This thesis describes the development and validation of a new computational procedure for the calculation of thermal transmittance (U-value) of existing building elements from the measurement of surface heat flux, and surface and nearby air temperatures. The U-value plays a key role in the determination of the final energy consumption of a dwelling, and, as in the current political scenario reducing carbon emissions is a growing concern, obtaining accurate and quick measurements of thermal transmittance is of particular relevance to the precise representation of the energy performance of the building sector. The calculation method developed is an extension of the RC network, a model based on the discretisation of building elements in resistors and capacitors in analogy with electrical circuits. The advances proposed in this work extend the discrete RC networks to a model based on the full heat equation, with continuous, spatially varying thermal prop- erties. The solution algorithm is inserted in a Bayesian framework that allows the reformulation of the problem in terms of probability distributions. Two solution schemes have been confronted: Markov Chain Monte Carlo and Ensemble Kalman Filters approximation. The model proposed has been validated on synthetic data, laboratory data collected in an environmental chamber on a solid and cavity wall, and in-situ data collected in 3 different locations (2 solid walls and 1 insulated steel frame construction). The results show that the model offers an improved characterisation of the heat transfer through the building elements, furthermore, the algorithm can be used to analyse different wall constructions without the necessity of changing the structure of the model, as opposed to the standard RC networks, and, finally, it offers the practical advantages of the uncertainty reduction on thermal transmittance (from 14-25% to 7-10%) and a diminution of the necessary monitoring period from a minimum of 3 days to 1 day or less. These advantages, in turn, benefit the building performance evaluation on different levels: in first instance, the practicality of measuring thermal transmittance in-situ is improved, thus making it easier to monitor the actual envelope performance and, secondly, the uncertainty reduction on the U-value leads to important reductions on the uncertainty surrounding the energy consumption predictions associated with a dwelling.

The main objective of this research is to enhance the performance of a solar powered Micro Gas Turbine (MGT) by exploring suitable methods to be applied to the turbomachinery components to increase their efficiency and improve the predictability of their performance over the operating range of the MGT. A novel idea of reducing turbine rotor friction losses through adding riblets to the rotor hub was explored thoroughly. Computational Fluid Dynamics (CFD) has been used to study the effects of those features at design point conditions of the MGT. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. To improve the predictability of performance of the turbomachinery components of the MGT over the operating envelope, a prediction methodology was developed during this research which used a combination of CFD and empirical correlations to account for losses that are not included in the CFD model. It was found that riblets reduce the cross-stream motion of the low momentum fluid flow near the hub surface of the rotor passage, and separate the streamwise vortex from interaction with the hub surface. The maximum drag reduction was found to occur with riblets of a relative height of 2.5% with respect to the rotor inlet blade height. The performance prediction method was successfully applied to a radial turbine and centrifugal compressor designed for a 6 kWe solar powered MGT. A purpose-built test rig was built and the actual performance map for the turbine was achieved while running it using warm compressed air from an external air supply. The comparison between the actual and the predicted data revealed a good match between both results, which indicates the validity of the demonstrated performance prediction method.

