Theoretical and experimental study of the molten polymer flow in the calender bank

The flow of molten polymers in the calender bank has been computed using a finite-element method with stream function and vorticity. Two nonsymmetrical-recirculating regions have been obtained fully in agreement with the experimental observations on poly(vinyl chloride) melt banks. The pressure distribution along the flow axis is very close to the one obtained using the classical-lubrication approximation.     

Theoretical and experimental modeling of the cooling of uranium hexafluoride vapor desublimation tanks

A physical and mathematical model has been developed for the cooling of a block of receiver tanks for uranium hexafluoride desublimation with cold air supplied to heat exchangers by a VKhM-0.54/0.6 air cooler. Calculations have been carried out for the most heat-intensive operating regime of the receiver tank block, in which four tanks are cold and operate in the product desublimation mode, two tanks are being cooled after the evaporation of the product, and six tanks are reserved, being maintained in the cooled state. Experimental data are presented for the cooling of the vapor desublimation tank section using the VKhM- 0.54/0.6 air cooler. The mathematical model of the gas dynamic processes of cold air flow in the pipeline and tank walls–air heat transfer is used to calculate the cooling of the six tanks with a cold air stream from the VKhM-0.54/0.6 cooler. A good quantitative fit between the calculated data and experimental measurements has been attained. The performance parameters of the VKhM-0.54/0.6 air cooler can ensure uranium hexafluoride recovery from the gas mixtures arriving from the collector of the condensation–evaporation apparatus and purification of the product.     

Theoretical and experimental study of the flow of a molten polymer in a micro-compounder

Micro-compounders are more and more used to characterize and optimize the formulations and the flow conditions of complex materials, with very low quantities, around a few grams. These machines are composed of a small-size conical twin-screw extruder, coupled with a recirculating channel, in which the material can be processed during a fixed time and a certain number of cycles, before being purged. However, the precise flow conditions inside these machines are not well known, what makes an optimal interpretation of the results difficult. Therefore, in this paper, a theoretical model based on continuum mechanics is proposed to calculate the flow in the recirculating mode. An experimental study on a well-chosen polymer is carried out to define the influences of the main processing parameters (screw speed, mass of material, barrel temperature) and to validate the model. Despite the simplicity of the theoretical approach, the calculated results are in satisfactory agreement with the experiments.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the later.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the latter.     

立式径向流吸附器中流体均布的理论分析

为提高空分用吸附器吸附效率,通常在内分布流道布置一锥体使内外分布流道沿轴向压降梯度相等以保证空气在吸附剂中流场均匀。通过对立式径向Z型吸附器内的压降分析,推导出一个可表征当空气在吸附剂中均匀分配时吸附器各参数应满足的量纲1微分控制方程。同时对一个实验径向吸附器进行设计,利用该量纲1微分控制方程获得了锥体截面半径随轴向高度的变化规律,为该类径向吸附器的设计提供了理论依据。     

A CFD methodology for the design of sedimentation tanks in potable water treatment: Case study: The influence of a feed flow control baffle

Computational fluid dynamics simulations are employed to assess the effect of adding a vertical baffle at the feed section of a full-scale sedimentation tank for the improvement of solids settling in potable water treatment. A general CFD-based simulation strategy is developed based on the specific features and conditions met in practice for potable water treatment. The linearity of the particle conservation equations allows separate calculations for each particle size class – but performed for all classes of interest – leading to the uncoupling of the CFD problem from a particular inlet particle size distribution. The usually unknown and difficult to be measured particle density is found by matching the theoretical to the easily measured experimental total settling efficiency. The proposed strategy is computationally much more efficient than the corresponding strategies used for the simulation of wastewater treatment. This work compares simulations from a standard and a baffle-equipped tank. It is found that the baffle decreases the inlet recirculation zone and enhances the settling of solids by directing them towards the bottom of the tank with high velocities. It is noteworthy that even small differences in the particle velocity can cause large changes in the percent of settled particles; in this work, the overall solids removal efficiency increased when using the baffle from 90.4 to 98.6% leading to a reduction of the effluent solids concentration of approximately 85%.     

Holdup in vertical two and three phase flow Part I: Theoretical analysis

A general one-dimensional theory for predicting the average holdup or column concentration in three phase flow is formulated. The analysis takes into account the local relative velocity between the phases, the non-uniform flow and holdup distribution across the column, and the effect of the concentration of the dispersed phase on the relative velocity. The present theory is compared with the previous analyses for two phase flow reported in the literature and it is shown that all of them are special cases of the general theory proposed here.     

