The time-dependent charging process of an insulating specimen under electron beam irradiation is calculated by taking into account the charge continuity equation, the Poisson equation, Ohm's law and the electron-beam-induced conductivity. The energy and the charge deposition distributions are calculated by the Monte Carlo simulation of electron trajectories taking into account the electric field distribution in the specimen. The time-dependent charge and potential distributions are obtained in the present calculation. As the electron beam energy is 10 keV and the specimen is a 1-mm-thick poly-methyl-methacrylate (PMMA) wafer, the surface potential increases to a positive value at first, and then becomes a negative one. This charging process agrees with experimental findings.
Characteristics of natural frequencies of an impeller and an equivalent disc were investigated in high-density gas to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications. The equivalent disc had outer and inner diameters equal to those of the impeller. We expected that natural frequencies would decrease with increasing the gas density because of the added-mass effect. However, we found experimentally that some natural frequencies of the impeller and the disc in high-density gas decreased but others increased. Moreover, we observed, under high-density condition, some resonance frequencies that we did not observe under low-density condition. These experimental results cannot be explained by only the added-mass effect. For simplicity, we focused on the disc to understand the mechanism of the behavior of natural frequencies. We developed a theoretical analysis of fluid-structure interaction considering not only the mass but also stiffness of gas. The analysis gave a qualitative explanation of the experimental results. In addition, we carried out a fluid-structure interaction analysis using the finite element method. The behavior of natural frequencies of the disc in high-density gas was predicted with errors less than 6%.
A prototype machine for a next generation microturbine system applying a simple humid air turbine system (design target of electrical output: 150 kW, electrical efficiency: 35% LHV) was developed for its laboratory evaluation. A low NOx combustor which applied a lean-lean zone combustion concept and water lubricated bearings were developed for the prototype machine. Operation using two water lines for the humid air turbine (HAT) was proposed as an effective way to obtain rated electric output to ambient temperature of 40 deg C. Tests for the main components were done successfully. Motoring tests, full speed test with no load, 50% load and 70% load tests as preliminary tests for rated load tests were also carried out successfully. Low NOx emission of 7.6 ppm and high efficiency of 95.6% for the power conversion system were achieved in the partial load tests. At the first rated load test without HAT and Water atomizing inlet air cooling (WAC) that followed those partial load tests, 150.3 kW electric output with electrical efficiency of 32% was obtained.
A prototype machine for a next generation microturbine system incorporating a simplified humid air turbine cycle has been developed for laboratory evaluation. Design targets of electrical output were 150 kW and of electrical efficiency, 35% LHV. The main feature of this microturbine system was utilization of water for improved electrical output, as lubricant for bearings and as coolant for the cooling system of the generator and the power conversion system Design specifications without WAC (Water Atomizing inlet air Cooling) and HAT (Humid Air Turbine) were rated output of 129 kW and efficiency of 32.5% LHV. Performance tests without WAC and HAT were done successfully. Electrical output of 135 kW with an efficiency of more than 33% was obtained in the rated load test. Operation tests for WAC and HAT were carried out under the partial load condition as preliminary tests. Water flow rates of WAC were about 0.43 weight % of inlet air flow rate of the compressor and of HAT, about 2.0 weight %. Effects of WAC and HAT were promptly reflected on electrical output power. Electrical outputs were increased 6 kW by WAC and 11kW by HAT, and efficiencies were increased 1.0 pt % by WAC and 2.0 pt % by HAT. Results of WAC and HAT performance tests showed significant effects on the electrical efficiency with an increase of 3.0 point % and electrical output with an increase of 20% by supplying just 2.4 weight % water as the inlet air flow rate of the compressor.
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