The emissions control regulations introduced by governments are set to improve the quality of the engines and reduce the impact automobiles have on the planet. The regulations imposed on the manufactures have proven very difficult to meet, with some of the leading names in the industry investing significant part of their funding in research and development. Their goal is to reduce the fuel consumption and exhaust emissions while increasing the engine performance and durability. The piston-ring and cylinder-liner interaction is the major source of frictional losses for reciprocating internal combustion engines. The failure of the piston-rings to effectively control the transportation of oil from the sump onto the cylinder walls results among others to lubricant consumption. The objective of this project is to assist with the investigation of phenomena that occur in the cylinder liner and piston ring interaction under different operating conditions. To achieve these the following investigations have been carried, flow and cavitation visualisation in a model lubricant rig, and cavitation visualisation in a newly designed optical engine. The main focus of the project was the design, manufacturing and assembly of an optical internal combustion reciprocating engine. The new engine has been based on the design of a 450cc Ricardo Hydra, where many parts had to be redesigned or modified. The engine was fitted with a custom cylinder liner designed to accommodate custom made windows that covers almost the full length of the liner over a width of 25mm; this visibility allows access not only into the contact point over the entire length of the liner, but also provides access to the combustion chamber to allow for flow visualisation and flow field measurements. The cooling system was modified to allow for the accurate control and maintaining of the engine temperature. The control of the engine is performed with a new custom engine management system build in LabView which allowed for the precise control of the engine and of all the auxiliary systems such as fuel, ignition, sensors and optical equipment. The new control system and the optical engine were tested successfully up to 3000 RPM with the same specification as the unmodified engine in terms of in cylinder pressure and maintaining the original engine tolerances. The design of the new optical engine was a great success and it would offer a useful and valuable testing device that would allow further investigation to be carried out. In parallel to the design of the engine, a parametric experimental study was undertaken and performed on 6 lubricant samples of different formulations at two lubricant flow rate of 0.02 and 0.05 L/min, three speeds at 100, 300 and 600 RPM, and two different temperatures at 30oC and 70oC. The study was performed on an existing test-rig to visualise lubricants cavitation using two high speed cameras coupled with three ARRI high intensity light sources. This optical test device is a quick, efficient and effective way to test different lubricant samples and compare their in-between performance. The captured video images were processed through a custom build algorithm designed around the lubrication rig. This algorithm allowed for the extraction of matrices such as cavity length, cavity width, area of cavitation and number of cavities present in the area between the piston ring and the cylinder liner interaction. This parametric study offered a set of valuable results from which the performance of each lubricant can be assessed and a direct link between the lubricant formulation and the operating conditions can be established. Cavitation visualisation of the lubricant in the new optical engine was performed under motorised and firing condition up to an engine speed of 300 RPM and produced high quality images from the usually inaccessible piston ring and cylinder liner interaction. This unique design allowed to investigate a number of phenomena around that specific area like cavitation, blow-by, fuel spray, flame propagation and oil transportation. The parametric study results investigated in the test-rig have been linked with those obtained in the conventional internal combustion engines while providing a very useful and very powerful piece of software.

The goal of this work is to study computationally the flow induced by the collision between a single gasoil droplet and a spherical catalytic particle under realistic Fluid Catalytic Cracking (FCC) conditions. FCC reactors are found in the fossil fuel refineries and are used to upgrade heavy fuel (gas oil) to lighter products (gasoline or LPG), which are industrially more important. Gasoil is injected in the reactor and atomizes; the produced droplets vaporize intensely and come in contact with the hot fluidized solid catalysts. The “cracking” reactions accommodated at the particle porous surface (ex. zeolite) result in the decomposition of gasoil to lighter products. The two-phase flow model developed solves the incompressible Navier-Stokes equations for mass and momentum, along with the energy conservation equation. The VOF methodology is used to track the liquid-gas interface, while a dynamic local grid refinement technique is adopted, so that high accuracy is achieved with a relative low computational cost. A local evaporation model coupled with the additional solution of the species transport equation is utilized to consider phase change. Cracking surface reactions are taken into account via a simplified 2-lump scheme. The model is successfully validated in fundamental droplet dynamics flow conditions, such as droplet acceleration, droplet impingement onto flat and solid surfaces under isothermal conditions and droplet evaporation. Insights into these phenomena provide important information that are missing from experimental measurements. The numerical novelties of the current work include the implementation of a new Wetting Force Model to simulate drop-solid interaction, as well as the proposition of a sharpening scheme for the volume fraction field, to suppress diffusion. Concerning FCC collisions, the numerical model is able to reproduce both the hydrodynamics (drop deformation, spreading, breakup), as well as the chemical products (gasoil converted to gasoline). It is found that droplets of similar size to the catalytic particles tend to be levitated more easily by hot catalysts, thus resulting in higher cracking reaction rates/cracking product yield, and limited possibility for liquid pore blocking. For larger sized droplets, solid-liquid contact increases. The main ambition of the current Thesis, which is to combine the droplet hydrodynamics with the chemical reactions acts as a novel step towards the understanding of such micro-scale physical phenomena that are difficult to capture/measure in experimental apparatus. This fundamental numerical tool can provide insight to the spray system strategy of an FCC reactor for a wide range of operating conditions.

