Optimisation of metallic fibre arrays for heat exchange applications

Networks of bonded metallic fibres represent an attractive candidate material for use in heat exchanger cores since they can offer a combination of high permeability, high specific surface area and high thermal conductivity. In addition, by varying fibre dimensions and processing conditions, the porosity and scale of fibrous materials can be varied over a wide range. This work concerns the determination of the optimal structure of fibrous material for use in heat exchange cores. The permeability and orientation dependent thermal conductivity of fibrous materials manufactured from copper and 446 steel are experimentally measured. The dependence of permeability on fibre volume fraction is described using the Carman Kozeny equation. An analytical model is proposed to describe thermal conductivity in short fibre porous materials, taking the effect of fibre orientation and fibre-fibre contact area into account. An analytical model for heat exchange in the steady state is proposed, and validated by comparison with experiment. Consideration is given to the effect of material and system parameters on heat exchange rate. A method is described for optimising material structure for a given application by linking the heat exchange model to both the amount of energy required to drive fluid flow, and the velocity dependent output which characterises many pumping systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo