• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • No language data
  • Tagged with
  • 61
  • 61
  • 61
  • 61
  • 61
  • 11
  • 11
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 2
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Coupling of a solid oxide fuel cell with a vapour absorption refrigeration system for refrigerated truck application

Venkataraman, Vikrant January 2017 (has links)
This PhD thesis presents a modelling and simulation approach for coupling a Solid Oxide Fuel Cell (SOFC) with a Vapour Absorption Refrigeration System (VARS) specifically for refrigerated trucks. Zero dimensional models were developed for the SOFC and VARS and detailed 1D and 3D models were developed for various components of the system. A major challenge in this work was the thermal coupling of two systems working at entirely different temperature levels. The SOFC operates between 700 oC and 800 oC and the VARS between 150 oC and 200 oC. These two systems were successfully coupled to one another using two methods- indirect coupling, using a thermal coupling fluid and direct coupling, using heat pipes. The concept of using heat pipes has been explored for the first time in a desorber and hence that presents the biggest novelty of this work. Design and modelling of all the components in the VARS is a major project in itself hence in this thesis only the desorber of the VARS was designed and modelled. Two different compact desorbers designs were explored. The first one being a plate heat exchanger desorber and the second one a heat pipe integrated desorber. This work is the first one on the combined use of SOFC and VARS for a mobile application. Such a system, if developed, could also have wider implications in areas besides refrigerated transport.
12

The aggregation of iron oxide nanoparticles in magnetic fields

Bradford, Peter January 2012 (has links)
The application of a magnetic field to a suspension of weakly magnetic nanoparticles should, based on previous work and theory, increase the aggregation between particles. This is due to the increase in the magnetic interaction in competition with repulsive forces due to the electric double layer. This hypothesis was tested using suspensions of magnetite and hematite nanoparticles. Magnetite particles were used to characterise the aggregation behaviour of strongly magnetic particles, which then served as a basis of comparison with hematite particles in a magnetic field. The expectation was that applying the magnetic field to the suspensions of weakly magnetic hematite particles would alter their aggregation behaviour to be more like that of the strongly magnetic magnetite particles. Experimental findings indicate this is not the case. No evidence was found indicating that the magnetic field altered particle interactions sufficiently to alter the aggregation. Aggregation behaviour was controlled by the chemical environment and shear forces. The magnetic field did influence the motion of the particles. In static experiments hematite particles were separated from suspension, the efficiency of which was related to the degree of aggregation and thus particle size. In stirred systems the balance between shear and Lorentz forces affected aggregate formation. As observed in previous work, small aggregation increases are possible but once aggregates reach a certain size the magnetic field affects the movement of particles and does not change interactions.
13

Surface pasteurisation of food packages by the inversion method

Challou, Floritsa January 2016 (has links)
Thermal processing is the most widely used and well established preservation method used in the food industry for ensuring food safety and extending the shelf life of food products. Besides from the food product, the package needs also to be decontaminated to achieve the required safety goals. This research is concerned with surface pasteurisation treatments in food packages by the method of inversion, primarily for hot-filled food products. Starch solutions and tomato soup, used as model fluids in the current work, were hot-filled in glass jars, were sealed and then inverted for thirty seconds at a filling temperature of 80oC for achieving a target process equivalent of 5 min at 70oC; the inversion step was used as a thermal treatment of the headspace and the lid. The inverted jars showed significantly higher process values for the headspace and the lid with the filling temperature being the most important parameter. The effectiveness of the inversion step during hot-fill treatments was quantified by the use of two monitoring techniques, the traditional temperature sensors and the alternative, enzymic based (Bacillus amyloliquefaciens α-amylase) Time Temperature Integrators (TTIs). TTIs are small devices with kinetics similar to the microorganisms, whose level of degradation is measured at the end of the thermal process. The enzyme activity obtained is integrated and the temperature history can be quantified. TTIs were tested for their reliability and accuracy under isothermal and non-isothermal conditions, and were then used for validating the hot-fill process.
14

