Acoustic waves can be used to transport energy. The interaction between thermodynamics and acoustics is called thermoacoustics. Thermoacoustic phenomena can be used to perform a thermodynamic cycle. This way, heat can be converted to work, as done in an engine, or work can be used to pump heat, as done in a refrigerator. This study is about thermoacoustic power generation, which means making acoustic power from heat, and generating electricity from acoustic power.
In a regenerator (figure 1), a temperature gradient is imposed on a compressible fluid. If the pressure and velocity of a plane wave are nearly in phase at the cold side of the regenerator inlet, the acoustic medium performs the Stirling cycle in the regenerator. As a result, the acoustic wave is amplified.
Figure 1: Schematic picture of a regenerator
The energy of the amplified wave is harvested in a linear alternator (figure 2), which converts acoustic energy to electric energy.
Theoretically, high efficiencies are achievable, due to the inherent reversibility of the Stirling cycle. The number of moving parts is limited to one (the linear alternator). Therefore the cost of this engine type is low compared to other common power technologies (i.e. the internal combustion engine, or the free piston stirling engine).
Figure 2: Schematic picture of a linear alternator
The research will focus on models to estimate the performance of thermoacoustic stirling engines for small scale power generation of 1 kWe). Specifically, we will look at sources of power loss in a thermoacoustic engine, such as:Viscothermal losses in all parts of the engine
- Turbulent dissipation (vortex shedding)
- Acoustic mass streaming (Rayleigh, Gedeon)
- Heat conduction losses
- Frictional and electrical losses in the linear alternatorDesign tools will be developed for the different design stadia, from simple lumped acoustic network diagrams (figure 3), to viscothermal acoustic finite element models to accurately predict the engine performance.
Figure 3: Lumped acoustic network model of the traveling wave thermoacoustic engine