• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 3
  • 1
  • 1
  • 1
  • Tagged with
  • 388
  • 36
  • 29
  • 26
  • 22
  • 10
  • 10
  • 9
  • 9
  • 8
  • 7
  • 6
  • 5
  • 5
  • 5
  • 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.
1

Seasonal aspects relating to the use of macroalgae as a biofuel

Redden, Hilary Louise January 2013 (has links)
To assess their suitability as a biofuel feedstock, principally for methane production from anaerobic digestion, this thesis investigates seasonal changes in biochemical composition of nine UK macroalgae; Ascophyllum nodosum, Fucus serratus, F. vesiculosis, Laminaria digitata, L. hyperborea, Mastocarpus stellatus, Palmaria palmata, Porphyra umbilicalis and Ulva lactuca. These represent three major phyla; Chlorophyta, Ochrophyta and Rhodophyta. This is the first analysis of seasonal biochemical changes in lypholized mass, fatty acid methyl esters (FAME), protein, soluble saccharides and anaerobic digestibility for the majority of the species listed. Biomass was sampled monthly over two years. Methods for analysing large sample sets were developed which reduced chemical usage and waste production. Statistical analysis was by ANOVA and the post-hoc Tukey method. There were differences (P<0.01) between species and overall mean lypholized weight ranged from 28.5 to 14.4 % and recovered FAME 3.32 to 0.70 %, protein 22.0 to 13.4 % and soluble saccharides 44.2 to 1.2 %. Within species, there were significant effects of year, season and month of collection. For anaerobic digestion, methane gas production varied between -1 species from 1.00 to 0.02 L g (P<0.01) and the percentage methane from 40.8 to 24.9 % (P<0.01). Macroalgae collected in winter and spring produced higher percentage methane (P < 0.05). Regression with subsets and principal component analysis of lypholized mass, fatty acid methyl esters (FAME), protein, soluble saccharides did not provide robust predictive models and other additional factors must influence methane gas production. Buffering was not required and stable anaerobic digestion was achieved in saline conditions of 35 ‰ with a pH of 7.0 to 7.6. Fucus serratus and F. vesiculosis suppressed the activity of the methanogenic biota compared to the control and the biochemical mechanisms employed by these species to achieve this merit further investigation. Laminaria digitata, L. hyperborea, Palmaria palmata and Porphyra umbilicalis show potential to be used as biofuel and large-scale biomass trials are recommended.
2

A knowledge-based system for low-grade waste heat recovery in the process industries

Law, Richard January 2014 (has links)
The ever-increasing price of energy, combined with increasingly stringent legislation to reduce greenhouse gas emissions, is driving the UK process industries toward increasing energy efficiency. Significant gains can be made in this sector, as up to 11.4TWh per annum (4% of total energy use) of the UK process industries’ energy consumption is lost as recoverable waste heat. Substantial recovery of this waste heat would have economic benefits of the order of £100s of million/year, and environmental benefits of the order of 100s of thousands of tonnes of carbon dioxide equivalent per year. This thesis describes the development of a knowledge-based system for the selection and preliminary design of equipment for low-grade waste heat recovery in the process industries. The system addresses two of the key barriers to low-grade waste heat recovery in the UK. Firstly, it provides a readily accessible and zero cost tool to replace expensive, time-consuming expert consultancy in the initial stages of waste heat recovery projects, and, secondly, it educates users regarding the range and benefits of novel waste heat recovery technologies. The system requires an input of easy-to-access data from the user. Based on this data, it then selects the most appropriate technologies for waste heat recovery for the case study in question from a database including various types of heat exchanger, vapour compression heat pumps, mechanical vapour recompression and organic Rankine cycles. It also generates a preliminary design including equipment size, efficiency/effectiveness, capital cost, cost savings, payback time and potential reductions in carbon emissions. This provides sufficient information to allow the user to make an educated decision regarding whether or not waste heat recovery is suitable for their needs. The knowledge-base of the system was built using a decision tree method that has been proven to be successful in the building of decision making tools for various engineering applications. The software is programmed using the Java language which allows widespread free dissemination to computers running all common operating systems. The system was tested using case studies based on data from both existing publications and collaborating companies. The results were validated against published results, common modelling software results and the views of expert consultants. Broadly, in terms of equipment specification and cost, the knowledge-based system produced the same results as the other methods. Furthermore, the preliminary designs generated were generally within 5% of the final figures from the other sources. In certain cases, the knowledge-based system suggested alternative technologies that were more viable (economically and/or practically) than those considered by the authors of published case studies. In all cases, system operating time (data input, and processing of results) was of the order of minutes, whereas studies by consultants or the use of existing modelling packages would be significantly more time-consuming (of the order of hours or days). Hence, the system can be used as a rapid optioneering tool for investigation of waste heat recovery technologies, requiring substantially less time than current available methods.
3

