Improving the energy efficiency of process plants is central to minimising operatingcosts and increasing profitability. Growing concerns on climate change is also anissue due to the increasing level of carbon dioxide emissions. Process industriesremain one of the largest consumers of energy. Maximising energy recovery in heatexchanger networks (HENs) reduce the total energy consumption in processindustries. However, cost effective retrofit of HENs remains a great challenge. Anideal retrofit design is one that has the right balance between efficient use of existingequipment and limited amount of modifications and downtime, while maximisingenergy recovery. The key objective of this thesis is to present novel methodologiesfor cost effective retrofit of HENs, while ensuring industrial applicability. The cost associated with the application of structural modifications and additionalheat transfer area, has led to an increased interest into the use of heat transferenhancement for retrofit. Heat transfer enhancement is beneficial, as it usuallyrequires low capital investment for fixed network topology, and no additional heattransfer area in existing heat exchangers. However, the challenges of heat transferenhancement for industrial applications are: (1) identifying the best heat exchangerto enhance; (2) dealing with downstream effects on the HEN after applyingenhancement; and (3) dealing with its effect on pressure drop. This thesis presentssequential based methodologies consisting of a combination of heuristics and a profitbased non-linear optimisation model for tackling these three issues. The robustnessof the new approach lies in its ability to provide useful insights into the interaction ofvarious units in a HEN whilst being pertinent for automation. Notwithstanding the drawbacks of structural modifications in retrofit, the degree ofenergy savings that can be obtained cannot be ignored. A robust retrofit strategy forthe application of structural modifications in retrofit is required. This thesis presentsa methodology that provides new fundamental insights into the application ofstructural modifications that ultimately leads to a faster retrofit procedure, withoutcompromising the performance and feasibility of the retrofitted HEN. The newapproach: (1) identifies the best location to apply a series of modifications; and (2)presents an algorithm that can be automated for the identification of the best singleand multiple modifications that provides maximum energy recovery for a givenHEN. The robustness of the new approach is tested by a comparison with the wellestablishedstochastic optimisation approach for structural modifications i.e.simulated annealing. To improve the retrofit result, this work also considerscombining the use of structural modifications and heat transfer enhancement. Theaim is to harnesses the benefits of both methods to obtain a cost effective retrofitdesign. The analysis carried out in this work is subject to minimising the energyconsumption and maximising the retrofit profit. A decision on the best retrofitstrategy to apply to a given HEN depends on the given retrofit objective. However,this work provides an adequate basis on which the decision can be made based onindustrial applicability, profit and energy saving.

Erosion of gas turbines operating in sandy or dusty environments can result in serious damage to the engine components, particularly the compressor unit. This phenomenon is a result of the ingestion of the sand particles into the engine and their consequent abrasive impacts on the blade surfaces. In order to understand the mechanism of sand ingestion and the resulting performance degradation, a general methodology has been developed for predicting the trajectories of particles, the erosion rates and blade profile changes, with predictive capabilities for performance degradations within more general configurations of turbomachines. This methodology was applied to an axial fan with upstream guide vanes (contra whirl) and was supported by experimental results. The numerical models for calculating the particle trajectory are based on the Lagrangian tracking technique and the eddy lifetime concept. The turbulence effect is assumed to prevail as long as the particle eddy interaction time is less than the eddy lifetime, and the displacement of a particle relative to the eddy is less than the eddy length. The flow field was solved separately using the Navier-Stokes finite volume flow solver ' TASCflow ' commercially available from ASC. The governing equations of the particle motion are solved using the Runge-Kutta Fehlberg technique. The tracking of particles and their locations is based on a finite element interpolation method. The developed Fortran code for predicting particle trajectory and erosion due to particle impact accounts for different types of boundary conditions and handles different frames of reference. The fragmentation of particles after rebound was also implemented. The number of particles seeded upstream of the IGV blades can be determined either by a user defined concentration profile or by a measured concentration profile. Also, particles can be seeded separately in a group at a release position. In the present study, the concentration profile and the initial particle velocity and angle of particle spread were determined from a laser transit anemometer. Two types of particles were used, a narrow size bandwidth (150-300micron) quartz particle and MIL-E5007E quartz particle, both of which have a normal distribution. The global rate of erosion, the reduced mass of blades and the changes of the blade geometry were predicted and compared with experimental results at different concentration levels. The baseline axial fan characteristics were measured at different mass flow conditions at a constant speed of rotation. To assess the effects of erosion, the characteristic measurement was repeated after each step of sand ingestion. The predicted aerodynamic performance; adiabatic efficiency, pressure rise coefficient and stall margin before and after erosion degradation were also determined from a developed Fortran program, which is basically a mean line method that uses advanced correlations for aerodynamic losses. Prediction of the particle trajectories show that high numbers of impacts (and maximum erosion) occurred near leading edge and tip region, which were also borne out by locally injected sand tests. The global rate of erosion and the consequent changes of the blade geometry were also predicted and compared with experimental results. The erosion pattern at high concentration of MIL-E5007E sand particles depicts net loss of material over the leading edge and the tip corner. The tip clearance increased markedly with a rounding of blade leading edge, which is the main cause of the decrease in efficiency, pressure rise, and surge margin. A parametric study with turbulence and fragmentation effects show that both parameters can influence the erosion rate and blade geometry deterioration. The results of the aerodynamic performance simulation using mean line method, which includes an erosion fault model, show good agreement with experimental results.

