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1
Koonaphapdeelert, Sirichai. "Ceramic hollow fibre membrane contactors". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501286.
Testo completo
2
Wicaksana, Filicia School of Chemical Engineering & Industrial Chemistry UNSW. "Submerged hollow fibre membranes in bubbling systems". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2006. http://handle.unsw.edu.au/1959.4/25998.
Testo completoAbstract (sommario):
This study focuses on the optimisation of submerged hollow fibre membrane performance by analysing the role of air sparging on the reduction of membrane fouling. In submerged hollow fibre membranes, rising bubbles have been shown to induce shear, liquid movement and fibre displacement. The interaction between fibre movement induced by bubbling and the microfiltration performance was assessed for various parameters (fibre tightness, fibre length, fibre diameter, air flowrate, nozzle size, and feed concentration). A model feed of yeast suspension and a series of isolated fibres were used. The fibre movement was assessed by monitoring the displacement using video recording. Bubble population parameters were also measured. The results suggest that bubbleinduced fibre movement plays an important role in controlling membrane fouling. Investigations of the critical flux at various operating conditions also supported these conclusions. Since energy consumption for aeration is a major contributor to the cost in submerged membranes, the potential to minimise the aeration cost has been tested by implementing intermittent aeration and different nozzle sizes. It was found that an optimum condition associated with a low fouling rate could be reached by combining various aeration intermittencies and nozzle sizes. An attempt to suppress fouling without aeration was made by incorporating vibrations into a submerged hollow fibre membrane system. The effects of vibration frequency, type of yeast (washed and unwashed) on the filtration performance were observed. The impact of coagulant addition on filtration enhancement was also analysed. The performance of microfiltration was evaluated based on its critical flux value. The findings in this preliminary study indicated potential fouling control by applying vibrations to submerged membranes. A semi-empirical model was developed to predict the filtration behaviour by taking into account the bubble-induced shear and fibre movement. The predicted critical flux values suggested that membrane fouling appears to be more prominent at low air flowrate, with tight fibres, and higher feed concentrations. The model fits the experimental data with discrepancies from approximately 0.3% to 20%. The predicted filtration profiles at different operating modes demonstrate the importance of bubble-induced shear and fibre movement in the improvement of filtration performance.
3
Deshmukh, Sandeep Prabhakar. "Composite hollow fibre membranes for gas separation". Thesis, University of Leeds, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423301.
Testo completo
4
Shearer, Holly. "Hollow fibre bioreactors for bone tissue engineering". Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441441.
Testo completo
5
Zhou, Jian. "Polyacrylonitrile hollow fibre membranes for gas separation". Thesis, University of Leeds, 1996. http://etheses.whiterose.ac.uk/424/.
Testo completoAbstract (sommario):
Polyacrylonitrile (PAN) hollow fibres have been spun by a dry-jet wet spinning technique, using a commercial PAN polymer (Courtelle) redissolved in dimethylformamide (DMF). After failure to produce satisfactory porous hollow fibres from PAN/DMF solutions, a series of studies on the porous substructure of PAN cast films prepared with a variety of additives in the casting solution and at varying temperatures of the coagulation bath were carried out. A porous and flexible PAN cast film was produced when it was precipitated in water at 55 °C with CuSO4 present in the casting solution. Hollow fibres produced from a spinning solution composed of 25wt% PAN, 70wt% DMF and 5wt% CuSO4 were more porous and flexible than those produced from 25wt% PAN and 75wt% DMF spinning solution, and appeared to be more suitable for gas separation studies. The permeability of the PAN hollow fibre membranes to single gases was studied. The experimental results showed that the calculated pore radius on the surface of the fibre was in the range of 4- 32 nm. After coating with silicone rubber, the membranes showed very poor gas permeability and selectivity. Since PAN has a low intrinsic gas permeability, the low permeability observed is ascribed to a thick skin layer. The low selectivity of the membranes is related to their high surface porosity (> 10-4), or to the large pores present which are imperfectly blocked. With such fibres, little or no gas will pass through the membranes by solution-diffusion in the PAN. In order to reduce the surface porosity on the skin layer of the hollow fibres, a dualbath coagulation spinning system was used. The gas permeability of H2 in these membranes is lower than that obtained by the single bath coagulation system, while the gas permeability of the other gases, such as CO2 and CH4, were too low to measure. These results indicate that a high selectivity can be obtained by the dual bath coagulation spinning system although the selectivity is accompanied by too low a permeability, which is itself caused by too thick a skin layer. Surface modifications of PAN hollow fibre were carried out in order to modify the surface porosity of the fibres. After the treatments, the hollow fibre membranes did not give significant improvement in gas permeability and selectivity. But, when PAN hollow fibres were treated with cuprammonium hydroxide solution at room temperature, the fibres became coloured and no longer soluble in the usual solvents. The insolubility of the fibres is presumed to be due to a newly-formed crosslinked structure. The crosslinking of the fibres is reversed when the fibres are treated with EDTA solution. It has been observed that the presence of the copper in the fibres increases the tensile strength and decreases the elongation of the hollow fibres. The interaction of the PAN fibre with the cuprammonium hydroxide gave no improvement in gas separation performance but might be the basis for general acrylic fibre modification.
6
Xu, Mengrong. "Advances in hollow core fibres and application to mid-infrared fibre gas lasers". Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760959.
Testo completoAbstract (sommario):
Anti-resonant hollow core fibre is a new kind of optical fibre waveguide in which light is trapped in a hollow core surrounded by the capillary formed microstructured cladding. This fibre exhibits high damage threshold, low dispersion and ultra-low nonlinearity with relatively low loss of a few tens of dB/km. Its intrinsic feature of multimode delivery limits the applications with high requirements of single mode transmission. In my thesis, I demonstrate how the design of hollow core fibre can be improved with single mode guidance. S2 imaging measurement was used to analyse the mode content of the solid core fibres. In my research, I established S2 measurement to measure the mode contents in hollow core fibres for the first time. Two hollow core fibres with 8 capillaries and 7 capillaries in their claddings were fabricated in same fashion and showed differences in low attenuations. By comparing the mode contents in both of the fibres via S2 imaging measurement, 7-capillary HCF was demonstrated to give better performance on single mode guidance. Among the applications of the HCF, the property of delivering high power in HCF makes the gas filled HCF laser possible. In my research, a continuous-wave mid-infrared acetylene filled hollow core laser was built with a slope efficiency of 33% and an output power of over 1 watt at the wavelength region of 3.1~3.2 μm. The pump source is an Erbium-doped fibre amplified tunable laser diode which works at C-band wavelength. The fibre without the gain medium has two transmission bands with low attenuation of 0.037 dB/m and 0.063 dB/m at pumping and lasing wavelengths respectively. This laser system works in either cavity-based configuration or single pass ASE configuration. The latter configuration shows a better performance in high output power and high slope efficiency. The optimized laser system was studied experimentally with the proper fibre length and gas pressure. This laser system could be extended to be filled with other molecules to longer wavelengths and has potential for high power output.
7
Zsirai, Tamas. "Fouling and clogging in hollow fibre membrane bioreactor". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8411.
Testo completoAbstract (sommario):
The sustainability of a large pilot-scale hollow fibre immersed membrane bioreactor (HF iMBR) has been investigated with specific reference to membrane surface fouling and membrane channel clogging. Studies were conducted at normal sludge solids concentration of around 8 g/L and were also extended to concentrations more associated with thickening processes (around 32 g/L). A review of mechanically- moved membranes was conducted with a view to exploring a low energy means of sustaining operation through suppressing clogging. Methods were devised to quantify the amount of clogged solids within the membrane fibre bundle, either through their separation and gravimetric analysis or in-situ gravimetic estimation of the clogged solids without their removal from the membrane HF bundle. Outcomes generally revealed clogging to be as important a contributor to suppression of permeability as fouling, the key differentiator being that chemical cleaning had no sustained impact on permeability recovery when clogging took place. It was further substantiated that the operating permeability of membranes, once they had been clogged, could not be returned to that of the preclogged state despite declogging (i.e. mechanical removal of the solids) followed by the repeated application of chemically-enhanced backwashing. This was attributed to membrane pore plugging. Cont/d.
8
Yeow, May Ling. "Fabrication of poly(vinylidene fluoride) hollow fibre membranes". Thesis, University of Bath, 2004. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426179.
