Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)

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https://dspace.lib.cranfield.ac.uk/handle/1826/17865

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Open Access
Characterisation of dwelling electricity demand with reference to DCHP
(2002-04) Geslot, Olivier; Newborough, Marcus
The research relates to the introduction of dwelling micro combined heat and power to the domestic sector as a mean of improving the efficiency with which primary energy is used, and the economic efficiency of supplying electricity via the national grid. Such small generators may constitute Stirling engine or solid polymer fuel cells. This research is orientated towards the electrical demand side issues. The context is to maximise the feasibility of such technologies when the typical domestic consumer's heat demand varies significantly with season and the associated electrical power varies substantially every minute of the day. The main issue was to ensure that the system could effectively and economically satisfy a considerable proportion of the electricity demand the typical demand profile is very peaky by virtue of the way inhabitants behave at home and the design of domestic appliances. To derive the characteristic of dwelling electricity demand, a total of 45 dwellings were sampled, monitored and classified, in order to analyse the parameters influencing the shape, magnitude and duration of the profile data collected. A survey was issued to . complete the research regarding appliances time of use. Then a model was designed with an interface allowing dynamism. The research concluded there are attractive reasons for micro combined heat and power to be implemented in dwelling. It could save up to 15% of primary fuel. On an annual basis, and with the 15 dwelling data provided by British Gas, the average saving for a constant lkWe DCHP is determined to be £44.78, and the saving is increased to £124.61 for a system that would allows a tumdown from lkWe DCHP during winter to 500We DCHP during summer. Furthermore utility companies should be gaining from this introduction because peak power demand reduction on the grid should reduce costs.
Open Access
Design of a decision support system for combined cycle schemes
(1998-01) Gayraud, S.; Singh, R.
The growing desire for sponsors of power generation projects to share risk with the lenders has promoted the use of computational tools, simulating and evaluating from a techno-economic viewpoint long-term, high-risk projects. Such models need to include reliable engine diagnostics, life cycle costing and risk analysis technique. This work consisted in designing a Decision Support System (DSS) for the assessment of power generation projects using industrial gas turbines in combined cycle. The software, programmed in Visual Basic in Excel in a windows-frame, runs an external application named Pythia, which has been developed by the Department of Propulsion, Power; Energy and Automotive Engineering at Cranfield University. It can perform gas turbine performance simulations, including off-design conditions, with or without degradation effects providing thus reliable engine diagnostics. Steam cycle models including different heat recovery steam generator configurations have been developed to simulate steam turbine design and off-design performance. Plant performance simulation takes into account off-design conditions, part-load governing strategies and degradation effects. Besides a robust economic mode and a life cycle costing model including maintenance planning assessments offer a wide range of possible operating and economic scenarios. The degree of uncertainty relating to technical and economic factors is assessed using normal distributions, and the level of risk is then evaluated using a risk analysis, technique based upon the Monte Carlo method. The DSS provides all sorts of charts and techno-economic figures in order to support the decision making through an effective user-friendly window-oriented interface.
Open Access
Design optimisation of axial flow steam turbines
(2004-05) Eyre, C. J.; Tourlidakis, A.
This study at Cranfield University was initiated by my sponsoring company’s desire to improve its Steam Turbine design capability. In particular it was thought that emerging Computational Fluid Dynamics software might provide an alternative and improved approach to existing turbomachinery design techniques in use. My course of study has enabled me to understand the fundamentals of the numerical approaches and methods employed by the commercially available software codes. The brief was to review and if appropriate select and implement a CFD solution into Peter Brotherhood Ltd. The current range of steam turbines have power outputs ranging from 500 kW to 30 MW. These machines are primarily Rateau impulse turbines operating under a pressure compounding arrangement. More recent developments particularly on condensing machines incorporating twisted and tapered blades have led to partial reaction stages being used. Most of the machines produced today are impulse combined with partial reaction. After a review of software vendors AEA TASCflow software was purchased and was used throughout this study. This work concentrates on the technical design o f steam turbine nozzles and blading. It proposes alternative blade and nozzle geometry along with new methods of construction and manufacture. It is recognised however that in order to evaluate nozzle performance it is necessary to consider the downstream blade and thus the performance of the complete turbine stage. Throughout comparisons are made with existing fortran PITCH software described in chapter 1. A literature survey investigated many approaches and factors that can improve turbine efficiency and power output. A selection of these more applicable to the smaller power output designs of turbine produced by Peter Brotherhood Ltd have been investigated to evaluate their merits. These are outlined in chapters 2, 3 and 4. Results from these studies indicate that new complex geometry nozzles when matched to improved blading with improved flow incidence angles, correct axial spacing and casing shroud flaring can lead to stage power increases of over 15%. CFD has provided a much improved insight into the three dimensional aspects and flow phenomena. The introduction of CFD has provided a boost to the design capability and it is used regularly with confidence as a development tool within turbomachinery research.