This thesis reports the development of a suite of FBG-based optical fibre sensors for non-destructive testing (NDT) and illustrating their potential for several specific industrial applications in the marine and railway sectors. These arose from work driven by the needs of project collaborators from these industries and are intended to be illustrative of the wider potential applications that optical fibre sensors have for measurements in different industrial sectors. The research has involved the development of new sensor system designs to meet these needs, building as they do upon a comprehensive review of NDT technologies and solutions, discussed in some detail. In this research for the marine sector, a single FBG-based acoustic sensor was specifically developed and evaluated and compared with the performance of conventional sensors. To do so, a metal plate to which the sensors were fixed was excited with a sonotrode, at a resonant frequency of 19.5 kHz. The signal reflecting that acoustic excitation was captured by the FBG sensors designed and implemented and their performance has been shown to be comparable with that from conventional, industry-standard piezoelectric transducers (PZTs). Preliminary work undertaken for the sponsors then lead to the further development of an acoustic sensor array comprising of 3 FBGs, which was subsequently validated against co-located PZTs which all were installed on a glass plate and excited in an industry-standard way, through the acoustic signal from a 0.2 g steel ball dropped onto the plate. When signals were analysed and compared, the positive comparative performance outcomes from the sensors used enabled further the design and implementation of instrumentation for a marine lifting surface using a different array, designed comprising 4 FBG-based acoustic sensors. Extensive tests on the smart marine lifting surface created were undertaken under water with a sonotrode set at 26 kHz as an excitation source. Based on the arrival time of acoustic signals captured by each grating and the use of triangulation method, the location of the excitation source could thus be determined, to meet the needs of the industrial sponsor and show good agreement with the outputs of conventional sensor systems. In parallel with the above, a further new industrial application of FBG-based sensor arrays was developed for a major player in the field, for the first time successfully instrumenting a railway current-collecting pantograph to allow reliable, remote in situ monitoring of key parameters: the contact force and contact location of the pantograph against the catenary. The optical fibre sensor approach has been shown to be an excellent means of measurement whose performance can be extrapolated to situations where the train is driven at high speeds up to 125 mph and powered from a high voltage line at 25 kV, in this design taking full advantages of the immunity of the optical fibre sensors to electromagnetic interference. In this research, key technical performance challenges were addressed and successfully overcome, including the temperature compensation needed for ‘all-weather’ performance, due to the intrinsic cross-sensitivity problems of using a FBG-based design being been fully addressed. This ensures the accurate measurement of the contact force/location between the pantograph and the catenary under all weathers. The research concludes by considering future directions for the work in these and other industry sectors.

Vortex-Induced Vibration (VIV) is one of the significant physics that encounter in the engineering practice. The good understanding of the structure response and technologies to suppress the significant vibration and undesirable forces induced by VIV is of vital importance for the entire design/planning procedure. However, for both the single-phase and multiphase flow, the main challenge is how to significantly improve the simulation efficiency and meanwhile maintain the accuracy. This research aims to develop a hybrid model which can simulate VIV significantly more efficiently. A novel framework for a hybrid model which is based on the functional decomposition is proposed. The theoretical hypothesis of the hybrid model is that the viscous effect is only significant near the offshore structures or breaking waves, and may be ignored in other areas. In this model, all physical variables are split into two parts. One part is solved by a quasi-turbulent model in whole domain and the other part solved by using a residual turbulent model in a smaller domain. The two models are implemented simultaneously based on their respective meshes and time steps. Due to this feature, the techniques such as the sub-cycle strategy are employed for the improvement of the efficiency without the deterioration of the accuracy. In this work, the equations and boundary conditions of the hybrid model for single phase and multiphase flow are derived. Corresponding algorithms and codes are developed using the open-source platform of OpenFOAM. The method is validated by simulating representative cases of flows past stationary and oscillating circular cylinder under various combinations of (Re, A/D, Fr) for single phase and of flows past stationary circular cylinder underneath an air-water interface for multiphase. It is demonstrated that the results of the hybrid model agree well with experimental data and with those obtained by using the original OpenFOAM. The investigation is also carried out on the efficiency of the hybrid model and indicate that the computational time of the hybrid model is significantly less than that of original OpenFOAM to obtain the similar results for the same cases. The investigation also indicates that the higher the Reynolds number, the larger the oscillation amplitude, the more computational time can be saved by using the new hybrid model. In some case, the hybrid model can save 80% of the computational time than using the original OpenFOAM solver.