Testo completo
9
Gbenedio, Ejirooghene Patrick. "Multifunctional inorganic hollow fibre membranes for chemical reactions". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6415.
Testo completoAbstract (sommario):
Over the last few decades, the availability of inorganic membranes which can withstand high temperatures and harsh chemical environments has resulted in a wide range of opportunities for the application of membranes in chemical reactions. In particular, the combination of membrane separation and catalytic reaction in a single operating unit is an attractive way to increase conversions, to achieve better yields and to make more efficient use of natural resources in many reactions. In this work, a highly compact multifunctional Pd and Pd-Ag/alumina hollow fibre membrane reactor (HFMR) have been developed and applied to catalytic chemical reactions. The developed HFMR consists of a thin and defect free Pd-based membrane coated onto the outer surface of an alumina hollow fibre substrate with a unique asymmetric pore structure, i.e. a sponge-like outer layer and a finger-like inner layer where catalyst is deposited. In one study, a Pd-Ag layer was coated onto the outer surface of the substrate followed by deposition of sub-micron sized Pt(0.5wt.%)/γ-alumina catalysts into the finger-like voids of the substrates. This design achieved propane conversion as high as 42 % at the initial stage of the reaction at 723 K and space-time yields (STY) of the HFMR were approximately 60 times higher than that of a fixed bed reactor (FBR). In order to further increase catalytic surface area in the reaction zone, a sol-gel method was used to deposit Pt(1 wt.%)/SBA-15 catalysts into the finger-like voids of a substrate to develop a Pd/alumina HFMR. Benefiting from this novel design, the functionalized alumina hollow fibre substrates with surface area/volume values of up to 1918.4 m2/m3 possess a specific surface area of about 31.8 m2/g for catalysts. It was observed that in comparison with a conventional FBR, greater propene selectivity and propene yield was achieved by using the HFMR for propane dehydrogenation. The generic advantages of the design of these compact HFMR systems can be applied to further applications such as the water-gas shift reaction, which was also carried out in this study.
10
Gouveia, Gil Ana Maria. "Catalytic hollow fibre membrane reactors for H2 production". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/39795.
Testo completoAbstract (sommario):
Pre-combustion decarbonisation is one of the three main routes widely discussed for CO2 capture from fossil fuels. This thesis focuses on the development of a catalytic hollow fibre membrane reactor for the combined steam methane reforming (SMR) and water-gas shift (WGS) reaction, using a Ni-based catalyst, and at a temperature window suitable for harvesting pure H2, a clean energy carrier, from the reaction by a Pd membrane. Apart from developing the catalyst and the Pd-based composite membrane, which are normally considered as the two essential components of a membrane reactor involving hydrogen separation, this study introduces the concept of incorporating the catalyst into a micro-structured ceramic hollow fibre substrate to promote mass transfer efficiency. Meanwhile, the impact of each fabrication step, i.e. catalyst composition and preparation, ceramic hollow fibre fabrication, catalyst incorporation and electroless plating of Pd membranes, on the assembly and final performance of the catalytic hollow fibre membrane reactor was systematically evaluated. In contrast to previous studies involving micro-structured ceramic hollow fibres for catalytic reactions, the one developed in this study possesses a plurality of unique micro-channels, with significant openings on the inner surface of the ceramic hollow fibre. In addition to reduced mass transfer resistance for both catalytic reaction and hydrogen permeation, a microstructure of this type significantly facilitates catalyst incorporation and, as a results, enable the application of this hollow fibres for a wider spectrum of catalytic reactions.
11
Anh, Viet Bui, of Western Sydney Hawkesbury University, of Science Technology and Environment College e of Science Food and Horticulture School. "A study of osmotic distillation in hollow fibre modul". THESIS_CSTE_SFH_Anh_V.xml, 2002. http://handle.uws.edu.au:8081/1959.7/4.
Testo completoAbstract (sommario):
Osmotic distillation is a process of removing water from an aqueous solution, driven by water vapour pressure gradient across a hydrophobic membrane. The process occurs at or below ambient temperature and under atmospheric pressure. This research project investigates the osmotic distillation process in hollow fibre modules using hollow fibres PP375, PV375 and PV660 supplied by Memcor Australia. Operating conditions such as temperature, feed concentration and brine cross flow velocity, but not the feed cross flow velocity, were found to have significant effect on the flux. Models for heat and mass transfers were used to study the polarisation phenomena in osmotic distillation. Temperature and concentration profiles at the membrane surfaces due to polarisation were quantified. Scholfield and Ordinary Diffusion models for flux prediction based on the bulk conditions were developed and validated. Models for water activity and viscosity of aqueous glucose and calcium chloride solutions were also developed and validated in this work.Master of Science (Hons)
12
Paris, Marc. "Modelling of a hollow fibre bioartificial liver and pancreas". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28452.pdf.
Testo completo
13
Anh, Viet Bui. "A study of osmotic distillation in hollow fibre module /". View thesis, 2002. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030728.144424/index.html.
Testo completo
14
Zydorczak, Barbara. "Oxygen production from air using ceramic hollow fibre membranes". Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526373.
Testo completo
15
Wright, Kevin Ian Trevor. "Dual hollow fibre bioreactor for the growth of hybridomas". Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/11611.
Testo completoAbstract (sommario):
The use of hollow fibre bioreactors in mammalian cell culture has provided a means by which large populations of viable cells can be grown continuously, for extended periods, in a relatively small volume of vessel. Bioreactors in which one set of fibres are used for nutrient and metabolite exchange from the cell mass are limited by their reliance on an axial flow regime. This pressure mediated flow pattern leads to the formation of nutrient gradients within the cell mass, which occur due to the large diffusional distances present in the growth space, resulting in cell death within the bioreactor. The Edinburgh Dual Hollow Fibre Bioreactor solves this diffusional problem by using two sets of fibres to mimic the arterio-venous flow found in the body. In this instance the diffusional distances are reduced due to the close proximity of the two sets of fibres. Using this design, and a murine hybridoma (ES4) which produces an IgM blood typing antibody, cells were grown to a maximum density of 1.2x107 viable cells ml-1, with a maximum antibody production rate of 0.16 mgh-1. This was a 10 fold improvement in the viable cell number obtained using an airlift fermenter. The successful operation of this design was found to be dependent upon the pressure profiles developed within the bioreactor, with a number of extended culture experiments having been carried out. The influence of bioreactor design, fibre selection and the methods by which these bioreactors should be operated are discussed in this work.
16
Tawari, Akram. "Development of a cellulose acetate hollow-fine-fibre membrane". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4253.
Testo completoAbstract (sommario):
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The goal of this study is to produce cellulose acetate (CA) hollow-fine-fibre membranes with good water flux performance in the 95 – 96% salt retention range for brackish water desalination from first principles. First, the acceptable range of fibre dimensions was determined by means of a collapse pressure calculation using the elastic buckling pressure equation (thin shell assumption). Second, the pressure drop across the fibre wall in the hollow-fine fibre was determined by using the Hagen-Poiseuille equation, in order to determine how this would affect the chosen fibre dimensions. It was determined that the acceptable range of fibre dimensions was 222 – 247 m, and the wall thickness was 50 m. Fibres with these dimensions exhibited a high resistance to brackish water operating pressure of 20 – 25 bar, without collapse. The pressure drop calculations of these dimensions showed a sufficiently low pressure drop across the fibres. A dry-wet spinning technique was used for the preparation of the hollow-fine-fibre membranes. Hollow-fine fibres were spun using CA dissolved in a suitable solvent and non-solvent mixture comprising acetone and formamide. The effects of the dope composition and spinning parameters such as solvent to non-solvent ratio, bore fluid ratio, take-up speed, dope extrusion rate and heat treatment on the membrane morphology and performance were investigated. The spun fibres showed a good morphological structure, with no macrovoids (sponge-like structure), which is favourable for reverse osmosis (RO) applications. The hollow-fine-fibre membranes showed a good brackish water desalination performance within brackish water operating conditions. Statistical analysis was used to generate a fabrication formulation for producing cellulose acetate hollow-fine-fibre membrane for brackish water desalination with improved salt retention and flux. A three-level three-factor factorial was used to the study of the effect of spinning parameters (solvent to non-solvent ratio, bore fluid ratio and air gap distance). A regression equation was successfully established and was used to predictably produce membranes with good performance within the limits of the factors studied. RO performance of these hollow-fine-fibre membranes was good: The salt retention ranged from 96 to 98% and the permeate flux ranged from 60 to 46 L/m2.d (2 000 ppm, NaCl, 20 bar, 24 oC).
