Thermoacoustic engines (TAE) offer effective conversion of low-grade heat into acoustic energy and mechanical work, reducing greenhouse gas emissions through the utilization of exhaust heat. However, a major challenge in optimizing TAE design and ensuring efficient operation is the reliable initiation of oscillations required for startup. While TAEs are promising for low-grade heat utilization, as demonstrated by experimental studies, the spontaneous initiation of thermoacoustic oscillations remains unresolved. To ensure reliable startup, the design of low-temperature TAEs for industrial energy-saving applications must address this issue. Experimental studies were conducted to investigate the thermophysical processes responsible for oscillations in low-temperature TAEs. It was proven for the first time that a longitudinal temperature gradient in the TAE matrix is necessary but insufficient for thermoacoustic oscillations to occur. Temperature trends of the TAE structural elements were obtained experimentally and used in CFD modeling. The problem was analyzed in a 3D, non-stationary setting. The CFD results revealed that during startup, complex thermoconvective flows formed dynamic vortex structures of varying scales and frequencies within the resonator. These findings confirm that the self-nucleation of thermoacoustic oscillations in TAEs is driven by thermoconvective effects. CFD simulations demonstrated that thermoconvective flows, arising from temperature differences between heaters and TAE elements, are the primary mechanism that induces thermoacoustic instability. Additionally, empirical data showed that the dynamic characteristics of heaters significantly affect TAE startup.
Abstract: Thermoacoustic engines (TAE) offer effective conversion of low-grade heat into acoustic energy and mechanical work, reducing greenhouse gas emissions through the utilization of exhaust heat. However, a major challenge in optimizing TAE design and ensuring efficient operation is the reliable initiation of oscillations required for startup. While TAEs are promising for low-grade heat utilization, as demonstrated by experimental studies, the spontaneous initiation of thermoacoustic oscillations remains unresolved. To ensure reliable startup, the design of low-temperature TAEs for industrial energy-saving applications must address this issue. Experimental studies were conducted to investigate the thermophysical processes responsible for oscillations in low-temperature TAEs. It was proven for the first time that a longitudinal temperature gradient in the TAE matrix is necessary but insufficient for thermoacoustic oscillations to occur. Temperature trends of the TAE structural elements were obtained experimentally and used in CFD modeling. The problem was analyzed in a 3D, non-stationary setting. The CFD results revealed that during startup, complex thermoconvective flows formed dynamic vortex structures of varying scales and frequencies within the resonator. These findings confirm that the self-nucleation of thermoacoustic oscillations in TAEs is driven by thermoconvective effects. CFD simulations demonstrated that thermoconvective flows, arising from temperature differences between heaters and TAE elements, are the primary mechanism that induces thermoacoustic instability. Additionally, empirical data showed that the dynamic characteristics of heaters significantly affect TAE startup.
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