Abstract
Abstract A microsteam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam is limited in the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely thin thermocouples (ø0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero- and one-dimensional predesign models correlate well with the experimental results, despite the small size of the turbine blades.
Highlights
Within the last two decades, several researchers demonstrated small-scale turbines, mainly for the application in air-to-electrical-power and micro gas turbine generator systems
(2) Since the literature does not provide any experimental realization and characterization of a micro radial-inflow steam turbine, this paper describes the design of such a device and outlines its experimental characterization
An extensive literature review demonstrated a lack of: (1) Experimental realization and characterization of a micro steam turbine, (2) a reliable test procedure to measure power and efficiency of micro turbines based on inlet and outlet enthalpies, and (3) a validation of simple zero- and one-dimensional models for micro turbines
Summary
Within the last two decades, several researchers demonstrated small-scale turbines, mainly for the application in air-to-electrical-power and micro gas turbine generator systems. Epstein [1] suggested a “shirtbutton-sized” gas turbine, featuring a 6 mm radial-inflow turbine with prismatic blades and rotating up to 1200 krpm. The radial-inflow turbine had three-dimensional blades made of silicon nitride and was supported on a shaft with ball bearings. At a rotational speed of 360 krpm and a combustor temperature of 800 ◦C to 900 ◦C, a self-sustained Brayton cycle was demonstrated. Externally pressurized gas film bearings were used; the entire system was cannot be considered as fully-self-sustained. In 2012, the Japenese IHI cooperation [4] added dynamic gas film bearings to the unit and demonstrated a fully autonomous operation with an electrical power of 60 W at a rotational speed of 330 krpm
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