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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Development and optimization of heat pipe based compound parabolic collector

Abdullahi, Bala January 2015 (has links)
Compound Parabolic Collector (CPC) has numerous advantages such as high optical efficiency and wide applications. This thesis describes experimental and theoretical investigations of the effects of solar radiation available, design and orientation on different configurations of low concentration CPCs for Kano, Nigeria. Two solar radiation models were developed for characterizing solar radiation for regions in the northern hemisphere like Kano. Results showed that tilting the collector to the monthly optimum angle gives the maximum radiation obtainable in each month with highest increase of 28.6 and 24.8% in December and January respectively. For seasonal tilt; the best angles were 27.05° (October to March) and 0° (April to September) while for fixed collector, tilting at 12.05° (latitude) provides the highest performance. Using advanced ray tracing technique, detailed investigations of the effects of acceptance angle, receiver radius, truncation, etc. were carried out on the CPC performance. While with the truncation of 70%, results showed that compound parabolic collector can achieve daily average optical efficiencies of 86.2% and 75.4% for acceptance angles of 60° and 40° respectively. The performance of the thermosyphon (receiver) was investigated both experimentally and numerically. Using an in house solar simulator developed in this work, the performance of the developed CPC fitted with thermosyphon was experimentally investigated. Results showed that the CPC can function well with thermosyphon inclination angle up to 40° where it gives efficiency between 76% and 66%. The outcome of this work shows the potential of using this developed system in Kano environment for cooling applications.
22

Solar absorption cycle for cooling/refrigeration

Al Juma, Marwan January 2014 (has links)
The purpose of this thesis is to critically highlight the development of solar absorption refrigeration technologies through time. The factors that have prompted the urgent need to reconsider this area of engineering will also be analyzed in depth. The relevant research in the area of solar absorption to date will be shown with specific emphasis on its contribution to industrial and domestic cooling systems. The Middle East may be awash with oil in the present circumstances with 48% of the known oil reserves in the world but challenges exist owing to fossil fuel being a finite resource and its exploitation fraught with environmental problems. Therefore developing solar cooling systems appears to be an essential and inevitable requisite for harnessing solar energy in order to make a lasting contribution to the development of the region, as well as the world Targeting the coefficient of performance (COP) of the solar absorption refrigeration systems was considered to be the fundamental part of this research. By investigating the absorber chamber in an absorption refrigeration system, it was found that enhancing the quality of the spray of the absorber fluid could raise the COP. Using a Phase Doppler Anemometry (PDA), a detailed analysis of the spray characteristics was achievable; this helped in targeting parameters which will have influence on the spray characteristics. These include the nozzle geometry, for instance, the size of orifice, as well as the internal forces of the liquid such as viscosity and surface tension. Operating parameters were also considered to influence the spray quality. The main operating parameter is to create a partial vacuum to simulate the absorber chamber working condition. Results revealed that high viscosity of the fluid and the vacuum had negative effects towards spray quality. But when combining these with a surfactant such as 2-ethyl-1-hexanol, the spray quality increases in terms of droplet diameter, which in turn decreases and thereby causes an increase in the surface area to volume ratio, resulting in the enhancement of COP.
23

Photo-electrochemical processes at the triple phase boundary

Collins, Andrew January 2012 (has links)
The main aim and ultimate final goal of the work carried out in this thesis is a drive towards a feasible system for light harvesting, which is in short, using the Sun’s energy to create electricity or a fuel for our energy requirements here on Earth. This work will see an approach using the triple phase boundary afforded by a microdroplet array. Although light harvesting is an ambition which has seen decades of work and uncountable man-hours, approaching it from the angle of utilizing the triple phase boundary between two immiscible liquids and a solid electrode is a new, and novel concept. Before any attempts towards a light harvesting technique can be made, we will need to have characterized and fully understood the mechanisms and nuances, both for dark and light processes, that are observed at the triple phase boundary. This initial process will start by selection of a suitable redox molecule, and exploring its reactivity in microdroplets under dark conditions. Once this has been achieved, an attempt can be made to use this knowledge, and implement it towards light harvesting. This will eventually include an attempt to couple photo-excited states with other molecules, this will be an important step if energy is ever able to be stored from such a system. This early phase will also see the need to employ many other techniques other than electrochemistry in an effort to aid in the understanding and characterization of the triple phase boundary at microdroplets. This will include travelling to other laboratories in search of specialized scientific skills and apparatus, such as electron paramagnetic resonance, or photocurrent spectroscopy. It will also see the need to build new equipment needed to conduct tests such as surface tension visualization, or new electrochemical cells for photocurrent measurement. In summary, this report will see initial characterization of the processes, both light and dark, that occur within the triple phase boundary of a microdroplet for a given redox molecule dissolved within. Early attempts at coupling excited states with other molecules are also explored. Serendipity has always played a part in scientific discovery and the work outlined in this report was no different. The choice of oil used for the organic phase microdroplet deposits yielded some interesting and unexpected results, and has been implicated as one of the key aspects of the photoreactions that have been explored.
24

