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The need for reduction of CO2 emission from refrigerator compressors has motivated the research which is described In this thesis. The main focus is the development of high efficiency linear motors for direct-drive linear compressor systems to be used in domestic refrigerators. Three design variants of tubular moving-magnet linear motors are identified as potential candidates. The analytical methods are established for predicting open-circuit flux density distribution, flux-linkage, back-emf and thrust force for each motor and the results are validated by finite element analysis.

Adsorption refrigeration is one method of using waste heat/solar thermal power to generate cooling. However, the current performance of adsorption chillers needs to be improved. The key to optimising the design of the chiller is to understanding the adsorption parameters for different working pairs. In these parameters, the most important ones are: (1) equilibrium adsorption capacity and (2) the kinetic adsorption rate. Based on measurements of capacity and adsorption rate coefficient, parameters used in the design of the chiller like the length of the fin, the thickness of the adsorbent bed and the cycle time were studied computationally. Therefore, this thesis concerns the measurement of adsorption process parameters experimentally, and thereafter, the modelling of a chiller design. The equilibrium capacities of silica-gel/water and two types of activated carbon cloth (Chemviron Tm FM10 and FM100)/methanol were measured by thermogravimetric experiments in the temperature range of 30 to 80 'C . The isotherms of silica-gel/water were fitted by Henry's Law (Uptake<35%) and the isotherms for two types of ACC/methanol were fitted by the Toth equation. A new torsion balance was designed and built to measure the kinetics of the working pairs under different temperatures. By testing this newly designed balance with different sample temperatures and materials, different rate coefficients were obtained. The experiments also indicated that the rate coefficient for adsorption of silica-gel/water increased with temperature: the adsorption rate coefficient doubled following heating from 30'C to 60"C . On the other hand, the rate coefficient of the ACE/methanol pairs appeared to be unaffected by the temperature of the adsorbent. A discussion of experimental error and underlying physic is given in this thesis. Measurements were used in a model of a coated f10 system. Fin length, bed thickness and cycle time were varied in order to get an optimised solution. The performance changes caused by different parameters are presented and discussed.