AFRIKAANSE OPSOMMING: Die studie het ten doel gehad om selluloseasetaat holveselmembrane vanaf eerste beginsels vir brakwaterontsouting te ontwikkel. Die ontsoutingsvlakke van die membrane moet tussen 95 en 96% lê met ’n aanvaarbare waterproduksievermoë. Aanvaarbare deursneë vir die holvesels is eerstens bepaal deur platval-berekeninge met behulp van die inmekaarvouvergelyking uit te voer (dunwand aanname). Hierna is drukval oor die wand van die holvesel met behulp van die Hagen-Poiseuille vergelyking bepaal ten einde vas te stel hoe dit die gekose dimensies sal beïnvloed. Daar is vasgestel dat vesel deursneë tussen 222 en 247 um met ’n 50 um wand aanvaarbaar is. Vesels met hierdie dimensies het ’n hoë weerstand teen inval getoon by brakwater opereringsdrukke tussen 20 en 25 bar. ’n Droë-nat spintegniek is in die voorbereiding van die holveselmembrane gebruik. Holvesel membrane is met ’n selluloseasetaat stroop gespin wat uit ’n oplosmiddel (asetoon) en nieoplossmiddel (formamied) bestaan het. Die effek van die spinstroop samestelling en spinparameters soos die oplosmiddel tot nieoplosmiddel verhouding, lumen-vloeistof verhouding, opneemspoed, spinstroop ekstrusie tempo en hittebehandeling op membraan morfologie en werkverrigting is ondersoek. Die gespinde vesels toon ’n sponsagtige struktuur sonder die teenwoordigheid van enige mikroleemtes wat voordelig is vir tru-osmose toepassings. Die holvesel membrane het aanvaarbare brakwater ontsoutings werkverrigting. Statistiese analise is gebruik in die generasie van produksieformulasies vir die produksie van brakwater ontsoutingsmembrane met verbeterde retensie en vloed. ’n Drie-vlak driefaktoriaal ontwerp is tydens die studie gebruik om die effek van spinparameters (oplosmiddel tot nie-oplosmiddel verhouding, lumen vloeistof verhouding, en lug-gaping) te ondersoek. ’n Regressie vergelyking is suksesvol daargestel en gebruik om voorspelbaar membrane met goeie werkverrigting binne die limiete van die studie te produseer. Die tru-osmose werkverrigting van die membrane was goed: die sout retensie het tussen 96 en 98% gelê en die permeaatvloed tussen 60 en 46 L/m2.d (2 000 ppm NaCl, 20 bar, 24oC).
17
Paine, Kevin Andrew. "Steel fibre reinforced concrete for prestressed hollow core slabs". Thesis, University of Nottingham, 1998. http://eprints.nottingham.ac.uk/11095/.
Testo completoAbstract (sommario):
An investigation of prestressed concrete containing steel fibres as secondary reinforcement to improve performance in shear, flexure and bond is reported. Emphasis is placed on the use of steel fibres in prestresssed extruded hollow core slabs, since these common precast elements have intrinsic difficulty in incorporating traditional secondary reinforcement due to their unique shape and manufacturing method. Two separate studies were carried out. The first study involved laboratory investigations into the bond between fibre reinforced concrete (FRC) and the prestressing strand, and the shear behaviour of laboratory-cast prestressed fibre reinforced concrete (PFRC) beams. The second part involved the factory production of fibre reinforced hollow core slabs in co-operation with a local manufacturer. The fibre reinforced hollow core slabs were subjected to conventional full-width shear tests, concentrated load shear tests, and to transverse flexure. For all laboratory cast elements, cubes, cylinders and prisms were cast to investigate compressive, tensile and flexural properties, respectively. Two types of steel fibre were investigated: hooked-end steel fibres at fibre volume fractions (Vf) of 0.5%, 1.0% and 1.5%; and amorphous metal fibres at Vf‘s of 0.28% and 0.56%. The trial production of fibre reinforced hollow core slabs necessitated the investigation of the effect of steel fibres on the extrusion manufacturing process. It was shown that fibre reinforced hollow core slabs could be adequately compacted with only slight increases in mixing water. Fibres were found to distribute randomly throughout the cross-section. However, the rotation of the augers affected the orientation of fibres, with fibres tending to align vertically in the web. It was shown that the addition of steel fibres to prestressed concrete has a negative effect on the bond between matrix and tendon, leading to longer transfer lengths. The effect of the increase in transfer length was to reduce cracking shear strengths by 4%. Shear tests showed that the incorporation of steel fibres could increase shear strength by as much as 45% for Vf = 1.5%. This increase in shear strength, known as the fibre contribution, was shown to be due to fibres bridging across the crack and an increased compressive resistance due to fibres arresting the propagation of cracks into the compressive zone. A semi-empirical equation for shear strength of PFRC elements is developed. It is given in two forms, one compatible with the present equations for prestressed concrete given in BS 8110 and Eurocode 2, and a second form compatible with that advocated for fibres in reinforced concrete. The equation makes use of equivalent flexural strength which is recognised as the most useful material property for design of FRC. The equation was found to give good correlation with the shear strength of single web beams cast both in the laboratory and under factory conditions. However, a overall strength reduction factor is required for full-width hollow core slabs to account for uneven load distribution and inconsistent web widths. This is consistent with tests on plain hollow core slabs found in the literature.
18
Abokhamis, Mousavi Seyed Mohammad. "Exploring optical nonlinearity in gas-filled hollow core fibre". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/428037/.
Testo completoAbstract (sommario):
The growing need for novel light sources in variety applications increases the demand for laser sources operating in many different range of spectrum. Despite the success in development of mid-infrared (mid-IR) lasers, which are essential in many applications such as: environmental science, bio-science and physics, there are still lack of reliable lasers in this range with existing fibre laser technology compatibility. Meanwhile the nonlinearity in gases has been explored extensively from the very beginning of nonlinear optics, however, new developments in pulsed lasers and fibre design provide opportunities for more applications. The introduction of Hollow Core Photonic Crystal Fibres (HC-PCF) has revolutionised the area of nonlinearity in gaseous media by offering a single-mode confined light beam for very long distances. In this thesis, the focus was on mid-IR pulse generation by Raman frequency conversion in a gas-filled HC-PCF. Due to reliable performance and compatibility of fibre lasers with HC-PCFs, and towards fully fiberized source, an erbium-doped fibre laser (1.55 μm) has been selected as the pump for this project. In order to reach as far as possible into the mid-IR region, hydrogen has been selected as the filling gas of fibre, due to its large frequency shift and high Raman gain. The large frequency shift and mid-IR operating range required a new fibre design with a broadband transmission window and relatively low loss in mid-IR. After studying conventional HC-PCF structures, the recently proposed Nested Anti-resonant Nodeless Fibre (NANF) has been selected as the most suitable option for the purpose of this thesis [71]. Two NANFs, made of silica and tellurite, have been designed and optimized through the use of the developed Finite Element Method (FEM) toolbox in this thesis for operating wavelengths at pump (1.55 μm) and 1st Stokes (4.35 μm). A novel design has also been introduced in NANFs which shows polarization maintaining feature as good as the latest state-of-the-art HC-PBGF type [77]. The proposed design also shows polarizing capability in addition to its polarization maintaining by presenting a large loss ratio (~30 dB) between different polarizations of propagating light through it. The pulse propagation throughout the hydrogen-filled NANFs has been investigated by modelling the Raman response of hydrogen and numerically solving the Generalized Nonlinear Schrödinger Equation (GNLSE). Simulations show promising results for frequency conversion towards mid-IR and the possibility of Raman lasers in this region by considering different gas and using the readily available air in HC fibres. Furthermore, in this work, the nonlinear dynamics of atmospheric air-filled HC fibres have been studied, ranging from Raman down conversion process to a high spectral power density supercontinuum spanning from 850 to 1600 nm. A semi-quantum model for air has been adopted and integrated into the GNLSE, which surpasses the limitations of simple model. Using the adopted model, the experimental results have been reproduced without any extra computational cost. A rigorous study has been performed on nonlinear dynamics of pulse propagation in air-filled HC fibres and the origin of many nonlinear phenomenon are identified.