Open Access
The development of the mathematical model of an RPV and an investigation on the use of an EKF for the identification of its aerodynamic derivatives
(1987-05) Milonidis, E.; Thomasson, P. G.
A six-degrees of freedom mathematical model of an experimental Remotely Piloted Vehicle (RPV) and the linearised longitudinal and lateral models at 30 m/sec are developed. The longitudinal and lateral dynamics are analysed and the equivalent discrete systems are used to provide baseline data for the identification of the aerodynamic derivatives of the RPV. An advanced aircraft parameter estimation method - the Extended Kalman F ilte r - is implemented for the estimation of the aerodynamic characteristics of the RPV. Conclusions are drawn about the id e n tifi- a b ility of the s tab ility and control derivatives from pitch, roll and yaw rate measurements.
Open Access
The effect of marine fouling on the corrosion of steel in the marine environment
(1990-04) Maitland, Julia R.; Robinson, M. J.
An investigation was made into the corrosion of steel immersed in seawater by electrochemical (LPR scans) and weight loss techniques. Steel samples in the form of studs or a specially designed corrosion probe were immersed in a re-circulating laboratory based flow loop inoculated with marine microorganisms. A paralled biological study into biofilm development on corroding steel was made using viable counts, scanning electron microscopy and radio-respirometric assays. The development of a biofilm on steel studs cathodically protected at -850 mV S.C.E. and -950 mV S.C.E. was studied using these three indices of biological activity. The corrosion of steel in the real marine environment and in a bacteria-free system were monitored. Results indicate that steel corrosion followed similar trends in all these investigations. Corrosion rates were initially very high, decreased, stabilised and rose slightly. Attempts to correlate results from weight losses and LPR scans were made. Biofilms on the steel surface were very similar, and not influenced by the use or level of cathodic protection nor period of exposure. Viable counts indicate higher levels of Sulphate Reducing Bacteria were present on corroding than on cathodically protected steel. The development of a biofilm could not be correlated with trends in corrosion rates.
Open Access
Flow measurement and monitoring using orifice plates
(1996-03) Papadopoulos, Christos E.; Yeung, Hoi
The orifice meter is still commonly used for natural gas measurement despite its many limitations. Considerable efforts in recent years have resulted in improved knowledge of factors such as installation effects and the value of discharge coefficient but a serious problem still remains with the measurement of differential pressure since, when line static pressures are as high as 200 bar, differential pressures of 500mbar have to be measured. Furthermore, the flow is never absolutely steady and the performance of the pressure transducers under such conditions is not yet fully understood. This thesis demonstrates the need to apply modern signal processing and analysis techniques to enhance the performance of process instrumentation systems. The use of two static pressure transducers of resonance type upstream and downstream the orifice meter, with a high frequency response, can offer the ability, by using spectral analysis and spectrum estimation methods, to extract additional information regarding the meter’s performance as well as diagnostic information about the whole process plant. It also demonstrates a method to check and, at the same time, to safeguard the flow information obtained from an orifice meter with the use of a third pressure transducer upstream of a Mitsubishi flow conditioner. Furthemore, information about the performance of the package orifice - conditioner using the discharge coefficient (Cd) and the amplitude spectrum from the three pressure transducers can be obtained.
