Abstract
Thermoacoustics is a relatively young discipline at the intersection of thermodynamics, thermal physics and acoustics. It offers a wide variety of effects based on the interaction between an oscillating, flowing fluid and a solid wall under a given temperature distribution. These complex effects are already finding concrete applications in the cooling and liquefaction of gases as well as in new generations of thermal energy to electrical energy converters of the same class as the Stirling machines with external heat input.
One of the main characteristics of thermoacoustic systems resides in the fact that they require no moving parts, thus of undeniable interest in conventional converters. A thermoacoustic heat engine can work in a wide range of heat qualities (70-200 °C), giving it the ability to be used for low-grade waste heat recovery. Although thermoacoustic systems offer several potential advantages, a certain number of engineering issues need further investigation to overcome the difficulties associated with producing a thermoacoustic system that satisfies the criteria of practicability, economic feasibility and efficiency.
Geometrical configurations describing the devices have been the subject of investigation to improve performance of thermoacoustic systems. In this work, a four-stage travelling-wave thermoacoustic electric generator, which uses air as working medium, was designed, manufactured and tested experimentally. It has been carried out its potential firstly as a low- grade heat recovery to acoustic converter and secondly as acoustic to electric energy converter, which efficiently transferred the acoustic power to the linear alternator. However, this multi- stage air-filled travelling-wave thermoacoustic electricity generator has been subject of multiple tests to evaluate its operating behaviour. Depending on the configuration, each thermoacoustic engine is supplied with a thermal power ranging from 0.357 kW up to 0.992 kW for a duration of 30 up to 45 minutes to record key parameters that contribute to the evaluation of the functioning of the system: onset time; onset temperature difference; sound pressure level (SPL); velocity of the travelling wave; temperature difference across the stack; dynamic pressure; and output voltage according to different configurations. It has been shown that two-stage and four-stage configurations operate at lower onset temperature differences, generate more acoustic power intensity and produce higher output voltage compared to one- stage and three-stage configurations.