Composite structural housing with integrated thermal management

As modern rotorcraft design shifts away from conventional power and towards more electrical systems, the need for efficient thermal regulation has never been higher. Systems are currently in place to combat this in rotorcraft but they would benefit from higher integration and optimisation. The key to achieving this may lie in further utilisation of materials that are already commonplace in the aerospace industry; composites. Composite materials, namely carbon and glass fibre reinforced composites (CFRPs/GFRPs) have widespread applications in modern aircraft and can comprise as much as 40-50% of structural components. The prevalence of composite materials is mainly due to their high strength-weight ratio and stiffness tailoring ability. They are however limited in temperature critical areas due to their poor thermal performance. This means they are generally unsuitable for structural applications around components that require a large amount of heat removal. However, if the thermal performance of these composite materials could be improved without compromising the mechanical properties of the material itself, the benefits would be numerous.

This project aims to investigate ways to improve the thermal characteristics of composite materials in ways that would aid the removal of heat from temperature critical components. There are currently a few novel concepts that can do this on a small scale, but current literature and research into the area is scarce. This likely means a new technique, or a combination of techniques would have to be used to achieve this. There are two types of techniques that could be used; passive and active cooling. A passively cooled system would employ microstructural or geometric features and take advantage of the surrounding environment to promote heat dissipation without the need for energy consumption. Microstructurally, this may include thermally conductive additives into the composite matrix or improved crystallinity within the matrix. Geometrically, this may involve ventilation features that take advantage of the surrounding conditions and the airspeed produced by the rotors. Possibly the most promising concept however would be to improve thermal conductivity in the through-thickness direction of the composite using z-pinning for tufting (stitching). This would create thermally conductive pathways within the structure with more conductive materials such as carbon or metals. These two techniques already have uses from a mechanical performance perspective, but their thermal effects have not been investigated in research. Preliminary experiments have already been carried out to investigate z-pinning as part of this project, with promising initial results.

An actively cooled system would require some means of energy consumption in order to remove heat from the system. This would most easily be done by pumping a cooling fluid around the surface of the structure. Some similar systems exist in the modern rotorcraft but integration into composite structures is very complex. Channels can however be embedded within the composite to create a 'vascular network' through which coolant can be pumped. Based on the limited literature, this technique offers the most potential to achieve the cooling effect required, and will form the bulk of the experimental work of this project. The size, configuration, and fabrication method of the channels are all factors that need to be investigated further, as well as choice of coolant and flow velocity. These variables will create a strong starting point for research.

The project will use a two pronged approach to evaluate both passive and active systems experimentally, before identifying the concept with the highest potential. This concept will then be evaluated in more detail and with a specific application in mind, in the hopes of raising the TRL level and furthering the research for future projects.

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.