The present study is the result of 4 years experimental research study aimed at understanding the hydrodynamic and heat transfer phenomena of a Diesel fuel droplet during the impact process with a heated flat and spherical surface. Such a phenomena are of a direct relevance to many engineering problems such as IC engines and fluid catalytic cracking (FCC). Due to the fact that the spray systems in the aforementioned applications may be comprised of millions of interacting droplets that prohibit detailed identification of the flow conditions during the impact of individual droplets, the current study focus on the characterisation of the impact dynamics of single droplets under well-controlled conditions. Several parameters, such as droplet velocity and diameter, liquid physical properties, surface conditions and geometry, wall surface temperature and ambient pressure are of key importance for the deformation of droplets upon impact and thus, define the impact outcome. An experimental investigation of micrometric Diesel droplets impacting on a heated aluminium and a millimetric brass particle surface was carried out. Dual view high-speed imaging has been employed to visualise the evolution of the impact process at various conditions. The parameters investigated include wall surface temperature ranging from room temperature to above Leidenfrost temperature (~420°C), impact Weber, and Reynolds numbers and ambient pressure of 1 and 2 bar. The observed post-impact outcome regimes are defined by means of hydrodynamic regimes and droplet morphology (stick, splash, break-up and rebound); then for each surface geometry, the identified impact outcomes were illustrated on regimes maps as a function of surface temperature and impact Weber number. Comparisons with the available experimental data for the single component fluids clearly shows significant differences, especially in terms of transition to Leidenfrost and breakup regimes; differences in liquid composition and non-homogeneity of the Diesel fuel droplet at the temperature above any of its component’s boiling temperature, results in different flow process and evaporating behaviour during the impact, and consequently the final outcome. Moreover, the temporal variation of the apparent dynamic contact angle and spreading factor has been determined as a function of the impact Weber number and surface temperature. The experimental results were compared against available numerical simulations, performed using a two-phase flow model with interface capturing, phase-change and variable physical properties in order to fully understand the physical mechanism behind the observed results; Increased surface temperature resulted to different spreading dynamic, in particular induced quicker and stronger recoiling behaviour, mostly attributed to the change of liquid viscosity. It has been also shown that the extension of the lamella spreading diameter on a spherical surface is larger than on a flat surface, which is due to the presence of the gravitational and centrifugal forces; yet the centrifugal force is the dominant effect. In addition, a series of experimental results focusing on: (i) the effect of physical properties and additives on isothermal impact of fuel droplets onto the flat and inclined substrates and (ii) oblique droplet-particle impact, are reported. These parts of the work are included in the appendices as such results were known already from the literature (Appendix A and B), or a pilot study and thus not conclusive (Appendix C) to be presented in the main body of the thesis.

