Effect of variable mechanical resistance on electrodynamic alternator efficiency

The rapidly growing energy market constantly discovers new alternatives for generating environmentally-friendly electricity from sustainable energy sources. An externally-heated traveling wave thermo acoustic Stirling heat engine is a leading candidate, operating using a variety of viable heat sources. Although this engine holds great promise for a low-cost and maintenance-free solution, its current reported efficiency still inhibits its market penetration, probably owing to the friction introduced by the single moving element - the linear alternator. This research quantifies the main parameters affecting the complex thermal-acoustical-electrical system, clarifying the critical role of frictional losses. An analytical model has been developed, enabling examination of the influence of the critical physical parameters on the electro-acoustic conversion efficiency. A measurement method for precise determination of the mechanical friction constant has been developed, which enables measuring the friction at the engine's working frequency. A direct measurement of an engine's transfer impedance at room temperature enables to find the exact natural frequency before field operation, and calibrate external hardware accordingly. A detailed simulation using DeltaEC (TM) indicates that the tight seal gap between the moving piston and its cylinder has a significant impact on the system's overall efficiency. (C) 2014 Elsevier Ltd. All rights reserved.