Optimisation of ocean-powered turbines for seawater desalination

In this research, a novel conceptual desalination system was introduced which can be powered by Horizontal Axis Tidal (HAT) and Vertical Axis Tidal (VAT) turbines. Since in the proposed design, the most important part is the tidal turbine, the focus has been placed on optimisation of the turbines. The energy required for desalinating 1 m3/h was determined. Accordingly, a VAT turbine and a HAT turbine were separately designed to fulfil this amount of energy. The greatest weakness of these turbines is the high price of design, development, and manufacturing. Traditionally, optimisation of turbine geometry can be achieved by running several numerical models of the turbine which can become computationally expensive. In this work, a combination of the Taguchi method and CFD modelling was used as a straightforward solution for optimisation of geometry of tidal turbines. Although improving the hydrodynamic performance is a key objective in the design of ocean-powered turbines, some factors affect the efficiency of the device during its operation. In this study, the impacts of a wide range of surface roughness, as a tribological parameter, on stream flow around a hydro turbine and its power loss were studied. A comprehensive program of 3D Computational Fluid Dynamics (CFD) modelling, as well as an extensive range of experiments were carried out on a tidal turbine in order to measure reduction in hydrodynamic performance due to surface roughness. The results showed that surface roughness of turbine blades plays an important role in the hydrodynamics of the flow around the turbine. The surface roughness increases turbulence and decreases the active fluid energy that is required for rotating the turbine, thereby reducing the performance of the turbine. The geometry of the HAT turbine was optimised with combination of only 16 CFD simulations using the Taguchi method. The effects of blade size, number of blades, hub radius, and hub shape were studied and optimised. The results revealed that the most important parameters influencing the power output of HAT turbine are the number of blades, size of blade, hub radius, and hub shape. Moreover, the superposition model showed that the minimum signal-to-noise (S/N) ratio was 5% less than the amount achieved in the Taguchi approach. The power coefficient (Cp) of the optimised HAT turbine was 0.44 according to the results of CFD simulations, which was 10% higher than that of the baseline model (0.40) at tip speed ratio (TSR) of 5. The weight of the optimised model was less than the baseline model by 17%. Moreover, a number of CFD simulations were carried out using the mixed-level modified Taguchi technique to determine the optimal hydrodynamic performance of a VAT turbine. The effects of four parameters: twist angle, camber position, maximum camber, and chord/radius ratio were studied. The interaction of these parameters was investigated using the Variance of Analysis (ANOVA) approach. The Taguchi analysis showed that the most significant parameter affecting hydrodynamic performance of the turbine is the twist angle and the least effective parameter is chord/radius ratio. The ANOVA interaction analysis showed that the twist angle, camber position and maximum camber have significant interaction with each other. Moreover, the results showed that the power coefficient (Cp) for the optimised VAT turbine was improved by 26% compared to the baseline design. In addition, the flow separation in the optimised model was greatly reduced in comparison with the baseline model, signifying that the twisted and cambered blade could be effective in normalising the spraying vortices over blades due to suppressing dynamic-stall. The findings of this thesis can provide guidelines for optimisation of tidal turbines

Optimization of a Horizontal Axis Tidal (HAT) turbine for powering a Reverse Osmosis (RO) desalination system using Computational Fluid Dynamics (CFD) and Taguchi method

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordHorizontal Axis Tidal (HAT) turbines can be used to power RO (reverse osmosis) desalination systems. The greatest weakness of these turbines is the high price of design, development, and manufacturing. Traditionally, optimization of turbine geometry is achieved by running several numerical models of the turbine which can become time consuming and expensive. The Taguchi-CFD (Computational Fluid Dynamics) approach has recently been introduced as an inexpensive and rapid tool for optimizing industrial devices. This technique can be used as a straightforward solution for optimization of geometry of HAT turbines. In this work, a conceptual design of a tidal power reverse osmosis (TPRO) desalination unit was proposed. Subsequently, the geometry of the HAT turbine, which can power the whole desalination system, was optimized with combination of only 16 CFD simulations using the Taguchi method. The effects of blade size, number of blades, hub radius, and hub shape were studied and optimized. The Taguchi results revealed that the most important parameters influencing the power output of HAT turbine are the number of blades, size of blade, hub radius, and hub shape respectively. Moreover, the results of the superposition model showed that the minimum signal-to-noise ratio (SNR) is 21% less than the amount achieved in the Taguchi approach. The power coefficient (Cp) of the optimized HAT turbine was 0.44 according to the results of CFD simulations, which was 10% higher than that of the baseline model (0.40) at tip speed ratio (TSR) of 5. The weight of the optimized model was less than the baseline model by 17%. The results of this study provide a comprehensive guidance for horizontal turbine optimization process.College of Engineering, Mathematics and Physical Sciences of the University of Exete

