Mass transfer performance for hollow fibre modules with shell-side axial feed flow: using an engineering approach to develop a framework

For several membrane separation processes, hollow fibre modules are either an already established or a promising type of module. Based on the analogy between mass and heat transfer, an engineering approach is proposed to estimate the shell-side mass transfer coefficient for axial flow in hollow fibre modules with due allowance for the void fraction. The approach enables one to take the entrance effects of the hydrodynamic and concentration profile into account. The trends obtained by this generalised approach are similar to those of empirical correlations found in the literature over a wide range of Reynolds numbers and module packing densities. The empirical correlations differ significantly one from the other. The differences between the mass transfer coefficients obtained by the empirical correlations compared to those obtained following the approach proposed in this study are discussed. The different effects influencing mass transfer in hollow fibre modules are identified and discussed as a function of void fraction. Further, an approach to reflect the influence of maldistribution on mass transfer performance is provided.     

Application of nanofiltration for removal of pesticides,nitrate and hardness from ground water: rejection properties and economic evaluation

The drinking water industry faces a growing number of difficulties in the treatment of ground water for drinking water production. Ground water sources are frequently contaminated with pesticides; nitrate concentrations are increasing and are often close to or above the legal standard of 50 mg/l. Moreover, partial removal of hardness is desirable for reasons of comfort.Nanofiltration is a process in which pesticides, hardness and nitrates can be simultaneously removed or partly removed, so that purification can be realized in one step. However, the removal properties in the nanofiltration step have to be examined, to make a good control of the membrane unit possible.In the first part of this paper, the removal of four pesticides (atrazine, simazine, diuron and isoproturon), the removal of hardness and the removal of nitrates with the membranes NF70, NF45, UTC-20 and UTC-60 is experimentally studied. The results show that pesticide rejections are satisfactory; hardness is also very efficiently removed, whereas only a small fraction of nitrate is removed for most membranes, except for NF70 where a 76% removal of nitrate was obtained. Rejection characteristics are explained, and used to calculate the properties for a double pass module design with recirculation of the concentrate in the second module to the feed of the first module. When this design is applied with NF70, all pesticide molecules are removed to well below the detection limit. The partial removal of nitrates may help to meet the legal standard of 50 mg/l, but is not a main objective for the filtration process. The hardness of the permeate might be too low, so that hardness should be readded.The second part of the paper discusses the economical side of the implementation of nanofiltration. This is indeed an important factor that has never been evaluated before. The outline of the calculation of the investment costs and the operating costs is summarized, and the calculations were used in an example calculation for a given production of drinking water, based on the experimental results from the first part of the paper. Price calculations at different pressures resulted in an optimal pressure of 8 bar. The final price for treatment of ground water is realistic, showing that nanofiltration is a valuable option for ground water treatment.     

A large strain plasticity model for anisotropic materials — composite material application

In this work a generalized anisotropic model in large strains based on the classical isotropic plasticity theory is presented. The anisotropic theory is based on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. In classical orthotropy theories it is necessary to use a special constitutive law for each material. The proposed theory is a generalization of classical theories and allows the use of models and algorithms developed for isotropic materials. It is based on establishing a one-to-one relationship between the behavior of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictious space and the results are transported to the real field. This theory is applied to simulate the behavior of each material in the composite. The whole behavior of the composite is modeled by incorporating the anisotropic model within a model based on a modified mixing theory.     

Micromechanical modeling of the elastic–viscoplastic behavior of polycrystalline steels

A self-consistent model developed to describe the elastic–viscoplastic behavior of heterogeneous materials is applied to low carbon steels to simulate tensile tests at various strain rates in the low temperature range. The choice of crystalline laws implemented in the model is discussed through the viscoplastic flow rule and several strain-hardening laws. Comparisons between three work-hardening models show that the account of dislocation annihilation improves the results on simulations at large strains. The evolution of the Lankford coefficients and texture development are also successfully simulated. Some microstructural aspects of deformation such as the stored energy and the evolution of the flow rates are discussed. By including the dislocation density on each slip system as internal variable, intragranular heterogeneities are underscored.     

Three-dimensional thermomechanical deformations of functionally graded rectangular plates

Three-dimensional thermomechanical deformations of simply supported, functionally graded rectangular plates are studied by using an asymptotic method. The locally effective material properties are estimated by the Mori–Tanaka scheme. The temperature, displacements and stresses of the plate are computed for different volume fractions of the ceramic and metallic constituents, and they could serve as benchmark results to assess two-dimensional approximate plate theories.     

On the propagation of nonlinear solitary waves in a distributed Schottky barrier diode transmission line

A nonlinear distributed Schottky barrier diode is analyzed and it is found to be similar to a 3-component quasi-neutral plasma consisting of negative ions and electrons that are neutralized with positive ions. In such a plasma, it has been shown that both KdV and mKdV solitons can exist. We obtain the criteria for the distributed Schottky barrier diode that will permit the propagation of both KdV and mKdV solitary waves.     

Embedded random matrix ensembles for complexity and chaos in finite interacting particle systems

Universal properties of simple quantum systems whose classical counter parts are chaotic, are modeled by the classical random matrix ensembles and their interpolations/deformations. However for finite interacting many-particle systems such as atoms, molecules, nuclei and mesoscopic systems (atomic clusters, helium droplets, quantum dots, etc.) for wider range of phenomena, it is essential to include information such as particle number, number of single-particle orbits, lower particle rank of the interaction, etc. These considerations led to resurgence of interest in investigating in detail the so-called embedded random matrix ensembles and their various deformed versions. Besides giving a overview of the basic results of embedded ensembles for the smoothed state densities and transition matrix elements, recent progress in investigating these ensembles with various deformations, for deriving a statistical mechanics (with relationships between quantum chaos, thermalization, phase transitions and Fock space localization, etc.) for isolated finite systems with few particles is briefly discussed. These results constitute new progress in deriving a basis for statistical spectroscopy (introduced and applied in nuclear structure physics and more recently in atomic physics) and its domains of applicability.     

Small-scale properties of the KPZ equation and dynamical symmetry breaking

A functional integral technique is used to study the ultraviolet or short distance properties of the Kardar–Parisi–Zhang (KPZ) equation with white Gaussian noise. We apply this technique to calculate the one-loop effective potential for the KPZ equation. The effective potential is (at least) one-loop ultraviolet renormalizable in 1, 2, and 3 space dimensions, but non-renormalizable in 4 or higher space dimensions. This potential is intimately related to the probability distribution function (PDF) for the spacetime averaged field. For the restricted class of field configurations considered here, the KPZ equation exhibits dynamical symmetry breaking (DSB) via an analog of the Coleman–Weinberg mechanism in 1 and 2 space dimensions, but not in 3 space dimensions.