65 research outputs found
Comparison of two models on simulating electric field in HVDC cable insulation
No full textSpace charge accumulation in cable insulation is one of the major technical problems in the further development of HVDC cables. A conductivity model and a bipolar charge transport model are developed to respectively calculate the space charge and electric field distribution in polymeric insulation. In this paper, both models are employed to simulate the field distribution in a medium voltage polymeric cable. Comparisons are made between theoretical and simulation results. The limitations of the conductivity model which is widely used in HVDC cable design are presented, and the results of the bipolar charge transport model are more consistent with the experimental observations. Moreover, transient current in the cable is simulated to anticipate the field distribution within the insulation when subjected to a thermal transient. The results suggest that the thermal transient can affect the space charge and electric field distribution significantly. A field inversion can only take place with higher temperature and larger temperature gradient, and this can be maintained even with temperature decreasing
Modelling space charge in HVDC cable insulation
No full textThe design of high-voltage direct-current extruded cable is one of the most challenging issues in the cable industry, as the electric field distribution across the insulation can be strongly affected by the presence of space charge, which can subsequently affect its long-term reliability and life expectancy. In this study, the bipolar charge transport model was utilized to calculate space charge and field distribution in a polymeric cable insulation, and the result was compared with the one obtained by the conductivity model which is commonly used in the cable industry. It is shown that the simulation results of the bipolar charge transport model are more comparable with the previous experimental work, and the shortcomings of the conductivity model are presented. At last, the feasibility and potential issues of the new method are discussed for further development
Polymer Surface Modification via Noncovalent Binding of Functional (Macro)molecules: Investigation of Entrapment Strategy and Mechanism
No full textEntrapment technique, served as one kind of polymer surface functionalization strategies, has been developed in recent decades. All previous studies focused on polar polymer surface modification. In this thesis, aiming to polymer surface hydrophilic and antifouling modification, a variety of (macro)molecules have been applied to entrap into polar polyestersulfone (PES) and nonpolar polypropylene (PP) surface respectively. It was found that the modification conditions for PES are not suitable for PP membrane surface; and the conditions for PP membrane are not exactly effective for PP film. Furthermore, the entrapment mechanism has been studied and discussed.
In the beginning of this thesis, polar PES microfiltration (MF) membrane has been used as base polymer. Two different routes, abbreviated as E1 and E2 have been tested for PES surface modification. In E1, the modifiers were anticipated to diffuse into swelling region in modifier solution, and then they were fixed into PES surface by deswelling in water (solvent extraction); in E2, the base polymer was swollen in solvent, and the modifiers were anticipated to entrap into PES surface quickly in water solution. Present studies revealed that PES surface can be hydrophilic modified via entrapment of poly(ethylene oxide) (PEO)-containing homo-/copolymers; and E1 showed much better efficiency than E2. Therefore, E1 was selected as the entrapment approach for the following studies of PP surface modification.
Then nonpolar PP surface was endowed with hydrophilicity, thermo-responsibility, as well as cationic charge after entrapment with corresponding modifiers respectively. For instance, it was validated that entrapment of small amphiphilic molecule octaethyleneglycol monooctadecylether (C18EO8) into Membrana PP MF membrane surface improved outer surface and inner surface hydrophilicity, as well as the corresponding antifouling properties. Wettability and water flux of poly(butyl acrylate)-b-poly(N-isopropylacrylamide) (PBA-b-PNIPAAm) entrapment modified PP membrane surface were time-dependent, which had abrupt change at the lower critical solution temperature (LCST) of PBA-b-PNIPAAm. This thermo-responsive property could be further used for protein desorption. In addition, non-porous Membrana PP plate surface was also functionalized with the same procedure, and modified PP plates showed similar modification efficiency and surface properties as for porous PP membranes. Moreover, zeta potential measurement validated that the Celgard PP film surface showed cationic after entrapment with methyl and octyl groups quarternized poly(n-butyl acrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PBA-b-PqDMAEMA).
