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In this paper, a numerical investigation of the thermal performance of a heat exchanger designed for aero engine applications is performed with the use of computational fluid dynamics (CFD). For this purpose, the exact geometry of the heat exchanger was modeled, and additionally the use of a porous medium methodology was adopted. For the latter the behaviour of the heat exchanger was described by experimentally derived pressure drop and heat transfer laws. The heat transfer performance of the heat exchanger can be described by the Nusselt number of the flow and the temperature distribution inside the heat exchanger. At the present work the CFD results regarding the overall and local Nusselt numbers and the temperature distributions were compared to available experimental data and were found to be in agreement. Thus, both approaches could be used for the detailed investigation of the thermal performance of the heat exchanger so that useful conclusions could be derived.

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Open-cell nickel foams with 92% porosity and uniform pore size and distribution were used in this study. The main objective of this work was to evaluate the behaviour of Ni-foam, when treated as volumetric receivers under concentrated solar radiation while improving their oxidation resistance, in order to make them attractive for such applications. The experimental investigation showed that their efficiency was depending on both materials parameters and flow conditions, the latter affecting the pressure drop and the heat transfer behaviour. The microstructural characterisation of oxide surface morphologies formed on the open-cell Ni foams exposed to concentrated solar radiation is investigated by the use of SEM and EDXS. SEM observations revealed a rapid homogeneous oxidation in the Ni-foam with three different surface oxide structures formed in relation with the process temperature. A novel slurry-based process for aluminising nickel foams while retaining their geometrical properties is applied in order to develop an aluminide-nickel intermetallic coating on a Ni foam thus enhancing the oxidation resistance. Scanning electron microscopy and X-ray diffraction were applied to assess the effectiveness of the aluminising process and determine the optimum parameters of the procedure (slurry composition, holding temperature and time).