19
Love, Adrian. "Hollow core optical fibre based gas discharge laser systems". Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760983.
Testo completoAbstract (sommario):
The humble electrically pumped gas laser has undergone little development in its fifty year life span due to the lack of an effective method to confine light within a hollow waveguide of any appreciable length in which an electrical discharge could be contained. New technologies in the field of anti-resonant guiding hollow core fibres present an opportunity to re-invent the gas laser. A recent breakthrough in the field demonstrated that DC pumped glow discharges of a helium and xenon gas mixture could not only be sustained in such a fibre, but also exhibited signs of gain on a number of mid-IR neutral xenon laser lines. The research presented in this thesis is a continuation of that project. The system was redesigned to incorporate two mirrors so that a cavity could be constructed. The previously hinted at gain on the 3:51 μm xenon line was confirmed through a series of CW measurements of the cavity, as was a polarisation of the laser due to a polarisation dependent output coupler. Further observation of the discharges revealed that they were of a pulsed nature, and that the mid-IR laser light was present in the discharge afterglow. A response to the cavity mirrors was observed in this afterglow pulse on the 3:11 and 3:36 μm xenon lines in addition to the 3:51 μm line previously seen. Through fast detection a modulation of the output power due to cavity mode beating effects was detected. The high gain and narrow bandwidth of the xenon laser lines resulted in a frequency pulling effect, and the mode separation in the 'hot' laser cavity was measured to be lower than in the 'cold' cavity. It was observed through pressure optimisation experiments in helium-xenon that higher output powers could be achieved by using lower partial pressures of xenon. This was exploited with neon-xenon mixtures, where the lower ionisation potential of neon allowed a lower pressure of xenon. Discharges were also achieved in helium-neon and argon gas mixtures.
20
Xu, Qian. "Optimizing the operation of direct-flow hollow fibre filtration". Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:9fa9886c-f4c0-4f80-abbe-d4c40e27d1b0.
Testo completoAbstract (sommario):
In current water industry, direct-flow hollow fibre filtration is increasingly used as an intermediate or complete water purification technique. Compare to classical crossflow filtration, direct-flow filtration avoids high pressure drop that incurs high energy cost in the feed channel and permits the use of smaller diameter fibres which increases the filtration area per unit volume. Such filtration is achieved by efficiently capping one end of the crossflow device and it is usually operated in dead-end mode with regular intermittent backwash. Direct-flow filtration therefore forms the dominant method for producing potable water from ground or surface water. This thesis focuses on the operational considerations and design aspects of the direct-flow filtration membrane modules, specifically those of the pressure driven inside feed format. From a comprehensive literature survey of direct-flow filtration it was established that there was a general lack of information on direct-flow filtration behaviours. In particular there were no tools to simulate the hydrodynamic efficiencies within these devices. This study therefore set out to develop various direct-flow filtration models which one can also apply in various industrial processes. With a dimensionless mathematical model for the fluid flow in an axisymmetric direct-flow pipe, simple investigations on direct-flow filtration was achieved. Then two realistic hollow fibre models which included finite wall thicknesses and fouling effects were developed. These models were used to investigate various influences upon the axial dependence of the transmembrane pressure and the cumulative filtration volume under non-fouling and fouling conditions. The current fouling model is limited to chemically inert, incompressible, suspended solids. Geometrical parameters including fibre radius, fibre wall thickness, fibre length, module void fraction and imposed average flux were varied over a broad range values encompassing the values applied in today's water industry. Various scenarios of membrane fouling and cleaning process in which fibres were subject to identical hydrodynamic conditions have been investigated. The study has proposed two important metrics and a strategy for optimizing them to promote the best filtration performance: the module productivity parameter, and the filtration uniformity factor. Overall, optimized design ranges and operating regimes of the direct-flow hollow fibre filtration devices were summarised, and the modelling results accord with commercial products as used in industrial practice that has evolved over the last 20 years and show guidance for future designs.
21
Rahman, Mukhlis Bin A. "Catalytic hollow fibre membrane micro-reactors for energy applications". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7097.
Testo completoAbstract (sommario):
An asymmetric ceramic hollow fibre is proposed as a substrate for the development of a catalytic hollow fibre microreactor (CHFMR) and a catalytic hollow fibre membrane microreactor (CHFMMR). The ceramic substrate that is prepared using the phase inversion and sintering technique has a finger-like structure and a sponge-like region in the inner region and the outer surface respectively. The finger-like structure consists of thousands of conical microchannels distributed perpendicularly to the lumen of ceramic hollow fibres onto which a catalyst is impregnated using the sol-gel Pechini method to improve a catalytic reaction. To further enhance the catalytic reaction, a membrane has been incorporated on the outer layer of ceramic hollow fibre. This study focuses on the use of palladium (Pd) and palladium/silver (Pd/Ag) membranes to separate hydrogen from reaction zones in the water-gas shift (WGS) reactions and the ethanol steam reforming (ESR) respectively. In the development of CHFMMR, the fabrication of Pd and Pd/Ag membranes is carried out prior to the catalyst impregnation process to avoid the dissolution of catalyst into the plating solution due to the presence of ammonia and ethylenediaminetetraacetic acid (EDTA). The catalytic activity tests show that the CHFMR, that does not have the Pd membrane on its outer surface, improves the carbon monoxide (CO) conversion compared with its fixed-bed counterpart. The presence of conical microchannels is expected to enhance the activities of the catalyst in the substrate. The incorporations of Pd and Pd/Ag membranes on the outer layer of ceramic hollow fibres enable pure hydrogen to be produced in the shell-side for both the WGS reaction and the ESR. The CHFMMR is used to remove one of the products enabling the WGS reaction to favour the formation of product. It also facilitates the small amount of catalyst to be used to produce significant amount of hydrogen in the ESR.
22
El-Amari, Abdulla Ali. "Separation of acidic gases using hollow fibre membrane contractors". Thesis, University of Salford, 2002. http://usir.salford.ac.uk/26653/.
Testo completoAbstract (sommario):
Gas absorption in hollow fibre contactors is being increasingly used due to their enormous surface area/volume ratio. The capability of the hollow fibre membrane modules for the removal of CO 2 and SO2 from a binary gas mixture has been investigated experimentally. Four different modules were used in this study. The membranes in modules one and two were made of microporous polypropylene. The third module was made of non-porous silicone rubber (polydimethylsiloxane) while the latter one was a polyvinylidenefluoride (PVDF) asymmetric hollow fibre membrane. The gas mixtures used in the experiments were composed of 9.5% CO2 and 1% SO2 in N 2 , which was introduced into the hollow fibre lumen, while the absorbent liquid was fed into the shell side of module. The absorbent liquids used were water, aqueous solutions of diethanolamine (DBA) and ammonia at different concentrations (5, 10 and 20 wt%). The effects of different operating conditions on the permeation process have been investigated for co-current and counter-current flow patterns. In addition, to improve the silicone rubber hollow fibre membrane performance, baffles were installed within the shell of the permeator to increase liquid fibre contact. The results obtained showed that the use of baffles within the shell of the permeator improved the separation performance of the non-porous membrane module without any substantial increase in the physical size of the contacting device. Studies also showed that improved performance was observed when the system was operated under a counter-current flow pattern. The results showed that the use of an absorbent liquid in the permeate side of the fibres increased the selectivity of the membranes used, and reduced the need to maintain a high pressure ratio across the membrane. A decrease in the feed gas flow rate or increase in liquid flow rate generally improved the removal of gases. The results showed that the use of aqueous reactive solutions as an absorbing medium in the permeate side of the hollow fibre permeator can significantly improve CO2 removal from the gas mixture. However, the main problem when using a microporous membrane coupled with aqueous solutions of diethanolamine as absorbent was wetting of the microporous membrane by amine solutions. For 862 separation, the highest removal was attained using the microporous membrane coupled with water as absorbent liquid. This demonstrates that a hollow fibre based device can be a very efficient gas liquid contactor. The separation process was simulated with a numerical model based on the effective permeabilities of gases and compared with the experimental results. The model simulations showed good agreement with the experimental observations.
23
Bateman, Samuel. "Hollow core fibre-based gas discharge laser systems and deuterium loading of photonic crystal fibres". Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648951.
Testo completoAbstract (sommario):
Research towards the development of a gas-discharge fibre laser using noble gases, with target emission wavelengths in the mid-IR. Additional and separate work on gas treatment methods for managing the formation of photo-induced defects in silica glass.
