Nobuyoshi Saji

Development of Microturbocharger and Microcombustor for a Three-Dimensional Gas Turbine at Microscale

A microscale gas turbine is under development at Tohoku University in Japan. Current objective of the project is to reveal the performance of the gas turbine at microscale with optimum aerodynamic shape. Therefore the engine to be tested will be fabricated by machining using a micro-5-axis end mill to realize three-dimensional modeling. The first step of the development has been split into the development of microturbocharger and microcombustor, to prevent the problem of the heat flow effect pointed out in the previous study [1]. The heat flow from the combustor to compressor will become relatively large at microscale, and this will degrade the performance of the compressor. The goal of the first step of the development is to achieve the required performance of the components to realize the gas turbine cycle, without the heat effect. Those are, 62% compressor efficiency, 870,000 rpm shaft rotating speed, and the self sustained combustion. A microscale turbocharger has been designed. The compressor impeller of diameter 10mm is expected to produce a pressure ratio of 3, and 68% compressor adiabatic efficiency. The bearings to realize the design rotational speed are hydrodynamic type gas bearing. Fabrication of the herring-bone grooves have been attempted, and successfully formed on a cylindrical surface by new etching procedure. A technique to fabricate three-dimensional turbine impellers at microscale by powder sintering of ceramics has been demonstrated. A semi-microcombustor has been fabricated and shown successful performance by burning hydrogen fuel.Copyright

Development of a highly reliable helium refrigeration system––R&D of a highly reliable helium refrigeration system (oil-free type)

Abstract The present paper reports the development of the highly reliable refrigeration system (three types), which is applied for 70 MW class superconducting generators. R&D of the oil-free turbo type: In the turbo type of advanced refrigeration system, a complete oil free 80 K cold compressor was developed. Moreover, the cold compressor driven by a coaxial turbine was developed to enhance the system efficiency and to save space. R&D of the oil-free screw type: In the oil-free screw rotors, taper rotors were planned to maintain a radial clearance between male and female rotors and the casing, to compensate their thermal deformation because of the heat of compression. Moreover, a seal technique was established that used a magnetic fluid and gas seals to prevent lubricating oil from bearings and the timing gear chamber into the rotor housing, under a higher rotational speed of 25,000 rpm.

Design of oilfree all turbo-type helium refrigerator

Abstract We have designed a high efficient, compact 300 W oilfree all turbo-type heliumrefrigerator capable of long maintenance free continuous operation. The main compressor at ambient temperature which is driven by a helium gas turbine attached to the same shaft, is supported by magnetic bearings, and, has an inlet and outlet pressure of 0.35 MPa and 0.7 MPa. Four turbo expanders are employed, including one at 80 K because LN 2 is not used in this system. Each expander drives a cold compressor, accompanying a generator brake by use of an induction motor. This provides very easy control. Variable nozzles are adopted to the expanders, and the number of valves are diminished as much as possible to reduce line pressure loss. Concerning a heat exchanger, we have examined a micro tube laminar flow heat exchanger which is compact and enables high efficiency at low temperature. This heat exchanger can reduce pressure loss greatly.

Design, Manufacture and Consideration for Test Result of Centrifugal Cold Compressor for TEVATRON Lower Temperature Upgrade

Publisher Summary This chapter discusses the designs and manufacturing of centrifugal cold compressor for TEVATRON lower temperature upgrade. In 1994, Fermilab completed to grade up the refrigeration system including capable of lowering two-phase temperature down to 3.5K with the satellite refrigerators equipped with cold compressors. The apparatus to depressurize liquid helium by directly inhaling evaporated gas and lower its temperature is the cold compressor. In cold compressor the shaft is supported by the dynamic gas bearings in the complete oilfree structure. The motor is air-cooled by a fan to eliminate possible trouble in the cooling water system and to get better maintenance. The cold compressors for Tevatron have been confirmed their reliability for a long operation and become practical machines that can be operated in great numbers at the same time. However, the cryostat vibration must be solved.