Sintered metal fiber structures from aluminum based fibers-manufacturing and properties

Highly porous sintered metal fiber structures have been prepared from melt extracted aluminum base alloy fibers. To this end, a liquid phase sintering approach was developed. Thermodynamic calculations were used to identify suitable amounts of alloying elements and optimum sintering conditions. In this paper, the manufacturing process is described and heat transfer properties are reported for air-flow through a sintered aluminum fiber core sandwich. S The measurements can be compared with the well known analytical results for the friction coefficient (X = 64/Re) and heat transfer (Nu = f(Re,Pr)) for an unfilled duct of equal dimensions. This comparison shows that the pressure drop of the fiber filled duct is approximately 25,000 times larger than that of the empty duct whereas the heat transfer is increased by a factor of only 7 to 14 as compared to the empty duct. These results have to be interpreted very carefully as in all measurements the outlet temperature was very close to the heated wall temperature, indicating that for the given conditions the system is 'oversized'. This means that heat transfer from the walls to the fluid is better than required and the system could be optimized by a number of different measures such as - lowering the surface density by increasing the porosity and/or increasing the fiber diameter -lowering the absolute internal surface by minimizing the length of the duct. The results presented here are the first of a large measurement campaign intended to characterize the heat transfer behavior of sintered fiber structures made from short melt extracted fibers. Current work includes the characterization of aluminum and copper fiber core sandwiches of varying porosity and fiber orientation. Eventually, this work should lead to a semi-empirical description of the heat transfer behavior which could be used to tailor the fiber structure to the respective application.