Investigation of a compact unglazed solar thermal façade for building integration

Shen, Jingchun January 2017 (has links)
In order to achieve the global carbon emission reduction target, it is expected to become essential for higher fraction of locally available renewable energy sources in energy mix, other than significant reduction of fossil energy consumption. Solar energy is one of the most promising renewable sources locally with various building applications. In addition, the Solar Thermal Facade (STF) system demonstrates a real sense of building integration that can be a potential solution towards energy efficiency improvement and operational cost reduction in contemporary built environment. This thesis presents a comprehensive investigation into a novel com-pact unglazed STF system that possesses the advantages of compact structure, economical cost and high feasibility in architectural design. The entire study follows in the basic methodology of combined theoretical and experimental analysis, including procedures of critical literature reviews, optimal concept design, theoretical study, analytical model development, prototype system construction, laboratory-controlled evaluation, techno-economic feasibility analysis and a design strategy for its application. Under the baseline testing condition, the collector efficiency factor F’, heat removal factor FR and channel flow factor F’’ were respectively high up to 0.993, 0.992, and 0.985, leading to a relatively high thermal efficiency at about 63.21%, exhibiting a better thermal performance. And the maximum theoretical possible useful heat gain capacity (intercept FRαp) of such STF at the given operating conditions was about 96.20%. And the mean slope (FRUL) was as much as about -13.06, representing a sharp decreasing trend of this SFT’s thermal efficiency against the (Tin-Ta)/I complying with the feature of no glazing cover attached in the front. So in case of current design, such STF could match the applications of heating load for pool heating, domestic hot water and radiant space heating in those areas with warm air temperature and sufficient solar radiation. Moreover, the techno-economic feasibility study identified that the overall contributions of the STF application in a reference residential building consist of direct solar thermal generation, indirect HVAC load reduction and savings in operation cost. Additionally, the financial outputs from the dedicated business model in Shanghai stated that: the proposed STF system was a profitable investment project with positive overall revenue and acceptable payback period within 6 years; and three different investment schemes have individual advantages in terms of investment risk, payback period and financial output. Lastly, the BIM associated STF design strategy was raised for building performance research in architectural practice. It is ultimately about the evaluation of multiple STF alternatives against different design priorities and the associated STF design information sharing with others to reduce duplication, minimize errors, streamline processes and facilitate collaboration towards sustainable STF integration. The entire research is expected to configure a technical breakthrough in the subject for the widespread market penetration of the STF technology, a feasible solution for solar thermal technology in future building application, as well as an advanced multi-functional STF development. The research outcomes of this study will conduce to the promotion of such a building integrated solar thermal technology, enrich low-carbon building design strategy, and thus contribute to achieving the domestic and international targets for energy saving, renewable energy utilization, and carbon emission reduction in the building sector.
25

Design and modelling of a photovoltaic driven fan solar air heater for drying woodchip in Scotland