Open Access
Heat transfer characteristics of heat pipe heat exchangers for low and medium temperature heat recovery
(1997-07) Kang, Heeyoon; Badr, Ossama
Heat pipe heat exchangers (HPHEs) offer many advantages over other types of heat exchangers for the recovery of heat from industrial gaseous waste streams in the low and medium temperature ranges. Heat pipes employed in industrial heat exchangers can be made with or without wicks. Although the thermal performances of single heat pipes and HPHEs have been extensively investigated, comparative studies concerning behaviours of HPHE with different types of heat pipes, at the same operating conditions, appear to be very limited. Such studies are useful in evaluating the significance of the parameters pertinent to thermal performance and in selecting the most appropriate HPHE for a particular application. Taking into account previous studies, the present work was focused on comparative studies between heat pipe and thermosyphon, at the same operating conditions, with following the objectives : • Further studying the heat transfer characteristics of heat pipe and thermosyphon to obtain additional information regarding thermal performance, at the same operating conditions. • Providing some guide-lines for HPHEs design which relate to the thermal performance of heat pipe and thermosyphon. To achieve these objectives, two computer models, a ‘Heat Pipe and Thermosyphon Thermal Performance Model’ and a ‘Heat Pipe Heat Exchangers Design Model’, were developed. The former model facilitates the prediction of the axial temperature distributions of the working fluid and the tube wall ; heat transport limitations; and the thermal performances of thermosyphons and heat pipes with different type of wicks. An experimental investigation of the steady-state behaviour of the thermosyphon was carried out to validate this computer model and the results were compared with the corresponding predictions of the computer model developed. According to the experimental results, Nusselt’s film theory for continuous liquid film could not be employed for predicting thermal performances in the condenser and evaporator film region of inclined thermosyphons. Liquid film could only be maintained circumferentially in vertical thermosyphon tubes, even though might not the smooth continuous film. In the evaporator pool region, the change in saturation temperature due to the hydrostatic height of the pool should be considered for predicting the axial temperature distributions. The results of the behaviours of heat pipes and thermosyphons were utilised to develop a ‘Heat Pipe Heat Exchangers Design Model’ to facilitate both the design and the prediction of performances of HPHEs. These models enable the designers of waste-heat recovery systems to choose the most appropriate type of heat-transfer elements and optimise the design parameters of a HPHE for a given application.
Open Access
A nutritional quality audit for food retailers
(1990-11) Hairsnape, Simon Phillip; Winkler, J.; Hughes, J.
There is increasing evidence that our diet is implicated in several common diseases including coronary heart disease, the single largest cause of death in Britain. The development and implementation of nutrition policies is seen as a way of modifying the diet of individuals and communities with the aim of reducing the prevalence of disease. To-date policy implementation has concentrated on health education aimed at the individual. The thesis suggests that this strategy has limited effectiveness and that health workers need to consider new strategies concerned with food availability. The thesis proposes that the food retail sector is the 'gate keeper' of the nation's food supply and that, po te ntially it could do much to promote individual and community nutrition. After analysing the various issues involved the thesis suggests that retailers are not doing as much as they could be, and what they are doing might be ineffective. It is further suggested that a major obstacle to produ ci ng strategies aimed at retailers is that no method exists for quantifying their contributions. It is proposed that a n e w research instrument is needed to enable health workers to develop such strategies and monitor their implementation. This research instrument would allow workers to undertake an objective, reliable and quantifiable method of analysing those areas that retailers are and are not using to promote nutrition. The thesis hypothesises that the ability to measure contributions might stimulate the retailer's competitive nature to do more. The thesis therefore proposes and pilots a nutritional quality audit for food retailers. The audit is not a standard research instrument and therefore requires the development of new concepts and methods for its design. The thesis concludes by suggesting how this new instrument might be further developed and used to encourage food retailers to realise their potential for promoting individual and community nutrition.
Open Access
A study of swirling flow in an orifice plate flowmeter
(1988-10) Tello-Campos, A.; Hemp, J.
This thesis presents a theoretical and experimental study of swirling flow in an orifice plate flowmeter. Firstly, a solid body rotation was considered as the inlet velocity profile of an orifice plate. The beta ratio considered was 0.4. The Reynolds number was 7.82xl04 . As a result, a theoretical value of the discharge coefficient was obtained. Secondly, Laser doppler anemometry was used to determine the axial and tangential velocity profiles at 3 upstream and 2 downstream cross-sections of an orifice plate with a beta ratio of 0.4. A double right angle bend in two perpendicular planes was placed 6.5 diameters upstream of the flowmeter. The axial velocity profile was found to be slightly asymmetrical. The corresponding tangential profile was found to have a form of a solid body rotation. A 20" mercury manometer was used to measure the pressure difference across the orifice. The results showed that the discharge coefficient decreased. Thirdly, a commercial computer program was used to calculate the swirling flow through an orifice plate. A solid body rotation was considered at the inlet of the orifice. With the pressure field calculated, the corresponding discharge coefficient was determined. An additional simulation was performed with a 1/7 power law inlet profile. The discharge coefficient under swirling flow conditions was smaller than the one under non swirling flow conditions. Based on the experimental and computational results, we can see that the swirling flow produced by a double bend greatly affects the performance of an orifice plate. It is recommended that the flowmeter must be located 70 diameters downstream of a double bend. The BS 1042 does not provide a reasonable straight length for this type of disturbance.
