The main goal of this project is the design of innovative and efficient air cooled heat sinks to cool the power electronics modules that are a key component of the more electrical aircraft power management centre design. The new design is expected to be developed in two stages. The first one should be covered by the implementation of Annealed Pyrolytic Graphite (APG) and folded brazed fins, while in the second the integration of Metal Matrix Composites (MMC) is expected. The final target of the development is the reduction of weight of the whole power management system (bay integrating four heat sinks), while maintaining an efficient and reliable cooling. Coming from advances in the power semiconductors field, by the use of high-temperature and more efficient materials such as Silicon Carbide (SiC) and Gallium Nitride (GAN), the thermal management strategy could take into consideration the implementation of air cooled solutions, which are expected to reduce the overall weight comparing to liquid or two-phase flow solutions, while also adding some benefits in terms of reliability and maintenance aspects.

Thermal management has become a critical issue in electronics because of increasing volumetric power densities and the harsh environments in which they are deployed. Active cooling is often required for high rates of heat dissipation because conventional passive cooling techniques are inadequate. Porous metal has been demonstrated to be highly efficient and cost effective in heat dissipation by forced fluid cooling. A main problem impeding its wider application is the high pumping power required to move the working fluid through the cooling device due to its large resistance to fluid flow. This project sets out to address the scientific and technical issues in thermal applications of porous metals manufactured by the space holder methods, which have distinctive porous structure and unique heat transfer behaviour. The aims of the research are to understand the mechanistic relationships between flow resistance, heat transfer and pore structure and to develop technologies to create tailored porous metal structures for significantly enhanced heat transfer performance with minimised flow resistance. A combination of manufacturing, properties characterisation, modelling and process development will be carried out to identify the fundamental structural properties underpinning the thermal fluid behaviour in porous metals, to quantify their effects on heat transfer coefficient and fluid flow resistance, and to design and create heterogeneous porous structures for a step change in overall active cooling performance. The global market for thermal management products is more than $10 billion with an annual growth rate of 6.8%. UK has a significant share in this market and is one of the leaders in developing new materials and technologies for active cooling devices for electronics. This project will provide scientific understanding and technical development underpinning the design and manufacture of a promising class of porous metals that are currently being developed by industry for thermal management applications. This research will ensure that UK maintains the leading position in this niche field. This research will also benefit the research and development of non-thermal porous products for environmental and energy applications, e.g., sound absorbers, porous electrodes and catalyst supports, where flow resistance has a deterministic effect.

This proposal is for a joint project between internationally-leading, UK heat transfer research groups at the Universities of Edinburgh, Brunel and Queen Mary, London in collaboration with four industrial partners (Thermacore, Oxford Nanosystems, Super Radiator Coils and Rainford Precision) in the areas of micro-fabrication and thermal management. Advances in manufacturing processes and subsequent use of smaller scale electronic devices operating at increased power densities have resulted in a critical demand for thermal management systems to provide intensive localised cooling. To prevent failure of electronic components, the temperature at which all parts of any electronic device operates must be carefully controlled. This can lead to heat removal rate requirements averaging at least 2 MW/m2 across the complete device, with peak rates of up to 10-15 MW/m2 at local 'hot spots'. Direct air cooling is limited to about 0.5 MW/m2 and liquid cooling systems are only capable of 0.7 MW/m2. Other techniques have not yet achieved heat fluxes above 1 MW/m2. Boiling in microchannels offers the best prospect of achieving such high heat fluxes with uniform surface temperature. In a closed system an equally compact and effective condenser is required for heat rejection to the environment. At high heat flux, evaporator dry-out poses a serious problem, leading to localised overheating of the surface and hence potentially to burn out of electronic components reliant on this evaporative cooling. Use of novel mixtures, termed 'self-rewetting fluids', whose surface tension properties lend themselves to improved wetting on hot surfaces, potentially offers scope for enhanced cooling technologies. In this project, two different aqueous alcohol solutions (one of which is self-rewetting) will be studied to ascertain whether they can provide the necessary evaporative and condensation characteristics required for a closed-loop cooling system capable of more than 2 MW/m2. Researchers at the University of Edinburgh will study the fundamentals of wetting and evaporation/condensation of the mixtures to establish the optimum mixture concentrations and heat transfer surface coating for both evaporation and condensation, using advanced imaging techniques. At Brunel University London, applications of the fluids in metallic single and multi microchannel evaporators will be investigated. Researchers at Queen Mary University London will carry out experimental and theoretical work on condensation of the mixtures in compact exchangers. The combined results will feed into the design of a complete microscale closed-loop evaporative cooling system. Thermacore will provide micro-scale heat exchangers and Oxford Nanosystems will provide structured surface coatings. Sustainable Engine Systems, Super Radiator Coils and will provide advice and represent additional ways of taking developments originating from this research to the market. Rainford Precision will provide Brunel University micro tools and support on their use in micromachining.

