Our focus on applied research and the needs of industry is evidenced by the support we currently enjoy from such diverse interests as: Engineering and Physical Sciences Research Council (EPSRC), the Royal Society, the European Union (EU), EON, Heart of England Primary Care Trust, Middlemarch Environmental, BBT Thermo-Technology Ltd (Bosch Group), Severn Trent Water, Sky Farms Ltd, the Indian Institute of Technology, Delhi, the Royal Melbourne Institute of Technology and the University of Nis in Serbia. The following case studies give examples of the work we carry out together with some of these organisations.
Case studies
by G. Lychnos and P. Davies
This experimental project was based on early theoretical studies that showed that concentrated seawater could be used to dry and cool air. It could have a number of advantages over better known liquids used for this purpose, such as lithium chloride. For example, seawater is non-toxic and abundantly available.
If sunlight is used to concentrate the seawater, this provides the basis for a solar-driven cooling system. Engineers wishing to design and optimise such systems need to know the properties of the seawater at different concentrations. To provide this information, we collected seawater and evaporated the water to make concentrated samples. Other samples were prepared by mixing salts in the laboratory. We measured the vapour pressure, viscosity and density of the samples and showed that these properties can be predicted by equations published in the scientific literature within an accuracy of about 5%.
The main ingredient giving seawater its hygroscopic property is magnesium chloride. Our measurements showed that concentrated seawater, though it contains many other salts, has very similar properties to a solution containing only magnesium chloride. This means that we can use magnesium chloride solution in laboratory experiments aimed at testing and improving the different components of the cooling system, including the solar regenerator, where sunlight drives water out of the seawater, and the desiccator where the concentrated seawater removes moisture from the air.
An important application foreseen for this system is to cool greenhouses for growing food in the world’s hot coastal regions, where sunlight and seawater are readily available.
Acknowledgements to the Royal Society and the Greek State Scholarship Foundation.
by A. Clay and G. Tansley
With a small number of components and opportunity for continuous running, the use of a MGT is ideally positioned to marry both the engineering and commercial demands of DCHP. However, the benefits of implementing turbomachinery over conventional DCHP Stirling or Diesel engine technologies can be compromised when small, high speed components are considered. This research project investigates the feasibility of a 1kW MGT for DCHP.
Combined Heat and Power describes the simultaneous extraction of electrical and thermal power from the shaft and exhaust of a prime mover, to better utilise the fuels potential energy. To practically accommodate delivery/storage of both energy streams simultaneously, power demand must be local to the prime mover. Replacing end of life boilers with DCHP units is seen as one commercial route to achieve this. Work has shown that dwellings with high heating and hot water demands such as pre WW2, 3 bed, semi detached, family properties will provide the maximum emission and cost savings.
Significant aerodynamic difficulties have found to exist for MGTs to deliver DCHP performance requirements, whilst the need for low cost introduces additional challenges to the design specification. After extensive gas turbine cycle analysis, the recuperator and compressor were established as the critical components to achieve the specification requirements. Work on increasing efficiency and reducing the cost of each component respectfully is currently being undertaken. Codes to design, analyse, and construct geometry have been written for use alongside commercial CFD software Gambit/Fluent to provide an iterative centrifugal impellor design loop. Whilst novel, low cost micro heat exchanger recuperator solutions are also being explored in parallel.
Acknowledgements to the EPSRC and BBT Thermotechnology UK Ltd
by P. Knowles and P. Davies
STW have hundreds of constructed reed beds to give a final polish to
sewage effluents before they enter watercourses. These facilities use
the natural cleaning power of common reeds and microbiological
processes, to achieve the effluent standards set by the Environment
Agency. Described as the 'kidneys of the landscape', wetlands (which
include reed-bed treatment systems) pose exciting possibilities for the
future of low-energy wastewater treatment. However, there are still
plenty of questions regarding the optimal operation of these
facilities, making this a hot-bed of current scientific research.
Though Severn Trent have improved the design over
the years, maintenance costs are still significant. Every 7 to 10
years, each reedbed has to be refurbished and this involves taking all
the gravel out and either replacing it, or increasingly, cleaning it
and putting it back again. The CASE award student from Aston's
Sustainable Environment Research Group is investigating how the fluid
hydraulics within reed beds deteriorate over time. The exact mechanism
by which the reed beds become clogged is of great interest to Severn
Trent and the rest of the research community alike:
"If we can model exactly what's happening, we
might be able to suggest ways of attenuating the clogging process. This
would increase the longevity of the facilities, entailing lower
maintenance costs and achieving a more sustainable technology overall."
Paul Griffin, Sludge Process Advisor at STW
Up until now a multitude of in-situ experiments
have been performed at several of STW's rural treatment works. It is
hoped that a more robust solution would allow eco-friendly wastewater
treatment systems to be effectively transferred to other parts of the
globe. Needless to say, the implications of this for population giants
such as China and India would be notable.
The project is being jointly funded by the
Engineering and Physical Science Research Council and Severn Trent
Water through a CASE studentship which fosters collaboration between
industry and academia.
Acknowledgements to Severn Trent Water. Edited by Emily Wakefield.
by P. Davies and P. Singh
The Sustainable Environment Research Group works with partner institutions in India to develop new ways of providing electricity and energy services in rural areas. Recently the Group hosted Prashant Pratap Singh, a student from the newly formed Indian Institute of Technology in Ropar, to undertake a summer internship at Aston. Singh is studying a number of thermodynamic cycles for solar energy conversion - including the organic Rankine cycle. He compared them to the ideal Carnot cycle which represents the best achievable efficiency of any heat engine. A novel thermodynamic cycle has been proposed which combines the advantages of the Rankine cycle and the less common Stirling cycle. The Rankine cycle requires only minimal work for the feed pump whereas the Stirling cycle achieves high efficiency. The new cycle has both these features and Singh’s calculations confirm that it is capable of achieving an efficiency close to that of Carnot.
The key to this high performance is the isothermal expansion of the working fluid. The fluid is introduced as a liquid into the cylinder of the engine, where it vaporises under the influence of sunlight focussed into the interior of the cylinder through a small window. As the vapour expands and does work against a moving piston, its temperature is maintained by the continuous addition of solar energy. The study is considering working fluids that have strong absorption in the solar spectrum. It is planned to construct a prototype later this year.
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