24
Doraswami, Uttam. "Modelling of Micro-tubular Hollow Fibre Solid Oxide Fuel Cells". Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520872.
Testo completo
25
Verrecht, Bart. "Optimisation of a hollow fibre membrane bioreactor for water reuse". Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/6779.
Testo completoAbstract (sommario):
Over the last two decades, implementation of membrane bioreactors (MBRs) has increased due to their superior effluent quality and low plant footprint. However, they are still viewed as a high-cost option, both with regards to capital and operating expenditure (capex and opex). The present thesis extends the understanding of the impact of design and operational parameters of membrane bioreactors on energy demand, and ultimately whole life cost. A simple heuristic aeration model based on a general algorithm for flux vs. aeration shows the benefits of adjusting the membrane aeration intensity to the hydraulic load. It is experimentally demonstrated that a lower aeration demand is required for sustainable operation when comparing 10:30 to continuous aeration, with associated energy savings of up to 75%, without being penalised in terms of the fouling rate. The applicability of activated sludge modelling (ASM) to MBRs is verified on a community-scale MBR, resulting in accurate predictions of the dynamic nutrient profile. Lastly, a methodology is proposed to optimise the energy consumption by linking the biological model with empirical correlations for energy demand, taking into account of the impact of high MLSS concentrations on oxygen transfer. The determining factors for costing of MBRs differ significantly depending on the size of the plant. Operational cost reduction in small MBRs relies on process robustness with minimal manual intervention to suppress labour costs, while energy consumption, mainly for aeration, is the major contributor to opex for a large MBR. A cost sensitivity analysis shows that other main factors influencing the cost of a large MBR, both in terms of capex and opex, are membrane costs and replacement interval, future trends in energy prices, sustainable flux, and the average plant utilisation which depends on the amount of contingency built in to cope with changes in the feed flow.
26
Welch, Matthew G. "Compressing and propagating solitons in hollow core photonic crystal fibre". Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520840.
Testo completoAbstract (sommario):
The development of photonic crystal fibre from conventional optical fibre follows a trend in the development of materials, to create composites and structured materials on smaller and smaller scales. In fact the great success of photonic crystal fibre is largely due to the ability to structure it on scales comparable to the wavelength of light. It is this micron size structure that allows the creation of an (out of plane) optical bandgap in silica and allows hollow core fibre to guide light in an air core freeing the guided mode from the properties of bulk silica. This thesis focuses on the propagation and compression of high peak power optical solitons in hollow core fibre. As the Kerr nonlinear response of air is approximately a thousand times less than that of silica, the air core of hollow core fibre can support much higher peak powers than conventional optical fibre without the manifestation of nonlinear effects, making it ideal for the delivery of high peak power laser pulses. Coupled with this, hollow core fibre has a large region of anomalous dispersion in its transmission window allowing optical pulses to be transmitted as temporal solitons freeing them from the effects of dispersion. The author started his Ph.D. in 2006, three years after the first demonstration of soliton propagation in hollow core fibre and as the first demonstrations of soliton compression in hollow core fibre were being undertaken. Work by the author to build upon these early demonstrations is presented in this thesis in the following manner: Chapters 1, 2 and 3 are theory chapters. Chapter 1 explains the background waveguide theory and theory of nonlinear optics that is used throughout the thesis. Chapter 2 details the properties of photonic crystal fibres focusing on hollow core fibre. Chapter 3 details recent papers relevant to the propagation and compression of solitons in hollow core fibre. Chapters 4, 5 and 6 are experimental chapters reporting work undertaken by the author. Chapter 4 focuses on modifying the nonlinearity of hollow core fibre and measuring the dispersion of hollow core fibre accurately. Chapter 5 focuses on the compression of chirped and unchirped picosecond pulses in dispersion decreasing hollow core fibre tapers. Chapter 6 reports the compression in hollow core fibre of femtosecond pulses centred at 540nm wavelength through soliton effect compression.
27
Harper, Davnet. "Novel applications of membrane technology". Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248220.
Testo completo
28
Williams, Gareth. "Development of self-healing carbon fibre reinforced plastic utilising an embedded hollow glass fibre delivery system". Thesis, University of Bristol, 2008. http://hdl.handle.net/1983/f6eeac30-dbc3-44f2-9911-8f5b6a877ba3.
Testo completoAbstract (sommario):
There is a drive for modem engineering structures to exploit the excellent specific properties of advanced fibre reinforced composite materials, particularly in aerospace, where manufacturers are under intense pressure to reduce costs and engineer lighter more efficient aircraft. However it is widely recognised that the susceptibility of these materials to transverse impact damage is restricting the extent to which these benefits can be exploited.
29
Senn, Simon Charles. "The preparation and characterization of hollow fibre membranes for gas separation". Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/405/.
Testo completoAbstract (sommario):
A dry-jet wet-spinning process developed industrially for the preparation of hollow fibre membranes suitable for gas separation applications, has been reproduced on a laboratory scale. Polysulphone hollow fibres were spun from a variety of solvents and their gas transport properties were characterized using equipment built during the course of the research. The phase inversion process of membrane formation was studied in order that the best morphological structure could be produced. The spinning parameters were studied to establish their influence on the fibre dimensions. Further relationships were then sought between the gas transport properties and the fibre dimensions and spinning parameters. The behaviour of the membranes to both single gases and gas mixtures was studied. Both the permeation rate constants and the separation factors determined from the mixture permeation were found to be lower than the values predicted from the single gas permeation experiments. A model was developed to help understand the competitive nature of the adsorption-diffusion process and explain the differences in values recorded from the single gas and mixture studies. Experiments aimed at improving membrane performance were based on modification of the already established polysulphone hollow fibre. Modification of the selective surface layer of the hollow fibre membranes was considered to be the best approach. Coating of the fibres, other than to repair damage to the skin layer, was found to result in too large a decrease in permeability. Sulphonation of the surface layer was achieved using sulphur trioxide, although little improvement in the membrane performance was recorded. The sulphonation experiment results were, however, sufficiently encouraging to recommend future work.
30
Ye, Hua. "Novel hollow fibre membrane bioreactor for growing three dimensional bone tissue". Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414306.
Testo completo
31
Kimura, Hajime. "A novel cellulose acetate hollow fibre haemodialysis membrane : preparation and evaluation". Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396694.
Testo completo
32
Aba, Nofarah Diana Binti. "Development of graphene oxide hollow fibre membranes for solution based applications". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/57114.
Testo completoAbstract (sommario):
Graphene oxide (GO) is a chemical derivative of graphene which possesses interesting characteristics, such as atomic thickness, a 2D structure and robust mechanical strength, as well as a complex chemical structure constituted by various oxygen functional groups. GO flakes can be easily stacked on top of each other in order to form large area thin-film membranes. Since 2012, when the membrane potential of the GO was demonstrated for the first time, GO membranes have continued to attract high levels of interest from research communities which sought to continuously develop high performance membranes within the framework of various disciplines of separation. Nevertheless, the transport mechanism of the GO membrane in the separation process is not entirely understood, thus significant efforts have been made in order to further explore the unique characteristics the GO has to offer as a new generation of membrane material. The first part of this thesis explores the feasibility of GO membranes in the case of nanofiltration separation. GO membranes are unstable in dry air due to the shrinkage problems occurring under such conditions. When a membrane is exposed to air, a high tensile stress is imposed, which is far beyond what the membrane can withstand. In order to overcome the shrinkage problem, GO membranes were kept in water so as to preserve their intrinsic microstructures. Prior to depositing the GO membranes in water, controlled drying was required in order to avoid the redispersion of the membranes in water due to the hydrophilic nature of the GO. Depositing the GO membranes in water has successfully preserved their nanofiltration performance over a three-week interval, during which time the membranes that were exposed to dry air failed to achieve similar results. At the end of this first part, the transport mechanism in nanofiltration is discussed. Although GO membranes have been found to be feasible in the case of nanofiltration separation, they have also been demonstrated to be incapable of removing smaller ionic species, such as magnesium chloride and sodium chloride, solely on the basis of their pristine nature. The second part of this thesis explores the feasibility of GO at the level of desalination applications. It is well known that the rejection of salts relies not only on the pore size of a membrane, but also on the charge of the membrane and the solute, thus creating electrostatic repulsion. Cross-linking GO membranes with Al3+ have successfully changed the negatively charge GO membranes to highly positive charge. On the basis of space charge model, the cross-linking has successfully increased the density of membrane charge, at the same time narrowing the effective channels for ion transport, simultaneously increasing the rejection towards salt solutions. The third part of this thesis further explores the feasibility of GO in the pervaporation dehydration of ethanol. For the pervaporation dehydration of ethanol, the surface of a GO membrane was modified with hydrophilic silane in order to turn it into a highly hydrophilic membrane. The performance of the modified GO membrane improved significantly with moderate separation factors. The transport mechanism in pervaporation is discussed at the end of this part. Moreover, the techno-economic analysis indicates that this modified GO membrane is environmentally benign and economically robust as a result of its small membrane area and energy requirements.