Clemente, Andres January 2011 (has links)
In the wood fuel supply chain, the water contained in the product determines one aspect of the quality of the wood. It is necessary to reduce the moisture content (MC) of the wood in order to reduce transport and storing costs and also to increase the heating value of the wood. In this thesis a solar thermal application has been developed to dry woodchips using exclusively solar energy. The novel solar woodchip dryer comprises a small woodchip dryer and a solar air thermal system (SATS) to increase the temperature of the drying air. The particularity of this woodchip dryer is that the input air flow is governed by a photovoltaic driven fan. Based on the experimental results obtained, the woodchip dryer and the SATS thermal performance were modelled and a simulation tool for predicting the dried woodchip production during a period of time has been developed. Two small capacity dryers, a thin and a thick layer dryer, have been designed and built to dry woodchip based on the flow capacity of the SATS. The drying performances are studied for both configurations comparing the drying times, drying rates and efficiencies at different test conditions. The drying curves obtained from each test are modelled as a function of key parameters, temperature and velocity employing the Page model equation. Based on the experimental results, a drying model has been successfully developed to predict the MC when the woodchip dryer operates within a range of drying conditions. A quantitative and qualitative analysis of the SATS thermal performance has been conducted employing various solar air collector configurations under Scottish weather conditions. The pneumatic characteristics of the solar dryer including the dryer are determining for the analysis of the system performance. Because of the PV driven fan electrical characteristics, the SATS presents a unique operation regime in which air flow depends exclusively on solar radiation. Thus the SATS thermal performance has been successfully modelled as a function of irradiance. The study necessarily includes the effect of environmental factors such as wind and cloudiness in the transient regime. The potential of using a solar woodchip dryer has been assessed based on the results obtained from modelling the dryer and the SATS together. The feasibility and employability of using the solar dryer for drying woodchips is discussed considering the productivity, the energy savings, costs and integration.
26

Solar thermal and photovoltaic electrical generation in Libya

Aldali, Yasser January 2012 (has links)
This thesis investigates the application of large scale concentrated solar (CSP) and photovoltaic power plants in Libya. Direct Steam Generation (DSG) offers a cheaper and less risky method of generating electricity using concentrated solar energy than Heat Transfer Fluid (HTF) plant. However, it is argued that the location of a DSG plant can be critical in realising these benefits, and that the South-East part of Libya is ideal in this respect. The models and calculations presented here are the result of an implementation of the 2007 revision of the IAPWS equations in a general application based on Microsoft Excel and VBA. The hypothetical design for 50MW DSG power plant discussed in this thesis is shown to yield an 76% reduction in greenhouse gas emissions compared to an equivalent gas-only plant over the ten-hour daily period of operation. Land requirement is modest at 0.7km2. A new method for improving the distribution of heat within the absorber tube wall was developed. Internal helical fins within the absorber tube have been proposed to provide a regularly pitched and orderly distribution of flow from the ‘hot' to the ‘cold' side of the absorber tube. Note that the irradiance profile on the absorber tube is highly asymmetric. A CFD simulation using FLUENT software was carried out for three types of pipes with different internal helical-fin pitch, and an aluminium pipe without fins. The results show that the thermal gradient between the upper and lower temperature for the pipe without a helical fin is considerably higher compared with the pipes with helical fins. Also, the thermal gradient between the two halves for the aluminium pipe (without a helical fin) is much lower when compared to the result for the traditional steel pipe (without a helical fin). A 50MW PV-grid connected (stationary and tracking) power plant design in Al-Kufra, Libya has been carried out presently. A hetero-junction with intrinsic thin layer (HIT) type PV module has been selected and modelled. The effectiveness of the use of a cooling jacket on the modules has been evaluated. A Microsoft Excel-VBA program has been constructed to compute slope radiation, dew-point, sky temperature, and then cell temperature, maximum power output and module efficiency for this system, with and without water cooling for stationary system and for tracking system without water cooling. The results for energy production show that the total energy output is 114GWh/year without a water cooling system, 119GWh/year with a water cooling system for stationary system and 148GWh/year for tracking system. The average module efficiency with and without a cooling system for the stationary system is 17.2% and 16.6% respectively and 16.2% for the tracking system. The electricity generation capacity factor (CF) and solar capacity factor (SCF) for stationary system were found to be 26% and 62.5% respectively and 34% and 82% for tracking system. The payback time for the proposed LS-PV power plant was found to be 2.75 years for the stationary system and 3.58 years for the tracking system. The modelling that was carried was based on the measurements conducted on the experimental system set in a city in the southern part of Turkey. Those measurements are recorded by a Turkish team at Iskanderun. As well as the current, voltage and cell temperature of the photovoltaic module, the environmental variables such as ambient temperature and solar irradiance were measured. These data were used for validation purposes. The correlation for the conversion of solar irradiation from horizontal to sloped surface indicated that the presently used model is highly successful reflected by the goodness of fit parameters: the coefficient of determination is 0.97, and the mean bias error -2.2W/m2. Similarly, the cell temperature model used in the present thesis is validated by the following correlation parameters R2 = 0.97 oC, while MBE is 0.7 and RMSE = 2.1 oC.
27

