No abstract

To optimize thermophysical performances, Sm3TaO7 was doped with Lu3+ and pressureless sintered at 1600 ?C. It was shown that Sm3+ is partly substituted by Lu3+ cations and the (Sm1-xLux)3TaO7 ceramics with a single pyrochlore structure are obtained.With increasing x value from 0 to 0.5, the band gap increases gradually from 4.677 to 4.880 eV. Owing to the enhanced phonon scattering caused by Lu3+ doping, the thermal conductivities at 800 ?C of the prepared samples are in the range of 0.95-1.44W?K?1?m?1. It was also confirmed that the phase transition is restrained effectively by substituting Sm3+ with Lu3+. Due to the reduction of crystal lattice energy and average electro-negativity difference, the thermal expansion coefficient (TEC) is heightened with increasing Lu content. TEC achieves the highest value (10.45 ? 10?6 K?1 at 1200 ?C) at the equal molar ratio between Sm3+ and Lu3+ cations (i.e. x = 0.5), which is much higher than those of 7YSZ and Sm2Zr2O7 ceramics.

The scramjet for cooling and heat recovery has been an issue in hypersonic vehicle. A Closed Brayton Cycle (CBC) for power generation system from the heat of cooling scramjet is proposed. Energy, in conjunction with exergy, analysis of the scramjet cooling heat driven Closed Brayton Cycle (CBC) is performed. It is observed from the analysis that, the energy and exergy efficiencies of the system are 33.90% and 24.95%, respectively. Furthermore, the exergy destruction, the output power and the conversion efficiency of CBC following the high-temperature (high-temp) heat exchanger outlet working fluid temperature and the cycle pressure ratio have been analyzed. The cycle pressure ratio, the high-temp heat exchanger outlet working fluid temperature and the low-temperature (low-temp) heat exchanger outlet fuel temperature have large effects on both energy and exergy efficiencies.

Regenerative cooling has been playing an important role on scramjets for safe sustained-operation [10]. However, fuel coolant can only cool the scramjet components such as combustion chamber, and the high temperature and heat flux of the scramjet wall have not been effectively utilized in a conventional thermal conversion way to produce electricity. There once existed a new Re-cooling Cycle which contained a turbine to transfer enthalpy from fuel to mechanical work and electric power [11,12]. However, only part of fuel heat is converted to mechanical power [13,14]. In general, the electrical efficiency of Re-cooling Cycle is relatively low.Energy recovery has been a hot issue in all kinds of engines in recent years. In the case of waste heat recovery the ORC is a device for directly converting thermal energy into electrical energy [15]. As a possible alternative to the effective use of limited resources to reduce the fuel flow for cooling, an ORC power generation system for cooling scramjet based on the thermodynamic principle is performed. ORC has been used in many fields for energy recovery [16][17][18]. Önder [19] has proposed an organic Rankine for

The scramjet cooling heat has a big potential work between the heat and the fuel coolant. However, there is no idea about the maximum potential work of the heat from cooling scramjet. Therefore, the potential work of the scramjet cooling heat is studied. The maximum available work from the heat of cooling scramjet is evaluated by the exergy analysis. The heat exergy analysis model is proposed under the heat sources condition according to the heat transfer performance of the scramjet wall and fuel coolant. It is supposed that a closed thermodynamic system is performed between hot source and cold source. The heat flow, the heat exergy and the available work from the scramjet wall are 543.1kW, 407.3kW and 370.3kW, respectively, when the temperature of scramjet wall is 1200K. And the exergy efficiency of the closed system is 68.2%. The exergy losses of external irreversible processes between the closed system and heat sources are analyzed by considering the heat exchanging temperature differences. The external exergy losses and the exergy efficiency have been largely changed with the heat exchanging temperature differences between the closed system and heat sources. The heat exchanging temperature differences are decreased, the external exergy losses are decreased and the exergy efficiency is increased. However, the heat exchanging temperature differences would be adapted to heat exchanging processes and decreasing the acreage of heat exchange. It is meaningful for having a guidance of power generation for hypersonic vehicle.