33
Liu, Yutie. "Novel ceramic hollow fibre membranes for fluid separation and chemical reaction". Thesis, Imperial College London, 2005. http://hdl.handle.net/10044/1/8271.
Testo completo
34
Couny, Francois. "Photonic solutions towards optical waveform synthesis". Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.478946.
Testo completoAbstract (sommario):
This thesis presents the development of photonic tools towards the realisation of an optical intensity waveform synthesiser and of an attosecond pulse synthesiser based on the generation and Fourier synthesis of a continuous-wave coherent spectral comb spanning more than 3 octaves (UV to mid-IR) by use of a gas-filled hollow core photonic crystal fibre (HC-PCF).
35
Yüceer, Ahmet. "Pressure drops along the bores of hollow fibre membranes their measurement, prediction and effect on fibre bundle performance /". Connect to e-thesis, 1985. http://theses.gla.ac.uk/976/.
Testo completoAbstract (sommario):
Thesis (Ph.D.) - University of Glasgow, 1985.BLL : D80152. Ph.D. thesis submitted to the Department of Mechanical Engineering, University of Glasgow, 1985. Includes bibliographical references. Print version also available.
36
Yuceer, Ahmet. "Pressure drops along the bores of hollow fibre membranes : their measurement, prediction and effect on fibre bundle performance". Thesis, University of Glasgow, 1985. http://theses.gla.ac.uk/976/.
Testo completo
37
Costello, Michael John School of Chemical Engineering & Industrial Chemistry UNSW. "SHELL-SIDE FLUID DYNAMICS AND MASS TRANSFER THROUGH HOLLOW FIBRE MEMBRANE MODULES". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 1995. http://handle.unsw.edu.au/1959.4/17042.
Testo completoAbstract (sommario):
There is a considerable volume of work available in literature which suggests that the performance of axial-flow hollow fibre membrane modules is limited by poorly distributed flow through the shell-side. This study was commissioned to examine the distribution of shell-side flow and its effect on mass transfer and to compare the performance measured by the axial-flow configuration to that obtained by a commonly used alternative known as the helically-wound module design. Laminar flow and mass transfer models have been developed to examine performance through axial-flow hollow fibre modules. These models also consider deviations from laminar flow in the form of turbulence and hydrodynamically undeveloped flow. Modelling analysis on four fibre bundle cross-sections quantify the extent to which channelling limits flow and mass transfer performance. Experimental flow and mass transfer work with locally fabricated hollow fibre modules demonstrated some inconsistencies with axial laminar flow modelling. Pressure drop and mass transfer results exceeded predictions from modelling. This thesis has hypothesised that fibres in axial-flow hollow fibre modules are not aligned as straight and parallel rods (as assumed in modelling) but interweave. Fibre interweaving results in flows between ducts. Such flows create mixing between ducts which results in more intimate contact between the flow and membrane surface, the consequence being higher pressure drop and higher mass transfer. The implication from this work was that axial flow and mass transfer modelling was limited in its use for characterisation of shell-side performance. The experience with helically-wound hollow fibre membrane modules (also fabricated locally) was that, by deliberately inducing flow between ducts, it was possible to considerably improve mass transfer performance. It was found that, whilst helically-wound modules could not be packed as tightly as axial-flow modules and required more sophisticated fabrication techniques, the benefit in their use arose from a substantial improvement in the level of shell-side mass transfer.
38
Costello, Michael John. "Shell-side fluid dynamics and mass transfer through hollow fibre membrane modules". [Sydney : University of New South Wales], 1995. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN1999.0043/index.html.
Testo completo
39
Smith, Stanton Russel. "Hydrodynamics and mass transfer in slug enhanced ultrafiltration using hollow fibre membranes". Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398235.
Testo completo
40
Lloyd, Jonathan Richard. "The physiological state of microbial cells immobilised in hollow-fibre membrane bioreactors". Thesis, University of Kent, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358565.
Testo completo
41
Alderman, Angela. "Extraction of metals from aqueous solution using hollow fibre supported liquid membranes". Thesis, University of Hertfordshire, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332223.
Testo completo
42
Meneghello, Giulia. "Development of a novel PVA-PLGA hollow fibre bioreactor for tissue engineering". Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535377.
Testo completoAbstract (sommario):
Tissue engineering offers a potential alternative therapy to overcome the limitations of organ transplantation, by employing biomaterials as scaffold for cell growth. For example, poly-lactic-co-glycolic acid (PLGA) is a synthetic biomaterial widely used in tissue engineering. However, the hydrophobicity of PLGA results in scaffolds that are poorly wettable, and which, therefore, possess poor mass transfer properties for the delivery of nutrients and the removal of waste. The present work aimed to develop more hydrophilic PLGA scaffolds, specifically hollow fibre membranes, within a bioreactor system, which enables co-culture of cells in order to direct stem cell differentiation. Large quantities of costly growth factors are required over long periods for stem cell differentiation. Therefore, this project also aimed to use a cell line as a “factory” for the inexpensive, in situ growth factor production. Hollow fibres were fabricated by wet spinning and a hydrophilic polymer, polyvinyl alcohol (PVA), was added to the PLGA solution at three different concentrations (1.25, 2.5, 5% w/w) in order to obtain a more hydrophilic membrane. Results indicated that 5% PVA-PLGA hollow fibres were the only membranes which allowed permeation of water, BSA and cell-secreted hepatocyte growth factor (HGF), thus indicating that they are the most suitable membranes for use in bioreactor devices. However, these membranes failed to improve cell-attachment. Cell secreted HGF was shown to be more stable in a dynamic culture environment than commercial HGF, thus suggesting its suitability for applications in bioreactor devices. However, using both commercial and cell-secreted HGF, mesenchymal stem cell differentiation was unsuccessful. In conclusion, this work has developed a hollow fibre membrane which is more permeable to water and proteins for a higher mass transfer of nutrients, and has realised a model system for the inexpensive production of growth factors for use in bioreactor devices and the differentiation of stem cells.
43
Bradley, Thomas David. "Atomic vapours filled hollow core photonic crystal fibre for magneto-optical spectroscopy". Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616871.
Testo completoAbstract (sommario):
This thesis describes developments in atomic vapour loading in hollow core photonic crystal fibre (HC-PCF) for fabrication of atomic vapour loaded photonic microcells (PMC). These developments have been targeted at addressing some of the issues associated with loading atomic vapours in confined waveguiding geometries such as increased dephasing and physio-chemical wall absorptions. Atomic vapour loaded HC-PCF and PMC’s have applications in laser metrology, coherent optics and magneto optical spectroscopy. State of the art HC-PCF have been fabricated for loading with atomic vapour including both photonic bandgap (PBG) guiding and inhibited coupling (IC) hypocycloidal core shape Kagome HC-PCF. Record loss of 70 dB/km has been achieved in IC hypocycloid core shape Kagome HC-PCF in the spectral region centred at 800 nm. This fibre retains excellent single mode propagation combined with large core and increased optical bandwidth in comparison with specialist PBG HC-PCF optimised for operation around 800 nm. Aluminosilicate sol-gel coatings have been developed and successfully applied to the inner core wall of HC-PCF’s to reduce the atomic vapour surface interaction. Confining atomic vapours in micron scaled HC-PCF results in increased dephasing rates because of the frequent atom wall collisions. Anti relaxation coating materials have been applied to the inner core wall and the longitudinal relaxation time has been measured in coated and uncoated fibres utilising a magneto optical technique. Additionally sub Doppler transparencies are investigated in anti relaxation coated and uncoated HC-PCF.
44
Jammi, Sindhu. "Towards quantum optics experiments with trapped atoms in a hollow-core fibre". Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49896/.
