99/02712 Enthalpy extraction and adiabatic efficiency of closed cycle disk MHD generator with Ar/Cs

Abstract

At Tokyo Institute of Technology experimental studies of disk CCMHD generator using Ar/Cs have been made. At T.I.Tech., recent researches have been focused on the improvement of adiabatic efficiency. In 1996, Disk-RLN2 that has a small area ratio of 4.25 was installed in experimental apparatus and lots of experiments have been made in various experimental conditions. As a result, an adiabatic efficiency of 40.5[%] and an enthalpy extraction of 16.8[%] were achieved in previous experiments in 1996. In the experiments, enthalpy extraction became higher as stagnation-gas-pressure became higher. Considering these results, present experiments were made at high stagnation-gas-pressure conditions. Moreover, to strengthen the MHD interaction, magnetic flux density was raised from 2.7[T] up to 3[T]. Experiments were made at two stagnation-gas-pressure (P0) of 0.21[MPa] and 0.29[MPa]. At P0=0.21[MPa], the maximum enthalpy extraction of 17.8[%] was achieved. Moreover, at P0=0.29[MPa], the maximum adiabatic efficiency for the disk MHD generator with radial flow was achieved, and that was 45.9[%]. At P0=0.21[MPa], the existences of optimal seed fraction, at which the maximum enthalpy extraction is achieved for each channel load resistance, are observed in most case of channel load resistance. At P0=0.29[MPa], high enthalpy extractions are achieved overall and a high enthalpy extractionmore » of 17.2[%] is achieved. However, the record of enthalpy extraction of 17.8[%] cannot be broken. In the present experiments at a higher stagnation-gas-pressure of 0.29[MPa], higher total-pressure-ratios compared with these at 0.21[MPa] were measured frequently. Then, a few adiabatic efficiencies of over 40[%] were obtained. Measured total-pressure-ratios are as follows. At P0=0.21[MPa], total-pressure-ratios are from 0.23 to 0.27 and at P0=0.29[MPa], these are from 0.25 to 0.33. To consider the cause of a high total-pressure- ratio in these experiments, simple estimates are made. From these estimates, it is considered that reduction of the pressure loss due to wall friction is the cause of high total-pressure-ratios. High exit Mach numbers are measured at each stagnation-gas-pressure. These results indicate the possibility of achieving a higher enthalpy extraction. Because, it is considered the flow have a sufficient energy to generate electric-output more. Under the optimal magnetic flux distribution, it is considered that more increase of enthalpy extraction is possible. The relationship of enthalpy extraction and fluctuation (deviation of the intensity to time mean of it) of cesium recombination cotinuum is discussed. The intensity of cesium recombination cotinuum stands for a number density of the electron approximately, therefor it is considered that suppressing the fluctuation is great useful for obtaining a uniform discharge structure, as a result, achievement of high enthalpy extraction. However in the present experiments, the fluctuation at P0=0.29[MPa] is slightly larger than that at P0=0.21[MPa]. In this point of view, an operation at a higher stagnation-gas-pressure doesn't necessarily have a good influence on enthalpy extraction, although that is advantageous for obtaining a high adiabatic efficiency.« less