Study On The Characteristics Of Regenerator Of Thermoacoustic Engine

Thermoacoustic engine is a novel heat engine based on the thermoacoustic effects. It has the merits of no moving parts and can be driven by thermal energy. The working fluids are inert gases. Compared with traditional engines, it is reliable and environment-friendly. Systems driven by thermoacoustic engine have a promising future in application of refrigeration and electricity generation and so on.Regenerator (or stack) is a components of thermoacoustic engine which convert thermal energy to acoustic power. Therefore, To improve the performance of the regenerator (or stack) is the aim that researchers always pursue. Looking through the thermoacoustic history, every renovation was associated with deeper understanding on regenerator. Therefore, the following work was carried out to study characteristics of regenerator of thermoacoustic engines theoretically and experimentally.1. CFD simulation and optimization on the concept of multilayer regenerator in a Stirling thermoacoustic engineAccording to the fact that the physical properties of working fluid changes with temperature, a multilayer regenerator was proposed in a Stirling thermoacoustic engine to reduce the regenerator loss and dynamic loss. CFD tools and DeltaE were used to calculate the pressure amplitude, velocity amplitude, and temperature distributions. The working fluid is nitrogen, the filling pressure is 2MPa, and the temperature of the heater is 766K. In the CFD simulation, the whole engine uses turbulent model except that the regenerator uses laminar model. The calculation results by CFD and DeltaE were compared with the experimental results, which show: (1) Both CFD results and DeltaE results show that the engine with multilayer regenerator can obtain higher pressure amplitude than the traditional one. (2) The pressure amplitude obtained by CFD simulation agrees better with the experimental results in some specific position (compliance, entrance of the resonator) than DeltaE (3) The nonlinear axial temperature distribution is obtained after the engine onsets, while the results by DeltaE are linear. The CFD results agrees better with the experimental results than DeltaE, which indicates that CFD tools are more suitable to predict the axial temperature distribution in the regenerator of Stirling thermoacoustic engine. Besides, The CFD results shows that the axial temperature distribution is linearized in multilayer regenerator, indicating that multilayer regenerator can reduce streaming flow loss. In addition, the analysis of the flow field in the tee joint shows that the pressure and velocity change violently during an oscillation cycle. Complicated flow states such as vortex, boundary layer separation have been observed, which causes energy loss, and this result provides a further improvement direction for the engine.2. Output characteristic of the screen stack and time rule of onset and damping process in a standing-wave thermoacoustic engineA miniature standing-wave thermoacosuitc engine with screen stack was designed by DeltaE and the engine was made in the experiment. The elementary experiment shows that the engine has good performance with 18-mesh screens. With nitrogen of 2.2 MPa, the engine can produce pressure amplitude as high as 0.2017MPa The further experimental research on output characteristic with different screen stacks was conducted to optimize the screen parameters.The results illustrate the best performance of the engine depends on the screen parameters. With lower filling pressure, the screens with smaller mesh number lead to smaller increase of heater temperature and wider range of heating power, which makes the engine work with best output performance. As the filling pressure increases, the screens with larger mesh number lead to smaller increase of heater temperature and wider range of heating power. In addition, the timing rule of the onset and damping process of the thermoacoustic engine with different screen parameters were measured. In the onset process, the frequency comes to the eigenfrequency first, at the same time the pressure increases little, and then increase sharply after the energy accumulates to certain amount. In the damping process, the pressure amplitude decrease sharply first, then the frequency disappears.