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Providing sustainable, cost-effective and environmentally friendly energy for consumer societies and industrial economies has been a major concern for industrialized and developing countries. For that reason, there is a renewed interest in the generation of energy from various solar technologies. Among others, Concentrated Solar Power (CSP) technologies has the potential to meet such demands. However, most recent solar energy harnessing technologies require substantial energy to attain efficient power production with compact plant size and the least payback time. Linear Fresnel coupled with organic Rankine cycle solar thermal power plant may prove to be a promising choice due to its capacity to overcome techno-commercial constraints related with conventional reflector based CSP Technologies. Theoretical and experimental studies for improving the design of a solar field and organic Rankine cycle turbine in a small Linear Fresnel Reflector solar thermal power plant is performed in this study. In the initial stage, the design and optimization of the 3D optical model of the LFR solar field is presented in an attempt to minimize the drift and variation in ray concentration and improve the optical performance. In the solar field optimization, key variables such as the mirror curvature, width, length, the distance between consecutive mirror centre lines and height were selected. Subsequently, a Monte Carlo Raytracing and thermal analysis were performed to investigate the impact of the optimized mirror elements on the optical performance of the solar field. A comparative analysis between two LFR configurations, Central LFR (CenLFR) and Compact LFR (ComLFR) is put forward by adopting a similar approach. Furthermore, a small-scale organic Rankine cycle turbine used for low-temperature applications capable of generating electrical power was theoretically and experimentally investigated. A single-stage axial turbine expander deploying R365mfc, and the new environmentally friendly Novec649 organic working fluids were selected. Modelling of the turbine and comparative analysis of the two working fluids is performed adopting a simple CFD approach proposed. The effect of the range of inlet definition variables such as temperature, pressure, rotational speed and key thermodynamic properties of the fluids on the work output and isentropic efficiency as well as the influence of rotor tip clearance (rotor gap) on the turbine power were investigated and analysed. In the closing stage, the shading analysis of the solar field and environs is performed using different approaches. In this context, shading resulting mainly from structures such as buildings and vegetation is considered. The analysis considers sun and shadow effects that can be easily and dynamically improved or even animated within the program to evaluate the timing and effect of obstructions and the resulting consequence on the optical performance of the solar field. The numerical approaches were validated with optical and thermal experimental data gathered from a linear Fresnel plant erected in Almatret, Spain. Results show a good correlation between the numerical approach and experimental study. Findings from the solar field study show that optimising key mirror elements such as the curvature, width, length, receiver height from the mirror plane, and the distance between two consecutive mirror centrelines can significantly impact the LFR solar field optical performance. This leads to an improved concentration factor which can enhance the energy conversion efficiency of LFR plants and greatly minimize the cost of thermal storage, which results in a low Levelized cost of electricity (LCOE) and offers LFR the economic potential to compete with other CSP power plants. Next to that, results of the comparative analysis show minimized drift in ray concentration and the computed energy efficiency for separate mirror elements, and the overall solar field show improved optical performance for the central configuration. Despite blocking and shading effect minimized in the compact configuration, findings show lower optical efficiency, mainly due to the receiver being fixed and its distance away from the primary mirrors. In both solar field studies, it was observed that losses are greatly influenced by the solar field orientation. As per the ORC turbine, it was observed that the inlet turbine temperature and pressure have the greatest effect on the power, work output and isentropic efficiency. The selection of an organic working fluid and its application in ORC turbine is a crucial aspect mainly due to the dependence of its categorization on the temperature of the heat source, defined by the fluid thermodynamic and thermophysical. As expected, the computed peak power output is generated by the "ideal" turbine expander design with zero clearance of blade tips. Exceeding the 200 μm rotor gap results in a sharp detrimental effect on the turbine performance. Shading analysis was found to be a fundamental step in the phase of design, installation and operation of a solar field. Shading of any form can have a negative influence on the performance of an entire solar field. Such estimations are significant, especially when designing collectors for places where the available land strip does not align with a particular orientation, as in the case of the north-south configuration.

