A numerical investigation, based on mathematical modelling of some important phenomena relating to the chemical vapour deposition (CVD) process in a furnace, has been undertaken. This thesis is concerned with investigating the furnace design which results in the maximum possible recovery of the material in the form of flat deposition flux profiles. A finite difference technique is used to solve the Navier-Stokes and the diffusion equations which arise from the CVD process. In Chapter One, the main ideas of the problem are introduced. The investigation of the rectangular duct furnace is discussed in Chapter Two, and the importance of the axial diffusion term is studied. Chapter Three deals with the Plane Parallel wall furnace and the effect of varying certain parameters (i.e. Re, Pe and a) on the deposition flux profiles and the percentage recovery of the material. In Chapter Four, we investigate the impingement jet furnace, while in Chapter Five we study several furnace designs including the cylindrical furnace, the Plane Parallel wall furnace with various outlet configurations and the angled wall furnace. Also the effects of surface kinetics are discussed. Chapter Six describes the multigrid method as a fast method to solve the Navier-Stokes and the diffusion equations.

This thesis reports on design and performance studies of a prototype combined air source heat pump and storage system, retro fitted to heat occupied spaces subjected to high ventilation rates. The source of heat is from the air in the extract duct. Two limiting thermal conditions exist. The first is the thermal capacity of air passing over the ducted heat exchangers. The second is the dew and freezing points of the exhaust air, because of the insulating effect of ice on exchanger fins and tubes. Both are alleviated to a significant extent with high mass flow rates passing down the duct, since more heat can be extracted for a set decline in exhaust air temperatures. This study identifies reasons for ventilation and building strategies involving high ventilation rates, including the physiological and emotional needs of people and the various economic, climatic and Governmental polices (climate change levy, public health legislation) that impact upon heating and ventilation design. The study recognises the need for reduced carbon dioxide emissions and explores issues of indoor air quality and sick building syndrome and how increased ventilation rates can address them. The proposition investigated in this thesis is that air source recovery and heating by heat pump systems, combined with a heat storage system, can economically allow increases in ventilation rates to well above current standards without incurring great increases in energy use and carbon emissions; and in some circumstances reducing them. The thesis discusses in depth and detail, the advantages and disadvantages of possible alternative methods of heating a building and ventilation recovery, comparing their effectiveness and cost. A prototype system has been designed and field trials of a retrofit application have produced performance data that has subsequently been used in a long term cost comparison. The rig's design and construction are fully documented and its function over a full heating season is comprehensively explained (recording methods, types of calibration, control choices etc). A theoretical estimate of the energy requirements could have been attained using simulation and degree day information, however, a real like-for-like comparison using field trials prepared and a model was developed which allowed test data to be used to predict costs. The rig was tested over two heating seasons and compared with actual reading from alternative heating systems, degree day calculations are discussed but the reliance is on the actual live data gathered. (although summer cooling is achievable with the test rig no readings were recorded or comparison made). The work shows that heat pump heating and recovery systems and combined storage ability out-performed the other systems investigated. The crucial elements of its functionality are the high temperature of the heat source and the vast volume (and thermal capacity) of air being used, extracting at 24 °C and delivering at 35°C. The Coefficient of performance varies through the heating season but, synthesis of theory with test rig performance demonstrate that the longer term cost of the system is attractive; and its attraction shall probably grow with anticipated future trends in consumer demands for comfort and air quality coupled with fuel costs and a philanthropic social and political attitude to emissions control.

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The overall aim of the research reported here was the development of a simple, low-cost passive solar heating system for operation in the Portuguese climate. The performance of this device is critically dependent on the rate of convective heat exchange across the cavity behind the heater plate. Both computational and experimental studies of the heat transfer characteristics of this new storage device, have been conducted. An experimental installation in full scale was designed and constructed to enable the measurement of local heat transfer rates. Computer simulations of the laminar flow under solar-driven conditions were made using an existing steady, threedimensional computational fluid dynamics (CFD) code based on the finite-volume method (PHOENICS Code shareware version 1.S). A boundary-fitted co-ordinate system was developed to fit the non-rectangular geometry of the cavity, that represented the water store, which provided the computational grid for the CFD code. The experimental data from the test rig was used to validate the CFD model. A solar water heating system was built to test the design under realistic weather conditions. The experimental thermal performance was evaluated in 48% while the theoretical was estimated in 51 %.

In response to environmental concerns, demands for improved energy efficiency and a desire to create a more pleasant working environment; building designers are looking for ways to make better use of natural light. However, whilst natural light is both free and non-polluting, it can also produce high levels of visual contrast and glare, and unwanted heat. Most current design techniques estimate the natural internal illumination that results from an overcast sky; they do not include the contribution by direct sunlight entering the space, which is often the source of unwanted characteristics. Whilst a sophisticated computer ray-tracing program (RADIANCE) exists that can predict the full range of natural illumination, each prediction can take several minutes (or longer) to calculate. The time required to examine how a natural lighting design behaves over a typical year can therefore be prohibitive. Techniques for estimating the illumination provided by artificial lights also predict illumination under static conditions. Current techniques are therefore unsuitable for examining the dynamic behaviour of a lighting design, which links the automatic control of artificial lights to the changing levels of natural light. The aim of this research was to develop a computer based lighting design tool that overcomes these limitations. Based on the calculation of lighting coefficients, the numeric relationship between the luminance of light sources and the illuminance they produce, the Dynamic Lighting System (DLS) is able to calculate time-varying illuminance from a combination of natural light and artificial lights controlled by a lighting control system. The DLS has been written using the platform independent programming language Java. It is therefore able to run unaltered on most computer platforms, although in practice is limited to platforms on which the ray-tracing program RADIANCE will run, as RADIANCE is used to calculate coefficients. The DLS has been tested by comparing predicted levels of illuminance with levels measured in a test room under real sky conditions. These comparisons showed a high degree of correlation, but with a few large discrepancies. Possible causes of these discrepancies are offered and suggestions made about how they might be eliminated.

The use of scroll compressors in refrigeration systems is becoming increasing popular. However the development and use of a scroll machine as an expander to replace a throttle valve has never been reported. This thesis describes the work carried out to develop a two phase scroll expander for use in vapour compression refrigeration systems. By this means the power requirements of the system would be decreased and the refrigeration effect increased. A computer simulation of the geometry of the scroll device was first developed. This was attached to a package of subroutines developed to analyse compressor and expander thermodynamic performance to obtain estimates of both scroll expander and compressor performance. The results of the expander compressor analyses were used to estimate the performance of a scroll expander driving a second scroll compressor in a sealed unit used in a large industrial chiller of 4MW thermal output. By this means the power requirement for the main compressor was reduced by approximately 10% while, due to the expansion in the expander being more nearly isentropic than in the throttle valve, the refrigeration effect was simultaneously increased by nearly 2%. This lead to an overall improvement in coefficient of performance of nearly 13.5%. Further investigation of the system and more specially on the scroll device appears to be justified. A 3D simulation was then performed by the use of a CFD package called CFX4. This gave an excellent understanding on the flow 'inside' the machine. From the flow patterns obtained it is obvious that the scroll device behaviour appears to be excellent as compressor but not so good as an expander. This is mainly due to the huge recirculation during the filling process and due to the significant pressure drop of approximately 2 bar (Max) associated with it.

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