流型"受限泡状流"的产生及其特性。对受限通道内流动沸腾过程中的流型转变准则进行了推导,绘制了相应的流型图,并进行了实验验证。研究表明,微细通道内沸腾流动气液两相流流型转变比绝热工况下有明显的推迟;而在流动沸腾工况、相同热通量和质量流速条件下,随着微细通道尺寸的减小,流型转化会在一定程度上提前产生。     

水平管气液两相变质量流流型从分层流向非分层流的转变

基于文献中提出的针对常规管中气液两相流分层流稳定性的分析,考虑管壁入流对流型的影响,通过公式推导和分析得出了水平管中气液两相变质量流流型从分层流向非分层流转变的准则。通过室内实验研究和预测计算,分析了3种不同的流型转变准则中多个入流流量下管壁入流对流型转变的影响。研究结果表明,实际水平井筒的单位入流流量通常较小,对本地管道单元流型预测的影响可以忽略不计,但是通过不断累积,使得下游管道中流动参数发生变化,从而影响了下游管道单元中气液流动的流型。因此水平孔缝管中气液两相变质量流的流型判别可以采用常规管流型判别准则,但要分段进行。     

A mapping tool using anisotropic unstructured meshes to study mixing in periodic flows

The objective of the present work is to describe a new mapping tool using anisotropic unstructured meshes to study mixing within a spatially periodic pipe flow. Instead of tracking the boundaries of elementary cell flow domains as it was done in the original mapping method established by Kruijt et al. (A.I.Ch.E. J. 47 (5) (2001a) 1005; Int. Polym. Process. 16 (2) (2001b) 151) and Galaktionov et al. (Comput. Fluids 30 (3) (2001) 271), the deformation of elementary triangles (only three nodal points) between the inlet and exit pipe cross-sections is followed. It is however necessary to adapt the initial mesh according to criteria which takes into account the spatial stretching and folding of fluid elements. The method developed is applied to the twisted curved pipes (TCP) three-dimensional (3D) flow. We show the evolution of concentration distributions along the TCP mixer for chaotic advection flow regimes. This method allows the emphasis of isolated unmixed regions (KAM islands). The flexibility of the method allows also the possibility of studying multiple stirring protocols, thus contributing to a better comprehension of the physical phenomena involved in chaotic mixing. The method developed is also applicable to 2D temporally periodic flows.     

A systematic approach for the design of a spiral mandrel die

An effective design strategy is presented for the determination of optimal flow channel geometry of a spiral mandrel die, which can produce annular, thin, and uniform products of polymer melt. This strategy includes two steps: First, a two-dimensional flow simulation associated with the Taguchi approach is applied to search several sets of die geometric parameters, from which process the flow uniformity is assessed. Second, the optimum one parameter set selected by further considering total pressure drop, mixing degree and residence time distribution (RTD). The strategy is illustrated through the design of a spiral mandrel die with four spirals traveling a full 360°, and the viscosity of polymer melt is assumed to be power law model. The results indicated that the design criteria such as high flow uniformity, low pressure drop, good mixing degree and narrow RTD are difficult to attain simultaneously. For a particular polymer melt, there exists a design window for the geometric parameters; within the window the geometric parameter set may satisfy most of the design criteria.     

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation.

Void fraction of the whole bed ε_f and the mean velocity of bubbles U_b were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air.

Void fraction of the emulsion phase ε _e was calculated on the basis of the above model. Correlating ε _e with superficial gas velocity U_ƒ, we found that ε _e was very close to ε _mƒ in the bubbling regime and that e, increased with increasing U_ƒ in the turbulent regime.

Calculated values of the volume fraction of bubble phase δ were correlated with U_ƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed     

The influence of geometric parameters on the ideal mixing range of liquid in a continuous flow stirred tank reactor

This work is a continuation of previous research in which criteria of ideal mixing have been determined for water and other more viscous liquids. These criteria, determining the region of ideal mixing of liquid by the inlet flow energy, as well as with use of mechanical stirring, have been generalized in the present work on systems with various diameters of tank and inlet tube.     

