Mechanical alloying by high energy ball milling is an attractive solid -state technique for synthesizing a diverse range of equilibrium and non-equilibrium phase materials. We have studied the synthesis of n -type thermoelectric Mg 2 Si 0.4 Sn 0.6 solid solution, aiming for a fundamental understanding of the mechanisms underlying this synthesis technique. The investigations on powders by XRD and SEM show that milling leads to welding of Mg and Sn but fracturing of Si. This fractured Si diffuses into the ductile matrix on longer milling times resulting in a phase mixture close to the nominal starting composition after 35h of milling. However, single phase pure material was only achievable after sintering, hence the synthesis of Mg 2 (Si,Sn) is a two -step process. Furthermore, a thorough study on the effect of varying synthesis parameters on the thermoelectric properties was performed. No strong influence of milling time on the thermoelectric properties was observed and just 2h of milling followed by compaction was sufficient to obtain a pellet with optimal thermoelectric properties. Moreover, increasing sinter temperature/time deteriorated carrier concentration hence degrading the electronic properties. Thus, optimized thermoelectric properties were obtained for the powder consolidated at 973K/20minutes. Mg 2 Si 0.4 Sn 0.6 synthesized by mechanical alloying achieved a thermoelectric figure of merit zT max~1 .4.

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This paper faces the problem of geometric optimisation for fins profile on tube of heat exchanger. In particular the tubes are being analysed under different conditions. The analysis is being performed on a single tube by mounting helical fines on it of different height and pitch within constant thickness. The methodological approach here is chosen as CFD software. The result are optimized by comparing the result after analysis.

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