This thesis describes a 6 year long study to improve the performance of an ammonia air cooler which is an important device in the search for low carbon cooling. The aim was to develop understanding of the internal flow regime, pressure drop and heat transfer as seen in ammonia air coolers. This included the effects of straight horizontal tubes, the effect of horizontal and vertical 1800 return bends and the liquid interface with the tube wall. A test rig was designed by the author and built to investigate the internal ammonia flow regime, pressure drop and heat transfer. With an increased understanding of these areas, it was identified that the use of stainless steel as a tube material in LPR ammonia air cooler coils resulted in poor heat transfer. Flow visualisation identified that stratified flow mostly occurs in LPR ammonia air coolers. Due to stainless steel’s poor conductivity, little cooling effect occurred at the top of the tube. To maintain the same heat transfer from the aluminium fins, a large temperature difference is required across a stainless tube which results in poor heat transfer performance. It was identified that a different tube material was required to conduct the cooling effect around the tube and reduce the temperature difference between the ammonia and the air. Aluminium was chosen to replace the poor conductivity stainless steel tube. Aluminium was found to highly conductivity and the material is compatible for use in ammonia refrigeration systems. A new LPR ammonia air cooler with an aluminium tube was designed, manufactured and installed on a site to replace an existing stainless steel tube LPR ammonia air cooler. The heat transfer co-efficient was over 100% greater for aluminium tube when the same cooler fin surface area was compared.

As European and US vehicle emissions regulations tighten, more effective methods of reducing diesel engines pollutants must be devised. Increasing the injection pressure results in smaller fuel droplets and consequently more efficient combustion with a reduction in emissions output. However, to gain acceptable levels of NO. and particulates, required pressures must be of the order of 1800 to 2400 bar. At this level the components within the diesel injector and pump experience an appreciable level of distortion, that can, in severe cases, lead to leakage and a loss in pumping efficiency. It is therefore critical that an accurate means of determining the distortion and associated leakage is established. An efficient analytical method of solution for the problem of mechanical distortion of a diesel pump is presented. Both the EUI (Electronic Unit Injector) and CR (Common Rail) injection systems use essentially in-line pumps for which this technique allows the individual components (principally the plunger and barrel) to be analysed. Also, combined fluid-elastic systems are considered in both CR and EUI cases. An elastic integral equation formulation is optimised for a cylindrical geometry and this is used to evaluate key features of the system such as pressure distributions and variations in film thickness during the pumping stroke. It is then straightforward to evaluate other parameters such as leakage and both magnitude and direction of fluid flow within the film thickness. Simplification of elastic models is not required and as such this thesis also considers the effect of ports on the fluid flow and pressure distribution and also the relative orientation and axial position of the plunger within the barrel. This allows a detailed description and explanation to be made of the behaviour of the diesel pump. A key advantage of the method is that the fluid and elastic solvers may be decoupled and developed separately. This provides a means of extending the scope of the method beyond that presented here.

Heat exchangers are important components of thermoacoustic devices. In oscillatory flow conditions, the flow and temperature fields around the heat exchangers can be quite complex, and may significantly affect heat transfer behaviour. As a result, one cannot directly apply the heat transfer correlations for steady flows to the design of heat exchangers for oscillatory flows. The fundamental knowledge of heat transfer in oscillatory flows, however, is still not well-established. The aim of the current work is to investigate the influence of certain geometric parameters of heat exchangers, and of operating conditions in oscillatory flow on heat transfer performance. The heat transferred between two heat exchangers forming a couple was measured over a range of testing conditions. Three couples of finned-tube heat exchangers with different fin spacing were selected for the experiment. The main parameters considered were fin spacing, fin length, thermal penetration depth and gas displacement amplitude. Their effects on the heat exchanger performance were studied. The results are summarised and analysed in terms of heat transfer rate, Nusselt number and heat transfer effectiveness; the latter defined by the ratio of the actual heat transfer rate to the maximum possible heat transfer rate. The measurement results are compared with results from models widely used in the design of thermoacoustic heat exchangers: Time-Average Steady-Flow Equivalent (TASFE), Root Mean Square Reynolds Number (RMSRe), boundary layer conduction model and selected correlations developed by different authors. Based on the experimental data, a new correlation is established aimed at improving the reliability of oscillatory flow heat transfer predictions. The correlation is proposed for the relationship between heat transfer effectiveness, and the normalized displacement amplitude and the normalized fin spacing (the ratio of fin spacing to thermal penetration depth). The uncertainties associated with the measurement of heat transfer rate are also considered.