水平液固循环流化床换热器传热性能评价

对管内插入Kenics静态混合器的水平液固循环流化床换热器进行实验研究,实验考察了静态混合器扭率、静态混合器安装方式、液体流速、颗粒体积分数对传热性能和流阻性能的影响,并运用综合强化传热性能评价指标（PEC）对其进行分析。实验发现,传热性能和阻力系数均随扭率增加而减小。当雷诺数在10000~45000之间时,扭率为1.5、2、2.5、3.5的Kenics静态混合器的PEC指标均大于1,说明了水平流化床换热器插入Kenics静态混合器能够改善传热。在雷诺数达到25000左右、Kenics静态混合器扭率为2.5、颗粒体积分数为4%时,水平流化床换热器的PEC指标最高达到1.18。当两个扭率均为2.5的Kenics静态混合器安装间距为200mm时,水平流化床换热器的PEC指标最高。     

磁流化床稳定性分析

应用Foscolo的颗粒床模型分析了磁流化床稳定性,得到了磁流化床的稳定判据;根据得到的判据分别对层流和湍流情况分析了磁场对磁流化床稳定性的影响。     

The importance of proper economic criteria and process modeling for single- and multi-objective optimizations

This paper provides an overview of the influences that different economic objectives have on the efficiencies of those optimal process designs obtained by using single- and multi-objective optimizations. Optimizations of monetary criteria, like the profit, lead to operationally and environmentally more efficient but economically less attractive designs than optimization of non-monetary economic objectives, like the internal rate of return. The net present value produces compromise designs with intermediate efficiencies and environmental impacts. These differences are significant only if the processes’ mathematical models are sufficiently accurate for establishing appropriate trade-offs between investment and cash flow. The Pareto curves obtained by different economic objectives vary regarding the maximum environmental impacts and in the intervals of the environmental indicators. The composed criteria that combine the economic and environmental indicators into one single objective produce smaller differences between optimum designs that are closer to those designs with minimum possible environmental impacts.     

Peel Adhesion: Influence of Surface Energies and Adhesive Rheology

The adhesion properties of polymers are known to be influenced by both intermolecular forces operative at the interface and the rheological history of both bonding and unbonding. Recent adsorption and viscoelastic theories of adhesion and cohesion are implemented in a comprehensive examination of these phenomena. Eight peel force “master curves” extending over 14 decades of reduced rate and representing glassy state to flow region rheology are superimposed to provide a composite response envelope. Each master curve represents rate-temperature reduced adhesion of an alkyl acrylate adhesive (γ_c = 26 dyne/cm) to substrates ranging from low adhesion fluorinated polymers (γ_c = 15 to 17 dyne/cm) to polar poly-amide surfaces (γ_c = 45 dyne/cm) and glass. The rate dependent transition from interfacial to cohesive failure, a subject not treated by adsorption theory, is shown to be coincident with the onset of entanglement slippage within the polymeric adhesive. Thermodynamic criteria of polymer adhesion are shown to be applicable only to the flow region of polymeric response. This study indicates that measured surface tensions or calculated surface energies of polymeric solids do not properly account for the contributions of three dimensional network structure of the polymeric bulk phase to its total work of cohesion. Evidence of true interfacial failure of a polymer-polymer bond is supported by critical surface tension measurements.     

ANALYSIS OF EXPERIMENTAL AND NUMERICAL RESULTS OF A TURBULENT SWIRLING FLOW IN A TUBE

In many applications swirling flow is used to enhance heat and mass transfer. One of the problems of modelling a turbulent swirling flow is the choice of the turbulent closure model which is acceptable for engineering purposes. To evaluate which model performs best, numerical results are compared with experimental data. Local velocity measurements are carried out on a swirling flow in a circular tube. The measurement method is hot-wire anemometry combined with visualization techniques. The numerical analysis is carried out using the k-ε model and the Algebraic Stress Model. In the experiment a symmetrical swirl was observed, Comparing the experimental data with the numerical results shows that the Algebraic Stress Model represents the experimental data quite well, whereas the k-ε model fails.     