Current developments and future trends in small-scale devices used in a variety of industries such as electronic equipment and micro-process and refrigeration systems, place an increasing demand for removing higher thermal loads from small areas. In some cases further developments are simply not possible unless the problem of providing adequate cooling is resolved. The progression from air to liquid and specifically flow boiling to transfer the high heat fluxes generated is thus the only possible way forward. Evaporative cooling can, not only transfer these loads but also offer greater temperature uniformity since the working fluid can be (in a carefully designed system) at a constant saturation temperature. The consideration of microchannel flow boiling processes has been made possible by developments in microfabrication techniques both in metals and substances such as silicon. However, there still remain fundamental fluid flow and heat transfer related questions that need to be addressed before a wider use of these micro heat exchangers is possible in industry. The specific challenges that will be researched - both fundamental and practical in nature - include flow instabilities and mal-distribution which are the result of interaction between the system manifolds and the external circuit. These can lead to flow reversal and dry-out in the heat exchanger with subsequent drastic reduction in heat transfer rates. The understanding of the fundamental physical phenomena and their relevance to industrial designs is one of the focal points and constitutes one of the major challenges of the proposed research. The effect of other parameters such as inlet sub-cooling, which again relates not only to the micro-heat exchanger itself but also to the overall design, will be addressed along with material/surface characteristics through the use of both metallic and silicon microchannels. The work proposed will include carefully contacted detailed experiments measuring relevant parameters such as local heat flux, temperature and pressure combined with flow visualization through industrially available and purposely developed and manufactured sensors. The research teams will not only develop or adapt advanced instruments for accurate measurements at these small scales but also develop new three-dimensional numerical tools capable of capturing the extremely complex physical phenomena at, for example the triple-line (vapour-liquid-solid). These techniques will not only help elucidate the current phenomena but can find wide application in similar research, both in thermal and biomedical flows. The proposal brings together two teams of academics working both in microfabrication/sensors and two-phase flow supported by industry (Thermacore, Selex Galileo, Sustainable Engine Systems and Rainford Precision) to tackle some of the key fundamental challenges that will enable a wider adoption of this cooling method hence meeting current and future needs in the industry. The proposed research will also have a wider impact on energy conservation and environmental footprint trough, for example, more efficient thermal management of data/supercomputing centres around the world that can lead to a reduction in energy consumption and reuse of heat that would otherwise be rejected.

Rapid expansion of utilisation of solar thermal energy for increasing energy efficiency of buildings have been adopted in short/medium- and long-term Energy Strategies of EU countries in line with regional actions with the European climate energy objectives as defined in the European Union’s “20-20-20” targets and in the European Commission’s Energy Roadmap 2050. The overall objective of this project is to develop an innovative high performance and cost effective 2-kWel/18-kWth solar heat and power system for application in individual dwellings and small business residential buildings for on-site electricity and heat generation using solar thermal energy at temperature levels of 250-280 deg.C. The proposed technology will be laboratory validated and undergo filed tests on a demonstration site. The project will utilise the expertise of the consortium members in the development of small Organic Rankine Cycle plants, linear Fresnel mirror solar energy concentrating collectors; advanced heat pipe technologies for the thermal management; high performance Thermal Energy Storage systems on the basis of Phase Change Materials; smart control units for integration of solar thermal and boiler heating circuits. Also participants of this Project are experienced in integration of Renewable energy technologies into buildings, optimisation of complex plants and in analysis and predictions of socio-economic impact and in commercialisation of new Renewable energy products; It is estimated that the proposed technology will deliver 60% of domestic energy requirements and provide 20% reduction in energy costs and Green House Gas (GHG) emissions compared to the best existing low carbon energy technologies. In this way the project will also assist in improving the quality of life of population within and outside the EU and provide clean, efficient and secure energy to dwellings.