This research presents a comparison between mainstream and emerging solar-thermal renewable energy technologies (RETs) using an integrated environmental and techno- economic assessment framework and the numerical modelling of heat pipes for solar thermal applications. Using the framework, the overall sustainability potential is quantified in terms of a novel environmental and techno-economic index (ETEI), combining the Levelised Life Cycle Impact (LLCI) with the Levelised Cost of Energy (LCOE). A set of three 'mainstream' (Photovoltaic-PV, Wind Turbine-WT, Bioenergy) and three 'solar- thermal' (Parabolic Trough Steam-driven turbine, Parabolic Trough and Linear Fresnel Reflectors, the latter two with Organic Rankine Cycle, respectively PT-ORC and LFR- ORC) RETs are used. Economic and environmental evaluation of the RETs for technological innovation is relevant in making an informed decision as to the value these technologies present. Hence, this study also assesses the efficiency of technical innovations of the six RETs, using the eco-efficiency approach by integrating life cycle assessment and life costing. A demonstration case study is presented for two sites with favourable renewable resources over 25-year operational life. The results show improved overall sustainability scores for solar-thermal, attributed mainly to the additional thermal energy recovery from the ORC. PV emerges as the most preferred option when only electricity generation is considered, whereas accounting for the additional thermal energy outputs makes PT-ORC as the most preferred option during to its technological maturity and LFR-ORC the second preferred option. The transient behaviour of a heat pipe, designed by an industrial partner of the Northumbria University team, leading Horizon 2020 R & I Activity Project on the development of a small solar thermal plant, was investigated numerically. The heat pipe is a part of the plant, and its operation was studied for different tilt angles (0 = 0°, 45°, 90°). The numerical solutions were obtained using a fully implicit Finite Difference Method that considered the motion of the liquid and a known time-varying temperature boundary condition at the liquid front. The liquid front position was found to be dependent on the applied heat flux, the initial conditions, and the thermophysical properties of the working fluid. Additionally, the distribution of power output and wall temperatures was predicted. The temperature distribution of the working fluid was consistent with experimental results from the previous literature and provided valuable insight into the room-temperature start- up phenomenon.

Solar power is a renewable energy source and can meet the growing world demand for electricity. The thermal energy produces by solar is an attractive solution to handle the environmental issues caused by fossil fuels. This research focuses on the theoretical modelling of components of solar thermal power plants for performance enhancement. It involves the modelling of the solar collector and organic Rankine power cycle. The overall solar thermal power plant comprises such components as a collector, evaporator, turbine, condenser, pump, heat exchanger, and thermal storage system. The present research studies the Linear Fresnel Reflector's performance in providing the heat input to the Organic Rankine Cycle and investigate the annual energy production of the power plant, located at the testing site in Almatret, Catalonia, Spain. The work includes step-by-step modification of the actual system design with a performance analysis of the non-concentrating and concentrating power plant systems. The mathematical model of the ORC was developed based on the thermodynamic equations with simulations performed using MATLAB/Thermolib software. The ORC system performance was investigated for different working fluids at their critical operating conditions. The considered working fluids include the HCFC-245fa, HCFC-134a, Propane, butane, ethanol, and methanol. The ORC model was upgraded by taking into account the heat exchanger to recover the system waste heat, and results were compared to that from a simple ORC model. The recovery of the heat in the cycle increases the thermal efficiency of the ORC, but its benefits depend on the critical parameters of the working fluid. The effect is considerable for R134a and negligible for Ethanol. The Solar Organic Rankine Cycle (SORC) mathematical model was developed, and simulation designed on the MATLAB/Thermolib software. The evacuated tube collector designed for the Almatret latitude position and supplied the power input to the Rankine system. The model based on the water heat transfer fluid of the solar field, and it is transferring the heat to HCFC-134fa, the working fluid of the Rankine cycle via a heat exchanger without a tracking and thermal storage system. The thermal performance of the model investigated base on the day scan results. The solar organic Rankine cycle has an area 600 m2 to generate peak thermal power 71 kW, and the mechanical output power of the Rankine cycle is 4.274 kW using 30 bar evaporation pressure and 10 bar condensation pressure. The Generic Algorithm code developed on MATLAB and connected with the Thermolib model to operate the SORC system with optimum variables and thermal efficiency increases from 10.58 % to 11.87 % using the peak value solar irradiance. Fresnel solar reflector model simulated by using the light tools simulation software and have a one-axis tracking system. The actual weather data was imported to the simulation software to investigate the system performance using