Optimization of the hydrodynamic performance of a vertical Axis tidal (VAT) turbine using CFD-Taguchi approach

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordVertical Axis Tidal (VAT) turbines are used as ocean-powered devices to generate electricity from movements in ocean as a renewable source of energy. In this research, a number of CFD simulations have been carried out using the mixed-level modified Taguchi technique to determine the optimal hydrodynamic performance of a VAT turbine. The influence of four parameters: twist angle, camber position, maximum camber, and chord/radius ratio has been studied. The interaction of these parameters is investigated using the Variance of Analysis (ANOVA) approach. The Taguchi analysis showed that the most significant parameter affecting hydrodynamic performance of the turbine is the twist angle and the least effective parameter is chord/radius ratio. The ANOVA interaction analysis showed that the twist angle, camber position and maximum camber have significant interaction with each other. The results showed that the power coefficient (Cp) for the optimized VAT turbine is improved by 24% compared to the baseline design. Analysis of the pressure coefficient (Qp) indicates that the hydrodynamic performance of VAT turbine is sensitive to cambered blade. Moreover, the flow separation in the optimized model is greatly reduced in comparison with the baseline model, signifying that the twisted and cambered blade could be effective in normalizing the spraying vortices over blades due to suppressing dynamic-stall. The findings of this research can provide guidelines for optimization of vertical turbines.University of Exete

Experimental and CFD analysis of impact of surface roughness on hydrodynamic performance of a Darrieus Hydro (DH) turbine

This is the final version. Available from the publisher via the DOI in this record.Although improving the hydrodynamic performance is a key objective in the design of ocean-powered devices, there are some factors that affect the efficiency of the device during its operation. In this study, the impacts of a wide range of surface roughness as a tribological parameter on stream flow around a hydro turbine and its power loss are studied. A comprehensive program of 3D Computational Fluid Dynamics (CFD) modeling, as well as an expansive range of experiments were carried out on a Darrieus Hydro (DH) turbine in order to measure reduction in hydrodynamic performance due to surface roughness. The results show that surface roughness of turbine blades plays an important role in the hydrodynamics of the flow around the turbine. The surface roughness increases turbulence and decreases the active fluid energy that is required for rotating the turbine, thereby reducing the performance of the turbine. The extent of the negative impact of surface roughness on the drag coefficient, pressure coefficient, torque, and output power is evaluated. It is shown that the drag coefficient of a turbine with roughness height of 1000 μm is about 20% higher than a smooth blade (zero roughness height) and the maximum percentage of reduction of output power could be up to 27% (numerically) and 22% (experimentally).</jats:p

CFD analyses of a tidal hydro-turbine (THT) for utilising in sea water desalination

This is the author accepted manuscript. The final version is available from ISERThis work presents a modified concept of a tidal hydro-turbine (THT) used in desalination of sea water. THT can be used for the entire desalination process to derive energy from the intake of feed water, pre-treatment and producing required pressure for the system. The turbines extract energy from the tidal movement and run the water pump in order to provide the hydraulic pressure of the desalination unit. The performance of the turbine was assessed and its graphs were plotted using Computational Fluid Dynamics (CFD) modelling. Index terms: Tidal hydro-turbine, CFD, desalination, ANSYS FLUENT, Wave power

An investigation of a Ɣ-type MTD Stirling engine prototype

This is the author accepted manuscript. The final version is available from UKACM via the link in this recordAlthough thermal efficiency of moderate temperature differential (MTD) Stirling engines is higher than low temperature (LTD) engines, the complexity of design of MTD engines has led to the lack of research in this field. In this work, a prototype of Ɣ-type moderate-temperature differential Stirling engine was manufactured, evaluated and structurally optimised. A mathematical evaluation was carried out based on a finite-dimension thermodynamics approach. The swept volume ratio was optimised based on the temperature difference of 450 . 0 . A computer program was thus written to simulate the Stirling engine performance under the assumed working conditions. Based on the mentioned temperature difference, the swept volume ratio of the engine was found to be 3. The engine dimensions were then adjusted to fulfil the computed swept volume ratio. The bore and stroke for power piston were chosen as 60 mm and 40 mm, respectively. For the displacer, they were selected as 90 mm and 60 mm, respectively based on the chosen swept volume ratio

