IMPROVEMENT ON ISENTROPIC EFFICIENCY OF PLASMA MHD GENERATOR BY HELIUM

本研究的目的是提高等离子体MHD发生器的等熵效率，以期提供非常高的热效率。2000财政年度，对超声速喷管内等离子体的形成进行了实验研究。实验结果表明，低种子馏分下等离子体形成困难，且取决于喷嘴负载阻力。此外，我们认为在高种子分数下，激波的出现导致了流速的显著降低，尽管等离子体的形成变得容易。结果表明，萃取焓很小，仅为9%。在2001财政年度对喷嘴抗负荷性能进行了优化，使焓萃取率从9%提高到14%。同时，功率输出提高到650 kW，证实了氦气中高流速的优势。等熵效率也显著提高，测得的电压-电流曲线显示出比氩气更高的电压。在2002财政年度，进一步优化了运行条件，并引入了进口涡流。因此，萃取焓提高到30.3%，等熵效率显著提高（= 63%）。还获得了1200千瓦的大功率输出。这些结果是世界上所有实验数据中最高的。这些结果鼓励我们进行下一步工作。下一步，我们计划利用超声速闭环实验装置来研究等离子体MHD发生器在长时间运行下的性能。

The objective of present study is to improve the isentropic efficiency of the plasma MHD generator which is expected to provide very high thermal efficiency.In the fiscal year 2000, the plasma formation in the supersonic nozzle was investigated experimentally. The experimental results indicated that the plasma formation is difficult at low seed fractions and depends on nozzle load resistance. Furthermore, it is suggested that the shock wave appears and as a result, the flow velocity is reduced significantly at high seed fractions, although the plasma formation becomes easy. As a result, the enthalpy extraction remained small and it was only 9 %.The nozzle load resistance was optimized in the fiscal year 2001 and the enthalpy extraction increased from 9 % to 14 %. At the same time, the power output increased up to 650 kW and the advantage of high flow velocity in helium was confirmed. The isentropic efficiency was also improved significantly and the measured voltage-current curve showed higher voltage compared with that for argon.In the fiscal year 2002, the operating condition was optimized further and an introduction of an inlet swirl was adopted. Therefore, the enthalpy extraction increased up to 30.3 % and the isentropic efficiency was remarkably improved (=63 %). The large power output of 1200 kW was also obtained. These results are the highest among all experimental data in the world.These results have encouraged us to proceed to the next step. In the next step, we have a plan to investigate performances of plasma MHD generator under long operation time using the supersonic closed loop experimental facility.