Theoretical and Experimental Development and Optimization of Regenerators with Axially Variable Matrix Structure to Enhance the Efficiency of Regenerative Cycles

再生循环，其中最著名的是斯特林循环，适用于顺时针运行的发动机和逆时针运行的制冷机，非常适合于有效的分散能量转换。在全球变暖的背景下，注意力特别集中在热电联产、联合冷却、热电联产（三联产）以及热驱动热泵领域的应用上。即使自1816年斯特林发动机专利被授予以来，众所周知的是，这些循环的热力学效率关键地取决于作为热能存储器的同名再生器，并且允许工作气体以几乎可忽略的损失在不同温度水平之间周期性地穿梭。高效的再生器特别需要在工作气体和存储基质之间以最小的流动压力损失和空隙体积进行优异的热传递。这些要求应沿整个长度沿着均匀地满足，尽管由于空间变化的质量和体积流量以及经常达到几百K的温差而使流动条件变化很大，并且显著地影响性能数据。这清楚地表明，通过在轴向方向上修改其结构，使基质适应这些变化的流动条件。虽然蓄热室的优化几十年来一直是一个主要的研究课题，但这种矩阵结构的轴向变化的优化潜力还几乎没有被研究，特别是对于热驱动循环。因此，在本项目中，应进行此类调查，主要关注烧结金属毡，因为其制造成本相对较低，但也考虑替代材料。为此，应利用通过基于相似性的缩放设计的现有实验机器，因为它由于增大的水力直径、容易接近的、相对较长的热再生器和其他建设性优点而特别适合。在矩阵的低温端，将安装一个细线热电偶传感器，以高时间分辨率记录流入和流出过程中工作气体的温度，从而通过焓流积分在实验基础上评估回热器损失。通过与具有均匀结构的回热器和相应的模拟结果的比较，由此将证明基体结构的轴向变化的优化潜力。实验验证的建模方法和一般的设计规则将推导和提供，从而有助于进一步提高再生循环的效率。

Regenerative cycles, the most well-known of which, the Stirling cycle, is adaptable to both engines in clockwise and refrigerators in counterclockwise operation, are well suited for an efficient decentralized energy transformation. Against the background of global warming, attention is particularly focused on applications in the field of cogeneration, combined cooling, heat and power production (trigeneration) as well as thermally actuated heat pumps. Even since the grant of the Stirling engine patent in 1816, it is well-known that the thermodynamic efficiency of these cycle is crucially dependent on the namesake regenerators acting as thermal energy stores and allowing the working gas to shuttle periodically between different temperature levels at almost negligible loss. Efficient regenerators particularly require an excellent heat transfer between the working gas and the storage matrix at minimum flow pressure loss an void volume. These demands should be evenly fulfilled along the entire length, although the flow conditions vary considerably due to spatially varying mass and volume flows as well as the temperature difference frequently amounting to several 100 K and considerably affecting the property data. This clearly suggests to adapt the matrix to these varying flow conditions by modifications of its structure in the axial direction. Although optimization of regenerators has been a mayor research topic for decades, the optimization potential of such axial variations of the matrix structure has hardly been investigated yet, particularly for thermally actuated cycles. In this project, such investigations shall therefore be performed, primarily focusing on sintered metal felts due to their comparatively low manufacturing cost, but also considering alternative materials. For this purpose, an existing experimental machine designed by similarity-based scaling shall be utilized, since it is particularly well suited due to enlarged hydraulic diameters, an easily accessible, comparatively long hot regenerator and other constructive advantages. At the low-temperature end of the matrix, a fine wire thermocouple sensor will be installed to record the temperature of the working gas during in- and outflow at a high temporal resolution and to thus evaluate the regenerator loss on an experimental basis by integration of the enthalpy flow. By comparison to regenerators with a uniform structure and to corresponding simulation results, the optimization potential of axial variations of the matrix structure will thus be demonstrated. Experimentally verified modelling approaches and general design rules will be derived and provided, thus contributing to a further enhancement of the efficiency of regenerative cycles.