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Concern over global warming and depletion of the ozone layer has stimulated research to develop cooling methods that do not employ environmentally damaging working fluids such as CFCs and HCFCs. Two methods that have been considered are absorption and thermoelectric `Peltier' cooling systems. Absorption systems, using H20/LiBr have the advantage of being able to use low-grade waste heat. However, the large volume, high capital cost and low performance of these systems have inhibited their widespread application. Thermoelectric systems were developed in the 1950s and use of this technology for air-conditioning applications was investigated as early as the 1960s. However, the continued development of thermoelectric systems was slow owing to technical difficulties and the superior performance of vapour-compression systems in terms of coefficient of performance (COP). It is known however that most working fluids employed in vapour-compression systems are damaging to the environment, and as vapour-compression systems contain moving parts, they have the further disadvantage of being noisy and requiring regular maintenance. In recent years therefore, there has been stimulated interest in using thermoelectric "Peltier" cooling systems for domestic refrigerators and air conditioning. Investigation of novel thermoelectric refrigeration systems was carried out in this research. The systems use thermoelectric "peltier" coolers (thermoelectric modules) to produce cooling or heating. Thermoelectric modules are solid state heat pump, which have the advantage of being environmentally friendly, being quiet, have no moving parts and can operate using direct current supplied from photovoltaic solar cells (PVs). This work mainly investigated a passive technology based on integration of a thermal diode and thermoelectric modules for building integrated heat pump. The heat pump uses thermoelectric modules to produce cooling or heating, and the thermal diode to transfer heat in or out of the building, and prevent reverse heat flow in the event of power failure. The heat pump was designed to have the following features: • Very compact and suitable for incorporation within the building structure; • Does not require a plant room and simple to construct; • Easily switched between cooling and heating modes; • Can prevent reverse heat flow in the event of power failure; • Low manufacturing cost; • Environmentally friendly; • Can be driven by solar photovoltaic panels. This work also investigated the potential application of phase change materials (PCMs) in the thermoelectric refrigeration system. The system employs phase change material to improve the performance of a thermoelectric refrigerator as well as the cooling storage capability. The refrigerator employing phase change material was designed to have following features: • Be able to overcome the peak loads and losses during door openings and power-off periods. • Prevent reverse heat flow via thermoelectric modules in the event of the power being turned off by integrating the thermosyphon with the phase change material. • Low manufacturing cost. • Environmentally friendly. • Can be driven by solar photovoltaic panels The research initially involved the investigation of the performance of the components of the thermoelectric refrigeration systems, including thermoelectric modules, heat pipes and heat sinks. The analytical models were developed to evaluate the heat transfer and optimise the design of these components. Correlations between heat transfer and fluid flow inside the heat pipes were explored by computer modelling. The research work further involved the design, modelling, construction and tests of a thermoelectric heat pump prototype. A computer model was developed to evaluate the performance of the heat pump system for two different modes, i. e., cooling and heating, under various operating and ambient temperatures. Laboratory tests were carried out to validate the modelling predictions and experimentally examine the thermal performance of the heat pump. Comparison was made between the modelling and testing results, and the reasons for error formation were analysed and correction was given. Further experimental investigation showed that reducing the temperature of the condenser of the thermal diode could provide a significant improvement of the efficiency of the coefficient of performance (COP) of the system in cooling mode. This can be achieved by using the evaporation of water on the heat sink attached to the condenser. The research work also involved the design, construction and tests of a thermoelectric refrigerator employing phase change material. The work intended to investigate the potential application of phase change materials (PCMs) in the thermoelectric refrigeration system. The system was first fabricated and tested using a conventional heat sink system as the cold heat sink. In order to improve the performance and the storage capability, the system was reconstructed and tested using an encapsulated PCM as a cold heat sink. Results of tests of the latter system showed an improved performance compared with the former system. However, to improve the storage capability, in particular during off-power periods, it was found necessary to integrate the PCM with a thermosyphons, which would allow heat flow in one direction only. Results of tests carried out on the system employing phase change material integrated with thermosyphons showed considerable improvement in the storage capability of the thermoelectric refrigeration system compared with the previous ones. On the basis of the above investigation the further work for improving the performance of the thermoelectric refrigeration system was suggested, which is illustrated in Chapter 7, and its key technical issues are discussed.

This thesis describes a theoretical and experimental investigation of the jet-pump refrigerator, and the application of Computational Fluid Dynamics (CFD) to improve the performance of the jet-pump, which lies at its heart. Within this thesis a number of new studies aimed at improving the COP of jet-pump refrigerators are carried out. These include an investigation of a novel jet-pump design methodology, (the Constant Rate of Momentum Change method), the application of CFD in the design of jet-pumps, the experimental testing of two new refrigerant fluids and finally, a comparative experimental investigation of performance benefits resulting from two cycle improvements that had not been tested before - these are the introduction of (i) a pre-heater (or recuperator) between the jet-pump and condenser, to preheat the liquid flow to the vapour generator, and (ii) a pre-cooler (or economiser) in the suction line between the evaporator and jet-pump, in order to sub-cool the liquid refrigerant in the line between the condenser and evaporator. Literature studies of jet-pump refrigerator technology and jet-pump design methodology are reviewed and discussed. A CFD model has been developed, assessed and validated against given experimental data. Simulations of a jet-pump that is part of a jet-pump refrigerator cycle was carried out to investigate the refrigerant flow structure and to assess the dominant influence of operating conditions and geometry. The validated CFD code was then used to optimize the design of the jet-pump for two new refrigerants (R236fa and R245fa). The resulting optimized jet-pumps were manufactured and tested experimentally over a wide range of operating conditions, using an adaptable test rig that was purpose-developed as part of this research work. Detailed experimental studies were carried out. All the experimentally determined results were compared to the CFD predicted values, and these showed good agreement for all the jet-pumps tested. These results showed that CFD has the potential to be an effective and powerful tool for simulating and optimising jet-pumps. The results also show that the jet-pump refrigerator should be considered if sources of low-grade heat are available.