the day scan results. The theoretical model derived to determine the system thermal energy and conduction, convection, and radiation heat transfer of the receiver tube. The thermal losses of the model investigated and derived solar angles of the specific day. The tracking system based on the incidence angle modifier model (IAM) and calculated the system optical efficiency corresponds to the IAM in terms of the longitudinal and transverse components of the incidence of rays. The analysis performed from ambient conditions to determine the peak value by using the Therminol-62 working fluid. The LFR field produces 106.425 kW thermal energy during peak hour using a high value of IAM, and the reflector area is 214.38 m2. The thermal losses during the peak time of day at 1:00 PM is 7.872 kW. The system advisor simulation software used to validate the solar power linear Fresnel system. The complete model simulated with the thermal storage system. The actual weather data and Therminol-62 heat transfer fluid and NOVECTM649 working fluid import to the simulation model. The simulation model based on the exact power plant is located in the Almatret location and investigated the model thermal performance. The results show that the LFR field with a tracking system and Therminol-62 working fluid increases the system thermal performance. The Therminol-62 have high-temperature ranges at low operating pressure as compare to the steam working fluid. The ORC has a higher value of thermal efficiency NOVECTM649 than HCFC-134a and produces 7.2 kW output power of the ORC plant during the peak hour of solar irradiance with specific operating conditions. The two-tank thermal storage system extends the Plant four hours of operation and produces the highest power output of 2160 kWh in July.

The depletion of fossil fuels coupled with the growing demands of the world energy has ignited the interest for renewable energies including biomass for energy production. A reliable affordable and clean energy supply is of major importance to the environment and economy of the society. In this context, modern use of biomass is considered a promising clean energy alternative for the reduction of greenhouse gas emissions and energy dependency. The use of biomass as a renewable energy source for industrial application has increased over the last decade and is now considered as one of the most promising renewable sources. The direct combustion of biomass in small scales often results in incomplete and inconsistent burning process which could produce carbon monoxide, particulates and other pollutants. Therefore, biomass is required to be transformed into more easily handled fuel such as gases, liquids and charcoal using technologies such as pyrolysis, gasification, fermentation, digestion etc. Biomass gasification upon which this thesis focuses is one of the promising routes amongst the renewable energy options for future deployment. Gasification is a process of conversion of solid biomass into combustible gas, known as producer gas by partial oxidation. This research work is carried out to investigate various methods employed for modelling biomass gasifiers, it also studies the chemistry of gasification and reviews various gasification models. In this work, a mathematical model is developed to simulate the behaviour of downdraft gasifiers operating under steady state and determine the synthesis gas composition. The model distinctly analyses the processes in each of the three zones of the gasifier; pyrolysis, oxidation and reduction zones. Air is used as the gasifying agent and is introduced into the pyrolysis and oxidation zones of the gasifier for both single and double air operations. These zones have been modelled based on thermodynamic equilibrium and kinetic modelling; the model equations are solved in MATLAB. Given the biomass properties, consumption, air input, moisture content and gasifier specifications, the MATLAB model is able to accurately predict the temperature and distribution of the molar concentrations of the synthesis gas constituents. The downdraft gasifier is also represented in Aspen HYSYS based on the same models to study the effect of both single and double air gasification operation. For known biomass properties, consumption, air input, moisture content and gasifier operating conditions, the Aspen HYSYS model can accurately predict the distributions of the molar concentrations of the syngas constituents (CO, CO2, H2, CH4, and N2). The models were validated by comparing obtained theoretical results with experimental data published in the open literature. Parametric studies were carried out to study the effects of equivalence ratio, moisture content, temperature on the gas compositions and its energy content. The proposed equilibrium model displayed a variable ability for the prediction of various product yields with this being a function of the feedstock studied. It also demonstrated the ability to predict product gases from various biomasses using both single and double stage air input. In the case of gasification with double air stage supply, higher amounts of methane are obtained with specific tendencies of the gases reaching a peak at certain conditions. The kinetic model was partially successful in predicting results and comparable with experimentally published results for a range of conditions. There were discrepancies particularly with CH4 formation and the operating temperatures predictions which were usually consistently lower than those actually measured experimentally. The use of the PFR, however, did show a greater potential for the use in further modelling.