In order to reduce emissions of carbon dioxide from the energy and transportation sectors, while still providing a reliable and affordable service, innovation in the fields of power generation and energy efficiency is needed. There exists a wide variety of low-temperature heat sources, such as waste heat from industry and transportation, solar thermal, biomass and geothermal, which contain large amounts of energy, but do not have sufficient temperature to be economically viable using traditional power generation techniques. Several technologies have been proposed to utilise these promising resources, of which the Organic Rankine Cycle is widely considered to be the technology with the most potential for large-scale commercial deployment. However, the low driving temperature differential available to Organic Rankine Cycles using these heat sources means that they face several technological challenges, some of which are addressed in this thesis. Firstly, they experience low efficiencies, which means that small absolute changes in efficiency and cost can be proportionally very significant, this makes cycle optimisation to achieve marginal gains a worthwhile exercise. Secondly, there is a lack of suitable working fluids for the Organic Rankine Cycle, meaning that they often have to operate with a fluid that is not tailored for the specific application. Producing tailor-made working fluids to a given heat source and sink temperature could represent a significant field for optimising the performance of ORCs. Thirdly, there is a lack of experimental validation of many theoretical aspects of the Organic Rankine Cycle, particularly for low heat source temperatures and power outputs. This thesis aims to contribute to the body of research on ORC technology by developing an analytical model to design an experimental rig. This rig is used to validate several theoretical predictions, which are then expanded upon to develop a novel method of cycle optimisation in an application with variable heat sink temperatures. Firstly, a thermodynamic model was developed in MATLAB to analyse a small-scale Organic Rankine Cycle. This model builds on well-established analytical modelling principles that frequently appear in the literature. This basic model was used as a tool to design a lab-scale experimental Organic Rankine Cycle rig, capable of addressing several gaps in the current literature, most notably the lack of research on the impact of a regenerator on the performance of an Organic Rankine Cycle, and the lack of experimental research on the performance of an Organic Rankine Cycle using a working fluid composed of a mixture of two working fluids, in this case r245fa and r134a. The model, its results and the design of the experimental rig are described in detail. The results from this experimental rig showed an increase in cycle efficiency and cycle output power with increasing heat source temperature and increasing cycle pressure ratio. The use of a regenerative cycle resulted in an increased cycle efficiency, but the extra flow resistance caused by the additional heat exchanger caused the mass flow rate of the cycle to drop, reducing the output power at the same time as reducing the evaporator heat demand and thereby increasing cycle efficiency. The addition of more r134a, which has a lower boiling point, to the working fluid mixture, increased the condenser pressure and thereby reduced the cycle pressure ratio, reducing output power and efficiency. The maximum efficiency achieved was 11.3%, for a regenerative cycle with a heat source temperature of 95°C and a pressure ratio of 4.56:1. Using the results from the experimental rig, and the model that they validate, the concept for the Dynamic Organic Rankine Cycle is presented. The Dynamic Organic Rankine Cycle was conceived as a solution to a problem identified in the literature, namely that an Organic Rankine Cycle using ambient air as the heat sink cannot fully utilise the driving temperature differential available to it during times of colder ambient temperature, as it must be designed to still function on the hottest day of the year. In order to address this, the Dynamic ORC Concept uses a variable working fluid composition, capable of shifting the composition between one working fluid component and the other by batch distillation in order to change the fluid’s bubble and dew points to match the heat sink temperature. The use of working fluid mixtures is in contrast to most current research, which has focused primarily on pure, single-component working fluids. A theoretical analysis of this cycle in MATLAB was carried out, and it was found that the cycle results in substantial increase in year-round power generation from the cycle, of the order of 8-10% for a heat source temperature of 150°C, increasing to 23% and higher for heat source temperatures of 100°C and below, while operating in a continental climate, such as that of Beijing, China. When operating in a climate with less temperature variation, the gains are lower, but still significant. Structurally, this paper presents a review of the relevant literature to the Organic Rankine Cycle, identifying the knowledge gaps that justify the work carried out. It then reviews the theory of the ORC, and how this was used both to build a computer model for analysis of the dynamic ORC and design the 1kW experimental rig. The experimental results from the rig are then presented and discussed. Finally, the results of the theoretical analysis of the dynamic ORC are presented, and analysed with the aid of the REFPROP fluid properties program to explain the trends observed in the data. Finally, suggestions for further work are made.