This thesis is concerned with factors affecting the thermal design of a compact recuperative type crossflowing heat exchanger for the primary heater of a Stirling engine. The exchanger is constructed of small diameter metal tubes (in the range of 3.0 mm to 6.0 mm) and close spacings are maintained between the tubes (i.e. in the range of 0.30 mm to 1.80 mm). These small slender tubes are usually arranged in single or double rows and are mounted around the combustion chamber. The exchanger is used to heat hydrogen or helium which act as a working fluid for the Stirling cycle. A survey of the published literature indicated that the available data does not include results for the tube Geometries of interest in this study. Consequently the heat transfers and hydraulic resistances were measured experimentally for a single row of small diameter, closelyspaced tubes situated in a crossflowing fluid stream. The Reynolds numbers (bc,.s ed on the mainstream fluid velocity and the tube diameter) ranged between 300 and 6500. Where possible the accuracy of the experimental procedure was checked by comparing the present results where possible with those obtained by previous workers. Several arrangements of both bare tubes and tubes fitted with extended surfaces were studied, The results were analysed and discussed, and where appropriate compared with those published in the open technical literature. In most comparative cases excellent agreement was experienced and any departure, could be explained. For the bare tube arrangements the influences of flow blockage ratio, mainstream turbulence intensity and surface roughness on the average heat transfer performance were investigated. A comparison of the heat transfers and pressure drops characteristics of the different tube arrangements led to proposals for an optimal exchanger geometry. The validity of the empirical corrections suggested by previous workers to account for the influence of flow blockage on average heat transfers was examinod. An alternative modified empirical expression was then proposed for the particularly high flow blockage situations (D/1I>0.85). It was found that at those high flow blockages the overall average heat transfers were independent of the mainstream turbulence intensity. However preliminary tests suggested that an increase in the tube surface roughness increases the average tube heat transfers. Since the proposed heat exchanger operates at the higheet possible mean metal temperatures, it is likely that 'hot spots' occurring due to variations in local heat transfers can lead to premature failure. Consequently a detailed study of the local heat transfer distributions is presented for various Geometrical conditions. The influences of blockage ratio and mainstream Reynolds numbers are examined and the results are analysed, and discussed, and where possible compared with other published data. The accuracy of experimental procedure employed in these tests was checked by comparing the results for a single cylinder ease with those reported by other investigators. The influence of fitting a single longitudinal fin to the rear of tubes on both the heat transfer and pumping power was studied. The tube diameter in these tests was kept constant, at 6.0 mm, but the angle of inclination of this longitudinal fin was varied incrementally so that an optimal angle for maximum performance is recommended. In a similar manner, transverse finned tubes with two different fin spacings were also investigated. The heat transfers and pressure losses obtained for the different finned tube arrangements were compared with each other and with those obtained for the bare tube geometries so that an optimal tube configuration was proposed . The data presented in this thesis were generalized, where possible, so that the results should be useful for future work. They should thus contribute to an understanding of the basic phenomena associated with modern compact heat exchangers. Recommendations for further work are also presented.