This research work aims to develop low- and medium-temperature thermal energy storage (TES) systems using metallic alloys and solar salt as phase change materials (PCMs) for accumulating thermal energy in the temperature ranges between 120 and 140 °C and 215 and 250 °C, respectively. The low purity metallic alloy Bi 58%-Sn 42% was selected as the PCM for low-temperature applications because it is non-hazardous, relatively inexpensive, and it has a suitable melting temperature range. Commercially available high-purity metallic alloys (99.99%) are expensive, whereas lower purity alloys can be a cost-competitive alternative for PCM applications. The sample of a low purity metal alloy, namely Bi 58%-Sn 42% with a purity of 97% was sintered in the laboratory, and its thermal properties were characterized for application as a PCM. Experimental investigations demonstrated that deterioration of the thermal properties of the low purity metal alloy is not substantial in comparison to the pure metallic alloy and that it can be efficiently used as a PCM. Solar salt (NaNO3 60% - KNO3 40%), selected as the PCM for medium-temperature applications due to its high latent heat value, has a relatively low thermal conductivity. Therefore, two techniques were adopted to improve the heat transfer in TES: deploying metallic fins and using graphite as an additive. The experimental tests demonstrate that both methods considerably improve heat transfer and data obtained was used to quantify these effects. In addition, the computational fluid dynamics (CFD) simulations were carried out to evaluate the thermal performance of the metallic alloy and solar salt TES systems with different concentrations of additives and number of fins in terms of the evolution of the liquid fraction and amount of energy stored and released during charging and discharging processes as a function of time. The comparison of numerical and experimental results demonstrated the acceptable accuracy of the developed CFD models. Both experimental and numerical results were used to derive dimensionless correlations for estimation of the heat transfer intensity and time required for charging and discharging of the studied TES systems. These generated dimensionless correlations can be successfully used in engineering practice to design TES systems.

The application of solar energy is one prospective solution to meet the sharp increase in global energy demand and alleviate the environmental issues, caused by the use of fossil fuels. Solar thermal energy has been actively utilized to operate small-scale desalination systems and solar water stills, which are one of the most promising technologies in the field of seawater desalination. A desalination system, consisting of multi-effect solar water still coupled to evacuated tube solar collectors and a novel modification of small fluid piston energy converter has been studied at Northumbria University. The task in this research was to experimentally test the possibility of the operation of system with capability to self-reduce the internal pressure inside the still in order to increase its productivity. It was demonstrated that the system was able to achieve vacuum conditions and maintain this level of pressure without using an external vacuum pump. In the theoretical investigation a thermodynamic mathematical model of the proposed system has been developed and used to solve the governing equations in a Matlab/Simulink environment. The output data was obtained in terms of variation of the pressure and temperatures inside the system as well as its distillate productivity. In the experimental investigation, the above described distillation system was developed at Northumbria University based on a laboratory prototype of a dynamic solar multi-effect water still and fluid piston energy converter designed and built previously by Prof K. Mahkamov. Series of experimental tests and numerical simulations were performed for the climatic conditions of Benghazi city in Libya. After validation of the mathematical model against previously published theoretical results and the experimental data obtained in this study, further investigations of the influence of decreasing internal pressure on the performance of the system was conducted. Overall, investigations confirm that this novel system demonstrates considerable improvement in the distillate productivity when compared to conventional solar stills.

