Numerical simulation investigating the influence of varied stack parameters on the energy conversion in thermoacoustic engines

The stack is a crucial component of the thermoacoustic heat engine, influencing its capacity to generate stable pressure amplitude and enhance efficiency. Utilizing the discontinuous Galerkin (DG) method, fully compressible Navier–Stokes equations were solved to simulate the energy exchange between the stack and surrounding air under various conditions. (1) Simulations were conducted under different stack wall boundary conditions, including linear temperature distribution wall, isothermal wall, and adiabatic wall. The work performed by 1 kg of gas at a specific position during one cycle was defined as local energy density to analyze the effect of different stack spacing, stack length and stack thickness. (2) Too small a stack spacing causes the inability to generate pressure amplitude. Increasing the stack spacing continuously enhances the generated pressure amplitude, with the energy density distribution near the hot heat exchanger becoming more significant. As the stack spacing continues to increase, the energy density decreases at positions farther from the wall, leading to a reduction in pressure amplitude. The generated acoustic streaming intensity diminishes faster with the continuous increase in stack spacing. (3) A smaller stack length results in reduced viscous dissipation at the wall, leading to a larger generated pressure amplitude. However, shorter stack lengths cause increased gas oscillation displacement, resulting in lower energy density concentrate around the stack. This raises the load on the two heat exchangers, consequently reducing the overall efficiency. (4) The pressure amplitude decreases with the increase in stack thickness. The vortex intensity at the gap between the hot heat exchanger and the stack increases with the stack thickness, leading to higher viscous losses for the fluid passing through this region. Consequently, the performance of the thermoacoustic engine declines. These findings provide valuable guidance for the design of thermoacoustic engines.