Ageing and crystallisation of polycaprolactone

Phillipson, Kate January 2016 (has links)
Partially crystalline polycaprolactone stored at different temperatures well above the glass transition temperature is found to age with the development of further crystallinity and an increase in melting point, yield stress and elastic modulus with time. The changes in mechanical properties are accounted for by the increased crystallinity, and the increase in melting point to an increase in lamellae thickness. Over the temperature range studied, the rate of ageing increase with temperature and the dependence of stem length on the square root of storage time observed are both consistent with diffusion control and inconsistent with nucleation control. It is concluded that partially crystalline polycaprolactone ages by a continuation of the crystallisation at a rate determined by the storage temperature and by the mechanism occurring prior to ageing.
15

Utilisation of coal fly ash in the manufacture of useful materials

Sommerville, Roberto Peter Zygmunt January 2017 (has links)
Disposal of CFA is a problem of increasing concern, due to the environmental impact of CFA. Beneficiation processes such as the RockTron process are capable of producing various value-added products, and the Delta product is apt for use in the synthesis of zeolites. The current study explores hydrothermal Si extraction, fusion assisted extraction and a novel microwave fusion process with a performance comparable to the fusion process. The extraction process was optimised for the Delta ash, and compared to other ashes and rice husk ash. In the optimisation of the crystallisation process, the influence of sodium aluminate addition on the properties of zeolites was examined. The effects of alkalinity, sodium source and salt concentration were investigated using XRD, SEM, AAS, CEC and PSD. A concurrent decrease in Si and Al in the crystallisation solution was observed as amorphous material was consumed. This crystal growth phase occurs earlier with higher concentrations of sodium aluminate and NaCl. Addition of NaCl can improve crystallinity, yield and CEC and decrease particle size. Optimised results demonstrated good repeatability. The best estimated yield was 264 g/kg FA, with a CEC of 4.8 meq/g. Buoyant zeolites were synthesised through seeding of the crystallisation process with cenospheres. The products consisted of 77% cenospheres and 23% zeolite.
16

The effects of various porphyrin species on the decomposition and hyerogenation of hydrocarbons

Carnell, Ian Daryl January 1990 (has links)
A tubular reactor was designed and constructed in order that the decomposition of hydrocarbon gases and vapours could be studied. Product distributions and kinetic data obtained from the cracking of n-butane agreed with the values available in the literature. Prom these results a reaction mechanism for the thermal decomposition of n-butane was proposed. The cracking of 2,2-dimethylbutane was investigated and a reaction mechanism postulated following the acquisition of product spectra and the calculation of kinetic data. This mechanism differed from others found in the literature. Base etioporphyrin was synthesised by two unrelated routes. A concentrate containing approximately two per cent petroporphyrins was isolated from Tia Juana Pesado topped crude. After demonstrating that porphyrins are thermally stable up to a temperature of 5^0 G the effects of nine different porphyrin species towards the cracking of 2,2-dimethylbutane were examined. All nine were shown to act as cracking catalysts. Following consideration of the product distributions and kinetic data obtained from the study of porphyrin catalysis a reaction mechanism has been proposed. This is based on increasing the rate of homolytic bond cleavage. Porphyrins were shown to catalyse the decomposition of 1-hexene over the temperature range 325 to 450°C. At a temperature of 150°C three porphyrins catalysed the hydrogenation of 1-hexene.
17

Adsorptive recovery of nanoparticulate protein products : physical and biochemical characterisation of candidate solid phases

Williams, Sharon Louise January 2002 (has links)
Adsorbent solid phases having suitable designs applicable to the generic recovery of nanoparticulate products have been demonstrated. Practical recovery of nanoparticulate mimics, of products such as plasmid DNA and viruses, as putative gene therapy vectors from both single component model systems and complex feedstocks has been studied. The adsorbents employed in the study had one of four discrete designs (Type I-IV), including (I) microporous (pore size 0.02um- 0.2um), (II) macroporous (pore size > 0.6um), (III) solid (non-porous) and (IV) pellicular (pore size 0.2nm-0.4um). Commercially available adsorbents (STREAMLINE, Amersham Biosciences; Toyopearl HW-40, Tosohaas; POROS SOD, Applied Biosystems) and custom designed adsorbents (PVA composites supplied by Igor Galaev, Lund University; Celbead adsorbents supplied by Arvind Lali, Mumbai University; 2% ZsA and perfluorocarbon emulsions developed at the University of Birmingham) were included in the study. Insect cell culture lysate was employed as an industrially relevant feedstock and experiments were completed exploiting representative nanoparticulate production systems. The adsorptive capacity and desorption efficiency of both nanoparticulate products and cellular component were strongly influenced by the physical design and geometry of the adsorbent solid phases together with the concentrations of interacting chemical ligands available for adsorption. Microporous adsorbents (as defined above) developed for the purification of macromolecular products appeared to be less suited for the recovery of nanoparticulate products from complex feedstocks than macroporous or pellicular adsorbents.
18

