Abstract
Thermoacoustic power converters consist of thermoacoustic engines and linear alternators. The former convert thermal energy into acoustic energy and the latter convert the acoustic energy into an electric output. In industrial applications, thermoacoustic power converters are connected to the electric grid, which is a non-linear load that imposes a certain impedance condition to this combined system. However, during initial testing in the laboratory and prior to connection to the grid, a certain electric load must be used to dissipate the electric output generated by the linear alternator and to provide a stable and controllable operating point to the combined system made of the thermoacoustic power converter and the load. This work experimentally examines the characteristic curves of the supply (thermoacoustic power converter) and dissipation (load) systems for linear and non-linear loading in terms of supplied/dissipated powers versus mechanical stroke. The issues that must be considered when using a linear load are presented. The effects of using non-linear versus linear loads on the performance indices of linear alternators are presented and discussed for a range of operating frequencies, mean gas pressures and gas mixture compositions. The experiments are carried-out at a range of values selected to reflect thermoacoustic-power-conversion conditions. The results show that non-linear loading can provide an un-expensive, easily-applied method to provide a stable and controllable method to test linear alternators in the development phase under off-grid conditions. The performance indices of the linear alternator are compared using linear and non-linear loading. For example, when the break-down voltage of the zener diode used to induce the non-linearity in the load was 25% of the open-circuit voltage, the acoustic-to-electric conversion efficiency decreased by 2.8%.