The use of solar thermal energy to drive both large and small scale power generation units is one of the prospective solutions to meet the dramatic increase in the global energy demand and tackle the environmental problems caused by fossil fuels. New energy conversion technologies need to be developed or improved in order to enhance their performance in conversion of renewable energy. The Organic Rankine Cycle (ORC) is considered as one of the most promising technologies in the field of small and medium scale combined heat and power (CHP) systems due to its ability to efficiently recover low-grade heat sources such as solar energy. This technology is especially in demand in isolated areas where connection to the grid is not a viable option. The present research provides thermodynamic performance evaluation and economic assessment for a small-scale (10 kW) hybrid solar/biomass ORC power system to operate in the UK climate conditions. This system consists of two circuits, namely organic fluid circuit and solar heating circuit in which thermal energy is provided by an array of solar evacuated tube collectors (ETCs) with heat pipes. A biomass boiler is also integrated to compensate for solar energy intermittence. A dynamic model for the hybrid ORC power system has been developed to simulate and predict the system behaviour over a day-long period for different annual seasons. In the thermodynamic investigation, an overall thermodynamic mathematical model of the proposed power system has been developed. The calculation model of the ORC plant consists of a number of control volumes and in each volume the mass and energy conservation equations are used to describe energy transfer processes. The set of equations were solved numerically using a toolbox called Thermolib which works in the MATLAB/Simulink® environment. The numerical results obtained on the performance of the ORC plant were validated against the theoretical and experimental data available in the open literature. The predicted results were in very good agreement with the data published in the literature. The comparison demonstrated that the developed simulation model of the ORC plant accurately predicts its performance with a maximum deviation of less than 7%. The developed mathematical model then has been used to carry out the parametric analysis to investigate the effect of different operating conditions on the system performance. The economic analysis has been performed with the use of equipment costing technique to estimate the system’s total capital investment cost. This approach is based on the individual costing correlation of each component in the system, considering all the direct and indirect costs of the proposed components. The system cost calculations have been conducted for a range of operating parameters and different working fluids for a fixed value of net power output. At the final stage of the research, a thermo-economic optimization procedure has been developed using Genetic Algorithm (GA) approach for selection of the rational set of design parameters and operating conditions for optimum system performance.

