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

再生循环，其中最著名的斯特林循环，既适用于顺时针方向的发动机，也适用于逆时针操作的冰箱，非常适合高效的分散式能量转换。在全球变暖的背景下，热电联产、联合冷却、热电联产(热电联产)以及热力驱动热泵等领域的应用尤其受到关注。即使自1816年斯特林发动机专利获得批准以来，众所周知，这些循环的热力学效率在很大程度上依赖于作为热能存储的同名回热器，并允许工作气体在不同温度水平之间周期性地传输，而损失几乎可以忽略不计。高效的再生器尤其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良好的换热。这些要求应该在整个长度上均匀地满足，尽管流动条件由于空间上不同的质量和体积流动以及经常高达几百K的温差而变化很大，并且对性能数据有很大影响。这清楚地表明，通过改变基质在轴向的结构，使其适应这些变化的流动条件。虽然回热器的优化是几十年来的一个主要研究课题，但这种轴向变化的基质结构的优化潜力还几乎没有被研究过，特别是对于热驱动循环。因此，在本项目中，应进行此类调查，主要集中在烧结金属毡，因为它们的制造成本相对较低，但也考虑替代材料。为此，应利用现有的基于相似比例尺设计的实验机，因为它特别适合于水力直径较大、易于接近、较长的热再生器和其他结构优势。在基质的低温端，将安装一个细丝热电偶传感器，以高时间分辨率记录工作气体在进出过程中的温度，从而通过对焓流的积分来在实验基础上评估回热器的损失。通过与均匀结构蓄热器的比较和相应的模拟结果，论证了矩阵结构轴向变化的优化潜力。将得出并提供经过实验验证的建模方法和一般设计规则，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.