This thesis presents investigations into the enhancement of heat transfer inside tubes using HiTRAN® tube inserts manufactured by Cal Gavin Ltd. The applicability of heat transfer enhancement in vertical thermo syphon reboilers was investigated using a computer simulation. In vacuum operation, reboilers can have a significant subcooled length (as high as 60 % of the tube length). Heat transfer coefficients in this region are lower than in the two-phase region. Using tube inserts, an increase is made in the heat transfer rate occurring in the sub-cooled region and, a corresponding increase in the length of the tube subjected to two-phase heat transfer and improvement of heat transfer performance results. Geometric variables of the tube insert were investigated experimentally, to study their influence on heat transfer and pressure drop performance. Loop density, loop wire diameter, core wire diameter, loop material and uniformity of loop density were investigated. Two experimental facilities were designed, commissioned and constructed to measure the heat transfer and pressure drop performance of these tube inserts. The new rig at UMIST is located in a flameproof location and was constructed with the intention of investigating a wide range of other processes in the future. Two tube inserts were tested over a Reynolds number range of 200 to 200000 using water as the working fluid. Adiabatic, cooling and heating tests were performed using an inside tube diameter of28.25 mm. At the Cal Gavin Ltd. facility, the rig was redesigned to extend the operating range of data collection. It was enhanced by the provision of automatic data collection, improved accuracy of temperature measurement and new equipment to allow cooling experiments. Tube inserts were tested between a Reynolds number of 100 to 2000 using a viscous oil as the working fluid. Again adiabatic, cooling and heating tests were performed. An inside tube diameter of 21.18 mm was used in the maj ority of the tests, but some preliminary results using a tube diameter of 28.45 mm are also reported. Using the results of the experimental work, pressure drop performance was correlated using an approach similar to that used for packed beds. It was found that 90 % of the data were correlated between ± 15 % of the prediction using specific insert dimensions and inside tube diameter. Further investigations into the prediction of heat transfer coefficients were made. However no general correlation could be developed from a fundamental basis, to predict heat transfer across the full range of Reynolds numbers investigated in this study. A recommendation is made for a suitable correlation. The influence of the insert geometry was associated with the fundamental pressure drop and heat transfer performance of the tube insert, leading to recommendations for the optimisation of tube insert design.

This thesis describes the development of a multi-objective automated optimisation system to be used for the design optimisation of micro-scale combustion devices. The developed system described within integrates a commercial computational fluid dynamics package and a multi-objective variant of the Tabu Search optimisation algorithm for continuous problems, which is a heuristic optimisation technique that exhibits local search characteristics. Recent advances in micro-fabrication techniques have resulted in increasing interest from industry and academia to investigate the possibility of replacing the current conventional power supply “battery” with a miniaturised combustion power generation system based on micro-electro-mechanical systems (MEMS) technology. The microcombustor is one of the crucial components of such a power system. The aim is to improve the main micro-scale combustor design characteristics and to satisfy manufacturability considerations from the very beginning of the whole design process. The main combustor design requirements, challenges and design parameters that influence the device performance at a micro-scale were first defined. Within the optimisation design cycle a robust parameterisation scheme, the geometry and numerical grid representations were implemented. These were achieved by incorporating the knowledge gained from the parametric design study by understanding the design space in depth and identifying issues and their solutions during this design study such as geometry overlapping and mesh refinement.

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Power generation companies are under a great deal of Government and other pressure to achieve and maintain their plants to a high efficiency standard with minimum release of CO2 into the atmosphere. Achieving and maintaining the required high level of operational integrity of large complex generating plants is a demanding task. One key requirement is to have data on the functional integrity of all major components of a power station plant This is to provide for removal from the plant of time expired components. This is particularly important for components that can only be replaced by shutting down the plant and having to do this very often is a problem. This dissertation relates to the life monitqfing of steam pipes and other components that are .subject to· demanding high temperatures and stresses. Life monitoring· of these components requires instrumentation that can withstand for long periods these very hostile conditions on and about the steam pipes. Creep monitoring is one key requirement and sensors need to be able to detect very small growth movements of the material and have the ability not to be affected by the hostile environment in which they are located. Ideally, for creep monitoring in steam pipe material, required is a precise point-to-point measurement in two or more directions together with strain mapping of the region in and about the point-ta-point sensors. E.ONUK is supporting this research to improve their life-monitoring systems and in so doing have regard for the trend to use even high temperature steam pipes in the next generation of power stations. To illustrate the above in this thesis, the development of a Strain Monitoring System is presented: the Auto Reference Creep Management And Control System (ARCMAC). This is a strain sensor system which is developed at Imperial College in collaboration with E.ON. UK. From design studies and operational experience of pipe degradation rates and failures, useful information is available as to parts of the pipe system that need to be monitored to obtain reliable data on the remaining life of the pipes. Also known is that a good and feasible monitoring method to reveal the onset of failure processes is the measurement of the increases in micra-strain generated in the outer skin of the pipe material. For these measurements, the ARCMAC system has been developed. The ARCMAC measurement system utilizes precision optics to capture successive images of a 'target' strain gauge and digital image processing is used to obtain estimates of creep s~in accumulated over the plant-operating period. The Digital Image Correlation (DIC) technique is also presented as an alternative measurement technique. In this technique a series of digital images of a surface is uSed under various levels of load, upon which a paint pattern has been applied. The first such pattern to be used in the UK on a power station was applied in Ratcliffe power station as part of this study. The DIC technique will be used in conjunction with ARCMAC gauges to evaluate any unusual strain distribution surrounding the gauge area in an effort to create a unified Strain Monitoring System combining both techniques. Full field case studies are examined and presented showing encouraging initial results.

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The primary theoretical contribution of this work is an enhanced Blade Element Momentum (BEM) method. Utilizing vortex theory to model induction, computationally efficient corrections are derived that are key in more accurately predicting performance for coned rotors. The theory is extended to include wake expansion, dynamic inflow, and yawed conditions, as well as considering centrifugal and radial-flow induced stall-delay. The theory is favourably validated against Computational Fluid Dynamics (CFD) and experimental results for both real and idealized rotors. BLADED^TM was to be modified with the enhanced BEM method for dynamic analyses. To support these analyses, a beam sectional model and Finite Element Method (FEM) approach to the generalized centrifugally stiffened beam problem were implemented. Ultimately, the linear structural theory in current codes precluded accurate predictions at large flap angles. In lieu of a fully non-linear flexible-body simulation, a rigid-body dynamic model of the system was developed. The coupled aerodynamic and structural models were then used to analyse steady-state and dynamic operation, including optimal control schedules. Parametric optimization studies were used to examine the interplay between design variables for the coning rotor, relative to a reference conventional machine. Increased blade length, shape and airfoil choice were found to be tightly coupled, yielding energy gains of 10-30% over conventional rotors. Airfoil choice and control mechanism were found critical to limiting torque and thrust. The fundamental non-linear open-loop dynamics were also examined, including flap and edgewise damping behaviour. Low-Frequency Noise (LFN) was computed with a properly implemented physics-based model, to quantify sensitivity to design and operational parameters. The current work is a preliminary, but critical step, in proving the worth of the coning rotor. Controlled design and an accurate flexible-body code will be required for full load-set simulations, to affect detailed component design and costing. Ultimately, prototype testing will be needed to validate the complicated stalling behaviour of the coning rotor.