Inhaltszusammenfassung

The ability to remove heat through the thickness of a composite has many possible applications. Leading edges in supersonic aircraft wings, inlet or exhaust areas of gas turbine engines, light weight heat exchangers, electronics packaging materials, hydraulic pump enclosures, and electro-magnetic interference (EMI) enclosures all are subject to localized thermal loads which would preferably be spread out over adjacent cooler areas for subsequent radiation/convection. One common approach, nam...The ability to remove heat through the thickness of a composite has many possible applications. Leading edges in supersonic aircraft wings, inlet or exhaust areas of gas turbine engines, light weight heat exchangers, electronics packaging materials, hydraulic pump enclosures, and electro-magnetic interference (EMI) enclosures all are subject to localized thermal loads which would preferably be spread out over adjacent cooler areas for subsequent radiation/convection. One common approach, namely loading the resin with thermally conductive particles, can increase the conductivity only insignificantly. One alternative approach of achieving significant increase in the through-thickness thermal conductivity is to manufacture composites based on 3-D woven fiber architectures where the through-thickness fibers have high thermal conductivities. Thermal conductivity measurements were performed of three-dimensionally reinforced composite samples. These tests resulted in a drastic difference between expected and measured data. One explanation of these results involves the existence of discrete thermally high conductive heat flux entry ports in the composite samples under investigation. Thus, the thermal conductivity of a 3-D composite material has to be considered as a system property and not a material property due to the heat flux distribution capability of the materials connected. Furthermore, the distances between these ports define the ability of the composite system to homogenize the heat flux and can be expressed by the distance between fibers derived via fiber diameter. The development of a purely analytical thermal conduction model seems to very difficult if not impossible due to the two-dimensional nature of heat flux. However, the introduction of two factors to the simple rule mixture based on a parallel thermal connection model by taking into account fiber spacing and adjoining material led to reasonably accurate model predictions for the samples tested. In addition, this investigation showed that with a z-fiber volume content of about 6 % the maximum possible out-of-plane thermal conductivity can be increased by a factor of eight. This opens the possibility to design composite parts in terms of heat transfer having the thermal conductivity as design aspect to varied by fiber architecture and thus to seen equal to mechanical design criteria such as Young?s modulus or strength. » weiterlesen» einklappen

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DDC Sachgruppe:
Ingenieurwissenschaften