The development of radioactive gas imaging for the study of chemical flow processes

Bell, Sarah Dawn January 2016 (has links)
The development and use of functional medical imaging has grown rapidly in importance over the last few decades. The field of medicine primarily uses nuclear imaging techniques for the non-invasive study of physiological processes within the human body. At the University of Birmingham a considerable research effort has been made into adapting these techniques for the study of flow and mixing in solid and liquid systems. However, despite capability, little work has been reported on imaging gases for industrial use. The emission tomography techniques available at Birmingham were adapted and utilised for the study of gaseous flow processes. The work presented in this thesis provides details of the development of a radioactive gas imaging technique capable of studying chemical flow processes. Feasibility studies were performed to compare the capabilities of Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) for imaging dynamic gas flows in a gas fluidised bed, a bubble column and a low pressure adsorption column leading to a more detailed study of CO\(_2\) adsorption at high pressure using PET. In order to verify the technique a comparison between breakthrough data obtained using a CO\(_2\) analyser and the PET image data was made and a qualitative study of the adsorption kinetics inside the column is provided.
19

Lithium amide halides for hydrogen storage

Davies, Rosalind January 2016 (has links)
The lithium amide halides are a promising series of materials for hydrogen storage as they release hydrogen at a lower temperature than lithium amide on reaction with lithium hydride. The amide chloride system has been studied in detail, and two phases with reduced chloride content, Li\(_7\)(NH\(_2\))\(_6\)Cl and Li\(_6\)Mg\(_1\)\(_/\)\(_2\)(NH\(_2\))\(_6\)Cl, have been identified by powder X-ray diffraction and Raman spectroscopy. Both were seen to release hydrogen on reaction with LiH at a lower temperature than lithium amide, and ammonia release was suppressed. Rehydrogenation of the imide products of reaction of both new phases occurred more readily under the conditions used than for the known phase Li\(_4\)(NH\(_2\))\(_3\)Cl. The hydrogen cycling properties of Li\(_7\)(NH\(_2\))\(_6\)Cl were investigated alongside Li\(_7\)(NH\(_2\))\(_6\)Br and Li\(_3\)(NH\(_2\))\(_2\)I. The systems successfully cycled hydrogen, and the reversible structural changes that happened during cycling were studied. All three materials, however, showed a capacity loss on cycling under dynamic vacuum. The conductivity of the amide and imide halides was studied using A.C. impedance and found to be higher than for LiNH\(_2\) and Li\(_2\)NH, respectively. This supports kinetic analyses that indicate ion diffusion is not rate-limiting for the hydrogen cycling of these systems.
20

High temperature processing of kaolinitic materials

Thomas, Rachel Elizabeth January 2010 (has links)
Calcination, is the process of heating a substance, to a temperature below its fusing point, with a resultant loss of water. It is one of the most important techniques currently used to enhance the properties, and therefore value, of kaolin. The overall aim of this project was to provide a better understanding of the principles of the kaolin calcination reaction in order to enhance the efficiency, quality and sustainability of the Imerys calcining operations. This research has shown a strong correlation between the chemistry of kaolin and the colour of the calcined product. This is due to the influence of contaminant materials on the colour of the hydrous kaolin, which in turn affects the calcined material. The strongest colour influencing factor is the presence of iron, particularly if it is present on the surface of the kaolin. Surface iron is currently reduced using a reductive bleaching process. This has an improving influence on even the most contaminated kaolins, however there can be quite a lot of interbatch variability. Despite its effect on colour the chemistry of kaolin has little influence on post calcination reactivity. Reactivity is due to physical factors such as particle and agglomerate size and the penetration of heat into the material. Any kaolin will calcine to produce a low reactivity product; provided the heat is able to penetrate into the bed and that the material is able to remain at temperature for sufficient time for the calcination reaction to occur. Another outcome of the research was the discovery that a higher temperature and shorter time period has little on the end calcined product but has implications for lower energy usage.

Page generated in 0.0741 seconds