Solar energy has been actively used to drive cooling cycles for domestic and industrial applications, especially in remote areas with a lack of electricity supply for running conventional refrigeration or air-conditioning systems. A number of solar cooling technologies exists but their market penetration level is relatively low due to the high capital costs involved and a long pay-back period. Extensive R & D activities are underway at Universities and industrial companies across many countries to improve performance and reduce capital and running costs of solar cooling systems. Systems based on application of a liquid piston converter for solar water pumping and dynamic water desalination have been developed at Northumbria University. Some preliminary work has been completed on the development of a new solar cooling system built around the above fluid piston converter. In this work, the task is to experimentally and numerically investigate performance of the solar cooling system with the fluid piston converter. The developed theoretical model then can be used for determination of its rational design parameters. Experimental tests were conducted in the Energy Laboratory of the Faculty. The test rig consisted of a solar simulator and evacuated tube solar collector, coupled to the liquid piston converters, equipped with a heat exchanger. Three different configurations of the solar cooling unit were tested and a data acquisition system with pressure, temperature and liquid piston displacement sensors was used to evaluate the experimental performance on the cooling capacity. In the theoretical part of the study, the thermodynamic model of the solar cooling system was developed. In the calculation scheme, the system was split into a number of control volumes and ordinary differential equations of energy and mass conservation were used to describe mass and heat transfer in each such volume. The system of ordinary equations then was solved numerically in MATLAB/Simulink environment and information on the variations of pressure and temperatures in the control volumes of the system over the cycle were obtained. Calibration of the mathematical model with the use of experimental data demonstrated that the model predicts the performance of the system with accuracy acceptable for engineering purposes. Experimental investigations showed that laboratory prototypes of the system demonstrate a stable operation during the tests with an amplitude and frequency of liquid piston oscillations being about 4- 6 cm and 3 Hz, respectively. The reduction in the air temperature in the cooling space was about 1 and 2 K, compared to the ambient temperature. The cooling effect increases with the raise in the heat input into the solar collector and in the flow rate of cooling water. The developed mathematical model of the system describes the pressure variation in the cycle, amplitude and frequency of oscillation of pistons with a level accuracy sufficient for performing engineering design calculations. Overall, both experimental and theoretical investigations confirm that the system demonstrates a capacity to produce a cooling effect with utilisation of solar energy. However, further R & D is required to enhance its performance.

This research is focused on the performance evaluation of micro Combined Heat and Power (mCHP) systems based on modern prime mover technologies using both theoretical and experimental analysis. Estimations of the environmental and economic impact associated with their deployment in residential conditions were also carried out. Experimental work was performed on assessing the dynamic and steady-state performance of the 1 kWe Stirling based mCHP system (Whispergen), the 0.75 kWe Proton Exchange Membrane Fuel Cell (PEMFC, PA Hilton Ltd) and the 5.5 kWe Internal Combustion Engine (ICE) based mCHP (Dachs). Results obtained from experiments (such as partial efficiencies, nominal capacities etc.) were fed directly in a theoretical model. Primary energy requirements corresponding to average UK domestic conditions were simulated based on real life technical data. All theoretical work was conducted using EnergyPlus building simulation tool in which the operation of several hydronic heating systems was modelled. Furthermore, attained experimental data and previously published research results were used to validate the theoretical modelling process. Several operating strategies of the Stirling based mCHP unit were simulated in order to determine the regime which offers highest reduction in carbon emissions and household expenditures. In addition, variations in a number of parameters that significantly affect the performance of the system were investigated including energy consumption profiles, occupancy characteristics, dwelling thermal requirements, domestic hot water tank volume, etc). For the optimum performance strategy, several configurations of co-generation systems with nominal capacity in the range from 1 to 3 kWe were simulated. All simulated mCHP scenarios were compared against a conventional heating equipment. Finally, the advantages of a mass installation on a district level, consisting of 60, 120 and 240 dwellings and utilising a mixture of different mCHP units (ICE, Stirling, PEMFC), were estimated.

This study is carried out to investigate the solar thermal energy conversion for generating power. This form of renewable energy can be utilised for power production deploying the free piston Stirling engines, which convert thermal energy into mechanical energy. Such systems have an advantage of production of work using low and high temperature differences in the cycle which could be created by different sources of heat including solar energy, combustion of a fuel, geothermal energy, nuclear energy or waste heat. The thermodynamic analysis of the free piston Stirling engine have been carried out and implemented in past studies with different methods of approach with various difficulties exhibited. In the present study isothermal, ideal adiabatic and Quasi steady flow models have been produced and used for investigation of the engine performance. The approach in this study deals with simultaneous mathematical modelling of thermodynamic processes and pistons dynamics. The steady state operation of the engine depends on the values of damping coefficients, spring stiffness and pressure drop within the heat exchangers during the engine’s operation, which is also a result of the energy transfer in each engine’s component. In order to design effective high performance engines it is necessary to develop such advanced mathematical models to perform the analysis of the engine’s operation and to predict its performance satisfactorily. The aim of this study was to develop several levels of mathematical models of free piston Stirling engines and to evaluate their accuracy using experimental and theoretical results available in published sources. The validation of the developed free piston Stirling engine models demonstrates a good agreement between the numerical results and experimental data. The validated model then was used for optimisation of the engine, deploying Genetic Algorithm approach with the purpose to determine its optimal design parameters. The developed optimisation procedure provides a noticeable improvement in the engine’s performance in terms of power output and efficiency.