Open Access
Vehicle active suspension system design using strategies based on state estimation by Kalman filters
(1990-06) Shakir, A. A.; Borrie, J.
The suspension system of a ground vehicle moving on or off road can be improved by so called "active control" using control strategies which require feedback of all or some of the system states. A stochastic state estimator, or "Kalman filter", can be used to estimate these states. Various Kalman filters suited to this problem are developed, and optimal control strategies suited to these Kalman filters are specified and assessed. It turns out that there are basic problems of unobservability and uncontrollability inherent in the behaviour of such suspension systems, and original solutions to these problems are suggested and explored. A laboratory equipment is designed and constructed to reveal the behaviour of hydraulic actuators in this context, and this is used to ensure that the strategies suggested are realistic. An Intel 8086 microprocessor based circuit in which a practical Kalman filter can be realized is designed. A considerable number of computer simulations are also used to test and assess the estimation and control strategies. All these represent original work by the author.
Open Access
Wake affected boundary layer flows within an embedded stage of a multi-stage axial compressor
(2001-06) Lee, D. Y.; Elder, R. L.; Bennett, Ian
Boundary Layer Flows in turbomachines have been recognised to crucially influence the stability and performance of gas turbine components particularly the compressor since its function is to provide a pressure rise through diffusion that is accompanied by an adverse pressure gradient. This brings about the danger of separation of flow and thus understanding the behaviour and control of the boundary layer is of great importance. The interaction between stationary and rotating blade rows inevitably make the flow environment within a multi-stage axial compressor unsteady. Dean (1959). Stator blades are subjected to periodic wakes from upstream rotor rows, which initiate transition that is very much unlike those encountered in a steady state (clean) flow conditions. This thesis describes the third stage of the fundamental research on boundary layer flows in turbomachinery at Cranfield University. The feature that makes this experimental work unique is that with constant temperature hot-wire anemometry (CTA) as the principal tool, detailed boundary layer surveys have been carried out within real turbomachinery environment of Cranfield University’s world renowned four-stage low-speed research compressor facility (LSRC). This is a considerable step from the flat plate and wind tunnel arrangement employed in the previous stages of this research programme. Two-dimensional flow field measurements taken downstream of an embedded rotor stage complement the boundary layer survey experiment to contribute toward a better understanding of the unsteady wake affected boundary layer flows that occur in turbomachinery. The current study was conducted with particular reference to a low speed 3 D end bend controlled diffusion blade design. X-array hot-wire measurements of the unsteady flow field have captured the strong wake features exhibiting periodic variations in thickness, which indicates blade loss fluctuations. This is more prominent at Near Stall conditions. Strong variations are present in the end-wall regions where comer stall and comer vortex and tip clearance flows dominate. Radial migration of flow deviation was also detected with each passage of a rotor wake indicating significant radial asymmetries in velocity profiles. Periodic fluctuation of the suction surface boundary layer on a stator blade has been detected starting from the first leading edge measurement location (i.e. 15%) until 37% chord where imminent separation was evident at design flow conditions. Different states of boundary layer flows exist at different heights of a fixed chord position, indicating that the inlet conditions to the stator vary throughout the span. This periodic alternating between laminar and turbulent of the boundary layer appeared to be primarily dependent on the state of the boundary layer itself rather than the wake passing frequency. Results from this first ever attempt of detailed boundary layer survey within turbomachinery environment at Cranfield, though qualitative, has shown that transitional flows occupy up to approximately 40% of the stator blade suction surface. Total separation of the flow, which had been detected at 65% chord in this investigation was not anticipated as the design of the current blading was aimed at delaying if not eliminating any separation until or near the trailing edge.

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