Improving the thermo-physical and tribological properties of lubricants has been a challenging subject of research. Over the last few years, nanolubricants, which are oils containing nanoparticle have been reported to possess exceptionally higher thermal and tribological properties than the traditional lubricants. However, nanolubricants complying with the American Petroleum Institute (API) and Society of Automotive Engineers (SAE) standards remain largely unexplored. In this dissertation, graphene based automotive lubricants meeting 20W50 API SN/CF and 20W50 API SJ/CF specifications have been investigated using a wide range of analytical methods. Thermal-physical and tribological properties have been thoroughly studied. A four-stroke IC engine test rig has been fabricated to investigate the performance of the formulated nanolubricant. By adding 0.01 wt% of 60 nm graphene and 1% lubricity additive to 20W50 API SN/CF oil, 21% and 23% enhancement in the coefficient of friction (μ) and thermal conductivity (k) at 80°C respectively was observed. Viscosity of SNCF with 0.01 wt% of 60 nm graphene and 1% lubricity increases by ~6% at 25°C, and ~9% at 105°C. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy suggest that many nano-tribo mechanisms occurring simultaneously or subsequently could be the reason for enhanced anti-wear and antifriction behaviour of the nanolubricant. Graphene found in the used engine oil indicates that the multilayer graphene exfoliates, rolls up to become helical coils or tube like structure and subsequently entangles with other flakes. As a result, gradually augmenting the thermal performance of the oil. Thermogravimetric analysis revealed that the onset temperature of oxidation for the SN/CF oil could be delayed by 13-17 °C in the presence of graphene. Moreover, the rate of oxidation when the weight loss of oil in the presence of graphene reaches 40% to 20% could be delayed by more than 30 °C. Resistance to oil degradation depends strongly on the graphene nanoparticle size and concentration. TGA kinetics studies show that the base oils have higher activation energy (Ea) and the addition of graphene significantly reduces Ea. Furthermore, 70% enhancement in heat transfer rate is also achieved in the presence of graphene. SEM images of the piston rings collected after 100 hours of engine operation show that the oil containing graphene (12 nm) decreases the piston wear compared to base oil without graphene. Elemental analysis indicates that the addition of a natural polymeric ester based lubricity additive helps even the graphene of highest thickness to perform better in boundary lubrication conditions. Essentially, this research has put forth a comprehensive understanding of a novel graphene based nanolubricant. The consolidated approach to understand tribological mechanism proposed in this research is expected to result in de novo strategies for engineering advanced nanolubricants in future.

Manufacturing makes ever-increasing demands for higher machining speeds. This is particularly true in car and aircraft production, but also for cutting tools. Vibration is used in various technological processes to improve the performance of the machines by intelligently exploiting the synergy of the oscillations. Vibration provides several benefits for various technologies, such as manufacturing, medical, communications, transport, industries, etc. Vibration assisted machining techniques have recently become an area of interest for many engineering applications. In machining processes, vibration can lead to improvements when applied in a controlled manner. Vibration assisted machining is a technique in which a certain frequency of vibration is applied to the cutting tool or the Workpiece to achieve better cutting performance The aim of this project is to apply vibration to the work-piece during milling process in order to improve the machining performance. In this project, a theoretical modelling and experimental implementation of vibratory milling process are presented and explored in depth. The modelling focused on the control system which tracked and regulated the vibration amplitude in the cutting zone during machining. Here, hardware and software of advanced technology of LabVIEW applications were used to develop implement and optimise the control system. The machine tool static, dynamic and compliance characteristics were investigated in terms of static analysis, natural frequencies and dynamic stiffness, using harmonic excitation, hammer impact test and the application of external forces. Preliminary studies were undertaken, where, the effect of cutting parameters were evaluated and the optimal cutting conditions were determined. Series of machining tests were undertaken, with the aim of recording process performance data in terms of cutting forces that were used for the development of the control system. A closed loop PID controller was developed using advanced Field-Programming-Gate-Array (FPGA) and Real-time Labview applications, using a non-interrupted real time target PC. An innovative and unique combination of FPGA and target PC allow the control system to have a very fast response in keeping the set amplitude of the vibration whilst recording simultaneously the machining data for further analysis. Aluminium and mild Steel were using in this investigation, along with a comparative study between conventional and vibratory milling and between open loop and closed loop control systems. The results of this investigation show the benefits of the superimposed vibration. The outperformance of the vibratory machining over the conventional milling provides a very promising outlook for the application of subsonic vibration into machining as an alternative to ultrasonic process.