A systematic approach to biomass and energy crop streams for co-firing

Altawell, Najib January 2009 (has links)
No description available.
4

PAH Emissions from diesel engines with PAH-free fuels including biofuels

Lea-Langton, Amanda Rachel January 2009 (has links)
No description available.
5

Upward flame spread on vertical surfaces

Tsai, Kuang-Chung January 2001 (has links)
Previous studies have demonstrated upward flame spread on vertical surfaces to be one of the most serious fire scenarios due to the concurrent direction of flame propagation and air flow. The unburned zone of the wall ahead of the pyrolysis zone consequently receives more heat from the flame, causing the temperature of the unburned wall to rise quickly and the flame to spread more rapidly. In order to prevent the occurrence of hazardous wall fires, there is a need to select materials which satisfy performance-based regulations. This approach needs information from reliable fire models which simulate accurately the fire behaviour of materials in their end-use configuration. However, none of the existing models are used in this way. This is because of the limitations of the models themselves, in particular the assumptions involved and uncertainties in the empirical correlations used in the models. This study focuses on the early stages of the upward flame spread. An existing model which uses data directly from the Cone Calorimeter test was examined. A non-standard test procedure was developed which gives results capable of giving better predictions from the model. The flame height and heat feedback to the unburned wall were also examined and more information obtained. The flame height was measured from steady burning vertical fuels and from a gas-fuelled panel to examine the commonly accepted relation that the flame height is proportional to the 2/3 rds power of the heat release rate per unit width of the wall fire <i>Q’. </i>In the former experiment, the flame height and <i>Q’ </i>were measured directly in the same experiments, providing data for the early stages of fire spread. In addition, the effect of different geometric configurations was examined. The latter experiment revealed a width effect, questioning the validity of <i>Q’  </i>being the only parameter determining the flame height. Experiments were also carried out to measure the heat transfer to the unburnt material above the pyrolysing zone. A lower value was found to be more representative than the ones used previously. With these modifications, the model was found to give good agreement with experimental measurements of vertical spread on sheets of PMMA. Two additional cases were studied: wall fires influenced by an inert parallel wall and by the proximity of a corner. The measurement of flame height and heat feedback provides data for further investigation and modelling work.
6

Examination of some liquid products derived from cannel coal

Stadnikiewicz, B. T. January 1952 (has links)
No description available.
7

The factors governing stability and combustion intensity in "mechanically" atomised oil flames