The mechanism of entrapment behavior was further investigated in the final section of this thesis. In case of Membrana PP MF surface modification in nonpolar solution, entrapment of a variety of ethyleneoxide-containing substances into PP surface was studied. All results revealed that PEGs were ineffective, while many nonionic amphiphilic substances, especially some tri-block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were very effective for PP surface hydrophilic modification. The relationship between modifier structure and architecture and entrapment behavior was investigated by studying the reverse micellization of amphiphilic modifiers in nonpolar solutions via pyrene-probe fluorescence and 1H NMR spectroscopy. The balanced structure of nonionic tri-block modifiers, the lowest reverse critical micelle concentration (RCMC) had been observed. It was concluded that a balance block copolymer structure and architecture promoting the self-association in the nonpolar solvent is the basis for a high entrapment efficiency. In case of modification in polar solution, the swelling degree for diffusion of modifier is one important factor. Moreover, the deswelling step in a second solvent is another important factor to entrap the modifier into base polymer surface
Preparation of thermo-responsive polypropylene membranes via surface entrapment of poly(N-isopropylacrylamide)-containing macromolecules
No full textDevelopment of hydrophilic membranes for challenging separation applications
No full textMembrane fouling and its control is one of the most critical parameters in the application of membrane processes. The degree of fouling depends on the application and on industrial scale, fouling is often observed as reduction in plant capacity over time. One approach to reduce fouling for the pressure driven processes microfiltration and ultrafiltration is to use hydrophilic membranes. This paper will show two examples of the development and use of hydrophilic membranes – ETNA and UFX membranes - for challenging microfiltration and ultrafiltration applications and will provide an overview on recent and future developments regarding hydrophilic membranes. The ETNA membrane is a surface-modified PVDF membrane with permanently hydrophilic properties on a polypropylene support. One of the key application areas for this membrane is the separation of oil-water mixtures, an application area which is driven by the increasing demand for efficient oil-water separation, e.g. produced water in the oil and gas industry, process water in the petrochemical industry and bilge water in the marine industry.The UFX membrane is a permanently hydrophilic polysulphone based membrane reinforced on a polypropylene support. The membrane has established itself as the standard for concentration and purifications of industrial enzymes but it should also have potential in the concept of future biorefineries in particular for the concentration and purification of hemicellulose. One current trend is the use of cellulose, a sustainable membrane material, which can either be used directly, or as regenerated cellulose, e.g. the European NanoSelect project which is aiming at the development of low fouling and adsorption membranes based on cellulosic fibrils, and the development of a new generation of regenerated cellulose membranes by Alfa Laval is in progress.Overall, the development and availability of hydrophilic membranes can reduce the fouling challenges in a wide range of industries
The effects of (macro)molecular structure on hydrophilic surface modification of polypropylene membranes via entrapment
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Research on the Passenger Flow Forecast of the Interurban Railway of Central Henan Urban Agglomeration in the Future
No full textContribution of effluent organic matter (EfOM) to ultrafiltration (UF) membrane fouling: Isolation, characterization, and fouling effect of EfOM fractions
No full textEfOM has been regarded as a major organic foulant resulting in UF membrane fouling in wastewater reclamation. To investigate fouling potential of different EfOM fractions, the present study isolated EfOM into hydrophobic neutrals (HPO-N), colloids, hydrophobic acids (HPO-A), transphilic neutrals and acids (TPI), and hydrophilics (HPI), and tested their fouling effect in both salt solution and pure water during ultrafiltration (UF). Major functional groups and chemical structure of the isolates were identified using Fourier transform infrared spectroscopy (FT-IR) and solid-state carbon nuclear magnetic resonance (13C NMR) analysis. The influence of the isolation process on the properties of EfOM fractions was minor because the raw and reconstituted secondary effluents were found similar with respect to UV absorbance, molecular size distribution, and fluorescence character. In membrane filtration tests, unified membrane fouling index (UMFI) and hydraulic resistance were used to quantify irreversible fouling potential of different water samples. Results show that under similar DOC level in feed water, colloids present much more irreversible fouling than other fractions. The fouling effect of the isolates is related to their size, chemical properties, and solution chemistry. Further investigations have identified that the interaction between colloids and other fractions also influences the performance of colloids in fouling phenomena. © 2014 Elsevier Ltd.The authors thank the project "Control of Emerging Contaminants for a Sustainable Reuse of Wastewater: Role of Effluent Organic Matter" funded by King Abdullah University of Science and Technology. The technical support of Emmanuelle Filloux (Universite de poitiers, France), Guodong Li (Workshop in KAUST), Dr. Tahir Yapici (core lab in KAUST), Dr. Victor Yangali, Tong Zhan and Ahamed Kasmi in Water Desalination and Reuse Center is highly appreciated. Helpful discussion with Dr. Haofei Guo from Alfa Laval Nakskov A/S and Dr. Allan Hjarbaek Holm from Grundfos A/S are also appreciated
Comparison of the Mechanical Properties of Different Tendon Profiles with External Prestressed Reinforcement
No full textAs a common method, external prestressing widely informs rehabilitation in existing structures. This paper presents the total prebending moment calculation of external prestressing with different tendon profiles. Meanwhile, the external prestressing loss and original internal prestressing loss are considered in the calculation in both the theoretical method and the finite element method. Then, we discuss the reinforcement efficiency of different tendons profiles and provide the reinforcement distribution ratio. The results show that the theoretical method is similar to the finite element method, and it can quickly evaluate the reinforcement effect by using different tendon profiles in engineering. By comparing the reinforcement efficiency under different external tendon profiles, the reinforcement scheme is determined according to the local damage and the overall damage of the beam, which effectively decreases the cost of reinforcement
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