A swirl stabilised dump combustor capable of imposing flow perturbations creating combustion instabilities has been designed and commissioned. The capability of supplying different fuel mixtures (methane hydrogen blends) has been incorporated. Additional capability is the facility to preheat the combustion air prior to chamber entry and to be able to introduce dilution air into the chamber. The chamber itself is of fused silica quartz to allow non-intrusive optical diagnostics. High speed CH* Chemiluminescence has been performed to qualitative characterise the unstable heat release rate of pure methane and methane hydrogen blended flames to allow analysis of the mean deconvoluted flame structure. High speed Stereoscopic Particle Imaging Velocimetry (SPIV) has been used to acquire the flow field throughout the chamber and focusing upon the Annulus entry. These diagnostics have been phase locked to the imposed perturbation. A selection of conditions is presented with three different perturbation frequencies within the low frequency range. These reveal vastly different reacting and flow field structures. The difference of structures is attributed to behaviour of the IRZ (Internal Recirculation Zone) and CRZ (Corner Recirculation Zone) in altering the flame shape. All conditions exhibited the axisymmetric/bubble vortex breakdown mechanism responsible for stabilisation. Both single cell and double cell structures were observed in the mean flow field vector maps. The mechanism of oscillating heat release rate is attributed to oscillations of flame surface area. Profiles of integrated heat release rate and flame exhibit the same profile shape and behaviour correlating very well. The inclusion of hydrogen had no quantifiable impact upon the mean reacting or flow field structures using the current diagnostics. Investigation into the nature of the turbulence of the shear layers close to the annulus is presented for three perturbation frequencies. This highlighted periodic structures within the turbulence corresponding to the imposed perturbation frequency. It was found that excitation of both shear layers for all turbulent components was not always true and depended upon the perturbation frequency and flow structure close to the annulus. Two oppositely rotating vorticity structures were revealed attached to the outer and inner circumference of the annulus. These structures protruded into the chamber and spread radially. Frequency analysis of these two structures revealed both were oscillating at the perturbation frequency indicating vorticity shedding. The mean vorticity structures are shown to be influenced also by the behaviour of the recirculation zones.

This thesis presents a techno-economic performance simulation and diagnostics computational system for the operations optimisation and risk management of a CCGT power station. The project objective was to provide a technological solution to a business problem originated at the Manx Electricity Authority (MEA). The CCGT performance simulation program was created from the integration of existing and new performance simulation codes of the main components of a CCGT power station using Visual Basic for Applications (VBA) in Excel ®. The specifications of the real gas turbine (GT) engines at MEA demanded the modification of Turbomatch, a GT performance simulation code developed at Cranfield University. The new capabilities were successfully validated against previous work in the public domain. In the case of the steam cycle, the model for a double pressure once-through steam generator (OTSG) was produced. A novel approach using theoretical thermohydraulic models for heat exchangers and empiric correlations delivered positive results. Steamomatch, another code developed at the university, was used for the steam turbine performance simulation. An economic module based on the practitioners’ definition for spark spread was developed. The economic module makes use of the technical results, which are permanently accessible through the user interface of the system. The assessment of an existing gas turbine engine performance diagnostics system, Pythia, was made. The study tested the capabilities of the program under different ambient and operating conditions, signal noise levels and sensor faults. A set of guidelines aimed to increase the success rate of the diagnostic under the data and sensor restricted scenario presented by at MEA was generated. Once the development phase was concluded, technical and economic studies on the particular generation schedule for a cold day of winter 2007 were conducted. Variable ambient and operating conditions for each of the 48 time block forming the schedule were considered. The results showed error values below the 2% band for key technical parameters such as fuel flow, thermal efficiency and power output. On the economic side, the study quantified the loss making operation strategy of the plant during the offpeak market period of the day. But it also demonstrated the profit made during the peak hours lead to an overall positive cash flow for the day. A number of optimisation strategies to increase the profitability of the plant were proposed highlighting the economic benefit of them. These scenarios were based on the technical performance simulation of the plant under these specific conditions, increasing the reliability of the study. Finally, a number of risk management strategies aimed to protect the operations of a power generator from the main technical and economic risk variables were outlined. It was concluded that the use of techno-economic advanced tools such as eCCGT and Pythia can positively affect the way an operator manages a power generation asset through the implementation of virtually proven optimisation and risk management strategies.

This thesis introduces a method for the coupling of the elastic Boundary Element Method (BEM) and the elastoplastic Finite Element Method (FEM) and the extension of this method to contact problems by using gap finite elements. A method for the coupling of BEM subregions and FEM subregions is derived which limits the transformation of nodal forces into nodal traction to the interface degrees of freedom. This method is also capable of modelling body forces. Then the coupling procedure is extended to allow for elastoplastic material models in the FEM parts of the structure. Additionally contact conditions are included by defining an extra artificial subregion which consists of gap finite elements. Incremental iterative algorithms are used to overcome the present nonlinearities resulting from plasticity, non-conforming contact and friction. A computer program based on the developed methods and algorithms was coded in FORTRAN77 and tested on PCs. Patch tests and case studies were run in order to validate the developed package against known analytical solutions or the commercial finite element package ABAQUS. It can be concluded that all the original ideas and methods developed in this work are successful. The coupled FEM/BEM is as accurate and reliable as the pure FEM for elastoplastic analysis, with FEM/BEM having the advantage of ininimising the modelling effort. The use of gap elements in an artificial subregion was found to be an ideal and accurate way of including contact conditions into the environment of the elastoplastic coupled FEM/BEM.