A theoretical and experimental study on cake filtration with sedimentation

Sedimentation occurs in almost all cake filtration. To study the role of sedimentation during filtration, filtration-permeations were carried out for suspensions of various concentrations. The average specific cake resistances calculated by the traditional method using the filtration data and initial concentration of suspension give different values according to the suspension concentrations. But the average specific cake resistances from the permeation period show almost the same values in spite of the various suspension concentrations. To exclude the influence of sedimentation, a complete sedimentation was performed before beginning filtration and then filtration-permeation of the sediment was performed. The average specific cake resistance from the filtration period calculated with the mass fraction of sediment and that from the permeation period coincide very well. These values also coincide well with the former average specific resistances during permeation within the experimental error limits. It can be concluded that the average specific cake resistances by permeation operation give almost the same values for various concentrations of suspension. A new definition of a cake and a new concept of the filter medium Rm are proposed based on the analysis of experimental results.     

几种框式桨搅拌槽内流动特性的比较研究

用粒子成像测速（PIV）技术对传统框式桨、传统框式组合桨和新型框式组合桨的流动特性进行研究,对比了三种框式桨在相同工况下搅拌槽内的速度、流型和湍动能。结果表明：传统框式桨搅拌槽内流体流动以水平环流为主,在框式桨上方和框式桨中间区域流体流动不充分;传统框式组合桨搅拌槽内框式桨上方由于二折叶桨的作用使得框式桨上部流体流速变大,槽内流体上下部的流动得到加强,但在框式桨中心区域依旧存在流动死区;新型框式组合桨搅拌槽内两层桨叶间的连接流得到了加强,框式桨底部和中间区域物质和能量的交换更加充分。在考察的三种框式桨中,新型框式组合桨的混合效果更好。研究结果可为新型框式组合桨应用于化工合成工业中提供参考。     

Self-Compacting Concrete: Theoretical and experimental study

This paper addresses experiments and theories on Self-Compacting Concrete. First, the features of “Japanese and Chinese Methods” are discussed, in which the packing of sand and gravel plays a major role. Here, the grading and packing of all solids in the concrete mix serves as a basis for the development of new concrete mixes. Mixes, consisting of slag blended cement, gravel (4-16 mm), three types of sand (0-1, 0-2 and 0-4 mm) and a polycarboxylic ether type superplasticizer, were developed. These mixes are extensively tested, both in fresh and hardened states, and meet all practical and technical requirements such as medium strength and low cost. It follows that the particle size distribution of all solids in the mix should follow the grading line as presented by Andreasen and Andersen. Furthermore, the packing behaviour of the powders (cement, fly ash, stone powder) and aggregates (three sands and gravel) used are analysed in detail. It follows that their loosely piled void fraction are reduced to the same extent (23%) upon vibration (aggregates) or mixing with water (powders). Finally, the paste lines of the powders are used to derive a linear relation between the deformation coefficient and the product of Blaine value and particle density.     

Theoretical and experimental study of crushing in a high-speed granulator

The results of the theoretical and experimental study of the crushing of particles in a high-speed granulator, which accompanies the agglomeration of particles, are presented. Relationships are derived that make it possible to evaluate the contribution of crushing in the granulation of particles in such a granulator and to determine the average mass of particles as a result of crushing.     

An experimental study of interfacial surface area concentration in a short vertical column subject to paper pulp-water-gas three-phase flow

The interfacial surface area concentration in a short vertical column subject to the through flow of a solid-liquid-gas slurry made by mixing aqueous fibrous paper pulp with a nitrogen-carbon dioxide gas mixture was measured in the study. The gas absorption technique was applied, using CO₂ as the transferred species and sodium hydroxide as the alkaline agent in water. The flow regimes in the experiments were visually identified, and the test section void fraction was measured using a Gamma-ray densitometer.The test section was a -long column with inner diameter. The ranges of experimental parameters were as follows: liquid-pulp superficial velocity 15-; average gas-superficial velocity 17-; pulp consistency in the water/pulp mixture 0.0-2.18%; and average mole fraction of carbon dioxide in the gas mixture 0.19-0.95. A total of 33 data points were obtained, each representing the average of three to nine tests that confirmed reasonable repeatability. Statistical analysis of the experimental data indicates strong dependence of interfacial area on average gas superficial velocity and void fraction; and a relatively weak dependence on pulp consistency and liquid superficial velocity. The effect of pulp consistency on the interfacial area concentration in the test section was particularly interesting. The test section average interfacial surface area concentration decreased with increasing consistency up to a consistency of 1.6%, but increased significantly when consistency was further increased to 2.18%. The experimental data were empirically correlated.     

