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Bi2Te2.7Se0.3-based alloys are conventional n-type thermoelectric materials for solid-state cooling and heat harvest near room temperature; high thermoelectric performance over a wide temperature range and superior mechanical properties are essential for their use in practical thermoelectric devices. In this work, we demonstrated that decent thermoelectric performance can also be realized in an unconventional composite with a nominal composition of Bi2Te2.3Se0.7since the emergence of a Bi2Te2Se phase with Se ordered occupation could induce an enlargement of the electronic band gap. Follow-up Cu/Na codoping could generate a dynamic optimization of carrier concentration, significantly broadening the temperature range of high thermoelectric performance. Further B incorporation and annealing treatment resulted in obvious grain refinement and stacking fault structures, which help pushing the ultimate maximal figure of merit up to ∼1.3 at 423 K with an average value of ∼1.2 at 300–573 K. This work might provide insights for further research on bismuth tellurides and other thermoelectric materials.

This paper numerically studied supersonic film cooling performance in a convergent divergent nozzle, for the purpose of exploring and extending the knowledge of high-efficient cooling techniques for exhaust nozzles in real working conditions. The work was conducted with a steady state RANS approach with the SST turbulence model. The boundary conditions were chosen to mimic a real engine condition. The slot height and the inlet pressure ratio were varied to investigate the effect of the geometrical condition and flow condition. The flow field was analyzed in detail to study the phenomena of the supersonic secondary flow injected into the transonic flow. Besides the cooling effectiveness, the thrust coefficient and the discharge coefficient for the cooling cases were discussed together with the baseline case, to evaluate the influence of the supersonic coolant injection on the nozzle performance. The work can be a basis for the design of cooling schemes in an aero-engine exhaust nozzle.