This work aims to explore the effect of novel obstacle geometries on flame acceleration and transition to detonation in pulse detonation engines. To this end, a pulse detonation engine ground test demonstration rig has been developed and tested using stoichiometric propane-air mixtures. Much of this work has been invested into rig and instrumentation development as well as performing and analysing experiments. The rig has been tested using two different combustion chamber diameters, 0.089m and 0.038m, with lengths of 1m and 1.18m respectively. In addition, experiments were carried out with an orifice filled tubular insert which restricted the internal diameter to 0.032m over a distance of 14 tube diameters. A semi-empirical model has also been developed and validated for use in the prediction of flame acceleration (FA) through circular orifice plates. This was validated for a range of obstacle blockage ratios (BR) and tube lengths. The model was found to perform well, within one order of magnitude in all cases. Where modelling predictions fell beyond one standard deviation of the experimental mean it is thought that the discrepancy is a result of insufficient purging. Experimental shock speed, pressure and flame speed have been analysed using statistical density functions for a range of orifice fractal dimensions, orifice plate BR and obstacle lengths. Of particular interest are the novel experimental results produced by varying orifice fractal dimension or BR in separate tests along the length of the obstacle. It was found that decreasing the orifice plate BR along the obstacle length increased the exit flame speed by a mean value of 27% over a constant 0.57BR orifice. Experimental results for higher fractal dimension orifice plates produced greater shock speeds than circular orifices with 12D long obstacles. This effect diminished with increased obstacle length.

No description available.

Traction systems generate high loads of waste heat, which need to be removed for efficient operations. A new transient heat sink is proposed, which is based on salt hydrate phase change material (PCM). The heat sink would absorb heat during the short stationary phase i.e. at stations in which the PCM melts, a process accelerated by aluminium foam as it increases the rate of heat transfer within the PCM. When the train moves, the PCM is solidified via a forced convection stack. This creates a passive and efficient thermal solution, especially once heat pipe is employed as heat conduit. At the outset, the characteristics of the foam needed to be accurately determined. The foam was uncommon as its pore morphology was irregular, therefore it was scanned in a medical computed tomography (CT) scanner, which allowed for the construction of a three dimensional (3D) model. The model accuracy was enhanced by software, resulting in an extremely useful analytical tool. The model enabled important structural parameters to be measured e.g. porosity and specific surface area, which were crucial for the subsequent thermal and fluid flow analyses. A defect dense region was also detected, the effect of which was further investigated. Interestingly in the volume devoid of this defect, the porosity and specific surface area were uniform. A test rig was constructed that mimicked liquid cooling (or in the planned application, heat pipe cooling) in power electronics. At the core was a heat sink of salt hydrate PCM, impregnated within the foam. The sink with its current specifications (with liquid cooling) was able to absorb a thermal load consistent from a group of 4-5 IGBTs, which dissipated a low power of 20W per module during stops. The heating period of 1600-3500s per cycle meant the sink could be fitted to intercity locomotives. The foam increased the effective thermal conductivity by a factor of 24, from 0.45 to 10.83 W/m.K. 3D volume averaged numerical simulation was validated by experiment, which could be used to facilitate scale up or redesign for further optimization. As well as a support structure for the storage component of the system, the foam could replace conventional fins in forced convection, adding value to the potential manufacturer of the system. Heat transfer coefficient calculation incorporated the actual surface area that was derived from the 3D model, a first for metal foam studies. Results have shown a good Nu/Re correlation, comparable with other metal foam works.

The aim of the present thesis is to model the conversion process of the fast pyrolysis vapours into liquid bio-oil in liquid collection systems. The study focuses on the two major types of condensation systems namely the indirect contact condensers and the direct contact condensers (quenching columns). In the first part of the research, the hydrodynamic and heat transfer characteristics of a bench scale quenching column are presented by conducting numerical simulations based on the immiscible Eulerian-Eulerian model. The simulations are compared with experimental observations on flooding phenomena and various design variants are proposed for their elimination. In the second part, a multiphase multi-component model, with the condensable vapours and non-condensable gases as the gaseous phase and the condensed bio-oil as the liquid phase, has been developed. Species transport modelling has been used to capture the detailed physical phenomena of 11 major compounds present in the pyrolysis vapours. The development of the condensation model relies on the saturation pressures of the individual compounds computed based on the corresponding state correlations. In the final part, detailed information is provided on the vapour phase change dynamics implemented on a disc and donut quenching column design obtained from the first part. The study investigates the effect of the different numbers of disc and donut pairs on the condensation performance of the column. The numerical simulations showed that different number of stages can significantly affect the final bio-oil composition. It is shown that heavy molecular weight compounds, condense rapidly even with a low number of stages, whereas an increased number of stages is needed to completely capture the heavier acidic fractions. The modelling results are in good agreement with data published in the existing literature.