Brown, Allan Mellows January 1964 (has links)
Problems of combustion instability and the need for wider range in firing rates have drawn attention to the need for more fundamental knowledge of the performance and the characteristics of pressure-jet atomized oil flames. A secondary problem is the complication and inconvenience of measurements on full scale equipment. In the present study various operational conditions for a typical modern burner with a pressure-jet atomizer and a swirled air supply were investigated. The variables chosen were fuel rate and spray angle. Data obtained consisted of gas composition, velocity and temperature measurements. The development of a laboratory unit was considered desirable to provide a means of facilitating measurements on flames of this type and a rig was constructed which consisted of a suitable combustion box and 3/10ths scale burner. It was shown that the matching of the spray angle to the air register aerodynamics affected the flame characteristics very markedly, Regions of high unburnt fuel occurred due to fuel penetration and poor mixing outside and downstream of the main part of the flame. The effect of widening the spray angle which usually occurs with wide range types of pressure-jet atomizers at the lower fuel rates was shown to be particularly unsatisfactory, and to effect the black smoke limit. The general course of mixing and the progress of combustion through the flame was deduced from calculation from the gas composition results. The distribution and effects of recirculation were shown from the velocity measurements. These were related to data for simple jets. In particular, it was deduced that internal recirculation in the core was largely responsible for flame stabilization. Theoretically derived scaling criteria were investigated by comparing full scale and model results. These showed that reasonable comparisons were possible between the two, with flames scaled either on the basis of similarity in velocity and relative momentum between spray and air, or on similarity in residence times in the flame. The former was thought probably to be better, Cold flow measurements were made, and showed differences in the size of the central recirculation core between hot and cold but not in the peak velocity to peak velocity diameter early in the flame. Combustion oscillation measurements on a marine boiler produced data which suggested strongly that these were of the "non-acoustic" type. None of the theories so far suggested appear to - ii - account with much accuracy for the observed data. In the course of experimental work various special Instruments for flow measurement were developed. It was concluded that the choice of spray distribution to suit a particular aerodynamic pattern was vital to the optimum performance of the burner. In all the cases investigated this was found to be to some extent imperfect. It is considered that decided improvements could be made to the air distribution in burners of this type. The following possibilities are suggested solutions, the use of a higher degree of swirl and a confining quarl, upstream air injection or the use of multiple oil nozzles and by avoiding devices where the spray angle varies widely over the operating range.
8

An appraisement of wood pyrolysis in a liquid medium

Morbitzer, Zbigniew January 1956 (has links)
No description available.
9

The effect of local confinement on the ignition of flammable vapour/air mixture at a hot surface

Duarte, Dayse Cavalcanti de Lemos January 1994 (has links)
Although ignition by hot surfaces has received some attention in the past, most of the data refer to flat surfaces and hot wires. The effect of 'local confinement' around the ignition source on the ignition process has not been extensively studied. The investigations of two well known accidents, the Tunnel Summit fire and the Piper Alpha disaster, showed that more data and knowledge about the ignition mechanism by heated surfaces are needed. In both cases, ignition at hot surfaces of complex geometry was identified as a possible cause of the fire, but the temperature was much lower than 900<SUP>o</SUP>C, the temperature considered necessary for ignition of a vapour/air mixture at a hot surface. There have been a number of studies of ignition by hot surfaces, in which the ignition sources were hot spheres, wires and strips. In all these studies the ignition sources were unconfined. However, it is important to understand the influence of the 'local confinement' around the ignition source on the ignition mechanism. The work described in this thesis is confined to the ignition of a flammable vapour/air mixture at a hot surface. The objective of the experimental work was to generate new data which could be used to help understand the effect of 'local confinement' on the ignition of flammable mixture at a hot surface. Electrically heated nichrome strips were used as the ignition source, and measurements were made of the effect of 'local confinement' on the minimum temperature required to cause ignition of a 3% propane/air mixture. It was found that the ignition temperature decreased as the depth of the confinement was increased. The results obtained were analysed using the thermal theory of Frank-Kamenetskii.
10

Joint PP and PS wave analysis for lithology and fluid prediction

Zhang, Jinghua January 2007 (has links)
In recent years, multicomponent seismology has gained wide acceptance in the oil industry as a useful tool for improving both seismic imaging and reservoir characterization. However, the anticipated breakthrough of multicomponent seismic into a mainstream technology is still to be realized. One of the bottlenecks lies in the interpretation and analysis of multicomponent seismic data: there is a still lack of understanding on how to link the multicomponent seismic information to rock properties directly. In this thesis, I intend to tackle this problem through a joint inversion of multicomponent PP and PS-seismic data in order to facilitate direct comparison of seismic information with rock properties.

Page generated in 0.0527 seconds