Optimisation of a conceptual aircraft model using a genetic algorithm and 3D Computational Fluid Dynamics (CFD)

This is the author accepted manuscript. The final version is available from UKACM via the link in this recordAircraft design is fundamentally a multidisciplinary design activity which involves different models and tools for various aspects of the design. This paper uses a Multidisciplinary Design Optimisation (MDO) for design of a simplified commercial aircraft, aiming to optimise the objectives of cost, weight and drag. NSGA-II is used to optimise the weight and cost by changing the geometry to introduce lightweight airframe materials and composites with lower density. Reducing weight of the structure is one of the major ways to improve the performance of aircraft. Lighter, stronger material will allow a higher speed and greater range which may contribute to reducing operational costs. Drag reduction is also a major factor in aircraft design. Reduction of drag in an aircraft means that it can have a lower fuel consumption or travel at higher speed, both of which are beneficial to plane performance. A smart structural optimisation algorithm helps to optimise the cost, weight and drag, while drag is analysed based on CFD modelling results. The results are validated against some wind tunnel tests

Experimental analysis and characterization of high-purity aluminum nanoparticles (Al-Nps) by electromagnetic levitation gas condensation (ELGC)

This is the final version. Available on open access from MDPI via the DOI in this recordThe production of high-purity aluminum nanoparticles (Al-NPs) is challenging due to the highly reactive nature of Al metals. Electromagnetic levitation gas condensation (ELGC) is a promising method to produce high-purity metallic particles as it avoids the interaction between molten metal and refractory-lined, which guarantees the removal of impurities such as oxygen (O). In this research, high-purity Al-NPs were successfully fabricated via ELGC process and fully characterized. The effects of power input and gas flow rate on particle size and distribution were analyzed using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and dynamic light scattering (DLS). The results showed that the Al-NPs have spherical morphologies with an average diameter of 17 nm and size distribution of NPs is narrow under helium (He) flow rate of 15 L/min at a constant temperature of 1683 ± 10 K. The purity of the NPs was confirmed by utilizing X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), and X-ray fluorescence (XRF). Finally, metal purity of 99.976% and 99.97% was measured by AAS and XRF analyses, respectively. Moreover, it was found that increasing gas flow rate and sample temperature results in a decrease in the particle size. The particle sizes for the Al-NPs obtained under He atmosphere were smaller than those obtained under Ar atmosphere

Analysis of the thermal efficiency of a compound parabolic Integrated Collector Storage solar water heater in Kerman, Iran

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThis paper presents an experimental study involving the design, manufacturing and testing of a prototype integrated collector storage (ICS) solar water heater (SWH) in combination with a compound parabolic concentrator (CPC). The thermal efficiency of the developed system is evaluated in Kerman (latitude 30.2907°N, longitude 57.0679°E), Iran. The developed system is intended to supply hot water for a family in remote rural areas. A 6-month experimental study was undertaken to investigate the performance of the ICS SWH system. The mean daily efficiency and overnight thermal loss coefficient of each experiment were analyzed to examine the appropriateness of these collectors for regions in Kerman. The results showed that mirror has the highest mean daily efficiency (66.7%), followed by steel sheet (47.6%) and aluminum foil (43.7%). The analysis of hourly and monthly operation diagrams for variations of water temperature for the developed ICS system showed that by increasing the amount of radiation entering the water heater, the thermal efficiency of the system decreases, such that the highest efficiency was in April and the lowest in July. With the distribution of radiation intensity in the months of August and September, the thermal efficiency of the system increased. This regional study illustrates how selecting a proper concentrator can increase the thermal efficiency of this solar-based system. It also shows how the temperature gradient between the ambient air and internal water in the storage tank can influence the performance of such systems, and how a controlled amount of hot water withdrawal can affect the system’s efficiency. Developing the ICSSWH system is an ideal sustainable solution in countries that benefit from a large amount of solar intensit

Investigating of the thermal performance of utilised materials for an Integrated Collector Storage Solar Water Heater

This is the author accepted manuscript. The final version is available from ISERExperiments are developed to investigate the performance of utilised materials for an environmental-friendly integrated collector storage (ICS) prototype as a solar water heater (SWH). The types of material of collectors have been investigated rigorously in order to obtain a real-dimensional curve of the deployed concentrator in the system. The parabola coordinates were found based on the observed variations of involute concentrator’s angle (ψ) and Parabolic concentrator’s angle (ω). The mean daily efficiency and the overnight thermal losses coefficient of mirror booster, steel sheet, and aluminum foil were calculated. The results are presented in the graphs