This study focuses on the design, construction and experimental evaluation of the prototypes of a thermoacoustic cooler driven by a thermoacoustic engine which is a part of the SCORE (Stove for COoking, Refrigeration and Electricity supply) project. In this study, there are two prototypes considered. The first prototype is the thermoacoustic cooler driven by a combustion-powered thermoacoustic engine based on a travelling-wave looped-tube configuration. A propane gas burner is used to simulate the thermal input from biomass combustion. The system operates at atmospheric pressure using air as a working medium which allows employing PVC pipes as parts for resonators. The locations of the cooler are investigated experimentally in order to find the optimum configuration. The minimum temperatures of -8.3°C and -3.9°C are achieved at the frequencies of 58.6 Hz and 70.3 Hz, respectively. The second rig is a linear configuration of a coaxial travelling-wave thermoacoustic cooler driven by a standing-wave thermoacoustic engine. Due to the requirements of higher cooling performance, compressed air at 10 bar is employed. The operating frequency is 46.4 Hz. The resistance heating wire is applied to simulate the biomass combustion at this stage. The system is optimised experimentally in both geometry and operating conditions, to offer the best performance. So far, the lowest temperature of -19.7°C has been obtained at a drive ratio of 3.25%, while the maximum COPR has been 5.94%. The experimental results also indicate that the proposed prototype can produce a sufficient cooling power for storing vital medicines which meets one of the objectives of the SCORE project. Additionally, some suggestions are made as to the re-design of the linear configuration to ensure a more compact and lightweight device. In the author opinion, the contributions to engineering science are: (i) the design and build of the prototypes based on low cost and simplicity, (ii) the introduction of phase tuning part, matching stub, into the low pressure system to match the cooler to the engine, (iii) the design of the linear configuration of a coaxial travelling-wave thermoacoustic cooler driven by a standing-wave thermoacoustic engine, (iv) improvement of the understanding of thermoacoustic technologies by application of DeltaEC programme, and (v) the application of DeltaEC simulations for optimisation of the coupled system.

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Convection is one of the most important mechanisms of heat transfer. This study reflects the need to develop a heat transfer fluid which offers greater capacity than current media, achieved by increasing the thermal conductivity of the fluid. The research investigated dispersions of conductive nanoparticles or nanofluids for use in the cooling of rotational moulds. The work systematically evaluated different shaped nanoparticles dispersed into a base fluid with the aim of increasing the thermal conductivity and therefore the convective heat transfer capability of the fluid. The stability of the dispersion was probed and found to be a key parameter in determining the success of increasing the thermal conductivity of the base fluid. The convective heat transfer capability of a number of fluids was investigated, showing that, in general, the heat transfer coefficient decreased upon addition of nanoparticles. A single formulation showed a heat transfer coefficient far in excess of that predicted and was therefore used in the rotational moulding study. A mathematical model was proposed to describe the thermal conductivity of the nanofluid. Uniquely, this included the influence of the surfactant coverage on the nanoparticle surface in estimating the thermal conductivity of the fluid. The rotational moulding study used a prototype mould, developed in conjunction with the Rotofast consortium. This allowed for induction heating and liquid cooling by circulating a fluid through the inductor pipe which was in contact with the mould. CFD simulations predicted that the cooling times for water and the nanofluid should be almost identical; however, the experiment showed that the nanofluid gave a cooling time for this apparatus which was longer than water but shorter than a thermal oil.

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Large eddy simulation (LES) is attractive as it provides a reasonable compromise between accuracy and cost, and is rapidly evolving as a practical approach for many engineering applications. This thesis is concerned with the application of large eddy simulation to unconfined swirl in turbulent non-premixed flames and isothermal flows. The LES methodology has been applied for the prediction of turbulent swirling reacting and non-reacting flows based on laboratory scale swirl burner known as the Sydney swirl burner, which has been a target flame of the workshop series of turbulent non-premixed flames (TNF). For that purpose a LES code was developed that can run wide range of applications. An algorithm was developed for LES of variable density reacting flow calculations. Particular attention was given to primitive conservation (mass, momentum and scalar) and kinetic energy of the flow and mixing field. The algorithm uses the primitive variables, which are staggered in both space and time. A steady laminar flamelet model which includes the detailed chemical kinetics and multi component mass diffusion, has been implemented in the LES code. An artificial inlet boundary condition method was implemented to generate instantaneous turbulent velocity fields that are imposed on the inflow boundary of the Cartesian grid. To improve the applicability of the code, various approaches were developed to improve stability and efficiency. LES calculations for isothermal turbulent swirling jets were successful in predicting experimentally measured mean velocities, their rms fluctuations and Reynolds shear stresses. The phenomenon of vortex breakdown (VB) and recirculation flow structures at different swirl and Reynolds numbers were successfully reproduced by the present large eddy simulations indicating that LES is capable of predicting VB phenomena which occurs only at certain conditions. For swirling flames, the LES predictions were able to capture the unsteady flow field, flame dynamics and showed good agreement with experimental measurements. The LES predictions for the mean temperature and major species were also successful.