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.

This application is for collaborative research on an area of cooling of great industrial and social significance by three teams with expertise in heat transfer, system simulation and component design. The lead team will be based at Newcastle University with the support teams at Oxford and South Bank UniversitiesIf the performance of electronic chips follow current trends and double every 18 months (Moore's Law), then it will soon not be possible to effectively cool them using conventional passive cooling and an alternative technique/devices must be found. This proposal is concerned with developing such a device. In particular it is concerned with a theoretical analysis and experimental evaluation of a miniature vapour compression refrigeration cycle optimised for the cooling of future electronic systems. The proposed work will consist of three distinct but interrelated activities that will be conducted at three centres by personnel with recognised skills, expertise, resources and experience to undertake this work. The proposed work is innovative in that it will examine issues associated with miniature refrigeration systems that have not been studied hitherto. It is intended to explore design criteria related to system stability and develop design codes to assist designers and manufacturers of such systems. The heat transfer performance of phase change in porous materials and the technology transfer associated with the compressor development all contribute to making this a very innovative project. The groups already have experience of working together and arrangements will be put in place to facilitate the exchange of ideas and expertise on a larger scale. The integrated approach will provide significant advantages compared to three unlinked projects and produce a significant step forward in electronic cooling technology. The work will be supported by several industrial partners and collaborators namely Thermacore, Panasonic and Honeywell who will all contribute technical and in kind resources to the project. Letters of support have been obtained from Panasonic, Thermacore, Honeywell-Hymatic and Hexag.

This application is for collaborative research on an area of cooling of great industrial and social significance by three teams with expertise in heat transfer, system simulation and component design. The lead team will be based at Newcastle University with the support teams at Oxford and South Bank UniversitiesIf the performance of electronic chips follow current trends and double every 18 months (Moore's Law), then it will soon not be possible to effectively cool them using conventional passive cooling and an alternative technique/devices must be found. This proposal is concerned with developing such a device. In particular it is concerned with a theoretical analysis and experimental evaluation of a miniature vapour compression refrigeration cycle optimised for the cooling of future electronic systems. The proposed work will consist of three distinct but interrelated activities that will be conducted at three centres by personnel with recognised skills, expertise, resources and experience to undertake this work. The proposed work is innovative in that it will examine issues associated with miniature refrigeration systems that have not been studied hitherto. It is intended to explore design criteria related to system stability and develop design codes to assist designers and manufacturers of such systems. The heat transfer performance of phase change in porous materials and the technology transfer associated with the compressor development all contribute to making this a very innovative project. The groups already have experience of working together and arrangements will be put in place to facilitate the exchange of ideas and expertise on a larger scale. The integrated approach will provide significant advantages compared to three unlinked projects and produce a significant step forward in electronic cooling technology. The work will be supported by several industrial partners and collaborators namely Thermacore, Panasonic and Honeywell who will all contribute technical and in kind resources to the project. Letters of support have been obtained from Panasonic, Thermacore, Honeywell-Hymatic and Hexag.

The proposed research will examine the use of heat pipes for effective thermoelectric heat pumping. The research will develop a themodynamic computer model for heat and mass transfer analysis of revolving heat pipes and thermoelectric devices. The work will investigate a novel, domestic-sized, mechanical-ventilation, heat pump system, using thermoelectric modules and revolving devices which act as both heat pipes and air impellers. The dual function of the revolving devices minimises the number of components, and size of the system. Rotation of the devices enhances heat transfer, both within the heat pipes and externally between the air and the finning. Owing to their rotation, the accumulation of dirt on the pipe surfaces will be small and so reduce the need for cleaning. The research will investigate the use of different types of thermoelectric devices, including novel thin-film thermoelectric materials that can offer high performance heat pumping. Passing electricity across a thermoelectric device produces a temperature gradient. Heat can thus be pumped from one side to another making them essentially solid state heat pumps. The revolving heat pipes will be used to transfer heat to and from the hot and cold sides of the thermoelectric devices. Thermoelectric devices have the advantage of no noise or vibration as they have no mechanical moving parts. Furthermore, they are compact light weight, highly reliable and inexpensive. The system will also be environmentally-friendly as CFC refrigerants are not required.

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.