Testo completoAbstract (sommario):
A proposal for performing quantum memory schemes with a light matter interface in Hollow Core Fibres is introduced. Various technical aspects of implementing such a scheme in the proposed interface are outlined and the different elements required to realize this scheme are discussed, primarily the detection of atomic levels and the extension of the scheme to magnetically trappable levels. A new method to dispersively measure populations and population difference of alkali atoms prepared in their two clock states is introduced, for future use in the Hollow Core Fibre interface. The method essentially detects the atom numbers based on the influence of the linear birefringence in the ensemble on the detection light beams via polarization homodyning. Sideband detection is performed after dressing the atoms with a radio-frequency field to circumvent low-frequency technical noises. The noise performance of this scheme is discussed along with design modifications aimed at reaching the atomic shot noise limit. Another technical aspect of realizing the quantum memory scheme in the proposed light-matter interface is the extension of the scheme to the trappable states of the atomic system as the atoms will be trapped in an atom chip magnetic field. We achieve this extension by showing the microwave spectroscopy of the ground state ensemble of radio-frequency dressed atoms which proves the existence of pseudo one-photon transitions between the trappable clock states. Finally, the preliminary designs and results of integrating an HCF in an atom chip experiment are discussed.
45
Mohamed, Dzahir Mohd Irfan Hatim. "Pd based inorganic hollow fibre membranes for H2 permeation and methylcyclohexane dehydrogenation". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6919.
Testo completoAbstract (sommario):
The availability of inorganic membranes which can withstand high temperatures and harsh chemical environments has resulted in a wide range of opportunities for the application of membranes in chemical reactions and separations. In particular, the combination of membrane separation and catalytic reaction into a single operating unit is an attractive way to increase conversions, improve yields and more efficient use of natural resources in many reactions. In this study, asymmetric alumina hollow fibres with different macrostructures consisting of finger-like macrovoids and a sponge-like packed pore structure in varying ratios have been prepared by a combined phase inversion/sintering technique. The asymmetric membranes in hollow fibre geometry possess superior surface area to volume ratios with less gas permeation resistance in comparison to commercial symmetric membranes in tubular and disk configurations. Such asymmetric hollow fibres are used as substrates onto which a Pd membrane is directly deposited by an electroless plating (ELP) technique without any pre-treatment of the substrate surface. A systematic study of the electroless plating of Pd and Ag onto an asymmetric alumina hollow fibre substrate has been carried out by direct measurement of one of the gaseous products, i.e. N2, using gas chromatography (GC). In addition, the influences of the substrate macrostructure on hydrogen permeation through the Pd/Al2O3 composite membranes have been investigated both experimentally and theoretically. Furthermore, a multifunctional Pd/alumina hollow fibre membrane reactor (HFMR) has been developed and employed for the catalytic dehydrogenation of methylcyclohexane (MCH) to toluene (TOL). The developed HFMR consists of a thin and defect-free Pd membrane coated directly onto the outer surface of an asymmetric alumina hollow fibre substrate. 50 wt% Ni/Al2O3 nano-sized catalysts were directly impregnated into the substrate. The performance of HFMR has also been compared with several different reactor configurations.
46
Droushiotis, Nicolas D. "Fabrication and characterization of hollow fibre micro-tubular solid oxide fuel cells". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9779.
Testo completoAbstract (sommario):
Despite three decades of development of solid oxide fuel cells (SOFCs) since the conception of the tubular Siemens–Westinghouse design, no practical alternatives to yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) electrolytes have been established. However, there have been considerable improvements in the performance of SOFCs, decreasing their specific overall costs, by decreasing operating temperatures, understanding their reaction kinetics, increasing specific surface areas of electrode / electrolyte / reactant three-phase boundaries, establishing new fabrication techniques and employing new geometric designs. So called micro-tubular SOFCs (MT-SOFCs) are one of the most promising geometric designs, though a misnomer, as tube diameters are normally several millimetres, significantly smaller than Siemens–Westinghouse SOFCs with 22 mm tube diameters. This three-year Ph. D. project was aiming to establish the feasibility of, and develop, a novel design of SOFC, fabricated using hollow fibres (HFs) with diameters of hundreds of micrometres, thereby increasing the specific surface area of electrodes, increasing the power output per unit volume/mass, facilitating sealing at high temperatures, and decreasing costs. Collaborators used a spinneret in phase inversion process to produce HFs with non-porous, gas-tight cores and porous outer layers ca. 50-100 μm thick; suspensions of YSZ or CGO particles were used to produce the precursor micro-tubes for electrolyte-supported structures. After sintering the HFs, Ni was deposited electrolessly onto their inner surfaces to form Ni-YSZ anodes, using aqueous nickel (II) solutions and (sodium) hypophosphite (H2PO2-) as the reducing agent. With YSZ electrolyte-supported structures, lanthanum strontium manganite (LSM)-YSZ particles were then coated onto outer surfaces of the HFs to form cathodes; these cells produced only 46-400 W m-2 at 800 oC, compared with ca. 800 W m-2 at 600 oC for CGO-supported cells. Anode-supported structures were also produced using non-conductive, porous NiO-YSZ HFs as anode precursors. YSZ particles were suspended in ethanol and electrophoretically deposited (EPD) onto the external surface of NiO-YSZ HFs, requiring electric fields of ca. 22 kV m-1 between a tubular Cu cathode, placed inside the porous HF precursor, and a tubular platinised titanium mesh anode; this implied they had an effective positive charge. The YSZ-coated NiO-YSZ fibres were then co-sintered at 1500 oC. Mixed (YSZ-LSM) and pure LSM cathode layers, for creating functional layers and enhanced current collector electrodes, were deposited using a paint brush and re-sintered at 1200 oC. The resulting anode-supported HF-MT-SOFCs delivered peak power density of 2 kW m-2 at 800 oC. Collaborators then used a triple orifice spinneret in the phase inversion process to co-extrude CGO/NiO-CGO dual layer-HFs, which were then co-sintered. Dispersions of CGO-LSCF particles were then painted or sprayed onto their outer surfaces, as "graded" LSCF-CGO porous cathode precursors that were then sintered at 1200 oC. HF-MT-SOFC fabrication was completed by winding a silver wire current collector spirally round the cathode. Similar arrangements were used for collecting the current from the HF lumen (anode). The use of functional cathode layers, higher porosity anodes, improved anode and cathode current collectors, and optimizing the thickness of the electrolyte layer and operating parameters, enabled maximum power densities of ca. 25 kW m-2 at ca. 600 oC, believed to be a record for a single MT-SOFC. The effects of electrolyte thickness (100-10 μm), cell length (10-50 mm), and anode morphologies / porosities were also determined. HF-MT-SOFCs were found to be stable to reduction/oxidation and thermal cycling for up to 8 days. Finally, a novel design for stacking individual HF-MT-SOFC in series (voltage scale up) and parallel (current scale up) was studied experimentally; 3 HF-MT-SOFCs in parallel delivered ca. 0.67 W (=3.4 kW m-2) at 7.5 kA m-2, 0.45 V and 600 oC.
47
Wu, Zhentao. "Dual-layer functional ceramic hollow fibre membranes for partial oxidation of methane". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9858.