The present research explores numerically and experimentally the process of melting and solidification of Phase Change Materials (PCM) in a latent heat thermal energy storage system (LHTESS). Further, the study will investigate various methods of intensification of heat transfer in such materials by means of metallic fins, filling particles or nanoparticles and by choosing the optimal system geometry for a rapid development of free convection flows during the melting process. The study includes three main parts. First, 3D CFD modelling was performed for the melting performance of a shell-and-tube thermal storage system with n-Octadecane as a PCM. The predicted model was in very good agreement with experimental data published in open literature. A series of numerical calculations were then undertaken to investigate the effect of nanoparticles on the heat transfer process. Dimensionless heat transfer correlations were derived for the system with Pure PCM and PCM mixed with nano-particles. In the second part of this study the experimental studies were carried out in order to investigate the performance of the laboratory thermal storage system with paraffin as the PCM. The thermal storage system was connected to evacuated tube solar collectors and its performance was evaluated in various conditions. 3D CFD model of the system was developed and numerical simulations were run for constant heat source conditions. Computational results were compared with experimental data obtained on the test rig at Northumbria University. Comparison revealed that the developed CFD model is capable to describe process of heat transfer in the system with high accuracy and therefore can be used with high confidence for modelling further cases. Finally, 3D CFD model was developed to predict the transient behaviour of a latent heat thermal energy storage system (LHTESS) in the form of a rectangular container with a central horizontal pipe surrounded by paraffin as PCM (melting temperature is 60 oC). Water was used as a heat transfer fluid (HTF). The enhancement of heat transfer in specific geometries by using external longitudinal fins on the tube and metallic porous matrix were numerically investigated. The influence of the number of fins and porosity of the matrix on the temperature distribution, melting process, melting time and natural convection phenomena were studied. Dimensionless heat transfer correlations were derived for calculation of the Nusselt number as function of Fourier, Stefan and Rayleigh numbers. These correlations to be used in the further designing process of similar thermal storage units at Northumbria University.

This research is in the field of CFD modelling of heat engines, particularly the advanced CFD methodologies for the performance characterization of solar Stirling Engines with complex geometrical topologies. The research aims to investigate whether these methods can provide a more inclusive picture of the engine performance and how this information can be used for the design improvement of Stirling engines and the investigation of more complex engine topologies.

This research is in the area of Thermal Energy Conversion, more specifically, in the conversion of solar thermal energy. This form of renewable energy can be utilised for production of power by using thermo-mechanical conversion systems – Stirling engines. The advantage of such the systems is in their capability to work on low and high temperature differences which is created by the concentrated solar radiation. To design and build efficient, high performance engines in a feasible period of time it is necessary to develop advanced mathematical models based on thermodynamic analysis which accurately describe heat and mass transfer processes taking place inside machines. The aim of this work was to develop such models, evaluate their accuracy by calibrating them against published and available experimental data and against more advanced three-dimensional Computational Fluid Dynamics models. The refined mathematical models then were coupled to Genetic Algorithm optimisation codes to find a rational set of engine’s design parameters which would ensure the high performance of machines. The validation of the developed Stirling engine models demonstrated that there was a good agreement between numerical results and published experimental data. The new set of design parameters of the engine obtained from the optimisation procedure provides further enhancement of the engine performance. The mathematical modelling and design approaches developed in this study with the use of optimization procedures can be successfully applied in practice for creation of more efficient and advanced Stirling engines for power production.