The development of object oriented Bayesian networks to evaluate the social, economic and environmental impacts of solar PV

Leicester, Philip A. January 2016 (has links)
Domestic and community low carbon technologies are widely heralded as valuable means for delivering sustainability outcomes in the form of social, economic and environmental (SEE) policy objectives. To accelerate their diffusion they have benefited from a significant number and variety of subsidies worldwide. Considerable aleatory and epistemic uncertainties exist, however, both with regard to their net energy contribution and their SEE impacts. Furthermore the socio-economic contexts themselves exhibit enormous variability, and commensurate uncertainties in their parameterisation. This represents a significant risk for policy makers and technology adopters. This work describes an approach to these problems using Bayesian Network models. These are utilised to integrate extant knowledge from a variety of disciplines to quantify SEE impacts and endogenise uncertainties. A large-scale Object Oriented Bayesian network has been developed to model the specific case of solar photovoltaics (PV) installed on UK domestic roofs. Three specific model components have been developed. The PV component characterises the yield of UK systems, the building energy component characterises the energy consumption of the dwellings and their occupants and a third component characterises the building stock in four English urban communities. Three representative SEE indicators, fuel affordability, carbon emission reduction and discounted cash flow are integrated and used to test the model s ability to yield meaningful outputs in response to varying inputs. The variability in the percentage of the three indicators is highly responsive to the dwellings built form, age and orientation, but is not just due to building and solar physics but also to socio-economic factors. The model can accept observations or evidence in order to create scenarios which facilitate deliberative decision making. The BN methodology contributes to the synthesis of new knowledge from extant knowledge located between disciplines . As well as insights into the impacts of high PV penetration, an epistemic contribution has been made to transdisciplinary building energy modelling which can be replicated with a variety of low carbon interventions.
28

Experimental measurement and mathematical modelling of meteorological parameters for solar energy applications

Al-Ayfari, Hadi H. K. January 1986 (has links)
A new meteorological research station has been established and set up in the Solar Energy Laboratory which measures solar radiation (total and diffuse) on a horizontal surface, ambient air temperature, wind speed and wind direction. An inexpensive data logger based on an APPLE II microcomputer was designed and built. This data logger was used for more than 21 months and provided processed data for transcribing onto a main frame computer. A microdata (M1600L) microprocessor based automatic data logger was used later for the continuous monitoring of measured parameters. Four years of monitored data were used for analysis. Two mathematical models have been developed for the estimation of both total and diffuse solar radiation on a horizontal surface from different meteorological parameters. Several mathematical models developed by others were used to relate solar radiation and meteorological parameters measured in Birmingham. The results of these were compared, analysed and the best six were identified. The best models were tested and evaluated with (a) Birmingham data, (b) data from nine different sites in Europe. The best results show that the Birmingham models give the best estimation for total and diffuse solar radiation. The work reported here forms part of a continuous project of the Solar Energy Laboratory in meteorological research applied to solar energy utilization.
29

Μελέτη θερμοσιφωνικού συστήματος επίπεδου συλλέκτη με χρήση του προγράμματος TRNSYS / Flat plate thermosyphonic unit's study with the simulation programme of TRNSYS

Ανδριοπούλου, Συμεώνη 08 February 2010 (has links)
Πειραματικη και υπολογιστική μελέτη θερμοσιφωνικού συστήματος επίπεδου συλλέκτη με χρήση του προγράμματος προσομοίωσης TRNSYS. / Experimental and computational study of a thermosyphonic unit system with the simulation programme of TRNSYS.
30

Compact solar thermal energy storage systems using phase change materials

Al-Maghalseh, Maher January 2014 (has links)
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.

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