Testo completoAbstract (sommario):
Due to the unique mechanism of oxygen permeation through dense ceramic membranes with the mixed ionic-electronic conducting property, these membranes have been widely studied for oxygen separation. It has been several decades since the use of a dense ceramic membrane reactor for methane conversion was proposed. One of the major reasons for persistent worldwide research efforts to develop such dense ceramic membrane reactors is the advantages that result from combining oxygen separation and catalytic reactions within a single unit. Besides the significant progress that has been made to date, more and more effort has been directed towards the development of more stable membrane materials with higher oxygen permeation, more advanced membrane micro-structures, membrane configurations with higher surface area per unit volume and better membrane reactor designs. By improving the aforementioned membrane and membrane reactor properties, lower operating temperatures, longer life time and reduced costs can be achieved. The evolution of membrane reactor designs has progressed through a number of stages, from an initial disk-type design to flat-sheet stack or tubular designs with higher surface areas. It is not until very recently that ceramic hollow fibre membrane with further increased surface area/volume ratios of up to 3000 m2/m3 has been developed. Although there has been a consistent progress in improving membrane configurations, the way that catalyst is employed in a membrane reactor is still based on packing catalyst particles on the membrane or inside the reactor. This occupies a considerable amount of space and as a consequence the actual surface area/volume ratio of a membrane reactor design is significantly lower than that of the membrane itself. In order to develop a highly compact membrane reactor design for partial oxidation of methane (POM) with the maximum possible surface area/volume ratio, this thesis focuses on the development of a functional ceramic hollow fibre membrane with a novel dual-layer structure. The outer layer is designed for oxygen separation while the inner layer can be considered as a catalytic substrate layer. Such dual-layer ceramic hollow fibre membranes can be fabricated by a novel single-step co-extrusion and co-sintering process. This new membrane fabrication process allows for the simultaneous formation of the dual-layer membrane structure with excellent adhesion between the two layers even at high operating temperatures. Moreover, as well as changes in the compositions of the membrane material, aspects of the membrane structure, such as the thickness of the outer oxygen separation layer, can be adjusted during the co-extrusion process, in order to achieve higher oxygen permeation and subsequently better reactor performance. Although the functional dual-layer ceramic hollow fibre membranes discussed in this thesis are designed for POM, there are generic advantages of such membrane structures and the membrane fabrication process. Therefore, membranes of this type can be transferred to other membrane processes of great importance, such as oxygen separation and solid oxide fuel cells (SOFC).
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Othman, Nur Hidayati Binti. "Micro-structured functional catalytic ceramic hollow fibre membrane reactor for methane conversion". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/28679.
Testo completoAbstract (sommario):
The most significant issue associated with the oxidative methane conversion processes is the use of pure oxygen, which is extremely expensive. By using a dense oxygen permeable membrane reactor, a possible decrease in the air separation cost can be expected due to the elimination of oxygen plants. Besides, higher reaction yields can be attained due to the selective dosing of oxygen into the reaction zone. This thesis focuses on the development and potential application of functional micro-structured catalytic ceramic hollow fibre membrane reactor (CHFMR) in oxidative methane conversion to syngas (known as partial oxidation of methane (POM)) and to ethane and ethylene (known as oxidative coupling of methane (OCM)). As the membrane reactor performance is crucially dependant on the oxygen permeation rate and good contact between oxygen and methane, two types of membrane reactor designs were proposed in this study. The first design involves the development of CHFMR that consists of two layers i.e.: an outer oxygen separation layer and an inner catalytic substrate layer, known as dual-layer catalytic hollow fibre membrane reactor (DL-CHFMR). The DL-CHFMR was fabricated via a novel single-step co-extrusion and co-sintering technique, in which the thickness and the composition of each functional layer can be controlled in order to improve reactor performance. The second design involves the development of CHFMR with an outer dense separation layer integrated with conical-shaped microchannels open at the inner surface, created via a viscous fingering induced phase inversion technique. Besides substantially reducing resistance across the membrane, the microchannels can also act as a structured substrate where catalyst can be deposited for the catalytic reaction to take place, forming a catalytic hollow fibre membrane microreactor (CHFMMR). Although the CHFMRs discussed in this study are designed particularly for POM and OCM, there are general advantages of such membrane structures and reactor designs for improving the overall reaction performance. Therefore, these reactor designs can be transferred to other important catalytic reactions.
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Zaidiza, David Ricardo Albarracin. "Modelling of Hollow Fibre Membrane Contactors : Application to Post-combustion Carbon Dioxide Capture". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0035/document.
Testo completoAbstract (sommario):
La capture du dioxyde de carbone (CO2) en postcombustion est une stratégie importante pour la limitation de l’effet de serre. Le procédé de référence est l’absorption du CO2 dans des solutions aqueuses aminées, suivie par une étape de stripage du solvant. La technologie mature associée à ce procédé est la colonne à garnissage. Toutefois, afin de rendre le procédé plus attractif, il convient de l’intensifier en réduisant le volume des équipements et le coût énergétique associé. Les contacteurs membranaires à fibres creuses (CMFC) constituent une alternative aux colonnes à garnissage. Les CMFC permettent de développer d’importantes aires spécifiques conduisant potentiellement à une intensification des transferts gaz-liquide. Ainsi, l’utilisation des CMFC réduirait la taille des installations, mais aussi diminuerait la consommation énergétique par la diminution de la quantité de vapeur de stripage. Cependant, l’utilisation de CMFC dans les étapes d’absorption et de stripage dans des conditions industrielles a été peu étudiée. Afin de combler cette lacune, des modèles à différents niveaux de complexité : monodimensionnel, bidimensionnel, isotherme et adiabatique ont été développés, comparés et validés. Ceci afin d’identifier le niveau de complexité approprié. Les résultats de simulation ont mis en évidence le potentiel d’intensification des CMFC dans l’étape d’absorption et aussi de stripage, se traduisant par une réduction en volume de 4 à 10 fois par rapport aux colonnes à garnissage. Néanmoins, les CMFC peuvent difficilement réduire le coût énergétique du procédé étant donné que l’étape de stripage fonctionne dans des conditions très proches de la limite thermodynamiquePost-combustion CO2 capture (PCC) is an important strategy in mitigating greenhouse effect. The reference process in PCC is the CO2 absorption into amine aqueous solutions, followed by the regeneration (or stripping) of the solvent. The robustness of packed columns makes it the standard technology for both absorption and stripping steps. However, the treatment of large quantities of flue gases requires itself equipment of a large size. Hollow fibre membrane contactors (HFMC) are considered as one of the most promising strategies for intensified CO2 absorption process, due to their significantly higher interfacial area than that of packed columns, allowing to reduce the equipment size. In addition, this would reduce the energy penalty of the process by reducing the required amount of stripping steam. However, despite the potential advantages of HFMC, very few investigations have studied implementing this technology for PCC within an industrial framework. To fill this lack, the performances of both absorption and stripping steps using HFMC under industrial conditions were estimated by modelling and simulation. To identify the optimal modelling strategy, transfer models with different levels of complexity were developed ranging from one-dimensional isothermal single-component to two-dimensional adiabatic multi-component. Simulation results of both absorption and stripping steps revealed that, compared to traditional packed columns, contactor volume reduction factors comprised between 4 and 10 might be achieved using HFMC. However, since the stripping operating conditions are very close to thermodynamic equilibrium, HFMC can hardly reduce the energy consumption of the process
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Moghareh, Abed Mohammad Reza. "Poly(vinylidene fluoride) (PVDF) based hydrophilic hollow fibre membranes : prospects for wastewater treatment". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9830.
Testo completoAbstract (sommario):
The growing need for suitable water resources has attracted attention to new water and wastewater treatment processes, such as membrane filtration. Due to the excellent properties of poly(vinylidene fluoride) (PVDF) polymer and membranes, such as excellent chemical and thermal resistance along with great mechanical strength, the PVDF membrane is a suitable candidate for the water and wastewater industry. As a result, there have been many attempts to improve the performance of PVDF membranes, particularly in terms of water flux and fouling resistance, in order to increase the membrane’s lifespan and reduce operating costs. This thesis explores such PVDF membrane performance improvements through hydrophilic modification of the bulk membrane. In this study, the recently developed process of atom transfer radical polymerisation (ATRP) was used to graft hydrophilic chains of poly(ethylene glycol) methyl ether methacrylate (POEM) onto the backbone of the PVDF polymer to synthesise an amphiphilic copolymer (PVDF-g-POEM). A new, environmentally-friendly and cost-effective method was introduced to purify the synthesised amphiphilic copolymer by using water instead of volatile solvents. The amphiphilic copolymer was used as a blend in the spinning dope and the effect of blending this amphiphilic copolymer on the prepared hollow fibres was studied in detail. A wide range of hydrophilic PVDF based hollow fibres was achieved by changing the spinning parameters and dope compositions. Moreover, nano-sized γ-Al2O3 particles were used as an additive to improve PVDF flat sheet membranes. By using alumina particles, the filtration performance, surface hydrophilicity and fouling resistance of membranes improved significantly. In addition, by using triethyl phosphate (TEP) as the solvent, PVDF hollow fibre membranes with interconnected pore structures were produced via a single step immersion precipitation technique. The resultant PVDF hollow fibre membranes displayed excellent mechanical properties because of their macro-void free structures. Polyethylene glycol (PEG) was used as an additive to improve the water flux of the produced membranes and PVDF hollow-fibre membranes suitable for water and wastewater treatments in the range of ultrafiltration were obtained.