Trickle-bed reactors: Criteria of negligible transport effects and of partial wetting

Dimensionless criteria are derived for determining the importance of intra- and interface heat and mass transfer in trickle-bed reactors. Only observable quantities are involved in the criteria. Also derived is a dimensionless criterion for determining whether the pellets are partially covered by liquid. Except for the Thiele modulus, all quantities are measurable. The criterion of partial wetting is applied to experimental data. It is shown that the criterion predicts rather accurately the liquid flow rate below which the pellets become partially wetted.     

Schädigungskriterien glasiger polymer im hinblick auf deren schlagzähmodifizierung

In rubber-modified, stiff and brittle polymers an applied stress generates multiaxial stress concentrations in the matrix material at the rubber interface and initiates a large number of limited regions of plastic deformation. In order to understand this toughening mechanism, one needs a certain knowledge of the kind of plastic flow which is initiated within a glassy polymer according to the type and amount of stress, the so-called failure criteria. Unlike criteria which apply to the onset of shear flow, craze criteria are still contro-versially discussed in the literature. Argon has suggested a theoretical criterion of bulk crazing. Sternstein et al. have studied experimentally the surface crazing of PMMA. Based on experimental results of Rehage and Goldbach and ourselves, calculations have given the following results: The Sternstein criterion, measured and formulated for surface crazing under the condition of plain stress has till now been incorrectly transformed for use in principal stress space. Correctly transformed, it deviates strongly from Argon's criterion in the range of states of stress with large portions of hydrostatic tension. The Sternstein criterion obviously lends itself to describing multiaxial corrosion. For rubber-modified systems, however, one needs bulk craze criteria, for which no experimental results exist. Preliminary results show that these can more easily be estimated for PS than for PMMA. These two polymers therefore show markedly different shapes of the failure surfaces.     

Physico-Chemical Criteria for Maximum Adhesion. Part I: Theoretical Concepts and Experimental Evidence

This paper presents an analysis of the literature with the aim of defining basic criteria and developing a general model to describe joint strength. Two particular cases of the relationship: cosθ = f(γ_L) have been identified as prerequisites for further analysis of interfacial phenomena and conditions governing their existence were discussed.

The fact has been pointed out, based on available experimental results, that for the most important case in practice where 0.6 ≤ cosθ ≤ 1.0, the relation cos θ = f(γ_L) can be treated as rectilinear. This finding will be utilized in the comprehensive development of criteria defining joint performance in Part II.

Variability of the interaction factor Φ for various systems has been investigated in relation to cos θ, for the identified particular cases of the relationship cos θ = f(γ_L) A special value of the interaction factor, ₀, was found. The importance of the rectilinear particular case of cos θ = f(γ_L) was shown, which involves constant factor Φ₀ instead of variable Φ.     

Chute Performance and Design for Rapid Flow Conditions

Many industrial chute applications are characterised by rapid flow conditions in which the bulk solid stream thickness or depth is less than the chute width. Under these conditions, it is possible to describe the stream flow by means of a lumped parameter model which takes into account the frictional drag around the chute boundaries as well as making allowance for inter‐particle friction. Equations of motion to describe the chute flow are presented and their application to the determination of chute profiles to achieve optimum flow is illustrated. By means of design examples, the problems associated with the feeding of bulk solids onto belt conveyors and conveyor transfers are discussed. Criteria for the selection of the most appropriate chute geometry to minimise chute wear and belt wear at the feed point are presented. The determination of optimum chute profiles to achieve specified performance criteria is outlined.