Numerical performance simulation of frozen helium plasma disk MHD generator

Abstract

SUMMARYMHD electrical power generation with frozen helium plasma (FHP) is examined numerically. The FHP can be initiated by preionized helium without the alkali metal seed at the generator inlet. Since the three-body recombination coefficient of helium ions is low at electron temperatures above 5000 K, the ionization degree can be kept almost constant in the entire region of the generator channel. The r-θ two-dimensional numerical results show that the performance of the FHP MHD generator is comparable to that of the seeded plasma MHD generator, if the additional power consumed to preionization is ignored. In the FHP MHD generator, the ionization degree at the inlet should be controlled precisely, as well as the seed fraction in the seeded plasma MHD generator. Under an adequate inlet ionization degree for sustaining the FHP plasma, the plasma maintains the uniform structure. On the other hand, a slightly excess ionization degree causes a strong Lorentz force in the upstream region of the generator, deteriorating the generator performance.

Influence of inlet ionization degree on performance of seed‐free MHD generator

“…On the other hand, in the recent years, studies have been done on seed‐free generation . Major methods of seed‐free generation are based on high‐temperature inert gas plasma and pre‐ionized inert gas plasma (frozen inert gas plasma) .…”

“…On the other hand, in the recent years, studies have been done on seed‐free generation . Major methods of seed‐free generation are based on high‐temperature inert gas plasma and pre‐ionized inert gas plasma (frozen inert gas plasma) . With high‐temperature inert gas plasma, generation is performed through thermal equilibrium plasma obtained when inlet total temperature reaches about 9000 K. Experiments and numerical simulations using a shock tube showed that plasma becomes nonuniform because of ionization instability at a low inlet total temperature ( = low inlet ionization degree), and generated output is low; however, at a high inlet total temperature ( = high inlet ionization degree), ionization instability is suppressed, and output increases so that generation performance becomes comparable with that of seeded‐plasma generation.…”

“…On the other hand, in case of pre‐ionized inert gas plasma, inert gas is pre‐ionized at generator's inlet by means of high‐frequency electromagnetic field and so on; as a result, power is generated at a relatively low working temperature about 2500 K. That is, such pre‐ionized inert gas plasma offers continuous operation at the performance level of seeded‐plasma generation, which can be realized as a commercial power plant. As regards pre‐ionized inert gas plasma, r ‐ θ analysis of disk shaped Hall type generator was conducted to show that performance at the level of seeded‐plasma generation can be obtained with optimal inlet ionization degree . In addition, influence of z ‐direction nonuniform distribution of inlet ionization degree on generation performance was explored by r ‐ z analysis .…”

“…[4][5][6][7][8][9][10][11][12][13][14] Major methods of seedfree generation are based on high-temperature inert gas plasma [4][5][6][7][8][9][10] and pre-ionized inert gas plasma (frozen inert gas plasma). [11][12][13][14] With high-temperature inert gas plasma, generation is performed through thermal equilibrium plasma obtained when inlet total temperature reaches about 9000 K. Experiments 5,6 and numerical simulations 7-9 using a shock tube showed that plasma becomes nonuniform because of ionization instability at a low inlet total temperature ( = low inlet ionization degree), and generated output is low; however, at a high inlet total temperature ( = high inlet ionization degree), ionization instability is suppressed, and output increases so that generation performance becomes comparable with that of seeded-plasma generation. In addition, numerical simulations of linear shaped Faraday type generators demonstrated that enthalpy extraction rate exceeds 30% due to expansion of generation region and appropriate design of magnetic field distribution.…”

“…As regards pre-ionized inert gas plasma, r-analysis of disk shaped Hall type generator was conducted to show that performance at the level of seeded-plasma generation can be obtained with optimal inlet ionization degree. [11][12][13] In addition, influence of z-direction nonuniform distribution of inlet ionization degree on generation performance was explored by r-z analysis. 14 At the same time, there are no studies on pre-ionized inert gas plasma MHD generation using linear shaped Faraday type generators that offered high performance in case of high-temperature inert gas plasma; there are also no studies on performance of disk shaped Hall type generators with regard to power required for pre-ionization.…”