Gas-liquid flow and bubble size distribution in stirred tanks

This work is aimed at investigating the turbulent two-phase flow and the bubble size distribution (BSD) in aerated stirred tanks by experiments and computational fluid dynamics (CFD) modelling. The experimental data were collected using a two-phase particle image velocimetry technique and a digital image processing method based on a threshold criterion. With the former technique, the liquid and the gas phase ensemble-averaged mean and r.m.s. velocities are measured simultaneously, while with the latter the dimensions of the bubbles dispersed inside the liquid are evaluated. On the modelling side, a CFD approach, based on the solution of Reynolds average Navier-Stokes equations in an Eulerian framework for both phases, is adopted. As for the bubble dimensions modelling, besides the mono-dispersed assumption, a population balance method, named MUSIG, with bubble break-up and coalescence models is considered. The BSD and the axial and radial velocity of the gas and the liquid phase are presented and discussed. The outcomes of the computational work are evaluated on the basis of the experimental results.     

轴向流固定床内流场的数值模拟与实验验证

The computational fluid dynamics model with porosity and drag coefficient was used to describe fluid flow in an axial flow fixed bed according to the characteristics of fluid flow in the fixed-bed of the reactor. The commercial computational fluid dynamics (CFD) code CFX was used to simulate the flow field in the axial flow fixed bed. The simulation predictions are in good agreement with experimental results of a large cold model. The influence of gas distributor on the flow field in the axial flow fixed bed was studied. A suitable gas distributor was used to attain less than 0.06 kPa radial pressure difference and less than 5.2% radial velocity difference in fixed bed.     

Fe-Zn film stripping voltammetry: Theoretical and experimental study

The voltammetric dissolution of an iron-zinc alloy film, deposited potentiostatically from −0.2 to −1.4 V, was studied. Dissolution curves of the film at different sweep rates showed only one anodic peak, whose current density (j_p) was higher than the divacancy current density, implying that Fe and Zn in the film dissolved simultaneously. Equations relating j_p to sweep rate (v) and peak potential (E_p) to v, for the dissolution process of thick alloy film, were developed on the basis of Brainina's theory of pure metal layer dissolution. These equations were applied to the dissolution of Fe-Zn alloy film. The results obtained showed that the j_p × v and E_p × v plots were linear, corroborating the equations developed based on Brainina's theory and indicating that this alloy dissolves as one metal.     

液体管外降膜的实验

在实验的基础上探讨了液体在垂直管外降膜的流动特性,分析了影响液体管外成膜均匀性和润湿性的影响因素,提出了布膜装置的环隙在0.5～2.0mm有一最佳值,喷淋密度在250～700kg/(m·h)之间有一最佳值,布膜装置的进液采用单管沿壁面旋转270°切向流的进液方式,并对液体管外降膜装置的设计提出了建议。     

Heat transfer and flow pattern in vertical liquid-solids flow

Wall-to-bed heat transfer in hydraulic transport of spherical glass particles of diameter 1.20, 1.94 and 2.98 mm and in single-phase flow regime was studied. Experiments were performed by transporting the spherical glass particles with water in a 25.4 mm I.D. copper tube equipped with a steam jacket.In the runs without particles, the tube Reynolds number varied between 2280 and 21,300, while in hydraulic transport runs, the tube Reynolds number varied between 3300 and 20,150. The loading ratio (G_p/G_f) was between 0.07 and 0.328, and the fluid superficial velocity was between 0.29·U_t and 2.86·U_t, where U_t represents the single particle terminal velocity. For these ratios, the voidage ranged from 0.715 to 0.895.The data for the heat transfer factor (j_H) in single-phase flow are correlated using a general form j_H=f(Re). The data for wall-to-bed heat transfer in the hydraulic transport of particles show that an analogy between heat and momentum transfer exists. The data were correlated by treating the flowing fluid-particle suspension as a pseudofluid, by introducing a modified suspension-wall friction coefficient (f_w) and a modified Reynolds number (Re_m).